Theropoda (; ), whose members are known as theropods, is a
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
clade
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...
that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of
saurischia
Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...
n dinosaurs. They were ancestrally
carnivorous
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other ...
, although a number of theropod groups evolved to become
herbivore
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...
s and
omnivore
An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nu ...
s. Theropods first appeared during the
Carnian
The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227 m ...
age of the late
Triassic
The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest per ...
period 231.4 million years ago (
Ma) and included all the large terrestrial carnivores from the
Early Jurassic
The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-J ...
until at least the close of the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
, about 66 Ma. In the
Jurassic
The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
,
bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...
s evolved from small specialized
coelurosauria
Coelurosauria (; from Greek, meaning "hollow tailed lizards") is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs.
Coelurosauria is a subgroup of theropod dinosaurs that includes compsognathids, t ...
n theropods, and are today represented by about 10,500 living species.
Biology
Diet and teeth
Theropods exhibit a wide range of diets, from insectivores to herbivores and carnivores. Strict carnivory has always been considered the ancestral diet for theropods as a group, and a wider variety of diets was historically considered a characteristic exclusive to the avian theropods (birds). However, discoveries in the late 20th and early 21st centuries showed that a variety of diets existed even in more basal lineages.
All early finds of theropod fossils showed them to be primarily
carnivorous
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other ...
. Fossilized specimens of early theropods known to scientists in the 19th and early 20th centuries all possessed sharp teeth with serrated edges for cutting flesh, and some specimens even showed direct evidence of predatory behavior. For example, a ''
Compsognathus longipes
''Compsognathus'' (; Greek ''kompsos''/κομψός; "elegant", "refined" or "dainty", and ''gnathos''/γνάθος; "jaw") is a genus of small, bipedal, carnivorous theropod dinosaur. Members of its single species ''Compsognathus longipes'' c ...
'' fossil was found with a
lizard
Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia altho ...
in its stomach, and a ''
Velociraptor mongoliensis
''Velociraptor'' (; ) is a genus of small dromaeosaurid dinosaur that lived in Asia during the Late Cretaceous epoch, about 75 million to 71 million years ago. Two species are currently recognized, although others have been assigned in the pa ...
'' specimen was found locked in combat with a ''
Protoceratops andrewsi
''Protoceratops'' (; ) is a genus of small protoceratopsid dinosaurs that lived in Asia during the Late Cretaceous, around 75 to 71 million years ago. The genus ''Protoceratops'' includes two species: ''P. andrewsi'' and the larger ''P. hellenik ...
'' (a type of
ornithischia
Ornithischia () is an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek ...
n dinosaur).
The first confirmed non-carnivorous fossil theropods found were the
therizinosaurs
Therizinosaurs (once called segnosaurs) were large herbivorous theropod dinosaurs whose fossils have been found across the Early to Late Cretaceous deposits in Asia and North America. Various features of the forelimbs, skull and pelvis unite thes ...
, originally known as "segnosaurs". First thought to be
prosauropods, these enigmatic dinosaurs were later proven to be highly specialized,
herbivorous
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...
theropods. Therizinosaurs possessed large abdomens for processing plant food, and small heads with
beak
The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for eating, preening, manipulating objects, killing prey, fighting, probing for fo ...
s and leaf-shaped teeth. Further study of
maniraptoran theropods and their relationships showed that therizinosaurs were not the only early members of this group to abandon carnivory. Several other lineages of early maniraptorans show adaptations for an
omnivorous
An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nut ...
diet, including seed-eating (some
troodontids
Troodontidae is a clade of bird-like theropod dinosaurs. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinosaurian lineages. More recent fossil discov ...
) and insect-eating (many
avialans
Avialae ("bird wings") is a clade containing the only living dinosaurs, the birds. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative definitions are occasionally used ...
and
alvarezsaurs
Alvarezsauroidea is a group of small maniraptoran dinosaurs. Alvarezsauroidea, Alvarezsauridae, and Alvarezsauria are named for the historian Gregorio Álvarez, not the more familiar physicist Luis Alvarez, or his son geologist Walter Alvarez w ...
).
Oviraptorosaurs,
ornithomimosaurs
Ornithomimosauria ("bird-mimic lizards") are theropod dinosaurs which bore a superficial resemblance to the modern-day ostrich. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period of Laurasia (now Asia, Europe and Nor ...
and advanced troodontids were likely omnivorous as well, and some early theropods (such as ''
Masiakasaurus knopfleri'' and the
spinosaurids
The Spinosauridae (or spinosaurids) are a clade or family of tetanuran theropod dinosaurs comprising ten to seventeen known genera. They came into prominence during the Cretaceous period. Spinosaurid fossils have been recovered worldwide, includi ...
) appear to have specialized in catching fish.
Diet is largely deduced by the tooth
morphology,
tooth marks on bones of the prey, and gut contents. Some theropods, such as ''
Baryonyx'', ''
Lourinhanosaurus'', ornithomimosaurs, and birds, are known to use
gastrolith
A gastrolith, also called a stomach stone or gizzard stone, is a rock held inside a gastrointestinal tract. Gastroliths in some species are retained in the muscular gizzard and used to grind food in animals lacking suitable grinding teeth. In oth ...
s, or gizzard-stones.
