Tyrannosauridae
Encyclopedia
Tyrannosauridae is a family
of coelurosauria
n theropod
dinosaur
s which comprises two subfamilies containing up to six genera
, including the eponym
ous Tyrannosaurus
. The exact number of genera is controversial, with some experts recognizing as few as three. All of these animals lived near the end of the Cretaceous
Period and their fossil
s have been found only in North America
and Asia
.
Although descended from smaller ancestors
, tyrannosaurids were almost always the largest predators
in their respective ecosystem
s, putting them at the apex
of the food chain
. The largest species
was Tyrannosaurus rex, one of the largest known land predators, which measured up to 13 metres (42.7 ft) in length and up to 6.8 tonnes (7.5 ST) in weight. Tyrannosaurids were bipedal carnivores with massive skull
s filled with large teeth. Despite their large size, their legs were long and proportioned for fast movement. In contrast, their arms were very small, bearing only two functional digits.
Unlike most other groups of dinosaurs, very complete remains have been discovered for most known tyrannosaurids. This has allowed a variety of research into their biology
. Scientific studies have focused on their ontogeny
, biomechanics
and ecology
, among other subjects. Soft tissue
, both fossilized and intact, has been reported from one specimen of Tyrannosaurus rex.
of an individual estimated at between 5 and 6 m (16.4 and 19.7 ) long has been discovered, although it is considered by some experts to be a juvenile. Albertosaurus
, Gorgosaurus
and Daspletosaurus
all measured between 8 and 10 m (26.2 and 32.8 ) long, while Tarbosaurus
reached lengths of 12 metres (39.4 ft) from snout to tail. The massive Tyrannosaurus was the largest, approaching 13 metres (42.7 ft) in the longest specimens.
Tyrannosaurid skull anatomy is well understood as complete skulls are known for all genera but Alioramus, which is known only from partial skull remains. Tyrannosaurus, Tarbosaurus, and Daspletosaurus had skulls which exceeded 1 metres (3.3 ft) in length, The largest discovered Tyrannosaurus skull measures over 1.5 metres (4.9 ft) long. Adult tyrannosaurids had tall, massive skulls, with many bones fused and reinforced for strength. At the same time, hollow chambers within many skull bones and large openings (fenestrae) between those bones helped to reduce skull weight. Many features of tyrannosaurid skulls were also found in their immediate ancestors, including tall premaxilla
e and fused nasal bone
s.
Tyrannosaurid skulls had many unique characteristics, including fused parietal bone
s with a prominent sagittal crest
, which ran longitudinally along the sagittal suture
and separated the two supratemporal fenestrae on the skull roof. Behind these fenestrae, tyrannosaurids had a characteristically tall nuchal crest, which also arose from the parietals but ran along a transverse plane
rather than longitudinally. The nuchal crest was especially well-developed in Tyrannosaurus, Tarbosaurus and Alioramus. Albertosaurus, Daspletosaurus and Gorgosaurus had tall crests in front of the eyes on the lacrimal bone
s, while Tarbosaurus and Tyrannosaurus had extremely thickened postorbital bones
forming crescent-shaped crests behind the eyes. Alioramus had a row of six bony crests on top of its snout, arising from the nasal bones; lower crests have been reported on some specimens of Daspletosaurus and Tarbosaurus, as well as the more basal
tyrannosauroid Appalachiosaurus
.
The skull was perched at the end of a thick, S-shaped neck, and a long, heavy tail acted as a counterweight
to balance out the head and torso, with the center of mass
over the hips. Tyrannosaurids are known for their proportionately very small two-fingered forelimbs, although remnants of a vestigial third digit are sometimes found. Tarbosaurus had the shortest forelimbs compared to its body size, while Daspletosaurus had the longest.
Tyrannosaurids walked exclusively on their hindlimbs, so their leg bones were massive. In contrast to the forelimbs, the hindlimbs were longer compared to body size than almost any other theropods. Juveniles and even some smaller adults, like more basal tyrannosauroids, had longer tibia
e than femora
, a characteristic of fast-running
dinosaurs like ornithomimids
. Larger adults had leg proportions characteristic of slower-moving animals, but not to the extent seen in other large theropods like abelisaurids
or carnosaurs
. The third metatarsals
of tyrannosaurids were pinched between the second and fourth metatarsals, forming a structure known as the arctometatarsus.
It is unclear when the arctometatarsus first evolved; it was not present in the earliest tyrannosauroids like Dilong
, but was found in the later Appalachiosaurus
. This structure also characterized troodontids
, ornithomimids
and caenagnathids, but its absence in the earliest tyrannosauroids indicates that it was acquired by convergent evolution
.
, with premaxillary teeth D-shaped in cross section
and smaller than the rest. Unlike earlier tyrannosauroids and most other theropods, the maxilla
ry and mandibular
teeth of mature tyrannosaurids are not blade-like but extremely thickened and often circular in cross-section. Tooth counts tend to be consistent within species, and larger species tend to have lower tooth counts than smaller ones. For example, Alioramus had 76 to 78 teeth in its jaws, while Tyrannosaurus had between 54 and 60.
William L. Abler observed in 2001 that Albertosaurus tooth serrations are so thin as to functionally be a crack
in the tooth. However, at the base of this crack is round void
called an ampulla
which would have functioned to distribute force over a larger surface area
, hindering the ability of the "crack" formed by the serration to propagate through the tooth. An examination of other ancient predators, a phytosaur
and Dimetrodon
found similarly crack-like serrations, but no adaptation
s for preventing crack propagation. Tyrannosaurid teeth were used as holdfasts for pulling meat
off a body, rather than knife
-like cutting functions. Tooth wear patterns hint that complex head shaking behaviors may have been involved in tyrannosaur feeding. When a tyrannosaur would have pulled back on a piece of meat, the force would tend to push the tip of tooth toward the front of the mouth and the anchored root would experience tension on the posterior side and compression from the front. This would typically incline the tooth to crack formation on the posterior side of the tooth, but the ampullae at the base of the already crack-like serrations would tend to diffuse potential crack-forming forces. This form resembles techniques used by guitar
makers to "impart alternating regions of flexibility and rigidity to a stick of wood." The use of a drill
to create an "ampulla" of sorts and prevent the propagation of cracks through an important material is also used to protect airplane surfaces. Abler demonstrated that a plexiglass bar with kerfs and drilled holes was more than 25% stronger than one with only regularly placed incisions.
The first remains of tyrannosaurids were uncovered during expeditions led by the Geological Survey of Canada, which located numerous scattered teeth. These distinctive dinosaur teeth were given the name Deinodon
("terrible tooth") by Joseph Leidy
in 1856. The first good speciemens of a tyrannosaurid were found in the Horseshoe Canyon Formation
of Alberta
, and consisted of nearly complete skulls with partial skeletons. These remains were first studied by Edward Drinker Cope
in 1876, who considered them a species of the eastern tyrannosauroid Dryptosaurus
. In 1905, Henry Fairfield Osborn
recognized that the Alberta remains differed considerably from Dryptosaurus, and coined a new name for them: Albertosaurus sarcophagus
("flesh-eating Alberta lizard"). Cope described more tyrannosaur material in 1892, in the form of isolated vertebrae, and gave this animal the name Manospondylus gigas. This discovery was mostly overlooked for over a century, and caused controversy in the early 2000s when it was discovered that this material actually belonged to, and had name priority over, Tyrannosaurus rex
.
In his 1905 paper naming Albertosaurus, Osborn described two additional tyrannosaur specimens that had been collected from in Montana
and Wyoming
during a 1902 expedition of the American Museum of Natural History
, led by Barnum Brown
. Initially, Osborn considered these to be distinct species. The first, he named Dynamosaurus imperiosus ("emperor power lizard"), and the second, Tyrannosaurus rex ("king tyrant lizard"). A year later, Osborn recognized that these two specimens actually came from the same species. Despite the fact that Dynamosaurus had been found first, the name Tyrannosaurus had appeared one page earlier in his original article describing both specimens. Therefore, according to the International Code of Zoological Nomenclature
(ICZN), the name Tyrannosaurus was used.
Barnum Brown went on to collect several more tyrannosaurid specimens from Alberta, including the first to preserve the shortened, two-fingered forelimbs characteristic of the group (which Lawrence Lambe
named Gorgosaurus libratus
, "balanced fierce lizard", in 1914). A second significant find attributed to Gorgosaurus was made in 1942, in the form of a well-preserved, though unusually small, complete skull. The specimen waited until after the end of World War II
to be studied by Charles W. Gilmore
, who named it Gorgosaurus lancesnis. This skull was re-studied by Robert T. Bakker
, Phil Currie, and Michael Williams in 1988, and assigned to the new genus Nanotyrannus
. It was also in 1946 that paleontologists from the Soviet Union
began expeditions into Mongolia
, and uncovered the first tyrannosaur remains from Asia. Evgeny Maleev
described new Mongolian species of Tyrannosaurus and Gorgosaurus in 1955, and one new genus: Tarbosaurus
("terrifying lizard"). Subsequent studies, however, showed that all of Maleev's tyrannosaur species were actually one species of Tarbosaurus at different stages of growth. A second species of Mongolian tyrannosaurid was found later, described by Sergei Kurzanov in 1976, and given the name Alioramus remotus
("remote different branch"), though its status as a true tyrannosaurid and not a more primitive tyrannosaur is still controversial.
While earlier tyrannosauroids are found on all three northern continents, tyrannosaurid fossils are known only from North America and Asia. Sometimes fragmentary remains uncovered in the Southern Hemisphere have been reported as "Southern Hemisphere tyrannosaurids," although these seem to have been misidentified abelisaurid
fossils. The exact time and place of origin of the family remain unknown due to the poor fossil record in the middle part of the Cretaceous on both continents, although the earliest confirmed tyrannosaurids lived in the early Campanian
stage in western North America.
Tyrannosaurid remains have never been recovered from eastern North America, while more basal tyrannosauroids like Dryptosaurus
and Appalachiosaurus
persisted there until the end of the Cretaceous, indicating that tyrannosaurids must have evolved in or dispersed
into western North America after the continent was divided in half by the Western Interior Seaway
in the middle of the Cretaceous. Tyrannosaurid fossils have been found in Alaska
, which may have provided a route for dispersal between North America and Asia. Alioramus and Tarbosaurus are found to be related in one cladistic analysis, forming a unique Asian branch of the family.
Of the two subfamilies, tyrannosaurines appear to have been more widespread. Albertosaurines are unknown in Asia, which was home to the tyrannosaurines Tarbosaurus and Alioramus. Both subfamilies were present in the Campanian and early Maastrichtian
stages of North America, with tyrannosaurines like Daspletosaurus ranging throughout the Western Interior, while the albertosaurines Albertosaurus and Gorgosaurus are currently known only from the northwestern part of the continent.
By the late Maastrichtian, albertosaurines appear to have gone extinct, while the tyrannosaurine Tyrannosaurus roamed from Saskatchewan
to Texas
. This pattern is mirrored in other North American dinosaur taxa. During the Campanian and early Maastrichtian, lambeosaurine
hadrosaurs
and centrosaurine
ceratopsia
ns are common in the northwest, while hadrosaurines
and chasmosaurines
were more common to the south. By the end of the Cretaceous, centrosaurines are unknown and lambeosaurines are rare, while hadrosaurines and chasmosaurines were common throughout the Western Interior.
can determine the age of a specimen when it died. Growth rates can be examined when the age of various individuals are plotted against their size on a graph. Erickson has shown that after a long time as juveniles, tyrannosaurs underwent tremendous growth spurts for about four years midway through their lives. After the rapid growth phase ended with sexual maturity
, growth slowed down considerably in adult animals. A tyrannosaurid growth curve is S-shaped, with the maximum growth rate of individuals around 14 years of age.
The smallest known Tyrannosaurus rex individual (LACM
28471, the "Jordan theropod") is estimated to have weighed only 29.9 kilograms (65.9 lb) at only 2 years old, while the largest, such as FMNH
PR2081 ("Sue
") most likely weighed over 5400 kg (11,905 lb), estimated to have been 28 years old, an age which may have been close to the maximum for the species. T. rex juveniles remained under 1800 kg (3,968.3 lb) until approximately 14 years of age, when body size began to increase dramatically. During this rapid growth phase, a young T. rex would gain an average of 600 kg (1,322.8 lb) a year for the next four years. This slowed after 16 years, and at 18 years of age, the curve plateaus again, indicating that growth slowed dramatically. For example, only 600 kg (1,322.8 lb) separated the 28-year-old "Sue" from a 22-year-old Canadian
specimen (RTMP
81.12.1). This sudden change in growth rate may indicate physical maturity, a hypothesis which is supported by the discovery of medullary tissue in the femur
of a 18-year-old T. rex from Montana (MOR
1125, also known as "B-rex"). Medullary tissue is found only in female birds during ovulation, indicating that "B-rex" was of reproductive age.
Other tyrannosaurids exhibit extremely similar growth curves, although with lower growth rates corresponding to their lower adult sizes. Compared to albertosaurines, Daspletosaurus showed a faster growth rate during the rapid growth period due to its higher adult weight. The maximum growth rate in Daspletosaurus was 180 kilograms (396.8 lb) per year, based on a mass estimate of 1800 kg (3,968.3 lb) in adults. Other authors have suggested higher adult weights for Daspletosaurus; this would change the magnitude of the growth rate but not the overall pattern. The youngest known Albertosaurus is a two-year-old discovered in the Dry Island bonebed, which would have weighed about 50 kg (110.2 lb) and measured slightly more than 2 metres (6.6 ft) in length. The 10 metres (32.8 ft) specimen from the same quarry is the oldest and largest known, at 28 years of age. The fastest growth rate is estimated to be around 12–16 years, reaching 122 kilograms (269 lb) per year, based on an adult 1300 kilograms (2,866 lb) which is about five times slower than for T.-rex. For Gorgosaurus the calculated maximum growth rate is about 110 kilograms (242.5 lb) during the rapid growth phase, which is comparable to that of Albertosaurus.
The end of the rapid growth phase suggests the onset of sexual maturity
in Albertosaurus, although growth continued at a slower rate throughout the animals' lives. Sexual maturation while still actively growing appears to be a shared trait among small and large dinosaurs as well as in large mammals such as humans and elephant
s. This pattern of relatively early sexual maturation differs strikingly from the pattern in birds, which delay their sexual maturity until after they have finished growing.
