FIRST COMPARATIVE PALEOHISTOLOGICAL STUDY OF SHELL BONES OF EOCENE ANTARCTIC TURTLES

Abstract

The Antarctic fossil record of reptiles is crucial to reconstructing the paleogeographic and paleoclimatic history of Southern Gondwana and the Austral Seas. However, this record is relatively scarce and, in several cases, extremely incomplete. Among turtles, only postcranial fragments are known, mainly consisting of isolated and generally poorly preserved shell bones. The Antarctic fossil record of turtles is restricted to the Late Cretaceous and Paleogene. Paleogene specimens are usually the most incomplete and consist of fragments of shell bones recovered mainly in the Seymour/Marambio Island identified as indeterminate Dermochelyidae, Chelonioidea, and Testudines. Although many of these fossils have been studied, a review is needed, including macro and micro morphological descriptions of the new unpublished materials. This work aims to present the first detailed comparative osteohistological and microanatomical study of shell bones from Eocene Antarctic turtles. For this, we included new materials from the La Meseta Formation (Mid-Late Eocene) and Submeseta Formation (Late Eocene) recovered at Seymour/Marambio Island, as well as living turtle taxa. The results show that the paleohistological variation of turtles recorded in the Mid-Late Eocene in Antarctica is greater than the macromorphological variation registered. However, given the nature of the material, we cannot be sure whether this variation responds to taxonomic, individual (e.g., ontogenetic) or interelemental variation.