The Early Cretaceous mammalGobiconodon(Mammalia, Triconodonta) from the Cloverly Formation in Montana

Abstract

Gobiconodon ostromi, sp. nov., described from two partial skeletons collected from the Cloverly Formation in southcentral Montana, is closely related to Gobiconodon borissiaki Trofimov (1978) from the Early Cretaceous of Mongolia. The unusual dental characters of this new form are enlarged caniniform incisors, reduced canines, and replacement of the molariform teeth that lie distal to the presumptive premolars. Despite the fact that the molariform occlusal pattern is the same as in Amphilestes of the Middle Jurassic and the overall structure of the molariform teeth is comparable to that in amphilestid triconodonts, the dentition is otherwise so anomalous that Gobiconodon is assigned to a new family. The scapula possesses a supraspinous fossa and an apparently large coracoid. The humerus exhibits large deltopectoral and medial crests, and protuberant epicondyles; the planes of the proximal and distal halves of this bone are substantially offset. The pelvis conforms to a generalized mammalian pattern. A deep fossa of unknown function occurs on the dorsal surface of the lesser trochanter; the greater trochanter extends distally well down onto the shaft. A spur-like bone appears to represent an extratarsal element. In overall body size, Gobiconodon ostromi, sp. nov., is comparable to Didelphis virginiana but in its limb and vertebral proportions is more robust.