Postcranial axial skeleton of Simosuchus clarki (Crocodyliformes: Notosuchia) from the Late Cretaceous of Madagascar

Abstract

ABSTRACT Simosuchus clarkiBuckley, Brochu, Krause, and Pol, 2000, a small, pug-nosed notosuchian crocodyliform from the Late Cretaceous of Madagascar, was described a decade ago in a preliminary report based on a single specimen that included the skull, lower jaw, and anterior portions of the postcranial skeleton; details of the preserved cervical and anterior dorsal vertebrae and ribs were not described. With the subsequent collection of several additional specimens, which collectively also preserve the posterior dorsal, sacral, and caudal regions of the vertebral column, the postcranial axial skeleton of S. clarki is now one of the most completely known of any basal mesoeucrocodylian. This report includes a detailed description of the vertebral and costal morphology of this bizarre notosuchian and an assessment of its functional and phylogenetic significance. Simosuchus had eight cervical, at least 15 dorsal, two sacral, and probably fewer than 20 caudal vertebrae. Most aspects of the vertebral morphology of Simosuchus are consistent with those generally observed within Crocodylomorpha, or more specifically within Crocodyliformes. However, the low number of caudal vertebrae indicates that the tail of Simosuchus was remarkably short, shorter than in any other known crocodylomorph. This short tail is interpreted to have had little to no functional utility in aquatic propulsion. Assessment of the hypothesis that Simosuchus and some other basal mesoeucrocodylians were fossorial on the basis of cervical morphology requires a more extensive comparative and functional analysis. The postcranial axial skeleton currently contributes little to the assessment of the phylogenetic position of Simosuchus.