The majority of theropod teeth are blade-like, with serration on the edges, called ziphodont. Others are pachydont or phyllodont depending on the shape of the tooth or
denticles. The morphology of the teeth is distinct enough to tell the major families apart,
which indicate different diet strategies. An investigation in July 2015 discovered that what appeared to be "cracks" in their teeth were actually folds that helped to prevent tooth breakage by strengthening individual serrations as they attacked their prey. The folds helped the teeth stay in place longer, especially as theropods evolved into larger sizes and had more force in their bite.
Integument (skin, scales and feathers)
Mesozoic
The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...
theropods were also very diverse in terms of skin texture and covering. Feathers or feather-like structures (filaments) are attested in most lineages of theropods (see
feathered dinosaur
A feathered dinosaur is any species of dinosaur possessing feathers. While this includes all species of birds, there is a hypothesis that many, if not all non-avian dinosaur species also possessed feathers in some shape or form.
It has been s ...
). However, outside the
coelurosaurs, feathers may have been confined to the young, smaller species, or limited parts of the animal. Many larger theropods had skin covered in small, bumpy scales. In some species, these were interspersed with larger scales with bony cores, or
osteoderm
Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct amp ...
s. This type of skin is best known in the ceratosaur ''
Carnotaurus'', which has been preserved with extensive skin impressions.
[Bonaparte, Novas, and Coria (1990). "''Carnotaurus sastrei'' Bonaparte, the horned, lightly built carnosaur from the Middle Cretaceous of Patagonia." ''Contributions in Science (Natural History Museum of Los Angeles County)'', 416: 41 pp.]
The coelurosaur lineages most distant from birds had feathers that were relatively short and composed of simple, possibly branching filaments.
Simple filaments are also seen in therizinosaurs, which also possessed large, stiffened "quill"-like feathers. More fully feathered theropods, such as
dromaeosaurids
Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek ('), meaning ...
, usually retain scales only on the feet. Some species may have mixed feathers elsewhere on the body as well. ''
Scansoriopteryx'' preserved scales near 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
''Anchiornis'' is a genus of small, four-winged paravian dinosaurs, with only one known species, the type species ''Anchiornis huxleyi'', named for its similarity to modern birds. The Latin name ''Anchiornis'' derives from a Greek word meaning " ...
'', which even had feathers on the feet and toes.
[Abstract]
/ref>
Size
''Tyrannosaurus
''Tyrannosaurus'' is a genus of large theropoda, theropod dinosaur. The species ''Tyrannosaurus rex'' (''rex'' meaning "king" in Latin), often called ''T. rex'' or colloquially ''T-Rex'', is one of the best represented theropods. ''Tyrannosa ...
'' was for many decades the largest known theropod and best known to the general public. Since its discovery, however, a number of other giant carnivorous dinosaurs have been described, including ''Spinosaurus
''Spinosaurus'' (; ) is a genus of spinosaurid dinosaur that lived in what now is North Africa during the Cenomanian to upper Turonian stages of the Late Cretaceous period, about 99 to 93.5 million years ago. The genus was known first f ...
'', '' Carcharodontosaurus'', and ''Giganotosaurus
''Giganotosaurus'' ( ) is a genus of theropod dinosaur that lived in what is now Argentina, during the early Cenomanian age of the Late Cretaceous period, approximately 99.6 to 95 million years ago. The holotype specimen was discovered in th ...
''. The original ''Spinosaurus'' specimens (as well as newer fossils described in 2006) support the idea that ''Spinosaurus'' is longer than ''Tyrannosaurus'', showing that ''Spinosaurus'' was possibly 3 meters longer than ''Tyrannosaurus'' though ''Tyrannosaurus'' could still be more massive than ''Spinosaurus''. Specimens such as Sue and Scotty are both estimated
Estimation (or estimating) is the process of finding an estimate or approximation, which is a value that is usable for some purpose even if input data may be incomplete, uncertain, or unstable. The value is nonetheless usable because it is der ...
to be the heaviest theropods known to science. There is still no clear explanation for why these animals grew so heavy and bulky compared to the land predators that came before and after them.
The largest extant theropod is the common ostrich
The common ostrich (''Struthio camelus''), or simply ostrich, is a species of flightless bird native to certain large areas of Africa and is the largest living bird species. It is one of two extant species of ostriches, the only living members ...
, up to 2.74 m (9 ft) tall and weighing between 90 and 130 kg (200 - 290 lb). The smallest non-avialan theropod known from adult specimens is the troodontid
Troodontidae is a clade of bird-like theropod dinosaurs. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinosaurian lineages. More recent fossil disco ...
''Anchiornis huxleyi
''Anchiornis'' is a genus of small, four-winged paravian dinosaurs, with only one known species, the type species ''Anchiornis huxleyi'', named for its similarity to modern birds. The Latin name ''Anchiornis'' derives from a Greek word meaning " ...
'', at 110 grams in weight and 34 centimeters (1 ft) in length. When modern birds are included, the bee hummingbird
The bee hummingbird, zunzuncito or Helena hummingbird (''Mellisuga helenae'') is a species of hummingbird, native to the island of Cuba in the Caribbean. It is the world's smallest bird.
