Shuvosaurus inexpectatus Chatterjee, 1993

Rauhut, Oliver W. M., 2003, The interrelationships and evolution of basal theropod dinosaurs, Special papers in palaeontology 69, pp. 1-213 : 18

Shuvosaurus inexpectatus Chatterjee, 1993

Age . Norian.

Occurrence. Cooper Canyon Formation of the Dockum Group, exas and New Mexico, USA.

Diagnosis. Maxilla block-like, strongly reduced in length and almost entirely excluded from the ventral rim of the antorbital fenestra; nasal forms the dorsal rim of the internal antorbital fenestra anteriorly; jugal elongated underneath the antorbital fenestra and forms a peg-and-socket articulation with the maxilla anteriorly; jugal without posterior quadratojugal process; quadratojugal with two anterior process, which subdivide the infratemporal fenestra in a smaller ventral and a larger dorsal part; postorbital with broad posterior process, overlapping the anterior end of the squamosal; dentary with medial platform anteriorly.

Remarks. Shuvosaurus is one of the most bizarre of supposed theropods described recently ( Text-fig. 4h ). The taxon is based on a fairly well-preserved skull of a juvenile individual, to which additional skull elements and a few postcranial bones were referred ( Chatterjee 1993). However, only the cranial parts that show some overlap with the holotype are accepted here as belonging to this taxon, since all the material came from the Post Quarry in the Dockum Group of Texas, which has yielded hundreds of specimens of all kinds of Triassic vertebrates (e.g. Chatterjee 1985, 1991, 1993; Long and Murry 1995), and thus the association of isolated postcranial material is rather questionable.

The genus was originally referred to the O rnithomimosauria by Chatterjee (1993). Long and Murry (1995) tentatively referred the holotype skull of Shuvosaurus to the genus Chatterjeea , a taxon of a possible poposaurian archosaur they named from the same locality. The reasons for this referral were the matching size of the specimens, the comparable preservation, and the lack of other cranial material that could have been referred to the otherwise common crurotarsan (Long and Murry 1995, p. 162). However, Shuvosaurus is radically different from all known crurotarsans in skull morphology (see e.g. Walker 1964; Krebs 1976; Chatterjee 1985; Parrish 1993; Long and Murry 1995), including the edentulous crurotarsan archosaur Lotosaurus (Zhang 1975; pers. obs. of a mounted skeleton in the IVPP). Rauhut (1997) presented a new reconstruction of the skull ( Text-fig. 4h ) and listed the following characters in favour of dinosaurian, saurischian, and theropodan affinities for Shuvosaurus : lack of postfrontal (convergent in crocodiles), paroccipital processes directed ventrolaterally rather than laterally or dorsolaterally as in other archosaurs, lacrimal elongated dorsoventrally and in the shape of an inverted L, presence of a deep basisphenoid recess, and possibly the presence of a deep ventral recess in the ectopterygoid (the identification of this element is questionable). Therefore, Shuvosaurus is included in the analysis here, although the highly apomorphic cranial morphology of this taxon makes it difficult to establish its theropod affinities beyond doubt, unless more material becomes available. As noted above, it might be possible that Gojirasaurus represents a junior synonym of Shuvosaurus .

Figures

text-fig. 4. Skull reconstructions of representatives of riassic OTUs in left lateral view, a, Euparkeria capensis, Early Triassic (Scythian-Anisian), Beaufort Group, South Africa; redrawn from Ewer (1965). B, basal ornithischian Lesothosaurus diagnostics, Early Jurassic (Hettangian-Sinemurian), Elliot Formation, Lesotho; redrawn from Sereno (1991b). c, prosauropod sauropodomorph Plateosaurus sp., Late riassic (Norian), Knollenmergel, Germany; based on MB R. 1937. D, Eoraptor lunensis, Late Triassic (Camian), Ischigualasto Formation, Argentina; based on PVSJ 512. E, Herrerasaurus ischigualastensis, Late Triassic (Camian), Ischigualasto Formation, Argentina; redrawn from Sereno and Novas (1993). F, Coelophysis bauri, Late riassic (Norian), Chinle Formation, south-western USA; modified from Paul (1993). G, Lilienstemus lilienstemi, Late riassic (Norian), Knollenmergel, Germany; based on MB R. 2175, unpreserved elements shaded. H, Shuvosaurus inexpectatus, Late riassic (Norian), Dockum Group, Texas, USA; based on TU P 9280. Abbreviations: a, angular; aof, antorbital fenestra; d, dentary; emf, external mandibular fenestra; en, external nares; eo, exoccipital; f, frontal; itf, infratemporal fenestra; j, jugal; 1, lacrimal; m, maxilla; n, nasal; o, orbit; oc, occipital condyle; op, opisthotic; pa, parietal; pd, predentary; pm, premaxilla; pm-mf, premaxillary-maxillary fenestra; po, postorbital; pof, postfrontal; q, quadrate; qf, quadrate foramen; qj, quadratojugal; sa, surangular; saf, surangular foramen; snf, subnarial foramen; sob, supraorbital; soc, supraoccipital; sp, splenial; sq, squamosal; stf, supratemporal fenestra. Scale bars represent 10 mm (a-b) and 50 mm (c-H).