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Theropoda (; from
ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...
, (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (
clades In biology, a clade (), also known as a monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach to taxonomy ...
) of
dinosaurs Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
, alongside
Ornithischia Ornithischia () is an extinct clade 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 ...
and
Sauropodomorpha Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lo ...
. Theropods, both extant and extinct, are characterized by hollow bones and three toes and claws on each limb. They 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 Ornithi ...
n dinosaurs, placing them closer to sauropodomorphs than to ornithischians. 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 nutrition and energy requirements are met by consumption of animal tissues (mainly mu ...
, although a number of theropod groups evolved to become
herbivore A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat ...
s and
omnivore An omnivore () is an animal that regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize t ...
s. Members of the subgroup
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, tyra ...
and possibly some other or all theropods were covered in
feathers Feathers are epidermis (zoology), epidermal growths that form a distinctive outer covering, or plumage, on both Bird, avian (bird) and some non-avian dinosaurs and other archosaurs. They are the most complex integumentary structures found in ...
. In the
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...
,
bird 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 ...
s evolved from small specialized coelurosaurian theropods, and are currently represented by about 11,000 living species, making theropods the only group of dinosaurs alive today. 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 227.3 ...
age of the late
Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...
period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...
231.4 million years ago ( Ma) and included the majority of 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 ...
until the end of the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
, about 66 Ma, including the largest terrestrial carnivorous animals ever, such as ''
Tyrannosaurus ''Tyrannosaurus'' () is a genus of large theropod dinosaur. The type species ''Tyrannosaurus rex'' ( meaning 'king' in Latin), often shortened to ''T. rex'' or colloquially t-rex, is one of the best represented theropods. It lived througho ...
'' and ''
Giganotosaurus ''Giganotosaurus'' ( ) is a genus of large theropod dinosaur that lived in what is now Argentina, during the early Cenomanian age of the Late Cretaceous period (geology), period, approximately 99.6 to 95 million years ago. The holotype specim ...
'', though non-avian theropods exhibited considerable size diversity, with some non-avian theropods like scansoriopterygids being no bigger than small birds.


Biology


Traits

Various
synapomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to ...
for Theropoda have been proposed based on which taxa are included in the group. For example, a 1999 paper by
Paul Sereno Paul Callistus Sereno (born October 11, 1957) is a professor of paleontology at the University of Chicago who has discovered several new dinosaur species on several continents, including at sites in Inner Mongolia, Argentina, Morocco and Niger. ...
suggests that theropods are characterized by traits such as an ectopterygoid fossa (a depression around the ectopterygoid bone), an intramandibular joint located within the
lower jaw In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...
, and extreme internal cavitation within the bones. However, since taxa like ''Herrerasaurus'' may not be theropods, these traits may have been more widely distributed among early saurischians rather than being unique to theropods. Instead, taxa with a higher probability of being within the Theropoda may share more specific traits, such as a prominent promaxillary fenestra,
cervical vertebrae In tetrapods, cervical vertebrae (: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In saurop ...
with pleurocoels in the anterior part of the centrum leading to a more pneumatic neck, five or more sacral
vertebrae Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...
, enlargement of the carpal bone, and a distally concave portion of the
tibia The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...
, among a few other traits found throughout the skeleton. Like the early sauropodomorphs, the second digit in a theropod's hand is enlarged. Theropods also have a very well developed
ball and socket joint The ball-and-socket joint (or spheroid joint) is a type of synovial joint in which the ball-shaped surface of one rounded bone fits into the cup-like depression of another bone. The distal bone is capable of motion around an indefinite number of ...
near their neck and head. Most theropods belong to the clade Neotheropoda, characterized by the reduction of several foot bones, thus leaving three toed footprints on the ground when they walk (tridactyl feet). Digit V was reduced to a remnant early in theropod evolution and was gone by the late
Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...
. Digit I is reduced and generally do not touch the ground, and greatly reduced in some lineages. They also lack a digit V on their hands and have developed a furcula which is otherwise known as a wishbone. Early neotheropods like the coelophysoids have a noticeable kink in the upper jaw known as a subnarial gap. Averostrans are some of the most derived theropods and contain the Tetanurae and Ceratosauria. While some used to consider coelophysoids and ceratosaurs to be within the same group due to features such as a fused hip, later studies showed that it is more likely that these were features ancestral to neotheropods and were lost in basal tetanurans. Averostrans and their close relatives are united via the complete loss of any digit V remnants, fewer teeth in the maxilla, the movement of the tooth row further down the maxilla and a lacrimal fenestra. Averostrans also share features in their hips and teeth.


