Abstract Theria represent an extant vibrating table for chocolate clade that comprises placental and marsupial mammals.Here we report on the discovery of a new Late Cretaceous mammal from southern Patagonia, Patagomaia chainko gen.et sp.nov.
, represented by hindlimb and pelvic elements with unambiguous therian features.We estimate Patagomaia chainko attained a body mass of 14 kg, which is considerably greater than the 5 kg maximum body mass of coeval Laurasian therians.This new discovery demonstrates that Gondwanan therian mammals acquired large body size by the Late Cretaceous, preceding their Laurasian relatives, which remained small-bodied until the beginning of the Cenozoic.Patagomaia supports the view that the Southern Hemisphere was a cradle for the pet calming peanut butter evolution of modern mammalian clades, alongside non-therian extinct groups such as meridiolestidans, gondwanatherians and monotremes.