Tyrannosaurus

Tyrannosaurus

Overview
Tyrannosaurus is a genus
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...

 of coelurosaurian 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...

. The 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...

 Tyrannosaurus rex (rex meaning "king" in Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

), 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 tyrannosaurids
Tyrannosauridae
Tyrannosauridae is a family of coelurosaurian theropod dinosaurs which comprises two subfamilies containing up to six genera, including the eponymous Tyrannosaurus. The exact number of genera is controversial, with some experts recognizing as few as three...

. Fossils are found in a variety of rock formations
Geologic formation
A formation or geological formation is the fundamental unit of lithostratigraphy. A formation consists of a certain number of rock strata that have a comparable lithology, facies or other similar properties...

 dating to the Maastrichtian
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...

 age of the upper 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, 67 to 65.5 million years ago.
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Encyclopedia
Tyrannosaurus is a genus
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...

 of coelurosaurian 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...

. The 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...

 Tyrannosaurus rex (rex meaning "king" in Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

), 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 tyrannosaurids
Tyrannosauridae
Tyrannosauridae is a family of coelurosaurian theropod dinosaurs which comprises two subfamilies containing up to six genera, including the eponymous Tyrannosaurus. The exact number of genera is controversial, with some experts recognizing as few as three...

. Fossils are found in a variety of rock formations
Geologic formation
A formation or geological formation is the fundamental unit of lithostratigraphy. A formation consists of a certain number of rock strata that have a comparable lithology, facies or other similar properties...

 dating to the Maastrichtian
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...

 age of the upper 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, 67 to 65.5 million years ago. It was among the last non-avian dinosaurs to exist before the Cretaceous–Paleogene extinction event.

Like other tyrannosaurids
Tyrannosauridae
Tyrannosauridae is a family of coelurosaurian theropod dinosaurs which comprises two subfamilies containing up to six genera, including the eponymous Tyrannosaurus. The exact number of genera is controversial, with some experts recognizing as few as three...

, Tyrannosaurus was a biped
Biped
Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs, or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning "two feet"...

al carnivore
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...

 with a massive skull balanced by a long, heavy tail. Relative to the large and powerful hindlimbs, Tyrannosaurus forelimbs were small, though unusually powerful for their size, and bore two clawed digits. Although other theropods rivaled or exceeded Tyrannosaurus rex in size
Dinosaur size
Size has been one of the most interesting aspects of dinosaur science to the general public. This article lists the largest and smallest dinosaurs from various groups, sorted in order of weight and length....

, it was the largest known tyrannosaurid and one of the largest known land predators, measuring up to 12.8 m (42 ft) in length, up to 4 metres (13.1 ft) tall at the hips, and up to 6.8 metric tons (7.5 ST) in weight. By far the largest carnivore in its environment, Tyrannosaurus rex may have been an 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...

, preying upon hadrosaurs and 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, although some experts have suggested it was primarily a 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...

. The debate over Tyrannosaurus as apex predator or scavenger is among the longest running in paleontology
Paleontology
Paleontology "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought") is the study of prehistoric life. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments...

.

More than 30 specimens of Tyrannosaurus rex have been identified, some of which are nearly complete skeletons. 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...

 and protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s have been reported in at least one of these specimens. The abundance of fossil material has allowed significant research into many aspects of its biology, including life history and 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...

. The feeding habits, physiology
Physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...

 and potential speed of Tyrannosaurus rex are a few subjects of debate. Its taxonomy
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...

 is also controversial, with some scientists considering Tarbosaurus bataar
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...

 from Asia to represent a second species of Tyrannosaurus and others maintaining Tarbosaurus as a separate genus. Several other genera of North American tyrannosaurids have also been synonymized with Tyrannosaurus.

Description



Tyrannosaurus rex was one of the largest land carnivores of all time; the largest complete specimen, 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...

"), measured 12.8 metres (42 ft) long, and was 4 metres (13.1 ft) tall at the hips. Mass estimates have varied widely over the years, from more than 7.2 metric tons (7.9 ST), to less than 4.5 metric tons (5 ST), with most modern estimates ranging between 5.4 and 6.8 MT (6 and 7.5 ST). Packard et al. (2009) tested dinosaur mass estimation procedures on elephants and concluded that dinosaur estimations are flawed and produce over-estimations; thus, the weight of Tyrannosaurus could be much less than usually estimated. Other estimations have concluded that the largest known Tyrannosaurus specimens had a weight exceeding 9 tonnes.

Although Tyrannosaurus rex was larger than the well known Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to  Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

 theropod 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...

, it was slightly smaller than two other Cretaceous carnivores, Spinosaurus
Spinosaurus
Spinosaurus is a genus of theropod dinosaur which lived in what is now North Africa, from the lower Albian to lower Cenomanian stages of the Cretaceous period, about 112 to 97 million years ago. This genus was first known from Egyptian remains discovered in 1912 and described by German...

 and 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...

.

The neck of Tyrannosaurus rex formed a natural S-shaped curve like that of other theropods, but was short and muscular to support the massive head. The forelimbs had only two clawed fingers, along with an additional small metacarpal representing the remnant of a third digit. In contrast the hind limbs were among the longest in proportion to body size of any theropod. The tail was heavy and long, sometimes containing over forty vertebrae, in order to balance the massive head and torso. To compensate for the immense bulk of the animal, many bones throughout the skeleton were hollow, reducing its weight without significant loss of strength.

The largest known Tyrannosaurus rex skulls measure up to 5 feet (1.5 m) in length. Large fenestrae
Fenestrae
Fenestræ is a Latin word that means "window".* In histology, fenestræ are small pores in endothelial cells that allow for rapid exchange of molecules between sinusoid blood vessels and surrounding tissue...

 (openings) in the skull reduced weight and provided areas for muscle attachment, as in all carnivorous theropods. But in other respects Tyrannosaurus's skull was significantly different from those of large non-tyrannosauroid theropods. It was extremely wide at the rear but had a narrow snout, allowing unusually good 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...

. The skull bones were massive and the nasals
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....

 and some other bones were fused, preventing movement between them; but many were pneumatized (contained a "honeycomb" of tiny air spaces) which may have made the bones more flexible as well as lighter. These and other skull-strengthening features are part of the tyrannosaurid trend towards an increasingly powerful bite, which easily surpassed that of all non-tyrannosaurids. The tip of the upper jaw was U-shaped (most non-tyrannosauroid carnivores had V-shaped upper jaws), which increased the amount of tissue and bone a tyrannosaur could rip out with one bite, although it also increased the stresses on the front teeth.
The teeth of Tyrannosaurus rex displayed marked heterodont
Heterodont
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...

y (differences in shape). The 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....

ry teeth at the front of the upper jaw were closely packed, D-shaped in cross-section, had reinforcing ridges on the rear surface, were incisiform
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...

 (their tips were chisel-like blades) and curved backwards. The D-shaped cross-section, reinforcing ridges and backwards curve reduced the risk that the teeth would snap when Tyrannosaurus bit and pulled. The remaining teeth were robust, like "lethal bananas" rather than daggers; more widely spaced and also had reinforcing ridges. Those in the upper jaw were larger than those in all but the rear of the lower jaw. The largest found so far is estimated to have been 30 centimetres (11.8 in) long including the root when the animal was alive, making it the largest tooth of any carnivorous dinosaur yet found.

