Tiny but seemingly fierce, members of a now-extinct group of mammals called dryolestoids scrabbled for existence 100 million years ago in the shadows of dinosaurs. Paleontologists recently unearthed rare skulls and other bones of these creatures in Argentina; in the Nov. 3 Nature, Guillermo Rougier, of the University of Louisville in Kentucky, and colleagues name the new species Cronopio dentiacutus, its name in part a nod to its acutely sharp teeth.
Dryolestoids are most closely related to a modern group of mammals called therians, which includes marsupials such as opossums and placental mammals such as people.
Few mammal fossils have been found in South America from this time period, before the age of dinosaurs gave way to the age of mammals. Scientists hope the discovery will reveal more about whether early mammals evolved differently in North and South America.