Description
The bee hummingbird is the smallest living ...
''Mellisuga helenae'' is smallest at 1.9 g and 5.5 cm (2.2 in) long.[Conservation International (Content Partner); Mark McGinley (Topic Editor). 2008. "Biological diversity in the Caribbean Islands." In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). irst published in the Encyclopedia of Earth May 3, 2007; Last revised August 22, 2008; Retrieved November 9, 2009 ]
Recent theories propose that theropod body size shrank continuously over a period of 50 million years, from an average of down to , eventually evolving into modern birds. This was based on evidence that theropods were the only dinosaurs to get continuously smaller, and that their skeletons changed four times as fast as those of other dinosaur species.
Growth rates
In order to estimate the growth rates of theropods, scientists need to calculate both age and body mass of a dinosaur. Both of these measures can only be calculated through fossilized bone and tissue, so regression analysis
In statistical modeling, regression analysis is a set of statistical processes for estimating the relationships between a dependent variable (often called the 'outcome' or 'response' variable, or a 'label' in machine learning parlance) and one ...
and extant animal growth rates as proxies are used to make predictions. Fossilized bones exhibit growth rings that appear as a result of growth or seasonal changes, which can be used to approximate age at the time of death. However, the amount of rings in a skeleton can vary from bone to bone, and old rings can also be lost at advanced age, so scientists need to properly control these two possibly confounding variables.
Body mass is harder to determine as bone mass only represents a small proportion of the total body mass of animals. One method is to measure the circumference of the femur, which in non-avian theropod dinosaurs has been shown to be a relatively proportional to quadrupedal mammals, and use this measurement as a function of body weight, as the proportions of long bones like the femur grow proportionately with body mass. The method of using extant animal bone proportion to body mass ratios to make predictions about extinct animals is known as the extant-scaling (ES) approach. A second method, known as the volumetric-density (VD) approach, uses full-scale models of skeletons to make inferences about potential mass. The ES approach is better for wide range studies including many specimens and doesn't require as much of a complete skeleton as the VD approach, but the VD approach allows scientists to better answer more physiological questions about the animal, such as locomotion
Locomotion means the act or ability of something to transport or move itself from place to place.
Locomotion may refer to:
Motion
* Motion (physics)
* Robot locomotion, of man-made devices
By environment
* Aquatic locomotion
* Flight
* Locomo ...
and center of gravity.
The current consensus is that non-avian theropods didn't exhibit a group wide growth rate, but instead had varied rates depending on their size. However, all non-avian theropods had faster growth rates than extant reptiles, even when modern reptiles are scaled up to the large size of some non-avian theropods. As body mass increases, the relative growth rate also increases. This trend may be due to the need to reach the size required for reproductive maturity. For example, one of the smallest known theropods was ''Microraptor zhaoianus
''Microraptor'' ( Greek, μικρός, ''mīkros'': "small"; Latin, ''raptor'': "one who seizes") is a genus of small, four-winged dromaeosaurid dinosaurs. Numerous well-preserved fossil specimens have been recovered from Liaoning, China. T ...
,'' which had a body mass of 200 grams, grew at a rate of approximately .33 grams per day. A comparable reptile of the same size grows at half of this rate. The growth rates of medium-sized non-avian theropods (100–1000 kg) approximated those of precocial birds, which are much slower than altricial birds. Large theropods (1500–3500 kg) grew even faster, similar to rates displayed by eutherian mammals. The largest non-avian theropods, like ''Tyrannosaurus rex
''Tyrannosaurus'' is a genus of large theropod dinosaur. The species ''Tyrannosaurus rex'' (''rex'' meaning "king" in Latin), often called ''T. rex'' or colloquially ''T-Rex'', is one of the best represented theropods. ''Tyrannosaurus'' live ...
'' had similar growth dynamics to the largest living land animal today, the African elephant, which is characterized by a rapid period of growth until maturity, subsequently followed by slowing growth in adulthood.
Stance and gait
As a hugely diverse group of animals, the posture adopted by theropods likely varied considerably between various lineages through time. All known theropods are bipedal
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' (from Latin ''bis'' 'double' ...
, with the forelimbs reduced in length and specialized for a wide variety of tasks (see below). In modern birds, the body is typically held in a somewhat upright position, with the upper leg (femur) held parallel to the spine and with the forward force of locomotion generated at the knee. Scientists are not certain how far back in the theropod family tree this type of posture and locomotion extends.
Non-avian theropods were first recognized as bipedal during the 19th century, before their relationship to birds was widely accepted. During this period, theropods such as carnosaurs
Carnosauria is an extinct large group of predatory dinosaurs that lived during the Jurassic and Cretaceous periods. Starting from the 1990s, scientists have discovered some very large carnosaurs in the carcharodontosaurid family, such as ''Gi ...
and tyrannosaurids
Tyrannosauridae (or tyrannosaurids, meaning " tyrant lizards") is a family of coelurosaurian theropod dinosaurs that comprises two subfamilies containing up to thirteen genera, including the eponymous '' Tyrannosaurus''. The exact number of ...