By tabulating the number of specimens of each age group, Erickson and his colleagues were able to draw conclusions about life history in tyranosauridae populations. Their analysis showed that while juveniles were rare in the fossil record, subadults in the rapid growth phase and adults were far more common. Over half of the known T. rex specimens appear to have died within six years of reaching sexual maturity, a pattern which is also seen in other tyrannosaurs and in some large, long-lived birds and mammals today. These species are characterized by high infant mortality rates, followed by relatively low mortality among juveniles. Mortality increases again following sexual maturity, partly due to the stresses of reproduction. While this could be due to preservation or collection biases
, Erickson hypothesized that the difference was due to low mortality among juveniles over a certain size, which is also seen in some modern large mammals like elephant
s. This low mortality may have resulted from a lack of predation, since tyrannosaurs surpassed all contemporaneous predators in size by the age of two. Paleontologists have not found enough Daspletosaurus remains for a similar analysis, but Erickson notes that the same general trend seems to apply.
The tyrannosaurids spent as much as half its life in the juvenile phase before ballooning up to near-maximum size in only a few years. This, along with the complete lack of predators intermediate in size between huge adult tyrannosaurids and other small theropods, suggests these niches may have been filled by juvenile tyrannosaurids. This is seen in modern Komodo dragon
s, where hatchlings start off as tree-dwelling insectivore
s and slowly mature into massive apex predator
s capable of taking down large vertebrates. For example, Albertosaurus have been found in aggregations that some have suggested to represent mixed-age packs
.
, since much of Tyrannosaurus’ mass was some distance from its center of gravity, like a human carrying a heavy timber.
Scientists have produced a wide range of maximum speed estimates, mostly around 11 metres per second (24.6 mph), but a few as low as 5 –, and a few as high as 20 metres per second (44.7 mph). Researchers have to rely on various estimating techniques because, while there are many tracks
of very large theropods walking, so far none have been found of very large theropods running — and this absence may indicate that they did not run.
Jack Horner and Don Lessem argued in 1993 that Tyrannosaurus was slow and probably could not run (no airborne phase in mid-stride). However, Holtz (1998) concluded that tyrannosaurids and their close relatives were the fastest large theropods. Christiansen (1998) estimated that the leg bones of Tyrannosaurus were not significantly stronger than those of elephants, which are relatively limited in their top speed and never actually run (there is no airborne phase), and hence proposed that the dinosaur's maximum speed would have been about 11 metres per second (24.6 mph), which is about the speed of a human sprinter. Farlow and colleagues (1995) have argued that a 6-8 ton Tyrannosaurus would have been critically or even fatally injured if it had fallen while moving quickly, since its torso would have slammed into the ground at a deceleration of 6 g (six times the acceleration due to gravity, or about 60 meters/s²) and its tiny arms could not have reduced the impact. However, giraffe
s have been known to gallop at 50 km/h (31 mph), despite the risk that they might break a leg or worse, which can be fatal even in a "safe" environment such as a zoo. Thus it is quite possible that Tyrannosaurus also moved fast when necessary and had to accept such risks; this scenario has been studied for Allosaurus too. Most recent research on Tyrannosaurus locomotion does not narrow down speeds further than a range from 17 to 40 km/h (10.6 to 24.9 mph), i.e. from walking or slow running to moderate-speed running. A computer model study in 2007 estimated running speeds, based on data taken directly from fossils, and claimed that T. rex had a top running speed of 8 metres per second (17.9 mph). (probably a juvenile individual).
structures have been preserved along with skeletal remains of numerous coelurosaurs from the Early Cretaceous Yixian Formation
and other nearby geological formations from Liaoning
, China. These filaments have usually been interpreted as "protofeathers," homologous
with the branched feathers found in birds and some non-avian theropods
, although other hypotheses have been proposed. A skeleton of Dilong was described in 2004 that included the first example of "protofeathers" in a tyrannosauroid. Similarly to down feather
s of modern birds, the "protofeathers" found in Dilong were branched but not pennaceous
, and may have been used for insulation
.
It has also been theoretized that tyrannosaurids had such protofeathers. However, rare skin impressions from adult tyrannosaurids in Canada and Mongolia show pebbly scales typical of other dinosaurs. While it is possible that protofeathers existed on parts of the body which have not been preserved, a lack of insulatory
body covering is consistent with modern multi-ton mammals such as elephant
s, hippopotamus
, and most species of rhinoceros
. As an object increases in size, its ability to retain heat increases due to its decreasing surface area
-to-volume
ratio. Therefore, as large animals evolve
in or disperse
into warm climates, a coat of fur or feathers loses its selective
advantage for thermal insulation and can instead become a disadvantage, as the insulation traps excess heat inside the body, possibly overheating the animal. Protofeathers may also have been secondarily lost during the evolution of large tyrannosaurids, especially in warm Cretaceous climates.
The eye-sockets of Tyrannosaurus are positioned so that the eyes would point forward, giving them binocular vision
slightly better than that of modern hawk
s. Jack Horner
also pointed out that the tyrannosaur lineage had a history of steadily improving binocular vision. It is hard to see how natural selection
would have favored this long-term trend if tyrannosaurs had been pure scavengers, which would not have needed the advanced depth perception
that stereoscopic vision
provides. In modern animals, binocular vision is found mainly in predators (the principal exceptions are primate
s, which need it for leaping from branch to branch).
Unlike Tyrannosaurus, Tarbosaurus had a narrower skull more typical of other tyrannosaurids in which the eyes faced primarily sideways. All of this suggests that Tarbosaurus relied more on its senses of smell and hearing than on its eyesight. In Gorgosaurus specimens, the eye socket
was circular rather than oval or keyhole-shaped as in other tyrannosaurid genera. In Daspletosaurus this was a tall oval, somewhere in between the circular shape seen in Gorgosaurus and the 'keyhole' shape of Tyrannosaurus.
Bony crests are found on the skulls of many theropods, including many of tyrannosaurids. Alioramus
, a possible tyrannosaurid from Mongolia, bears a single row of five prominent bony bumps on the nasal bones; a similar row of much lower bumps is present on the skull of Appalachiosaurus, as well as some specimens of Daspletosaurus
, Albertosaurus, and Tarbosaurus. In Albertosaurus, Gorgosaurus and Daspletosaurus
, there is a prominent horn in front of each eye on the lacrimal bone. The lacrimal horn is absent in Tarbosaurus and Tyrannosaurus, which instead have a crescent-shaped crest behind each eye on the postorbital bone
. These head crests may have been used for display
, perhaps for species recognition or courtship behavior.
ic ("cold-blooded") reptilian metabolism
but was challenged by scientists like Robert T. Bakker
and John Ostrom
in the early years of the "Dinosaur Renaissance
", beginning in the late 1960s. Tyrannosaurus rex itself was claimed to have been endothermic
("warm-blooded"), implying a very active lifestyle. Since then, several paleontologists have sought to determine the ability of Tyrannosaurus to regulate
its body temperature
. Histological evidence of high growth rates in young T. rex, comparable to those of mammals and birds, may support the hypothesis of a high metabolism. Growth curves indicate that, as in mammals and birds, T. rex growth was limited mostly to immature animals, rather than the indeterminate growth
seen in most other vertebrate
s. It has been indicated that the temperature difference may have been no more than 4 to 5°C (7 to 9°F) between the vertebrae of the torso and the tibia
of the lower leg. This small temperature range between the body core and the extremities was claimed by paleontologist Reese Barrick and geochemist
William Showers to indicate that T. rex maintained a constant internal body temperature (homeothermy
) and that it enjoyed a metabolism somewhere between ectothermic reptiles and endothermic mammals. Later they found similar results in Giganotosaurus
specimens, who lived on a different continent and tens of millions of years earlier in time. Even if Tyrannosaurus rex does exhibit evidence of homeothermy, it does not necessarily mean that it was endothermic. Such thermoregulation may also be explained by gigantothermy
, as in some living sea turtle
s.
In the Dinosaur Park Formation, Gorgosaurus lived alongside a rarer species of the tyrannosaurine Daspletosaurus. This is one of the few examples of two tyrannosaur genera coexisting. Similarly-sized predators in modern predator guilds
are separated into different ecological niche
s by anatomical, behavioral or geographical differences that limit competition. Niche differentiation between the Dinosaur Park tyrannosaurids is not well-understood. In 1970, Dale Russell hypothesized
the more common Gorgosaurus actively hunted fleet-footed hadrosaurs, while the rarer and more troublesome ceratopsia
ns and ankylosauria
ns (horned and heavily armoured
dinosaurs) were left to the more heavily-built Daspletosaurus
. However, a specimen of Daspletosaurus (OTM 200) from the contemporaneous Two Medicine Formation
of Montana preserves the digested remains of a juvenile hadrosaur in its gut region.
Unlike some other groups of dinosaurs, neither genus was more common at higher or lower elevations than the other. However, Gorgosaurus appears more common in northern formations like the Dinosaur Park, with species of Daspletosaurus more abundant to the south. The same pattern is seen in other groups of dinosaurs. Chasmosaurine ceratopsians and hadrosaurine hadrosaurs are also more common in the Two Medicine Formation of Montana and in southwestern North America during the Campanian, while centrosaurine and lambeosaurines dominate in northern latitudes. Holtz has suggested this pattern indicates shared ecological preferences between tyrannosaurines, chasmosaurines and hadrosaurines. At the end of the later Maastrichtian stage, tyrannosaurines like Tyrannosaurus rex, hadrosaurines like Edmontosaurus
and chasmosaurines like Triceratops
were widespread throughout western North America, while albertosaurines and centrosaurines went extinct, and lambeosaurines were rare.
A young specimen of the Dinosaur Park Daspletosaurus species (TMP
94.143.1) shows bite marks on the face that were inflicted by another tyrannosaur. The bite marks are healed over, indicating that the animal survived the bite. A full-grown Dinosaur Park Daspletosaurus (TMP 85.62.1) also exhibits tyrannosaur bite marks, showing that attacks to the face were not limited to younger animals. While it is possible that the bites were attributable to other species, intraspecific aggression, including facial biting, is very common among predators. Facial bites are seen in other tyrannosaurs like Gorgosaurus and Tyrannosaurus, as well as in other theropod genera like Sinraptor
and Saurornitholestes
. Darren Tanke
and Phil Currie hypothesize that the bites are due to intraspecific competition
for territory or resources, or for dominance within a social group.
Evidence that Daspletosaurus lived in social groups comes from a bonebed found in the Two Medicine Formation of Montana. The bonebed includes the remains of three Daspletosaurus, including a large adult, a small juvenile, and another individual of intermediate size. At least five hadrosaurs are preserved at the same location. Geologic evidence indicates that the remains were not brought together by river currents
but that all of the animals were buried simultaneously at the same location. The hadrosaur remains are scattered and bear many marks from tyrannosaur teeth, indicating that the Daspletosaurus were feeding on the hadrosaurs at the time of death. The cause of death is unknown. Currie speculates that the daspletosaurs formed a pack
, although this cannot be stated with certainty. Other scientists are skeptical of the evidence for social groups in Daspletosaurus and other large theropods; Brian Roach and Daniel Brinkman have suggested that Daspletosaurus social interaction would have more closely resembled the modern Komodo dragon
, where non-cooperative individuals mob carcasses, frequently attacking and even cannibalizing
each other in the process.
The Dry Island bonebed discovered by Barnum Brown and his crew contains the remains of 22 Albertosaurus, the most individuals found in one locality of any Cretaceous theropod, and the second-most of any large theropod dinosaur behind the Allosaurus
assemblage at the Cleveland Lloyd Dinosaur Quarry
in Utah
. The group seems to be composed of one very old adult; eight adults between 17 and 23 years old; seven sub-adults undergoing their rapid growth phases at between 12 and 16 years old; and six juveniles between the ages of 2 and 11 years, who had not yet reached the growth phase. The near-absence of herbivore
remains and the similar state of preservation between the many individuals at the Albertosaurus bonebed quarry led Phil Currie to conclude that the locality was not a predator trap like the La Brea Tar Pits
in California
, and that all of the preserved animals died at the same time. Currie claims this as evidence of pack behavior. Other scientists are skeptical, observing that the animals may have been driven together by drought, flood or for other reasons.
Tyrannosaur tooth marks are the most commonly preserved feeding traces of carnivorous dinosaurs. They have been reported from ceratopsians, hadrosaurs and other tyrannosaurs. Tyrannosaurid bones with tooth marks represent about 2% of known fossils with preserved tooth marks. Tyrannosaurid teeth were used as holdfasts for pulling meat
off a body, rather than knife
-like cutting functions. Tooth wear patterns hint that complex head shaking behaviors may have been involved in tyrannosaur feeding.
Speculation on the pack-hunting habits of Albertosaurus were made by a few researchers who suggest that the younger members of the pack may have been responsible for driving their prey towards the adults, who were larger and more powerful, but also slower. Juveniles may also have had different lifestyles than adults, filling predator niches
between those of the enormous adults and the smaller contemporaneous theropods, the largest of which were two orders of magnitude
smaller than an adult Albertosaurus in mass. However, as the preservation of behavior in the fossil record is exceedingly rare, these ideas cannot readily be tested. Phil Currie speculates that the Daspletosaurus formed packs to hunt
, although this cannot be stated with certainty. There is no evidence of such gregarious behavior in Gorgosaurus.
The debate about whether Tyrannosaurus was a predator
or a pure scavenger
is as old as the debate about its locomotion. Lambe (1917) described a good skeleton of Tyrannosaurus’ close relative Gorgosaurus
and concluded that it and therefore also Tyrannosaurus was a pure scavenger, because the Gorgosaurus’ teeth showed hardly any wear. This argument is no longer taken seriously, because theropods replaced their teeth quite rapidly. Ever since the first discovery of Tyrannosaurus most scientists have agreed that it was a predator, although like modern large predators it would have been happy to scavenge or steal another predator's kill if it had the opportunity.
Noted hadrosaur
expert Jack Horner
is currently the major advocate of the idea that Tyrannosaurus was exclusively a scavenger and did not engage in active hunting at all. Horner has presented several arguments to support the pure scavenger hypothesis. The presence of large olfactory bulb
s and olfactory nerve
s suggests a highly developed sense of smell for sniffing out carcasses over great distances. The teeth could crush bone, and therefore could extract as much food (bone marrow
) as possible from carcass remnants, usually the least nutritious parts. At least some of its potential prey could move quickly, while evidence suggests that it walked instead of ran.
