Theropoda
Encyclopedia
Theropoda is both a suborder of bipedal saurischian dinosaur
s, and a clade
consisting of that suborder and its descendants (including modern
bird
s). Dinosaurs belonging to the suborder theropoda were primarily carnivorous
, although a number of theropod groups evolved herbivory
, omnivory
, and insectivory
. Theropods first appeared during the Carnian
age of the late Triassic
period about 230 million years ago (Ma) and included the sole large terrestrial carnivores from the Early Jurassic
until at least the close of the Cretaceous
, about 65 Ma. In the Jurassic
, birds evolved from small specialized coelurosauria
n theropods, and are today represented by 9,900 living species.
Among the features linking theropod dinosaurs to birds are the three-toed foot, a furcula
(wishbone), air-filled bones and (in some cases) feathers and brooding of the eggs
.
While historically generalized as exclusively carnivorous dinosaurs, theropods in fact displayed a wide range of diets. All early finds of theropod fossils showed them to be primarily carnivorous
. Theropod specimens known to scientists in the 19th and early 20th centuries all showed sharp teeth with serrated edges for cutting flesh, and some specimens even showed direct evidence of predatory behavior. For example, a Compsognathus
fossil was found with a lizard
in its stomach, and a Velociraptor
specimen was found locked in combat with a Protoceratops
(a type of ornithischian dinosaur).
The first confirmed non-carnivorous theropods found were the therizinosaur
s, originally known as segnosaurs. First thought to be prosauropods, these enigmatic dinosaurs were later proven to be highly specialized, herbivorous
theropods. Therizinosaurs possessed large abdomens for processing plant food, and small heads with beaks and leaf-shaped teeth. Further study of maniraptora
n theropods and their relationships showed that therizinosaurs were not the only member of this group to abandon carnivory. Several other lineages of maniraptors show adaptations for an omnivorous
diet, including seed-eating (some troodontids
) and insect-eating (many avialans
and alvarezsaurs
). Oviraptorosaurs
, ornithomimosaurs
and advanced troodontids were likely omnivorous as well, and some theropods (such as Masiakasaurus
and the spinosaurids
) appear to have specialized in catching fish.
n dinosaurs, evidence of feathers or feather-like structures has not been reported for any theropods less advanced than the coelurosaurs
. More primitive theropods show evidence that their skin was covered in small, bumpy scales. In some species, these were interspersed with larger scales with bony cores, or osteoderms. This type of skin is best known in the ceratosaur Carnotaurus
, which has been preserved with extensive skin impressions.
The most primitive known protofeathered theropods are the compsognathids
and early tyrannosauroids
, both coelurosaurs. These early forms had feathers which were relatively short and composed of simple, possibly branching filaments. Simple filaments are also seen in therizinosaur
s, which also possessed large, stiffened "quill"-like feathers.
Most feathered theropods, including modern birds, usually retain scales only on the feet. Some forms seem to have mixed feathers elsewhere on the body as well. Scansoriopteryx
preserved scales on the underside of the tail, and Juravenator
may have been predominantly scaly with some simple filaments interspersed. On the other hand, some theropods were completely covered with feathers, such as the troodontid Anchiornis
, which even had feathers on the feet and toes.
was the largest and most popular theropod known to the general public for many decades. Since its discovery, however, a number of other giant carnivorous dinosaurs have been described, including Spinosaurus
, Carcharodontosaurus
, and Giganotosaurus
. The original Spinosaurus specimens (as well as newer fossils described in 2006) support the idea that Spinosaurus is larger than Tyrannosaurus, showing that Spinosaurus was possibly 6 meters longer and at least 1 metric ton heavier than Tyrannosaurus. There is still no clear explanation for exactly why these animals grew so much larger than the predators that came before and after them.
The smallest non-avialan theropod known from adult specimens is the troodontid
Anchiornis huxleyi
, at 110 grams in weight and 34 centimeters (1 ft) in length. When modern birds are included, the Bee Hummingbird
Mellisuga helenae is smallest at 1.9 g and 5.5 cm (2.2 in) long.
ids (such as Carnotaurus
) and the tyrannosaurids
(such as Tyrannosaurus
). This trait was, however, not universal: spinosaurids had well developed forelimbs, so also did many coelurosaurs. One genus, Xuanhanosaurus
, has also been claimed to have been quadrupedal because of its comparatively robust forelimbs, but this is no longer thought to be likely.
The hands are also very different among the different groups. the most common is an appendage consisting of 3 fingers, the digits I, II and III (or possibly II, III and IV) with sharp claws. Some basal theropods (Herrerasaurus
, Eoraptor
) had 4 digits, and also a reduced metacarpal V. Ceratosauria
ns usually had 4 digits, while most tetanurans had 3.
The forelimbs' scope of use is also believed to have also been different among different families. The spinosaurids could have used their powerful forelimbs to hold fishes. Some small coelurosaurus (dromaeosaurids, scansoriopterygids
) are believed to have used their forelimbs to climb in trees, and birds, which are believed to be descendants of theropods, use them for flight.
Contrary to the way theropods have often been reconstructed in art and the popular media, the range of motion of theropod forelimbs was severely limited, especially compared with the forelimb dexterity of humans and other primates. Most notably, theropods and other bipedal saurischian dinosaurs (including the bipedal prosauropods) could not pronate
their hands—that is, they could not rotate the forearm so that the palms faced the ground or backwards towards the legs. In humans, pronation is achieved by motion of the radius
relative to the ulna
(the two bones of the forearm). In saurischian dinosaurs, however, the end of the radius near the elbow was actually locked into a groove of the ulna, preventing any movement. Movement at the wrist was also limited in many species, forcing the entire forearm and hand to move as a single unit with little flexibility. In theropods and prosauropods, the only way for the palm to face the ground would have been by lateral splaying of the entire forelimb, as in a bird raising its wing.
In carnosaurs like Acrocanthosaurus
, the hand itself retained a relatively high degree of flexibility, with mobile fingers. This was also true of more basal theropods such as herrerasaurs and dilophosaurs
. Coelurosaurs
showed a shift in the use of the forearm, with greater flexibility at the shoulder allowing the arm to be raised towards the horizontal plane, and to even greater degrees in flying birds. However, in coelurosaurs such as ornithomimosaurs
and especially dromaeosaurs
, the hand itself had lost most flexibility, with highly inflexible fingers. Dromaeosaurs and other maniraptora
ns also showed increased mobility at the wrist not seen in other theropods, thanks to the presence of a specialized half-moon shaped wrist bone (the semi-lunate carpal) that allowed the whole hand to fold backward towards the forearm in the manner of modern birds.
from 10 families. Pathologies were found in theropods of all body size although they were less common in fossils of small theropods, although this may be an artifact of preservation. They are very widely represented throughout the different parts of theropod anatomy. The most common sites of preserved injury and disease in theropod dinosaur in the ribs and tail vertebrae. Despite being abundant in ribs and vertebrae, injuries seem to be "absent... or very rare" on the bodies' primary weight supporting bones like the sacrum
, femur
, and tibia
. The lack of preserved injuries in these bones suggests that they were selected by evolution for resistance to breakage. The least common sites of preserved injury are the cranium and forelimb, with injuries occurring in about equal frequency at each site. Most pathologies preserved in theropod fossils are the remains of injuries like fractures, pits, and punctures, often likely originating with bites. Some theropod paleopathologies seem to be evidence of infections, which tended to be confined only to small regions of the animal's body. Evidence for congenital malformities have also been found in theropod remains. Such discoveries can provide information useful for understanding the evolutionary history of the processes of biological development. Unusual fusion
s in cranial elements or asymmetries in the same are probably evidence that one is examining the fossils of an extremely old individual rather than a diseased one.
