A new immigrant mustelid (Carnivora, Mammalia) from themiddle Miocene Temblor Formation of central California

摘要

A new mustelid genus from the Barstovian (middle Miocene) marine Temblor Formation in California is described.The material of Legionarictis fortidens includes an incomplete cranium with partial upper dentition. The straight lingualborder and slightly expanded posterointernal cingulum of M1 are plesiomorphic traits, as in the European Dehmictis.However, the M1 is not as posteriorly expanded, and the P4 does not have a lingual hypoconal crest, differentiatingL. fortidens from younger North American forms. Furthermore, the P4 protocone is posteriorly placed from the para-style crest, as in the extant South American Eira. An autapomorphic feature of L. fortidens is its highly hypertrophiedP4 paracone with a bulbous crown. The robust upper carnassial, very strong development of the sagittal crest, andderived enamel microstructure all suggest a hard food component in its diet. The coastal depositional environmentindicated by the presence of marine taxa in the Temblor Formation suggests that hard shelled invertebrates might havebeen a food source of L. fortidens. A combination of plesiomorphic and derived dental characteristics puts the newform at an evolutionary stage basal to otters and closer to the living Eira. Cladistic analysis of craniodental characterssuggests that L. fortidens is more derived than generalized basal mustelines of the Old World, and may have divergedfrom the lutrine lineage in a separate immigration event to the New World.