Mammal Diversity Explosion Occurred After the Dinosaurs Went Extinct

What caused the explosion of mammals that eventually led to the ecosystem we see today? Scientists have taken a closer look at this event, and have found that the diversity of mammals began in earnest about 10 million years after dinosaurs went extinct.

"When dinosaurs went extinct, a lot of competitors and predators of mammals disappeared, meaning that a great deal of the pressure limiting what mammals could do ecologically was removed," said Anjali Goswami, one of the researchers, in a news release. "They clearly took advantage of that opportunity, as we can see by their rapid increases in body size and ecological diversity. Mammals evolved a greater variety of forms in the first few million years after the dinosaurs went extinct than in the previous 160 million years of mammal evolution under the rule of dinosaurs."

In this latest study, the researchers looked at the early evolution of placental mammals, which is the group including elephants, sloths, cats, dolphins and humans. Placental mammal fossils from this period have been previously overlooked since they were hard to place in the mammal tree of life because they lack many features that help to classify the living groups of placental mammals. Now, researchers have solved that issue by creating a new tree of life for placental mammals, including these early forms.

"The mass extinction that wiped out the dinosaurs 66 million years ago is traditionally acknowledged as the start of the 'Age of Mammals' because several types of mammal appear for the first time immediately afterwards," said Thomas Halliday, first author of the new paper. "Many recent studies suggest that little changed in mammal evolution during the Paleocene but these analyses don't include fossils from that time. When we look at the mammals that were present, we find a burst of evolution into new forms, followed by specialization that finally resulted in the groups of mammals we see today.

The findings reveal a bit more about the evolution of mammals and shows how these creatures first stepped onto our planet.

The findings are published in the journal Biological Journal of the Linnean Society.

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