Dinosaur Poop Holds a 66-Million-Year-Old Secret About Bird Survival

An Unlikely Fossil From the Most Unlikely Place

About 66 million years ago, a dinosaur — maybe a T. rex or a Nanotyrannus — ate a bird. The record of that meal, in the form of fossilized poop, has survived to today, preserving the best example of a feather ever found from the age of dinosaurs. It is, by any measure, one of the most improbable scientific discoveries in recent memory — and it may help crack open one of paleontology's most enduring mysteries.

Unearthed in Montana, the feathery find belonged to a bird that had once been devoured and excreted by a predatory dinosaur — possibly a Tyrannosaurus rex or a smaller cousin — just before the asteroid strike that unleashed the extinction event 66 million years ago, according to a new study published in the journal *Current Biology*. The specimen was discovered in 2016 by David DeMar Jr., a research scientist and the Hell Creek Project collections manager at the University of Washington Burke Museum and co-author of the paper, while conducting fieldwork in northeastern Montana when an unusual rock caught his attention.

What the Poop Actually Contains

The coprolite contained multiple feathers, tiny fish scales from a gar, and leg bones from a hesperornithiform bird. Since the bones and feathers were found together, it stands to reason that the feathers came from that bird. After analyzing its mineral composition, specialists scanned it using computed tomography, which made it possible to see the fossil's internal structure without destroying it.

Hesperornithiforms were aquatic birds, ecologically similar to loons. Most couldn't fly, and instead used their specialized feet to dive down into the water to hunt for things like fish. Their feathers showed adaptations for being underwater that we see in living aquatic birds. Two of the feathers, including the one exposed at the surface of the coprolite, have features found only in those of living birds and their immediate ancestors — including a square feather shaft with a sponge-like center. No other Mesozoic feather has this combination of features.

The Feather Clue That Could Explain Everything

In the aftermath of Earth's collision with an asteroid 66 million years ago, nearly all the dinosaurs, including nearly all the birds, went extinct. But one group of birds, Neornithes, survived, and every living bird today is one of their descendants. One of the biggest mysteries in paleontology is why this one small group of birds survived when all the other birds and all the other dinosaurs died out.

Some paleontologists had hypothesized that the birds that survived did so because they lived near water, and something about this habitat helped buffer them from the effects of the mass extinction. But the hesperornithiforms also lived by water — and they went extinct. That complication pushes researchers toward a different explanation. According to lead researcher Jingmai O'Connor, "The hesperornithiforms retain primitive feather types that may not have been as efficient for insulation as modern plumaceous feathers, and that could explain why they went extinct along with the enantiornithines."

After the asteroid impact, dust and debris in the atmosphere reduced the amount of sunlight and contributed to cooling described as an "impact winter." If the primitive plumage of hesperornithiforms and enantiornithine birds provided weaker thermal insulation than the feathers of Neornithes, this could have affected their ability to survive such conditions. In other words, the warmth provided by better feathers may have been the difference between life and extinction.

A New Window Into Ancient Ecosystems

This study took O'Connor into unusual territory: feathers preserved inside fossilized feces, known as coprolites. "As far as I know, no one has ever thought to look for feathers or to study feathers in coprolites, so this project was really exciting," she says. The feathers found in the coprolite are the first hesperornithiform feathers ever found, and their features seem to represent a middle ground between the feathers of enantiornithines and modern birds.

To confirm the hypothesis, paleontologists would need to find a Neornithes fossil from just before the asteroid strike and examine its plumage to confirm that it does not retain feathers with primitive traits, O'Connor said. The researchers also believe that computed tomography of other coprolites may help find previously unnoticed remains of feathers, bones, and other evidence of ancient ecosystems, including data on the diets of prehistoric predators. Sometimes the most revolutionary scientific insights come from the most unglamorous sources — and a 66-million-year-old chunk of dinosaur dung may have just rewritten the story of how birds came to inherit the Earth.