A delphinid mandible from the Lower Pliocene of Morocco: further fossil evidence of high dietary niche partitioning in true dolphins

We describe a left mandible of Delphinidae (Cetacea, Odontoceti) from the Lower Pliocene of the Asilah Basin, northwestern Morocco. Despite its fragmentary nature, the specimen reveals key morphological features that support affinities with extant Globicephalinae, i.e., a short mandibular symphysis; a reduced alveolar portion; and a posteroalveolar portion characterized, laterally, by a nearly straight dorsal margin and a ventral margin that sharply curves posteroventrally. However, the Asilah mandible differs from all known extant and fossil globicephalines in its unique character combination, and therefore is here referred to Globicephalinae gen. and sp. indet. pending the discovery of more complete materials. The overall morphology of the reconstructed Asilah mandibles implies a feeding strategy intermediate between suction and grasping. Therefore, this fossil seemingly provides further evidence of a Pliocene generalist delphinid lacking specialized features towards either suction or macropredation, which in turn would have evolved independently multiple times across the family. More generally, this record further supports a high disparity within Delphinidae as early as in Pliocene times, which may correlate with high dietary niche partitioning