Other evidence suggests hunting behavior in Tyrannosaurus. The eye-sockets of tyrannosaurs are positioned so that the eyes would point forward, giving them binocular vision
slightly better than that of modern hawk
s. Tyrannosaur-inflicted damage has been found on skeletons of hadrosaurs and Triceratops
that seemed to have survived initial attacks. Some researchers argue that if Tyrannosaurus were a scavenger, another dinosaur had to be the top predator in the Amerasian Upper Cretaceous. The top prey were the larger marginocephalia
ns and ornithopod
s. The other tyrannosaurids share so many characteristics with Tyrannosaurus that only small dromaeosaurs
remain as feasible top predators. In this light, scavenger hypothesis adherents have suggested that the size and power of tyrannosaurs allowed them to steal kills
from smaller predators. Most paleontologists accept that Tyrannosaurus was both an active predator and a scavenger.
in 1866 for this family, and continued to be used in place of the newer name Tyrannosauridae through the 1960s. The type genus of the Deinodontidae is Deinodon
, which was named after isolated teeth from Montana
. However, in a 1970 review of North American tyrannosaurs, Dale Russell
concluded that Deinodon was not a valid taxon, and used the name Tyrannosauridae in place of Deinodontidae, stating that this was in accordance with ICZN
rules. Therefore, Tyrannosauridae is preferred by modern experts.
Tyrannosaurus was named by Henry Fairfield Osborn
in 1905, along with the family Tyrannosauridae. The name is derived from the Ancient Greek
words τυραννος/tyrannos ('tyrant') and σαυρος/sauros ('lizard'). The very common suffix
-idae is normally appended to zoological
family names and is derived from the Greek suffix -ιδαι/-idai, which indicates a plural noun.
in rank-based Linnaean taxonomy
, within the superfamily
Tyrannosauroidea
and the suborder
Theropoda
.
Tyrannosauridae is uncontroversially divided into two subfamilies. Albertosaurinae comprises the North American genera Albertosaurus and Gorgosaurus, while Tyrannosaurinae includes Daspletosaurus, Tarbosaurus and Tyrannosaurus itself. Some authors include the species Gorgosaurus libratus in the genus Albertosaurus and Tarbosaurus bataar in the genus Tyrannosaurus, while others prefer to retain Gorgosaurus and Tarbosaurus as separate genera. Albertosaurines are characterized by more slender builds, lower skulls, and proportionately longer tibiae than tyrannosaurines. In tyrannosaurines, the sagittal crest on the parietals continues forward onto the frontals. Some authors, such as George Olshevsky and Tracy Ford, have created finer subdivisions or tribes
for various combinations of tyrannosaurs within the subfamilies. However, these have not been phylogenetically defined, and usually consisted of genera which are now considered synonymous with other genera or species.
FAMILY TYRANNOSAURIDAE
Brusatte
et al. 2010
Carr
et al. 2005
*Note: Carr et al. regard Gorgosaurus libratus as a species of Albertosaurus and Tarbosaurus bataar as a species of Tyrannosaurus
Currie
et al. 2003
With the advent of phylogenetic taxonomy
in vertebrate paleontology, Tyrannosauridae has been given several explicit definitions. The original was produced by Paul Sereno
in 1998, and included all tyrannosauroids closer to Tyrannosaurus than to either Alectrosaurus
, Aublysodon
or Nanotyrannus
. However, Nanotyrannus is often considered to be a juvenile Tyrannosaurus rex, while Aublysodon is usually regarded as a nomen dubium
unsuitable for use in the definition of a clade
. Definitions since then have been based on more well-established genera.
In 2001 Thomas R. Holtz, Jr. published a cladistic analysis of the tyrannosauridae. He concluded that there were two subfamilies, a more primitive Aublysodontinae "characterized by unserrated premaxillary teeth," and the tyrannosaurinae. The Aublysodontinae included Aublysodon, the "Kirtland
Aublysodon", and Alectrosaurus
. Holtz also found that Siamotyrannus
exhibited some of the synapomorphies of the tyrannosauridae, but lay "outside the[ family
] proper."
Later in the same paper he proposed that Tyrannosauridae be defined as "all descendants of the most recent common ancestor of Tyrannosaurus and Aublysodon." He also criticized definitions previously proposed by other workers, like one proposed by Paul Sereno
, that the Tyrannosauridae was "all taxa closer to "Tyrannosaurus" than to Alectrosaurus, Aublysodon, and Nanotyrannus
." Holtz observed that since Nanotyrannus was probably a misidentified T. rex juvenile, Sereno's proposed definition would have the family Tyrannosauridae as a subtaxon of the genus Tyrannosaurus! Further, his proposed definition of the subfamily Tyrannosaurinae would also be limited to Tyrannosaurus.
A 2003 attempt by Christopher Brochu included Albertosaurus
, Alectrosaurus
, Alioramus
, Daspletosaurus
, Gorgosaurus
, Tarbosaurus
and Tyrannosaurus in the definition. Holtz redefined the clade in 2004 to use all of the above as specifiers except for Alioramus and Alectrosaurus, which his analysis could not place with certainty. However, in the same paper, Holtz also provided a completely different definition, including all theropods more closely related to Tyrannosaurus than to Eotyrannus. The most recent definition is that of Sereno in 2005, which defined Tyrannosauridae as the least inclusive clade containing Albertosaurus, Gorgosaurus and Tyrannosaurus.
Cladistic
analyses of tyrannosaurid phylogeny
often find Tarbosaurus and Tyrannosaurus to be sister taxa
, with Daspletosaurus more basal than either. A close relationship between Tarbosaurus and Tyrannosaurus is supported by numerous skull features, including the pattern of sutures
between certain bones, the presence of a crescent-shaped crest on the postorbital bone behind each eye, and a very deep maxilla with a noticeable downward curve on the lower edge, among others. An alternative hypothesis
was presented in a 2003 study by Phil Currie and colleagues, which found weak support for Daspletosaurus as a basal member of a clade
also including Tarbosaurus and Alioramus, both from Asia, based on the absence of a bony prong connecting the nasal and lacrimal bones. Alioramus was found to be the closest relative of Tarbosaurus in this study, based on a similar pattern of stress distribution in the skull.
A related study also noted a locking mechanism in the lower jaw shared between the two genera. In a separate paper, Currie noted the possibility that Alioramus might represent a juvenile Tarbosaurus, but stated that the much higher tooth count and more prominent nasal crests in Alioramus suggest it is a distinct genus. Similarly, Currie uses the high tooth count of Nanotyrannus
to suggest that it may be a distinct genus, rather than a juvenile Tyrannosaurus as most other experts believe.
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
of coelurosauria
Coelurosauria
Coelurosauria is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs. In the past, it was used to refer to all small theropods, although this classification has been abolished...
n theropod
Theropoda
Theropoda is both a suborder of bipedal saurischian dinosaurs, and a clade consisting of that suborder and its descendants . Dinosaurs belonging to the suborder theropoda were primarily carnivorous, although a number of theropod groups evolved herbivory, omnivory, and insectivory...
dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s which comprises two subfamilies containing up to six genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
, including the eponym
Eponym
An eponym is the name of a person or thing, whether real or fictitious, after which a particular place, tribe, era, discovery, or other item is named or thought to be named...
ous Tyrannosaurus
Tyrannosaurus
Tyrannosaurus meaning "tyrant," and sauros meaning "lizard") is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex , commonly abbreviated to T. rex, is a fixture in popular culture. It lived throughout what is now western North America, with a much wider range than other...
. The exact number of genera is controversial, with some experts recognizing as few as three. All of these animals lived near the end of the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
Period and their fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s have been found only in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
and Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
.
Although descended from smaller ancestors
Tyrannosauroidea
Tyrannosauroidea is a superfamily of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent beginning in the Jurassic Period...
, tyrannosaurids were almost always the largest predators
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
in their respective ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
s, putting them at the apex
Apex predator
Apex predators are predators that have no predators of their own, residing at the top of their food chain. Zoologists define predation as the killing and consumption of another organism...
of the food chain
Food chain
A food web depicts feeding connections in an ecological community. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs...
. The largest species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
was Tyrannosaurus rex, one of the largest known land predators, which measured up to 13 metres (42.7 ft) in length and up to 6.8 tonnes (7.5 ST) in weight. Tyrannosaurids were bipedal carnivores with massive skull
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
s filled with large teeth. Despite their large size, their legs were long and proportioned for fast movement. In contrast, their arms were very small, bearing only two functional digits.
Unlike most other groups of dinosaurs, very complete remains have been discovered for most known tyrannosaurids. This has allowed a variety of research into their biology
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
. Scientific studies have focused on their ontogeny
Ontogeny
Ontogeny is the origin and the development of an organism – for example: from the fertilized egg to mature form. It covers in essence, the study of an organism's lifespan...
, biomechanics
Biomechanics
Biomechanics is the application of mechanical principles to biological systems, such as humans, animals, plants, organs, and cells. Perhaps one of the best definitions was provided by Herbert Hatze in 1974: "Biomechanics is the study of the structure and function of biological systems by means of...
and ecology
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
, among other subjects. Soft tissue
Soft tissue
In anatomy, the term soft tissue refers to tissues that connect, support, or surround other structures and organs of the body, not being bone. Soft tissue includes tendons, ligaments, fascia, skin, fibrous tissues, fat, and synovial membranes , and muscles, nerves and blood vessels .It is sometimes...
, both fossilized and intact, has been reported from one specimen of Tyrannosaurus rex.
Description
The known tyrannosaurids were all large animals. A single specimen of AlioramusAlioramus
Alioramus is a genus of tyrannosaurid theropod dinosaur from the Late Cretaceous period of Asia. The type A. remotus, is known from a partial skull and three metatarsals recovered from Mongolian sediments which were deposited in a humid floodplain between 70 and 65 million years ago. These...
of an individual estimated at between 5 and 6 m (16.4 and 19.7 ) long has been discovered, although it is considered by some experts to be a juvenile. Albertosaurus
Albertosaurus
Albertosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, more than 70 million years ago. The type species, A. sarcophagus, was apparently restricted in range to the modern-day Canadian province of Alberta, after which...
, Gorgosaurus
Gorgosaurus
Gorgosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, between about 76.5 and 75 million years ago. Fossil remains have been found in the Canadian province of Alberta and possibly the U.S. state of Montana....
and Daspletosaurus
Daspletosaurus
Daspletosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America between 77 and 74 million years ago, during the Late Cretaceous Period. Fossils of the only named species were found in Alberta, although other possible species from Alberta and Montana await...
all measured between 8 and 10 m (26.2 and 32.8 ) long, while Tarbosaurus
Tarbosaurus
Tarbosaurus is a genus of tyrannosaurid theropod dinosaur that flourished in Asia about 70 million years ago, at the end of the Late Cretaceous Period. Fossils have been recovered in Mongolia, with more fragmentary remains found further afield in parts of China. Although many species have been...
reached lengths of 12 metres (39.4 ft) from snout to tail. The massive Tyrannosaurus was the largest, approaching 13 metres (42.7 ft) in the longest specimens.
Tyrannosaurid skull anatomy is well understood as complete skulls are known for all genera but Alioramus, which is known only from partial skull remains. Tyrannosaurus, Tarbosaurus, and Daspletosaurus had skulls which exceeded 1 metres (3.3 ft) in length, The largest discovered Tyrannosaurus skull measures over 1.5 metres (4.9 ft) long. Adult tyrannosaurids had tall, massive skulls, with many bones fused and reinforced for strength. At the same time, hollow chambers within many skull bones and large openings (fenestrae) between those bones helped to reduce skull weight. Many features of tyrannosaurid skulls were also found in their immediate ancestors, including tall premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
e and fused nasal bone
Nasal bone
The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....
s.
Tyrannosaurid skulls had many unique characteristics, including fused parietal bone
Parietal bone
The parietal bones are bones in the human skull which, when joined together, form the sides and roof of the cranium. Each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is named from the Latin pariet-, wall....
s with a prominent sagittal crest
Sagittal crest
A sagittal crest is a ridge of bone running lengthwise along the midline of the top of the skull of many mammalian and reptilian skulls, among others....
, which ran longitudinally along the sagittal suture
Sagittal suture
The sagittal suture is a dense, fibrous connective tissue joint between the two parietal bones of the skull. The term is derived from the Latin word Sagitta, meaning "arrow". The derivation of this term may be demonstrated by observing how the sagittal suture is notched posteriorly, like an arrow,...
and separated the two supratemporal fenestrae on the skull roof. Behind these fenestrae, tyrannosaurids had a characteristically tall nuchal crest, which also arose from the parietals but ran along a transverse plane
Transverse plane
The transverse plane is an imaginary plane that divides the body into superior and inferior parts. It is perpendicular to the coronal and sagittal planes....
rather than longitudinally. The nuchal crest was especially well-developed in Tyrannosaurus, Tarbosaurus and Alioramus. Albertosaurus, Daspletosaurus and Gorgosaurus had tall crests in front of the eyes on the lacrimal bone
Lacrimal bone
The lacrimal bone, the smallest and most fragile bone of the face, is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders.-Lateral or orbital surface:...
s, while Tarbosaurus and Tyrannosaurus had extremely thickened postorbital bones
Postorbital
The postorbital is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some vertebrates, the postorbital is fused with the postfrontal...
forming crescent-shaped crests behind the eyes. Alioramus had a row of six bony crests on top of its snout, arising from the nasal bones; lower crests have been reported on some specimens of Daspletosaurus and Tarbosaurus, as well as the more basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
tyrannosauroid Appalachiosaurus
Appalachiosaurus
Appalachiosaurus is a genus of tyrannosauroid theropod dinosaur from the Late Cretaceous Period of eastern North America. Like almost all theropods, it was a bipedal predator. Only a juvenile skeleton has been found, representing an animal over 7 meters long and weighing over...
.
