Jingmai O'Connor, associate curator of fossil reptiles at Chicago's Field Museum and lead author of the new species description in the journal Palaeontologica Electronica, first identified the specimen at the Shandong Tianyu Museum of Nature. "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," says O'Connor. "I immediately knew it was a new species."
The fossil is about the size of a modern sparrow but shares key anatomy with a larger fossil bird called Longipteryx, including pronounced teeth at the tip of the beak. "It had really big teeth at the end of its beak, just like Longipteryx, but it's a tiny little guy. So based on that, I knew it was something new."
Closer examination under a microscope revealed an unusual concentration of stones in the bird's esophagus, pressed against the neck vertebrae. "I noticed that it had this really weird mass of stones in its esophagus, right up against the neck bones," says 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." Geologic context and chemical signatures indicate the stones were ingested during life, not introduced later as the carcass settled on the lakebed where it fossilized.
Many animals swallow stones, known as gastroliths, either deliberately or accidentally. Some living birds, such as chickens, retain small stones in a muscular stomach called a gizzard to help grind food. However, despite thousands of specimens from the same broader fossil bird group, no other examples have been reported with stones in the digestive tract that function as gizzard material.
To test whether this fossil simply represents the first known gizzard-stone case in its group, O'Connor and colleagues drew on previous work in which they CT scanned fossil birds with confirmed gizzards. "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," says O'Connor. "We CT scanned this new fossil so we could compare it to these other birds with gizzards."
The new scans show that the concentrated mass in the throat differs from gizzard stones in size distribution, total number, and inferred density. "We found over 800 tiny stones in this bird's throat - way more than we would have expected in other birds with gizzards. And based on their density, some of these stones weren't even really stones, they seemed to be more like tiny clay balls," says O'Connor. "With these data, we can very clearly say that these stones weren't swallowed to help the bird crush its food."
Because the stones do not match normal gizzard material, the team suggests a different explanation for their presence. "When birds are sick, they start doing weird things," says O'Connor. "So we put forth a tentative hypothesis that this 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."
Beyond being the first fossil animal O'Connor knows of with a throat packed with stones, the specimen offers a rare window into cause of death. "It's pretty rare to be able to know what caused the death of a specific individual in the fossil record," says O'Connor. "But 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."
The fossil also extends the known diversity of Cretaceous birds. It represents a new species of dinosaur-era bird that O'Connor has named Chromeornis funkyi (kroh-me-or-nis fun-key), after the techno-funk duo Chromeo, linking the musical association to the idea that birds produce sounds. Researchers cannot reconstruct its exact calls, but O'Connor notes that it likely made some kind of vocalizations even if it did not sing like modern songbirds.
Chromeo members David "Dave 1" Macklovitch and Patrick "P-Thugg" Gemayel responded to the naming with a mix of humor and appreciation. "We've been doing this for 20 years but this is the first time someone's called us a dinosaur! 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."
Chromeornis belongs to the enantiornithines, a major group of birds that dominated during the Cretaceous. When the asteroid impact struck 66 million years ago, enantiornithines disappeared along with nearly all non-avian dinosaurs, while only the lineage leading to today's birds persisted. "During that environmental disaster, the enantiornithines went from being the most successful group of birds to being wiped out," says O'Connor. "Understanding why they were successful but also why they were vulnerable can help us predict the course of the mass extinction we're in now. Learning about Chromeornis and other birds that went extinct could ultimately help guide conservation efforts today."
Research Report:A new small-bodied longipterygid (Aves: Enantiornithes) from the Aptian Jiufotang Formation preserving unusual gastroliths
Related Links
Field Museum
Explore The Early Earth at TerraDaily.com
| Subscribe Free To Our Daily Newsletters |
| Subscribe Free To Our Daily Newsletters |
