Zupaytheriumrex File

We describe a new genus and species of large-bodied eutriconodontan mammal, Zupaytherium rex gen. et sp. nov., from the Late Cretaceous (Campanian–Maastrichtian) Allen Formation of Río Negro Province, Argentina. The holotype consists of a partial skull, dentary, and associated postcranial remains (MPCN-PV-9876). Zupaytherium is characterized by robust, sectorial cheek teeth with three main cusps in a straight line, a deep masseteric fossa, and an estimated body mass of 45–60 kg, making it one of the largest Mesozoic mammals known from South America. Phylogenetic analysis places it within the eutriconodontan family Gobiconodontidae. The discovery extends the temporal and geographic range of large predatory mammals into the uppermost Cretaceous of Gondwana and suggests that mammals competed directly with small theropod dinosaurs for apex mesopredator roles.

Large gobiconodontid with dentary length >12 cm; lower molars with three subequal cusps separated by deep notches; m1 trigonid length 8.2 mm; enamel with vertical ridges; femur with a distinct fourth trochanter.

The dentary is robust, with a deep masseteric fossa extending below m2. The lower molars are highly sectorial, with cusp a (protoconid) slightly taller than cusp b (paraconid) and cusp c (metaconid). Wear facets indicate carnivorous function with a vertical shearing motion. Estimated femoral length suggests a body mass of ~52 kg using allometric equations for extant carnivorans. zupaytheriumrex

Mesozoic mammals have traditionally been viewed as small, nocturnal insectivores. Recent discoveries from Laurasia ( Repenomamus , Gobiconodon ) have challenged this paradigm, revealing carnivorous mammals exceeding 10 kg. However, no large-bodied Mesozoic mammals have been described from South America. Here we report Zupaytherium rex , a new predator from the latest Cretaceous of Patagonia.

Mammalia Linnaeus, 1758 Eutriconodonta Kermack, Mussett & Rigney, 1973 Gobiconodontidae Chow & Rich, 1984 Zupaytherium gen. nov. We describe a new genus and species of

MPCN-PV-9876, an associated partial skeleton including a right dentary with m1–m3, a fragmentary maxilla with M2–M4, axis vertebra, and partial right femur.

From Zupay (Mapudungun: "demon" or "evil spirit") + therium (Greek: "beast"). Species epithet rex (Latin: "king"). The holotype consists of a partial skull, dentary,

Cerro Cóndor Norte, Río Negro Province, Argentina; Allen Formation (Campanian–Maastrichtian, ~75–68 Ma).