First postcranial remains of the Late Cretaceous gondwanatherian mammal Vintana sertichi

Postcranial remains of gondwanatherian mammals were previously known by only a single specimen, an essentially complete skull and postcranial skeleton constituting the holotype and only known specimen of Adalatherium hui (UA 9001), from the uppermost Cretaceous (Maastrichtian) Anembalemba Member of the Maevarano Formation, Mahajanga Basin, northwestern Madagascar. Here we report the discovery of a caudal vertebra (DMNH EPV.141354) that we provisionally refer to a much larger gondwanatherian, Vintana sertichi, also from the Maevarano Formation. V. sertichi, the largest known mammal from the Mesozoic of Gondwana, was previously represented only by a cranium from the Lac Kinkony Member, which represents a nearshore, peritidal paleoenvironment, but the caudal vertebra was recovered from the underlying Anembalemba Member, which represents an earlier, more fully terrestrial fluvial/floodplain paleoenvironment. The presence of V. sertichi in the latter rock unit therefore expands the age (making it more fully contemporaneous with A. hui) and the known paleoenvironmental range for the species. Comparing various metrics of vertebral body proportions suggests that (1) gondwanatherians are unique among Mesozoic mammals in possessing mid-caudal vertebral centra that are anteroposteriorly short; and (2) the tail of V. sertichi was relatively wider and shorter than that of A. hui.