Morphological and size diversity of extinct and living Chelus

Abstract

Testudines is a clade composed of two sister lineages, Cryptodira and Pleurodira, with living and fossil representatives, and which differ mainly by how the neck is retracted into the shell: vertically and laterally, respectively. Fossil Testudines are quite com-mon throughout the South American Cenozoic since most fossils are represented by elements of the carapace and plastron, which are structures that are easily preserved due to the morphology of the shell of composition resistance that makes it difficult to disarticulate during the taphonomic processes. Currently, the genus Chelus is formed by four species, two living, Chelus fimbriatus and Chelus orinocensis, and two fossils, Chelus colombianus and Chelus lewisi. Still, there are many discussions about the morphological characteristics that define these four species, with some authors de-fending that morphological variations are just intraspecific differences. Body size is a feature of great paleontological importance in understanding the paleoenvironment and its relationship with the size variations found in fossils. It is sometimes a diagnos-tic feature for different species, as in cases of gigantism. For this BEPE project, the applicant aims to perform a detailed description of extant Chelus species and create an anatomical atlas. It is also expected to analyze which intraspecific variations occur in living species based on the qualitative analysis of specimens deposited in scientific collections. Moreover, this research also will estimate the body size of fossil speci-mens, applying linear regression models. It is expected to describe the largest speci-men ever described for the genus. (AU)