During the late Triassic
, a number of primitive proto-theropod and theropod dinosaurs existed and evolved alongside each other.
The earliest and most primitive of the theropod dinosaurs were the carnivorous Eodromaeus
and the herrerasaurids
of Argentina
(as well as, possibly, the omnivorous Eoraptor
). The herrerasaurs existed during the early late Triassic (Late Carnian
to Early Norian
). They were found in North America and South America and possibly also India and Southern Africa. The herrerasaurs were characterised by a mosaic
of primitive and advanced features. Some paleontologists have in the past considered the herrerasaurians to be members of Theropoda, while other theorized the group to be basal
saurischians, and may even have evolved prior to the saurischian-ornithischian split. Cladistic analysis following the discovery of Tawa
, another Triassic dinosaur, suggests the herrerasaurs likely were early theropods.
The earliest and most primitive unambiguous theropods (or alternatively, "Eutheropoda" – 'True Theropods') are the Coelophysoidea
. The Coelophysoidea were a group of widely distributed, lightly built and potentially gregarious animals. They included small hunters like Coelophysis and (possibly) larger predators like Dilophosaurus
. These successful animals continued from the Late Carnian (early Late Triassic) through to the Toarcian
(late Early Jurassic
). Although in the early cladistic classifications they were included under the Ceratosauria
and considered a side-branch of more advanced theropods, they may have been ancestral to all other theropods (which would make them a paraphyletic group).
The somewhat more advanced ceratosaurs
(including Ceratosaurus
and Carnotaurus
) appeared during the Early Jurassic and continued through to the Late Jurassic in Laurasia
. They competed alongside their more anatomically advanced tetanuran relatives and—in the form of the abelisaur
lineage—lasted to the end of the Cretaceous in Gondwana
.
The Tetanurae
are more specialised again than the ceratosaurs. They are subdivided into the basal Megalosauroidea
(alternately Spinosauroidea) and the more derived Avetheropoda. Megalosauridae were primarily Middle Jurassic to Early Cretaceous predators, and their spinosaurid
relatives' remains are mostly from Early and Middle Cretaceous rocks. Avetheropoda, as their name indicates, were more closely related to birds and are again divided into the Allosauroidea
(the diverse carcharodontosaurs) and the Coelurosauria
(a very large and diverse dinosaur group including the birds).
Thus, during the late Jurassic, there were no fewer than four distinct lineages of theropods—ceratosaurs, megalosaurs, allosaurs, and coelurosaurs—preying on the abundance of small and large herbivorous dinosaurs. All four groups survived into the Cretaceous, and three of those—the ceratosaurs, coelurosaurs, and allosaurs—survived to end of the period, where they were geographically separate, the ceratosaurs and allosaurs in Gondwana, and the coelurosaurs in Laurasia
.
Of all the theropod groups, the coelurosaurs were by far the most diverse. Some coelurosaur groups that flourished during the Cretaceous were the tyrannosaurids
(including Tyrannosaurus
) the dromaeosaurids
(including Velociraptor
and Deinonychus
, which are remarkably similar in form to the oldest known bird, Archaeopteryx
), the bird-like troodontids
and oviraptorosaurs
, the ornithomimosaurs
(or "ostrich dinosaurs"), the strange giant-clawed herbivorous therizinosaur
s, and the avialans
, which include modern birds and is the only dinosaur lineage to survive the Cretaceous-Paleogene extinction event. While the roots of these various groups are found in the Middle Jurassic, they only became abundant during the Early Cretaceous. A few paleontologists, such as Gregory S. Paul
, have suggested that some or all of these advanced theropods were actually descended from flying dinosaurs or proto-birds like Archaeopteryx that lost the ability to fly and returned to a terrestrial habitat.
The name Theropoda (meaning "beast feet") was first coined by O.C. Marsh
in 1881. Marsh initially named Theropoda as a suborder
to include the family
Allosauridae, but later expanded its scope, re-ranking it as an order
to include a wide array of "carnivorous" dinosaur families, including Megalosauridae, Compsognathidae
, Ornithomimidae, Plateosauridae
and Anchisauridae
(now known to be herbivorous prosauropods) and Hallopodidae (now known to be relatives of crocodilians). Due to the scope of Marsh's Order Theropoda, it came to replace a previous taxonomic group that Marsh's rival E.D. Cope
had created in 1866 for the carnivorous dinosaurs, Goniopoda ("angled feet").
By the early 20th century, some paleontologists, such as Friedrich von Huene
, no longer considered carnivorous dinosaurs to have formed a natural group. Huene abandoned the name Theropoda, instead using Harry Seeley
's Order Saurischia
, which Huene divided into the suborders Coelurosauria
and Pachypodosauria. Huene placed most of the small theropod groups into Coelurosauria, and the large theropods and prosauropods into Pachypodosauria, which he considered ancestral to the Sauropoda
(prosauropods were still thought of as carnivorous at this time, owing to the incorrect association of rauisuchia
n skulls and teeth with prosauropod bodies, in animals such as Teratosaurus
). In W.D. Matthew and Barnum Brown
's 1922 description of the first known dromaeosaurid
(Dromaeosaurus albertensis
), they became the first paleontologists to exclude prosauropods from the carnivorous dinosaurs, and attempted to revive the name Goniopoda for that group, though neither of these suggestions were accepted by other scientists.
It was not until 1956 that Theropoda came back into use as a taxon
containing the carnivorous dinosaurs and their descendants, when Alfred Romer
re-classified the Order Saurischia into two suborders, Theropoda and Sauropoda
. This basic division has survived into modern paleontology, with the exception of, again, the Prosauropoda, which Romer included as an infraorder
of theropods. Romer also maintained a division between Coelurosauria and Carnosauria
(which he also ranked as infraorders). This dichotomy was upset by the discovery of Deinonychus
and Deinocheirus
in 1969, neither of which could be classified easily as "carnosaurs" or "coelurosaurs." In light of these and other discoveries, by the late 1970s Rinchen Barsbold created a new series of theropod infraorders: Coelurosauria, Deinonychosauria
, Oviraptorosauria
, Carnosauria, Ornithomimosauria
, and Deinocheirosauria.