Classification


Tyrannosaurus is the type
Biological type
In biology, a type is one particular specimen of an organism to which the scientific name of that organism is formally attached...

 genus of the superfamily 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...

, the family
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...

 Tyrannosauridae
Tyrannosauridae
Tyrannosauridae is a family of coelurosaurian theropod dinosaurs which comprises two subfamilies containing up to six genera, including the eponymous Tyrannosaurus. The exact number of genera is controversial, with some experts recognizing as few as three...

, and the subfamily Tyrannosaurinae; in other words it is the standard by which paleontologists decide whether to include other species in the same group. Other members of the tyrannosaurine subfamily include the North American 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...

 and the 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...

n Tarbosaurus, both of which have occasionally been synonymized with Tyrannosaurus. Tyrannosaurids were once commonly thought to be descendants of earlier large theropods such as megalosaurs and 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...

, although more recently they were reclassified with the generally smaller coelurosaurs
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...

.

In 1955, Soviet paleontologist
Paleontology
Paleontology "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought") is the study of prehistoric life. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments...

 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...

 named a new species, Tyrannosaurus bataar, from 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...

. By 1965, this species had been renamed Tarbosaurus bataar. Despite the renaming, many phylogenetic analyses have found Tarbosaurus bataar to be the sister taxon of Tyrannosaurus rex, and it has often been considered an Asian species of Tyrannosaurus. A recent redescription of the skull of Tarbosaurus bataar has shown that it was much narrower than that of Tyrannosaurus rex and that during a bite, the distribution of stress in the skull would have been very different, closer to that of 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...

, another Asian tyrannosaur. A related cladistic analysis found that Alioramus, not Tyrannosaurus, was the sister taxon of Tarbosaurus, which, if true, would suggest that Tarbosaurus and Tyrannosaurus should remain separate.

Other tyrannosaurid fossils found in the same formations as Tyrannosaurus rex were originally classified as separate taxa, including Aublysodon and Albertosaurus megagracilis, the latter being named Dinotyrannus megagracilis in 1995. However, these fossils are now universally considered to belong to juvenile Tyrannosaurus rex. A small but nearly complete skull from Montana, 60 centimetres (2 ft) long, may be an exception. This skull was originally classified as a species of 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....

 (G. lancensis) 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...

 in 1946, but was later referred to a 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:...

. Opinions remain divided on the validity of N. lancensis. Many paleontologists consider the skull to belong to a juvenile Tyrannosaurus rex. There are minor differences between the two species, including the higher number of teeth in N. lancensis, which lead some scientists to recommend keeping the two genera separate until further research or discoveries clarify the situation.

Manospondylus


The first named fossil specimen which can be attributed to Tyrannosaurus rex consists of two partial vertebrae (one of which has been lost) found 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 1892. Cope believed that they belonged to an "agathaumid" (ceratopsid
Ceratopsidae
Ceratopsidae is a speciose group of marginocephalian dinosaurs including Triceratops and Styracosaurus...

) dinosaur, and named them Manospondylus gigas, meaning "giant porous vertebra" in reverence to the numerous openings for blood vessels he found in the bone. The M. gigas remains were later identified as those of a theropod rather than a ceratopsid, and H.F. Osborn recognized the similarity between M. gigas and Tyrannosaurus rex as early as 1917. However, due to the fragmentary nature of the Manospondylus vertebrae, Osborn did not synonymize the two genera.

In June 2000, the Black Hills Institute located the type locality of M. gigas in South Dakota and unearthed more tyrannosaur bones there. These were judged to represent further remains of the same individual, and to be identical to those of Tyrannosaurus rex. According to the rules of 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 system that governs the scientific naming of animals, Manospondylus gigas should therefore have priority over Tyrannosaurus rex, because it was named first. However, the Fourth Edition of the ICZN, which took effect on 1 January 2000, states that "the prevailing usage must be maintained" when "the senior synonym or homonym has not been used as a valid name after 1899" and "the junior synonym or homonym has been used for a particular taxon, as its presumed valid name, in at least 25 works, published by at least 10 authors in the immediately preceding 50 years ..." Tyrannosaurus rex may qualify as the valid name under these conditions and would most likely be considered a nomen protectum ("protected name") under the ICZN if it is ever formally published on, which it has not yet been. Manospondylus gigas could then be deemed a nomen oblitum
Nomen oblitum
A nomen oblitum is a technical term, used in zoological nomenclature, for a particular kind of disused scientific name....

 ("forgotten name").

Life history


The identification of several specimens as juvenile Tyrannosaurus rex has allowed scientists to document ontogenetic
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...

 changes in the species, estimate the lifespan, and determine how quickly the animals would have grown. The smallest known individual (LACM 28471, the "Jordan theropod") is estimated to have weighed only 30 kg (66.1 lb), 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). Histologic
Histology
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...

 analysis of Tyrannosaurus rex bones showed LACM 28471 had aged only 2 years when it died, while "Sue" was 28 years old, an age which may have been close to the maximum for the species.

Histology has also allowed the age of other specimens to be determined. Growth curves can be developed when the ages of different specimens are plotted on a graph along with their mass. A Tyrannosaurus rex growth curve is S-shaped, with juveniles remaining 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 Tyrannosaurus rex would gain an average of 600 kg (1,322.8 lb) a year for the next four years. 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). Another recent histological study performed by different workers corroborates these results, finding that rapid growth began to slow at around 16 years of age. 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 16 to 20-year-old Tyrannosaurus 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. Further study indicates an age of 18 for this specimen. Other tyrannosaurids exhibit extremely similar growth curves, although with lower growth rates corresponding to their lower adult sizes.

Over half of the known Tyrannosaurus 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. One study suggests that the rarity of juvenile Tyrannosaurus rex fossils is due in part to low juvenile mortality rates; the animals were not dying in large numbers at these ages, and so were not often fossilized. However, this rarity may also be due to the incompleteness of the fossil record or to the bias of fossil collectors towards larger, more spectacular specimens.

Sexual dimorphism


As the number of specimens increased, scientists began to analyze the variation between individuals and discovered what appeared to be two distinct body types, or morphs, similar to some other theropod species. As one of these morphs was more solidly built, it was termed the 'robust' morph while the other was termed 'gracile'. Several morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

 differences associated with the two morphs were used to analyze sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...

 in Tyrannosaurus rex, with the 'robust' morph usually suggested to be female. For example, the pelvis
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...

 of several 'robust' specimens seemed to be wider, perhaps to allow the passage of eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

. It was also thought that the 'robust' morphology correlated with a reduced chevron
Chevron (anatomy)
A chevron is one of a series of bones on the ventral side of the tail in many reptiles, dinosaurs , and some mammals such as kangaroos and manatees....

 on the first tail vertebra, also ostensibly to allow eggs to pass out of the reproductive tract
Reproductive system
The reproductive system or genital system is a system of organs within an organism which work together for the purpose of reproduction. Many non-living substances such as fluids, hormones, and pheromones are also important accessories to the reproductive system. Unlike most organ systems, the sexes...

, as had been erroneously reported for crocodile
Crocodile
A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...

s.

