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

Abstract

Lesothosaurus diagnosticus from the upper Elliot Formation of South Africa and Lesotho (?HettangianSinemurian) is an important early representative of Ornithischia. In previous studies it has been recovered in several positions on the ornithischian tree including as the earliest known member of Thyreophora, the earliest known member of Neornithischia and as a member of an even a more basal ornithischian lineage, one that diverged before these major groups appeared. Given this taxon's important position as one of the few well-known early ornithischians, it is surprising that details of much of its anatomy remain unpublished. A second nonheterodontosaurid ornithischian taxon, also from the upper Elliot Formation, Stormbergia dangershoeki, has also been recovered as the earliest known member of Neornithischia; however, the validity of this taxon has been challenged. Hence, a reassessment of the taxonomic statuses and systematic positions of L. diagnosticus and S. dangershoeki within Ornithischia is required as an important step in the investigation of the early evolution of this group. A comprehensive redescription of the post-cranial material of L. diagnosticus and a re-evaluation of other 'fabrosaur' material (including the hypodigm of S. dangershoeki) was carried out to provide new information on the anatomy of these taxa and to better resolve the relationships at the base of the ornithischian tree. This study has found that the material of L. diagnosticus and S. dangershoeki almost certainly represents the same taxon and that the apparent differences between these genera is probably a product of ontogentic (rather than taxonomic) differences. A revision of the phylogenetic relationships of L. diagnosticus (when synonymized with S. dangershoeki) recovers it as the basal most member of Neornithischia.

A new phylogeny of Stegosauria (Dinosauria, Ornithischia)

“…Pisanosaurus mertii, a taxon generally considered to be the most basal ornithischian (e.g. Butler et al 2008;Boyd 2015;Baron et al 2016) was used Raven, T. J. and Maidment, S. C. R. In press. Palaeontology 5 as the outgroup.…”

“…Laquintasaura venezuelae, although originally described as a basal ornithischian (Barrett et al 2014) has recently been recovered as a basal thyreophoran (Baron et al 2016), so we also included this taxon.…”

“…Full justification for these updates can be found in the Online Supporting Information (OSI). Thirty-one new characters were identified from recent publications describing new specimens (Maidment et al 2015;Baron et al 2016;Maidment et al in review) and personal observations, and added to the character list. The final character list contains 114 characters, of which 24 are continuous.…”

“…C. R. In press. Palaeontology 4 Furthermore, character transitions in the stegosaurian 'stem lineage' are now better understood, thanks to the recognition that the basal ornithischian Lesothosaurus diagnosticus may well be a thyreophoran (Butler et al 2008;Boyd 2015), and the discovery of a probable new basal thyreophoran taxon, Laquintasaura venezuelae (Barrett et al 2014;Baron et al 2016).…”

Digital reconstruction of the mandible of an adultLesothosaurus diagnosticuswith insight into the tooth replacement process and diet

“…On the basis of a comprehensive review of the evidence at hand, Knoll, Padian & Ricqlès, (2010) made a case for recognising Stormbergia dangershoeki as a junior synonym of Lesothosaurus diagnosticus . The synonymy was rejected by Maidment & Barrett (2011), but confirmed by Baron, Norman & Barrett (2017). The main difference between the two species is the apparent lack of an obturator process on the ischium in Lesothosaurus .…”