With the advent of cladistics
and phylogenetic nomenclature
in the 1980s, and their development in the 1990s and 2000s, a clearer picture of theropod relationships began to emerge. Several major theropod groups were named by Jacques Gauthier
in 1986, including the clade
Tetanurae
for one branch of a basic theropod split with another group, the Ceratosauria
. As more information about the link between dinosaurs and birds came to light, the more bird-like theropods were grouped in the clade Maniraptora
(also named by Gauthier in 1986). These new developments also came with a recognition among most scientists that birds arose directly from maniraptoran theropods and, with the abandonment of ranks in cladistic classification, the re-evaluation of birds as a subset of theropod dinosaurs that happened to have survived the Mesozoic extinctions into the present.
Theropods are a highly diverse group, and many major Mesozoic lineages have been identified:
is adapted from Weishampel et al., 2004. It retains Coelophysoidea
as possible ceratosaurs, as opposed to many recent studies placing them outside ceratosaurs and ancestral to both ceratosaurs and tetanurae
.
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s, and a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
consisting of that suborder and its descendants (including modern
Modern birds
Modern birds are the most recent common ancestor of all living birds and all its descendants.Modern birds are characterised by feathers, a beak with no teeth , the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a lightweight but strong skeleton...
bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s). Dinosaurs belonging to the suborder theropoda were primarily carnivorous
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...
, although a number of theropod groups evolved herbivory
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
, omnivory
Omnivore
Omnivores are species that eat both plants and animals as their primary food source...
, and insectivory
Insectivore
An insectivore is a type of carnivore with a diet that consists chiefly of insects and similar small creatures. An alternate term is entomophage, which also refers to the human practice of eating insects....
. Theropods first appeared during the Carnian
Carnian
The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...
age of the late Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
period about 230 million years ago (Ma) and included the sole large terrestrial carnivores from the Early Jurassic
Early Jurassic
The Early Jurassic epoch is the earliest of three epochs of the Jurassic period...
until at least the close of the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
, about 65 Ma. In the 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...
, birds evolved from small specialized coelurosauria
Coelurosauria
Coelurosauria is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs. In the past, it was used to refer to all small theropods, although this classification has been abolished...
n theropods, and are today represented by 9,900 living species.
Among the features linking theropod dinosaurs to birds are the three-toed foot, a furcula
Furcula
The ' is a forked bone found in birds, formed by the fusion of the two clavicles. In birds, its function is the strengthening of the thoracic skeleton to withstand the rigors of flight....
(wishbone), air-filled bones and (in some cases) feathers and brooding of the 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...
.
Diet
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...
. Theropod specimens known to scientists in the 19th and early 20th centuries all showed sharp teeth with serrated edges for cutting flesh, and some specimens even showed direct evidence of predatory behavior. For example, a 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...
fossil was found with a 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...
in its stomach, and a Velociraptor
Velociraptor
Velociraptor is a genus of dromaeosaurid theropod dinosaur that existed approximately 75 to 71 million years ago during the later part of the Cretaceous Period. Two species are currently recognized, although others have been assigned in the past. The type species is V. mongoliensis; fossils...
specimen was found locked in combat with a Protoceratops
Protoceratops
Protoceratops is a genus of sheep-sized herbivorous ceratopsian dinosaur, from the Upper Cretaceous Period of what is now Mongolia. It was a member of the Protoceratopsidae, a group of early horned dinosaurs...
(a type of ornithischian dinosaur).
The first confirmed non-carnivorous theropods found were the therizinosaur
Therizinosaur
Therizinosaurs are theropod dinosaurs belonging to the clade Therizinosauria. Therizinosaur fossils have been found in Early through Late Cretaceous deposits in Mongolia, the People's Republic of China and Western North America...
s, originally known as segnosaurs. First thought to be prosauropods, these enigmatic dinosaurs were later proven to be highly specialized, herbivorous
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
theropods. Therizinosaurs possessed large abdomens for processing plant food, and small heads with beaks and leaf-shaped teeth. Further study of maniraptora
Maniraptora
Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Deinonychosauria, Oviraptorosauria and Therizinosauria. Ornitholestes and the Alvarezsauroidea...
n theropods and their relationships showed that therizinosaurs were not the only member of this group to abandon carnivory. Several other lineages of maniraptors show adaptations for an omnivorous
Omnivore
Omnivores are species that eat both plants and animals as their primary food source...
diet, including seed-eating (some 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...
) and insect-eating (many avialans
Avialae
Avialae is a clade of dinosaurs containing their only living representatives, birds , and the most immediate extinct relatives of birds.-Competing definitions:...
and alvarezsaurs
Alvarezsauridae
Alvarezsauridae is an enigmatic family of small, long-legged running dinosaurs. Although originally thought to represent the earliest known flightless birds, a consensus of recent work suggests that they are primitive members of the Maniraptora. Other work found them to be the sister group to the...
). Oviraptorosaurs
Oviraptorosauria
Oviraptorosaurs are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot - like skulls, with or without bony crests atop the head...
, ornithomimosaurs
Ornithomimosauria
The Ornithomimosauria, ornithomimosaurs or ostrich dinosaurs were theropod dinosaurs which bore a superficial resemblance to modern ostriches. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period of Laurasia...
and advanced troodontids were likely omnivorous as well, and some theropods (such as Masiakasaurus
Masiakasaurus
Masiakasaurus was a small predatory theropod dinosaur from the Late Cretaceous of Madagascar. It was named in 2001 by Scott D. Sampson, Matthew Carrano, and Catherine A. Forster. Unlike most theropods, the front teeth of Masiakasaurus projected forward instead of straight down...
and the spinosaurids
Spinosauridae
Spinosauridae is a family of specialised theropod dinosaurs. Members of this family were large, bipedal predators with elongated, crocodile-like skulls, sporting conical teeth with no or only very tiny serrations. The front dentary teeth fanned out, giving the animal a characteristic look...
) appear to have specialized in catching fish.
Skin, scales and feathers
Mesozoic theropods were also very diverse in terms of skin texture and covering. Though feather-like structures are known in the related ornithischiaOrnithischia
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, evidence of feathers or feather-like structures has not been reported for any theropods less advanced than the 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...
. More primitive theropods show evidence that their skin was covered in small, bumpy scales. In some species, these were interspersed with larger scales with bony cores, or osteoderms. This type of skin is best known in the ceratosaur Carnotaurus
Carnotaurus
Carnotaurus was a large predatory dinosaur. Only one species, Carnotaurus sastrei has been described so far.Carnotaurus lived in Patagonia, Argentina during the Campanian or Maastrichtian stage of the Late Cretaceous...
, which has been preserved with extensive skin impressions.
The most primitive known protofeathered theropods are the compsognathids
Compsognathidae
Compsognathidae is a family of small carnivorous dinosaurs, generally conservative in form, from the Jurassic and Cretaceous Periods. Compsognathids lie at or near the origin of feathers—skin impressions are known from four genera, Compsognathus, Sinosauropteryx, Sinocalliopteryx, and Juravenator...
and early tyrannosauroids
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...
