Taxonomy, phylogeny and sexual dimorphism of allodesmus spp. (Pinnipedia: Desmatophocidae) from the middle miocene Altamira Shale and Round Mountain Silt Formation

Abstract

A new pinniped from the family Desmatophocidae is described from the Middle Altamira Shale (14.9-13.1 Ma) of the Monterey Formation of California. The specimen was added to a osteological character state matrix of 25 ingroup taxa and 1000 replicates using the tree-bisection-reconnection algorithm. In our most parsimonious tree, the specimen was recovered as a new species of the genus Allodesmus, being sister taxon of the clade comprising Al. kernensis, Al. demerei and Al. uraiporensis. Allodesmus sp. nov. was collected from the same formation as a second species of the family, Atopotarus courseni, which indicates that both species where living at the same time and place during the Miocene of California. A Principal Component Analysis (PCA) was carried individually for Allodesmus kernensis skulls (including the specimen described), mandibles, astragali and calcanei. Except for the skulls, all data sets (mandibles, astragali and calcanei) show similar patterns where adult males are clustered separately from adult females and juveniles. In general, the PCA is interpreted as sexually dimorphic species with adult males of the genus Allodesmus kernensis larger in size than adult females.