From the inside: Pathologies from a histological perspective of two elasmosaurids from the Upper Cretaceous of Antarctica and Argentina

Abstract

Histopathology plays a fundamental role in the detailed analysis of various pathologies, as it allows for diagnosing diseases through microscopic examination of the affected tissues. These studies on Mesozoic marine reptiles are scarce, and almost non-existent in plesiosaurs. Here, two elasmosaurid plesiosaur specimens were examined: specimen MLP-PV 93-I-5-1, recovered from the lower Maastrichtian Snow Hill Island Formation (Vega Island, Antarctica), and specimen MML-PV 5, retrieved from the upper Maastrichtian Jagüel Formation (Salinas de Trapalcó, Río Negro). To obtain the histological sections, a fragmented rib was selected from the first specimen; and a transverse process, dorsal rib, and phalanx were chosen from the second. Pathological bone callus was observed on the rib sections of MLP-PV 93-I-5-1. Periosteal growth perpendicular to the long axis of the bone was observed on the transverse process, dorsal rib, and phalanx sections of MML-PV 5. The characteristics observed in specimen MLP-PV 93-I-5-1 are consistent with the diagnosis of a healing fracture. The characteristics observed in specimen MML-PV 5 are indicative of periostitis. Based on the histopathological study of the two elasmosaurid specimens, it was possible to identify abnormal internal variations in bone tissue and determine that both pathologies developed during the life of the elasmosaurids.