, both coelurosaurs. These early forms had feathers which were relatively short and composed of simple, possibly branching filaments. Simple filaments are also seen in therizinosaur
Therizinosaur
Therizinosaurs are theropod dinosaurs belonging to the clade Therizinosauria. Therizinosaur fossils have been found in Early through Late Cretaceous deposits in Mongolia, the People's Republic of China and Western North America...
s, which also possessed large, stiffened "quill"-like feathers.
Most feathered theropods, including modern birds, usually retain scales only on the feet. Some forms seem to have mixed feathers elsewhere on the body as well. Scansoriopteryx
Scansoriopteryx
Scansoriopteryx is a genus of avialan dinosaur. Described from only a single juvenile fossil specimen found in Liaoning, China, Scansoriopteryx is a sparrow-sized animal that shows adaptations in the foot indicating an arboreal lifestyle. It possessed an unusual, elongated third finger...
preserved scales on the underside of the tail, and Juravenator
Juravenator
Juravenator is a genus of small coelurosaurian dinosaur, which lived in the area which would someday become the Jura mountains of Germany, about 151 or 152 million years ago. It is known from a single, juvenile specimen...
may have been predominantly scaly with some simple filaments interspersed. On the other hand, some theropods were completely covered with feathers, such as the troodontid Anchiornis
Anchiornis
Anchiornis is a genus of small, feathered, deinonychosaurian dinosaur. The genus Anchiornis contains the type species Anchiornis huxleyi, named in honor of Thomas Henry Huxley, an early proponent of biological evolution, and the first to propose a close evolutionary relationship between birds and...
, which even had feathers on the feet and toes.
Size
TyrannosaurusTyrannosaurus
Tyrannosaurus meaning "tyrant," and sauros meaning "lizard") is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex , commonly abbreviated to T. rex, is a fixture in popular culture. It lived throughout what is now western North America, with a much wider range than other...
was the largest and most popular theropod known to the general public for many decades. Since its discovery, however, a number of other giant carnivorous dinosaurs have been described, including 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...
, Carcharodontosaurus
Carcharodontosaurus
Carcharodontosaurus was a gigantic carnivorous carcharodontosaurid dinosaur that lived around 100 to 93 million years ago, during the late Albian to early Cenomanian stages of the mid-Cretaceous Period...
, 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 original Spinosaurus specimens (as well as newer fossils described in 2006) support the idea that Spinosaurus is larger than Tyrannosaurus, showing that Spinosaurus was possibly 6 meters longer and at least 1 metric ton heavier than Tyrannosaurus. There is still no clear explanation for exactly why these animals grew so much larger than the predators that came before and after them.
The smallest non-avialan theropod known from adult specimens is the troodontid
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...
Anchiornis huxleyi
Anchiornis
Anchiornis is a genus of small, feathered, deinonychosaurian dinosaur. The genus Anchiornis contains the type species Anchiornis huxleyi, named in honor of Thomas Henry Huxley, an early proponent of biological evolution, and the first to propose a close evolutionary relationship between birds and...
, at 110 grams in weight and 34 centimeters (1 ft) in length. When modern birds are included, the Bee Hummingbird
Bee Hummingbird
The Bee Hummingbird or Zunzuncito is a species of hummingbird that is endemic to Cuba and Isla de la Juventud...
Mellisuga helenae is smallest at 1.9 g and 5.5 cm (2.2 in) long.
Nervous system and senses
Although rare, complete casts of theropod endocrania are known from fossils. Theropod endocrania can also be reconstructed from preserved brain cases without damaging valuable specimens by using a computed tomography scan and 3D reconstruction software. These finds are of evolutionary significance because they help document the emergence of the neurology of modern birds from that of earlier reptiles. An increase in the proportion of the brain occupied by the cerebrum seems to have occurred with the advent of the Coelurosauria and "continued throughout the evolution of maniraptorans and early birds."Forelimb morphology
Shortened forelimbs in relation to hind legs was a common trait among theropods, most notably in the abelisaurAbelisaur
Abelisaurs were a group of ceratosaurian dinosaurs which lived in the Southern hemisphere during the Cretaceous period. Some well-known dinosaurs of this group include Abelisaurus, Carnotaurus, and Majungasaurus. They are known for their small arms...
ids (such as Carnotaurus
Carnotaurus
Carnotaurus was a large predatory dinosaur. Only one species, Carnotaurus sastrei has been described so far.Carnotaurus lived in Patagonia, Argentina during the Campanian or Maastrichtian stage of the Late Cretaceous...
) and the 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...
(such as Tyrannosaurus
Tyrannosaurus
Tyrannosaurus meaning "tyrant," and sauros meaning "lizard") is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex , commonly abbreviated to T. rex, is a fixture in popular culture. It lived throughout what is now western North America, with a much wider range than other...
). This trait was, however, not universal: spinosaurids had well developed forelimbs, so also did many coelurosaurs. One genus, Xuanhanosaurus
Xuanhanosaurus
Xuanhanosaurus is a genus of theropod dinosaur which lived during the Jurassic of China.The type species Xuanhanosaurus qilixiaensis was named by Dong Zhiming in 1984. The generic name refers to Xuanhan County in Sichuan. The specific name is derived from the town of Qilixia...
, has also been claimed to have been quadrupedal because of its comparatively robust forelimbs, but this is no longer thought to be likely.
The hands are also very different among the different groups. the most common is an appendage consisting of 3 fingers, the digits I, II and III (or possibly II, III and IV) with sharp claws. Some basal theropods (Herrerasaurus
Herrerasaurus
Herrerasaurus was one of the earliest dinosaurs. All known specimens of this carnivore have been discovered in rocks of late Ladinian age in northwestern Argentina...
, Eoraptor
Eoraptor
Eoraptor was one of the world's earliest dinosaurs. It was a two-legged saurischian, close to the ancestry of theropods and sauropodomorphs. It lived ca. 231.4 million years ago, in what is now the northwestern region of Argentina...
) had 4 digits, and also a reduced metacarpal V. Ceratosauria
Ceratosauria
Ceratosaurs are members of a group of theropod dinosaurs defined as all theropods sharing a more recent common ancestry with Ceratosaurus than with birds. There is presently no universally agreed upon listing of species or diagnostic characters of Ceratosauria, though they were less derived...
ns usually had 4 digits, while most tetanurans had 3.
The forelimbs' scope of use is also believed to have also been different among different families. The spinosaurids could have used their powerful forelimbs to hold fishes. Some small coelurosaurus (dromaeosaurids, scansoriopterygids
Scansoriopterygidae
Scansoriopterygidae is a family of maniraptoran dinosaurs, known from three well-preserved fossils unearthed in the Daohugou fossil beds of Liaoning, China....
) are believed to have used their forelimbs to climb in trees, and birds, which are believed to be descendants of theropods, use them for flight.
Forelimb movement
Pronation
In anatomy, pronation is a rotational movement of the forearm at the radioulnar joint, or of the foot at the subtalar and talocalcaneonavicular joints. For the forearm, when standing in the anatomical position, pronation will move the palm of the hand from an anterior-facing position to a...
their hands—that is, they could not rotate the forearm so that the palms faced the ground or backwards towards the legs. In humans, pronation is achieved by motion of the radius
Radius
In classical geometry, a radius of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment, which is half the diameter. If the object does not have an obvious center, the term may refer to its...
relative to the ulna
Ulna
The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form...