Counterweight
A counterweight is an equivalent counterbalancing weight that balances a load.-Uses:A counterweight is often used in traction lifts , cranes and funfair rides...
to balance out the head and torso, with the center of mass
Center of mass
In physics, the center of mass or barycenter of a system is the average location of all of its mass. In the case of a rigid body, the position of the center of mass is fixed in relation to the body...
over the hips. Tyrannosaurids are known for their proportionately very small two-fingered forelimbs, although remnants of a vestigial third digit are sometimes found. Tarbosaurus had the shortest forelimbs compared to its body size, while Daspletosaurus had the longest.
Tyrannosaurids walked exclusively on their hindlimbs, so their leg bones were massive. In contrast to the forelimbs, the hindlimbs were longer compared to body size than almost any other theropods. Juveniles and even some smaller adults, like more basal tyrannosauroids, had longer tibia
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
e than femora
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
, a characteristic of fast-running
Cursorial
Cursorial is a biological term that describes an organism as being adapted specifically to run. It is typically used in conjunction with an animal's feeding habits or another important adaptation. For example, a horse can be considered a "cursorial grazer", while a wolf may be considered a...
dinosaurs like ornithomimids
Ornithomimosauria
The Ornithomimosauria, ornithomimosaurs or ostrich dinosaurs were theropod dinosaurs which bore a superficial resemblance to modern ostriches. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period of Laurasia...
. Larger adults had leg proportions characteristic of slower-moving animals, but not to the extent seen in other large theropods like abelisaurids
Abelisauridae
Abelisauridae is a family of ceratosaurian theropod dinosaurs. Abelisaurids thrived during the Cretaceous Period, on the ancient southern supercontinent of Gondwana, and today their fossil remains are found on the modern continents of Africa and South America, as well as on the Indian...
or carnosaurs
Carnosauria
Carnosauria is a group of large predatory dinosaurs that lived during the Jurassic and Cretaceous periods. While it originally contained a wide assortment of giant theropods that were not closely related, the group has since been defined to encompass only the allosaurs and their closest kin...
. The third metatarsals
Metatarsus
The metatarsus or metatarsal bones are a group of five long bones in the foot located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the medial side : the first, second, third, fourth, and fifth...
of tyrannosaurids were pinched between the second and fourth metatarsals, forming a structure known as the arctometatarsus.
It is unclear when the arctometatarsus first evolved; it was not present in the earliest tyrannosauroids like Dilong
Dilong (dinosaur)
Dilong is a genus of small tyrannosauroid dinosaur. The only species is Dilong paradoxus. It is from the Lower Cretaceous Yixian Formation near Lujiatun, Beipiao, in the western Liaoning province of China. It lived about 130 million years ago...
, but was found in the later Appalachiosaurus
Appalachiosaurus
Appalachiosaurus is a genus of tyrannosauroid theropod dinosaur from the Late Cretaceous Period of eastern North America. Like almost all theropods, it was a bipedal predator. Only a juvenile skeleton has been found, representing an animal over 7 meters long and weighing over...
. This structure also characterized troodontids
Troodontidae
Troodontidae is a family of bird-like theropod dinosaurs. During most of the 20th century, troodontid fossils were few and scrappy and they have therefore been allied, at various times, with many dinosaurian lineages...
, ornithomimids
Ornithomimosauria
The Ornithomimosauria, ornithomimosaurs or ostrich dinosaurs were theropod dinosaurs which bore a superficial resemblance to modern ostriches. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period of Laurasia...
and caenagnathids, but its absence in the earliest tyrannosauroids indicates that it was acquired by convergent evolution
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
.
Teeth
Tyrannosaurids, like their tyrannosauroid ancestors, were heterodontHeterodont
The anatomical term heterodont refers to animals which possess more than a single tooth morphology. For example, members of the Synapsida generally possess incisors, canines , premolars, and molars. The presence of heterodont dentition is evidence of some degree of feeding/hunting specialization...
, with premaxillary teeth D-shaped in cross section
Cross section (geometry)
In geometry, a cross-section is the intersection of a figure in 2-dimensional space with a line, or of a body in 3-dimensional space with a plane, etc...
and smaller than the rest. Unlike earlier tyrannosauroids and most other theropods, the maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
ry and mandibular
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
teeth of mature tyrannosaurids are not blade-like but extremely thickened and often circular in cross-section. Tooth counts tend to be consistent within species, and larger species tend to have lower tooth counts than smaller ones. For example, Alioramus had 76 to 78 teeth in its jaws, while Tyrannosaurus had between 54 and 60.
William L. Abler observed in 2001 that Albertosaurus tooth serrations are so thin as to functionally be a crack
Fracture
A fracture is the separation of an object or material into two, or more, pieces under the action of stress.The word fracture is often applied to bones of living creatures , or to crystals or crystalline materials, such as gemstones or metal...
in the tooth. However, at the base of this crack is round void
Void
-In science and engineering:*Void , the empty spaces between galaxy filaments*Lack of matter, or vacuum*Void, in boiling heat transfer, formed where there is a departure from nucleate boiling, causing a critical heat flux...
called an ampulla
Ampulla
An ampulla was, in Ancient Rome, a "small nearly globular flask or bottle, with two handles" . The word is used of these in archaeology, and of later flasks, often handle-less and much flatter, for holy water or holy oil in the Middle Ages....
which would have functioned to distribute force over a larger surface area
Surface area
Surface area is the measure of how much exposed area a solid object has, expressed in square units. Mathematical description of the surface area is considerably more involved than the definition of arc length of a curve. For polyhedra the surface area is the sum of the areas of its faces...
, hindering the ability of the "crack" formed by the serration to propagate through the tooth. An examination of other ancient predators, a phytosaur
Phytosaur
Phytosaurs are an extinct group of large semi-aquatic Late Triassic archosaurs. Phytosaurs belong to the family Phytosauridae and the order Phytosauria. They were long-snouted and heavily armoured, bearing a remarkable resemblance to modern crocodiles in size, appearance, and lifestyle, an example...
and Dimetrodon
Dimetrodon
Dimetrodon was a predatory synapsid genus that flourished during the Permian period, living between 280–265 million years ago ....
found similarly crack-like serrations, but no adaptation
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
s for preventing crack propagation. Tyrannosaurid teeth were used as holdfasts for pulling meat
Meat
Meat is animal flesh that is used as food. Most often, this means the skeletal muscle and associated fat and other tissues, but it may also describe other edible tissues such as organs and offal...
off a body, rather than knife
Knife
A knife is a cutting tool with an exposed cutting edge or blade, hand-held or otherwise, with or without a handle. Knives were used at least two-and-a-half million years ago, as evidenced by the Oldowan tools...
-like cutting functions. Tooth wear patterns hint that complex head shaking behaviors may have been involved in tyrannosaur feeding. When a tyrannosaur would have pulled back on a piece of meat, the force would tend to push the tip of tooth toward the front of the mouth and the anchored root would experience tension on the posterior side and compression from the front. This would typically incline the tooth to crack formation on the posterior side of the tooth, but the ampullae at the base of the already crack-like serrations would tend to diffuse potential crack-forming forces. This form resembles techniques used by guitar
Guitar
The guitar is a plucked string instrument, usually played with fingers or a pick. The guitar consists of a body with a rigid neck to which the strings, generally six in number, are attached. Guitars are traditionally constructed of various woods and strung with animal gut or, more recently, with...
makers to "impart alternating regions of flexibility and rigidity to a stick of wood." The use of a drill
Drill
A drill or drill motor is a tool fitted with a cutting tool attachment or driving tool attachment, usually a drill bit or driver bit, used for drilling holes in various materials or fastening various materials together with the use of fasteners. The attachment is gripped by a chuck at one end of...
to create an "ampulla" of sorts and prevent the propagation of cracks through an important material is also used to protect airplane surfaces. Abler demonstrated that a plexiglass bar with kerfs and drilled holes was more than 25% stronger than one with only regularly placed incisions.
History of discovery
Deinodon
Deinodon is a name assigned to tyrannosaurid teeth of the Late Cretaceous of Montana by paleontologist Joseph Leidy in 1856...
("terrible tooth") by Joseph Leidy
Joseph Leidy
Joseph Leidy was an American paleontologist.Leidy was professor of anatomy at the University of Pennsylvania, and later was a professor of natural history at Swarthmore College. His book Extinct Fauna of Dakota and Nebraska contained many species not previously described and many previously...
in 1856. The first good speciemens of a tyrannosaurid were found in the Horseshoe Canyon Formation
Horseshoe Canyon Formation
The Horseshoe Canyon Formation is part of the Edmonton Group and is up to 230m in thickness. It is Late Campanian to Early Maastrichtian in age and is composed of mudstone, sandstone, and carbonaceous shales...
of Alberta
Alberta
Alberta is a province of Canada. It had an estimated population of 3.7 million in 2010 making it the most populous of Canada's three prairie provinces...
, and consisted of nearly complete skulls with partial skeletons. These remains were first studied by Edward Drinker Cope
Edward Drinker Cope
Edward Drinker Cope was an American paleontologist and comparative anatomist, as well as a noted herpetologist and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested in science; he published his first scientific paper at the age of nineteen...
in 1876, who considered them a species of the eastern tyrannosauroid Dryptosaurus
Dryptosaurus
Dryptosaurus was a genus of primitive tyrannosaur that lived in Eastern North America during the middle Maastrichtian stage of the Late Cretaceous period. Although largely unknown now outside of academic circles, a famous painting of the genus by Charles R...
. In 1905, Henry Fairfield Osborn
Henry Fairfield Osborn
Henry Fairfield Osborn, Sr. ForMemRS was an American geologist, paleontologist, and eugenicist.-Early life and career:...
recognized that the Alberta remains differed considerably from Dryptosaurus, and coined a new name for them: Albertosaurus sarcophagus
Albertosaurus
Albertosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, more than 70 million years ago. The type species, A. sarcophagus, was apparently restricted in range to the modern-day Canadian province of Alberta, after which...
("flesh-eating Alberta lizard"). Cope described more tyrannosaur material in 1892, in the form of isolated vertebrae, and gave this animal the name Manospondylus gigas. This discovery was mostly overlooked for over a century, and caused controversy in the early 2000s when it was discovered that this material actually belonged to, and had name priority over, Tyrannosaurus rex
Tyrannosaurus
Tyrannosaurus meaning "tyrant," and sauros meaning "lizard") is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex , commonly abbreviated to T. rex, is a fixture in popular culture. It lived throughout what is now western North America, with a much wider range than other...
.
In his 1905 paper naming Albertosaurus, Osborn described two additional tyrannosaur specimens that had been collected from in Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
and Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...
during a 1902 expedition of the American Museum of Natural History
American Museum of Natural History
The American Museum of Natural History , located on the Upper West Side of Manhattan in New York City, United States, is one of the largest and most celebrated museums in the world...
, led by Barnum Brown
Barnum Brown
Barnum Brown , a paleontologist born in Carbondale, Kansas, and named after the circus showman P.T. Barnum, discovered the second fossil of Tyrannosaurus rex during a career that made him one of the most famous fossil hunters working from the late Victorian era into the early 20th century.Sponsored...
. Initially, Osborn considered these to be distinct species. The first, he named Dynamosaurus imperiosus ("emperor power lizard"), and the second, Tyrannosaurus rex ("king tyrant lizard"). A year later, Osborn recognized that these two specimens actually came from the same species. Despite the fact that Dynamosaurus had been found first, the name Tyrannosaurus had appeared one page earlier in his original article describing both specimens. Therefore, according to the International Code of Zoological Nomenclature
International Code of Zoological Nomenclature
The International Code of Zoological Nomenclature is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals...
(ICZN), the name Tyrannosaurus was used.
Barnum Brown went on to collect several more tyrannosaurid specimens from Alberta, including the first to preserve the shortened, two-fingered forelimbs characteristic of the group (which Lawrence Lambe
Lawrence Lambe
Lawrence Morris Lambe was a Canadian geologist and palaeontologist from the Geological Survey of Canada .His published work, describing the diverse and plentiful dinosaur discoveries from the fossil beds in Alberta, did much to bring dinosaurs into the public eye and helped usher in the Golden...
named Gorgosaurus libratus
Gorgosaurus
Gorgosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, between about 76.5 and 75 million years ago. Fossil remains have been found in the Canadian province of Alberta and possibly the U.S. state of Montana....
, "balanced fierce lizard", in 1914). A second significant find attributed to Gorgosaurus was made in 1942, in the form of a well-preserved, though unusually small, complete skull. The specimen waited until after the end of World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
to be studied by Charles W. Gilmore
Charles W. Gilmore
Charles Whitney Gilmore was an American paleontologist, who named dinosaurs in North America and Mongolia, including the Cretaceous sauropod Alamosaurus, Alectrosaurus, Archaeornithomimus, Bactrosaurus, Brachyceratops, Chirostenotes, Mongolosaurus, Parrosaurus, Pinacosaurus, Styracosaurus and...
, who named it Gorgosaurus lancesnis. This skull was re-studied by Robert T. Bakker
Robert T. Bakker
Robert T. Bakker is an American paleontologist who helped reshape modern theories about dinosaurs, particularly by adding support to the theory that some dinosaurs were endothermic...
, Phil Currie, and Michael Williams in 1988, and assigned to the new genus Nanotyrannus
Nanotyrannus
Nanotyrannus is a genus of tyrannosaurid dinosaur, known only from two juvenile specimens, which may in fact represent juvenile specimens of the contemporary species Tyrannosaurus rex.-History:...
. It was also in 1946 that paleontologists from the Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
began expeditions into Mongolia
Mongolia
Mongolia is a landlocked country in East and Central Asia. It is bordered by Russia to the north and China to the south, east and west. Although Mongolia does not share a border with Kazakhstan, its western-most point is only from Kazakhstan's eastern tip. Ulan Bator, the capital and largest...
, and uncovered the first tyrannosaur remains from Asia. Evgeny Maleev
Evgeny Maleev
Evgeny Aleksandrovich Maleev was a Russian paleontologist who named the armoured dinosaur Talarurus, the fearsome Tarbosaurus, and the enigmatic Therizinosaurus. Maleev did research on Tarbosaurus brains by cutting open fossilized braincases with a diamond saw...
described new Mongolian species of Tyrannosaurus and Gorgosaurus in 1955, and one new genus: Tarbosaurus
Tarbosaurus
Tarbosaurus is a genus of tyrannosaurid theropod dinosaur that flourished in Asia about 70 million years ago, at the end of the Late Cretaceous Period. Fossils have been recovered in Mongolia, with more fragmentary remains found further afield in parts of China. Although many species have been...