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 nutrition and energy requirements are met by consumption of animal tissues (mainly mu ...
. 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 Lizard is the common name used for all Squamata, squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most Island#Oceanic isla ...
in its stomach, and a ''
Velociraptor mongoliensis ''Velociraptor'' (; ) is a genus of small dromaeosaurid dinosaurs 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 ...
'' 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. helleni ...
'' (a type of
ornithischia Ornithischia () is an extinct clade 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). This was likely caused by a
sand dune A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, flat ...
blowing over the two
animals Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia (). With few exceptions, animals consume organic material, breathe oxygen, have myocytes and are able to move, can reproduce sexually, and grow from a ...
mid combat, resulting in
fossilization A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
. The first confirmed non-carnivorous fossil theropods found were the
therizinosaurs Therizinosaurs (; once called segnosaurs) are an extinct group of large herbivorous theropod dinosaurs whose fossils have been mainly discovered from Cretaceous deposits in Asia and North America. Potential fragmentary remains have also been foun ...
, originally known as "segnosaurs". First thought to be
prosauropods Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lo ...
, these enigmatic dinosaurs were later proven to be highly specialized,
herbivorous A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat n ...
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 pecking, grasping, and holding (in probing for food, eating, manipulating and ...
s and leaf-shaped teeth. Further study of
maniraptora Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to ''Ornithomimus velox''. It contains the major subgroups Avialae, Dromaeosauridae, Troodontidae, ...
n 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 regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize ...
diet, including seed-eating (some
troodontids Troodontidae is a clade of bird-like theropod dinosaurs from the Late Jurassic to Late Cretaceous. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinos ...
) and insect-eating (many
avialans Avialae ("bird wings") is a clade containing the only living dinosaurs, the birds, and their closest relatives. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative defi ...
and
alvarezsaurs Alvarezsauroidea (from the Argentine historian, writer and physician Gregorio Álvarez) is a group of small maniraptoran dinosaurs. The group was first formally proposed by Choiniere and colleagues in 2010, to contain the family Alvarezsauridae ...
).
Oviraptorosaurs Oviraptorosaurs ("egg thief lizards") 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 wi ...
,
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 (geology), Period of Laurasia (now Asia ...
and advanced troodontids were likely omnivorous as well, and some early theropods (such as ''
Masiakasaurus knopfleri ''Masiakasaurus'' is a genus of small predatory noasaurid theropod dinosaurs from the Late Cretaceous of Madagascar. In Malagasy, ''masiaka'' means "vicious"; thus, the genus name means "vicious lizard". The type species, ''Masiakasaurus knopf ...
'' and the
spinosaurids Spinosauridae (or spinosaurids) is a clade or family of tetanuran theropod dinosaurs comprising ten to seventeen known genera. Spinosaurid fossils have been recovered worldwide, including Africa, Europe, South America, and Asia. Their remains have ...
) appear to have specialized in catching fish. Diet is largely deduced by the tooth
morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...
, tooth marks on bones of the prey, and gut contents. Some theropods, such as ''
Baryonyx ''Baryonyx'' () is a genus of theropod dinosaur which lived in the Barremian stage of the Early Cretaceous period, about 130–125 million years ago. The first skeleton was discovered in 1983 in the Smokejack Clay Pit, of Surrey, England, in ...
'', ''
Lourinhanosaurus ''Lourinhanosaurus'' (meaning "Lourinhã lizard") was a genus of carnivorous theropod dinosaur that lived during the Late Jurassic Period ( Kimmeridgian/Tithonian) in Portugal. It is one of many large predators discovered at the Lourinhã Format ...
'', 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 ...
s, or gizzard-stones. The majority of theropod teeth are blade-like, with serration on the edges, called ziphodont. Others are pachydont or folidont 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 is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...
theropods were also very diverse in terms of skin texture and covering. Feathers or feather-like structures (filaments) are attested in most lineages of
coelurosaurs 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, tyran ...
(see
feathered dinosaur A feathered dinosaur is any species of dinosaur possessing feathers. That includes all species of birds, and in recent decades evidence has accumulated that many non-avian dinosaur species also possessed feathers in some shape or form. The exte ...
). 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. This type of skin is best known in the
ceratosaur Ceratosaurs are members of the clade Ceratosauria, a group of dinosaurs defined as all theropods sharing a more recent common ancestor with ''Ceratosaurus'' than with birds. The oldest known ceratosaur, ''Saltriovenator'', dates to the earliest ...
''
Carnotaurus ''Carnotaurus'' (; ) is a genus of Theropoda, theropod dinosaur that lived in South America during the Late Cretaceous period, probably sometime between 72 and 69 million years ago. The only species is ''Carnotaurus sastrei''. Known from a si ...
