Postcranial anatomy of Pissarrachampsa sera (Crocodyliformes, Baurusuchidae) from the Late Cretaceous of Brazil: insights on lifestyle and phylogenetic significance.

Pedro L Godoy,Estevan Eltink,Giovanne M Cidade,Júlio C De A Marsola,Mario Bronzati,Felipe C Montefeltro,Max C Langer

doi:10.7717/peerj.2075

Abstract

The postcranial anatomy of Crocodyliformes has historically been neglected, as most descriptions are based solely on skulls. Yet, the significance of the postcranium in crocodyliforms evolution is reflected in the great lifestyle diversity exhibited by the group, with members ranging from terrestrial animals to semi-aquatic and fully marine forms. Recently, studies have emphasized the importance of the postcranium. Following this trend, here we present a detailed description of the postcranial elements of Pissarrachampsa sera (Mesoeucrocodylia, Baurusuchidae), from the Adamantina Formation (Bauru Group, Late Cretaceous of Brazil). The preserved elements include dorsal vertebrae, partial forelimb, pelvic girdle, and hindlimbs. Comparisons with the postcranial anatomy of baurusuchids and other crocodyliforms, together with body-size and mass estimates, lead to a better understanding of the paleobiology of Pissarrachampsa sera, including its terrestrial lifestyle and its role as a top predator. Furthermore, the complete absence of osteoderms in P. sera, a condition previously known only in marine crocodyliforms, suggests osteoderms very likely played a minor role in locomotion of baurusuchids, unlike other groups of terrestrial crocodyliforms. Finally, a phylogenetic analysis including the newly recognized postcranial features was carried out, and exploratory analyses were performed to investigate the influence of both cranial and postcranial characters in the phylogeny of Crocodyliformes. Our results suggest that crocodyliform relationships are mainly determined by cranial characters. However, this seems to be a consequence of the great number of missing entries in the data set with only postcranial characters and not of the lack of potential (or synapomorphies) for this kind of data to reflect the evolutionary history of Crocodyliformes.

Highlights

Baurusuchids are important components of the Late Cretaceous crocodyliform faunas (Montefeltro, Larsson & Langer, 2011; Godoy et al, 2014)
Comparisons to more complete baurusuchids such as the 1.9 m long specimen referred to Baurusuchus salgadoensis, the 1.3 m long holotype of Baurusuchus albertoi, and the 1.1 m long holotype of Aplestosuchus sordidus (Nascimento, 2008; Vasconcellos & Carvalho, 2010; Godoy et al, 2014) suggest that it is unlikely that any of these specimens reached the maximum length estimated for Pissarrachampsa sera (3.49 m) using the regressions
The study of the postcranial skeleton of Pissarrachampsa sera allowed the recognition of some exclusive features of this taxon in the context of Baurusuchidae, such as the short and sharp crest at the craniolateral margin of the distal tibial expansion, the raised and proximodistally elongated iliofibularis trochanter of the fibula, and the more proximally placed contact between the fibular distal hook and the tibia

Summary

Introduction

Baurusuchids are important components of the Late Cretaceous crocodyliform faunas (Montefeltro, Larsson & Langer, 2011; Godoy et al, 2014). As typical for descriptive works on crocodyliforms (e.g., Wu, Sues & Sun, 1995; Buckley et al, 2000; Gasparini, Pol & Spalletti, 2006; Novas et al, 2009; O’Connor et al, 2010; Iori & Carvalho, 2011) the original description of Pissarrachampsa sera as exclusively based on its skull morphology. This practice does not seem to be related to the nature of the findings itself, as fossil crocodyliforms are typically found with associated postcranium, as in the case of P. sera. Later expeditions to the type locality, between 2008 and 2010, recovered additional material referred to P. sera, including the postcranial elements described here

Methods

Results

Conclusion