Patagomaia is an extinct mammal of uncertain affinities, originally described as a therian mammal, from the Maastrichtian Chorrillo Formation of Argentina. It is the largest Mesozoic mammal yet known, with weight estimates of around 14kg (31lb).[1] The type species is P. chainko.
Patagomaia chainko is known from the distal end of the left ulna, two fragments of the preacetabular wing of the left ilium, acetabular region of the left hemipelvis, fragment of the ischial blade, proximal end of the right femur; distal end of the left femur, proximal end of the left tibia, and other indeterminate bone fragments. It is estimated to weigh over 14kg (31lb), narrowly beating the previous Mesozoic mammal contender, Repenomamus giganticus.[2]
Patagomaia chainko is tentatively described as a therian mammal. However, it does not match any early Cenozoic South American therian group. Püschel et al. (2024) subsequently argued that Patagomaia might be a large gondwanatherian, possibly synonymous with Magallanodon,[3] but Chimento, Agnolín & Novas (2024) did not consider their arguments to be conclusive.[4]
Patagomaia chainko was found alongside the monotreme Patagorhynchus, the meridiolestidan Orretherium, the gondwanathere Magallanodon and several dinosaurs.
Alongside Malagasy gondwanatheres like Adalatherium and Vintana and South American mesungulatid meridiolestidans, Patagomaia chainko provides evidence that Late Cretaceous Gondwanan mammal faunas tended to achieve larger sizes than their northern counterparts.[1]