'', which has been preserved with extensive skin impressions.
Osteoderms Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of Extant taxon, extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, Temnospondyli, ...
, scales with a bony core, are known from ''
Ceratosaurus ''Ceratosaurus'' (from Greek 'horn' and 'lizard') is a genus of carnivorous theropod dinosaur that lived in the Late Jurassic period (Kimmeridgian to Tithonian ages). The genus was first described in 1884 by American paleontologist Othni ...
'', which was discovered with segments of osteoderms on top of its neck and tail, probably forming a continuous row in life. Rectangular scutate scales are known from the top of the feet and the underside of the tail and neck in the
carnosaurs Carnosauria is an extinct group of carnivorous theropod dinosaurs that lived during the Jurassic and Cretaceous periods. While Carnosauria was historically considered largely synonymous with Allosauroidea, some recent studies have revived Carn ...
''
Concavenator ''Concavenator'' (meaning Cuenca hunter) is a genus of carcharodontosaurian dinosaur that lived in Spain during the Early Cretaceous epoch, about 125 million years ago. The genus contains a single species, ''Concavenator corcovatus'', named and ...
'' and ''
Allosaurus ''Allosaurus'' ( ) is an extinct genus of theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic period ( Kimmeridgian to late Tithonian ages). The first fossil remains that could definitively be ascribed to th ...
''. There is evidence of some lineages of theropods being ancestrally feathered but losing them in favor of scales in later members. In
tyrannosauroids Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent b ...
, the early members '' Dilong'' and ''
Yutyrannus ''Yutyrannus'' (meaning "feathered tyrant") is a genus of proceratosaurid tyrannosauroid dinosaur which contains a single known species, ''Yutyrannus huali''. This species lived during the early Cretaceous period in what is now northeastern Ch ...
'' are preserved with evidence of feathers, while in the later
tyrannosaurids Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family of coelurosaurian theropod dinosaurs that comprises two subfamilies containing up to fifteen genera, including the eponymous ''Tyrannosaurus''. The exact number of genera i ...
like ''
Tyrannosaurus ''Tyrannosaurus'' () is a genus of large theropod dinosaur. The type species ''Tyrannosaurus rex'' ( meaning 'king' in Latin), often shortened to ''T. rex'' or colloquially t-rex, is one of the best represented theropods. It lived througho ...
'', ''
Tarbosaurus ''Tarbosaurus'' ( ; meaning "alarming lizard") is a genus of large tyrannosaurid dinosaur that lived in Asia during the Late Cretaceous epoch, about 70 million years ago (Maastrichtian age). It contains the single type species: ''Tarbosaurus ...
'', ''
Albertosaurus ''Albertosaurus'' (; meaning "Alberta lizard") is a genus of large tyrannosaurid theropod dinosaur that lived in northwestern North America during the early to middle Maastrichtian age of the Late Cretaceous period, about 71 million yea ...
'', ''
Gorgosaurus ''Gorgosaurus'' ( ; ) is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period (Campanian), between about 76.5 and 75 million years ago. Fossil remains have been found in the Ca ...
,'' and ''
Daspletosaurus ''Daspletosaurus'' ( ; meaning "frightful lizard") is a genus of tyrannosaurid dinosaur that lived in Laramidia between about 77 and 74.4 million years ago, during the Late Cretaceous Period. The genus ''Daspletosaurus'' contains three named ...
,'' there is evidence of scales, though it is unknown if they lost all feathers entirely. 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 Therizinosaurs (; once called segnosaurs) are an extinct group of large herbivorous theropod dinosaurs whose fossils have been mainly discovered from Cretaceous deposits in Asia and North America. Potential fragmentary remains have also been foun ...
, which also possessed large, stiffened "quill"-like feathers. More fully feathered theropods, such as
dromaeosaurids Dromaeosauridae () is a family of feathered coelurosaurian theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Gree ...
, usually retain scales only on the feet. Some species may have mixed feathers elsewhere on the body as well. ''
Scansoriopteryx ''Scansoriopteryx'' ("climbing wing") is a genus of maniraptoran 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 indicati ...
'' preserved scales near the underside of the tail, and ''
Juravenator ''Juravenator'' is a genus of small (75 cm long) coelurosaurian theropod dinosaur (although a 2020 study proposed it to be a hatchling megalosauroid), which lived about 151 or 152 million years ago in the area that would someday become the ...
'' 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 Paraves, 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 m ...
'', which even had feathers on the feet and toes.Abstract
/ref> Based on a relationships between tooth size and skull length and also a comparison of the degree of wear of the teeth of non-avian theropods and modern
lepidosaurs The Lepidosauria (, from Greek meaning ''scaled lizards'') is a Order (biology), superorder or Class (biology), subclass of reptiles, containing the orders Squamata and Rhynchocephalia. Squamata also includes Lizard, lizards and Snake, snakes. Sq ...
, it is concluded that theropods had lips that protected their teeth from the outside. Visually, the snouts of such theropods as ''
Daspletosaurus ''Daspletosaurus'' ( ; meaning "frightful lizard") is a genus of tyrannosaurid dinosaur that lived in Laramidia between about 77 and 74.4 million years ago, during the Late Cretaceous Period. The genus ''Daspletosaurus'' contains three named ...
'' had more similarities with lizards than crocodilians, which lack lips.


