Ceratosaurus nasicornis Marsh, 1884

Rauhut, Oliver W. M., 2003, The interrelationships and evolution of basal theropod dinosaurs, Special papers in palaeontology 69, pp. 1-213 : 24-25

Ceratosaurus nasicornis Marsh, 1884

Age . Kimmeridgian-Tithonian.

Occurrence. Morrison Formation, Utah, Colorado, USA.

Diagnosis. Narrow rounded ho rn core centrally placed on the fused nasals; median oval groove on nasals behind hom core; pubis with large, rounded notch underneath the obturator foramen; small epaxial osteoderms.

Remarks. Ceratosaurus ( Text-fig. 5 g ) certainly represents one of the more distinctive theropods of the Morrison Formation. The taxon long remained enigmatic, but the recent description of two new specimens by Madsen and Welles (2000) has greatly improved our knowledge of the anatomy of this genus, hitherto only known from the type specimen ( Marsh 1884, 1892, 1896; Hay 1908; Gilmore 1920). However, the referral by Madsen and Welles (2000) of these new specimens to two new species, C. dentisulcatus and C. magnicornis is not accepted here, since the differences used to distinguish them are subjective (e.g. relative ‘massiveness ’) or size-related and most probably lie within the individual variation of a single species.

Figures

text-fig. 5. Skull reconstructions of representatives of Jurassic OTUs in left lateral view, a, Dilophosaurus wetherilli, Early Jurassic (Sinemurian-Pliensbachian), Kayenta Formation, Arizona, USA; based on UCMP V 4214 and V 6468. B, Syntarsus rhodesiensis, Early Jurassic (Hettangian-Sinemurian), Forest Sandstone, Zimbabwe; composite reconstruction based on many isolated skull elements from the National Museum of Natural History in Harare (see Appendix), c, Magnosaurus oxoniensis, Middle Jurassic (Callovian), Oxford Clay, England; based on OUM J 13558, unpreserved elements shaded. D, Monolophosaurus jiangi, Middle Jurassic, Wucaiwan Formation, China; redrawn from Zhao and Currie (1993b). E, Allosaurus fragilis, Late Jurassic (Kimmeridgian-Tithonian), Morrison Formation, USA; based on MOR 693. f, basal bird Archaeopteryx sp., Late Jurassic (Tithonian), lithographic limestones of Solnhofen, Germany; based on Wellnhofer (1974), Elzanowski and Wellnhofer (1996), and the Berlin, Eichstätt, and Munich specimens. G, Ceratosaurus sp., Late Jurassic (Kimmeridgian-Tithonian), Morrison Formation, USA; based on USNM 4735 and UMNH VP 5278. H, Ornitholestes hermanni, Late Jurassic (Kimmeridgian-Tithonian), Morrison Formation, USA, based on AMNH 619. Abbreviations as in Text-figure 4, and: If, lacrimal fenestra; mf, maxillary fenestra; nf, nasal foramen; pmf, promaxillary fenestra. Scale bars represent 10 mm (b, f, h), 50 mm (c) and 100 mm (a, d, e, g).