SPECIES OR SEXES? TAXONOMY AND DIMORPHISM IN PALAEOGALE

The carnivoran Palaeogale is as paleobiologically important as it is enigmatic. Its importance derives from its convergence on a mustelid body plan (having originally been assigned to that family despite its feliform affinity) and its Holarctic distribution (first appearing in the late Eocene of Montana and dispersing to Central Asia and Europe prior to its extinction in the early Miocene). Palaeogale remains enigmatic in part due to a history of taxonomic uncertainty. Many species are differentiated based on size, and this has long prompted suggestions that large and small coeval Palaeogale “species” may actually represent a single, sexually dimorphic species. We tested this hypothesis by using published first lower molar lengths as a proxy for body size in two pairs of contemporaneous Palaeogale species: P. minuta and P. dorothiae from the Arikareean North American Land Mammal Age (late Oligocene-early Miocene) and P. minuta and P. praehyaenoides from the Agenian European Land Mammal Age (early Miocene). Both European species have been recovered from Amöneburg, Germany, allowing a site-specific size comparison for these taxa. Size differences between these putative species were compared to those between males and females within extant species of small carnivorans based on museum records of mass. The smaller Palaeogale species (P. minuta in both cases) is between 71%-82% the size of the larger species (P. dorothiae or P. praehyaenoides). Several species of mustelid, mephitid, and procyonid have comparable body mass ratios between males and females, all of which are sexually dimorphic. This calls the validity of P. dorothiae and P. praehyaenoides into question, as size is one of the primary traits used to distinguish these species from P. minuta. It is important to note that the sample size for each of these species is small (n=14) and will be augmented considerably by the inclusion of unpublished specimens. A more detailed review of Palaeogale phylogenetics and systematics that includes such traditionally overlooked components of the skeleton as the skull and upper dentition is necessary for a clearer picture of diversity within Palaeogale and for building a strong foundation for the study of this biogeographically and evolutionarily significant carnivore.