The First Near-Complete Skull of a Late Cretaceous Multituberculate From North America: Testing Hypotheses of Relationship and Vicariance

Duke University, Durham NC

Investigators

Abstract

The first near-complete skull of a Late Cretaceous multituberculate to be found in North America will be described in detail. This is a skull of Meniscoessus robustus, discovered in the Maastrichtian Hell Creek Formation of South Dakota. The specimen preserves finely detailed external structures of the basicranium, ear region, nasal region, and palate. Internal features of the braincase and skull cavities will also be visible, without destructive analysis, through the use of high-resolution X-ray computed tomography (CT scanning). In addition, the site that yielded this skull produced partial skull and mandibular fragments of several individuals of the same species. Study and description of these more fragmentary specimens will make possible the assessment of intraspecies ariation. Because the mammalian skull is a rich source of morphological data useful in phylogenetic analysis, this material will allow evaluation of the hypothesis that Late Cretaceous Asian multituberculates belong to an endemic clade, an hypothesis that was not fully testable while no contemporaneous North American skulls were known. Although North America and Asia were joined by a land bridge for at least part of the Late Cretaceous, and there was faunal exchange among dinosaurs, there may have been barriers to mammalian dispersal, leading to the development of phylogenetically distinct mammalian faunas. The new material will provide a wealth of data useful in determining the relationships among North American multituberculates. Meniscoessus robustus has been hypothesized to be closely related to the Paleocene Catopsalis and Taeniolabis; now that a skull of Meniscoessus is available to be compared to those of Taeniolabis, we can discover whether this is indeed a single lineage that survived the Cretaceous-Tertiary extinction, or whether it is an instance of extinction followed by immigration of a similar form. This will contribute to an improved and more reliable classification of mammals.