Paleontologists have found the fossilized seeds of gymnosperm trees — relatives of today’s conifers and ginkgos — in stomachs of two specimens of Longipteryx chaoyangensis, one of the earliest known birds and one of the strangest. The discovery shows that these birds were eating fruits, despite a long-standing hypothesis that they feasted on fish, and more recent hypotheses it ate insects, with its incredibly strong teeth.
Skull of Longipteryx chaoyangensis. Image credit: Xiaoli Wang.
Longipteryx chaoyangensis lived in what is now northeastern China during the Cretaceous period, some 120 million years ago.
First described in 2000, this ancient bird had a long skull and teeth only at the tip of its beak.
“Tooth enamel is the hardest substance in the body, and Longipteryx’s tooth enamel is 50 microns thick,” said Alex Clark, a Ph.D. student at the Field Museum and the University of Chicago.
“That’s the same thickness of the enamel on enormous predatory dinosaurs like Allosaurus that weighed 4,000 pounds, but Longipteryx was the size of a bluejay.”
Scientists previously suggested that a kingfisher-like elongated skull of Longipteryx chaoyangensis meant that it hunted fish. However, this hypothesis has been challenged by a number of studies.
“There are other fossil birds, like Yanornis, that ate fish, and we know because specimens have been found with preserved stomach contents, and fish tend to preserve well,” said Dr. Jingmai O’Connor, associate curator of fossil reptiles in the Field Museum.
“Plus, these fish-eating birds had lots of teeth, all the way along their beaks, unlike how Longipteryx only has teeth at the very tip of its beak. It just didn’t add up.”
However, no specimens of Longipteryx chaoyangensis had been found with fossilized food still in their stomachs for scientists to confirm what it ate — until now.
In the new research, the paleontologists examined two new specimens of this species.
They were able to determine that the tiny, round structures in the birds’ stomachs were gymnosperm seeds.
Since Longipteryx chaoyangensis lived in a temperate climate, it probably wasn’t eating fruits year-round.
The authors suspect that it had a mixed diet which included things like insects when fruits weren’t available.
Longipteryx chaoyangensis is part of a larger group of prehistoric birds called the enantiornithines, and this discovery marks the first time that scientists have found any stomach contents from an enantiornithine in China’s Jehol Biota despite thousands of uncovered fossils.
“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,” Dr. O’Connor said.
Since Longipteryx chaoyangensis apparently wasn’t hunting for fish, that leaves a question: what was it using its long, pointy beak and crazy-strong teeth for?
“The thick enamel is overpowered, it seems to be weaponized,” Clark said.
“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,” Dr. O’Connor added.
“Weaponized beaks in hummingbirds have evolved at least seven times, allowing them to compete for limited resources.”
The findings were published today in the journal Current Biology.
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Jingmai O’Connor et al. Direct evidence of frugivory in the Mesozoic bird Longipteryx contradicts morphological proxies for diet. Current Biology, published online September 10, 2024; doi: 10.1016/j.cub.2024.08.012
