Colorado Dig Offers Insight on the Rise of Mammals, Post-Extinction Event

Raccoon-size Loxolophus and other mammals evolved surprisingly quickly after the end-Cretaceous extinction. (HHMI Tangled Studios via Science)

(CN) – Most professional and amateur paleontologists had written off the Corral Bluffs in Colorado Springs as a site where everything that could be found had been found. Then vertebrate paleontologist Tyler Lyson had an idea: Instead of looking for bones, he started looking for concretion – minerals known to form around bones.

“I split open a concretion and saw a mammal skull smiling back at me,” Lyson said. “Once you have the right search image, you could see fossils everywhere.”

Suddenly the barren desert looked like a gold mine, offering scientists the clearest picture to date of how life recovered after the last known mass extinction event 66 million years ago.

Research published in Science on Thursday contextualizes thousands of flora and fauna findings with time and temperature in unprecedented detail.

The Cretaceous Period came to a crashing end 66 million years ago when (the prevailing theory argues) an asteroid collided with Earth, killing off the dinosaurs and 75% of the planet’s life. A poor fossil record left what happened between the mass extinction event and the dawn of the mammals over the next millennia largely a mystery.

Until now, researchers only knew that ferns proliferated in the post-disaster world.

“We documented changes in the landscape after the impact, from a world dominated by palms to a world dominated by a more diverse group of trees. And then we saw the animal species change in lockstep fashion. And then we lined that up with changes in the environment, temperature,” said paleobotanist Ian Miller, a curator at the Denver Museum of Nature & Science which sponsored the project.

“It turns out we really were able to paint a picture of the emergence of our modern world,” Miller explained.

(Denver Museum of Nature & Science, adapted by C. Bickel / Science)

Researchers found biodiversity gathered around three warming pulses that occurred during the early Paleocene and hypothesized links between the co-evolution of plants and animals.

“No one scientist could put this story together – it’s impossible,” Lyson noted. “There was a lot of blood, sweat, and tears. We ended up collecting nearly a thousand vertebrate fossils, over 6,000 plant fossils, and our colleagues counted over 37,000 pollen grains as part of this study.”

Over the first 300,000 years of the Paelocene, researchers found the earliest sightings of beans as well as a variety of nuts related to modern-day walnuts – energy-rich food for mammals which were growing larger and increasingly specialized in diet.

In addition to early placental mammals, herbivores and omnivores related to modern hoofed ungulates, the dig also uncovered the first North American sighting of Taeniolabis taoensis, an extinct Paleocene mammal with big front teeth that lived in grass.

From nearly 1,000 fossils, researchers named 16 mammalian taxa and an abundance of vertebrates, as well as some clear ecological niches: baenid turtles lived near channel margins, but chelydroid turtles were concentrated out on the floodplain.

Earlier Lancian mammals grew only as big as about 18 pounds and subsisted off omnivorous sources and insects, whereas the later periptychid mammals could grow larger than 40 pounds and selectively lived off plants.

Researchers noted striking similarity between the recovery of life post-asteroid with how modern environments recover following natural disasters, albeit on a different time scale. While it may take a forest between 10 and 1,000 years to fully recover from a devastating wildfire, researchers estimate healing from a mass extinction event requires 10,000 to 1 million years.

Researchers optimistically concluded “detailed records of post-mass extinction biotic recovery, such as the one presented here, will provide a critical framework for predicting ecosystem recovery following mass extinction events including the one we currently face.”

The Denver Museum of Science and Nature worked with the U.S. Geological Survey’s National Unmanned Aircraft Systems Project.

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