were thought to have walked with vertical femurs and spines in an upright, nearly erect posture, using their long, muscular tails as additional support in a kangaroo-like tripodal stance. Beginning in the 1970s, biomechanical studies of extinct giant theropods cast doubt on this interpretation. Studies of limb bone articulation and the relative absence of trackway evidence for tail dragging suggested that, when walking, the giant, long-tailed theropods would have adopted a more horizontal posture with the tail held parallel to the ground. However, the orientation of the legs in these species while walking remains controversial. Some studies support a traditional vertically oriented femur, at least in the largest long-tailed theropods, while others suggest that the knee was normally strongly flexed in all theropods while walking, even giants like the tyrannosaurids.[K. Padian, P.E. Olsen, (1989). "Ratite footprints and the stance and gait of Mesozoic theropods." Pp. 231–241 in: D.D. Gillette, M.G. Lockley (Eds.), ''Dinosaur Tracks and Traces'', Cambridge University Press, Cambridge.] It is likely that a wide range of body postures, stances, and gaits existed in the many extinct theropod groups.
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
In computer vision and computer graphics, 3D reconstruction is the process of capturing the shape and appearance of real objects.
This process can be accomplished either by active or passive methods. If the model is allowed to change its shape ...
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."["Abstract", in Chure (2001). Pg. 19.]
Studies show that theropods had very sensitive snouts. It is suggested they might have been used for temperature detection, feeding behavior, and wave detection.
Forelimb morphology
Shortened forelimbs in relation to hind legs was a common trait among theropods, most notably in the abelisaurids (such as '' Carnotaurus'') and the tyrannosaurids (such as ''Tyrannosaurus''). This trait was, however, not universal: spinosaurids had well developed forelimbs, as did many coelurosaurs. The relatively robust forelimbs of one genus, '' Xuanhanosaurus'', led Dong Zhiming to suggest that the animal might have been quadrupedal. However, this is no longer thought to be likely.
The hands are also very different among the different groups. The most common form among non-avian theropods is an appendage consisting of three fingers; the digits I, II and III (or possibly II, III and IV), with sharp claws. Some basal theropods (e.g. ''Herrerasaurus
''Herrerasaurus'' is a genus of saurischian dinosaur from the Late Triassic period. This genus was one of the earliest dinosaurs from the fossil record. Its name means "Herrera's lizard", after the rancher who discovered the first specimen i ...
'', ) had four digits, and also a reduced metacarpal
In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones ar ...
V. Ceratosaurians usually had four digits, while most tetanurans
Tetanurae (/ˌtɛtəˈnjuːriː/ or "stiff tails") is a clade that includes most theropod dinosaurs, including megalosauroids, allosauroids, tyrannosauroids, ornithomimosaurs, compsognathids and maniraptorans (including birds). Tetanurans ar ...
had three.
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 fish. Some small maniraptorans such as scansoriopterygids
Scansoriopterygidae (meaning "climbing wings") is an extinct family of climbing and gliding maniraptoran dinosaurs. Scansoriopterygids are known from five well-preserved fossils, representing four species, unearthed in the Tiaojishan Formatio ...
are believed to have used their forelimbs to climb in trees. The wings of modern birds are used primarily for flight, though they are adapted for other purposes in certain groups. For example, aquatic birds such as penguin
Penguins (order Sphenisciformes , family Spheniscidae ) are a group of aquatic flightless birds. They live almost exclusively in the Southern Hemisphere: only one species, the Galápagos penguin, is found north of the Equator. Highly adap ...
s use their wings as flippers.
Forelimb movement
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 primate
Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians ( monkeys and apes, the latter includin ...
s. 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
In classical geometry, a radius (plural, : radii) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', ...
relative to the ulna
The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...
(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. 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 dromaeosaurids, the hand itself had lost most flexibility, with highly inflexible fingers. Dromaeosaurids and other maniraptorans 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
Ralph E. Molnar is a paleontologist who had been Curator of Mammals at the Queensland Museum and more recently associated with the Museum of Northern Arizona. He is also a research associate at the Texas natural Science Centre. He co-authored descr ...
published a survey of pathologies
Pathology is the study of the causes and effects of disease or injury. The word ''pathology'' also refers to the study of disease in general, incorporating a wide range of biology research fields and medical practices. However, when used in ...
in theropod dinosaur bone. He found pathological features in 21 genera
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...
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 dinosaurs are the ribs
The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels.
The sternum, together known as the thoracic cage, is a semi- ...
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
The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30.
The sacrum situates at the upper, back part o ...
, femur
The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates ...
, and tibia
The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it conn ...
. 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
The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...
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 infection
An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable di ...
s, 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 fusions
Fusion, or synthesis, is the process of combining two or more distinct entities into a new whole.
Fusion may also refer to:
Science and technology Physics
* Nuclear fusion, multiple atomic nuclei combining to form one or more different atomic nuc ...
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.[Molnar, R. E., 2001, Theropod paleopathology: a literature survey: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p. 337-363.]
Swimming
The trackway of a swimming theropod, the first in China of the ichnogenus
An ichnotaxon (plural ichnotaxa) is "a taxon based on the fossilized work of an organism", i.e. the non-human equivalent of an artifact. ''Ichnotaxa'' comes from the Greek ίχνος, ''ichnos'' meaning ''track'' and ταξις, ''taxis'' meaning ...
named ''Characichnos'', was discovered at the Feitianshan Formation
The Feitianshan Formation is a geological Formation (geology), formation in China. It dates back to the Early Cretaceous. Among the known ichnofossils are footprints of Dinosaur, dinosaurs.