("terrifying lizard"). Subsequent studies, however, showed that all of Maleev's tyrannosaur species were actually one species of Tarbosaurus at different stages of growth. A second species of Mongolian tyrannosaurid was found later, described by Sergei Kurzanov in 1976, and given the name Alioramus remotus
Alioramus
Alioramus is a genus of tyrannosaurid theropod dinosaur from the Late Cretaceous period of Asia. The type A. remotus, is known from a partial skull and three metatarsals recovered from Mongolian sediments which were deposited in a humid floodplain between 70 and 65 million years ago. These...
("remote different branch"), though its status as a true tyrannosaurid and not a more primitive tyrannosaur is still controversial.
Distribution
Abelisauridae
Abelisauridae is a family of ceratosaurian theropod dinosaurs. Abelisaurids thrived during the Cretaceous Period, on the ancient southern supercontinent of Gondwana, and today their fossil remains are found on the modern continents of Africa and South America, as well as on the Indian...
fossils. The exact time and place of origin of the family remain unknown due to the poor fossil record in the middle part of the Cretaceous on both continents, although the earliest confirmed tyrannosaurids lived in the early Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
stage in western North America.
Tyrannosaurid remains have never been recovered from eastern North America, while more basal tyrannosauroids like Dryptosaurus
Dryptosaurus
Dryptosaurus was a genus of primitive tyrannosaur that lived in Eastern North America during the middle Maastrichtian stage of the Late Cretaceous period. Although largely unknown now outside of academic circles, a famous painting of the genus by Charles R...
and Appalachiosaurus
Appalachiosaurus
Appalachiosaurus is a genus of tyrannosauroid theropod dinosaur from the Late Cretaceous Period of eastern North America. Like almost all theropods, it was a bipedal predator. Only a juvenile skeleton has been found, representing an animal over 7 meters long and weighing over...
persisted there until the end of the Cretaceous, indicating that tyrannosaurids must have evolved in or dispersed
Biological dispersal
Biological dispersal refers to species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
into western North America after the continent was divided in half by the Western Interior Seaway
Western Interior Seaway
The Western Interior Seaway, also called the Cretaceous Seaway, the Niobraran Sea, and the North American Inland Sea, was a huge inland sea that split the continent of North America into two halves, Laramidia and Appalachia, during most of the mid- and late-Cretaceous Period...
in the middle of the Cretaceous. Tyrannosaurid fossils have been found in Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
, which may have provided a route for dispersal between North America and Asia. Alioramus and Tarbosaurus are found to be related in one cladistic analysis, forming a unique Asian branch of the family.
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
stages of North America, with tyrannosaurines like Daspletosaurus ranging throughout the Western Interior, while the albertosaurines Albertosaurus and Gorgosaurus are currently known only from the northwestern part of the continent.
By the late Maastrichtian, albertosaurines appear to have gone extinct, while the tyrannosaurine Tyrannosaurus roamed from Saskatchewan
Saskatchewan
Saskatchewan is a prairie province in Canada, which has an area of . Saskatchewan is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, and on the south by the U.S. states of Montana and North Dakota....
to Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
. This pattern is mirrored in other North American dinosaur taxa. During the Campanian and early Maastrichtian, lambeosaurine
Hadrosaurid
Hadrosaurids or duck-billed dinosaurs are members of the family Hadrosauridae, and include ornithopods such as Edmontosaurus and Parasaurolophus. They were common herbivores in the Upper Cretaceous Period of what are now Asia, Europe and North America. They are descendants of the Upper...
hadrosaurs
Hadrosaurid
Hadrosaurids or duck-billed dinosaurs are members of the family Hadrosauridae, and include ornithopods such as Edmontosaurus and Parasaurolophus. They were common herbivores in the Upper Cretaceous Period of what are now Asia, Europe and North America. They are descendants of the Upper...
and centrosaurine
Centrosaurinae
The Centrosaurinae is a subfamily of ceratopsid dinosaurs named by paleontologist Lawrence Lambe, in 1915, with Centrosaurus as the type genus...
ceratopsia
Ceratopsia
Ceratopsia or Ceratopia is a group of herbivorous, beaked dinosaurs which thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. The earliest known ceratopsian, Yinlong downsi, lived between 161.2 and 155.7...
ns are common in the northwest, while hadrosaurines
Hadrosaurid
Hadrosaurids or duck-billed dinosaurs are members of the family Hadrosauridae, and include ornithopods such as Edmontosaurus and Parasaurolophus. They were common herbivores in the Upper Cretaceous Period of what are now Asia, Europe and North America. They are descendants of the Upper...
and chasmosaurines
Ceratopsidae
Ceratopsidae is a speciose group of marginocephalian dinosaurs including Triceratops and Styracosaurus...
were more common to the south. By the end of the Cretaceous, centrosaurines are unknown and lambeosaurines are rare, while hadrosaurines and chasmosaurines were common throughout the Western Interior.
Growth
Paleontologist Gregory Erickson and colleagues have studied the growth and life history of tyrannosaurids. Analysis of bone histologyHistology
Histology is the study of the microscopic anatomy of cells and tissues of plants and animals. It is performed by examining cells and tissues commonly by sectioning and staining; followed by examination under a light microscope or electron microscope...
can determine the age of a specimen when it died. Growth rates can be examined when the age of various individuals are plotted against their size on a graph. Erickson has shown that after a long time as juveniles, tyrannosaurs underwent tremendous growth spurts for about four years midway through their lives. After the rapid growth phase ended with sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
, growth slowed down considerably in adult animals. A tyrannosaurid growth curve is S-shaped, with the maximum growth rate of individuals around 14 years of age.
Natural History Museum of Los Angeles County
The Natural History Museum of Los Angeles County opened in Exposition Park, Los Angeles, California, USA in 1913 as the Museum of History, Science, and Art. The moving force behind it was a museum association founded in 1910. Its distinctive main building, with fitted marble walls and domed and...
28471, the "Jordan theropod") is estimated to have weighed only 29.9 kilograms (65.9 lb) at only 2 years old, while the largest, such as FMNH
Field Museum of Natural History
The Field Museum of Natural History is located in Chicago, Illinois, USA. It sits on Lake Shore Drive next to Lake Michigan, part of a scenic complex known as the Museum Campus Chicago...
PR2081 ("Sue
Sue (dinosaur)
"Sue" is the nickname given to FMNH PR 2081, which is the largest, most extensive and best preserved Tyrannosaurus rex specimen ever found. It was discovered in the summer of 1990 by Sue Hendrickson, a paleontologist, and was named after her...
") most likely weighed over 5400 kg (11,905 lb), estimated to have been 28 years old, an age which may have been close to the maximum for the species. T. rex juveniles remained under 1800 kg (3,968.3 lb) until approximately 14 years of age, when body size began to increase dramatically. During this rapid growth phase, a young T. rex would gain an average of 600 kg (1,322.8 lb) a year for the next four years. This slowed after 16 years, and at 18 years of age, the curve plateaus again, indicating that growth slowed dramatically. For example, only 600 kg (1,322.8 lb) separated the 28-year-old "Sue" from a 22-year-old Canadian
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
specimen (RTMP
Royal Tyrrell Museum of Palaeontology
The Royal Tyrrell Museum is a popular Canadian tourist attraction and a leading centre of palaeontological research noted for its collection of more than 130,000 fossils....
81.12.1). This sudden change in growth rate may indicate physical maturity, a hypothesis which is supported by the discovery of medullary tissue in the femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
of a 18-year-old T. rex from Montana (MOR
Museum of the Rockies
The Museum of the Rockies, is located in Bozeman, Montana. The museum, originally affiliated with Montana State University in Bozeman, and now, also the Smithsonian Institution, is known for its paleontological collections, although these are not its sole focus...
1125, also known as "B-rex"). Medullary tissue is found only in female birds during ovulation, indicating that "B-rex" was of reproductive age.
Other tyrannosaurids exhibit extremely similar growth curves, although with lower growth rates corresponding to their lower adult sizes. Compared to albertosaurines, Daspletosaurus showed a faster growth rate during the rapid growth period due to its higher adult weight. The maximum growth rate in Daspletosaurus was 180 kilograms (396.8 lb) per year, based on a mass estimate of 1800 kg (3,968.3 lb) in adults. Other authors have suggested higher adult weights for Daspletosaurus; this would change the magnitude of the growth rate but not the overall pattern. The youngest known Albertosaurus is a two-year-old discovered in the Dry Island bonebed, which would have weighed about 50 kg (110.2 lb) and measured slightly more than 2 metres (6.6 ft) in length. The 10 metres (32.8 ft) specimen from the same quarry is the oldest and largest known, at 28 years of age. The fastest growth rate is estimated to be around 12–16 years, reaching 122 kilograms (269 lb) per year, based on an adult 1300 kilograms (2,866 lb) which is about five times slower than for T.-rex. For Gorgosaurus the calculated maximum growth rate is about 110 kilograms (242.5 lb) during the rapid growth phase, which is comparable to that of Albertosaurus.
Life history
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
in Albertosaurus, although growth continued at a slower rate throughout the animals' lives. Sexual maturation while still actively growing appears to be a shared trait among small and large dinosaurs as well as in large mammals such as humans and elephant
Elephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...
s. This pattern of relatively early sexual maturation differs strikingly from the pattern in birds, which delay their sexual maturity until after they have finished growing.
By tabulating the number of specimens of each age group, Erickson and his colleagues were able to draw conclusions about life history in tyranosauridae populations. Their analysis showed that while juveniles were rare in the fossil record, subadults in the rapid growth phase and adults were far more common. Over half of the known T. rex specimens appear to have died within six years of reaching sexual maturity, a pattern which is also seen in other tyrannosaurs and in some large, long-lived birds and mammals today. These species are characterized by high infant mortality rates, followed by relatively low mortality among juveniles. Mortality increases again following sexual maturity, partly due to the stresses of reproduction. While this could be due to preservation or collection biases
Biased sample
In statistics, sampling bias is when a sample is collected in such a way that some members of the intended population are less likely to be included than others. It results in a biased sample, a non-random sample of a population in which all individuals, or instances, were not equally likely to...
, Erickson hypothesized that the difference was due to low mortality among juveniles over a certain size, which is also seen in some modern large mammals like elephant
Elephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...
s. This low mortality may have resulted from a lack of predation, since tyrannosaurs surpassed all contemporaneous predators in size by the age of two. Paleontologists have not found enough Daspletosaurus remains for a similar analysis, but Erickson notes that the same general trend seems to apply.
The tyrannosaurids spent as much as half its life in the juvenile phase before ballooning up to near-maximum size in only a few years. This, along with the complete lack of predators intermediate in size between huge adult tyrannosaurids and other small theropods, suggests these niches may have been filled by juvenile tyrannosaurids. This is seen in modern Komodo dragon
Komodo dragon
The Komodo dragon , also known as the Komodo monitor, is a large species of lizard found in the Indonesian islands of Komodo, Rinca, Flores, Gili Motang and Gili Dasami. A member of the monitor lizard family , it is the largest living species of lizard, growing to a maximum length of in rare cases...
s, where hatchlings start off as tree-dwelling insectivore
Insectivore
An insectivore is a type of carnivore with a diet that consists chiefly of insects and similar small creatures. An alternate term is entomophage, which also refers to the human practice of eating insects....
s and slowly mature into massive apex predator
Apex predator
Apex predators are predators that have no predators of their own, residing at the top of their food chain. Zoologists define predation as the killing and consumption of another organism...
s capable of taking down large vertebrates. For example, Albertosaurus have been found in aggregations that some have suggested to represent mixed-age packs
Pack hunter
A pack hunter is a predator belonging to the animal kingdom, which has evolved to hunt its prey by working together with other members of its species. Normally, such animals are closely related. The most commonly known pack hunter is the Gray Wolf, the ancestor of all breeds of domesticated dogs...
.
Locomotion
Locomotion abilities are best studied for Tyrannosaurus and there are two main issues concerning this: how well it could turn; and what its maximum straight-line speed was likely to have been.Tyrannosaurus may have been slow to turn, possibly taking one to two seconds to turn only 45° – an amount that humans, being vertically oriented and tail-less, can spin in a fraction of a second. The cause of the difficulty is rotational inertiaMoment of inertia
In classical mechanics, moment of inertia, also called mass moment of inertia, rotational inertia, polar moment of inertia of mass, or the angular mass, is a measure of an object's resistance to changes to its rotation. It is the inertia of a rotating body with respect to its rotation...
, since much of Tyrannosaurus’ mass was some distance from its center of gravity, like a human carrying a heavy timber.
Scientists have produced a wide range of maximum speed estimates, mostly around 11 metres per second (24.6 mph), but a few as low as 5 –, and a few as high as 20 metres per second (44.7 mph). Researchers have to rely on various estimating techniques because, while there are many tracks
Trackway
A trackway is an ancient route of travel for people or animals. In biology, a trackway can be a set of impressions in the soft earth, usually a set of footprints, left by an animal. A fossil trackway is the fossilized imprint of a trackway. Trackways have been found all over the world...
of very large theropods walking, so far none have been found of very large theropods running — and this absence may indicate that they did not run.
Jack Horner and Don Lessem argued in 1993 that Tyrannosaurus was slow and probably could not run (no airborne phase in mid-stride). However, Holtz (1998) concluded that tyrannosaurids and their close relatives were the fastest large theropods. Christiansen (1998) estimated that the leg bones of Tyrannosaurus were not significantly stronger than those of elephants, which are relatively limited in their top speed and never actually run (there is no airborne phase), and hence proposed that the dinosaur's maximum speed would have been about 11 metres per second (24.6 mph), which is about the speed of a human sprinter. Farlow and colleagues (1995) have argued that a 6-8 ton Tyrannosaurus would have been critically or even fatally injured if it had fallen while moving quickly, since its torso would have slammed into the ground at a deceleration of 6 g (six times the acceleration due to gravity, or about 60 meters/s²) and its tiny arms could not have reduced the impact. However, giraffe
Giraffe
The giraffe is an African even-toed ungulate mammal, the tallest of all extant land-living animal species, and the largest ruminant...
s have been known to gallop at 50 km/h (31 mph), despite the risk that they might break a leg or worse, which can be fatal even in a "safe" environment such as a zoo. Thus it is quite possible that Tyrannosaurus also moved fast when necessary and had to accept such risks; this scenario has been studied for Allosaurus too. Most recent research on Tyrannosaurus locomotion does not narrow down speeds further than a range from 17 to 40 km/h (10.6 to 24.9 mph), i.e. from walking or slow running to moderate-speed running. A computer model study in 2007 estimated running speeds, based on data taken directly from fossils, and claimed that T. rex had a top running speed of 8 metres per second (17.9 mph). (probably a juvenile individual).
