Plesiosaurs Had Evolved by the Carnian Triassic

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

Authors:

1. Matteo Fabbri (a)
2. Fabio M. Dalla Vecchia (b)
3. Andrea Cau (c)

Affiliations:

a. Dipartimento di Scienze della Terra , Università degli studi di Firenze , Via La Pira 4, I-50121 , Firenze , Italy

b. Institut Català de Paleontologia ‘Miquel Crusafont’ , C/Escola Industrial 23, E-08201 , Sabadell , Spain

c. Museo Geologico e Paleontologico ‘Giovanni Capellini’

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.