Revision of the Extinct Pseudoceratinae (Artiodactyla: Ruminantia: Gelocidae)

Abstract

The Pseudoceratinae is a North American clade of small, hornless ruminant artiodactyls known from the late middle Miocene to the earliest Pliocene. Two genera and three species are recognized: Pseudoceras skinneri Frick 1937 (including P. potteri Frick 1937 and P. wilsoni Frick 1937 as junior synonyms); Floridameryx floridanus new genus and species; and Floridameryx klausi (Frick 1937), new combination. Originally regarded as small, aberrant members of the Camelidae, cranial (especially basicranial), dental, and postcranial characters clearly place the Pseudoceratinae instead within the artiodactyl suborder Ruminantia, and more precisely within the extinct family Gelocidae. Among the derived ruminant (pecoran) character states exhibited by the pseudoceratines, the following are most notable: broad postglenoid process; fully developed odontoid process of axis; lack of upper incisors; forelimb length nearly equal to that of hindlimb; third and fourth metacarpals and metatarsals fully fused into cannon bones with well developed distal keels; metatarsal with deep, distally bridged anterior groove; fused cuboid and navicular; and parallel-sided astragalus. Floridameryx differs from Pseudoceras by having a wider skull with weaker parietal and sagittal crests, reduced premolars, higher crowned molars, and shorter metatarsals.

The Withlacoochee River 4A locality in north-central Florida produces the largest population sample of pseudoceratines, with a minimum of 26 individuals represented, and is the only known site to have a pseudoceratine as the most common ungulate. About half of the mandibles bear small, procumbent, incisiform canines, as is typical in advanced ruminants, while the other half have large, upright canines which occluded with the upper canines. This is interpreted as sexual dimorphism, with the former morphology presumably representing females and the latter males. The abundance of pseudoceratinates in the Withlacoochee 4A fauna, seen in its paleoecological context, is attributed to a preference for very mesic, densely forested environments.