A Chilean-led research team has identified a new mammal species, Yeutherium pressor, from a 74-million-year-old fossil unearthed in Patagonia’s Rio de las Las Chinas Valley. The specimen—a fragment of lower jaw bearing one complete molar and parts of two others—was recovered about 3,000 kilometres south of Santiago in the Magallanes region. Weighing an estimated 30–40 grams, roughly the size of a modern mouse, Yeutherium pressor is the smallest Cretaceous-era mammal yet documented in South American Patagonia. Tooth morphology suggests the animal either laid eggs, like today’s platypus, or reared young in a pouch, and it probably fed on hard vegetation. The discovery, detailed in the British journal Proceedings of the Royal Society B, was led by paleontologist Hans Puschel of the University of Chile and the Millennium Nucleus research centre. It provides rare evidence of mammalian life on the ancient Gondwana landmass and adds to understanding of how early mammals co-existed with dinosaurs before disappearing at the Cretaceous-Paleogene mass extinction 66 million years ago.