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Tetanurae (/ˌtɛtəˈnjuːriː/ or "stiff tails") is a clade 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 ...
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 ...
s, including megalosauroids, allosauroids, and
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 ...
(which includes
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 ...
,
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 ...
, compsognathids and
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, ...
ns, the latter including living
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). Tetanurans are defined as all theropods more closely related to modern birds than to ''
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 contain the majority of predatory dinosaur diversity. Tetanurae likely diverged from its sister group,
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 ...
, during the late Triassic. Tetanurae first appeared in the fossil record by the Early Jurassic about 190 mya and by the Middle Jurassic had become globally distributed. The group was named by Jacques Gauthier in 1986 and originally had two main subgroups: Carnosauria and Coelurosauria, the clade containing birds and related dinosaurs such as compsognathids, tyrannosaurids, ornithomimosaurs, and maniraptorans. The original Carnosauria was a polyphyletic group including any large carnivorous theropod. Many of Gauthier's carnosaurs, such as tyrannosaurids, have since been re-classified as coelurosaurs or primitive tetanurans. Carnosauria has been reclassified as a group containing allosaurids that split from the Coelurosauria at the Neotetanurae/Avetheropoda node. Members of Megalosauroidea are believed to represent basal tetanurans, but recent discoveries have shown that they might be members of Carnosauria expanding Carnosauria back to its original meaning. It is however agreed that Megalosauroids, Allosauroids and Coelurosaurians are all members of the Orionides, a subset within Tetanurae that contains dinosaurs more derived than animals such as Chuandongcoelurus and Kayentavenator. Tetanuran evolution was characterized by parallel diversification of multiple lineages, repeatedly attaining large body size and similar locomotor morphology. ''Cryolophosaurus'' has been claimed as the first true member of the group, but subsequent studies have disagreed on whether it is a dilophosaurid or tetanuran. Arcucci and Coria (2003) classified ''Zupaysaurus'' as an early tetanuran, but it was later placed as a sister taxon to the clade containing dilophosaurids, ceratosaurs, and tetanurans. Shared tetanuran features include a ribcage indicating a sophisticated air-sac-ventilated lung system similar to that in modern birds. This character would have been accompanied by an advanced circulatory system. Other tetanuran characterizing features include the absence of the fourth digit of the hand, placement of the maxillary teeth anterior to the orbit, a strap-like scapula, maxillary fenestrae, and stiffened tails. During the Late Jurassic and Early Cretaceous, large spinosaurids and allosaurs flourished but possibly died out in the northern hemisphere before the end of the Cretaceous, and were replaced as apex predators by tyrannosauroid coelurosaurs. At least in South America, carcharodontosaurid allosaurs may have persisted until the end of the Mesozoic Era, and died out at the same time as the non-avian coelurosaurs.


Morphology


Anatomy

Tetanurans have two basic skull morphologies. The first skull type, typical in large theropods such as ''Allosaurus'', is common within ceratosaurs and may be primitive for tetanurans. In this type, the skull is about three times longer than tall, with a blunter snout and frequent elaborations such as horns or spikes along the lacrimals, nasals, and frontals. In the second skull type, the skull is lower and longer, with a less elaborated skull roof and a more elongated snout. Shared tetanuran features include the maxillary fenestra (an opening in the antorbital fossa), a pneumatic excavation in the jugal, and the position of the maxillary teeth anterior to the orbit. The posterior skull is little modified in tetanurans, except within Spinosauridae. The presence of an antorbital tooth row in tetanurans may be associated with macropredatory habits. In the postcranial skeleton, tetanurans transition between the most primitive theropod morphologies in basal tetanurans towards more derived, bird-like states in coelurosaurs. Most tetanurans possess specialized wrist bones, the absence or reduction of the fourth digit of the hand, a strap-like scapula, stiffened tails, and a laminar astragalar ascending process. Advanced tetanurans would have possessed a sophisticated air-sac-ventilated lung system similar to birds, and an advanced circulatory system. In megalosaurids and allosaurids, the orientation of the femoral head is anteromedial such as in ceratosaurs, but in avetheropods this orientation is fully medial. Tetanuran locomotor morphology is relatively generalized, with few variations between taxa. The hands of tetanurans, unlike those of the closely related ceratosaurs, lack a fourth finger. Early tetanurans still possessed metacarpal IV, but it was vestigial and not part of a finger anymore. The tridactyl manus was preserved in birds. Evidence from the basal ceratosaur ''
Saltriovenator ''Saltriovenator'' (meaning " Saltrio hunter") is a genus of ceratosaurian dinosaur that lived during the Sinemurian stage of the Early Jurassic in what is now Italy. The type and only species is ''Saltriovenator zanellai''; in the past, the sp ...
'' indicates the tetanuran digits are I, II and III instead of II, III and IV.


