On the cranial osteology of the short-tailed opossum Monodelphis brevicaudata (Didelphidae, Marsupialia)

Abstract

The Section of Mammals, Carnegie Museum of Natural History houses 54 partial and complete skulls of the short-tailed opossum Monodelphis. Described in detail and illustrated are the external surfaces of the bones of the skull for M. brevicaudata CM 52729 and the external and internal surfaces of one bone of the basicranium, the petrosal, for Monodelphis sp. CM 5024. The disposition of cranial foramina ranging in size from the foramen magnum to tiny emissary and nutrient foramina was studied in all 54 specimens, which in addition to 16 M. brevicaudata, includes four M. dimidiata, 29 M. domestica, two M. osgoodi, and three Monodelphis sp. Three categories of foramina were identified: (1) foramina bilaterally present in all specimens that show no significant variation; (2) bilateral and midline foramina present in ail specimens that show variation in size, number, position, distinctness from other foramina, or elements contributing to their walls; and (3) foramina that are not present in ail specimens that also vary in size, number, and position. Comparisons were made with four outgroups, the didelphid Didelpkis albiventris, the dasyurid Dasyurus maculatus, the early Paleocene metatherian Pucadelphys andinus, and the Late Cretaceous eutherian Zalambdalestes lechei, in order to evaluate the foramina of Monodelphis in a phylogenetic context. Of the foramina considered here, four distinguish Monodelphis; three distinguish Didelphidae; 15 distinguish Marsupialia; nine distinguish Metatheria; and seven occur across Theria.