In recent years, evidence for sexual dimorphism has been weakened. A 2005 study reported that previous claims of sexual dimorphism in crocodile chevron anatomy were in error, casting doubt on the existence of similar dimorphism between Tyrannosaurus rex genders. A full-sized chevron was discovered on the first tail vertebra of "Sue", an extremely robust individual, indicating that this feature could not be used to differentiate the two morphs anyway. As Tyrannosaurus rex specimens have been found 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 New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...

, differences between individuals may be indicative of geographic variation rather than sexual dimorphism. The differences could also be age-related, with 'robust' individuals being older animals.

Only a single Tyrannosaurus rex specimen has been conclusively shown to belong to a specific gender. Examination of "B-rex" demonstrated the preservation of 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...

 within several bones. Some of this tissue has been identified as a medullary tissue, a specialized tissue grown only in modern birds as a source of calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 for the production of eggshell
Eggshell
An eggshell is the outer covering of a hard-shelled egg and of some forms of eggs with soft outer coats.- Insect eggs :Insects and other arthropods lay a variety of styles and shapes of eggs. Some have gelatinous or skin-like coverings, others have hard eggshells. Softer shells are mostly protein....

 during ovulation
Ovulation
Ovulation is the process in a female's menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum . Ovulation also occurs in the estrous cycle of other female mammals, which differs in many fundamental ways from the menstrual cycle...

. As only female birds lay eggs, medullary tissue is only found naturally in females, although males are capable of producing it when injected with female reproductive hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...

s like estrogen
Estrogen
Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...

. This strongly suggests that "B-rex" was female, and that she died during ovulation. Recent research has shown that medullary tissue is never found in crocodiles, which are thought to be the closest living relatives of dinosaurs, aside from birds. The shared presence of medullary tissue in birds and theropod dinosaurs is further evidence of the close evolution
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...

ary relationship between the two.

Posture



Like many bipedal dinosaurs, Tyrannosaurus rex was historically depicted as a 'living tripod', with the body at 45 degrees or less from the vertical and the tail dragging along the ground, similar to a kangaroo
Kangaroo
A kangaroo is a marsupial from the family Macropodidae . In common use the term is used to describe the largest species from this family, especially those of the genus Macropus, Red Kangaroo, Antilopine Kangaroo, Eastern Grey Kangaroo and Western Grey Kangaroo. Kangaroos are endemic to the country...

. This concept dates from 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...

's 1865 reconstruction of Hadrosaurus
Hadrosaurus
Hadrosaurus is a valid genus of hadrosaurid dinosaur. In 1858, a skeleton of a dinosaur from this genus was the first dinosaur skeleton known from more than isolated teeth to be found in North America. In 1868, it became the first ever mounted dinosaur skeleton...

, the first to depict a dinosaur in a bipedal posture. Henry Fairfield Osborn
Henry Fairfield Osborn
Henry Fairfield Osborn, Sr. ForMemRS was an American geologist, paleontologist, and eugenicist.-Early life and career:...

, former president 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...

 (AMNH) in New York City, who believed the creature stood upright, further reinforced the notion after unveiling the first complete Tyrannosaurus rex skeleton in 1915. It stood in this upright pose for 77 years, until it was dismantled in 1992. By 1970, scientists realized this pose was incorrect and could not have been maintained by a living animal, as it would have resulted in the dislocation
Dislocation (medicine)
Joint dislocation, or luxation , occurs when bones in a joint become displaced or misaligned. It is often caused by a sudden impact to the joint. The ligaments always become damaged as a result of a dislocation...

 or weakening of several joint
Joint
A joint is the location at which two or more bones make contact. They are constructed to allow movement and provide mechanical support, and are classified structurally and functionally.-Classification:...

s, including the hips and the articulation between the head and the spinal column. The inaccurate AMNH mount inspired similar depictions in many films and paintings (such as Rudolph Zallinger
Rudolph F. Zallinger
Rudolph Franz Zallinger was an American-based artist notable for his mural The Age of Reptiles at Yale's Peabody Museum of Natural History and for the popular illustration known as March of Progress , one of the world's most recognizable scientific images.-Biography:Zallinger was born in Irkutsk,...

's famous mural The Age Of Reptiles in Yale University
Yale University
Yale University is a private, Ivy League university located in New Haven, Connecticut, United States. Founded in 1701 in the Colony of Connecticut, the university is the third-oldest institution of higher education in the United States...

's Peabody Museum of Natural History) until the 1990s, when films such as Jurassic Park
Jurassic Park (film)
Jurassic Park is a 1993 American science fiction adventure film directed by Steven Spielberg. The film is based on the novel of the same name by Michael Crichton. It stars Sam Neill, Laura Dern, Jeff Goldblum, Richard Attenborough, Martin Ferrero, and Bob Peck...

 introduced a more accurate posture to the general public. Modern representations in museums, art, and film show Tyrannosaurus rex with its body approximately parallel to the ground and tail extended behind the body to balance the head.

Arms



When Tyrannosaurus rex was first discovered, the humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....

 was the only element of the forelimb known. For the initial mounted skeleton as seen by the public in 1915, Osborn substituted longer, three-fingered forelimbs like those of 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...

. However, a year earlier, 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...

 described the short, two-fingered forelimbs of the closely related 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....

. This strongly suggested that Tyrannosaurus rex had similar forelimbs, but this 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 not confirmed until the first complete Tyrannosaurus rex forelimbs were identified in 1989, belonging to MOR 555 (the "Wankel rex"). The remains of "Sue" also include complete forelimbs. Tyrannosaurus rex arms are very small relative to overall body size, measuring only 1 metres (3.3 ft) long. However, they are not vestigial but instead show large areas for muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...

 attachment, indicating considerable strength. This was recognized as early as 1906 by Osborn, who speculated that the forelimbs may have been used to grasp a mate during copulation. It has also been suggested that the forelimbs were used to assist the animal in rising from a prone position. Another possibility is that the forelimbs held struggling prey while it was killed by the tyrannosaur's enormous jaws. This hypothesis may be supported by biomechanical
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...

 analysis.

Tyrannosaurus rex forelimb bones exhibit extremely thick cortical bone, indicating that they were developed to withstand heavy loads. The biceps brachii muscle of a full-grown Tyrannosaurus rex was capable of lifting 199 kilograms (439 lb) by itself; other muscles such as the brachialis would work along with the biceps to make elbow flexion even more powerful. The M. biceps muscle of T. rex was 3.5 times as powerful as the human equivalent
Human equivalent
The term human equivalent is used in a number of different contexts. This term can refer to human equivalents of various comparisons of animate and inanimate things.-Animal models in chemistry and medicine:...

. A Tyrannosaurus rex forearm also had a reduced range of motion, with the shoulder and elbow joints allowing only 40 and 45 degrees of motion, respectively. In contrast, the same two joints in Deinonychus
Deinonychus
Deinonychus was a genus of carnivorous dromaeosaurid dinosaur. There is one described species, Deinonychus antirrhopus. This 3.4 meter long dinosaur lived during the early Cretaceous Period, about 115–108 million years ago . Fossils have been recovered from the U.S...

 allow up to 88 and 130 degrees of motion, respectively, while a human arm can rotate 360 degrees at the shoulder and move through 165 degrees at the elbow. The heavy build of the arm bones, extreme strength of the muscles, and limited range of motion may indicate a system evolved to hold fast despite the stresses of a struggling prey animal. Carpenter and Smith dismissed notions that the forelimbs were useless or that Tyrannosaurus rex was an obligate scavenger.

