Mammal Diversity Exploded Only After Dinosaurs Went Extinct

Early mammals only began diversifying after the extinction of dinosaurs about 66 million years ago, a new study finds.

AsianScientist (Jul. 8, 2016) – An Australian study shows that humans’ early mammal relatives were likely to have diversified 66 million years ago—after the extinction of dinosaurs opened up space for animals such as big cats, horses, elephants and eventually apes to evolve.

Queensland University of Technology (QUT) evolutionary biologist Matthew Phillips used molecular dating from DNA sequences to challenge the dominant scientific theory that placental mammals diversified 20 million years before dinosaurs became extinct.

In a paper published in Systematic Biology, Phillips said biases in models of DNA evolution inflated estimates of when modern mammals, which were once no larger than a guinea pig, diversified and evolved into the animals familiar to us today.

“We can infer that some placental mammals did co-exist with dinosaurs,” Phillips said. “But for 20 years or so the current dominant theory has suggested that their diversification happened more than 80 million years ago, well before dinosaurs became extinct.

“It now appears that the major diversification of placental mammals closely followed the extinction of dinosaurs 66 million years ago, an event that would have opened up ecological space for mammals to evolve into.”

In the present study, Phillips showed that the fossils of known age used to calibrate the rate of DNA evolution in different lineages were causing distorted dating estimates. According to Phillips, the calibrations were based on poorly resolved fossil placements or from within groups of very large or long-lived mammals such as whales.

“When I took the remaining set of calibrations, the major diversification of placental mammals coincided with the extinction of dinosaurs,” Phillips explained.

Fossil records have long proven that the ancestors of many modern placental mammal groups can be traced back to the period right after the dinosaur extinction, noted Phillips.

“Many scientists focused on DNA sequencing have brushed aside aspects of the fossil data, but when you minimize the potential biases in molecular dating, you instead get a story that matches the fossil evidence.”

The article can be found at: Phillips (2016) Geomolecular Dating and the Origin of Placental Mammals.


Source: Queensland University of Technology; Photo: Pixabay.
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