Size

''
Tyrannosaurus ''Tyrannosaurus'' () is a genus of large theropod dinosaur. The type species ''Tyrannosaurus rex'' ( meaning 'king' in Latin), often shortened to ''T. rex'' or colloquially t-rex, is one of the best represented theropods. It lived througho ...
'' 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 large spinosaurid theropod dinosaurs that lived in what now is North Africa during the Cenomanian faunal stage, stage of the Late Cretaceous Period (geology), period, about 100 to 94 annum, million year ...
'', ''
Carcharodontosaurus ''Carcharodontosaurus'' (; ) is a genus of large carnivorous theropod dinosaur that lived in Northwest Africa from about 100 to 94 million years ago during the Cenomanian age of the Cretaceous. Two teeth of the genus, now lost, were first des ...
'', and ''
Giganotosaurus ''Giganotosaurus'' ( ) is a genus of large theropod dinosaur that lived in what is now Argentina, during the early Cenomanian age of the Late Cretaceous period (geology), period, approximately 99.6 to 95 million years ago. The holotype specim ...
''. The original ''Spinosaurus'' specimens (as well as newer fossils described in 2006) support the idea that ''Spinosaurus'' was probably 3 meters longer than ''Tyrannosaurus'', though ''Tyrannosaurus'' might have been more massive than ''Spinosaurus''. Specimens such as Sue and
Scotty Scotty is a common nickname for a Scottish people, Scottish man, or for a Scottish Terrier dog. Scotty may also refer to: People Given name or nickname *Scotty Alcock (1885–1973), American baseball player *Scotty Allan (1867–1941), American ...
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 de ...
to be the heaviest theropods known to science. It is still not clear 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 areas of Africa. It is one of two extant species of ostriches, the only living members of the genus ''Struthio'' in the ratite group ...
, up to 2.74 m (9 ft) tall and weighing between 90 and 130 kg (200 - 290 lb). The smallest non-avian theropod known from adult specimens is the
troodontid Troodontidae is a clade of bird-like theropod dinosaurs from the Late Jurassic to Late Cretaceous. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinos ...
''
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 smallest known bird. The bee hummingbird feeds on nectar of flowers and bugs foun ...
(''Mellisuga helenae'') is smallest at 1.9 g and 5.5 cm (2.2 in) long. 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 over 11,000 species of 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 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 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,'' which had a body mass of 200 grams, grew at a rate of approximately 0.33 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 theropoda, theropod dinosaur. The type species ''Tyrannosaurus rex'' ( meaning 'king' in Latin), often shortened to ''T. rex'' or colloquially t-rex, is one of the best represented theropods. It live ...
'' had similar growth dynamics to the largest living land animal today, the
African elephant African elephants are members of the genus ''Loxodonta'' comprising two living elephant species, the African bush elephant (''L. africana'') and the smaller African forest elephant (''L. cyclotis''). Both are social herbivores with grey skin. ...
, 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 animal moves by means of its two rear (or lower) 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'' ...
, 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 group of carnivorous theropod dinosaurs that lived during the Jurassic and Cretaceous periods. While Carnosauria was historically considered largely synonymous with Allosauroidea, some recent studies have revived Carn ...
and
tyrannosaurids Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family of coelurosaurian theropod dinosaurs that comprises two subfamilies containing up to fifteen genera, including the eponymous ''Tyrannosaurus''. The exact number of genera i ...
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. 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 i ...
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 Abelisauridae (meaning "Abel's lizards") is a family (biology), family (or clade) of ceratosaurian theropod dinosaurs. Abelisaurids thrived during the Cretaceous Period (geology), period, on the ancient southern supercontinent of Gondwana, and ...
(such as ''
Carnotaurus ''Carnotaurus'' (; ) is a genus of Theropoda, theropod dinosaur that lived in South America during the Late Cretaceous period, probably sometime between 72 and 69 million years ago. The only species is ''Carnotaurus sastrei''. Known from a si ...
'') 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 D. 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, like most
Ceratosauria Ceratosaurs are members of the clade Ceratosauria, a group of dinosaurs defined as all theropods sharing a more recent common ancestor with '' Ceratosaurus'' than with birds. The oldest known ceratosaur, '' Saltriovenator'', dates to the earlies ...
ns, had four digits, and also a reduced
metacarpal In human anatomy, the metacarpal bones or metacarpus, also known as the "palm bones", are the appendicular bones that form the intermediate part of the hand between the phalanges (fingers) and the carpal bones ( wrist bones), which articulate ...
V (e.g. ''
Dilophosaurus ''Dilophosaurus'' ( ) is a genus of theropod dinosaurs that lived in what is now North America during the Early Jurassic, about 186 million years ago. Three skeletons were discovered in northern Arizona in 1940, and the two best preserv ...
''). The majority of
tetanurans Tetanurae (/ˌtɛtəˈnjuːriː/ or "stiff tails") is a clade that includes most theropod dinosaurs, including megalosauroids, allosauroids, and coelurosaurs (which includes tyrannosauroids, ornithomimosaurs, compsognathids and maniraptorans, ...
had three, but some had even fewer. 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 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 are a group of aquatic flightless birds from the family Spheniscidae () of the order Sphenisciformes (). They live almost exclusively in the Southern Hemisphere. Only one species, the Galápagos penguin, is equatorial, with a sm ...
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 is an order (biology), order of mammals, which is further divided into the Strepsirrhini, strepsirrhines, which include lemurs, galagos, and Lorisidae, lorisids; and the Haplorhini, haplorhines, which include Tarsiiformes, tarsiers a ...
s. Most notably, theropods and other bipedal saurischian dinosaurs (including the bipedal
prosauropod Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the Sauropoda, sauropods and their ancestral relatives. Sauropods generally grew to very large siz ...
s) could not
pronate Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...
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 (: radii or radiuses) 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 radius of a regular polygon is th ...
relative to the
ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...
(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'' ( ; ) is a genus of carcharodontosaurid dinosaurs that existed in what is now North America during the Aptian and early Albian stages of the Early Cretaceous, from 113 to 110 million years ago. Like most dinosaur genera, ...
'', 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 published a survey of
pathologies Pathology is the study of disease. 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 the context of modern medical treatme ...
in theropod dinosaur bone. He found pathological features in 21 
genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...
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 or thoracic cage is an endoskeletal enclosure in the thorax of most vertebrates that comprises the ribs, vertebral column and sternum, which protect the vital organs of the thoracic cavity, such as the heart, lungs and great vessels ...
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 (: sacra or sacrums), in human anatomy, is a 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 of the pelvic cavity, ...
,
femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...
, and
tibia The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...
. 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, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...
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 tissue (biology), tissues by pathogens, their multiplication, and the reaction of host (biology), host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmis ...
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 nucl ...
in cranial elements or
asymmetries Asymmetry is the absence of, or a violation of, symmetry (the property of an object being invariant to a transformation, such as reflection). Symmetry is an important property of both physical and abstract systems and it may be displayed in pre ...
in the same are probably evidence that one is examining the fossils of an extremely old individual rather than a diseased one.


