The Pikermian tortoises (Testudines, Testudinidae) from the late Miocene of the South Balkans

This article deals with the fossil tortoises of one of the most iconic fossil localities of the Neogene of the Old World, the upper Miocene locality of Pikermi, near Athens, Greece. We describe the type, previously published, and new material of the fossil tortoises from Pikermi, along with new material from the coeval Azmaka 6 locality in Bulgaria. This combined information results in the complete revision of the 'marble tortoise' Testudo marmorum, which is the first turtle species ever named from Greece. Besides the challenges and difficulties of working with material from the old collections of Pikermi, we present a complete revision of this species and identify its presence outside its type locality in the South Balkan Peninsula. The presence of numerous shells of the 'marble tortoise' allows us to discuss the observed variation and attempt to interpret it as the result of intraspecific variation, ontogenetic changes, or sexual dimorphism. For the first time, we observe the absence of the characteristic hypo-xiphiplastral hinge in female individuals of Testudo marmorum, which in turn challenges the traditional phylogenetic position of this species. We further describe previously published and new material of the giant tortoise Titanochelon from Pikermi. Based on the updated information, we can suggest that the Pikermian giant tortoise probably represents a distinct taxon. Our results signal Pikermi as one of the most important localities to understand the evolution of tortoises in the eastern Mediterranean during the last parts of the Neogene.