Cosmopolitanism among Gondwanan Late Cretaceous mammals

Consistent with geophysical evidence for the breaking up of Pangaea, it has been hypothesized that Cretaceous vertebrates on progressively isolated landmasses exhibit generally increasing levels of provincialism1,2,3, with distinctly heightened endemism occurring at the beginning of the Late Cretaceous4. The Cretaceous fossil record from the southern supercontinent of Gondwana has been much too poor to test this hypothesis with regards to mammals (Fig. 1 ). Early Cretaceous mammals are known only from isolated sites in Argentina5, Australia6,7, Cameroon8,9 and Morocco10. Apart from several occurrences in South America11, knowledge of Late Cretaceous Gondwanan mammals is limited to a single site in India that previously yielded a few specimens of placental mammals12,13, and a site in Madagascar that previously yielded only one indeterminate tooth fragment14. Here we report the occurrence of a highly specialized and distinctive group of extinct mammals, the Sudamericidae (Gondwanatheria), in the Late Cretaceous of Madagascar and India. These new records comprise the first evidence of gondwanatheres outside South America and the first indication of cosmopolitanism among Late Cretaceous Gondwanan mammals. Antarctica may have served as an important Cretaceous biogeographic link between South America and Indo-Madagascar. Figure 1 Maps showing distribution of Gondwanan landmasses and known mammal localities in the Early (top) and Late Cretaceous (bottom). Shaded areas indicate the distribution of subaerially exposed land (adapted from ref. 26); dots indicate mammal localities; stars indicate mammal localities that have yielded gondwanatheres. Madagascar (M), with the Indian subcontinent (I) attached to its current eastern margin, separated from Africa ∼165 Myr ago and attained its current position relative to the mainland ∼124 Myr (refs 23, 25, 29, 30). Strike-slip motion between the Indian subcontinent and Madagascar began ∼135 Myr (ref. 25), as India rifted from Antarctica, but they remained in proximity until ∼88 Myr (ref. 22), several million years before deposition of the Maevarano Formation18. Indo-Madagascar (I-M) and eastern Antarctica were connected until at least ∼120 Myr (ref. 25), and possibly as late as 80 Myr (ref. 26), across the Kerguelen Plateau (KP). The Antarctic Peninsula remained very close to, or maintained contact with, South America in the Late Cretaceous and into the early Tertiary23,24,26.