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. ''Ichnotaxon'' comes from the Ancient Greek (''íchnos'') meaning "track" and English , itself derived from ...
named ''Characichnos'', was discovered at the
Feitianshan Formation The Feitianshan Formation is a geological formation in China. It dates back to the Early Cretaceous. Among the known ichnofossils are footprints of dinosaurs Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first a ...
in Sichuan. These 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 are 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 million to 66 million years ago). Pterosaurs are the earli ...
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. Extinct crocodylomorphs were considerably more ...
. 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 ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...
, 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 (phylogenetics), 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) I ...
'' and, possibly, the herrerasaurids of
Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...
. 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 227.3 ...
to Early
Norian The Norian is a division of the Triassic geological period, Period. It has the rank of an age (geology), age (geochronology) or stage (stratigraphy), stage (chronostratigraphy). It lasted from ~227.3 to Mya (unit), million years ago. It was prec ...
). 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 (masonry), mortar, and covering a surface. Mosaics are often used as floor and wall decoration, and ...
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 Cladistics ( ; from Ancient Greek 'branch') 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 ...
following the discovery of '' Tawa'', another Triassic dinosaur, suggests the herrerasaurs likely were early theropods.. The earliest and most primitive unambiguous theropods are the
Coelophysoidea Coelophysoidea is an extinct clade of theropod dinosaurs common during the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivorous forms with a ...
. The coelophysoids were a group of widely distributed, lightly built and potentially gregarious animals. They included small hunters like ''
Coelophysis ''Coelophysis'' ( Traditional English pronunciation of Latin, traditionally; or , as heard more commonly in recent decades) is a genus of coelophysid Theropoda, theropod dinosaur that lived Approximation, approximately 215 to 201.4 million y ...
'' and ''
Camposaurus ''Camposaurus'' ( ) is a coelophysid dinosaur genus from the Norian stage of the Late Triassic period of North America. The pertinent fossil remains date back to the early to middle Norian stage, and is widely regarded as the oldest known neothe ...
''. These successful animals continued from the Late Carnian (early Late Triassic) through to the
Toarcian The Toarcian is, in the International Commission on Stratigraphy, ICS' geologic timescale, an age (geology), age and stage (stratigraphy), stage in the Early Jurassic, Early or Lower Jurassic. It spans the time between 184.2 Megaannum, Ma (million ...
(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 ...
). Although in the early cladistic classifications they were included under the
Ceratosauria Ceratosaurs are members of the clade Ceratosauria, a group of dinosaurs defined as all theropods sharing a more recent common ancestor with '' Ceratosaurus'' than with birds. The oldest known ceratosaur, '' Saltriovenator'', dates to the earlies ...
and considered a side-branch of more advanced theropods, they may have been ancestral to all other theropods (which would make them a
paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...
group). Neotheropoda (meaning "new theropods") is a
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
that includes
coelophysoid Coelophysoidea is an extinct clade of theropod dinosaurs common during the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivorous forms with a ...
s and more advanced
theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...
dinosaurs Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
, and is the only group of theropods that survived the
Triassic–Jurassic extinction event The Triassic–Jurassic (Tr-J) extinction event (TJME), often called the end-Triassic extinction, marks the boundary between the Triassic and Jurassic periods, . It represents one of five major extinction events during the Phanerozoic, profoundly ...
. Neotheropoda was named by R.T. Bakker in 1986 as a group including the relatively derived theropod subgroups
Ceratosauria Ceratosaurs are members of the clade Ceratosauria, a group of dinosaurs defined as all theropods sharing a more recent common ancestor with '' Ceratosaurus'' than with birds. The oldest known ceratosaur, '' Saltriovenator'', dates to the earlies ...
and
Tetanurae Tetanurae (/ˌtɛtəˈnjuːriː/ or "stiff tails") is a clade that includes most Theropoda, theropod dinosaurs, including Megalosauroidea, megalosauroids, Allosauroidea, allosauroids, and Coelurosauria, coelurosaurs (which includes Tyrannosauroi ...
, and excluding
coelophysoids Coelophysoidea is an extinct clade of theropod dinosaurs common during the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivorous forms with a ...
. However, most later researchers have used it to denote a broader group. Neotheropoda was first defined as a
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
by
Paul Sereno Paul Callistus Sereno (born October 11, 1957) is a professor of paleontology at the University of Chicago who has discovered several new dinosaur species on several continents, including at sites in Inner Mongolia, Argentina, Morocco and Niger. ...
in 1998 as ''
Coelophysis ''Coelophysis'' ( Traditional English pronunciation of Latin, traditionally; or , as heard more commonly in recent decades) is a genus of coelophysid Theropoda, theropod dinosaur that lived Approximation, approximately 215 to 201.4 million y ...
'' plus modern
bird 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 ...
s, which includes almost all theropods except the most primitive species. Dilophosauridae was formerly considered a small clade within Neotheropoda, but was later considered to be
paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...
. By 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 ...
, all non-averostran neotheropods had gone extinct. Averostra (or "bird snouts") is a
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
within Neotheropoda that includes most
theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...
dinosaurs Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
, namely
Ceratosauria Ceratosaurs are members of the clade Ceratosauria, a group of dinosaurs defined as all theropods sharing a more recent common ancestor with '' Ceratosaurus'' than with birds. The oldest known ceratosaur, '' Saltriovenator'', dates to the earlies ...
and
Tetanurae Tetanurae (/ˌtɛtəˈnjuːriː/ or "stiff tails") is a clade that includes most Theropoda, theropod dinosaurs, including Megalosauroidea, megalosauroids, Allosauroidea, allosauroids, and Coelurosauria, coelurosaurs (which includes Tyrannosauroi ...
. It represents the only group of post-Early Jurassic theropods. One important diagnostic feature of Averostra is the absence of the fifth metacarpal. Other
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 Ornithi ...
ns retained this bone, albeit in a significantly reduced form. The somewhat more advanced ceratosaurs (including ''
Ceratosaurus ''Ceratosaurus'' (from Greek 'horn' and 'lizard') is a genus of carnivorous theropod dinosaur that lived in the Late Jurassic period (Kimmeridgian to Tithonian ages). The genus was first described in 1884 by American paleontologist Othni ...
'' and ''
Carnotaurus ''Carnotaurus'' (; ) is a genus of Theropoda, theropod dinosaur that lived in South America during the Late Cretaceous period, probably sometime between 72 and 69 million years ago. The only species is ''Carnotaurus sastrei''. Known from a si ...
'') 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 Ceratosaurs are members of the clade Ceratosauria, a group of dinosaurs defined as all theropods sharing a more recent common ancestor with '' Ceratosaurus'' than with birds. The oldest known ceratosaur, '' Saltriovenator'', dates to the earlie ...
lineage—lasted to the end of the Cretaceous in
Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...
. The
Tetanurae Tetanurae (/ˌtɛtəˈnjuːriː/ or "stiff tails") is a clade that includes most Theropoda, theropod dinosaurs, including Megalosauroidea, megalosauroids, Allosauroidea, allosauroids, and Coelurosauria, coelurosaurs (which includes Tyrannosauroi ...
are more specialised again than the ceratosaurs. They are subdivided into the basal
Megalosauroidea 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 ...
(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 s ...
) and the more derived Avetheropoda.
Megalosauridae Megalosauridae is a monophyletic Family (taxonomy), family of Carnivore, carnivorous theropod dinosaurs within the group Megalosauroidea. Appearing in the Middle Jurassic, megalosaurids were among the first major radiation of large theropod dino ...
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 Carnosauria is an extinct group of carnivorous theropod dinosaurs that lived during the Jurassic and Cretaceous periods. While Carnosauria was historically considered largely synonymous with Allosauroidea, some recent studies have revived Carn ...
(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 dinosaurs 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 Dromaeosauridae, dromaeosaurid Theropoda, theropod dinosaur with one described species, ''Deinonychus antirrhopus''. This species, which could grow up to long, lived during the early Cretaceous Period (ge ...
'', 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 (''archaîos''), meaning "ancient", and (''ptéryx''), meaning "feather" ...
''), 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 K–T extinction, was the extinction event, mass extinction of three-quarters of the plant and animal species on Earth approximately 66 million years ago. The event cau ...
. 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 Gregory Scott Paul (born December 24, 1954) is an American freelance researcher, author and illustrator who works in paleontology. He is best known for his work and research on theropoda, theropod dinosaurs and his detailed illustrations, both l ...
, 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 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"; : furculae) or wishbone is a forked bone found in most birds and some species of non-avian dinosaurs, and is either an interclavicle or formed by the fusion of the two clavicles. In birds, its primary function is ...
(wishbone),
pneumatized Skeletal pneumaticity is the presence of air spaces within bones. It is generally produced during development by excavation of bone by pneumatic diverticula (air sacs) from an air-filled space, such as the lungs or nasal cavity. Pneumatization is h ...
bones,
brooding Broodiness is the action or behavioral tendency to sit on a clutch of eggs to Egg incubation, incubate them, often requiring the non-expression of many other behaviors including feeding and drinking.Homedes Ranquini, J. y Haro-García, F. Zoogen ...
of the
eggs An egg is an organic vessel in which an embryo begins to develop. Egg, EGG or eggs may also refer to: Biology * Egg cell, the female reproductive cell (gamete) in oogamous organisms Food * Eggs as food Places * Egg, Austria * Egg, Switzerland ...
, 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 an exa ...
s.


