Abstract

“Carpodaptes” jepseni is a morphologic intermediate between Carpodaptes and Carpolestes, with the number and position of cusps on p4 more consistent with placement in Carpodaptes but relative size of p4 more like Carpolestes. The type and only previously known specimen of “C.” jepseni, a partial dentary with p4–m2, is from Divide Quarry (Tiffanian Land-Mammal Age) in the Fort Union Formation of the Bighorn Basin, Wyoming. New specimens of “C.” jepseni from Divide Quarry include a nearly complete dentary with p4–m3 and alveoli for all anterior teeth, and the first known upper dentitions with P1–M2 and an alveolus for C1. Specimens of Carpodaptes cygneus are also described from Divide Quarry, demonstrating the occurrence of two distinct carpolestid species at the same locality. Stratocladistic analysis of the thirteen known carpolestid species, using thirty-two morphologic characters and stratigraphic order, produced eight most-parsimonious phylogenetic trees associated with a single cladogram. The topology of the cladogram generated using stratocladistics is identical to that of the single most-parsimonious cladogram from cladistic analysis of the same morphologic data, but stratocladistics allows greater resolution than cladistics at the level of phylogenetic trees. New specimens demonstrate extreme shortening of the anterior jaw of C. jepseni, a derived state not present in other carpolestids. This suggests that C. jepseni occupies a side-branch close to, but not at, the ancestry of the Carpolestes clade (an ancestor-descendant lineage composed of the sequence C. dubius, C. nigridens, and C. simpsoni, in that order). “C.” jepseni is here placed in a new genus, Carpomegodon.