Why did this ancient bird die with tiny rocks in its throat?

Fossils may reveal what type of animal died millions of years ago, but they rarely depict exactly how they perished. Even rarer are the examples that clearly showcase an animal’s exact cause of death. In fact, a 120-million-year-old bird specimen housed at China’s Shandong Tianyu Museum of Nature may be the only fossilized remains of its kind.

“There are thousands of bird fossils at the Shandong Tianyu Museum, but on my last trip to visit their collections, this one really jumped out at me,” Chicago’s Field Museum associate curator of fossil reptiles Jingmai O’Connor said in a statement. “I immediately knew it was a new species.”

Although its physiology and large teeth resembled a larger bird known as Longipteryx, the mystery avian was only about as large as a present-day sparrow. And then there was also the surprising discovery found while analyzing the fossils under a microscope, as O’Connor described in a study published on December 5 in the journal Palaeontologica Electronica.

“I noticed that it had this really weird mass of stones in its esophagus, right up against the neck bones,” said O’Connor. “This is really weird, because in all of the fossils that I know of, no one has ever found a mass of stones inside the throat of an animal.”

That this ancient bird swallowed stones wasn’t surprising on its own. Multiple species throughout the evolutionary timeline are known gastroliths, meaning they either intentionally or accidentally consume small rocks while they eat. Chickens store tiny stones in their gizzard that help grind the food they ingest. Biologists have also documented similar behavior in crocodiles, ostriches, and even sea lions.

But was the mystery bird a previously undiscovered gastrolith? To figure that out, O’Connor and colleagues reviewed their work using CT scans of fossils from birds who definitely relied on gizzard stones.

“We had quantified the average volume of the stones, the number of stones that these other fossil birds had in their gizzards, the size of the gizzard stone mass compared to the total size of the bird,” O’Connor said.

After examining a wide array of bird fossils, the paleontologists surprisingly uncovered that over 800 small stones in the specimen’s throat weren’t gizzard stones. Some were not even stones at all.

“They seemed to be more like tiny clay balls,” explained O’Connor. “With these data, we can very clearly say that these stones weren’t swallowed to help the bird crush its food.”

With one question answered, another immediately arose: If the bird didn’t eat them as gizzard stones, then why did it ingest them at all? Luckily, O’Connor’s team already has a solid theory.

“When birds are sick, they start doing weird things,” she said.

They now believe the ill animal started eating stones, then tried to regurgitate them as one large mass. Unfortunately, the mass was simply too big at that point, causing it to get stuck in the bird’s esophagus.

“Even though we don’t know why this bird ate all those stones, I’m fairly certain that regurgitation of that mass caused it to choke, and that’s what killed that little bird,” said O’Connor.

After theorizing on the fossilized bird’s cause of death, the paleontologists decided on the new species’ name: Chromeornis funkyi. It might not roll off the tongue, but Chromeornis is still an ode to one of O’Connor’s favorite bands, the techno-funk duo Chromeo.

“We’ve been doing this for 20 years but this is the first time someone’s called us a dinosaur,” Chromeo said in a statement. “Jokes aside, this is an incredible honor to add to a career full of surprises. We’re glad to bring a little fossil funk to the great science of paleontology.”

 

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