Feathers
Long filamentousProtein filament
In biology, a filament is a "long chain of proteins, such as those found in hair, muscle, or in flagella". They are often bundled together for strength and rigidity. Some cellular examples include:*Actin filaments*Microtubules*Intermediate filaments...
structures have been preserved along with skeletal remains of numerous coelurosaurs from the Early Cretaceous Yixian Formation
Yixian Formation
The Yixian Formation is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans 11 million years during the early Cretaceous period...
and other nearby geological formations from Liaoning
Liaoning
' is a province of the People's Republic of China, located in the northeast of the country. Its one-character abbreviation is "辽" , a name taken from the Liao River that flows through the province. "Níng" means "peace"...
, China. These filaments have usually been interpreted as "protofeathers," homologous
Homology (biology)
Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...
with the branched feathers found in birds and some non-avian theropods
Feathered dinosaurs
The realization that dinosaurs are closely related to birds raised the obvious possibility of feathered dinosaurs. Fossils of Archaeopteryx include well-preserved feathers, but it was not until the early 1990s that clearly non-avialan dinosaur fossils were discovered with preserved feathers...
, although other hypotheses have been proposed. A skeleton of Dilong was described in 2004 that included the first example of "protofeathers" in a tyrannosauroid. Similarly to down feather
Down feather
The down of birds is a layer of fine feathers found under the tougher exterior feathers. Very young birds are clad only in down. Powder down is a specialized type of down found only in a few groups of birds. Down is a fine thermal insulator and padding, used in goods such as jackets, bedding,...
s of modern birds, the "protofeathers" found in Dilong were branched but not pennaceous
Pennaceous feather
Pennaceous feathers are also known as contour feathers. This type of feather is present in most modern birds, and has been shown in some species of maniraptoran dinosaurs....
, and may have been used for insulation
Thermal insulation
Thermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...
.
It has also been theoretized that tyrannosaurids had such protofeathers. However, rare skin impressions from adult tyrannosaurids in Canada and Mongolia show pebbly scales typical of other dinosaurs. While it is possible that protofeathers existed on parts of the body which have not been preserved, a lack of insulatory
Thermal insulation
Thermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...
body covering is consistent with modern multi-ton mammals such as elephant
Elephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...
s, hippopotamus
Hippopotamus
The hippopotamus , or hippo, from the ancient Greek for "river horse" , is a large, mostly herbivorous mammal in sub-Saharan Africa, and one of only two extant species in the family Hippopotamidae After the elephant and rhinoceros, the hippopotamus is the third largest land mammal and the heaviest...
, and most species of rhinoceros
Rhinoceros
Rhinoceros , also known as rhino, is a group of five extant species of odd-toed ungulates in the family Rhinocerotidae. Two of these species are native to Africa and three to southern Asia....
. As an object increases in size, its ability to retain heat increases due to its decreasing surface area
Surface area
Surface area is the measure of how much exposed area a solid object has, expressed in square units. Mathematical description of the surface area is considerably more involved than the definition of arc length of a curve. For polyhedra the surface area is the sum of the areas of its faces...
-to-volume
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....
ratio. Therefore, as large animals evolve
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
in or disperse
Biological dispersal
Biological dispersal refers to species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
into warm climates, a coat of fur or feathers loses its selective
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
advantage for thermal insulation and can instead become a disadvantage, as the insulation traps excess heat inside the body, possibly overheating the animal. Protofeathers may also have been secondarily lost during the evolution of large tyrannosaurids, especially in warm Cretaceous climates.
Vision
Binocular vision
Binocular vision is vision in which both eyes are used together. The word binocular comes from two Latin roots, bini for double, and oculus for eye. Having two eyes confers at least four advantages over having one. First, it gives a creature a spare eye in case one is damaged. Second, it gives a...
slightly better than that of modern hawk
Hawk
The term hawk can be used in several ways:* In strict usage in Australia and Africa, to mean any of the species in the subfamily Accipitrinae, which comprises the genera Accipiter, Micronisus, Melierax, Urotriorchis and Megatriorchis. The large and widespread Accipiter genus includes goshawks,...
s. Jack Horner
Jack Horner (paleontologist)
John "Jack" R. Horner is an American paleontologist who discovered and named Maiasaura, providing the first clear evidence that some dinosaurs cared for their young. He is one of the best-known paleontologists in the United States...
also pointed out that the tyrannosaur lineage had a history of steadily improving binocular vision. It is hard to see how natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
would have favored this long-term trend if tyrannosaurs had been pure scavengers, which would not have needed the advanced depth perception
Depth perception
Depth perception is the visual ability to perceive the world in three dimensions and the distance of an object. Depth sensation is the ability to move accurately, or to respond consistently, based on the distances of objects in an environment....
that stereoscopic vision
Stereopsis
Stereopsis refers to impression of depth that is perceived when a scene is viewed with both eyes by someone with normal binocular vision. Binocular viewing of a scene creates two slightly different images of the scene in the two eyes due the the eyes' different positions on the head...
provides. In modern animals, binocular vision is found mainly in predators (the principal exceptions are primate
Primate
A primate is a mammal of the order Primates , which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment...
s, which need it for leaping from branch to branch).
Unlike Tyrannosaurus, Tarbosaurus had a narrower skull more typical of other tyrannosaurids in which the eyes faced primarily sideways. All of this suggests that Tarbosaurus relied more on its senses of smell and hearing than on its eyesight. In Gorgosaurus specimens, the eye socket
Orbit (anatomy)
In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents...
was circular rather than oval or keyhole-shaped as in other tyrannosaurid genera. In Daspletosaurus this was a tall oval, somewhere in between the circular shape seen in Gorgosaurus and the 'keyhole' shape of Tyrannosaurus.
Bony crests
Alioramus
Alioramus is a genus of tyrannosaurid theropod dinosaur from the Late Cretaceous period of Asia. The type A. remotus, is known from a partial skull and three metatarsals recovered from Mongolian sediments which were deposited in a humid floodplain between 70 and 65 million years ago. These...
, a possible tyrannosaurid from Mongolia, bears a single row of five prominent bony bumps on the nasal bones; a similar row of much lower bumps is present on the skull of Appalachiosaurus, as well as some specimens of Daspletosaurus
Daspletosaurus
Daspletosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America between 77 and 74 million years ago, during the Late Cretaceous Period. Fossils of the only named species were found in Alberta, although other possible species from Alberta and Montana await...
, Albertosaurus, and Tarbosaurus. In Albertosaurus, Gorgosaurus and Daspletosaurus
Daspletosaurus
Daspletosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America between 77 and 74 million years ago, during the Late Cretaceous Period. Fossils of the only named species were found in Alberta, although other possible species from Alberta and Montana await...
, there is a prominent horn in front of each eye on the lacrimal bone. The lacrimal horn is absent in Tarbosaurus and Tyrannosaurus, which instead have a crescent-shaped crest behind each eye on the postorbital bone
Postorbital
The postorbital is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some vertebrates, the postorbital is fused with the postfrontal...
. These head crests may have been used for display
Display (zoology)
Display is a form of animal behaviour, linked to survival of the species in various ways. One example of display used by some species can be found in the form of courtship, with the male usually having a striking feature that is distinguished by colour, shape or size, used to attract a female...
, perhaps for species recognition or courtship behavior.
Thermoregulation
Tyrannosaurus, like most dinosaurs, was long thought to have an ectothermEctotherm
An ectotherm, from the Greek εκτός "outside" and θερμός "hot", refers to organisms that control body temperature through external means. As a result, organisms are dependent on environmental heat sources and have relatively low metabolic rates. For example, many reptiles regulate their body...
ic ("cold-blooded") reptilian metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
but was challenged by scientists like Robert T. Bakker
Robert T. Bakker
Robert T. Bakker is an American paleontologist who helped reshape modern theories about dinosaurs, particularly by adding support to the theory that some dinosaurs were endothermic...
and John Ostrom
John Ostrom
John H. Ostrom was an American paleontologist who revolutionized modern understanding of dinosaurs in the 1960s, when he demonstrated that dinosaurs are more like big non-flying birds than they are like lizards , an idea first proposed by Thomas Henry Huxley in the 1860s, but which had garnered...
in the early years of the "Dinosaur Renaissance
Dinosaur renaissance
The dinosaur renaissance was a small-scale scientific revolution that started in the late 1960s, and led to renewed academic and popular interest in dinosaurs...
", beginning in the late 1960s. Tyrannosaurus rex itself was claimed to have been endothermic
Warm-blooded
The term warm-blooded is a colloquial term to describe animal species which have a relatively higher blood temperature, and maintain thermal homeostasis primarily through internal metabolic processes...
("warm-blooded"), implying a very active lifestyle. Since then, several paleontologists have sought to determine the ability of Tyrannosaurus to regulate
Thermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...
its body temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
. Histological evidence of high growth rates in young T. rex, comparable to those of mammals and birds, may support the hypothesis of a high metabolism. Growth curves indicate that, as in mammals and birds, T. rex growth was limited mostly to immature animals, rather than the indeterminate growth
Indeterminate growth
In biology and especially botany, indeterminate growth refers to growth that is not terminated in contrast to determinate growth that stops once a genetically pre-determined structure has completely formed. Thus, a plant that grows and produces flowers and fruit until killed by frost or some other...
seen in most other vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s. It has been indicated that the temperature difference may have been no more than 4 to 5°C (7 to 9°F) between the vertebrae of the torso and the tibia
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
of the lower leg. This small temperature range between the body core and the extremities was claimed by paleontologist Reese Barrick and geochemist
Geochemistry
The field of geochemistry involves study of the chemical composition of the Earth and other planets, chemical processes and reactions that govern the composition of rocks, water, and soils, and the cycles of matter and energy that transport the Earth's chemical components in time and space, and...
William Showers to indicate that T. rex maintained a constant internal body temperature (homeothermy
Warm-blooded
The term warm-blooded is a colloquial term to describe animal species which have a relatively higher blood temperature, and maintain thermal homeostasis primarily through internal metabolic processes...
) and that it enjoyed a metabolism somewhere between ectothermic reptiles and endothermic mammals. Later they found similar results in Giganotosaurus
Giganotosaurus
Giganotosaurus is a genus of carcharodontosaurid dinosaur that lived around 97 million years ago during the early Cenomanian stage of the Late Cretaceous Period. It included some of the largest known terrestrial carnivores, slightly larger than the largest Tyrannosaurus, but smaller than the...
specimens, who lived on a different continent and tens of millions of years earlier in time. Even if Tyrannosaurus rex does exhibit evidence of homeothermy, it does not necessarily mean that it was endothermic. Such thermoregulation may also be explained by gigantothermy
Gigantothermy
Gigantothermy is a phenomenon with significance in biology and paleontology, whereby large, bulky ectothermic animals are more easily able to maintain a constant, relatively high body temperature than smaller animals by virtue of their smaller surface area to volume ratio...
, as in some living sea turtle
Sea turtle
Sea turtles are marine reptiles that inhabit all of the world's oceans except the Arctic.-Distribution:...
s.
Coexistence of Daspletosaurus and Gorgosaurus
Guild (ecology)
A guild is any group of species that exploit the same resources, often in related ways. As can be seen from the list of examples below, it does not follow that the species within a guild occupy the same, or even similar, ecological niches...
are separated into different ecological niche
Ecological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...
s by anatomical, behavioral or geographical differences that limit competition. Niche differentiation between the Dinosaur Park tyrannosaurids is not well-understood. In 1970, Dale Russell hypothesized
Hypothesis
A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...
the more common Gorgosaurus actively hunted fleet-footed hadrosaurs, while the rarer and more troublesome ceratopsia
Ceratopsia
Ceratopsia or Ceratopia is a group of herbivorous, beaked dinosaurs which thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. The earliest known ceratopsian, Yinlong downsi, lived between 161.2 and 155.7...
ns and ankylosauria
Ankylosauria
Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. They are first known to have appeared in the early Jurassic Period of...
ns (horned and heavily armoured
Armour (zoology)
Armour in animals is external or superficial protection against attack by predators, formed as part of the body , usually through the hardening of body tissues, outgrowths or secretions. It has therefore mostly developed in 'prey' species...
dinosaurs) were left to the more heavily-built Daspletosaurus
Daspletosaurus
Daspletosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America between 77 and 74 million years ago, during the Late Cretaceous Period. Fossils of the only named species were found in Alberta, although other possible species from Alberta and Montana await...
. However, a specimen of Daspletosaurus (OTM 200) from the contemporaneous Two Medicine Formation
Two Medicine Formation
The Two Medicine Formation is a geologic formation, or rock body, that was deposited between 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma , during Campanian time, and is located in northwestern Montana...
of Montana preserves the digested remains of a juvenile hadrosaur in its gut region.
Unlike some other groups of dinosaurs, neither genus was more common at higher or lower elevations than the other. However, Gorgosaurus appears more common in northern formations like the Dinosaur Park, with species of Daspletosaurus more abundant to the south. The same pattern is seen in other groups of dinosaurs. Chasmosaurine ceratopsians and hadrosaurine hadrosaurs are also more common in the Two Medicine Formation of Montana and in southwestern North America during the Campanian, while centrosaurine and lambeosaurines dominate in northern latitudes. Holtz has suggested this pattern indicates shared ecological preferences between tyrannosaurines, chasmosaurines and hadrosaurines. At the end of the later Maastrichtian stage, tyrannosaurines like Tyrannosaurus rex, hadrosaurines like Edmontosaurus
Edmontosaurus
Edmontosaurus is a genus of crestless hadrosaurid dinosaur. It contains two species: Edmontosaurus regalis and Edmontosaurus annectens. Fossils of E. regalis have been found in rocks of western North America that date from the late Campanian stage of the Cretaceous Period 73 million years ago,...
and chasmosaurines like Triceratops
Triceratops
Triceratops is a genus of herbivorous ceratopsid dinosaur which lived during the late Maastrichtian stage of the Late Cretaceous Period, around 68 to 65 million years ago in what is now North America. It was one of the last dinosaur genera to appear before the great Cretaceous–Paleogene...
were widespread throughout western North America, while albertosaurines and centrosaurines went extinct, and lambeosaurines were rare.
