It was just a tooth and a fragment of jaw bone—discovered in an excavation layer of the Chorrillo Formation, a unique geological formation in Patagonia, Argentina. Field researchers found it amongst fossils of both terrestrial and aquatic mollusks, frogs, turtles, and snakes, as well as theropod and sauropod dinosaur fossils. Based on the sediment layer, the tooth dates from the Maastrichtian Stage, a timeframe at the end of the Late Cretaceous ranging from 72.1 million to 66 million years ago.
Click here for original story, Oldest evidence of South American egg-laying mammals found in Patagonia
Source: Phys.org