Abstract
Today, monachine seals display the largest body sizes in pinnipeds. However, the evolution of larger body sizes has been difficult to assess due to the murky taxonomic status of fossil seals, including fossils referred to Callophoca obscura, a species thought to be present on both sides of the North Atlantic during the Neogene. Several studies have recently called into question the taxonomic validity of these fossils, especially those from the USA, as the fragmentary lectotype specimen from Belgium is of dubious diagnostic value. We find that the lectotype isolated humerus of C. obscura is too uninformative; thus, we designate C. obscura as a nomen dubium. More complete cranial and postcranial specimens from the Pliocene Yorktown Formation are described as a new taxon, Sarcodectes magnus. The cranial specimens display adaptations towards an enhanced ability to cut or chew prey that are unique within Phocidae, and estimates indicate S. magnus to be around 2.83 m in length. A parsimony phylogenetic analysis found S. magnus is a crown monachine. An ancestral state estimation of body length indicates that monachines did not have a remarkable size increase until the evolution of the lobodontins and miroungins.
Highlights
The Phocidae subfamily Monachinae displays a high degree of morphological disparity, with species that exhibit adaptations for filter feeding [1,2], durophagy [3], longirostry [4], and both large [5] and small [6] body sizes
With C. obscura being found to be a nomen dubium and restricted to the lectotype, we conclude that the Yorktown Formation material should be described as a new taxon, S. magnus
This taxonomic reassessment enables the reliable inclusion of the large Yorktown Formation monachine into phylogenetic analyses of Phocidae
Summary
The Phocidae subfamily Monachinae (southern true seals) displays a high degree of morphological disparity, with species that exhibit adaptations for filter feeding [1,2], durophagy [3], longirostry [4], and both large [5] and small [6] body sizes. Trends in the evolution of body size within monachines have been difficult to assess in the fossil record. Previous work on the phocid material of the Yorktown Formation (early Pliocene) of North Carolina has referred multiple monachine specimens to this species on the basis of large size [8]. These specimens have dubious association with the fragmentary lectotype (an isolated humerus) from Belgium ([7,8], figure 1), which has little to no overlap in anatomy with these more complete specimens
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