A radiation of arboreal basal eutherian mammals beginning in the Late Cretaceous of India

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Abstract
India's Late Cretaceous fossil mammals include the only undisputed pre-Tertiary Gondwanan eutherians, such asDeccanolestes. Recent studies have suggested a relationship betweenDeccanolestesand African and European Paleocene adapisoriculids, which have been variably identified as stem euarchontans, stem primates, lipotyphlan insectivores, or afrosoricids. Support for a close relationship betweenDeccanolestesand any of these placental mammal clades would be unique in representing a confirmed Mesozoic record of a placental mammal. However, some paleogeographic reconstructions place India at its peak isolation from all other continents during the latest Cretaceous, complicating reconstructions of the biogeographic history of the placental radiation. Recent fieldwork in India has recovered dozens of better-preserved specimens of Cretaceous eutherians, including several new species. Here, we incorporate these new specimens into an extensive phylogenetic analysis that includes every clade with a previously hypothesized relationship toDeccanolestes. Our results support a robust relationship betweenDeccanolestesand Paleocene adapisoriculids, but do not support a close affinity between these taxa and any placental clade, demonstrating thatDeccanolestesis not a Cretaceous placental mammal and reinforcing the sizeable gap between molecular and fossil divergence time estimates for the placental mammal radiation. Instead, our expanded data push Adapisoriculidae, includingDeccanolestes, into a much more basal position than in earlier analyses, strengthening hypotheses that scansoriality and arboreality were prevalent early in eutherian evolution. This comprehensive phylogeny indicates that faunal exchange occurred between India, Africa, and Europe in the Late Cretaceous-Early Paleocene, and suggests a previously unrecognized ∼30 to 45 Myr “ghost lineage” for these Gondwanan eutherians.