New information on Bobosaurus forojuliensis (Reptilia: Sauropterygia): implications for plesiosaurian evolution

Abstract

Preparation of the holotype specimen of Bobosaurus forojuliensis, a large sauropterygian from the lower Carnian of northeastern Italy, revealed new morphological data relevant in establishing its phylogenetic affinities among pistosauroid taxa and its relationships with plesiosaurians. Inclusion of B. forojuliensis in two phylogenetic analyses focusing, respectively, on sauropterygians and pistosauroids agreed in placing the Italian taxon as closer to plesiosaurians than to other pistosauroids. The phylogenetic interpretation of Bobosaurus was not biased by assumptions on character weighting, is consistent with its relatively younger age compared to most pistosauroids, extends the fossil record of the plesiosaurian basal lineage back to the Carnian and supports the earliest diversification of the clade during the Late Triassic in agreement with the record of several distinct lineages of rhomaleosaurids, plesiosauroids and pliosauroids in the lowermost Jurassic. Bobosaurus shows that the evolution of the plesiosaurian body plan from the ancestral pistosauroid grade was a step-wise process, and that some of the vertebral and appendicular specialisations of Jurassic and Cretaceous plesiosaurians had already developed in the earliest Late Triassic.

Keywords::

• Sauropterygia
• Pistosauroidea
• Plesiosauria
• Bobosaurus forojuliensis
• Upper Triassic
• Italy

Acknowledgements

This study has been the object of the Triennal thesis by the first author (University of Florence, years 2010–2011). We thank G. Muscio (Museo Friulano di Storia Naturale of Udine) for the permission to study the specimen, T. Scheyer (University of Zurich) and N. Klein (University of Bonn), who kindly provided the copy of the data matrix of Neenan et al. (2013) and Roberto Rigo for the collaboration. We thank N. Klein and an anonymous reviewer for the comments and suggestions that improved the quality of the manuscript. Marco Auditore is thanked for the skeletal reconstruction in Figure 1. The programme TNT is being made available with the sponsorship of the Willi Hennig Society.