Ornithischia Seeley, 1887

Rauhut, Oliver W. M., 2003, The interrelationships and evolution of basal theropod dinosaurs, Special papers in palaeontology 69, pp. 1-213 : 16

Ornithischia Seeley, 1887

Included taxa. Lesothosaurus , Technosaurus, Pisanosaurus, Thyreophora, Ornithopoda, and Marginocephalia , and all dinosaurs that are more closely related to these taxa than to saurischians.

Temporal range. Camian-Maastrichtian.

Distribution. Global.

Diagnosis. Ossified palpebral over the orbit; presence of an unpaired predentary; maxillary and dentary tooth crowns triangular in lateral view; ossified epaxial tendons along the neural spines; ilium with elongate, dorsoventrally low preacetabular process; opisthopubic pelvis; pubic shafts slender, rod-like.

Remarks. Seeley (1887, 1888) first noted the fundamental differences in the pelvic girdles of different taxa of dinosaurs, and referred all the opisthopubic members then known to a clade he named Orn ithischia, in reference to the opisthopubic condition of the pelvis in birds. Whereas the monophyly of the other major group of dinosaurs, the Saurischia , has repeatedly been doubted (e.g. Charig et al. 1965; Bakker and Galton 1974; Bakker 1986), the Orn ithischia were generally accepted as a monophyletic group, even after the discovery of nonavian theropod dinosaurs with an opisthopubic pelvis ( Barsbold 1979).

The monophyly of the Omithischia is supported by a large number of synapomorphies ( Sereno 1986), many of which are in some way related to the herbivorous diet of all known members of this clade. Following Sereno (1986, 1991 b, 1997), Lesothosaurus ( Text-fig. 4b ) and basal Thyreophora (Scutellosaurus, Scelidosaurus, Emausaurus ) are regarded here as some of the most basal taxa of o rn ithischians, and most character codings are based on these animals.

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).