Allosaurus fragilis Marsh, 1877

Nesbitt, Sterling J., 2011, The Early Evolution Of Archosaurs: Relationships And The Origin Of Major Clades, Bulletin of the American Museum of Natural History 2011 (352), pp. 1-292 : 56

Allosaurus fragilis Marsh, 1877

AGE: Kimmeridian-Tithonian, Late Jurassic ( Foster, 2007).

OCCURRENCE: Morrison Formation, western United States.

NEOTYPE: UUVP 6000, a complete skull and partial skeleton only lacking first caudal vertebra, chevrons, ribs, forearms, and some digits of the pes ( Madsen, 1976).

REFERRED MATERIAL: Various materials from UUVP and AMNH.

REMARKS: Allosaurus is one of the best Jurassic theropods known to date. The taxon is represented by many articulated and disarticulated elements found throughout the Morrison Formation in North America. Allosaurus has been used in many phylogenetic analyses examining the relationships of theropods (e.g., Turner et al., 2007; Rauhut, 2003).

Allosaurus fragilis possesses the following unique characters: distinct ‘‘step’’ in the ventral margin of the jugal, leading to a significant ventral displacement of the posterior part in relation to the anterior portion; neomorphic bone (5 antarticular of Madsen, 1976); well-developed notch in the anteroventral margin of the prearticular ( Rauhut, 2003).

KEY REFERENCES: Marsh, 1877; Madsen, 1976; Brusatte and Sereno, 2008.