(the two bones of the forearm). In saurischian dinosaurs, however, the end of the radius near the elbow was actually locked into a groove of the ulna, preventing any movement. Movement at the wrist was also limited in many species, forcing the entire forearm and hand to move as a single unit with little flexibility. In theropods and prosauropods, the only way for the palm to face the ground would have been by lateral splaying of the entire forelimb, as in a bird raising its wing.
In carnosaurs like Acrocanthosaurus
Acrocanthosaurus
Acrocanthosaurus is a genus of theropod dinosaur that existed in what is now North America during the Aptian and early Albian stages of the Early Cretaceous. Like most dinosaur genera, Acrocanthosaurus contains only a single species, A. atokensis. Its fossil remains are found mainly in the U.S...
, the hand itself retained a relatively high degree of flexibility, with mobile fingers. This was also true of more basal theropods such as herrerasaurs and dilophosaurs
Dilophosauridae
Dilophosauridae is a family of early carnivorous dinosaurs. They are well-known for their distinctive head crests, which were probably used for mating displays, or to intimidate rivals. The family was proposed by Alan Charig and Andrew Milner in 1990 to contain only the type genus, Dilophosaurus...
. 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...
showed a shift in the use of the forearm, with greater flexibility at the shoulder allowing the arm to be raised towards the horizontal plane, and to even greater degrees in flying birds. However, in coelurosaurs such as ornithomimosaurs
Ornithomimosauria
The Ornithomimosauria, ornithomimosaurs or ostrich dinosaurs were theropod dinosaurs which bore a superficial resemblance to modern ostriches. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period of Laurasia...
and especially 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'...
, the hand itself had lost most flexibility, with highly inflexible fingers. Dromaeosaurs and other maniraptora
Maniraptora
Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Deinonychosauria, Oviraptorosauria and Therizinosauria. Ornitholestes and the Alvarezsauroidea...
ns also showed increased mobility at the wrist not seen in other theropods, thanks to the presence of a specialized half-moon shaped wrist bone (the semi-lunate carpal) that allowed the whole hand to fold backward towards the forearm in the manner of modern birds.
Paleopathology
In 2001, Ralph E. Molnar published a survey of pathologies in theropod dinosaur bone. He found pathological features in 21 generaGenera
Genera is a commercial operating system and development environment for Lisp machines developed by Symbolics. It is essentially a fork of an earlier operating system originating on the MIT AI Lab's Lisp machines which Symbolics had used in common with LMI and Texas Instruments...
from 10 families. Pathologies were found in theropods of all body size although they were less common in fossils of small theropods, although this may be an artifact of preservation. They are very widely represented throughout the different parts of theropod anatomy. The most common sites of preserved injury and disease in theropod dinosaur in the ribs and tail vertebrae. Despite being abundant in ribs and vertebrae, injuries seem to be "absent... or very rare" on the bodies' primary weight supporting bones like the sacrum
Sacrum
In vertebrate anatomy the sacrum is a large, triangular bone at the base of the spine and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones. Its upper part connects with the last lumbar vertebra, and bottom part with the coccyx...
, 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...
, and 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....
. The lack of preserved injuries in these bones suggests that they were selected by evolution for resistance to breakage. The least common sites of preserved injury are the cranium and forelimb, with injuries occurring in about equal frequency at each site. Most pathologies preserved in theropod fossils are the remains of injuries like fractures, pits, and punctures, often likely originating with bites. Some theropod paleopathologies seem to be evidence of infections, which tended to be confined only to small regions of the animal's body. Evidence for congenital malformities have also been found in theropod remains. Such discoveries can provide information useful for understanding the evolutionary history of the processes of biological development. Unusual fusion
Fusion
Fusion or synthesis, it refers to the connection of two or more distinct things/bodies:*Cell fusion, an event in the maturation of cells*Fusion cuisine, the combination of elements of various culinary traditions...
s in cranial elements or asymmetries in the same are probably evidence that one is examining the fossils of an extremely old individual rather than a diseased one.
Evolutionary history
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
, a number of primitive proto-theropod and theropod dinosaurs existed and evolved alongside each other.
The earliest and most primitive of the theropod dinosaurs were the carnivorous Eodromaeus
Eodromaeus
Eodromaeus is an extinct genus of basal theropod dinosaur known from the Late Triassic period of Argentina. It has been cited by Sereno as resembling a supposed common ancestor to all dinosaurs, the "Eve" of the dinosaurs....
and the herrerasaurids
Herrerasauridae
Herrerasaurids are among the oldest known dinosaurs, appearing in the fossil record 231.4 million years ago . They became extinct by the end of the Triassic period. Herrerasaurids were small-sized carnivorous theropods or basal saurischians...
of Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
(as well as, possibly, the omnivorous Eoraptor
Eoraptor
Eoraptor was one of the world's earliest dinosaurs. It was a two-legged saurischian, close to the ancestry of theropods and sauropodomorphs. It lived ca. 231.4 million years ago, in what is now the northwestern region of Argentina...
). The herrerasaurs existed during the early late Triassic (Late Carnian
Carnian
The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...
to Early Norian
Norian
The Norian is a division of the Triassic geological period. It has the rank of an age or stage . The Norian lasted from 216.5 ± 2.0 to 203.6 ± 1.5 million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.-Stratigraphic definitions:The Norian was named after the Noric Alps in...
). They were found in North America and South America and possibly also India and Southern Africa. The herrerasaurs were characterised by a mosaic
Mosaic evolution
Mosaic evolution is the concept that evolutionary change takes place in some body parts or systems without simultaneous changes in other parts...
of primitive and advanced features. Some paleontologists have in the past considered the herrerasaurians to be members of Theropoda, while other theorized the group to be basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
saurischians, and may even have evolved prior to the saurischian-ornithischian split. Cladistic analysis following the discovery of Tawa
Tawa (dinosaur)
Tawa is a genus of theropod dinosaur from the Late Triassic period. It is estimated to have been 2 m long...
, another Triassic dinosaur, suggests the herrerasaurs likely were early theropods.
The earliest and most primitive unambiguous theropods (or alternatively, "Eutheropoda" – 'True Theropods') are the Coelophysoidea
Coelophysoidea
Coelophysoids were common dinosaurs of the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivorous forms with a superficial similarity to the coelurosaurs, with which they were formerly...
. The Coelophysoidea were a group of widely distributed, lightly built and potentially gregarious animals. They included small hunters like Coelophysis and (possibly) larger predators like Dilophosaurus
Dilophosaurus
Dilophosaurus was a theropod dinosaur from the Sinemurian stage of the Early Jurassic Period, about 193 million years ago. The first specimens were described in 1954, but it was not until over a decade later that the genus received its current name...