Body Size

Basal tetanurans were the first theropods to achieve truly giant body sizes, with both megalosauroid and allosauroid taxa weighing over 1 ton. Sequential temporal appearances of large body size in subsequent clades suggest a pattern of size-cycles, with the extinction of incumbent giant forms allowing for replacement with a new, more bird-like theropod group that then also evolved giant body size. It is, however, possible that more than one giant tetanuran existed at a time in the same paleoenvironment, perhaps with feeding habit variations. Within most dinosaur clades, body size tended to increase over time along a lineage according to Cope's rule. Coelurosaurian theropods are the notable exception to the pattern of body size increases.


History of study


History of classification

Tetanurae was recognized and named by Gauthier in 1986. The earliest-discovered non-avian tetanuran is ''Megalosaurus''. For a century after the description of ''Megalosaurus'', most large carnivorous dinosaurs were serially arrayed into the family Megalosauridae within the order Theropoda. In 1914, Friedrich von Huene separated small, lightly built forms into the infraorder Coelurosauria and larger taxa into the infraorder Pachypodosauria. Later, he transferred large, carnivorous taxa to the new infraorder Carnosauria, which came to include all known large-bodied carnivores other than ''Ceratosaurus''. The size-based arrangement persisted until Gauthier, who redefined Carnosauria and Coelurosauria based on new cladistic analyses but retained the terms. Gauthier defined Coelurosauria as a taxon comprising birds and theropods closer to birds than to Carnosauria, and listed within Carnosauria several large-bodied theropod taxa but did not formally define the group. Many of these original carnosaurs have since been reclassified as coelurosaurs or primitive tetanurans, and Carnosauria has now been defined as ''Allosaurus'' and all Avetheropods closer to ''Allosaurus'' than to birds. Initial cladistics studies supported the arrangement of primitive megalosaurs as serial outgroups to a clade of allosaurids, followed by the Coelurosauria. Subsequent studies have discovered that many of these basal tetanurans formed a true clade, termed Megalosauroidea or alternatively Spinosauroidea.


