Analysis of the sexual variability in the shell of the Spanish upper cretaceous turtle dortoka vasconica(pan-pleurodira, dortokidae)

Abstract

The present study characterizes the morphological variability related to the sexual dimorphism in the shells of the Spanish Upper Cretaceous turtle Dortoka vasconica. This study is based on the material from its type locality: Laño, Burgos. Two morphotypes were identified there based on the posterior plastral area as well as two for the anterior plastral lobe. However, a correlation with the previously indicated morphotypes could not be established due to the disarticulation of the specimens and the limited information available on the sexual dimorphism of Pleurodira. The morphological variability previously identified for Dortoka vasconica is analysed here through a quantitative approach to evaluate the role that sexual dimorphism plays in the plastron. Comparative material of the main extinct and extant groups of pleurodires is included in this study. The results evidenced a noticeable sexual dimorphism in the anal notch of Dortoka vasconica. Likewise, the comparison of species belonging to several pleurodiran clades shows a wide range of variability in the direction and magnitude of the sexual dimorphism. Thus, a single evolutionary trend cannot be recognized, so that previous assumptions about which morphotype corresponds to each sexual dimorph in some extinct taxa and especially lineages (including basal pan-pleurodires) cannot be confirmed.