Allaeochelys libyca, a New Carettochelyine Turtle from the Middle Miocene (Langhian) of Libya

Fossil carettochelyine turtles are well known from the Paleogene of Europe (Allaeochelys), North America and Asia (Anosteira); however, the previously known Neogene fossil record is highly fragmentary and was therefore unsuitable for taxonomic analysis. In this work, we present a new carettochelyine taxon, Allaeochelys libyca, from the Middle Miocene (Langhian) of Gebel Zelten (Libya) based on an incomplete skull and disarticulated postcranial elements. The new taxon is diagnosed relative to the extant Carettochelys insculpta based on the placement of the foramen posterius canalis carotici interni close to the fenestra postotica, the horizontal orientation of the tubercula basioccipitalis, the substantial contribution of the opisthotic to the base of the tubercula basioccipitalis, the presence of a triangular pterygoid fossa, the arrangement of the mandibular condyles along a plane and the presence of an extremely well-developed fossa at the base of the processus mandibularis. A phylogenetic analysis of pancarettochelyids confirms the monophyly of Carettochelyidae and Carettochelyinae but resulted in a paraphyletic taxon, Allaeochelys. For the sake of nomenclatural stability, we provisionally retain the genus Allaeochelys as paraphyletic relative to the extant Carettochelys insculpta.