Vertebrate ichnofauna
References
Further read ...
in Sichuan. These new swim tracks support the hypothesis that theropods were adapted to swimming and capable of traversing moderately deep water. Dinosaur swim tracks are considered to be rare trace fossils, and are among a class of vertebrate swim tracks that also include those of pterosaur
Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 ...
s and crocodylomorphs
Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction.
During Mesozoic and early Cenozoic times, cr ...
. The study described and analyzed four complete natural molds of theropod foot prints that are now stored at the Huaxia Dinosaur Tracks Research and Development Center (HDT). These dinosaur footprints were in fact claw marks, which suggest that this theropod was swimming near the surface of a river and just the tips of its toes and claws could touch the bottom. The tracks indicate a coordinated, left-right, left-right progression, which supports the proposition that theropods were well-coordinated swimmers.[
]
Evolutionary history
During the late Triassic
The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest per ...
, 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'' (meaning "dawn runner") is an extinct genus of probable basal theropod dinosaurs from the Late Triassic of Argentina. Like many other of the earliest-known dinosaurs, it hails from the Carnian-age (~230 Ma) Ischigualasto Forma ...
'' and, possibly, the herrerasaurids
Herrerasauridae is a Family (biology), family of carnivore, carnivorous dinosaurs, possibly basal (phylogenetics), basal to either theropods or even all of saurischians, or even their own branching from dracohors, separate from dinosauria altoget ...
of Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the List of South American countries by area, second-largest ...
. The herrerasaurs existed during the early late Triassic (Late Carnian
The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227 m ...
to Early Norian
The Norian is a division of the Triassic Period. It has the rank of an age ( geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.
Stratigraphic ...
). They were found in North America and South America and possibly also India and Southern Africa. The herrerasaurs were characterised by a mosaic
A mosaic is a pattern or image made of small regular or irregular pieces of colored stone, glass or ceramic, held in place by plaster/mortar, and covering a surface. Mosaics are often used as floor and wall decoration, and were particularly pop ...
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
Coelophysoidea 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 ...
. The coelophysoids were a group of widely distributed, lightly built and potentially gregarious animals. They included small hunters like '' Coelophysis'' and '' Camposaurus''. These successful animals continued from the Late Carnian (early Late Triassic) through to the Toarcian
The Toarcian is, in the ICS' geologic timescale, an age and stage in the Early or Lower Jurassic. It spans the time between 182.7 Ma (million years ago) and 174.1 Ma. It follows the Pliensbachian and is followed by the Aalenian.
The Toar ...
(late Early Jurassic
The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-J ...
). Although in the early cladistic classifications they were included under the Ceratosauria and considered a side-branch of more advanced theropods,[Rowe, T., and Gauthier, J., (1990). "Ceratosauria." Pp. 151–168 in Weishampel, D. B., Dodson, P., and Osmólska, H. (eds.), ''The Dinosauria'', University of California Press, Berkeley, Los Angeles, Oxford.] they may have been ancestral to all other theropods (which would make them a paraphyletic
In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...
group).[Mortimer, M. (2001).]
Rauhut's Thesis
, Dinosaur Mailing List Archives, 4 Jul 2001.
The somewhat more advanced ceratosaurs (including ''Ceratosaurus
''Ceratosaurus'' (from Greek κέρας/κέρατος, ' meaning "horn" and σαῦρος ' meaning "lizard") was a carnivorous theropod dinosaur in the Late Jurassic period ( Kimmeridgian to Tithonian). The genus was first described in 1 ...
'' and '' Carnotaurus'') appeared during the Early Jurassic and continued through to the Late Jurassic in Laurasia
Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pa ...
. 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
Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final sta ...
.
The Tetanurae
Tetanurae (/ˌtɛtəˈnjuːriː/ or "stiff tails") is a clade that includes most theropod dinosaurs, including megalosauroids, allosauroids, tyrannosauroids, ornithomimosaurs, compsognathids and maniraptorans (including birds). Tetanurans ar ...
are more specialised again than the ceratosaurs. They are subdivided into the basal Megalosauroidea (alternately Spinosauroidea
Megalosauroidea (meaning 'great/big lizard forms') is a superfamily (or clade) of tetanuran theropod dinosaurs that lived from the Middle Jurassic to the Late Cretaceous period. The group is defined as ''Megalosaurus bucklandii'' and all taxa sh ...
) 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
Allosauroidea is a superfamily or clade of theropod dinosaurs which contains four families — the Metriacanthosauridae, Allosauridae, Carcharodontosauridae, and Neovenatoridae. Allosauroids, alongside the family Megalosauroidea, were amo ...
(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
''Velociraptor'' (; ) is a genus of small dromaeosaurid dinosaur that lived in Asia during the Late Cretaceous epoch, about 75 million to 71 million years ago. Two species are currently recognized, although others have been assigned in th ...
'' and ''Deinonychus
''Deinonychus'' ( ; ) is a genus of dromaeosaurid theropod dinosaur with one described species, ''Deinonychus antirrhopus''. This species, which could grow up to long, lived during the early Cretaceous Period, about 115–108 million y ...