Classification


History of classification

O. C. Marsh Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of paleontology. A prolific fossil collector, Marsh was one of the preeminent paleontologists of the nineteenth century. Among his legacies are the discovery or ...
coined the name Theropoda (meaning "beast feet") in 1881. Marsh initially named Theropoda as a
suborder Order () 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 recognized ...
to include the
family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
Allosauridae Allosauridae is an extinct family of medium to large bipedal, carnivorous allosauroid theropod dinosaurs from the Late Jurassic. Allosauridae is a fairly old taxonomic group, having been first named by the American paleontologist Othniel Cha ...
, but later expanded its scope, re-ranking it as an
order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...
to include a wide array of "carnivorous" dinosaur families, including
Megalosauridae Megalosauridae is a monophyletic Family (taxonomy), family of Carnivore, carnivorous theropod dinosaurs within the group Megalosauroidea. Appearing in the Middle Jurassic, megalosaurids were among the first major radiation of large theropod dino ...
,
Compsognathidae Compsognathidae is a family of coelurosaurian theropod dinosaurs. Compsognathids were small carnivores, generally conservative in form, hailing from the Jurassic and Cretaceous Period (geology), Periods. The bird-like features of these species, a ...
,
Ornithomimidae Ornithomimidae (meaning "bird-mimics") is an extinct family of theropod dinosaurs which bore a superficial resemblance to modern ostriches. Ornithomimids were fast, omnivorous or herbivorous dinosaurs known mainly from the Late Cretaceous Period ...
,
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 restrict ...
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 Upper Portland Formation, Northeastern United States, which was deposited from ...
(now known to be herbivorous
sauropodomorphs Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lo ...
) 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 Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontologist, comparative anatomist, herpetologist, and ichthyologist. Born to a wealthy Quaker family, he distinguished himself as a child prodigy interested i ...
had created in 1866 for the carnivorous dinosaurs: Goniopoda ("angled feet"). By the early 20th century, some palaeontologists, such as
Friedrich von Huene Baron Friedrich Richard von Hoyningen-Huene (22 March 1875 – 4 April 1969) was a German nobleman paleontologist who described a large number of dinosaurs, more than anyone else in 20th-century Europe. He studied a range of Permo-Carbonife ...
, no longer considered carnivorous dinosaurs to have formed a natural group. Huene abandoned the name "Theropoda", instead using
Harry Seeley Harry Govier Seeley (18 February 1839 – 8 January 1909) was a British paleontologist. Early life Seeley was born in London on 18 February 1839, the second son of Richard Hovill Seeley, a goldsmith, and his second wife Mary Govier. When his fa ...
'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 Ornithi ...
, 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, tyra ...
and
Pachypodosauria 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 ...
. 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 ''wikt:sauro-, sauro-'' + ''wikt:-pod, -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative t ...
(prosauropods were still thought of as carnivorous at that time, owing to the incorrect association of
rauisuchia "Rauisuchia" is a paraphyletic group of mostly large and carnivorous Triassic archosaurs. Rauisuchians are a category of archosaurs within a larger group called Pseudosuchia, which encompasses all archosaurs more closely related to crocodilians ...
n skulls and teeth with prosauropod bodies, in animals such as ''
Teratosaurus ''Teratosaurus'' is a genus of rauisuchians known from the Triassic Stubensandstein ( Löwenstein Formation - Norian stage) of Germany. It is estimated to be 6.2 meters (20.35 ft) long. Discovery In 1860, Sixt Friedrich Jakob von Kapff ...
''). Describing the first known dromaeosaurid (''
Dromaeosaurus albertensis ''Dromaeosaurus'' (; ) is a genus of dromaeosaurid theropod dinosaur that lived during the Late Cretaceous period (middle late Campanian and Maastrichtian), sometime between 80 and 69 million years ago, in Alberta, Canada and the western United ...
'') in 1922,
W. D. Matthew William Diller Matthew FRS (February 19, 1871 – September 24, 1930) was a vertebrate paleontologist who worked primarily on mammal fossils, although he also published a few early papers on mineralogy, petrological geology, one on botany, one on ...
and
Barnum Brown Barnum Brown (February 12, 1873 – February 5, 1963), commonly referred to as Mr. Bones, was an American paleontologist. He discovered the first documented remains of ''Tyrannosaurus'' during a career that made him one of the most famous fossil ...
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''; : 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 name and ...
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 () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between Family_(biology), family and Class_(biology), class. In biological classification, the order is a taxonomic rank used in the classific ...
of theropods. Romer also maintained a division between Coelurosauria and
Carnosauria Carnosauria is an extinct group of carnivorous theropod dinosaurs that lived during the Jurassic and Cretaceous periods. While Carnosauria was historically considered largely synonymous with Allosauroidea, some recent studies have revived Ca ...
(which he also ranked as infraorders). This dichotomy was upset by the discovery of ''
Deinonychus ''Deinonychus'' ( ; ) is a genus of Dromaeosauridae, dromaeosaurid Theropoda, theropod dinosaur with one described species, ''Deinonychus antirrhopus''. This species, which could grow up to long, lived during the early Cretaceous Period (ge ...
'' 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 ...
'' 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 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 Mesozo ...
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., Marti ...
,
Oviraptorosauria Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period (geology), Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot-like s ...
, Carnosauria, Ornithomimosauria, and Deinocheirosauria. With the advent of
cladistics Cladistics ( ; from Ancient Greek 'branch') is an approach to Taxonomy (biology), biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesiz ...