. These successful animals continued from the Late Carnian (early Late Triassic) through to the Toarcian
Toarcian
The Toarcian is, in the ICS' geologic timescale, an age or stage in the Early or Lower Jurassic. It spans the time between 183.0 Ma and 175.6 Ma...
(late Early Jurassic
Early Jurassic
The Early Jurassic epoch is the earliest of three epochs of the Jurassic period...
). Although in the early cladistic classifications they were included under the Ceratosauria
Ceratosauria
Ceratosaurs are members of a group of theropod dinosaurs defined as all theropods sharing a more recent common ancestry with Ceratosaurus than with birds. There is presently no universally agreed upon listing of species or diagnostic characters of Ceratosauria, though they were less derived...
and considered a side-branch of more advanced theropods, they may have been ancestral to all other theropods (which would make them a paraphyletic group).
The somewhat more advanced ceratosaurs
Ceratosauria
Ceratosaurs are members of a group of theropod dinosaurs defined as all theropods sharing a more recent common ancestry with Ceratosaurus than with birds. There is presently no universally agreed upon listing of species or diagnostic characters of Ceratosauria, though they were less derived...
(including Ceratosaurus
Ceratosaurus
Ceratosaurus meaning "horned lizard", in reference to the horn on its nose , was a large predatory theropod dinosaur from the Late Jurassic Period , found in the Morrison Formation of North America, in Tanzania and Portugal...
and Carnotaurus
Carnotaurus
Carnotaurus was a large predatory dinosaur. Only one species, Carnotaurus sastrei has been described so far.Carnotaurus lived in Patagonia, Argentina during the Campanian or Maastrichtian stage of the Late Cretaceous...
) appeared during the Early Jurassic and continued through to the Late Jurassic in Laurasia
Laurasia
In paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...
. They competed alongside their more anatomically advanced tetanuran relatives and—in the form of the abelisaur
Abelisaur
Abelisaurs were a group of ceratosaurian dinosaurs which lived in the Southern hemisphere during the Cretaceous period. Some well-known dinosaurs of this group include Abelisaurus, Carnotaurus, and Majungasaurus. They are known for their small arms...
lineage—lasted to the end of the Cretaceous in Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
.
The Tetanurae
Tetanurae
Tetanurae, or "stiff tails", is a clade that includes most theropod dinosaurs, as well as birds. Tetanurans first appear during the early or middle Jurassic Period.-Definition:...
are more specialised again than the ceratosaurs. They are subdivided into the basal Megalosauroidea
Megalosauroidea
Megalosauroidea is a group of tetanuran theropod dinosaurs that lived from the Middle Jurassic to the Late Cretaceous period.-Classification:...
(alternately Spinosauroidea) and the more derived Avetheropoda. Megalosauridae were primarily Middle Jurassic to Early Cretaceous predators, and their spinosaurid
Spinosauridae
Spinosauridae is a family of specialised theropod dinosaurs. Members of this family were large, bipedal predators with elongated, crocodile-like skulls, sporting conical teeth with no or only very tiny serrations. The front dentary teeth fanned out, giving the animal a characteristic look...
relatives' remains are mostly from Early and Middle Cretaceous rocks. Avetheropoda, as their name indicates, were more closely related to birds and are again divided into the Allosauroidea
Allosauroidea
Allosauroidea is a superfamily or clade of theropod dinosaurs which contains four families — the Sinraptoridae, Allosauridae, Carcharodontosauridae, and Neovenatoridae...
(the diverse carcharodontosaurs) and the Coelurosauria
Coelurosauria
Coelurosauria is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs. In the past, it was used to refer to all small theropods, although this classification has been abolished...
(a very large and diverse dinosaur group including the birds).
Thus, during the late Jurassic, there were no fewer than four distinct lineages of theropods—ceratosaurs, megalosaurs, allosaurs, and coelurosaurs—preying on the abundance of small and large herbivorous dinosaurs. All four groups survived into the Cretaceous, and three of those—the ceratosaurs, coelurosaurs, and allosaurs—survived to end of the period, where they were geographically separate, the ceratosaurs and allosaurs in Gondwana, and the coelurosaurs in Laurasia
Laurasia
In paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...
.
Of all the theropod groups, the coelurosaurs were by far the most diverse. Some coelurosaur groups that flourished during the Cretaceous were the 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...
(including Tyrannosaurus
Tyrannosaurus
Tyrannosaurus meaning "tyrant," and sauros meaning "lizard") is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex , commonly abbreviated to T. rex, is a fixture in popular culture. It lived throughout what is now western North America, with a much wider range than other...
) the dromaeosaurids
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'...
(including Velociraptor
Velociraptor
Velociraptor is a genus of dromaeosaurid theropod dinosaur that existed approximately 75 to 71 million years ago during the later part of the Cretaceous Period. Two species are currently recognized, although others have been assigned in the past. The type species is V. mongoliensis; fossils...
and 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...
, which are remarkably similar in form to the oldest known bird, Archaeopteryx
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...
), the bird-like 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...
and oviraptorosaurs
Oviraptorosauria
Oviraptorosaurs are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot - like skulls, with or without bony crests atop the head...
, the ornithomimosaurs
Ornithomimosauria
The Ornithomimosauria, ornithomimosaurs or ostrich dinosaurs were theropod dinosaurs which bore a superficial resemblance to modern ostriches. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period of Laurasia...
(or "ostrich dinosaurs"), the strange giant-clawed herbivorous therizinosaur
Therizinosaur
Therizinosaurs are theropod dinosaurs belonging to the clade Therizinosauria. Therizinosaur fossils have been found in Early through Late Cretaceous deposits in Mongolia, the People's Republic of China and Western North America...
s, and the avialans
Avialae
Avialae is a clade of dinosaurs containing their only living representatives, birds , and the most immediate extinct relatives of birds.-Competing definitions:...
, which include modern birds and is the only dinosaur lineage to survive the Cretaceous-Paleogene extinction event. While the roots of these various groups are found in the Middle Jurassic, they only became abundant during the Early Cretaceous. A few paleontologists, such as Gregory S. Paul
Gregory S. Paul
Gregory Scott Paul is a freelance researcher, author and illustrator who works in paleontology, and more recently has examined sociology and theology. He is best known for his work and research on theropod dinosaurs and his detailed illustrations, both live and skeletal...
, have suggested that some or all of these advanced theropods were actually descended from flying dinosaurs or proto-birds like Archaeopteryx that lost the ability to fly and returned to a terrestrial habitat.
History of classification
Othniel Charles Marsh
Othniel Charles Marsh was an American paleontologist. Marsh was one of the preeminent scientists in the field; the discovery or description of dozens of news species and theories on the origins of birds are among his legacies.Born into a modest family, Marsh was able to afford higher education...
in 1881. Marsh initially named Theropoda as a suborder
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
to include 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...
