A study of a bizarre prehistoric bird's fossilized remains has uncovered fascinating new details regarding its behavior.
Living around 120 million years ago, the species, Longipteryx chaoyangensis, is among the earliest known birds, and one of the strangest—not least because it had a set of incredibly strong teeth at the end of its very long beak.
"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," study lead author Jingmai O'Connor, associate curator of fossil reptiles with the Field Museum's Negaunee Integrative Research Center, said in a press release.
"Tooth enamel is the hardest substance in the body, and Longipteryx's tooth enamel is 50 microns thick. That's the same thickness of the enamel on enormous predatory dinosaurs like Allosaurus that weighed 4,000 pounds, but Longipteryx is the size of a bluejay," study co-author Alex Clark, a Ph.D. student at the Field Museum and the University of Chicago, said in the release.
After its discovery more than two decades ago, researchers hypothesized that the bird used its long beak and strong teeth to hunt fish. But no one had ever found a specimen with fossilized fish remains in its belly—or indeed, any other type of food—meaning researchers were not able to confirm what it feasted on. More recent research suggested that it may have eaten insects.
Now, a study published in the peer-reviewed journal Current Biology has described two specimens of Longipteryx with bellies full of seeds, indicating that the species ate "fruit." This finding has led the authors to rethink how this bizarre bird used its unusual teeth.
"Our description of two new specimens of Longipteryx at long last reveals what this strange bird was eating, and it is significantly different from all previous hypotheses," O'Connor told Newsweek. "Longipteryx was primarily eating the fruit-like reproductive structures of gymnosperms (non-flowering plants), hinting also at how birds would have been important to the evolution of gymnosperms as far back as 120 million years ago."
What the researchers found where the birds stomachs were once located are seeds that used to be covered in flesh rather than "true fruits"—which are only seen in flowering plants. The prehistoric trees that Longipteryx appears to have fed from were gymnosperms, relatives of today's conifers and ginkgos. Flowering plants were only just starting to flourish when the bird lived around 120 million years ago.
Longipteryx lived in a temperate climate in what is now northeastern China. As a result, the researchers suggest that it was probably not eating the fruit-like food all year round, potentially mixing up its diet by consuming things like insects when they were not available.
The latest findings raise new questions about how the bird may have used its long, pointy beak and strong teeth. The authors now suspect that these features served as a weapon, which Longipteryx wielded when fighting others for mates or territory. This has parallels with some modern species.
"The thick enamel is overpowered, it seems to be weaponized," Clark said in the release. "One of the most common parts of the skeleton that birds use for aggressive displays is the rostrum, the beak. Having a weaponized beak makes sense, because it moves the weapon further away from the rest of the body, to prevent injury."
"There are no modern birds with teeth, but there are these really cool little hummingbirds that have keratinous projections near the tip of the rostrum that resemble what you see in Longipteryx, and they use them as weapons to fight each other," O'Connor added in the release.
Besides providing new insights into the life of Longipteryx, the study also has wider paleontological implications—touching on a significant problem in the field. Namely, that the physical characteristics of a fossil do not always reveal the full picture about how a prehistoric animal lived or behaved.
"These stomach contents also tell us that many long-standing traits associated with eating meat—or at least the remains of other animals like insects, fish, etcetera—cannot be used to predict diet in fossils, at least for birds," O'Connor told Newsweek. "Longipteryx has large, recurved, sharp, and serrated teeth—all classic signs of hypercarnivory to paleontologists—yet direct evidence shows us that was not the case."
This is an indication that paleontologists should not necessarily make assumptions about long extinct organisms based on qualitative assessments of skeletal traits, according to O'Connor.
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Reference
O'Connor, J., Clark, A., Herrera, F., Yang, X., Wang, X., Zheng, X., Hu, H., & Zhou, Z. (2024). Direct evidence of frugivory in the Mesozoic bird Longipteryx contradicts morphological proxies for diet. Current Biology. https://doi.org/10.1016/j.cub.2024.08.012
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