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 method, by which taxon names are defined by a '' type'', which c ...
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 ...
named several major theropod groups in 1986, including the
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
Tetanurae Tetanurae (/ˌtɛtəˈnjuːriː/ or "stiff tails") is a clade that includes most Theropoda, theropod dinosaurs, including Megalosauroidea, megalosauroids, Allosauroidea, allosauroids, and Coelurosauria, coelurosaurs (which includes Tyrannosauroi ...
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 Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to ''Ornithomimus velox''. It contains the major subgroups Avialae, Dromaeosauridae, Troodontidae, ...
(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 is an extinct clade of theropod dinosaurs common during the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivorous forms with a ...
(small, early theropods; includes ''
Coelophysis ''Coelophysis'' ( Traditional English pronunciation of Latin, traditionally; or , as heard more commonly in recent decades) is a genus of coelophysid Theropoda, theropod dinosaur that lived Approximation, approximately 215 to 201.4 million y ...
'' and close relatives) *†
Ceratosauria Ceratosaurs are members of the clade Ceratosauria, a group of dinosaurs defined as all theropods sharing a more recent common ancestor with '' Ceratosaurus'' than with birds. The oldest known ceratosaur, '' Saltriovenator'', dates to the earlies ...
(generally elaborately horned, the dominant southern carnivores of the Cretaceous; includes ''
Carnotaurus ''Carnotaurus'' (; ) is a genus of Theropoda, theropod dinosaur that lived in South America during the Late Cretaceous period, probably sometime between 72 and 69 million years ago. The only species is ''Carnotaurus sastrei''. Known from a si ...
'' and close relatives, like ''
Majungasaurus ''Majungasaurus'' (; ) is a genus of abelisaurid theropod dinosaur that lived in Madagascar from 70 to 66 million years ago, at the end of the Cretaceous Period, making it one of the last-known non-avian dinosaurs that went extinct during th ...
'' and '' Chenanisaurus'') *
Tetanurae Tetanurae (/ˌtɛtəˈnjuːriː/ or "stiff tails") is a clade that includes most Theropoda, theropod dinosaurs, including Megalosauroidea, megalosauroids, Allosauroidea, allosauroids, and Coelurosauria, coelurosaurs (which includes Tyrannosauroi ...
("stiff tails"; includes most theropods) :*†
Megalosauroidea 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 ...
(early group of large carnivores including the semi-aquatic spinosaurids) :*†
Allosauroidea Carnosauria is an extinct group of carnivorous theropod dinosaurs that lived during the Jurassic and Cretaceous periods. While Carnosauria was historically considered largely synonymous with Allosauroidea, some recent studies have revived Carn ...
(''
Allosaurus ''Allosaurus'' ( ) is an extinct genus of theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic period ( Kimmeridgian to late Tithonian ages). The first fossil remains that could definitively be ascribed to th ...
'' and close relatives, like ''
Carcharodontosaurus ''Carcharodontosaurus'' (; ) is a genus of large carnivorous theropod dinosaur that lived in Northwest Africa from about 100 to 94 million years ago during the Cenomanian age of the Cretaceous. Two teeth of the genus, now lost, were first des ...
'') :*†
Megaraptora Megaraptora is a clade of carnivorous theropod dinosaurs. Its derived members, the Megaraptoridae are noted for their large hand claws and powerfully-built forelimbs, which are usually reduced in size in other large theropods. Although undoubt ...
(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, tyra ...
(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 Period (geology), Periods. The bird-like features of these species, a ...
(early coelurosaurs with reduced forelimbs) ::*†
Tyrannosauroidea Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent ...
(''
Tyrannosaurus ''Tyrannosaurus'' () is a genus of large theropod dinosaur. The type species ''Tyrannosaurus rex'' ( meaning 'king' in Latin), often shortened to ''T. rex'' or colloquially t-rex, is one of the best represented theropods. It lived througho ...
'' and close relatives; had reduced forelimbs) ::*†
Ornithomimosauria 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 No ...
("
ostrich Ostriches are large flightless birds. Two living species are recognised, the common ostrich, native to large parts of sub-Saharan Africa, and the Somali ostrich, native to the Horn of Africa. They are the heaviest and largest living birds, w ...
-mimics"; mostly toothless; carnivores to possible herbivores) ::*
Maniraptora Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to ''Ornithomimus velox''. It contains the major subgroups Avialae, Dromaeosauridae, Troodontidae, ...
("hand snatchers"; had long, slender arms and fingers) :::*†
Alvarezsauroidea Alvarezsauroidea (from the Argentine historian, writer and physician Gregorio Álvarez) is a group of small maniraptoran dinosaurs. The group was first formally proposed by Choiniere and colleagues in 2010, to contain the family Alvarezsauridae ...
(small insectivores with reduced forelimbs each bearing one enlarged claw) :::*†
Therizinosauria Therizinosaurs (; once called segnosaurs) are an extinct group of large herbivorous Theropoda, theropod dinosaurs whose fossils have been mainly discovered from Cretaceous deposits in Asia and North America. Potential fragmentary remains have als ...
(bipedal herbivores with large hand claws and small heads) :::*†
Scansoriopterygidae Scansoriopterygidae (meaning "climbing wings") is an extinct family (biology), family of climbing and gliding maniraptoran dinosaurs. Scansoriopterygids are known from five well-preserved fossils, representing four species, unearthed in the Tiaoj ...
(small, arboreal maniraptors with long third fingers) :::*†
Oviraptorosauria Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period (geology), Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot-like s ...
(mostly toothless; their diet and lifestyle are uncertain) :::*
Paraves Paraves are a widespread group of theropod dinosaurs that originated in the Middle Jurassic period. In addition to the extinct dromaeosauridae, dromaeosaurids, troodontidae, troodontids, Anchiornithidae, anchiornithids, and possibly the scansor ...
("near-birds"; generally carnivorous, sickle-claws) ::::*†
Anchiornithidae Anchiornithidae is a family of small Paraves, paravian dinosaurs. Anchiornithids have been classified at varying positions in the paravian tree, with some scientists classifying them as a distinct family, a basal subfamily of Troodontidae, membe ...