Allosauridae, but later expanded its scope, re-ranking it as an order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
to include a wide array of "carnivorous" dinosaur families, including Megalosauridae, Compsognathidae
Compsognathidae
Compsognathidae is a family of small carnivorous dinosaurs, generally conservative in form, from the Jurassic and Cretaceous Periods. Compsognathids lie at or near the origin of feathers—skin impressions are known from four genera, Compsognathus, Sinosauropteryx, Sinocalliopteryx, and Juravenator...
, Ornithomimidae, Plateosauridae
Plateosauridae
Plateosauridae is a family of plateosaurian sauropodomorphs. Plateosaurids were early sauropodomorph dinosaurs which existed in Asia, Europe and South America during the Late Triassic period. Although several dinosaurs have been classified as plateosaurids over the years, a 2007 study by Adam M....
and Anchisauridae
Anchisauridae
The Anchisauridae were a group of early sauropodomorph dinosaurs first proposed by Othniel Charles Marsh in 1885. The clade consists of Anchisaurus and its nearest relatives. However, it is not clear which other genera are included in the family; many of the dinosaurs once included have since been...
(now known to be herbivorous prosauropods) and Hallopodidae (now known to be relatives of crocodilians). Due to the scope of Marsh's Order Theropoda, it came to replace a previous taxonomic group that Marsh's rival E.D. 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...
had created in 1866 for the carnivorous dinosaurs, Goniopoda ("angled feet").
By the early 20th century, some paleontologists, such as Friedrich von Huene
Friedrich von Huene
Friedrich von Huene was a German paleontologist who named more dinosaurs in the early 20th century than anyone else in Europe.-Biography:...
, no longer considered carnivorous dinosaurs to have formed a natural group. Huene abandoned the name Theropoda, instead using Harry Seeley
Harry Seeley
Harry Govier Seeley was a British paleontologist.-Career:Seeley was born in London, the son of Richard Hovill Seeley, goldsmith, and his second wife Mary Govier. He attended classes at the Royal School of Mines, Kensington before becoming an assistant to Adam Sedgwick at the Woodwardian Museum,...
's Order Saurischia
Saurischia
Saurischia meaning 'lizard' and ischion meaning 'hip joint') is one of the two orders, or basic divisions, of dinosaurs. In 1888, Harry Seeley classified dinosaurs into two orders, based on their hip structure...
, which Huene divided into the suborders Coelurosauria
Coelurosauria
Coelurosauria is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs. In the past, it was used to refer to all small theropods, although this classification has been abolished...
and Pachypodosauria. Huene placed most of the small theropod groups into Coelurosauria, and the large theropods and prosauropods into Pachypodosauria, which he considered ancestral to the Sauropoda
Sauropoda
Sauropoda , or the sauropods , are an infraorder of saurischian dinosaurs. They had long necks, long tails, small heads , and thick, pillar-like legs. They are notable for the enormous sizes attained by some species, and the group includes the largest animals to have ever lived on land...
(prosauropods were still thought of as carnivorous at this time, owing to the incorrect association of rauisuchia
Rauisuchia
Rauisuchia is a group of predatory and mostly large Triassic archosaurs. As a clade, Rauisuchia includes these Triassic forms and all crocodylomorphs, which are descendants of Triassic rauisuchians. The group in its traditional sense is paraphyletic, because it does not include crocodylomorph...
n skulls and teeth with prosauropod bodies, in animals such as Teratosaurus
Teratosaurus
Teratosaurus was a genus of rauisuchian known from the Triassic Stubensandstein of Germany...
). In W.D. Matthew and 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...
's 1922 description of the first known dromaeosaurid
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'...
(Dromaeosaurus albertensis
Dromaeosaurus
Dromaeosaurus was a genus of theropod dinosaur which lived during the Late Cretaceous period , sometime between 76.5 and 74.8 million years ago, in the western United States and Alberta, Canada. The name means 'running lizard'....
), they became the first paleontologists to exclude prosauropods from the carnivorous dinosaurs, and attempted to revive the name Goniopoda for that group, though neither of these suggestions were accepted by other scientists.
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
containing the carnivorous dinosaurs and their descendants, when Alfred Romer
Alfred Romer
Alfred Sherwood Romer was an American paleontologist and comparative anatomist and a specialist in vertebrate evolution.-Biography:...
re-classified the Order Saurischia into two suborders, Theropoda and Sauropoda
Sauropoda
Sauropoda , or the sauropods , are an infraorder of saurischian dinosaurs. They had long necks, long tails, small heads , and thick, pillar-like legs. They are notable for the enormous sizes attained by some species, and the group includes the largest animals to have ever lived on land...
. This basic division has survived into modern paleontology, with the exception of, again, the Prosauropoda, which Romer included as an infraorder
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
of theropods. Romer also maintained a division between Coelurosauria and Carnosauria
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...
(which he also ranked as infraorders). This dichotomy was upset by the discovery of 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...
and Deinocheirus
Deinocheirus
Deinocheirus is a genus of large theropod dinosaur, possibly an ornithomimosaurian, which lived in what is now southern Mongolia, during the late Cretaceous Period .-Discovery and naming:...
in 1969, neither of which could be classified easily as "carnosaurs" or "coelurosaurs." In light of these and other discoveries, by the late 1970s Rinchen Barsbold created a new series of theropod infraorders: Coelurosauria, Deinonychosauria
Deinonychosauria
The Deinonychosauria were a clade of coelurosaurian theropod dinosaurs from the Late Jurassic and Cretaceous periods. These omnivores and carnivores are known for their switchblade-like second toe claws and for displaying numerous bird-like characteristics. The clade has been divided into two...
, Oviraptorosauria
Oviraptorosauria
Oviraptorosaurs are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot - like skulls, with or without bony crests atop the head...
, Carnosauria, Ornithomimosauria
Ornithomimosauria
The Ornithomimosauria, ornithomimosaurs or ostrich dinosaurs were theropod dinosaurs which bore a superficial resemblance to modern ostriches. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period of Laurasia...
, and Deinocheirosauria.
With the advent of cladistics
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
and phylogenetic nomenclature
Phylogenetic nomenclature
Phylogenetic nomenclature or phylogenetic taxonomy is an alternative to rank-based nomenclature, applying definitions from cladistics . Its two defining features are the use of phylogenetic definitions of biological taxon names, and the lack of obligatory ranks...
in the 1980s, and their development in the 1990s and 2000s, a clearer picture of theropod relationships began to emerge. Several major theropod groups were named by Jacques Gauthier
Jacques Gauthier
Jacques Armand Gauthier is a vertebrate paleontologist, comparative morphologist, and systematist, and one of the founders of the use of cladistics in biology....
in 1986, including the clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
Tetanurae
Tetanurae
Tetanurae, or "stiff tails", is a clade that includes most theropod dinosaurs, as well as birds. Tetanurans first appear during the early or middle Jurassic Period.-Definition:...
for one branch of a basic theropod split with another group, the Ceratosauria
Ceratosauria
Ceratosaurs are members of a group of theropod dinosaurs defined as all theropods sharing a more recent common ancestry with Ceratosaurus than with birds. There is presently no universally agreed upon listing of species or diagnostic characters of Ceratosauria, though they were less derived...