Social behavior
There is limited evidence of social behavior among the tyrannosaurids. For example, the "Sue" T.-rex specimen apparently died from a massive bite to the head, which could only have been inflicted by another tyrannosaur. Researchers reported that a subadult and a juvenile skeleton were found in the same quarry as the "Sue" specimen, which has been used to support the hypothesis that tyrannosaurs may have lived in social groups of some kind. While there is no evidence of gregarious behavior in Gorgosaurus, there is evidence of some pack behavior for Albertosaurus and Daspletosaurus.A young specimen of the Dinosaur Park Daspletosaurus species (TMP
Royal Tyrrell Museum of Palaeontology
The Royal Tyrrell Museum is a popular Canadian tourist attraction and a leading centre of palaeontological research noted for its collection of more than 130,000 fossils....
94.143.1) shows bite marks on the face that were inflicted by another tyrannosaur. The bite marks are healed over, indicating that the animal survived the bite. A full-grown Dinosaur Park Daspletosaurus (TMP 85.62.1) also exhibits tyrannosaur bite marks, showing that attacks to the face were not limited to younger animals. While it is possible that the bites were attributable to other species, intraspecific aggression, including facial biting, is very common among predators. Facial bites are seen in other tyrannosaurs like Gorgosaurus and Tyrannosaurus, as well as in other theropod genera like Sinraptor
Sinraptor
Sinraptor is a genus of theropod dinosaur from the Late Jurassic. The name Sinraptor comes from the Latin prefix "Sino", meaning Chinese, and "Raptor" meaning thief. The specific name dongi honours Dong Zhiming...
and Saurornitholestes
Saurornitholestes
Saurornitholestes is a genus of carnivorous dromaeosaurid theropod dinosaur from the late Cretaceous of Alberta, Montana and New Mexico....
. Darren Tanke
Darren Tanke
Darren H. Tanke is a Canadian fossil preparation technician of the Dinosaur Research Program at the Royal Tyrrell Museum of Palaeontology in Drumheller, Alberta. Born in Calgary, Tanke became interested in natural history at an early age. In 1979, Tanke began working for Philip J...
and Phil Currie hypothesize that the bites are due to intraspecific competition
Intraspecific competition
Intraspecific competition is a particular form of competition in which members of the same species vie for the same resource in an ecosystem...
for territory or resources, or for dominance within a social group.
Current (stream)
A current, in a river or stream, is the flow of water influenced by gravity as the water moves downhill to reduce its potential energy. The current varies spatially as well as temporally within the stream, dependent upon the flow volume of water, stream gradient, and channel geometrics...
but that all of the animals were buried simultaneously at the same location. The hadrosaur remains are scattered and bear many marks from tyrannosaur teeth, indicating that the Daspletosaurus were feeding on the hadrosaurs at the time of death. The cause of death is unknown. Currie speculates that the daspletosaurs formed a pack
Pack hunter
A pack hunter is a predator belonging to the animal kingdom, which has evolved to hunt its prey by working together with other members of its species. Normally, such animals are closely related. The most commonly known pack hunter is the Gray Wolf, the ancestor of all breeds of domesticated dogs...
, although this cannot be stated with certainty. Other scientists are skeptical of the evidence for social groups in Daspletosaurus and other large theropods; Brian Roach and Daniel Brinkman have suggested that Daspletosaurus social interaction would have more closely resembled the modern Komodo dragon
Komodo dragon
The Komodo dragon , also known as the Komodo monitor, is a large species of lizard found in the Indonesian islands of Komodo, Rinca, Flores, Gili Motang and Gili Dasami. A member of the monitor lizard family , it is the largest living species of lizard, growing to a maximum length of in rare cases...
, where non-cooperative individuals mob carcasses, frequently attacking and even cannibalizing
Cannibalism (zoology)
In zoology, cannibalism is the act of one individual of a species consuming all or part of another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded for more than 1500 species...
each other in the process.
The Dry Island bonebed discovered by Barnum Brown and his crew contains the remains of 22 Albertosaurus, the most individuals found in one locality of any Cretaceous theropod, and the second-most of any large theropod dinosaur behind the Allosaurus
Allosaurus
Allosaurus is a genus of large theropod dinosaur that lived 155 to 150 million years ago during the late Jurassic period . The name Allosaurus means "different lizard". It is derived from the Greek /allos and /sauros...
assemblage at the Cleveland Lloyd Dinosaur Quarry
Cleveland Lloyd Dinosaur Quarry
The Cleveland Lloyd Dinosaur Quarry National Natural Landmark, located in The San Rafael Swell, near Cleveland, Utah contains the densest concentration of Jurassic dinosaur fossils ever found. Well over 15,000 bones have been excavated from this Jurassic 'predator trap' and there are many...
in Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...
. The group seems to be composed of one very old adult; eight adults between 17 and 23 years old; seven sub-adults undergoing their rapid growth phases at between 12 and 16 years old; and six juveniles between the ages of 2 and 11 years, who had not yet reached the growth phase. The near-absence of herbivore
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
remains and the similar state of preservation between the many individuals at the Albertosaurus bonebed quarry led Phil Currie to conclude that the locality was not a predator trap like the La Brea Tar Pits
La Brea Tar Pits
The La Brea Tar Pits are a cluster of tar pits around which Hancock Park was formed, in the urban heart of Los Angeles. Asphaltum or tar has seeped up from the ground in this area for tens of thousands of years. The tar is often covered with water...
in California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, and that all of the preserved animals died at the same time. Currie claims this as evidence of pack behavior. Other scientists are skeptical, observing that the animals may have been driven together by drought, flood or for other reasons.
Feeding
Meat
Meat is animal flesh that is used as food. Most often, this means the skeletal muscle and associated fat and other tissues, but it may also describe other edible tissues such as organs and offal...
off a body, rather than knife
Knife
A knife is a cutting tool with an exposed cutting edge or blade, hand-held or otherwise, with or without a handle. Knives were used at least two-and-a-half million years ago, as evidenced by the Oldowan tools...
-like cutting functions. Tooth wear patterns hint that complex head shaking behaviors may have been involved in tyrannosaur feeding.
Speculation on the pack-hunting habits of Albertosaurus were made by a few researchers who suggest that the younger members of the pack may have been responsible for driving their prey towards the adults, who were larger and more powerful, but also slower. Juveniles may also have had different lifestyles than adults, filling predator niches
Ecological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...
between those of the enormous adults and the smaller contemporaneous theropods, the largest of which were two orders of magnitude
Order of magnitude
An order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. In its most common usage, the amount being scaled is 10 and the scale is the exponent being applied to this amount...
smaller than an adult Albertosaurus in mass. However, as the preservation of behavior in the fossil record is exceedingly rare, these ideas cannot readily be tested. Phil Currie speculates that the Daspletosaurus formed packs to hunt
Pack hunter
A pack hunter is a predator belonging to the animal kingdom, which has evolved to hunt its prey by working together with other members of its species. Normally, such animals are closely related. The most commonly known pack hunter is the Gray Wolf, the ancestor of all breeds of domesticated dogs...
, although this cannot be stated with certainty. There is no evidence of such gregarious behavior in Gorgosaurus.
The debate about whether Tyrannosaurus was a predator
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
or a pure scavenger
Scavenger
Scavenging is both a carnivorous and herbivorous feeding behavior in which individual scavengers search out dead animal and dead plant biomass on which to feed. The eating of carrion from the same species is referred to as cannibalism. Scavengers play an important role in the ecosystem by...
is as old as the debate about its locomotion. Lambe (1917) described a good skeleton of Tyrannosaurus’ close relative Gorgosaurus
Gorgosaurus
Gorgosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, between about 76.5 and 75 million years ago. Fossil remains have been found in the Canadian province of Alberta and possibly the U.S. state of Montana....
and concluded that it and therefore also Tyrannosaurus was a pure scavenger, because the Gorgosaurus’ teeth showed hardly any wear. This argument is no longer taken seriously, because theropods replaced their teeth quite rapidly. Ever since the first discovery of Tyrannosaurus most scientists have agreed that it was a predator, although like modern large predators it would have been happy to scavenge or steal another predator's kill if it had the opportunity.
Noted hadrosaur
Hadrosaurid
Hadrosaurids or duck-billed dinosaurs are members of the family Hadrosauridae, and include ornithopods such as Edmontosaurus and Parasaurolophus. They were common herbivores in the Upper Cretaceous Period of what are now Asia, Europe and North America. They are descendants of the Upper...
expert Jack Horner
Jack Horner (paleontologist)
John "Jack" R. Horner is an American paleontologist who discovered and named Maiasaura, providing the first clear evidence that some dinosaurs cared for their young. He is one of the best-known paleontologists in the United States...
is currently the major advocate of the idea that Tyrannosaurus was exclusively a scavenger and did not engage in active hunting at all. Horner has presented several arguments to support the pure scavenger hypothesis. The presence of large olfactory bulb
Olfactory bulb
The olfactory bulb is a structure of the vertebrate forebrain involved in olfaction, the perception of odors.-Anatomy:In most vertebrates, the olfactory bulb is the most rostral part of the brain. In humans, however, the olfactory bulb is on the inferior side of the brain...
s and olfactory nerve
Olfactory nerve
The olfactory nerve, or cranial nerve I, is the first of twelve cranial nerves. It is instrumental in the sense of smell. Derived from the embryonic nasal placode, the olfactory nerve is capable of regeneration.-Anatomy:...
s suggests a highly developed sense of smell for sniffing out carcasses over great distances. The teeth could crush bone, and therefore could extract as much food (bone marrow
Bone marrow
Bone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...
) as possible from carcass remnants, usually the least nutritious parts. At least some of its potential prey could move quickly, while evidence suggests that it walked instead of ran.
Other evidence suggests hunting behavior in Tyrannosaurus. The eye-sockets of tyrannosaurs are positioned so that the eyes would point forward, giving them binocular vision
Binocular vision
Binocular vision is vision in which both eyes are used together. The word binocular comes from two Latin roots, bini for double, and oculus for eye. Having two eyes confers at least four advantages over having one. First, it gives a creature a spare eye in case one is damaged. Second, it gives a...
slightly better than that of modern hawk
Hawk
The term hawk can be used in several ways:* In strict usage in Australia and Africa, to mean any of the species in the subfamily Accipitrinae, which comprises the genera Accipiter, Micronisus, Melierax, Urotriorchis and Megatriorchis. The large and widespread Accipiter genus includes goshawks,...
s. Tyrannosaur-inflicted damage has been found on skeletons of hadrosaurs and Triceratops
Triceratops
Triceratops is a genus of herbivorous ceratopsid dinosaur which lived during the late Maastrichtian stage of the Late Cretaceous Period, around 68 to 65 million years ago in what is now North America. It was one of the last dinosaur genera to appear before the great Cretaceous–Paleogene...
that seemed to have survived initial attacks. Some researchers argue that if Tyrannosaurus were a scavenger, another dinosaur had to be the top predator in the Amerasian Upper Cretaceous. The top prey were the larger marginocephalia
Marginocephalia
Marginocephalia is a clade of ornithischian dinosaurs that includes the thick-skulled pachycephalosaurids, and horned ceratopsians. They were all herbivores, walking on two or four legs, and are characterized by a bony ridge or frill the back of the skull...
ns and ornithopod
Ornithopod
Ornithopods or members of the clade Ornithopoda are a group of ornithischian dinosaurs that started out as small, bipedal running grazers, and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world, and dominated the North American...
s. The other tyrannosaurids share so many characteristics with Tyrannosaurus that only small dromaeosaurs
Dromaeosauridae
Dromaeosauridae is a family of bird-like theropod dinosaurs. They were small- to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek dromeus meaning 'runner' and sauros meaning 'lizard'...
remain as feasible top predators. In this light, scavenger hypothesis adherents have suggested that the size and power of tyrannosaurs allowed them to steal kills
Kleptoparasitism
Kleptoparasitism or cleptoparasitism is a form of feeding in which one animal takes prey or other food from another that has caught, collected, or otherwise prepared the food, including stored food...
from smaller predators. Most paleontologists accept that Tyrannosaurus was both an active predator and a scavenger.
Classification
The name Deinodontidae was coined by Edward Drinker CopeEdward Drinker Cope
Edward Drinker Cope was an American paleontologist and comparative anatomist, as well as a noted herpetologist and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested in science; he published his first scientific paper at the age of nineteen...
in 1866 for this family, and continued to be used in place of the newer name Tyrannosauridae through the 1960s. The type genus of the Deinodontidae is Deinodon
Deinodon
Deinodon is a name assigned to tyrannosaurid teeth of the Late Cretaceous of Montana by paleontologist Joseph Leidy in 1856...
, which was named after isolated teeth from Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
. However, in a 1970 review of North American tyrannosaurs, Dale Russell
Dale Russell
Dale A. Russell is a Canadian geologist/palaeontologist, currently Research Professor at The Department of Marine Earth and Atmospheric Sciences of North Carolina State University...
concluded that Deinodon was not a valid taxon, and used the name Tyrannosauridae in place of Deinodontidae, stating that this was in accordance with ICZN
International Code of Zoological Nomenclature
The International Code of Zoological Nomenclature is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals...
rules. Therefore, Tyrannosauridae is preferred by modern experts.
Tyrannosaurus was named by Henry Fairfield Osborn
Henry Fairfield Osborn
Henry Fairfield Osborn, Sr. ForMemRS was an American geologist, paleontologist, and eugenicist.-Early life and career:...
in 1905, along with the family Tyrannosauridae. The name is derived from the Ancient Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
words τυραννος/tyrannos ('tyrant') and σαυρος/sauros ('lizard'). The very common suffix
Suffix
In linguistics, a suffix is an affix which is placed after the stem of a word. Common examples are case endings, which indicate the grammatical case of nouns or adjectives, and verb endings, which form the conjugation of verbs...