Legs



The metatarsal of the middle main toe (toe III, see this image) tapers to nothing.

Soft tissue


In the March 2005 issue of Science
Science (journal)
Science is the academic journal of the American Association for the Advancement of Science and is one of the world's top scientific journals....

, Mary Higby Schweitzer
Mary Higby Schweitzer
Mary Higby Schweitzer is a paleontologist at North Carolina State University known for leading the groups which discovered the remains of blood cells in dinosaur fossils and later discovered soft tissue remains in the Tyrannosaurus rex specimen MOR 1125, as well as evidence that the specimen was a...

 of North Carolina State University
North Carolina State University
North Carolina State University at Raleigh is a public, coeducational, extensive research university located in Raleigh, North Carolina, United States. Commonly known as NC State, the university is part of the University of North Carolina system and is a land, sea, and space grant institution...

 and colleagues announced the recovery of soft tissue from the marrow cavity of a fossilized leg bone, from a Tyrannosaurus rex. The bone had been intentionally, though reluctantly, broken for shipping and then not preserved in the normal manner, specifically because Schweitzer was hoping to test it for soft tissue. Designated as the Museum of the Rockies specimen 1125, or MOR 1125, the dinosaur was previously excavated from the Hell Creek Formation
Hell Creek Formation
The Hell Creek Formation is an intensely-studied division of Upper Cretaceous to lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana...

. Flexible, bifurcating blood vessel
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...

s and fibrous but elastic bone
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...

 matrix tissue were recognized. In addition, microstructures resembling blood cell
Blood cell
A blood cell, also called a hematocyte, is a cell normally found in blood. In mammals, these fall into three general categories:* red blood cells — Erythrocytes* white blood cells — Leukocytes* platelets — Thrombocytes...

s were found inside the matrix and vessels. The structures bear resemblance to ostrich
Ostrich
The Ostrich is one or two species of large flightless birds native to Africa, the only living member of the genus Struthio. Some analyses indicate that the Somali Ostrich may be better considered a full species apart from the Common Ostrich, but most taxonomists consider it to be a...

 blood cells and vessels. Whether an unknown process, distinct from normal fossilization, preserved the material, or the material is original, the researchers do not know, and they are careful not to make any claims about preservation. If it is found to be original material, any surviving proteins may be used as a means of indirectly guessing some of the DNA content of the dinosaurs involved, because each protein is typically created by a specific gene. The absence of previous finds may merely be the result of people assuming preserved tissue was impossible, therefore simply not looking. Since the first, two more tyrannosaurs and a hadrosaur have also been found to have such tissue-like structures. Research on some of the tissues involved has suggested that birds are closer relatives to tyrannosaurs than other modern animals.

In studies reported in the journal Science in April 2007, Asara and colleagues concluded that seven traces of collagen
Collagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...

 proteins detected in purified Tyrannosaurus rex bone most closely match those reported in chicken
Chicken
The chicken is a domesticated fowl, a subspecies of the Red Junglefowl. As one of the most common and widespread domestic animals, and with a population of more than 24 billion in 2003, there are more chickens in the world than any other species of bird...

s, followed by frogs and newts. The discovery of proteins from a creature tens of millions of years old, along with similar traces the team found in a mastodon bone at least 160,000 years old, upends the conventional view of fossils and may shift paleontologists' focus from bone hunting to biochemistry. Until these finds, most scientists presumed that fossilization replaced all living tissue with inert minerals. Paleontologist Hans Larsson of McGill University in Montreal, who was not part of the studies, called the finds "a milestone", and suggested that dinosaurs could "enter the field of molecular biology and really slingshot paleontology into the modern world".

Subsequent studies in April 2008 confirmed the close connection of Tyrannosaurus rex to modern birds. Postdoctoral biology researcher Chris Organ at Harvard University
Harvard University
Harvard University is a private Ivy League university located in Cambridge, Massachusetts, United States, established in 1636 by the Massachusetts legislature. Harvard is the oldest institution of higher learning in the United States and the first corporation chartered in the country...

 announced, "With more data, they would probably be able to place T. rex on the evolutionary tree between alligator
Alligator
An alligator is a crocodilian in the genus Alligator of the family Alligatoridae. There are two extant alligator species: the American alligator and the Chinese alligator ....

s and chickens and ostrich
Ostrich
The Ostrich is one or two species of large flightless birds native to Africa, the only living member of the genus Struthio. Some analyses indicate that the Somali Ostrich may be better considered a full species apart from the Common Ostrich, but most taxonomists consider it to be a...

es." Co-author John M. Asara added, "We also show that it groups better with birds than modern reptiles, such as alligators and green anole lizards."

The presumed soft tissue was called into question by Thomas Kaye of the University of Washington
University of Washington
University of Washington is a public research university, founded in 1861 in Seattle, Washington, United States. The UW is the largest university in the Northwest and the oldest public university on the West Coast. The university has three campuses, with its largest campus in the University...

 and his co-authors in 2008. They contend that what was really inside the tyrannosaur bone was slimy biofilm
Biofilm
A biofilm is an aggregate of microorganisms in which cells adhere to each other on a surface. These adherent cells are frequently embedded within a self-produced matrix of extracellular polymeric substance...

 created by bacteria that coated the voids once occupied by blood vessels and cells. The researchers found that what previously had been identified as remnants of blood cells, because of the presence of iron, were actually framboid
Framboid
The term framboid describes a micromorphological feature common to certain sedimentary minerals, particularly pyrite . The first known use of the term is ascribed to Rust in 1935 and is derived from the French ‘la framboise’, meaning ‘raspberry’, reflecting the appearance of the structure under...

s, microscopic mineral spheres bearing iron. They found similar spheres in a variety of other fossils from various periods, including an ammonite
Ammonite
Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct subclass within the Molluscan class Cephalopoda which are more closely related to living coleoids Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct...

. In the ammonite they found the spheres in a place where the iron they contain could not have had any relationship to the presence of blood. However, Schweitzer has strongly criticized Kaye's claims and maintains that she really did find blood cells, and argues that there’s no reported evidence that biofilms can produce branching, hollow tubes like those noted in her study. San Antonio, Schweitzer and colleagues published an analysis in 2011 of what parts of the collagen had been recovered, finding that it was the inner parts of the collagen coil that had been preserved, as would have been expected from a long period of protein degradation.

Skin and feathers


In 2004, the scientific journal Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...

 published a report describing an early tyrannosauroid, Dilong paradoxus, from the famous 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...

 of China. As with many other theropods discovered in the Yixian, the fossil skeleton was preserved with a coat of filamentous structures which are commonly recognized as the precursors of feather
Feather
Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They...

s. It has also been proposed that Tyrannosaurus and other closely related tyrannosaurids had such protofeathers. However, skin impressions from large tyrannosaurid specimens show mosaic scales. 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 elephants, 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 like Tyrannosaurus, especially in warm Cretaceous climates.

