New data from the first discovered paleoparadoxiid (Desmostylia) specimen shed light into the morphological variation of the genus Neoparadoxia

Abstract

Desmostylia is an extinct clade of marine mammals with two major sub-clades, Desmostylidae and Paleoparadoxiidae, known from Oligocene to Miocene strata of the North Pacific coastline. Within Paleoparadoxiidae, three genera have been identified: Archaeoparadoxia, Paleoparadoxia, and Neoparadoxia. The latter taxon is the geochronologically youngest palaeoparadoxiid and characterized by a comparatively larger body size, although it is known only from a few specimens within a short temporal and geographic range. Here we report the discovery of an isolated tooth identified as Neoparadoxia cf. N. cecilialina, constituting only the second individual specimen of Neoparadoxia with preserved dentition yet reported. This specimen was collected near Corona, California, USA, and we attribute it to the “Topanga” Formation, becoming the first record of Neoparadoxia from this unit. While the exact geographic locality was not properly recorded for this specimen when it was collected in 1913, we establish two potential localities based on the associated hand-written museum label and new stratigraphic information. Although this specimen wasinitially identified as Desmostylus hesperus, it was collected 10 years before the first named paleoparadoxiid from Japan. This new occurrence data adds to interpretations of marine mammal assemblages, especially in Southern California where paleoparadoxiids co-occur with desmostylids and sirenians.