. As more information about the link between dinosaurs and birds came to light, the more bird-like theropods were grouped in the clade Maniraptora
Maniraptora
Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Deinonychosauria, Oviraptorosauria and Therizinosauria. Ornitholestes and the Alvarezsauroidea...
(also named by Gauthier in 1986). These new developments also came with a recognition among most scientists that birds arose directly from maniraptoran theropods and, with the abandonment of ranks in cladistic classification, the re-evaluation of birds as a subset of theropod dinosaurs that happened to have survived the Mesozoic extinctions into the present.
Major groups
- †HerrerasauridsHerrerasauridaeHerrerasaurids are among the oldest known dinosaurs, appearing in the fossil record 231.4 million years ago . They became extinct by the end of the Triassic period. Herrerasaurids were small-sized carnivorous theropods or basal saurischians...
, probably early theropods, though they may be more primitive saurischians or even non-dinosaurs - †CoelophysoidsCoelophysoideaCoelophysoids were common dinosaurs of the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivorous forms with a superficial similarity to the coelurosaurs, with which they were formerly...
, primitive theropods including CoelophysisCoelophysisCoelophysis , meaning "hollow form" in reference to its hollow bones , is one of the earliest known genera of dinosaur... - †DilophosauridsDilophosauridaeDilophosauridae is a family of early carnivorous dinosaurs. They are well-known for their distinctive head crests, which were probably used for mating displays, or to intimidate rivals. The family was proposed by Alan Charig and Andrew Milner in 1990 to contain only the type genus, Dilophosaurus...
, crested theropods sometimes allied with the coelophysoids - †CeratosauriaCeratosauriaCeratosaurs are members of a group of theropod dinosaurs defined as all theropods sharing a more recent common ancestry with Ceratosaurus than with birds. There is presently no universally agreed upon listing of species or diagnostic characters of Ceratosauria, though they were less derived...
ns, including CeratosaurusCeratosaurusCeratosaurus meaning "horned lizard", in reference to the horn on its nose , was a large predatory theropod dinosaur from the Late Jurassic Period , found in the Morrison Formation of North America, in Tanzania and Portugal...
and abelisaurAbelisaurAbelisaurs were a group of ceratosaurian dinosaurs which lived in the Southern hemisphere during the Cretaceous period. Some well-known dinosaurs of this group include Abelisaurus, Carnotaurus, and Majungasaurus. They are known for their small arms...
ids. The latter were important Late Cretaceous predators in southern continents - TetanuransTetanuraeTetanurae, or "stiff tails", is a clade that includes most theropod dinosaurs, as well as birds. Tetanurans first appear during the early or middle Jurassic Period.-Definition:...
, a major grouping of more advanced theropods- †MegalosauroidsMegalosauroideaMegalosauroidea is a group of tetanuran theropod dinosaurs that lived from the Middle Jurassic to the Late Cretaceous period.-Classification:...
, including the crocodile-skulled spinosaurids - Avetheropods, more advanced and bird-like theropods
- †AllosauroidsAllosauroideaAllosauroidea is a superfamily or clade of theropod dinosaurs which contains four families — the Sinraptoridae, Allosauridae, Carcharodontosauridae, and Neovenatoridae...
, including AllosaurusAllosaurusAllosaurus 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...
and close relatives like the carcharodontosauridsCarcharodontosauridaeCarcharodontosaurids were a group of carnivorous theropod dinosaurs. In 1931 Ernst Stromer named Carcharodontosauridae as a family, in modern paleontology this name indicates a clade within Carnosauria... - CoelurosauriaCoelurosauriaCoelurosauria 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...
ns, a diverse lineage with a wide range of body sizes, diets and niches- †TyrannosauroidsTyrannosauroideaTyrannosauroidea 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...
, small to gigantic carnivores, often with reduced forelimbs - †OrnithomimosauriaOrnithomimosauriaThe Ornithomimosauria, ornithomimosaurs or ostrich dinosaurs were theropod dinosaurs which bore a superficial resemblance to modern ostriches. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period of Laurasia...
ns, "ostrichOstrichThe 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...
-mimics", mostly toothless and probably omnivorous - ManiraptoraManiraptoraManiraptora is a clade of coelurosaurian dinosaurs which includes the birds and the dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Deinonychosauria, Oviraptorosauria and Therizinosauria. Ornitholestes and the Alvarezsauroidea...
ns, birds and their closest relatives, all possessed feathers, many omnivorous or herbivorous- †TherizinosaurTherizinosaurTherizinosaurs are theropod dinosaurs belonging to the clade Therizinosauria. Therizinosaur fossils have been found in Early through Late Cretaceous deposits in Mongolia, the People's Republic of China and Western North America...
s, bipedal herbivores with large hand claws and small heads - †AlvarezsaursAlvarezsauridaeAlvarezsauridae is an enigmatic family of small, long-legged running dinosaurs. Although originally thought to represent the earliest known flightless birds, a consensus of recent work suggests that they are primitive members of the Maniraptora. Other work found them to be the sister group to the...
, small bird-like insectivores with extremely short forelimbs - †OviraptorosauriaOviraptorosauriaOviraptorosaurs are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot - like skulls, with or without bony crests atop the head...
ns, mostly toothless; their diet and lifestyle are uncertain - †DeinonychosaursDeinonychosauriaThe Deinonychosauria were a clade of coelurosaurian theropod dinosaurs from the Late Jurassic and Cretaceous periods. These omnivores and carnivores are known for their switchblade-like second toe claws and for displaying numerous bird-like characteristics. The clade has been divided into two...
, popularly known as "raptors", extremely bird-like omnivores with some pure carnivores - AvialansAvialaeAvialae is a clade of dinosaurs containing their only living representatives, birds , and the most immediate extinct relatives of birds.-Competing definitions:...
, the group including modern birds (the only living dinosaurs) and other winged theropods- †ScansoriopterygidsScansoriopterygidaeScansoriopterygidae is a family of maniraptoran dinosaurs, known from three well-preserved fossils unearthed in the Daohugou fossil beds of Liaoning, China....
, small insectivorous theropods that may have lived in trees - AviansBirdBirds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
, traditional birds
- †Scansoriopterygids
- †Therizinosaur
- †Tyrannosauroids
- †Allosauroids
- †Megalosauroids
Relationships
The following cladogramCladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
is adapted from Weishampel et al., 2004. It retains Coelophysoidea
Coelophysoidea
Coelophysoids were common dinosaurs of the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivorous forms with a superficial similarity to the coelurosaurs, with which they were formerly...
as possible ceratosaurs, as opposed to many recent studies placing them outside ceratosaurs and ancestral to both ceratosaurs and tetanurae
Tetanurae
Tetanurae, or "stiff tails", is a clade that includes most theropod dinosaurs, as well as birds. Tetanurans first appear during the early or middle Jurassic Period.-Definition:...
.
See also
- BirdBirdBirds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
- Sauropod
- OrnithopodOrnithopodOrnithopods 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...
- Marginocephalian
- Thyreophoran