Thermoregulation



Tyrannosaurus, like most dinosaurs, was long thought to have an ectotherm
Ectotherm
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...

. The idea of dinosaur ectothermy 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. Histological evidence of high growth rates in young Tyrannosaurus 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, Tyrannosaurus 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.

Oxygen isotope
Isotopes of oxygen
There are three stable isotopes of oxygen that lead to oxygen having a standard atomic mass of 15.9994 u. 17 radioactive isotopes have also been characterized, with mass numbers from 12O to 28O, all short-lived, with the longest-lived being 15O with a half-life of 122.24 seconds...

 ratios in fossilized bone are sometimes used to determine the temperature at which the bone was deposited, as the ratio between certain isotopes correlates with temperature. In one specimen, the isotope ratios in bones from different parts of the body indicated a temperature difference of 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 Tyrannosaurus rex maintained a constant internal body temperature (homeotherm
Homeotherm
Homeothermy is thermoregulation that maintains a stable internal body temperature regardless of external influence. This temperature is often, though not necessarily, higher than the immediate environment...

y) and that it enjoyed a metabolism somewhere between ectothermic reptiles and endothermic mammals. Other scientists have pointed out that the ratio of oxygen isotopes in the fossils today does not necessarily represent the same ratio in the distant past, and may have been altered during or after fossilization (diagenesis
Diagenesis
In geology and oceanography, diagenesis is any chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface alteration and metamorphism. These changes happen at relatively low temperatures and pressures...

). Barrick and Showers have defended their conclusions in subsequent papers, finding similar results in another theropod dinosaur from a different continent and tens of millions of years earlier in time (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...

). Ornithischia
Ornithischia
Ornithischia or Predentata is an extinct order of beaked, herbivorous dinosaurs. The name ornithischia is derived from the Greek ornitheos meaning 'of a bird' and ischion meaning 'hip joint'...

n dinosaurs also showed evidence of homeothermy, while varanid
Varanidae
Varanidae is a group of lizards of the superfamily Varanoidea. The family is a group of carnivorous lizards which includes the largest living lizard, the Komodo dragon, and the crocodile monitor. Varanidae contains the living genus Varanus and a number of extinct taxa...

 lizard
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...

s from the same formation did not. 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.

Footprints



Two isolated fossilized footprint
Footprint
Footprints are the impressions or images left behind by a person walking. Hoofprints and pawprints are those left by animals with hooves or paws rather than feet, while "shoeprints" is the specific term for prints made by shoes...

s have been tentatively assigned to Tyrannosaurus rex. The first was discovered at Philmont Scout Ranch
Philmont Scout Ranch
Philmont Scout Ranch is a large, rugged, mountainous ranch located near the town of Cimarron, New Mexico, covering approximately of wilderness in the Sangre de Cristo Mountains of the Rocky Mountains of northern New Mexico...

, New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...

, in 1983 by American geologist Charles Pillmore. Originally thought to belong to a hadrosaurid
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...

, examination of the footprint revealed a large 'heel' unknown in 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...

 dinosaur tracks, and traces of what may have been a hallux
Hallux
In tetrapods, the hallux is the innermost toe of the foot. Despite its name it may not be the longest toe on the foot of some individuals...

, the dewclaw-like fourth digit of the tyrannosaur foot. The footprint was published as the ichnogenus Tyrannosauripus pillmorei in 1994, by Martin Lockley
Martin Lockley
Dr. Martin G. Lockley is an English paleontologist specializing in dinosaur tracks. He is a Professor of Geology at the University of Colorado at Denver, in the United States, and founder and director of the Dinosaur Trackers Research Group.-Biography:...

 and Adrian Hunt. Lockley and Hunt suggested that it was very likely the track was made by a Tyrannosaurus rex, which would make it the first known footprint from this species. The track was made in what was once a vegetated wetland mud flat. It measures 83 centimetres (32.7 in) long by 71 centimetres (28 in) wide.

A second footprint that may have been made by a Tyrannosaurus was first reported in 2007 by British paleontologist Phil Manning, from the Hell Creek Formation
Hell Creek Formation
The Hell Creek Formation is an intensely-studied division of Upper Cretaceous to lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana...

 of Montana. This second track measures 76 centimetres (29.9 in) long, shorter than the track described by Lockley and Hunt. Whether or not the track was made by Tyrannosaurus is unclear, though Tyrannosaurus and Nanotyrannus are the only large theropods known to have existed in the Hell Creek Formation. Further study of the track (a full description has not yet been published) will compare the Montana track with the one found in New Mexico.

Locomotion


There are two main issues concerning the locomotory abilities of Tyrannosaurus: how well it could turn; and what its maximum straight-line speed was likely to have been. Both are relevant to the debate about whether it was a hunter or a scavenger (see below).

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 tailless, can spin in a fraction of a second. The cause of the difficulty is rotational inertia, since much of Tyrannosaurus’ mass was some distance from its center of gravity, like a human carrying a heavy timber — although it might have reduced the average distance by arching its back and tail and pulling its head and forelimbs close to its body, rather like the way ice skaters pull their arms closer in order to spin faster.

Scientists have produced a wide range of maximum speed estimates, mostly around 11 m/s (39.6 km/h; 24.6 mph), but a few as low as 5 –, and a few as high as 20 m/s (72 km/h; 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. Scientists who think that Tyrannosaurus was able to run point out that hollow bones and other features that would have lightened its body may have kept adult weight to a mere 4.5 metric tons (5 ST) or so, or that other animals like ostrich
Ostrich
The Ostrich is one or two species of large flightless birds native to Africa, the only living member of the genus Struthio. Some analyses indicate that the Somali Ostrich may be better considered a full species apart from the Common Ostrich, but most taxonomists consider it to be a...

es and horse
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...

s with long, flexible legs are able to achieve high speeds through slower but longer strides. Additionally, some have argued that Tyrannosaurus had relatively larger leg muscles than any animal alive today, which could have enabled fast running 40 –.

Jack Horner and Don Lessem argued in 1993 that Tyrannosaurus was slow and probably could not run (no airborne phase in mid-stride), because its ratio of femur (thigh bone) to tibia (shin bone) length was greater than 1, as in most large theropods and like a modern elephant
Elephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...

. However, Holtz (1998) noted that tyrannosaurids and some closely related groups had significantly longer distal hindlimb components (shin plus foot plus toes) relative to the femur length than most other theropods), and that tyrannosaurids and their close relatives had a tightly interlocked metatarsus
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...

 that more effectively transmitted locomotory forces from the foot to the lower leg than in earlier theropods ("metatarsus" means the foot bones, which function as part of the leg in digitigrade
Digitigrade
A digitigrade is an animal that stands or walks on its digits, or toes. Digitigrades include walking birds , cats, dogs, and many other mammals, but not plantigrades or unguligrades...

 animals). He therefore 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 m/s (39.6 km/h; 24.6 mph), which is about the speed of a human sprinter. But he also noted that such estimates depend on many dubious assumptions.

Farlow and colleagues (1995) have argued that a Tyrannosaurus weighing 5.4 metric tons (6 ST) to 7.3 metric tons (8 ST) 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 kilometres per hour (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.

