A Tyrannosaur Ate a Feathery Meal—and It Was Frozen in Time
Dinosaur poop—possibly from a juvenile T. rex or Nanotyrannus—containing feathers, bone fragments, and fish scales provides a look at a Cretaceous-era food web.
The little aquatic bird had no idea it had just eaten its last meal. Its stomach was still full of scaly fish when a hungry, feathery dinosaur scooped it up, snapping its jaws shut in a puff of plumage.
After a shake and a swallow, the bird slid down the predator’s throat. From there, most of it journeyed into the carnivore’s core to be broken down and folded into the creature’s own tissues. The remainder was excreted as dino dung.
Now, some 66 million years later, researchers have found a feather and the gut contents from that bird preserved in the dinosaur’s fossilized poop. The coprolite, as paleontologists call it, contains a Cretaceous food web from just before the asteroid strike and adds a new wrinkle to the story of which birds survived and which went extinct.
“This is the first fossil feather found in a coprolite,” says Jingmai O’Connor, a paleontologist at the Field Museum in Chicago. She and her colleagues published their findings Thursday in the journal Current Biology.
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Known by its catalog number "UWBM 103150," the fossilized feces consist of three rocky globs. It was likely expelled by a medium-sized carnivorous dinosaur that lived in Montana, perhaps a juvenile Tyrannosaurus rex or the mini-tyrant Nanotyrannus. The lithified plops are flecked with tiny pieces of bone that best match a group of flightless, toothed birds called hesperornithiformes, which swam in prehistoric seas.
“The preservation is truly amazing, almost as if it was in amber,” says Matthew Shawkey, a paleontologist from Ghent University in Belgium, who was not involved in the research.
Every dinosaur coprolite is like a time capsule. The dung often contains tatters of the dinosaur’s most recent meal. Duck-billed dinosaurs, hungry for essential nutrients to form their eggs, munched on rotting logs filled with tiny invertebrates. Scientists found wood and exoskeletons in their droppings. An eight-inch-long scat attributed to T. rex was found to contain bone fragments and even undigested pieces of muscle.
“Since bits of bone pass through large theropod digestive systems, it’s not unsurprising that whole small feathers also pass through,” O’Connor says.
Dinosaurs had elevated body temperatures and fast metabolisms, features associated with a quicker digestive system. That means that not everything they guzzled down was digested into nothingness, giving feathers a chance to make it through whole. Despite seeming fragile, feathers are made of a tough and fibrous material called keratin.
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“Very, very few animals are able to digest keratin, so it is reasonable to expect that feathers might be common in feces,” says Karen Chin, a paleontologist at the University of Colorado and an author on the study.
The ancient plumage found within UWBM 103150 did not match any known Mesozoic feathers. Its multi-branching structures seemed adapted to keep water out, as in modern aquatic birds, but scientists had not observed these specific structures before. So to identify the type of bird the fossilized fecal feathers belonged to, O’Connor and her colleagues looked at what else was preserved within the poop.
They found bone fragments that were denser than most bird bones. Aquatic birds of the time, like Hesperornis, a fish eater that looked something like a toothed loon, had dense bones like the ones seen in the poop. Compact bones helped birds swim underwater because their weight counteracted the buoyancy of the air in their bodies, allowing them to put more energy into swimming rather than staying submerged.
“The bones looked like hesperornithiform bones, as they’re very dense, so then the feathers should show aquatic adaptations,” O’Connor says, “and voilà! They did.”
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The most likely scenario, O’Connor and her team propose, is that the bones and feathers belonged to a Hesperornis-like bird. And based upon the tiny gar scales also found in the coprolite, the researchers think the bird had recently fed on fish before being swallowed up, too.
The evidence backs up this interpretation, Shawkey says, adding that the researchers “have done some pretty rigorous comparative work and built a convincing case.”
The coprolite also gives scientists insight into the end of the Cretaceous Period. Big carnivorous dinosaurs vanished during that fiery extinction, as well as toothed birds like Hesperornis. Paleontologists have long wondered why such birds would vanish when other birds, particularly the neornithes—the ancestors of all avians alive today—survived. The partially digested feathers may offer a new clue.
While similar to feathers of living birds like ducks and grebes, the anatomy of these fossilized feathers indicates that the plumage was less efficient at trapping air against the body to retain warmth. This may have sealed the fate of these birds. One of the after-effects of the devastating asteroid impact 66 million years ago was an “impact winter” created by soot, debris, and sun-blocking compounds thrown into the atmosphere by the disastrous strike.
If birds like Hesperornis somehow survived the fires of the first days after the impact, they may have perished as temperatures plummeted during the ensuing three years of darkness. That might mean the coprolite preserves more than a fleeting interaction between predators and prey: it shows how lives intertwined in a lost world were forever changed by the sudden arrival of an asteroid.
