New early Oligocene water frog (Anura: Ranidae: Pelophylax) occurrence from southeastern France

The widespread frog family Ranidae first appears in the European fossil record during the early Oligocene. Here we describe MAB19654, a near-complete and articulated male ranid frog skeleton from the early Oligocene Marnes du Bois d’Asson of southeastern France. The assignment of Ranidae is based on the presence of elongate posterior apophyses, cylindrical sacral apophyses and non-imbricated vertebrae. The assignment of Pelophylax is based on the robust humerus bearing a low crista medialis that does not reach midshaft. Additionally, we take measurements of limb bone ratios and sacral angulation of various extant osteological and fossil Pelophylax specimens for comparisons, and document morphological variation in the apophysis of V4. Our sample includes 58 P. ridibundus, 59 P. lessonae, 89 P. perezi, and one fossil P. aquensis , supplemented with the literature. We find that MAB19654 most closely resembles P. ridibundus in terms of limb bone proportions and sacral angulation. The tarsus reduces relative to the femur in P. perezi , while P. lessonae evolves a more elongate femur and narrower sacral angulation with respect to MAB19654. Interestingly, we find simple parallel V4 apophyses in ridibundus + lessonae , while complex shapes, as in MAB19654, are prevalent in the early-branching P. perezi . This suggests V4 morphology was complex in early Pelophylax and tentatively proves useful for species determination.