Most recent research on Tyrannosaurus locomotion does not support speeds faster than 40 kilometres per hour (24.9 mph), i.e. moderate-speed running. For example, a 2002 paper in the journal Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...

 used a mathematical model (validated by applying it to three living animals, alligator
Alligator
An alligator is a crocodilian in the genus Alligator of the family Alligatoridae. There are two extant alligator species: the American alligator and the Chinese alligator ....

s, chicken
Chicken
The chicken is a domesticated fowl, a subspecies of the Red Junglefowl. As one of the most common and widespread domestic animals, and with a population of more than 24 billion in 2003, there are more chickens in the world than any other species of bird...

s, and human
Human
Humans are the only living species in the Homo genus...

s; additionally later eight more species including emus and ostriches) to gauge the leg muscle mass needed for fast running (over 40 km/h or 24.9 mph). They found that proposed top speeds in excess of 40 kilometres per hour (24.9 mph) were unfeasible, because they would require very large leg muscles (more than approximately 40–86% of total body mass). Even moderately fast speeds would have required large leg muscles. This discussion is difficult to resolve, as it is unknown how large the leg muscles actually were in Tyrannosaurus. If they were smaller, only 18 kilometres per hour (11.2 mph) walking/jogging might have been possible.

A study in 2007 used computer models to estimate running speeds, based on data taken directly from fossils, and claimed that Tyrannosaurus rex had a top running speed of 8 m/s (28.8 km/h; 17.9 mph). An average professional football (soccer) player would be slightly slower, while a human sprinter can reach 12 m/s (43.2 km/h; 26.8 mph). Note that these computer models predict a top speed of 17.8 m/s (64.1 km/h; 39.8 mph) for a 3 kilograms (6.6 lb) Compsognathus
Compsognathus
Compsognathus was a small, bipedal, carnivorous theropod dinosaur. The animal was the size of a turkey and lived around 150 million years ago, the early Tithonian stage of the late Jurassic Period, in what is now Europe. Paleontologists have found two well-preserved fossils, one in Germany...

 (probably a juvenile individual).

Those who argue that Tyrannosaurus was incapable of running estimate the top speed of Tyrannosaurus at about 17 kilometres per hour (10.6 mph). This is still faster than its most likely prey species, hadrosaurid
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...

s and 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. In addition, some advocates of the idea that Tyrannosaurus was a predator claim that tyrannosaur running speed is not important, since it may have been slow but still faster than its probable prey. However, Paul and Christiansen (2000) argued that at least the later ceratopsians had upright forelimbs and the larger species may have been as fast as rhinos
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....

. Healed Tyrannosaurus bite wounds on ceratopsian fossils are interpreted as evidence of attacks on living ceratopsians (see below). If the ceratopsians that lived alongside Tyrannosaurus were fast, that casts doubt on the argument that Tyrannosaurus did not have to be fast to catch its prey.

Feeding strategies


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 speculated that it was a predator; like modern large predators it would readily scavenge or steal another predator's kill if it had the opportunity.

Paleontologist 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...

 has been a major advocate of the idea that Tyrannosaurus was exclusively a scavenger and did not engage in active hunting at all, though Horner himself has claimed that he never published this idea in the peer reviewed scientific literature and used it mainly as a tool to teach a popular audience, particularly children, the dangers of making assumptions in science (such as assuming T. rex was a hunter) without using evidence. Nevertheless, Horner presented several arguments in the popular literature to support the pure scavenger hypothesis:
  • Tyrannosaur arms are short when compared to other known predators. Horner argues that the arms were too short to make the necessary gripping force to hold on to prey.
  • Tyrannosaurs had 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 (relative to their brain size). These suggest a highly developed sense of smell which could sniff out carcasses over great distances, as modern vulture
    Vulture
    Vulture is the name given to two groups of convergently evolved scavenging birds, the New World Vultures including the well-known Californian and Andean Condors, and the Old World Vultures including the birds which are seen scavenging on carcasses of dead animals on African plains...

    s do. Research on the olfactory bulbs of dinosaurs has shown that Tyrannosaurus had the most highly developed sense of smell of 21 sampled dinosaurs. Opponents of the pure scavenger hypothesis have used the example of vultures in the opposite way, arguing that the scavenger hypothesis is implausible because the only modern pure scavengers are large gliding birds, which use their keen senses and energy-efficient gliding to cover vast areas economically. However, researchers from Glasgow concluded that an ecosystem as productive as the current Serengeti
    Serengeti
    The Serengeti ecosystem is a geographical region in Africa. It is located in north Tanzania and extends to south-western Kenya between latitudes 1 and 3 S and longitudes 34 and 36 E. It spans some ....

     would provide sufficient carrion
    Carrion
    Carrion refers to the carcass of a dead animal. Carrion is an important food source for large carnivores and omnivores in most ecosystems. Examples of carrion-eaters include vultures, hawks, eagles, hyenas, Virginia Opossum, Tasmanian Devils, coyotes, Komodo dragons, and burying beetles...

     for a large theropod scavenger, although the theropod might have had to be cold-blooded in order to get more calories from carrion than it spent on foraging (see Metabolism of dinosaurs). They also suggested that modern ecosystems like Serengeti have no large terrestrial scavengers because gliding birds now do the job much more efficiently, while large theropods did not face competition for the scavenger 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...

     from gliding birds.
  • Tyrannosaur 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. Karen Chin and colleagues have found bone fragments in coprolite
    Coprolite
    A coprolite is fossilized animal dung. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour rather than morphology. The name is derived from the Greek words κοπρος / kopros meaning 'dung' and λιθος / lithos meaning 'stone'. They...

    s (fossilized feces) that they attribute to tyrannosaurs, but point out that a tyrannosaur's teeth were not well adapted to systematically chewing bone like hyena
    Hyena
    Hyenas or Hyaenas are the animals of the family Hyaenidae of suborder feliforms of the Carnivora. It is the fourth smallest biological family in the Carnivora , and one of the smallest in the mammalia...

    s do to extract marrow.
  • Since at least some of Tyrannosauruss potential prey could move quickly, evidence that it walked instead of ran could indicate that it was a scavenger. On the other hand, recent analyses suggest that Tyrannosaurus, while slower than large modern terrestrial predators, may well have been fast enough to prey on large hadrosaurs and ceratopsians.


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. Horner also pointed out that the tyrannosaur lineage had a history of steadily improving binocular vision. It is not obvious why 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 provides. In modern animals, binocular vision is found mainly in predators.

A skeleton of the hadrosaurid Edmontosaurus annectens
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,...

 has been described from Montana with healed tyrannosaur-inflicted damage on its tail vertebrae. The fact that the damage seems to have healed suggests that the Edmontosaurus survived a tyrannosaur's attack on a living target, i.e. the tyrannosaur had attempted active predation. There is also evidence for an aggressive interaction between a 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...

 and a Tyrannosaurus in the form of partially healed tyrannosaur tooth marks on a Triceratops brow horn and squamosal
Squamosal
The squamosal is a bone of the head of higher vertebrates. It is the principal component of the cheek region in the skull, lying below the temporal series and otic notch and bounded anteriorly by postorbital. Posteriorly, the squamosal articulates with the posterior elements of the palatal complex,...

