A Little Dinosaur Ate Too Many Rocks, Died, and Left Behind a 120-Million-Year-Old Mystery

At the beginning of the Cretaceous period, a palm-sized bird made a fatal mistake. Its fossil shows a tight mass of tiny stones stuck in its throat – a snapshot of a creature captured in its final moments. The pile includes more than 800 rocks, far more than any known bird uses for digestion, and they are so high in the gorge that scientists say the animal probably choked.

The fossil belongs to Chromeornis funkyia newly identified dinosaur species described in Electronic paleontology which offers a window into the evolution of early risers. CT scans showed that its throat stones were not used for digestion, suggesting that the fossil preserves an unusual moment that hints at the quirks and vulnerabilities of this now-extinct lineage.

“It’s pretty rare to be able to know what caused the death of a specific individual in the fossil record. But even though we don’t know why this bird ate all these stones, I’m pretty certain that the regurgitation of this mass caused it to choke, and that’s what killed this little bird,” Jingmai O’Connor, associate curator of fossil reptiles at the Field Museum in Chicago and lead author of the study, said in a press release.

Newly identified species

It wasn’t the stones in the fossil that initially caught O’Connor’s attention. The bird itself was small – about the size of a sparrow – but sported the type of teeth at the end of its beak that are typically seen in larger early birds, such as Longipteryx. The combination of features does not match any known specimen in enantiornithinesthe largest group of birds at the time. This mix of traits suggested that the fossil represented a new species.

It was only after identifying its distinctive anatomy that the throat’s oddity became impossible to ignore. Modern birds like chickens sometimes swallow small stones to help grind food in a muscular stomach called a gizzard; These stones, called gastroliths, accumulate deep in the digestive tract.

But the stones of this fossil were located much higher, near the neck bones. No other enantiornithine has been found with gastroliths of all kinds, let alone in the throat.

Learn more: The smallest dinosaur ever was only 11 inches long and had beautiful tail feathers

Scanning the final moments of a fossil

To make sense of the stones, the team used CT scanning to map each particle inside the fossil’s throat. They compared these measurements to previous work quantifying the number, volume and overall size of gizzard stones in other fossil birds known to use them. These birds had clear, repeatable measurements: small groups of stones contained deep in the digestive system.

Chromeornis did not meet any of these criteria. His analyzes revealed hundreds of tightly packed stones and clay pellets piled high in the gorge, forming a mass unlike anything seen in any other fossil bird. The unusual size, composition and location of the stones indicated behavior outside of normal feeding.

Linking the fate of a bird to mass extinction

With digestion excluded, the team looked at what behaviors might produce such an overcrowded cluster. The most likely explanation was stress or illness: modern birds sometimes swallow unusual objects when they are unwell.

“When birds are sick, they start doing weird things,” O’Connor said. “So we tentatively hypothesized that it was a sick bird that was eating stones because it was sick. It swallowed too many and it tried to regurgitate them in one big mass. But the mass of stones was too big and it got lodged in the esophagus.”

The fossil’s importance reflects unusual behavior in a group that once dominated the Cretaceous but completely disappeared at the end of the era the asteroid struck.

“During this environmental disaster, the enantiornithines “Understanding why they were successful but also why they were vulnerable can help us predict the course of the mass extinction we now find ourselves in.” Read more at Chromeornis and other extinct birds could ultimately help guide conservation efforts today.

Learn more: Eggshells fill 30-million-year fossil gap for dinosaur migration

Article sources

Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review them for scientific accuracy and editorial standards. See the sources used below for this article:

• This article references information from a recent study published in P.Aleontological electronics: A new small-bodied longipterygid (Aves: Enantiornithes) from the Aptian Jiufotang Formation preserving unusual gastroliths