(small, winged protobirds) ::::*†
Dromaeosauridae Dromaeosauridae () is a family of feathered coelurosaurian theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from ...
(small to medium-sized theropods) ::::*†
Troodontidae Troodontidae is a clade of bird-like theropod dinosaurs from the Late Jurassic to Late Cretaceous. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinos ...
(small, gracile theropods) ::::*
Avialae Avialae ("bird wings") is a clade containing the only living dinosaurs, the birds, and their closest relatives. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to Deinonychosauria, deinonychosaurs, though ...
(birds and extinct relatives) :::::*†
Omnivoropterygidae Omnivoropterygidae (meaning "omnivorous wings") is a family of primitive avialan dinosaurs known exclusively from the Jiufotang Formation of China, though putative omnivoropterygids are known from the Maevarano Formation of the Maastrichtian of ...
(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 Avialae, avialans ("birds" in the broad sense), the most abundant and diverse group known from the Mesozoic era. Almost all retained teet ...
(primitive tree-dwelling, flying birds) :::::*
Euornithes Euornithes (from Greek ' meaning "true birds") is a natural group which includes the most recent common ancestor of all avialans closer to modern birds than to the enantiornithines. This group was defined in the ''PhyloCode'' by Juan Benito an ...
(advanced flying birds) ::::::*†
Yanornithiformes Yanornithiformes is an order of ornithuromorph dinosaurs from the early Cretaceous Period of China. All known specimens come from the Yixian Formation and Jiufotang Formation, dating to the early Aptian The Aptian is an age (geology), age in ...
(toothed Cretaceous Chinese birds) ::::::*†
Hesperornithes Hesperornithes is an extinct and highly specialized group of aquatic Avialae, avialans closely related to the ancestors of modern birds. They inhabited both marine and freshwater habitats in the Northern Hemisphere, and include genus, genera such ...
(specialized aquatic diving birds) ::::::*
Aves 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 lightweight ...
(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. Averostra was named by G.S. Paul in 2002 as an apomorphy-based
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
defined as the group including the
Dromaeosauridae Dromaeosauridae () is a family of feathered coelurosaurian theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from ...
and other Avepoda with (an ancestor with) a promaxillary fenestra (''fenestra promaxillaris'') which can also be referred to as a maxillary fenestra, an extra opening in the front outer side of the
maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...
, the bone that makes up the upper jaw. It was later re-defined by
Martin Ezcurra Martin may refer to: Places Antarctica * Martin Peninsula, Marie Byrd Land * Port Martin, Adelie Land * Point Martin, South Orkney Islands Europe * Martin, Croatia, a village * Martin, Slovakia, a city * Martín del Río, Aragón, Spain * M ...
and
Gilles Cuny The Gilles are the oldest and principal participants in the Carnival of Binche in Belgium. They go out on Shrove Tuesday from 4 a.m. until late hours and dance to traditional songs. Other cities, such as Ressaix, Leval, Buvrinnes, Épinois, ...
in 2007 as a node-based clade containing ''
Ceratosaurus nasicornis ''Ceratosaurus'' (from Greek 'horn' and 'lizard') is a genus of carnivorous theropod dinosaur that lived in the Late Jurassic period (Kimmeridgian to Tithonian ages). The genus was first described in 1884 by American paleontologist Othni ...
'', ''
Allosaurus fragilis ''Allosaurus'' ( ) is an extinct genus of theropoda, theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic Geologic time scale, period (Kimmeridgian to late Tithonian Geologic time scale, ages). The first fossil ...
'', their
last common ancestor A most recent common ancestor (MRCA), also known as a last common ancestor (LCA), is the most recent individual from which all organisms of a set are inferred to have descended. The most recent common ancestor of a higher taxon is generally assu ...
and all its descendants. Mickey Mortimer commented that Paul's original apomorphy-based definition may make Averostra a much broader clade than the ''Ceratosaurus''+''Allosaurus'' node, potentially including all of Avepoda or more. A large study of early dinosaurs by Dr Matthew G. Baron, David Norman and Paul M. Barrett (2017) published in the journal ''
Nature Nature is an inherent character or constitution, particularly of the Ecosphere (planetary), ecosphere or the universe as a whole. In this general sense nature refers to the Scientific law, laws, elements and phenomenon, phenomena of the physic ...
'' suggested that Theropoda is actually more closely related to
Ornithischia Ornithischia () is an extinct clade 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 Ornithoscelida () is a proposed clade that includes various major groupings of dinosaurs. An order Ornithoscelida was originally proposed by Thomas Henry Huxley but later abandoned in favor of Harry Govier Seeley's division of Dinosauria into ...
. 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 Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lo ...
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 Ornithi ...
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.


Footnotes


See also

*
Feathered dinosaurs A feathered dinosaur is any species of dinosaur possessing feathers. That includes all species of birds, and in recent decades evidence has accumulated that many non-avian dinosaur species also possessed feathers in some shape or form. The exte ...
*
Origin of birds The scientific question of which larger group of animals birds evolved within has traditionally been called the "origin of birds". The present scientific consensus is that birds are a group of maniraptoran theropod dinosaurs that originated du ...
* Other major clades of
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
** Marginocephalia **
Ornithopoda Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (). They represent one of the most successful groups of herbivorous dinosaurs during the Cretaceous. The most primitive members of the group were bipedal and relatively sm ...
**
Sauropodomorpha Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lo ...
**
Thyreophora Thyreophora ("shield bearers", often known simply as "armored dinosaurs") is a group of armored ornithischian dinosaurs that lived from the Early Jurassic until the end of the Cretaceous. Thyreophorans are characterized by the presence of bod ...


References


External links

* {{Authority control Dinosaur clades