New materials of the rare fossil mustelid Cernictis hesperus (Carnivora, Mammalia) from the Pinole Tuff genotype locality in California

The Neogene fossil record of predatory mammals indicates periodic dispersals across the Beringian land bridge. Among the documented immigrant species in the weasel family (Mustelidae), Cernictis hesperus is among the most poorly known genotype species because of the highly fragmentary holotype. Here I report a new specimen representing the species from its type locality in the Pinole Tuff Formation, California. Associated left and right dentaries show that C. hesperus possesses a first premolar, unlike all other known species of the genus. Furthermore, incisor alveoli indicate the presence of a full incisor toothrow that is similarly crowded compared to the cheek teeth. These new morphological characteristics improve the diagnosis of the genus and species for the first time in nearly a century since the initial publication on the taxon.