AN ONTOGENETIC INVESTIGATION OF A CRETACEOUS NORTH AMERICAN MAMMAL, DIDELPHODON VORAX (METATHERIA: MARSUPIALIFORMES: STAGODONTIDAE), THROUGH QUANTITATIVE AND DESCRIPTIVE ANALYSIS OF THE DENTARY

Didelphodon vorax is a North American stagodontid metatherian closely related to today’s marsupials and is one of the largest mammals of the Late Cretaceous. Fossil finds for this taxon are rare and geographically constrained to the North American Western Interior, which often impedes comparative, intraspecific studies. A collection of dentary specimens from the Hell Creek, Horseshoe Canyon, and Lance formations, spanning a wide range of developmental stages, allows for the analysis of each specimen within the context of ontogeny. Through quantitative and qualitative measures, including calculations of mandibular bending forces, comparisons to extant marsupials, and general physical descriptions, we interpret the morphological changes through development and associated changes in feeding ecology. Although D. vorax is posited to have been durophagous (i.e., feeding on hard shelled organisms or bone), the resultant mandibular bite force profiles, tooth eruption patterns, and tooth morphology suggest that juvenile forms would not have been well suited for durophagy. Our results inform on a limited body of knowledge pertaining to the developmental patterns of ancestral marsupials and Mesozoic mammals more broadly, as well as provide further insight on the relative success of certain mammalian forms across the Cretaceous-Paleogene boundary.