First porpoise fossils (Cetacea: Phocoenidae) from the western North Atlantic, South Carolina

Abstract The Pliocene marine mammal fauna is the best sampled and most intensely studied in the world, preserving many modern genera of cetaceans. Today, harbor porpoises ( Phocoena phocoena Linnaeus, 1758) as well as other extant genera of odontocetes ( Tursiops , Stenella , Lagenorhynchus , Physeter , Pseudorca , Globicephala ) inhabit the western North Atlantic. Many similar forms were reported from the early Pliocene Yorktown Formation—except for porpoises (Phocoenidae), which are key members of modern marine ecosystems, but surprisingly absent from the fossil record in this region. Hence, there are unresolved questions concerning the dispersal and biogeography of this group. In this study, we report the first fossil Phocoenidae from the western North Atlantic, a series of four isolated periotics of Phocoena sp. from Pliocene strata near Charleston, South Carolina, USA, and describe the bony labyrinth of one of these. The periotics show several external anatomical characters diagnostic for phocoenids, and we used μCT scanning to reconstruct a three-dimensional model of the bony labyrinth to further test this interpretation. We performed 13 measurements on the model surface and compared those with a sampling of other phocoenid specimens. By assessing the taxonomic affinity of the fossils, we gain a better understanding of marine ecosystems through a dynamic interval of the Neogene and shed light on the origins and dispersal of a major odontocete clade.