Allosauroidea
Allosauroidea is a superfamily or clade of theropod dinosaurs which contains four families — the Metriacanthosauridae, Allosauridae, Carcharodontosauridae, and Neovenatoridae. Allosauroids, alongside the family Megalosauroidea, were among the apex predators that were active during the Middle Jurassic to Late Cretaceous periods. The most famous and best understood allosauroid is the North American genus Allosaurus.
| Allosauroids Temporal range: Middle Jurassic–Late Cretaceous, (Possible Late Toarcian and Late Maastrichtian records) | |
|---|---|
| Allosaurus fragilis skull, San Diego Natural History Museum | |
| Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Infraorder: | †Carnosauria |
| Superfamily: | †Allosauroidea Marsh, 1878 |
| Type species | |
| †Allosaurus fragilis Marsh, 1877 | |
| Subgroups | |
| |
The oldest-known allosauroid, Shidaisaurus jinae, appeared in the early Middle Jurassic about 174 million years ago (Earliest Aalenian stage) of China. The last known definitive surviving members of the group died out around 89 million years ago in Asia (Shaochilong) and South America (Mapusaurus), though the megaraptorans, which survived until the end of Maastrichtian, may belong to the group as well. A frontal assigned to an allosauroid found to be most closely related to Sinraptor has also been found in the Coniacian (89-86.3 Ma) of Argentina, however this has been reinterpreted to belong to a megaraptoran, which may or may not be allosauroids. Additional, but highly fragmentary, remains were suggested to belong to carcharodontosaurids are known from the Late Maastrichtian (70-66 Ma ago) in Brazil, but were later interpreted as those of abelisaurids. Furthermore, an indeterminate toe bone from the Campanian of New Zealand has also been noted to share features with allosauroids, but until more material of this taxon is unearthed, its taxonomy is uncertain. The enigmatic Unquillosaurus from the Campanian or Maastrichtian Los Blanquitos Formation in Argentina has been found to likely be a carcharodontosaurid by Carrano et al. (2012).
Allosauroids had long, narrow skulls, large orbits, three-fingered hands, and usually had "horns" or ornamental crests on their heads. Although allosauroids vary in size, the group maintains a similar center of mass and hip position on their bodies. Allosauroids also exhibit reptilian-style immune systems, secreting fibrin at injured sites to prevent infections from spreading through the bloodstream. This characteristic has been observed by examining injuries and infections on allosauroid bones. It is possible that allosauroids were social animals, as many remains of allosauroids have been found in close proximity to each other. Allosauroids were likely active predators, and from studying endocasts, probably best responded to odors and loud low-frequency noises.