Blair W. McPhee

A new basal sauropod from the pre-Toarcian Jurassic of South Africa: evidence of niche-partitioning at the sauropodomorph-sauropod boundary?

The early evolution of sauropod dinosaurs remains poorly understood, with a paucity of unequivocal sauropod taxa known from the first twenty million years of the Jurassic. Recently, the Early Jurassic of South Africa has yielded an assemblage of dental and post-cranial remains displaying a more apomorphic character suite than any other similarly aged sauropodomorph. These remains are interpreted as a new species of basal sauropod and recovered cladistically as the sister taxon to Vulcanodon +more derived Sauropoda, underscoring its importance for our understanding of this pivotal period of sauropod evolution. Key changes in the dentition, axial skeleton and forelimb of this new species suggest a genuine functional distinction occurring at the sauropodiform-sauropod boundary. With reference to these changes, we propose a scenario in which interdependent refinements of the locomotory and feeding apparatus occurred in tandem with, or were effected by, restrictions in the amount of vertical forage initially available to the earliest sauropods. The hypothesized instance of niche-partitioning between basal sauropodan taxa and higher-browsing non-sauropodan sauropodomorphs may partially explain the rarity of true sauropods in the basal rocks of the Jurassic, while having the added corollary of couching the origins of Sauropoda in terms of an ecologically delimited ‘event’.

A Second Species of Eucnemesaurus Van Hoepen, 1920 (Dinosauria, Sauropodomorpha): New Information on the Diversity and Evolution of the Sauropodomorph Fauna of South Africa's Lower Elliot Formation (Latest Triassic)

ABSTRACT The Late Triassic—Early Jurassic Elliot Formation of South Africa is one of the most important geological formations worldwide for understanding the early evolution of sauropodomorph dinosaurs. However, many of the taxa currently recognized as valid within its lower strata remain either poorly understood, vaguely diagnosed, or both. The recent discovery of an articulated partial skeleton of a single individual of the enigmatic lower Elliot genus Eucnemesaurus provides an important opportunity to expand our understanding of the anatomy and phylogeny of this poorly known taxon. A comprehensive investigation of the morphological relationships of this new specimen identified key features, pertaining primarily to the femoral shaft and distal tibia, which distinguish it from the only other previously named species of Eucnemesaurus—E. fortis. A new species, E. entaxonis, is erected within which to accommodate it. A cladistic analysis confirms the monophyly of Eucnemesaurus, as well as its continued inclusion within the low-diversity ‘Riojasauridae.’ Nonetheless, this result highlights continued uncertainties regarding the constituency of the Riojasaurus hypodigm. The relatively robust pedal architecture of E. entaxonis suggests an unexpectedly early experiment in a slower, subgraviportal form of locomotion within Late Triassic basal Massopoda, whereas the intriguing mosaic of plesiomorphic and derived characters evident in E. entaxonis raises questions regarding the hypothesized population dynamics of the basal-most sauropodomorph taxa of the lower Elliot Formation. This latter concern has particular bearing on newly observed inconsistencies in the prevailing hypodigms of other lower Elliot basal sauropodomorph taxa such as Melanorosaurus.

Advances in Nonmarine Karoo Biostratigraphy: Significance for Understanding Basin Development

The nonmarine Permo-Jurassic deposits of the Karoo Supergroup of South Africa have long been a world standard for tetrapod biostratigraphy. Recent and ongoing research is revising the palaeoflora and palaeofauna of these sedimentary strata with an unprecedented level of stratigraphic precision. This work has shown that: Permian palynomorphs are useful for correlating time-equivalent lithostratigraphic units in different sectors of the basin; that there is a marked end-Guadalupian diversity drop in tetrapods; that the Dicynodon Assemblage Zone can be subdivided, and should be renamed as the Daptocephalus Assemblage Zone; that the Cynognathus Assemblage Zone has a robust threefold subdivision; and that the name Euskelosaurus for the Euskelosaurus Range Zone is invalid and should be replaced. This work, together with new radiometric dates from the Karoo Supergroup, has dramatically enhanced our understanding of the timing of major evolutionary events in terrestrial ecosystems and provides strong evidence for tectonic controls on accommodation and sedimentation in the Karoo Basin during the Permo-Jurassic, within an overall flexural basinal setting.

A revision of Sanpasaurus yaoi Young, 1944 from the Early Jurassic of China, and its relevance to the early evolution of Sauropoda (Dinosauria)

The Early Jurassic of China has long been recognized for its diverse array of sauropodomorph dinosaurs. However, the contribution of this record to our understanding of early sauropod evolution is complicated by a dearth of information on important transitional taxa. We present a revision of the poorly known taxon Sanpasaurus yaoi Young, 1944 from the late Early Jurassic Ziliujing Formation of Sichuan Province, southwest China. Initially described as the remains of an ornithopod ornithischian, we demonstrate that the material catalogued as IVPP V156 is unambiguously referable to Sauropoda. Although represented by multiple individuals of equivocal association, Sanpasaurus is nonetheless diagnosable with respect to an autapomorphic feature of the holotypic dorsal vertebral series. Additional material thought to be collected from the type locality is tentatively referred to Sanpasaurus. If correctly attributed, a second autapomorphy is present in a referred humerus. The presence of a dorsoventrally compressed pedal ungual in Sanpasaurus is of particular interest, with taxa possessing this typically ‘vulcanodontid’ character exhibiting a much broader geographic distribution than previously thought. Furthermore, the association of this trait with other features of Sanpasaurus that are broadly characteristic of basal eusauropods underscores the mosaic nature of the early sauropod–eusauropod transition. Our revision of Sanpasaurus has palaeobiogeographic implications for Early Jurassic sauropods, with evidence that the group maintained a cosmopolitan Pangaean distribution.