Averostra, or "bird snouts", is a clade that includes most theropod
dinosaurs
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 the ...
, 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 earliest ...
and
Tetanurae
Tetanurae (/ˌtɛtəˈnjuːriː/ or "stiff tails") is a clade that includes most theropod dinosaurs, including megalosauroids, allosauroids, tyrannosauroids, ornithomimosaurs, compsognathids and maniraptorans (including birds). Tetanurans a ...
, and represent the only group of post-Early Jurassic theropods. Both survived into the Cretaceous period. When the
Cretaceous–Paleogene extinction event
The Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary extinction) was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. With th ...
occurred, ceratosaurians,
megaraptorans
Megaraptora is a clade of carnivorous tetanuran theropod dinosaurs with controversial relations to other theropods. Its derived members, the Megaraptoridae are noted for their elongated hand claws and proportionally large arms, which are usuall ...
an ''incertae sedis'' group within Tetanurae, and two groups of tetanurans within the clade Coelurosauria, the
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 supercontin ...
and
Maniraptoriformes
Maniraptoriformes is a clade of dinosaurs with pennaceous feathers and wings that contains ornithomimosaurs and maniraptorans. This group was named by Thomas Holtz, who defined it as "the most recent common ancestor of ''Ornithomimus'' and bird ...
, were still extant. Only one subgroup of Maniraptoriformes,
Aves
Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...
, survived the extinction event and persisted to the present day.
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 Ornithis ...
ns retained this bone, albeit in a significantly reduced form.
Definition
Averostra was named by Gregory S. Paul in 2002 as an apomorphy-based clade defined as the group including the
Dromaeosauridae
Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek ('), meaning ...
and other
Avepoda
Neotheropoda (meaning "new theropods") is a clade that includes coelophysoids and more advanced theropod dinosaurs, and is the only group of theropods that survived the Triassic–Jurassic extinction event. All neotheropods became extinct by the ...
with (an ancestor with) a promaxillary fenestra (''fenestra promaxillaris''), an extra opening in the front outer side of the maxilla, the bone that makes up the upper jaw. It was later re-defined by
Martin Ezcurra Martin may refer to:
Places
* Martin City (disambiguation)
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Antarctica
* Martin Peninsula, Marie Byrd Land
* Port Martin, Adelie Land
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Aus ...
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 am until late hours and dance to traditional songs. Other cities, such as La Louvière and Nivelles, have a traditi ...
in 2007 as a node-based clade containing ''
Ceratosaurus nasicornis
''Ceratosaurus'' (from Greek κέρας/κέρατος, ' meaning "horn" and σαῦρος ' meaning "lizard") was a carnivorous theropod dinosaur in the Late Jurassic period (Kimmeridgian to Tithonian). The genus was first described in 1884 ...
'', ''
Allosaurus fragilis
''Allosaurus'' () is a genus of large carnosaurian theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic epoch (Kimmeridgian to late Tithonian). The name "''Allosaurus''" means "different lizard" alluding to ...
'', their
last common ancestor
In biology and genetic genealogy, the most recent common ancestor (MRCA), also known as the last common ancestor (LCA) or concestor, of a set of organisms is the most recent individual from which all the organisms of the set are descended. The ...
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.
The clade formed by Ceratosauria and Tetanurae while excluding Coelophysoidea was first named Neotheropoda by