Birds evolved from dinosaurs. They share a common ancestor and physical traits — some dinosaurs even had feathers. But while these dinosaurs are thought to have had “fuzzy” or “downy” feathers, ancient birds were more likely to have had feathers that look similar to the birds of today.
A University of Washington-led research team has discovered the best-preserved fossil feathers from the Mesozoic era — in a fossilized dinosaur poop, also known as a “coprolite.” Some of these feathers have features that look like modern birds’ feathers. In a paper published Sept. 10 in Current Biology, the team describes this finding and how it can help researchers better understand why and how some birds survived the catastrophic event 66 million years ago that killed 75% of life on the planet.
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This fossil with the exposed feather is on permanent display at the Burke Museum as part of the “Drama at the K-Pg” exhibit.
“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,” said co-author Gregory Wilson Mantilla, a UW professor of biology and the curator of vertebrate paleontology at the Burke Museum. “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.”
The team discovered the feathers in 2016 at a research site in eastern Montana in the badland exposures of the geological formation called the Hell Creek Formation.
“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,” said co-author David DeMar Jr., a UW research scientist in the biology department and the Hell Creek Project collections manager at the Burke Museum. “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 100 years of prospecting.”
Back in the lab, the researchers examined the specimen’s mineral composition and took CT scans of it — essentially, thousands of X-rays that are digitally stacked to reveal the contents of an object.
“Every hour processing the data revealed another feather, another scale, another bone — in stunning 3D,” said co-author Nathan Carroll, a paleontologist at the Carter County Museum.
The coprolite contained multiple feathers, tiny fish scales from a gar and leg bones from a hesperornithiform, an extinct group of birds that are ecologically similar to loons. The researchers reasoned that the feathers must have also come from this same bird. These are the first hesperornithiform feathers ever found.
“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,” DeMar said. “This includes a square feather shaft with a sponge-like center. No other Mesozoic feather has this combination of features. The next oldest record of this sponge-like center is from the early Eocene of Denmark, which is about 10 million years younger than this new feather record from the Hell Creek Formation.”
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Through the Hell Creek Project, led by Gregory Wilson Mantilla, researchers have discovered many prominent fossils in the Hell Creek Formation, including a T. rex skull and bones from a juvenile duckbill dinosaur.
The hesperornithiforms are close cousins of the birds that survived the mass extinction and still live today. Some scientists have 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.
“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,” said lead author Jingmai O’Connor, associate curator of fossil reptiles at the Field Museum. “Some of these diving birds’ feathers seem to have been modern-looking and waterproof, but they also had some smaller fuzzy, primitive body feathers that we associate with dinosaurs.”
If the feathers on hesperornithiforms and other extinct bird species weren’t as good at keeping their bodies warm, the researchers hypothesize, maybe that’s why they weren’t able to survive the extinction event.
“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,” O’Connor said. “I usually work with fossils that are preserved in big stone slabs, and the entire skeleton and even the soft tissue is preserved — they make it easy for me. But with this project, we just had this coprolite — and its contents — to go off of, and it made me feel like a detective, piecing together all these little clues. And 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.”
Elliott Armour Smith, UW doctoral student in biology; Michael Holland, the Hell Creek Project Fossil Preparator at the Burke Museum of Natural History; Karen Chin at the University of Colorado, Boulder; Alexander Clark at the Field Museum and the University of Chicago; Christian Cooper at the Field Museum; Pei-Chen Kuo at the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences; Thomas Tobin at the University of Alabama; Aaron Celestian at the Natural History Museum of Los Angeles County; David Bottjer at the University of Southern California; and Luis Chiappe at the Natural History Museum of Los Angeles County are also co-authors on this paper. This research was funded by donations to the Hell Creek Project.
For more information, contact Wilson Mantilla at gpwilson@uw.edu and DeMar at ddemar@uw.edu.
Adapted from a release from The Field Museum.