Rise of the Mammals

A remarkable new trove of fossils has been unearthed in Coloradoa discovery that reveals one of the most important but least understood chapters in the history of life. It’s an unprecedented look at the time when the great dinosaurs were replaced by our own group, the mammals, and the world as we know it began. 

The story of the discovery is the subject of a new documentary, NOVA Rise of the Mammals, streaming now.

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When the Cataclysm Struck

Sixty-six million years ago, a meteorite larger than Mount Everest slammed into Earth. This was the single worst day for life on our planet, when 75 percent of species went extinct in a geologic blink of an eye.

Obviously, the planet and living creatures rebounded. Humans are testament to the recovery of life. But how did it happen? For decades, scientists have tried to squeeze every bit of data possible out of the rocks from the first million years after the dinosaur extinction. But, the results of over 100 years of hammering away are just fragments of teeth, an occasional jaw, and an ultra-rare skull once every few decades. As a consequence, we don’t know much about the mammals that survived. Until now.

The Discovery of a Lifetime

The discovery of an extraordinary treasure trove of fossils near Colorado Springs by Drs. Tyler Lyson and Ian Miller from the Denver Museum of Nature & Science reveals in striking detail how life recovered after the catastrophic asteroid impact that wiped out the dinosaurs.

Their new research, published in Science Magazine, paints a vivid portrait of the first million years after the impact.

Read the Publication

The Light Bulb Moment

A monumental breakthrough occurred in 2016 when Lyson and Miller concentrated their efforts in an area called Corral Bluffs. They believed this Denver Basin locale showed promise because a handful of relatively complete vertebrate fossils had been found there over the decades.  

So, they set their eyes to the ground, looking for bits of bone, the way they were trained to find fossils. They came up with only fragments.

However, Lyson was convinced they weren’t keying in on the right material, perhaps not seeing what was right in front of their noses. He recalled his fossil hunting experience with South African colleagues in the deserts of the Karoo, where the key to finding fossils was not searching for bone fragments but for a particular kind of rock called a concretion.

So what if the team searched Corral Bluffs for concretions instead of the usual bone? It was the light bulb moment that changed the game completely.

Science takes a village. Sixteen authors have worked on the initial research publication, with many more contributing to the project in the coming years.

Meet the Team

Cracking the Code

The team went back to the site, but this time they set their eyes on finding concretions. It wasn’t long before Lyson picked up a knobby, whitish-colored rock that looked more like a rotting loaf of bread than anything else. With a single, well-placed crack of his rock hammer, Lyson split open the concretion and saw the cross-section of a complete mammal skull staring back at him. He was completely stunned. After 20 years of combing the badlands of North Dakota for elusive fossils from just after the extinction of the dinosaurs, Lyson was holding the best fossil he’d ever found from this important slice of time. 

Miller and Lyson looked around and saw the same unassuming concretions covering the ravines and gullies. In a frenzy, they gently cracked open concretions at their feet and in no time found four more complete mammal skulls. Paleontologists who study this time period go whole careers without finding one complete mammal skull from this time period; Miller and Lyson found four in just a couple of hours! 

They had cracked the code.

Concretions generally form around an organic nucleus and come in a variety of shapes, sizes, and chemical composition. These rocks also sometimes preserve truly amazing fossils.

The Creatures Unearthed

Lyson and Miller and their excavation team spent about 10,000 hours in the field at Corral Bluffs, working through blazing sun, torrential rain, and even snowstorms. Close to a thousand vertebrate fossils have been unearthed from the site, from the skull that cracked the case—Carsioptychus coarctatus, an early relative of hoofed animals about the size of a pig—to skulls and skeletons of other mammals, turtles, and crocodilians, including many new species. They also found the most complete specimens of many known species from this time period. 

See the Mammals

The Plants

Miller and the team excavated 65 fossil plant localities and collected more than 6,000 leaves. Fossilized leaves reconstruct environments to show how the forests rebounded from the shockwaves, fires, darkness, and cold generated by the asteroid impact. A particularly exciting moment occurred when a Teen Science Scholar interning with Miller cracked open a rock containing the oldest bean pod ever discovered! In the modern world, there are more than 19,000 species of legumes, representing the second most important plant crop for humans after grains. The oldest legume was found right in Colorado by a high school student.

See the Plants