PHYLOGENY OF XENOSMILUS HODSONAE

The rare Pleistocene saber-toothed cat Xenosmilus hodsonae is known primarily from two partial skeletons discovered in Irvingtonian deposits from Florida. While hypotheses have been made about the relationships of this taxon since its description in 1999, there has been no published phylogenetic analysis to assess its systematic relationships. The osteology of Xenosmilus clearly places it in the subfamily Machairodontinae along with the other saber-toothed felids, but Xenosmilus is unusual in showing a mosaic of characters that prevent it from being easily classified with either the “dirk toothed” Smilodontini (short limbs, robust body form), or the “scimitar toothed” Homotherini (coarsely serrated, robust, and elongated upper canines). This presentation describes a phylogenetic analysis of this felid and several of its probable relatives from the subfamily Machairodontinae. Data for Xenosmilus comes primarily from my examination of the paratype at the Florida Museum of Natural History. I used fifty characters from the skull, dentition, and postcranial skeleton in an attempt to get a clear view of its relationships. Once these characters were coded, several variations of exhaustive maximum parsimony analyses were used to examine the phylogeny of this felid. Many different possibilities of outgroup, taxa, and character variations were attempted to assess their effect on the phylogeny as well. The result of these analyses is that Xenosmilus hodsonae belongs to the tribe Homotherini. In the single most parsimonious tree, Xenosmilus was within the Machairodontinae, excluded from the monophyletic tribe Smilodontini, and most closely related to the taxon Homotherium serum.