Wednesday, July 1, 2015

[Paleontology • 2015] Sefapanosaurus zastronensis • A New Basal Sauropodiform from South Africa and the Phylogenetic Relationships of Basal Sauropodomorphs

Sefapanosaurus zastronensis
Otero, Krupandan, Pol, Chinsamy & Choiniere, 2015  doi: 10.1111/zoj.12247

We present a new medium-sized basal sauropodomorph, Sefapanosaurus zastronensis gen. et sp. nov., from the Upper Triassic−Lower Jurassic Elliot Formation of South Africa. It is represented by parts of the postcranial skeleton of at least four individuals, including: cervical, dorsal, sacral and caudal vertebrae, most of the forelimb, and part of the hindlimb. Sefapanosaurus bears several autapomorphies of the astragalus, and referred material also shows autapomorphic features. The inclusion of Sefapanosaurus in a phylogenetic analysis places it within the group of sauropodomorphs more closely related to sauropods than to Massospondylus (i.e. Sauropodiformes), increasing the currently known diversity of the so-called ‘transitional forms’ leading to Sauropoda. Character optimization revealed the presence of several features that are common for taxa placed within the transitional branches basal to Sauropoda. Sefapanosaurus, together with other transitional sauropodomorphs reported during the last decade, highlights the importance of Gondwanan taxa for understanding the palaeobiodiversity, global distribution, and macroevolutionary changes in the group related to the rise of sauropods.  

Keywords: Anchisauria; Elliot Formation; Gondwana; Sauropoda − Sauropodiformes

Systematic palaeontology
Dinosauria Owen, 1842
Saurischia Seeley, 1887

Sauropodomorpha Huene, 1932
Massopoda Yates, 2007

Anchisauria Galton & Upchurch, 2004
Sauropodiformes Sereno, 2007

Sefapanosaurus zastronensis gen. et sp. nov.

Holotype: BP/1/386, incomplete articulated left pes including astragalus, calcaneum, a putative distal tarsal IV, proximal portions of metatarsals III and IV, and almost complete metatarsal V.

Etymology: From the Sesotho language sefapano, meaning ‘cross’, and from the Greek saurus, meaning ‘lizard’, in reference to the cross T-shaped ascending process of the astragalus. The specific name makes reference to Zastron, the type locality.

Figure 19. Simplified reduced consensus tree showing the calibrated phylogeny of basal sauropodomorphs close to Sauropoda with their respective distributions on the continents where they were found.
Abbreviation: Pliensbach., Pliensbachian. || doi: 10.1111/zoj.12247

Sefapanosaurus zastronensis increases our knowledge on the diversity of basal sauropodiforms (sauropod outgroups) in the Triassic−Jurassic of Gondwana. It displays a set of characters in the ulna, manus, fibula, and ankle that identifies it as a distinct taxon within Sauropodomorpha, corroborating its taxonomic separation from Aardonyx, contrary to previous hypotheses/assumptions (McPhee et al., 2014).

The new taxon also adds significant anatomical and phylogenetic information about the transition of basal sauropodomorphs to Sauropoda, especially with regard to characters of the manus and the pes. The identification of Sefapanosaurus as a taxon closely related to Sauropoda, together with other taxa discussed here, highlights the importance of Gondwanan taxa for understanding the evolutionary origin of sauropods.

Alejandro Otero, Emil Krupandan, Diego Pol, Anusuya Chinsamy and Jonah Choiniere. 2015. A New Basal Sauropodiform from South Africa and the Phylogenetic Relationships of Basal Sauropodomorphs.
Zoological Journal of the Linnean Society. 174(3), 589–634. doi: 10.1111/zoj.12247