'', which are remarkably similar in form to the oldest known bird, ''Archaeopteryx
''Archaeopteryx'' (; ), sometimes referred to by its German name, "" ( ''Primeval Bird''), is a genus of bird-like dinosaurs. The name derives from the ancient Greek (''archaīos''), meaning "ancient", and (''ptéryx''), meaning "feather" ...
''),[Paul, G.S. (1988). ''Predatory Dinosaurs of the World''. New York: Simon and Schuster Co. ()] the bird-like troodontids and oviraptorosaurs, the ornithomimosaurs (or "ostrich Dinosaurs"), the strange giant-clawed herbivorous therizinosaurs, and the avialans, which include modern birds and is the only dinosaur lineage to survive the Cretaceous–Paleogene extinction event
The Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary extinction) was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. With the ...
.[Dingus, L. and Rowe, T. (1998). ''The Mistaken Extinction: Dinosaur Evolution and the Origin of Birds''. Freeman.] While the roots of these various groups are found in the Middle Jurassic, they only became abundant during the Early Cretaceous. A few palaeontologists, 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.[Paul, G.S. (2002). ''Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds.'' Baltimore: Johns Hopkins University Press. 472 pp. ()]
The evolution of birds from other theropod dinosaurs has also been reported, with some of the linking features being the furcula
The (Latin for "little fork") or wishbone is a forked bone found in most birds and some species of non-avian dinosaurs, and is formed by the fusion of the two pink
clavicles. In birds, its primary function is in the strengthening of the thoracic ...
(wishbone), pneumatized bones, brooding
Egg incubation is the process by which an egg, of oviparous (egg-laying) animals, develops an embryo within the egg, after the egg's formation and ovipositional release. Egg incubation is done under favorable environmental conditions, possib ...
of the eggs, and (in coelurosaurs, at least) feather
Feathers are epidermal growths that form a distinctive outer covering, or plumage, on both avian (bird) and some non-avian dinosaurs and other archosaurs. They are the most complex integumentary structures found in vertebrates and a premie ...
s.
Classification
History of classification
O. C. Marsh
Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of Paleontology in Yale College and President of the National Academy of Sciences. He was one of the preeminent scientists in the field of paleontology. Among h ...
coined the name Theropoda (meaning "beast feet") in 1881. Marsh initially named Theropoda as a suborder
Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...
to include the family
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
Allosauridae, but later expanded its scope, re-ranking it as an order
Order, ORDER or Orders may refer to:
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
* Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...
to include a wide array of "carnivorous" dinosaur families, including Megalosauridae, Compsognathidae
Compsognathidae is a family of coelurosaurian theropod dinosaurs. Compsognathids were small carnivores, generally conservative in form, hailing from the Jurassic and Cretaceous Periods. The bird-like features of these species, along with other d ...
, Ornithomimidae, Plateosauridae
Plateosauridae is a family of plateosaurian sauropodomorphs from the Late Triassic of Europe, Greenland, Africa and Asia. Although several dinosaurs have been classified as plateosaurids over the years, the family Plateosauridae is now restric ...
and Anchisauridae
''Anchisaurus'' is a genus of basal sauropodomorph dinosaur. It lived during the Early Jurassic Period, and its fossils have been found in the red sandstone of the Portland Formation, Northeastern United States, which was deposited from the H ...
(now known to be herbivorous sauropodomorphs) and Hallopodidae (subsequently revealed as 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").[Rauhut, O.W. (2003). ''The Interrelationships and Evolution of Basal Theropod Dinosaurs''. Blackwell Publishing, 213 pp. ]
By the early 20th century, some palaeontologists, such as Friedrich von Huene
Friedrich von Huene, born Friedrich Richard von Hoinigen, (March 22, 1875 – April 4, 1969) was a German paleontologist who renamed more dinosaurs in the early 20th century than anyone else in Europe. He also made key contributions about v ...
, no longer considered carnivorous dinosaurs to have formed a natural group. Huene abandoned the name "Theropoda", instead using Harry Seeley's Order Saurischia
Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...
, which Huene divided into the suborders Coelurosauria
Coelurosauria (; from Greek, meaning "hollow tailed lizards") is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs.
Coelurosauria is a subgroup of theropod dinosaurs that includes compsognathids, t ...
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 (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their b ...
(prosauropods were still thought of as carnivorous at that time, owing to the incorrect association of rauisuchian skulls and teeth with prosauropod bodies, in animals such as '' Teratosaurus''). Describing the first known dromaeosaurid ('' Dromaeosaurus albertensis'') in 1922, W. D. Matthew and Barnum Brown
Barnum Brown (February 12, 1873 – February 5, 1963), commonly referred to as Mr. Bones, was an American paleontologist. Named after the circus showman P. T. Barnum, he discovered the first documented remains of '' Tyrannosaurus'' during a career ...
became the first paleontologists to exclude prosauropods from the carnivorous dinosaurs, and attempted to revive the name "Goniopoda" for that group, but other scientists did not accept either of these suggestions.