 (a bone of the neck frill
Neck frill
Neck frill is the popular term for the relatively extensive margin seen on the back of the heads of reptiles with either a bony support such as those present on the skulls of dinosaurs of the suborder Marginocephalia or a cartilaginous one as in the Frill-necked Lizard...

); the bitten horn is also broken, with new bone growth after the break. It is not known what the exact nature of the interaction was, though: either animal could have been the aggressor. When examining 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...

, paleontologist Pete Larson
Pete Larson
Peter Larson is an American paleontologist from the Black Hills Institute of Geological Research that led the team that excavated "Sue", one of the most complete specimens of Tyrannosaurus rex found to date. He also co-authored the book "Rex Appeal" which relates the story of how the U.S....

 found a broken and healed fibula and tail vertebrae, scarred facial bones and a tooth from another Tyrannosaurus embedded in a neck vertebra. If correct, these might be strong evidence for aggressive behavior between tyrannosaurs but whether it would have been competition for food and mates or active cannibalism
Cannibalism
Cannibalism is the act or practice of humans eating the flesh of other human beings. It is also called anthropophagy...

 is unclear. However, further recent investigation of these purported wounds has shown that most are infections rather than injuries (or simply damage to the fossil after death) and the few injuries are too general to be indicative of intraspecific conflict. A 2009 study showed that holes in the skulls of several specimens might have been caused by Trichomonas
Trichomonas
Trichomonas is a genus of anaerobic protists that are parasites of vertebrates. They are included with the parabasalids.Species of Trichomonas include:*Trichomonas vaginalis, an organism generally living inside the vagina of humans...

-like parasites that commonly infect avians.

Some researchers argue that if Tyrannosaurus were a scavenger, another dinosaur had to be the top predator in the Amerasian Upper Cretaceous. Top prey was 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 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'...

 and 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...

 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, although they may have had a hard time finding enough meat to scavenge, being outnumbered by smaller theropods. Most paleontologists accept that Tyrannosaurus was both an active predator and a scavenger like most large carnivores.

Tyrannosaurus may have had infectious saliva used to kill its prey. This theory was first proposed by William Abler
William Abler
William L. Abler or simply known as Bill Abler is a paleontologist who has mostly studied the teeth of dinosaurs.He has studied tyrannosaurine teeth and has come up with the conclusion that Tyrannosaurus had infectious saliva that could have helped it kill prey...

. Abler examined the teeth of tyrannosaurids between each tooth serration; the serrations may have held pieces of carcass with bacteria, giving Tyrannosaurus a deadly, infectious bite much like the 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...

 was thought to have. However, Jack Horner regards Tyrannosaurus tooth serrations as more like cubes in shape than the serrations on a Komodo monitor's teeth, which are rounded. All forms of saliva contain possibly hazardous bacteria, so the prospect of it being used as a method of predation is disputable.

Cannibalism


A study from Currie, Horner, Erickson and Longrich in 2010 has been put forward as evidence of cannibalism in the genus Tyrannosaurus. They studied some Tyrannosaurus specimens with tooth marks in the bones, attributable to the same genus. The tooth marks were identified in the humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....

, foot bones and metatarsals, and this was seen as evidence for opportunistic scavenging, rather than wounds caused by intraspecific combat. In a fight, they proposed it would be difficult to reach down to bite in the feet of a rival, making it more likely that the bitemarks were made in a carcass. As the bitemarks were made in body parts with relatively scantly amounts of flesh, it is suggested that the Tyrannosaurus was feeding on a cadaver in which the more fleshy parts already had been eaten up. They were also open to the possibility that other tyrannosaurids practiced cannibalism.

Paleopathology


In 2001, Bruce Rothschild and others published a study examining evidence for stress fractures and tendon avulsions in theropod dinosaurs and the implications for their behavior. Since stress fractures are caused by repeated trauma rather than singular events they are more likely to be caused by regular behavior than other types of injuries. Of the 81 Tyrannosaurus foot bones examined in the study one was found to have a stress fracture, while none of the 10 hand bones were found to have stress fractures. The researchers found tendon avulsions only among Tyrannosaurus and 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...

. An avulsion injury left a divot on the humerus of Sue the T. rex, apparently located at the origin of the deltoid
Deltoid
Deltoid can refer to:* The deltoid muscle, a muscle in the shoulder* Kite , also known as a deltoid, a type of quadrilateral* A deltoid curve, a three-sided hypocycloid* A leaf shape* The deltoid tuberosity, a part of the humerus...

 or teres major muscles. The presence of avulsion injuries being limited to a the forelimb and shoulder in both Tyrannosaurus and Allosaurus suggests that theropods may have had a musculature more complex and functionally different than those of birds. The researchers concluded that Sue's tendon avulsion was probably obtained from struggling prey. The presence of stress fractures and tendon avulsions in general provide evidence for a "very active" predation-based diet rather than obligate scavenging.

History



Henry Fairfield Osborn
Henry Fairfield Osborn
Henry Fairfield Osborn, Sr. ForMemRS was an American geologist, paleontologist, and eugenicist.-Early life and career:...

, president 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...

, named Tyrannosaurus rex in 1905. The generic name is derived from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 words τυράννος (tyrannos, meaning "tyrant") and σαύρος (sauros, meaning "lizard"). Osborn used the Latin word rex, meaning "king", for the specific name. The full binomial
Binomial nomenclature
Binomial nomenclature is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages...

 therefore translates to "tyrant lizard the king" or "King Tyrant Lizard", emphasizing the animal's size and perceived dominance over other species of the time.

Earliest finds


Teeth from what is now documented as a Tyrannosaurus rex were found in 1874 by A. Lakes near Golden, Colorado
Golden, Colorado
The City of Golden is a home rule municipality that is the county seat of Jefferson County, Colorado, United States. Golden lies along Clear Creek at the edge of the foothills of the Front Range of the Rocky Mountains. Founded during the Pike's Peak Gold Rush on 16 June 1859, the mining camp was...

. In the early 1890s, J. B. Hatcher collected postcranial elements in eastern 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...

. The fossils were believed to be from a large species of Ornithomimus (O. grandis) but are now considered Tyrannosaurus rex. Vertebral fragments found by E. D. Cope in western South Dakota in 1892 and named as Manospondylus gigas have also been recognized as belonging to Tyrannosaurus rex.

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...

, assistant curator 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...

, found the first partial skeleton of Tyrannosaurus rex in eastern Wyoming in 1900. H. F. Osborn originally named this skeleton Dynamosaurus imperiosus in a paper in 1905. Brown found another partial skeleton in the Hell Creek Formation
Hell Creek Formation
The Hell Creek Formation is an intensely-studied division of Upper Cretaceous to lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana...

 in Montana in 1902. Osborn used this holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...

 to describe Tyrannosaurus rex in the same paper in which D. imperiosus was described. In 1906, Osborn recognized the two as synonyms, and acted as first revisor by selecting Tyrannosaurus as the valid name. The original Dynamosaurus material resides in the collections of the Natural History Museum
Natural History Museum
The Natural History Museum is one of three large museums on Exhibition Road, South Kensington, London, England . Its main frontage is on Cromwell Road...

, London.

