Gondwanatheria and ?Multituberculata (Mammalia) from the Late Cretaceous of Madagascar

Abstract

In addition to four isolated mammalian teeth from the Late Cretaceous (Maastrichtian) of Madagascar described previously and allocated to Gondwanatheria, Marsupialia, and Mammalia incertae sedis, here I put on record five more specimens. Four of these, a virtually complete lower molariform cheek tooth, two fragmentary cheek teeth, and a fragmentary lower incisor, are referred to the Sudamericidae (Gondwanatheria). The internal structure of the hypsodont cheek teeth, as revealed by micro-computed tomography scans to simulate different stages of wear, is highly variable. Limited knowledge of intra-individual morphological and size variability in the dentition of sudamericids, which are known almost exclusively from isolated teeth, precludes a conclusive assessment of whether some or all of the new specimens belong to Lavanify miolaka, the only previously described sudamericid from Madagascar, or to a new taxon. Conservatively, therefore, pending the recovery of better material, all four specimens are referred to Sudamericidae gen. et sp. indet. The fifth specimen, a molar fragment, is tentatively allocated to the Multituberculata, thereby adding to the controversial specimens that comprise the very sparse and questionable record of this clade on the southern supercontinent Gondwana. The new specimens do not provide any profound insight into the origins of the highly endemic and imbalanced extant mammalian fauna on Madagascar; rather, they provide only more negative evidence. Like those previously described, they do not represent the basal stocks of any of the five mammalian clades that live on the island today and therefore further support the growing consensus that representatives of the extant clades arrived in the Cenozoic.