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.
Though fictional in this context, a plausible backstory for might involve fragmentary remains found in South America’s Los Blanquitos Formation or similar late Cretaceous sites. Let us imagine that in 2018, a team of Argentine and Brazilian paleontologists unearthed a partial femur, a fragmented skull with unusual dentition, and several caudal vertebrae. The bones were too large for any known local fauna and displayed a mix of theropod-like and mammalian features. Due to funding shortages, the remains were nicknamed “Zupaytheriumrex” informally until formal description. zupaytheriumrex
Despite its non-official status, the keyword has appeared in blog comments, forum signatures, and speculative evolution wikis. There are three likely reasons: We describe a new genus and species of
– Possibly derived from “Zupay,” a term with unclear roots. It could reference a location (e.g., the Zupay region in Bolivia or a fictional land), a local deity, or be a corruption of Zupaysaurus – a real genus of basal theropod dinosaur from the late Triassic of Argentina. Zupaysaurus means “devil lizard” (from Quechua supay = demon). Thus, “Zupay” likely carries diabolical or powerful connotations. The holotype consists of a partial skull, dentary,