Why did birds survive when dinos didn’t? Poop may reveal answer

By Stephen Beech

A feather preserved inside dinosaur dung could help explain why birds survived the mass extinction that wiped out most life on Earth.

Scientists say a dinosaur, possibly a tyrannosaur, ate a bird around 66 million years ago and the meal has survived until today in the form of fossilized poo, preserving the best example of a feather ever found from the dinosaur age.

By studying the feather, researchers have found clues that help explain why birds are the only group of dinosaurs that survived the mass extinction on Earth 66 million years ago.

Study lead author Jingmai O'Connor said: "It's such a beautiful, well-preserved feather, from such an unexpected source, and it's exciting that it could help us answer this huge question in paleontology."

She explained that the earliest known bird is Archaeopteryx, from 150 million years ago, and birds continued to evolve and coexist alongside their fellow dinosaurs for nearly 100 million years.

In the aftermath of the asteroid impact 66 million years ago, nearly all dinosaurs — including most birds — were wiped out.

But one group of birds, Neornithes, survived, and every living bird today is one of their descendants.

O'Connor has spent years studying fossil birds to try to find out why only they survived.

But the new study, published in the journal Current Biology, is the first time she's analyzed feathers that were preserved inside fossilized droppings, known as coprolites.

O'Connor, associate curator of fossil reptiles at the Field Museum in Chicago, said: "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."

The fossil was discovered in 2016, by study co-author David DeMar Jr., while conducting fieldwork in Montana.

He said: "I was crawling up a rocky outcrop collecting fish fossils when I came across a dark, reddish-brown nodule about half the size of a golf ball.

"I picked it up and scanned its surface through my hand lens, and that's when I couldn't believe what I was seeing, a tiny fossil feather.

"I was cautiously optimistic about its discovery, because feathers had not yet been found in the Hell Creek Formation, even after more than 150 years of prospecting."

Scientists examined the specimen's mineral composition and took CT scans of it.

Co-author Nate Carroll, paleontologist at the Carter County Museum in Montana, said: "I suspected it might be a coprolite, but it wasn't until we got it into the micro-CT scanner that the full feathery fabric of this fossil feces became apparent.

"Every hour processing the data revealed another feather, another scale, another bone - in stunning 3D.

"As someone who had been relying on far-flung amber mines as my main source of 3D feather data, realizing that fossil poop from my home state could yield such exceptional specimens was a game changer."

The coprolite contained multiple feathers, tiny fish scales from a gar and leg bones from a hesperonithiform bird.

O'Connor said: "Hesperornithiforms were aquatic birds, ecologically similar to loons.

"Most couldn't fly, and instead, they used their specialized feet to dive down into the water to hunt for things like fish.

"The feathers showed adaptations for being underwater that we see in living aquatic birds."

She explained that the hesperornithiforms are close cousins of the Neornithes birds that survived the mass extinction and still live today, but they were not part of Neornithes themselves.

O'Connor said: "The most common birds alive in the Cretaceous were part of a group called the enantiornithines.

"The modern Neornithes branch of birds were separate from that group, and so were the hesperornithiforms."

She believes one of the main reasons Neornithes survived is down to differences in their feathers.

O'Connor said: "We think the types of feathers that these birds had, and/or the way they molted those feathers, may have been one of the underlying causes of the selectivity of the end-Cretaceous mass extinction - essentially, why some birds died out and why others survived."

The feathers found in the droppings are the first hesperornithiform feathers ever found, and their features seem to represent a middle ground between the feathers of enantiornithines and modern birds.

O'Connor said: "Some of these diving birds' feathers seem to have been modern-looking and water-proof, but they also had some smaller, fuzzy, primitive body feathers that we associate with dinosaurs and enantiornithines."

She says the feathers on a bird's body help insulate it from the cold.

If the hesperornithiforms' and enantiornithines' feathers weren't as good at keeping their bodies warm as Neornithes' feathers, O'Connor believes that could have been a major factor in their abilities to survive the impact winter following the asteroid strike.

She said: "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."

Study co-author Greg Wilson Mantilla, from the University of Washington, said: "We rarely find fossils of birds and even more rarely their feathers, giving us such important insight into the evolution of this key aspect of their biology.

"On top of that, these bird feathers found within a large fossilized dinosaur dung give us an incredible window into predator-prey interactions 66 million years ago."

O'Connor added: "Since no one has studied feathers in coprolites before, this opens up a whole new avenue for investigation.

"We only knew to look at this one because of how it happened to be split open, with the feather exposed - it was literally a lucky break.

"I hope more scientists start CT scanning coprolites and taking a closer look at them to see what might be inside."