-idae is normally appended to zoological
Zoology
Zoology |zoölogy]]), is the branch of biology that relates to the animal kingdom, including the structure, embryology, evolution, classification, habits, and distribution of all animals, both living and extinct...
family names and is derived from the Greek suffix -ιδαι/-idai, which indicates a plural noun.
Taxonomy
Tyrannosauridae is a familyFamily (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
in rank-based Linnaean taxonomy
Linnaean taxonomy
Linnaean taxonomy can mean either of two related concepts:# the particular form of biological classification set up by Carl Linnaeus, as set forth in his Systema Naturæ and subsequent works...
, within the superfamily
Taxonomic rank
In biological classification, rank is the level in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, and class. Each rank subsumes under it a number of less general categories...
Tyrannosauroidea
Tyrannosauroidea
Tyrannosauroidea is a superfamily of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent beginning in the Jurassic Period...
and the suborder
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Theropoda
Theropoda
Theropoda is both a suborder of bipedal saurischian dinosaurs, and a clade consisting of that suborder and its descendants . Dinosaurs belonging to the suborder theropoda were primarily carnivorous, although a number of theropod groups evolved herbivory, omnivory, and insectivory...
.
Tyrannosauridae is uncontroversially divided into two subfamilies. Albertosaurinae comprises the North American genera Albertosaurus and Gorgosaurus, while Tyrannosaurinae includes Daspletosaurus, Tarbosaurus and Tyrannosaurus itself. Some authors include the species Gorgosaurus libratus in the genus Albertosaurus and Tarbosaurus bataar in the genus Tyrannosaurus, while others prefer to retain Gorgosaurus and Tarbosaurus as separate genera. Albertosaurines are characterized by more slender builds, lower skulls, and proportionately longer tibiae than tyrannosaurines. In tyrannosaurines, the sagittal crest on the parietals continues forward onto the frontals. Some authors, such as George Olshevsky and Tracy Ford, have created finer subdivisions or tribes
Tribe (biology)
In biology, a tribe is a taxonomic rank between family and genus. It is sometimes subdivided into subtribes.Some examples include the tribes: Canini, Acalypheae, Hominini, Bombini, and Antidesmeae.-See also:* Biological classification* Rank...
for various combinations of tyrannosaurs within the subfamilies. However, these have not been phylogenetically defined, and usually consisted of genera which are now considered synonymous with other genera or species.
FAMILY TYRANNOSAURIDAE
- Subfamily Albertosaurinae
- Tribe Albertosaurini
- AlectrosaurusAlectrosaurusAlectrosaurus is a genus of tyrannosaurid theropod dinosaur from the Late Cretaceous Period of Inner Mongolia. It was a bipedal carnivore with a body shape similar to its much larger relative, Tyrannosaurus rex...
- AlbertosaurusAlbertosaurusAlbertosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, more than 70 million years ago. The type species, A. sarcophagus, was apparently restricted in range to the modern-day Canadian province of Alberta, after which...
- GorgosaurusGorgosaurusGorgosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, between about 76.5 and 75 million years ago. Fossil remains have been found in the Canadian province of Alberta and possibly the U.S. state of Montana....
- Alectrosaurus
- Tribe Albertosaurini
- Subfamily Tyrannosaurinae
- AlioramusAlioramusAlioramus is a genus of tyrannosaurid theropod dinosaur from the Late Cretaceous period of Asia. The type A. remotus, is known from a partial skull and three metatarsals recovered from Mongolian sediments which were deposited in a humid floodplain between 70 and 65 million years ago. These...
- DaspletosaurusDaspletosaurusDaspletosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America between 77 and 74 million years ago, during the Late Cretaceous Period. Fossils of the only named species were found in Alberta, although other possible species from Alberta and Montana await...
- TeratophoneusTeratophoneusTeratophoneus is a genus of carnivorous tyrannosaurid theropod dinosaur which lived during the late Cretaceous period in what is now Utah, USA. It is known from an incomplete skull and postcranial skeleton recovered from the Kaiparowits Formation. Teratophoneus was named by Thomas D. Carr, Thomas E...
- ZhuchengtyrannusZhuchengtyrannusZhuchengtyrannus is an extinct genus of carnivorous theropod dinosaur from the Late Cretaceous period. It is a tyrannosaurine tyrannosaurid which lived during the late Cretaceous period in what is now Zhucheng, Shandong Province of China...
- Tribe Tarbosaurini
- TarbosaurusTarbosaurusTarbosaurus is a genus of tyrannosaurid theropod dinosaur that flourished in Asia about 70 million years ago, at the end of the Late Cretaceous Period. Fossils have been recovered in Mongolia, with more fragmentary remains found further afield in parts of China. Although many species have been...
- Tarbosaurus
- Tribe Tyrannosaurini
- ?NanotyrannusNanotyrannusNanotyrannus is a genus of tyrannosaurid dinosaur, known only from two juvenile specimens, which may in fact represent juvenile specimens of the contemporary species Tyrannosaurus rex.-History:...
- TyrannosaurusTyrannosaurusTyrannosaurus meaning "tyrant," and sauros meaning "lizard") is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex , commonly abbreviated to T. rex, is a fixture in popular culture. It lived throughout what is now western North America, with a much wider range than other...
- ?Nanotyrannus
- Alioramus
- Nomen dubia
- AublysodonAublysodonAublysodon is a name given to a large number of carnivorous dinosaur teeth of a certain form found in numerous late Cretaceous period geological formations...
- DeinodonDeinodonDeinodon is a name assigned to tyrannosaurid teeth of the Late Cretaceous of Montana by paleontologist Joseph Leidy in 1856...
- Aublysodon
Phylogeny
Stephen L. Brusatte
Stephen Louis Brusatte , is an American paleontologist.-Biography:He is the author of the 2002 book Stately Fossils: A Comprehensive Look at the State Fossils and Other Official Fossils and the 2008 book Dinosaurs...
et al. 2010
Thomas Carr (paleontologist)
Thomas D. Carr is a vertebrate paleontologist who received his Ph.D. from the University of Toronto in 2005. He is now a member of the biology faculty at Carthage College in Kenosha, Wisconsin. Much of his work centers on tyrannosauroid dinosaurs...
et al. 2005
*Note: Carr et al. regard Gorgosaurus libratus as a species of Albertosaurus and Tarbosaurus bataar as a species of Tyrannosaurus
Philip Currie
Philip Henry Wodehouse Currie, 1st Baron Currie GCB , known as Sir Philip Currie between 1885 and 1899, was a British diplomat. He was Ambassador to the Ottoman Empire from 1893 to 1898 and Ambassador to Italy from 1898 to 1902.-Background and education:Currie was the son of Raikes Currie, Member...
et al. 2003
With the advent of phylogenetic taxonomy
Phylogenetic nomenclature
Phylogenetic nomenclature or phylogenetic taxonomy is an alternative to rank-based nomenclature, applying definitions from cladistics . Its two defining features are the use of phylogenetic definitions of biological taxon names, and the lack of obligatory ranks...
in vertebrate paleontology, Tyrannosauridae has been given several explicit definitions. The original was produced by Paul Sereno
Paul Sereno
Paul Callistus Sereno is an American paleontologist from the University of Chicago who discovered several new dinosaur species on several continents. He has conducted excavations at sites as varied as Inner Mongolia, Argentina, Morocco, and Niger...
in 1998, and included all tyrannosauroids closer to Tyrannosaurus than to either Alectrosaurus
Alectrosaurus
Alectrosaurus is a genus of tyrannosaurid theropod dinosaur from the Late Cretaceous Period of Inner Mongolia. It was a bipedal carnivore with a body shape similar to its much larger relative, Tyrannosaurus rex...
, Aublysodon
Aublysodon
Aublysodon is a name given to a large number of carnivorous dinosaur teeth of a certain form found in numerous late Cretaceous period geological formations...
or Nanotyrannus
Nanotyrannus
Nanotyrannus is a genus of tyrannosaurid dinosaur, known only from two juvenile specimens, which may in fact represent juvenile specimens of the contemporary species Tyrannosaurus rex.-History:...
. However, Nanotyrannus is often considered to be a juvenile Tyrannosaurus rex, while Aublysodon is usually regarded as a nomen dubium
Nomen dubium
In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...
unsuitable for use in the definition of a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
. Definitions since then have been based on more well-established genera.
In 2001 Thomas R. Holtz, Jr. published a cladistic analysis of the tyrannosauridae. He concluded that there were two subfamilies, a more primitive Aublysodontinae "characterized by unserrated premaxillary teeth," and the tyrannosaurinae. The Aublysodontinae included Aublysodon, the "Kirtland
Kirtland Formation
The Kirtland Formation is a sedimentary geological formation. It is the product of alluvial muds and overbank sand deposits from the many channels draining the coastal plain that existed on the inland seashore of North America, in the late Cretaceous period. It overlies the Fruitland Formation...
Aublysodon", and Alectrosaurus
Alectrosaurus
Alectrosaurus is a genus of tyrannosaurid theropod dinosaur from the Late Cretaceous Period of Inner Mongolia. It was a bipedal carnivore with a body shape similar to its much larger relative, Tyrannosaurus rex...
. Holtz also found that Siamotyrannus
Siamotyrannus
Siamotyrannus is a genus of theropod dinosaur from the early Cretaceous . It is known from a partial skeleton which includes part of the pelvis, the sacrum, and a number of vertebrae. The fossils were found in 1993 by Somchai Traimwichanon in the Sao Khua Formation of northeastern Thailand...
exhibited some of the synapomorphies of the tyrannosauridae, but lay "outside the
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Later in the same paper he proposed that Tyrannosauridae be defined as "all descendants of the most recent common ancestor of Tyrannosaurus and Aublysodon." He also criticized definitions previously proposed by other workers, like one proposed by Paul Sereno
Paul Sereno
Paul Callistus Sereno is an American paleontologist from the University of Chicago who discovered several new dinosaur species on several continents. He has conducted excavations at sites as varied as Inner Mongolia, Argentina, Morocco, and Niger...
, that the Tyrannosauridae was "all taxa closer to "Tyrannosaurus" than to Alectrosaurus, Aublysodon, and Nanotyrannus
Nanotyrannus
Nanotyrannus is a genus of tyrannosaurid dinosaur, known only from two juvenile specimens, which may in fact represent juvenile specimens of the contemporary species Tyrannosaurus rex.-History:...
." Holtz observed that since Nanotyrannus was probably a misidentified T. rex juvenile, Sereno's proposed definition would have the family Tyrannosauridae as a subtaxon of the genus Tyrannosaurus! Further, his proposed definition of the subfamily Tyrannosaurinae would also be limited to Tyrannosaurus.
A 2003 attempt by Christopher Brochu included Albertosaurus
Albertosaurus
Albertosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, more than 70 million years ago. The type species, A. sarcophagus, was apparently restricted in range to the modern-day Canadian province of Alberta, after which...
, Alectrosaurus
Alectrosaurus
Alectrosaurus is a genus of tyrannosaurid theropod dinosaur from the Late Cretaceous Period of Inner Mongolia. It was a bipedal carnivore with a body shape similar to its much larger relative, Tyrannosaurus rex...
, Alioramus
Alioramus
Alioramus is a genus of tyrannosaurid theropod dinosaur from the Late Cretaceous period of Asia. The type A. remotus, is known from a partial skull and three metatarsals recovered from Mongolian sediments which were deposited in a humid floodplain between 70 and 65 million years ago. These...
, Daspletosaurus
Daspletosaurus
Daspletosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America between 77 and 74 million years ago, during the Late Cretaceous Period. Fossils of the only named species were found in Alberta, although other possible species from Alberta and Montana await...
, Gorgosaurus
Gorgosaurus
Gorgosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, between about 76.5 and 75 million years ago. Fossil remains have been found in the Canadian province of Alberta and possibly the U.S. state of Montana....
, Tarbosaurus
Tarbosaurus
Tarbosaurus is a genus of tyrannosaurid theropod dinosaur that flourished in Asia about 70 million years ago, at the end of the Late Cretaceous Period. Fossils have been recovered in Mongolia, with more fragmentary remains found further afield in parts of China. Although many species have been...
and Tyrannosaurus in the definition. Holtz redefined the clade in 2004 to use all of the above as specifiers except for Alioramus and Alectrosaurus, which his analysis could not place with certainty. However, in the same paper, Holtz also provided a completely different definition, including all theropods more closely related to Tyrannosaurus than to Eotyrannus. The most recent definition is that of Sereno in 2005, which defined Tyrannosauridae as the least inclusive clade containing Albertosaurus, Gorgosaurus and Tyrannosaurus.
Cladistic
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
analyses of tyrannosaurid phylogeny
Phylogenetics
In biology, phylogenetics is the study of evolutionary relatedness among groups of organisms , which is discovered through molecular sequencing data and morphological data matrices...
often find Tarbosaurus and Tyrannosaurus to be sister taxa
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
, with Daspletosaurus more basal than either. A close relationship between Tarbosaurus and Tyrannosaurus is supported by numerous skull features, including the pattern of sutures
Suture (anatomical)
In anatomy, a suture is a fairly rigid joint between two or more hard elements of an animal, with or without significant overlap of the elements....
between certain bones, the presence of a crescent-shaped crest on the postorbital bone behind each eye, and a very deep maxilla with a noticeable downward curve on the lower edge, among others. An alternative hypothesis
Hypothesis
A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...
was presented in a 2003 study by Phil Currie and colleagues, which found weak support for Daspletosaurus as a basal member of a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
also including Tarbosaurus and Alioramus, both from Asia, based on the absence of a bony prong connecting the nasal and lacrimal bones. Alioramus was found to be the closest relative of Tarbosaurus in this study, based on a similar pattern of stress distribution in the skull.
A related study also noted a locking mechanism in the lower jaw shared between the two genera. In a separate paper, Currie noted the possibility that Alioramus might represent a juvenile Tarbosaurus, but stated that the much higher tooth count and more prominent nasal crests in Alioramus suggest it is a distinct genus. Similarly, Currie uses the high tooth count of Nanotyrannus
Nanotyrannus
Nanotyrannus is a genus of tyrannosaurid dinosaur, known only from two juvenile specimens, which may in fact represent juvenile specimens of the contemporary species Tyrannosaurus rex.-History:...
to suggest that it may be a distinct genus, rather than a juvenile Tyrannosaurus as most other experts believe.
External links
- Tyrannosauridae specimen list and discussion at The Theropod Database