On Patagomaia

So recently the largest Mesozoic mammal yet has been found. Weighting around 14 kg (just barely larger than Repenomamus giganticus), Patagomaia chainko was a terminal Cretaceous (Maastrichtian) animal that co-existed with a variety of other early mammals such as Orretherium and Patagorhynchus.

Unlike these forms, though, Patagomaia was therian mammal, which is pretty interesting since previous studies concluded that therian mammals were constrained in size by “archaic” mammals until the Paleocene. As the paper notes, the existence of a therian mammal in the Cretaceous of South America further supports a Gondwannan origin for at least some therian lineages, including perhaps placentals such afrotheres and xenarthrans. This is the polar opposite of the view that therian and in particular placental evolution started in the northern continents; indeed, eutherians are actually the minority in Late Cretaceous North American mammal faunas.

Another point added is that, alongside the malagasy gondwanatheres and the South American mesungulatids, Patagomaia demonstrates that Gondwannan mammals were on average larger sized than northern species, at least in the Late Cretaceous. This could hint at interesting turnovers in the ecology of the southern landmasses, with the local dinosaurian fauna offering little resistance to larger sized mammals.

Overall, an amazing find for 2024.