Ornitholestes hermanni Osborn, 1903

Rauhut, Oliver W. M., 2003, The interrelationships and evolution of basal theropod dinosaurs, Special papers in palaeontology 69, pp. 1-213 : 26-27

Ornitholestes hermanni Osborn, 1903

Age . Kimmeridgian-Tithonian.

Occurrence. Morrison Formation, Wyoming, Utah, Colorado, USA.

Diagnosis. Premaxillary teeth massive, larger than maxillary teeth, with distally flattened tip, and without serrations; articular facet of quadrate subrectangular in outline; retroarticular processes offset medially from lateral margin of mandible.

Remarks. Orn itholestes ( Text-fig. 5h ) is the only small theropod dinosaur from the Morrison Formation that is represented by a fairly complete skeleton and is, therefore, of considerable interest. The original material comprises a crushed skull and partial postcranium ( Osborn 1903, 1916). A partial articulated manus from the same locality was referred to the same taxon ( Osborn 1903), although this referai is questionable ( Holtz 2000, pers. comm. 2001). It is rather surprising that no detailed description of the material has been published so far. Fortunately, the type skull (AMNH 619) has recently been reprepared, so that many important cranial characters are visible now for the first time.

Paul (1988tz, 6) argued for a close relationship between Orn itholestes and Proceratosaurus , and reconstructed the skull of the former taxon with a nasal horn. My observations of the type specimen of Ornitholestes (AMNH 619) revealed little evidence for the presence of such a structure; the apparent upward flexure of the posterior border of the external nares on the left side of the skull is caused by a break and subsequent ventral displacement of the ascending process of the maxilla and the nasals.

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).