Averostra

Averostra, or "bird snouts", is a clade that includes most theropod dinosaurs that have a promaxillary fenestra (fenestra promaxillaris), an extra opening in the front outer side of the maxilla, the bone that makes up the upper jaw. The two groups of averostrans, Ceratosauria and Tetanurae, both survived into the Cretaceous period. When the Cretaceous–Paleogene extinction event occurred, ceratosaurians and two groups of tetanurans within the clade Coelurosauria, the Tyrannosauroidea and Maniraptoriformes, were still extant. Only one subgroup of maniraptoriformes, Aves, survived the extinction event and persisted to the present day.

Averostrans
Temporal range:
Early Jurassic–Present, 201–0 Ma
Skeleton of a juvenile Ceratosaurus, Dinosaur Discovery Museum
Skeleton of Allosaurus fragilis
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Clade: Neotheropoda
Clade: Averostra
Paul, 2002
Subgroups

Definition

Averostra was named by Gregory S. Paul in 2002 as an apomorphy-based clade defined as the group including the Dromaeosauridae and Avepoda with (an ancestor with) a promaxillary fenestra.[1] It was later re-defined by Martin Ezcurra and Gilles Cuny in 2007 as a node-based clade containing Ceratosaurus nasicornis, Allosaurus fragilis, their last common ancestor and all its descendants.[2] 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.[3]

A 2020 monograph supported the classification of very early large Jurassic theropods such as Dilophosaurus as not members of Averostra (as defined by Ezcurra and Cuny), but related to basal members.[4]

References
  1. Paul, 2002. Dinosaurs of the Air. The Johns Hopkins University Press, Baltimore and London. 460 pp.
  2. Ezcurra M.D. and Cuny, G., 2007. The coelophysoid Lophostropheus airelensis, gen. nov.: A review of the systematics of "Liliensternus" airelensis from the Triassic-Jurassic outcrops of Normandy (France). Journal of Vertebrate Paleontology. 27(1), 73-86
  3. Mortimer, Mickey (2010-11-15). "The Theropod Database Blog: Averostra and Avepoda". The Theropod Database Blog. Retrieved 2020-09-06.
  4. Marsh, A., & Rowe, T. (2020). A comprehensive anatomical and phylogenetic evaluation of Dilophosaurus wetherilli (Dinosauria, Theropoda) with descriptions of new specimens from the Kayenta Formation of northern Arizona. Journal of Paleontology, 94(S78), 1-103. doi:10.1017/jpa.2020.14
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