Variability of the Dermal Elements of the Pectoral Girdle in Platyoposaurus (Temnospondyli, Archegosauridae) from the Middle Permian of Eastern Europe

Abstract

The variability of the dermal elements of the pectoral girdle (clavicle, interclavicle), as the most morphologically informative part of the postcranial skeleton in the archegosaurid amphibian Platyoposaurus from the Middle Permian of Eastern Europe, was studied. Based on the considered morphological characters of the clavicle and interclavicle in P. watsoni , the increasing complexity of ornamentation of the dermal elements (a growth of the cellular area in the ossification center as additional cells appear, more complex branching of the radial grooves) with size was established for the first time using the morphometric parameters. The age-related ornament transformation favored the acquisition of additional strength with an increase in the load on the shoulder girdle during the growth process and in the body weight. It was found that the structural characters of the cellular area and radial ridges and also the morphometric parameters (lateral inclination angle of the dorsal process, the ratio of the width of the interclavicle plate to its length from the posterior end to the ossification center) can serve as additional diagnostic features to distinguish both Platyoposaurus from others archegosauroids and between the species of the genus under consideration. Individual differences were detected mainly in the analysis of the structure of the dorsal process of the same-sized clavicles: the lamina posterior is straightened or arcuate; the lamina anterior is straight or arcuate.