Mammals Ruled Long Before Death of Dinosaurs

Mammals ruled long before death of dinosaurs, researchers say. Previous studies led to the belief that mammals only began to thrive after dinosaurs had died. A new study, however, comes to contradict the theory. It seems that our ancestors were already diversifying before the huge and dangerous creatures went extinct.

The research was conducted by a team of scientists from the Committee on Evolutionary Biology at the University of Chicago, USA, and the Faculty of Engineering and the Environment at the University of Southampton, UK. The paper on the study – named “Therian mammals experience an ecomorphological radiation during the Late Cretaceous and selective extinction at the K–Pg boundary” – was published June 8 in journal Proceedings of the Royal Society B.

"Mammals Ruled Long Before Death of Dinosaurs"

The new study was based on the investigation of fossilized early mammals’ molars. The key finding was that mammals that co-existed with the dinosaurs had widely diverse tooth shapes. This means they had varied diets. The mammals’ diets proved that many of its species went extinct at the same time with the dinosaurs.

Researchers say that mammals ruled long before death of dinosaurs, about 10 to 20 million years before the mass extinction of the creatures. Our ancestors weren’t big in size, no mammals coexisting with dinosaurs were. They were not much bigger than a dog but took advantage of a wide variety of habitats and foods to grow larger bodies.

Now that we know that mammals thrived before the extinction of dinosaurs, scientists wonder what actually changed? It looks like, at the end of the Cretaceous period, flowering plants diversified as well. This provided mammals with enough food sources to live thriving lives. This provides proof that mammals started rising to dominance before the mass extinction of dinosaurs.

Scientists add that dinosaurs began declining around that time. the Cretaceous-Tertiary extinction decimated about three-quarters of the plant and animal species on Earth, not just dinosaurs that could not fly.

Some experts, however, aren’t quick in supporting this new theory. Paleontologist Stephen Brusatte from the University of Edinburgh in Scotland, for example, considers the mass extinction to be the critical moment that allowed mammals to thrive. If not for the dinosaur-killer asteroid, we would’ve had dinosaurs living alongside us today, Brusatte thinks. After the asteroid event, new forms of mammals and primates emerged in the less dangerous world.