120-million-year-old fossil’s stomach content reveals bird was a fruit-eater

In a recent development, researchers uncovered fossilized seeds in the stomachs of one of the earliest bird species, revealing that these birds consumed fruits.

This challenges the long-held belief that this bird species primarily ate fish, as well as more recent theories suggesting it fed on insects, owing to its remarkably strong teeth.

Longipteryx chaoyangensis , which lived 120 million years ago in present-day northeastern China, is not only one of the oldest known birds but also one of the most unusual.

“ Longipteryx is one of my favorite fossil birds, because it’s just so weird— it has this long skull, and teeth only at the tip of its beak,” said Jingmai O’Connor, the study’s lead author.

The bird with the toothed beak

Longipteryx was first discovered in 2000, and at the time researchers proposed that its elongated, kingfisher-like skull indicated a fish-based diet. However, this theory has since been questioned by multiple scientists, including O’Connor.

She pointed out that other fossil birds, like Yanornis , were known to have eaten fish because their stomach contents had been preserved, and fish fossils tend to remain well-preserved. Additionally, fish-eating birds had numerous teeth along their beaks, whereas Longipteryx only had teeth at the tip, making the fish-eating hypothesis seem unlikely.

Despite this, scientists had previously been unable to confirm Longipteryx’s diet, as no specimens had been found with preserved stomach contents—until the recent discovery of fruit remains in the stomach contents of a specimen.

O’Connor and her team believe that, given Longipteryx’s temperate climate, it likely had a varied diet, turning to insects or other food sources when fruits were out of season.

Not fish, but fruit?

Longipteryx belongs to a larger group of ancient birds known as enantiornithines. This recent discovery is the first instance in which scientists have found stomach contents from any enantiornithine within China’s Jehol Biota, despite the thousands of fossils unearthed from the region.

“It’s always been weird that we didn’t know what they were eating, but this study also hints at a bigger picture problem in paleontology, that physical characteristics of a fossil don’t always tell the whole story about what animal ate or how it lived,” said O’Connor in the press release .

With evidence suggesting Longipteryx wasn’t hunting fish, researchers are now left to wonder what its long, pointed beak and unusually strong teeth were used for. Researchers noted that the thick enamel on its teeth appeared too powerful for typical feeding purposes, speculating that they might have been adapted for another use.

They proposed that Longipteryx’s beak and teeth may have evolved as weapons, possibly driven by social or sexual selection.

Researching the complex behaviors of prehistoric birds

The researchers emphasize that their work goes beyond uncovering details about the life of one peculiar prehistoric bird . They hope it will contribute to broader discussions in paleontology about the reliability of skeletal traits in interpreting animal behavior.

O’Connor explained that the goal is to encourage paleontologists to consider the complexity of behaviors these early birds might have exhibited, beyond just their diet. She noted that traits like the beak should be examined in greater depth, as various factors could have influenced their development.

“We’re trying to open up a new area of research for these early birds and get paleontologists to look at these structures, like the beak, and think about the complexity of the behaviors that these animals might have engaged in beyond just what they were eating,” O’Connor concluded.

The study has been published in the journal Current Biology.