Feather Found in 66-Million-Year-Old Dinosaur Droppings May Explain Why Birds Survived

About 66 million years ago, a large dinosaur, possibly a Tyrannosaurus rex or a smaller relative called Nanotyrannus, swallowed a diving bird. The meal survived as a fossilized dropping, or coprolite, that scientists say holds the finest feather specimen yet found from the age of dinosaurs. The findings were published in the journal Current Biology.

"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," said Jingmai O'Connor, lead author of the study and associate curator of fossil reptiles at the Field Museum in Chicago. The question is why one bird lineage, called Neornithes, survived the asteroid impact and gave rise to every bird alive today, while close relatives died out.

The fossil was found in 2016 by David DeMar Jr. of the University of Washington's Burke Museum, while he was collecting fish fossils in northeastern Montana. He spotted a small reddish-brown nodule and, under a hand lens, saw a tiny fossil feather -- the first ever recovered from the Hell Creek Formation despite more than 150 years of fossil-hunting there. CT scans at the University of Southern California later revealed feathers, fish scales, and leg bones from a hesperornithiform bird packed inside the same nodule.

Hesperornithiforms were mostly flightless diving birds, similar to today's loons, that used specialized feet to hunt underwater. The feathers in the coprolite -- the first ever identified from this group -- show adaptations for swimming. Hesperornithiforms were close relatives of Neornithes but belonged to a separate lineage that went extinct along with most other Cretaceous birds.

One theory held that Neornithes survived partly because many lived around water, which may have offered protection after the asteroid struck. Hesperornithiforms also lived in and around water, yet their line still vanished, suggesting habitat alone cannot explain the difference. O'Connor said the type of feathers these birds had, or how they molted them, may explain why some birds died out at the end of the Cretaceous Period while others survived.