A new species of a bony spur-thighed tortoise from the Early Pliocene (MN15) of Jradzor site, Armenia, and the origin of the Testudo graeca (Testudines, Testudinidae) complex

Abstract

The origin of the Testudo graeca complex has been suggested to be in the Caucasus. Poor fossil records and incomplete preservation of available fossils limit deep-time reconstructions of the paleobiogeographic history of the complex. The present work describes recently discovered tortoise species found from the Early Pliocene Jradzor site, Armenia. Apart from being one of the few well-preserved and complete species of the genus in the fossil record, the Jradzor species is the only well-dated (∼4.16 and 3.98 Ma) form among fossil representatives of the genus. The tortoise material is numerous and comprises several complete and partial shells, including some rare cranial elements and numerous postcranial bones, including the presence of bony thigh spurs. The material clearly belongs to a testudinid taxon, based on the alternating neural plates, the coincidence between the costal/peripheral sutures and the pleural/marginal sulci, the presence of a well-developed epiplastral lip, and the complete fusion of the trochanters of the femur, reaching an average carapace length of 30 cm. Furthermore, the presence of a clear hypo-xiphiplastral hinge on the plastron indicates that the Jradzor tortoise is a member of the true Testudo (or sensu stricto) lineage. Our morphological and phylogenetic analysis placed the Jradzor tortoise within the context of the Eurasian Testudinini, showing that the recovered material should be described as a new species, that is phylogenetically placed as a sister group to the extant Testudo graeca complex. The new material allows an evaluation of the validity of previously known and relevant taxa and their inclusion in a new phylogenetic analysis like Testudo eldarica and Testudo kuchurganica, excluding Testudo burtsсhaki that should be considered as a nomen dubium. The new material presented herein sheds light on the origin and early evolution of the modern Mediterranean tortoises.