Paleontologists have described a trove of hyaenodont fossils from the early Miocene Santa Cruz Formation in southern Patagonia, Argentina—including a brand-new species that was among the largest carnivorous mammals ever to stalk South America.

Published May 29, 2026, in Journal of Mammalian Evolution, the study details partial skulls, jaws, and postcranial elements recovered from coastal outcrops near Río Gallegos. The star specimen belongs to Patagonohyaena gigantea (“giant Patagonian hyaenodont”), estimated at 150–200 kg—roughly the size of a modern lion—with mᴀssive, shearing carnᴀssial teeth and a powerfully built skull suited for bone-crushing.

Radiometric dating of ᴀssociated volcanic ash places the fossils at ~18 million years ago, during the “Age of the Southern Plains” when Patagonia hosted diverse ungulates, giant birds, and early marsupial carnivores. P. gigantea coexisted with smaller sparᴀssodonts but occupied a distinct hypercarnivorous niche, its robust denтιтion indicating it could tackle prey larger than itself.

Lead author Dr. Laura Chornogubsky (Museo Argentino de Ciencias Naturales) explains: “These are the first definitive hyaenodont remains from Miocene South America. They show that true creodonts crossed into the continent via a temporary North American land bridge and thrived before being outcompeted by placental carnivorans.” The new species’ unique premolar morphology sets it apart from African and Eurasian relatives, suggesting rapid local adaptation.

The discovery challenges the long-held view that hyaenodonts were absent south of the equator after the Eocene. Instead, they briefly dominated as apex predators in lush, riverine landscapes before the Great American Biotic Interchange. As additional material is prepared, Patagonohyaena promises to reshape our understanding of Cenozoic predator guilds across the Americas. A forgotten giant returns from the windswept badlands of Patagonia.