OnProphocaandLeptophoca(Pinnipedia, Phocidae) from the Miocene of the North Atlantic realm: redescription, phylogenetic affinities and paleobiogeographic implications

Abstract

BackgroundProphocaandLeptophocarepresent the oldest known genera of phocine seals, dating from the latest early to middle Miocene. Originally,Prophoca rousseauiandProphoca proximawere described based on fragmentary remains from the Miocene of Belgium. However, several researchers contested the union ofProphoca rousseauiandProphoca proximainto one genus, without providing evidence. The stratigraphic context ofProphocaremained poorly constrained due to the lack of precise data associated with the original specimens collected in the area of Antwerp (north of Belgium).MethodsProphocaandLeptophocaare redescribed and their phylogenetic position among Phocidae is reassessed using PAUP. Dinoflagellate biostratigraphy has been carried out on sediment samples associated with specimens fromProphocaandLeptophocato elucidate their approximate ages.ResultsWhereas the speciesProphoca rousseauiis redescribed,Prophoca proximais considered synonymous toLeptophoca lenis, with the proposal of a new combinationLeptophoca proxima(Van Beneden, 1877). Sediment samples from specimens of both taxa have been dated to the late Langhian–early Serravallian (middle Miocene). Following a reinvestigation ofLeptophoca amphiatlantica, characters from the original diagnosis are questioned and the specimens ofLeptophoca amphiatlanticaare consideredLeptophocacf.L. proxima. In a phylogenetic analysis,Prophoca rousseauiandLeptophoca proximaconstitute early branching stem-phocines.DiscussionLeptophoca proximafrom the North Sea Basin is younger than the oldest known find ofLeptophoca proximafrom North America, which does not contradict the hypothesis that Phocinae originated along the east coast of North America during the late early Miocene, followed by dispersal to Europe shortly after. Morphological features of the appendicular skeleton indicate thatProphoca rousseauiandLeptophoca proximahave archaic locomotory modes, retaining a more prominent use of the fore flipper for aquatic propulsion than extant Phocidae.