The Basicranial Anatomy of the Nimravidae (Mammalia: Carnivora): Character Analyses and Phylogenetic Inferences

Abstract

The phylogenetic relationships of the Nimravidae (Oligocene through latest Miocene catlike carnivorans) are controversial: they have been placed either within the family Felidae, or as sister group to the Felidae, to the modern aeluroid Carnivora, or to the Caniformia. Adoption of cladistic analysis is not sufficient to resolve this controversy: all of the last three hypotheses of relationship have resulted from cladistic analyses. Competing hypotheses of phylogenetic relationship are here demonstrated to be primarily the result of disagreement about the identification and distribution of characters. Such disagreements reflect the need for a rigorous method of character analysis to enable explicit testing of character identifications and distributions–i.e. homologies–prior to a cladistic analysis. (In cladistic analysis, characters can be tested only weakly, by inclusion in a cladogram; refutation produces only ad hoc hypotheses, difficult to test). I present a method of character analysis that enables stronger tests of hypotheses of homology by using toplogical and developmental relationships, prior to simple cladistic analysis, and by using a parsimony criterion to choose among competing hypotheses of character identifications and distributions. Results are compared with examples of persistent errors arising from the uncritical, blind use of homological morphotypes (producing unquestioned identifications, never subsequently tested) and ancestral morphotypes (producing untested polarities). Several problems and inadequacies of cladistic analysis as presently formulated are described, most important of which is the method\u27s inability to distinguish between a true or correct multichotomy and an unresolved multichotomy . Detailed analysis of the basicranial anatomy of the Nimravidae demonstrates the value of the method of character analysis formulated here. These odd carnivorans are shown to have lacked any medial branch of the internal carotid artery or a fully ossified bulla, and to have possessed instead a lateral branch of the internal carotid (a promontory artery ), a peculiar, thick, partially ossified entotympanic, and a separate posterior petrobasilar foramen. Many aelurcid synapomorphies exclude the Nimravidae from that group, no synapomorphies place them as sister group to the aeluroids, evidence for any caniform relationship is sparse and contradictory, while overall parsimony places the Nimravidae as sister group to the rest of the Carnivora