Mammalsâ€™ Rise Began Before Dinosaursâ€™ Fall
It was long believed that mammals began to diversify and flourish only after dinosaurs died out in the mass extinction at the end of the Cretaceous period, about 66 million years ago. But a new study in the journal Nature suggests that some mammals diversified well before that.
Using 3-D imaging and CT scanning, he and his colleagues studied the teeth of multituberculates, a group of rodentlike mammals that lived from 165 million years ago to about 35 million years ago. Some of the teeth were tiny: as small as four-hundredths of an inch across. The researchers found that over time, the mammalsâ€™ teeth evolved to have more patches, or bumps. From that, the researchers inferred that the multituberculates diversified at least 20 million years before dinosaurs disappeared.