In 1956, "Theropoda" came back into use—as a taxon
In biology, a taxon ( back-formation from '' taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular n ...
containing the carnivorous dinosaurs and their descendants—when Alfred Romer
Alfred Sherwood Romer (December 28, 1894 – November 5, 1973) was an American paleontologist and biologist and a specialist in vertebrate evolution.
Biography
Alfred Romer was born in White Plains, New York, the son of Harry Houston Romer an ...
re-classified the Order Saurischia into two suborders, Theropoda and Sauropoda. This basic division has survived into modern palaeontology, with the exception of, again, the Prosauropoda, which Romer included as an infraorder
Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...
of theropods. Romer also maintained a division between Coelurosauria and Carnosauria
Carnosauria is an extinct large group of predatory dinosaurs that lived during the Jurassic and Cretaceous periods. Starting from the 1990s, scientists have discovered some very large carnosaurs in the carcharodontosaurid family, such as '' G ...
(which he also ranked as infraorders). This dichotomy was upset by the discovery of ''Deinonychus
''Deinonychus'' ( ; ) is a genus of dromaeosaurid theropod dinosaur with one described species, ''Deinonychus antirrhopus''. This species, which could grow up to long, lived during the early Cretaceous Period, about 115–108 million y ...
'' and ''Deinocheirus
''Deinocheirus'' ( ) is a genus of large ornithomimosaur that lived during the Late Cretaceous around 70 million years ago. In 1965, a pair of large arms, shoulder girdles, and a few other bones of a new dinosaur were first discovered in the N ...
'' 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
, Rinchyengiin Barsbold, born December 21, 1935 in Ulaanbaatar) is a Mongolian paleontologist and geologist. He works with the Institute of Geology, at Ulaanbaatar, Mongolia. He is an expert in vertebrate paleontology and Mesozoic stratigraphy.
Bar ...
had created a new series of theropod infraorders: Coelurosauria, Deinonychosauria
Deinonychosauria is a clade of paravian dinosaurs which lived from the Late Jurassic to the Late Cretaceous periods. Fossils have been found across the globe in North America, Europe, Africa, Asia, South America, and Antarctica,Case, J.A., Mar ...
, Oviraptorosauria, Carnosauria, Ornithomimosauria, and Deinocheirosauria.
With the advent of cladistics
Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups (" clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived cha ...
and phylogenetic nomenclature
Phylogenetic nomenclature is a method of nomenclature for taxa in biology that uses phylogenetic definitions for taxon names as explained below. This contrasts with the traditional approach, in which taxon names are defined by a '' type'', which ...
in the 1980s, and their development in the 1990s and 2000s, a clearer picture of theropod relationships began to emerge. Jacques Gauthier
Jacques Armand Gauthier (born June 7, 1948 in New York City) is an American vertebrate paleontologist, comparative morphologist, and systematist, and one of the founders of the use of cladistics in biology.
Life and career
Gauthier is the so ...
named several major theropod groups in 1986, including the clade
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...
Tetanurae
Tetanurae (/ˌtɛtəˈnjuːriː/ or "stiff tails") is a clade that includes most theropod dinosaurs, including megalosauroids, allosauroids, tyrannosauroids, ornithomimosaurs, compsognathids and maniraptorans (including birds). Tetanurans ar ...
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, on the abandonment of ranks in cladistic classification, with the re-evaluation of birds as a subset of theropod dinosaurs that survived the Mesozoic extinctions and lived into the present.
Major groups
The following is a simplified classification of theropod groups based on their evolutionary relationships, and organized based on the list of Mesozoic dinosaur species provided by Holtz. A more detailed version can be found at dinosaur classification.
The dagger (†) is used to signify groups with no living members.
*†Coelophysoidea
Coelophysoidea 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 ...
(small, early theropods; includes '' Coelophysis'' and close relatives)
*† Ceratosauria (generally elaborately horned, the dominant southern carnivores of the Cretaceous; includes '' Carnotaurus'' and close relatives, like '' Majungasaurus'' and '' Chenanisaurus'')
*Tetanurae
Tetanurae (/ˌtɛtəˈnjuːriː/ or "stiff tails") is a clade that includes most theropod dinosaurs, including megalosauroids, allosauroids, tyrannosauroids, ornithomimosaurs, compsognathids and maniraptorans (including birds). Tetanurans ar ...
("stiff tails"; includes most theropods)
:*† Megalosauroidea (early group of large carnivores including the semi-aquatic spinosaurids)
:*†Allosauroidea
Allosauroidea is a superfamily or clade of theropod dinosaurs which contains four families — the Metriacanthosauridae, Allosauridae, Carcharodontosauridae, and Neovenatoridae. Allosauroids, alongside the family Megalosauroidea, were amo ...
(''Allosaurus
''Allosaurus'' () is a genus of large carnosaurian theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic epoch ( Kimmeridgian to late Tithonian). The name "''Allosaurus''" means "different lizard" alludin ...
'' and close relatives, like '' Carcharodontosaurus'')
:*†Megaraptora
Megaraptora is a clade of carnivorous Tetanurae, tetanuran theropod dinosaurs with controversial relations to other theropods. Its Derived (phylogenetics), derived members, the Megaraptoridae are noted for their elongated hand claws and proporti ...
