Interpreting character variation in turtles: Araripemys barretoi (Pleurodira: Pelomedusoides) from the Araripe Basin, Early Cretaceous of Northeastern Brazil.

Saulo Limaverde,Gustavo R Oliveira,Niels Bonde,Rafael Damasceno,Maria E.C Leal,Chiara Villa,Rodrigo Vargas Pêgas

doi:10.7717/peerj.9840

Abstract

The Araripe Basin (Northeastern Brazil) has yielded a rich Cretaceous fossil fauna of both vertebrates and invertebrates found mainly in the Crato and Romualdo Formations, of Aptian and Albian ages respectively. Among the vertebrates, the turtles were found to be quite diverse, with several specimens retrieved and five valid species described to this date for the Romualdo Formation. There were also records of turtles from Ipubi and Crato Formations, mainly fragmentary material which precluded proper specific identification; however, Araripemys barretoi is supposed to occur on both Crato and Romualdo Formations. Here we describe thirteen specimens of A. barretoi-including the first description of an almost complete individual, bearing a skull, from the Crato Formation. We report a great amount of morphological variation, interpreted as being essentially of intraspecific nature, including individual, sexual and ontogenetic variation.

Highlights

The Testudines are remarkable reptiles that possess a bony shell alongside other unique morphological characters, such as a shoulder girdle enclosed by the ribcage
We offer here a revised diagnosis for Araripemys barretoi and provide interpretations for the nature of the reported variations
We have presented above a plethora of morphological variation within specimens of Araripemys

Summary

Introduction

The Testudines are remarkable reptiles that possess a bony shell alongside other unique morphological characters, such as a shoulder girdle enclosed by the ribcage. The Testudines are nowadays split in two monophyletics groups: Pleurodire (side-necked) and Cryptodire (hiddennecked) turtles (Gaffney, 1975; Joyce et al 2004). Pleurodires show less species diversity than cryptodires and, currently, are restricted only to fresh water habitats in the southern hemisphere (e.g. Gaffney et al 2006; Romano & Azevedo, 2006; Sereno & ElShafie, 2013). The diversity of species and habitats, and the geographic range of pleurodires were considerably larger in the past and seem to have reached its peak between the beginning of the. The pleurodire crown-group potentially appears for the first time in the fossil record at the Early Cretaceous (Valanginian) with the remains of the potentially oldest podocnemidoid turtle: a left costal and a peripheral bone from the Rosablanca

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