Abstract
BackgroundDiscovered on the southern margin of the North Sea Basin, “Phoca” vitulinoides represents one of the best-known extinct species of Phocidae. However, little attention has been given to the species ever since its original 19th century description. Newly discovered material, including the most complete specimen of fossil Phocidae from the North Sea Basin, prompted the redescription of the species. Also, the type material of “Phoca” vitulinoides is lost.Methods“Phoca” vitulinoides is redescribed. Its phylogenetic position among Phocinae is assessed through phylogenetic analysis. Dinoflagellate cyst biostratigraphy is used to determine and reassess the geological age of the species. Myological descriptions of extant taxa are used to infer muscle attachments, and basic comparative anatomy of the gross morphology and biomechanics are applied to reconstruct locomotion.ResultsDetailed redescription of “Phoca” vitulinoides indicates relatively little affinities with the genus Phoca, but rather asks for the establishment of a new genus: Nanophoca gen. nov. Hence, “Phoca” vitulinoides is recombined into Nanophoca vitulinoides. This reassignment is confirmed by the phylogenetic analysis, grouping the genus Nanophoca and other extinct phocine taxa as stem phocines. Biostratigraphy and lithostratigraphy expand the known stratigraphic range of N. vitulinoides from the late Langhian to the late Serravallian. The osteological anatomy of N. vitulinoides indicates a relatively strong development of muscles used for fore flipper propulsion and increased flexibility for the hind flipper.DiscussionThe extended stratigraphic range of N. vitulinoides into the middle Miocene confirms relatively early diversification of Phocinae in the North Atlantic. Morphological features on the fore- and hindlimb of the species point toward an increased use of the fore flipper and greater flexibility of the hind flipper as compared to extant Phocinae, clearly indicating less derived locomotor strategies in this Miocene phocine species. Estimations of the overall body size indicate that N. vitulinoides is much smaller than Pusa, the smallest extant genus of Phocinae (and Phocidae), and than most extinct phocines.
Highlights
The fossil record of Phocidae Gray, 1821 (Mammalia, Carnivora) is poorly known and largely consists of isolated and fragmentary material (Ray, 1976; Koretsky, 2001)
The specimens of “Ph.” Vitulinoides from the Van Beneden collection (1871, 1876, 1877) were collected by the military during the 1860s fortification works around the city of Antwerp (Van Beneden, 1877)
Our phylogenetic analysis suggests (1) that all included extinct Phocinae, Devinophoca, K. benegasorum, L. proxima, N. vitulinoides, and Praepusa vindobonensis, are stem Phocinae, and (2) that N. vitulinoides is the sister taxon to crown Phocinae. This points toward a strong early diversification of stem Phocinae prior to the evolution of the crown group
Summary
The fossil record of Phocidae Gray, 1821 (Mammalia, Carnivora) is poorly known and largely consists of isolated and fragmentary material (Ray, 1976; Koretsky, 2001). The family Phocidae is subdivided in two extant subfamilies: Monachinae Gray, 1869 and Phocinae Gray, 1821; and one extinct subfamily: Devinophocinae Koretsky & Holec, 2002. Despite the co-occurrence of both subfamilies in the Northern Hemisphere during the Neogene (Koretsky & Ray, 2008), they are currently biogeographically separated: Monachinae include the Antarctic seals, the subtropical monk seals (Monachus spp.), and the elephant seals (Mirounga spp.) along the eastern North Pacific and subantarctic waters, while Phocinae are restricted to the Northern temperate and Arctic coasts. Discovered on the southern margin of the North Sea Basin, “Phoca” vitulinoides represents one of the best-known extinct species of Phocidae. Morphological features on the fore- and hindlimb of the species point toward an increased use of the fore flipper and greater flexibility of the hind flipper as compared to extant Phocinae, clearly indicating less derived locomotor strategies
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