In total, Brown found five Tyrannosaurus partial skeletons. In 1941, Brown's 1902 find was sold to the Carnegie Museum of Natural History
Carnegie Museum of Natural History
Carnegie Museum of Natural History, located at 4400 Forbes Avenue in the Oakland neighborhood of Pittsburgh, Pennsylvania, USA, was founded by the Pittsburgh-based industrialist Andrew Carnegie in 1896...

 in Pittsburgh, Pennsylvania. Brown's fourth and largest find, also from Hell Creek, is on display in 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...

 in New York.

Although there are numerous skeletons in the world, only one track has been documented — at Philmont Scout Ranch
Philmont Scout Ranch
Philmont Scout Ranch is a large, rugged, mountainous ranch located near the town of Cimarron, New Mexico, covering approximately of wilderness in the Sangre de Cristo Mountains of the Rocky Mountains of northern New Mexico...

 in northeast New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...

. It was discovered in 1983 and identified and documented in 1994.

Notable specimens


Sue Hendrickson
Sue Hendrickson
Susan "Sue" Hendrickson is an American paleontologist. Hendrickson is best known for her discovery of the remains of a Tyrannosaurus rex in South Dakota on August 12, 1990. Her discovery was the largest specimen of a T. rex found and one of the most complete skeletons. This skeleton is now known...

, amateur
Amateur
An amateur is generally considered a person attached to a particular pursuit, study, or science, without pay and often without formal training....

 paleontologist, discovered the most complete (approximately 85%) and, until 2001, the largest, Tyrannosaurus fossil skeleton known in the Hell Creek Formation
Hell Creek Formation
The Hell Creek Formation is an intensely-studied division of Upper Cretaceous to lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana...

 near Faith, South Dakota
Faith, South Dakota
Faith is a city in Meade County, South Dakota, United States. The population was 421 at the 2010 census. Sue, the most complete Tyrannosaurus rex skeleton known, was discovered about 15 miles north and east of Faith in December 1990.-Geography:...

, on 12 August 1990. This Tyrannosaurus, nicknamed "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...

" in her honor, was the object of a legal battle over its ownership. In 1997 this was settled in favor of Maurice Williams, the original land owner. The fossil collection was purchased by the Field Museum of Natural History
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...

 at auction for USD 7.6 million, making it the most expensive dinosaur skeleton to date. From 1998 to 1999 Field Museum of Natural History
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...

 preparators spent over 25,000 man-hours taking the rock off each of the bones. The bones were then shipped off to New Jersey where the mount was made. The finished mount was then taken apart, and along with the bones, shipped back to Chicago for the final assembly. The mounted skeleton opened to the public on May 17, 2000 in the great hall (Stanley Field Hall) at the Field Museum of Natural History
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...

. A study of this specimen's fossilized bones showed that "Sue" reached full size at age 19 and died at age 28, the longest any tyrannosaur is known to have lived. Early speculation that Sue may have died from a bite to the back of the head was not confirmed. Though subsequent study showed many pathologies in the skeleton, no bite marks were found.
Damage to the back of the skull may have been caused by post-mortem trampling. Recent speculation indicates that "Sue" may have died of starvation after contracting a parasitic infection from eating diseased meat; the resulting infection would have caused inflammation in the throat, ultimately leading "Sue" to starve because she could no longer swallow food. This hypothesis is substantiated by smooth-edged holes in her skull which are similar to those caused in modern-day birds that contract the same parasite.

Another Tyrannosaurus, nicknamed "Stan", in honor of amateur paleontologist Stan Sacrison, was found in the Hell Creek Formation near Buffalo, South Dakota
Buffalo, South Dakota
Buffalo is a town in Harding County, South Dakota, United States. The population was 330 at the 2010 census. It is the county seat of Harding County.-History:Buffalo was established in 1909...

, in the spring of 1987. It was not collected until 1992, as it was mistakenly thought to be a Triceratops skeleton. Stan is 63% complete and is on display in the Black Hills Institute of Geological Research in Hill City, South Dakota
Hill City, South Dakota
Hill City is the oldest existing city in Pennington County, South Dakota, United States. The population was 948 at the 2010 census. Hill City is located southwest of Rapid City on State Highway 16 and on U.S. Route 385 that connects Deadwood to Hot Springs...

, after an extensive world tour during 1995 and 1996. This tyrannosaur, too, was found to have many bone pathologies, including broken and healed ribs, a broken (and healed) neck and a spectacular hole in the back of its head, about the size of a Tyrannosaurus tooth.

In the summer of 2000, Jack Horner discovered five Tyrannosaurus skeletons near the Fort Peck Reservoir in Montana. One of the specimens, dubbed "C. rex", was reported to be perhaps the largest Tyrannosaurus ever found.

In 2001, a 50% complete skeleton of a juvenile Tyrannosaurus was discovered in the Hell Creek Formation in Montana, by a crew from the Burpee Museum of Natural History
Burpee Museum of Natural History
The Burpee Museum of Natural History is located along the Rock River in downtown Rockford, Illinois at 737 North Main Street.-Museum History:...

 of Rockford, Illinois. Dubbed "Jane
Jane (dinosaur)
Jane is a fossil specimen of small tyrannosaurid dinosaur , officially known as BMRP 2002.4.1, discovered in the Hell Creek Formation in southern Montana....

", the find was initially considered the first known skeleton of the pygmy tyrannosaurid 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:...

 but subsequent research has revealed that it is more likely a juvenile Tyrannosaurus. It is the most complete and best preserved juvenile example known to date. Jane has been examined by 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...

, Pete Larson, Robert Bakker, Greg Erickson
Gregory M Erickson
Gregory M. Erickson, Ph.D. in paleobiology at Florida State University.Erickson have produced many papers on the ontogeny and forces alligators and dinosaurus, especially on the theropod Tyrannosaurus rex. Erickson has also been contributing when naming and describing some dinosaur genera, like...

, and several other renowned paleontologists, because of the uniqueness of her age. "Jane" is currently on exhibit at the Burpee Museum of Natural History in Rockford, Illinois.

In a press release on 7 April 2006, Montana State University revealed that it possessed the largest Tyrannosaurus skull yet discovered. Discovered in the 1960s and only recently reconstructed, the skull measures 59 inches (150 cm) long compared to the 55.4 inches (141 cm) of "Sue's" skull, a difference of 6.5%.

Appearances in popular culture



Since it was first described in 1905, Tyrannosaurus rex has become the most widely recognized dinosaur species in popular culture
Popular culture
Popular culture is the totality of ideas, perspectives, attitudes, memes, images and other phenomena that are deemed preferred per an informal consensus within the mainstream of a given culture, especially Western culture of the early to mid 20th century and the emerging global mainstream of the...

. It is the only dinosaur that is commonly known to the general public by its full scientific name (binomial name
Binomial nomenclature
Binomial nomenclature is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages...

) (Tyrannosaurus rex), and the scientific abbreviation T. rex has also come into wide usage. 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...

 notes this in The Dinosaur Heresies
The Dinosaur Heresies
The Dinosaur Heresies: New Theories Unlocking the Mystery of the Dinosaurs and Their Extinction was a 1986 book published by Robert T. Bakker, a prominent paleontologist....

 and explains that a name like "Tyrannosaurus rex is just irresistible to the tongue."

External links