Current phylogeny

Current phylogeny agrees on a monophyletic Tetanurae that includes a series of generally large-bodied basal taxa outside a monophyletic Coelurosauria. Coelophysoids are basal to Tetanurae, with Ceratosauria forming a sister taxa that diverged during the late Triassic. After their initial appearance, Tetanurae radiated into two main clades, Spinosauroidea or Megalosauroidea and Avetheropoda or Neotetanurae. Spinosauroidea are believed to represent basal Tetanurans. At the Neotetanurae/Avetheropoda node, allosaurids split from the Coelurosauria. Tyrannosauridae has been placed within Coelurosauria. The allosaurids and their closest relatives form a reconstituted Carnosauria. Debate persists about whether the allosaurids form a clade with spinosauroids/megalosauroids, and whether Allosauroidea belongs in Avetheropoda with Coelurosauria or forms a sister taxa to Megalosauroidea, and whether Megalosauroidea forms a valid clade. Although many
phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...
analyses found basal tetanurans that were outside both
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 ...
and Avetheropoda, the core
dichotomy A dichotomy () is a partition of a set, partition of a whole (or a set) into two parts (subsets). In other words, this couple of parts must be * jointly exhaustive: everything must belong to one part or the other, and * mutually exclusive: nothi ...
was named only in 2012. Carrano, Benson and Sampson (2012) named that clade Orionides, and defined it as the
node In general, a node is a localized swelling (a "knot") or a point of intersection (a vertex). Node may refer to: In mathematics * Vertex (graph theory), a vertex in a mathematical graph *Vertex (geometry), a point where two or more curves, lines ...
comprising
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 ...
, Avetheropoda, their most recent common ancestor, and all its descendants. In 2015, Hendrickx, Hartman and Mateus clarified this definition, specifying it as the least inclusive clade including ''
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 ...
'', ''
Megalosaurus bucklandii ''Megalosaurus'' (meaning "great lizard", from Ancient Greek, Greek , ', meaning 'big', 'tall' or 'great' and , ', meaning 'lizard') is an extinct genus of large carnivorous theropod dinosaurs of the Middle Jurassic Epoch (Bathonian stage, 166 ...
'', and ''
Passer domesticus The house sparrow (''Passer domesticus'') is a bird of the sparrow family Passeridae, found in most parts of the world. It is a small bird that has a typical length of and a mass of . Females and young birds are coloured pale brown and grey, ...
''. The clade name "Orionides" was first established by Matthew T. Carrano, Roger B. J. Benson and Scott D. Sampson in
2012 2012 was designated as: *International Year of Cooperatives *International Year of Sustainable Energy for All Events January *January 4 – The Cicada 3301 internet hunt begins. * January 12 – Peaceful protests begin in the R ...
. It is derived from
Orion Orion may refer to: Common meanings * Orion (constellation), named after the mythical hunter * Orion (mythology), a hunter in Greek mythology Arts and media Fictional entities Characters and species * Orion (character), a DC Comics c ...
, the giant hunter of
Greek mythology Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, and a genre of ancient Greek folklore, today absorbed alongside Roman mythology into the broader designation of classical mythology. These stories conc ...
in references to the large size and carnivorism of basal orionidans. The name also refers to the alternative name for the
constellation of Orion Orion is a prominent set of stars visible during winter in the northern celestial hemisphere. It is one of the 88 modern constellations; it was among the 48 constellations listed by the 2nd-century astronomer Ptolemy. It is named after a hun ...
, Alektropodion, meaning "rooster foot". The smaller clade, Avetheropoda was named by
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 ...
in 1988, and 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 Currie and Padian in 1997, to include ''
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 ...
'', 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, and other animals descended from their most recent ancestor. In 1999,
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. ...
named another group, Neotetanurae, for the clade containing
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 ...
and
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 excluding other tetanurans such as megalosauroids, but this definition was published slightly later. A monophyletic Avetheropoda is recovered in many papers; however, recent findings suggest a monophyletic Carnosauria model with allosauroids and megalosauroids as each other's closest relatives instead of Allosauroids and Coelurosaurs. The
cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...
presented below follows a phylogenetic analysis published by Zanno and Makovicky in 2013. In 2019, Rauhut and Pol described ''
Asfaltovenator vialidadi ''Asfaltovenator'' (meaning "Cañadón Asfalto Formation hunter" after the fossil formation in which its fossils were found) is a genus of possibly allosauroid dinosaur from the Lower Jurassic (Middle Toarcian) Cañadón Asfalto Formation of Chubu ...
'', a basal allosauroid displaying a mosaic of primitive and derived features seen within Tetanurae. Their phylogenetic analysis found traditional
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 ...
to represent a basal
grade Grade most commonly refers to: * Grading in education, a measurement of a student's performance by educational assessment (e.g. A, pass, etc.) * A designation for students, classes and curricula indicating the number of the year a student has reach ...
of carnosaurs,
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 ...
with respect to Allosauroidea.


Paleobiology


Biogeography

The biogeographical history of non-avian Tetanurae spans over 110 million years and all continents. The presence of major lineages prior to the breakup of Pangaea implies wide dispersal of these clades, with later absences indicating regional extinctions or dispersal failure. The density of sampling is currently insufficient to provide a detailed analysis of biogeographical evolution for the Tetanurae.


Diversity

Tetanurae and Ceratosauria likely diverged during the late Triassic, more than 200 mya. By the Early Jurassic, Tetanurae fossils appear in the fossil record and reached global distribution by the Middle Jurassic. In the Late Jurassic, the fossil record demonstrates widespread presence of multiple clades within both megalosauroids and avetheropods. The Megalosauroidea contained high diversity with two Jurassic clades, Piatnitzkysauridae and Megalosauridae, as well as the Cretaceous Spinosauridae. Tetanuran evolution appears to exhibit waves of diversification, although this may be due to uneven sampling. During the Late Jurassic and Early Cretaceous, large spinosaurids and allosaurids flourished, but the latter possibly died out before the end of the Cretaceous due to the
Cenomanian-Turonian boundary event The Cenomanian-Turonian boundary event, also known as the Cenomanian-Turonian extinction, Cenomanian-Turonian Oceanic Anoxic Event ( OAE 2), and referred to also as the Bonarelli Event or Level, was an anoxic extinction event in the Cretaceous p ...
, while spinosaurids are known from the Santonian. Soon afterwards the niche of terrestrial apex predator was filled by ceratosaurs and tyrannosaurids, which dominated terminal Cretaceous terrestrial ecosystems. Coelurosaurs persisted through the end of the Mesozoic Era. Modern birds are the only living representatives of the Tetanurae.


References

{{Taxonbar, from=Q131391 Dinosaur clades