An Unprecedented Fossil Find Shows How Mammals Rose to Rule the Earth

Top: A collection of four mammal skulls collected from Corral Bluffs, Colorado. Bottom: CGI rendering of ancient Taeniolabis mammal taken from the PBS NOVA special, Rise of the Mammals. (Credit: HHMI Tangled Bank Studios)

The asteroid that slammed into our planet 66 million years ago was arguably Earth’s biggest calamity. It wiped out not only the dinosaurs, but three quarters of all types of organisms. Scientists’ understanding of how plants and animals recovered from this annihilation has remained murky, until now.
In a breakthrough discovery, reported in Science, a team of scientists, including Professor Stephen Chester (GC/Brooklyn, Anthropology), found and analyzed a treasure trove of fossils from the first million years following the mass extinction. The thousands of remarkably well preserved plant and animal fossils reveal in unprecedented detail how life recovered from the disaster and how mammals, like us, emerged to rule the planet.
Tyler Lyson, curator of the Denver Museum of Nature & Science and a leading paleontologist, discovered the fossils. Well versed in finding glinting dinosaur fossils from the late Cretaceous period — immediately before the dinosaurs disappeared — he had yet to find complete fossils from the creatures that survived the asteroid impact. Then, inspiration struck. Based on a fossil he found in a museum drawer and some techniques used by colleagues in South Africa, he started hunting in the Denver Basin for egg-shaped rocks called concretions.
The concretions he and his Denver Museum colleague Ian Miller found yielded wonders, including the skulls of mammals from the early generations that survived the extinction. Lyson, who specializes in dinosaurs and turtles, turned to Chester, a paleontologist and longtime collaborator whose specialty is the origin and early evolutionary history of primates and other mammals, to analyze the mammal fossils.

mammal skull fossils
 Prepared mammal skull fossils retrieved from Corral Bluffs, Colorado (Credit: HHMI Tangled Bank Studios)

Chester led a team effort to identify the mammals and document their size and anatomy to understand how they evolved in the first million years after the extinction. His role in the study is documented in a new NOVA production, Rise of the Mammals, and the Denver Museum of Nature & Science just opened an accompanying exhibition on the fossils and the story of their discovery.

 CGI rendering of ancient Loxolophus mammal
CGI rendering of ancient Loxolophus mammal shown in the palm dominated forests found within the first 300,000 years after the dinosaur extinction. Image used in the PBS NOVA special, Rise of the Mammals, (Credit: HHMI Tangled Bank Studios)

CGI rendering of ancient Carsioptychus mammal
CGI rendering of ancient Carsioptychus mammal depicted in a newly diversified forest, ~300,000 years after the mass extinction. Image used for PBS NOVA special, Rise of the Mammals, (Credit: HHMI Tangled Bank Studios) 

“What’s amazing about these fossils from the Denver Basin is that they are extraordinarily complete,” Chester says. “Most extinct mammals from this time period are known only from jaws and teeth. But this discovery shows the skulls of many of these extinct mammals for the first time.”
From the fossilized skulls and teeth, the researchers assessed how large the mammals were and what they ate. As indicated in the paper, mammals increased in size and diversity quickly in those first million years.
Because plants were preserved as well, scientists can see in much clearer detail how plants and animals evolved throughout time and how they are potentially linked to climate changes.
“This study provides a better understanding of how the Earth recovers following a mass extinction event,” Chester says. “It has significant implications given that we are currently facing what many scientists call the sixth mass extinction. And it’s only the beginning. This discovery has produced a lifetime’s worth of fossils to work on, which will continue to provide us with a clearer view of the beginning of the age of mammals.”

Submitted on: OCT 24, 2019

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