The anatomy of the basal ornithischian dinosaur Eocursor parvus from the lower Elliot Formation (Late Triassic) of South Africa

Abstract

Ornithischia is a morphologically and taxonomically diverse clade of dinosaurs that originated during the Late Triassic and were the dominant large-bodied herbivores in many Cretaceous ecosystems. The early evolution of ornithischian dinosaurs is poorly understood, as a result in part of a paucity of fossil specimens, particularly during the Triassic. The most complete Triassic ornithischian dinosaur yet discovered is Eocursor parvus from the lower Elliot Formation (Late Triassic: Norian-Rhaetian) of Free State, South Africa, represented by a partial skull and relatively complete postcranial skeleton. Here, the anatomy of Eocursor is described in detail for the first time, and detailed comparisons are provided to other basal ornithischian taxa. Eocursor is a small-bodied taxon (approximately 1 m in length) that possesses a plesiomorphic dentition consisting of unworn leaf-shaped crowns, a proportionally large manus with similarities to heterodontosaurids, a pelvis that contains an intriguing mix of plesiomorphic and derived character states, and elongate distal hindlimbs suggesting well-developed cursorial ability. The ontogenetic status of the holotype material is uncertain. Eocursor may represent the sister taxon to Genasauria, the clade that includes most of ornithischian diversity, although this phylogenetic position is partially dependent upon the uncertain phylogenetic position of the enigmatic and controversial clade Heterodontosauridae.

Postcranial anatomy ofLesothosaurus diagnosticus(Dinosauria: Ornithischia) from the Lower Jurassic of southern Africa: implications for basal ornithischian taxonomy and systematics

“…By contrast, the majority of other Late Triassic/Early Jurassic ornithischian taxa are known from more fragmentary material, comprising either incomplete specimens (e.g. Pisanosaurus, Eocursor, many heterodontosaurids: Bonaparte, 1976;Butler, 2010;Porro et al, 2011;Sereno, 2012) or disarticulated bonebed material (e.g. Laquintasaura, Barrett et al, 2014), although Heterodontosaurus (e.g.…”

“…In recent years, a variety of new specimens and revisions of previously known material have helped to better constrain the timing of major events in ornithischian evolution, as well as giving insights into their early diversity (e.g. Knoll, 2002;Butler, 2005Butler, , 2010Butler, Smith & Norman, 2007;Irmis et al, 2007;Butler, Porro & Norman, 2008b;Butler, Upchurch & Norman, 2008a;Norman et al, 2011;Pol, Rauhut & Becerra, 2011;Porro et al, 2011;Sereno, 2012;Barrett et al, 2014). Although the early ornithischian record is richer than previously recognized , it is still poor in comparison with that of early saurischians.…”

“…Butler (2005) discussed the taxonomic status of L. diagnosticus but only re-described those elements of its anatomy that were necessary to permit detailed comparisons with a proposed new taxon from the upper Elliot Formation, Stormbergia dangershoeki. Similarly, Butler et al (2007) and Butler (2010) discussed L. diagnosticus for the purposes of comparison, this time with the Late Triassic taxon Eocursor parvus. Finally, Knoll, Padian & de Ricql es (2010) compared selected specimens of early ornithischians from the upper Elliot Formation and proposed that Lesothosaurus and Stormbergia were synonymous.…”

The origin and early radiation of dinosaurs

“…The earliest ornithischians, such as Pisanosaurus and Eocursor, were small-bodied, with known specimens reaching just over a meter in body length (Bonaparte, 1976;Butler et al, 2007;Butler, 2010). Distal elements of the hindlimb (tibia, metatarsals) are elongate, suggesting well-developed cursorial abilities.…”

“…Finally, Butler et al (2007) and Butler (2010) described Eocursor from the lower Elliot Formation of South Africa, based upon a relatively complete skeleton of a single individual. Eocursor is the most completely known Triassic ornithischian and was identified as the sister taxon to Genasauria, a clade comprising most post-Triassic ornithischian diversity Butler, 2010).…”