NEW MATERIAL OF THE STEM SEAL ALLODESMUS FROM THE TOPANGA FORMATION OF ORANGE COUNTY

Pinnipeds, the group of marine mammals that include seals, sea lions, and walruses, has a fossil record that begins in the Oligocene. The major extant lineages of pinnipeds first appear in the middle Miocene. Orange County boasts an undescribed diversity of fossil pinnipeds, the oldest of which are from the early-middle Miocene Topanga Formation. This unit has produced important new fossils of stem walruses (reported in 2013) and the recently described Eotaria crypta, the oldest known stem sea lion (described in 2015). Here we report on stem seal (stem phocid) material from the Topanga Formation, which we refer to the taxon Allodesmus. Allodesmus is the best-known fossil pinniped, and six species have been described from middle Miocene sites in California and Japan, with additional reports from Washington and Baja California. However, some of these species may not be valid, but instead may be based on individual variation and ontogenetic differences; the clade is in need of revision. The Topanga Allodesmus is interesting because in addition to having the smallest adult size, it is probably the oldest material referable to this genus. We compare the new Orange County material to other species of Allodesmus, especially the material from the nearly contemporaneous Sharktooth Hill