(A group of medium to large Orionides with unknown affinities, quite common in the southern hemisphere)
:*Coelurosauria
Coelurosauria (; from Greek, meaning "hollow tailed lizards") is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs.
Coelurosauria is a subgroup of theropod dinosaurs that includes compsognathids, t ...
(feathered theropods, with a range of body sizes and niches)
::*†Compsognathidae
Compsognathidae is a family of coelurosaurian theropod dinosaurs. Compsognathids were small carnivores, generally conservative in form, hailing from the Jurassic and Cretaceous Periods. The bird-like features of these species, along with other d ...
(early coelurosaurs with reduced forelimbs)
::*†Tyrannosauridae
Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family of coelurosaurian theropod dinosaurs that comprises two subfamilies containing up to thirteen genera, including the eponymous ''Tyrannosaurus''. The exact number of genera ...
(''Tyrannosaurus
''Tyrannosaurus'' is a genus of large theropoda, theropod dinosaur. The species ''Tyrannosaurus rex'' (''rex'' meaning "king" in Latin), often called ''T. rex'' or colloquially ''T-Rex'', is one of the best represented theropods. ''Tyrannosa ...
'' and close relatives; had reduced forelimbs)
::*† Ornithomimosauria ("ostrich
Ostriches are large flightless birds of the genus ''Struthio'' in the order Struthioniformes, part of the infra-class Palaeognathae, a diverse group of flightless birds also known as ratites that includes the emus, rheas, and kiwis. There ...
-mimics"; mostly toothless; carnivores to possible herbivores)
::* Maniraptora ("hand snatchers"; had long, slender arms and fingers)
:::*† Alvarezsauroidea (small insectivores with reduced forelimbs each bearing one enlarged claw)
:::*† Therizinosauria (bipedal herbivores with large hand claws and small heads)
:::*† Scansoriopterygidae (small, arboreal maniraptors with long third fingers)
:::*† Oviraptorosauria (mostly toothless; their diet and lifestyle are uncertain)
:::*† Archaeopterygidae (small, winged protobirds)
:::*†Dromaeosauridae
Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek ('), meaning ...
(small to medium-sized theropods)
:::*†Troodontidae
Troodontidae is a clade of bird-like theropod dinosaurs. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinosaurian lineages. More recent fossil discov ...
(small, gracile theropods)
:::*Avialae
Avialae ("bird wings") is a clade containing the only living dinosaurs, the birds. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative definitions are occasionally use ...
(birds and extinct relatives)
::::*†Omnivoropterygidae
Omnivoropterygidae (meaning "omnivorous wings") is a family of primitive avialans known exclusively from the Jiufotang Formation of China, though putative omnivoropterygids are known from the Maevarano Formation of the Maastrichtian of Madagasc ...
(large, early short-tailed avialans)
::::*†Confuciusornithidae
Confuciusornithidae is an extinct family of pygostylian avialans known from the Early Cretaceous, found in northern China. They are commonly placed as a sister group to Ornithothoraces, a group that contains all extant birds along with their clo ...
(small toothless birds)
::::*†Enantiornithes
The Enantiornithes, also known as enantiornithines or enantiornitheans in literature, are a group of extinct avialans ("birds" in the broad sense), the most abundant and diverse group known from the Mesozoic era. Almost all retained teeth and cla ...
(primitive tree-dwelling, flying birds)
::::* Euornithes (advanced flying birds)
:::::*† Yanornithiformes (toothed Cretaceous Chinese birds)
:::::*†Hesperornithes
Hesperornithes is an extinct and highly specialized group of aquatic avialans closely related to the ancestors of modern birds. They inhabited both marine and freshwater habitats in the Northern Hemisphere, and include genera such as '' Hesperorn ...
(specialized aquatic diving birds)
:::::*Aves
Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...
(modern, beaked birds and their extinct relatives)
Relationships
The following family tree illustrates a synthesis of the relationships of the major theropod groups based on various studies conducted in the 2010s.
A large study of early dinosaurs by Dr Matthew G. Baron, David Norman and Paul M. Barrett (2017) published in the journal ''Nature
Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans are ...
'' suggested that Theropoda is actually more closely related to Ornithischia
Ornithischia () is an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek ...
, to which it formed the sister group
In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree.
Definition
The expression is most easily illustrated by a cladogram:
Taxon A and ...
within the clade Ornithoscelida. This new hypothesis also recovered Herrerasauridae
Herrerasauridae is a family of carnivorous dinosaurs, possibly basal to either theropods or even all of saurischians, or even their own branching from dracohors, separate from dinosauria altogether. They are among the oldest known dinosaurs, ...
as the sister group to Sauropodomorpha in the redefined Saurischia
Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...
and suggested that the hypercarnivore morphologies that are observed in specimens of theropods and herrerasaurids were acquired convergently. However, this phylogeny remains controversial and additional work is being done to clarify these relationships.
See also
* Marginocephalian
* Origin of birds
The scientific question of within which larger group of animals birds evolved has traditionally been called the "origin of birds". The present scientific consensus is that birds are a group of maniraptoran theropod dinosaurs that originated ...
* Ornithopod
Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (), 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 w ...
* Thyreophoran
References
External links
{{Authority control
Carnian first appearances
Extant Late Triassic first appearances
Taxa named by Othniel Charles Marsh