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Ancient Bird’s Diet Revealed Through Fossilized Seeds

A recent discovery involving 120-million-year-old fossilized stomach contents is reshaping our understanding of the diet of some of Earth’s earliest bird species. Contrary to the previously held belief that these avians primarily consumed fish, paleontologists have now identified seeds from ancient plants within the remains of Longipteryx chaoyangensis, an early bird from the Cretaceous period, as detailed in a study published in the journal Current Biology on September 10.

The specimens examined belong to the extinct Longipteryx chaoyangensis, a small bird characterized by its unusually long beak and robust teeth, which inhabited what is now northeastern China approximately 120 million years ago.

Jingmai O’Connor, an associate curator of fossil reptiles at the Field Museum and co-author of the study, expressed her fascination with Longipteryx: “It’s such a unique fossil bird with a long skull and teeth localized at the tip of its beak.”

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The structure of Longipteryx’s teeth is particularly notable; Alex Clark, a co-author and PhD student, indicated that the thickness of its tooth enamel—50 microns—is comparable to that found in large predatory dinosaurs such as the Allosaurus, despite Longipteryx being the size of a blue jay.

Longipteryx was first described in 2000, at which point paleontologists hypothesized it was a fish hunter due to its elongated skull, reminiscent of modern kingfishers. However, this interpretation has faced scrutiny, with researchers noting that fish-eating birds typically possess a full array of teeth along their beaks, unlike Longipteryx.

According to O’Connor, “Other fossil birds like Yanornis have been uncovered with stomach contents confirming their fish diet, which are better preserved than other types of food. It simply didn’t fit with Longipteryx, which only had teeth at the beak tip.”

A photograph of the stomach contents of a fossil Longipteryx; the three round structures are seeds. CREDIT: Photo by Xiaoli Wang.

During a visit to the Shandong Tianyu Museum of Nature, O’Connor discovered two specimens of Longipteryx that contained preserved items in their stomachs. Fabiany Herrera, a paleobotanist and associate curator of fossil plants at the Field Museum, identified these items as seeds from an ancient flowering tree. Specifically, these were “true fruits”—flesh-covered seeds distinct to flowering plants—which emerged about 120 million years ago, coinciding with the presence of Longipteryx.

Although it lived in a temperate environment, suggesting fruits were not a year-round food source, the research team hypothesizes that Longipteryx had a varied diet, likely including insects when fruits were scarce.

Longipteryx falls within the broader category of prehistoric birds known as enantiornithines, which were typically similar in size to modern starlings or sparrows. The discovery of identifiable stomach contents from an enantiornithine in China’s Jehol Biota marks a significant milestone, given the abundance of fossils uncovered in the region without prior evidence of their diets.

O’Connor noted, “It has always been puzzling that we lacked insights into their diets, and this research reveals a broader issue in paleontology: that the physical characteristics of fossils don’t always fully capture an animal’s dietary habits or lifestyle.”

Nonetheless, a critical question persists: What purpose did its elongated beak and exceptionally strong teeth serve, if not for fishing?

Clark speculated that, much like some modern birds whose beaks serve as tools for aggressive interactions, Longipteryx may have evolved its striking tooth structure for similar reasons. “A robust beak can act as a weapon while keeping it at a distance from the body to prevent injury during fights,” he remarked.

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Drawing parallels with contemporary hummingbirds, which possess keratinous features at the tips of their beaks for competitive confrontations, Clark hypothesizes that the teeth and beak of Longipteryx may have also been adapted for combat, possibly influenced by social or sexual selection.

A modern hummingbird, Androdon aequatorialis, showcases similar tooth-like structures at the beak’s tip used in combat. CREDIT: Kate Golembiewski.

This research aims not only to enhance the understanding of Longipteryx but also to provoke further inquiry into the dietary and behavioral complexities of early avian species.

O’Connor concluded, “We strive to explore new dimensions of research on these primitive birds, encouraging paleontologists to consider the intricacy of the behaviors these animals may have exhibited beyond merely their diets. Many aspects could influence the structural characteristics we observe.”

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