Some roughly 120-million-year-old seeds are telling a new story about what the Earth’s first birds ate. Paleontologists found the seeds in the fossilized stomachs of an early bird species, despite a long-standing hypothesis that these species primarily dined on fish. The findings are detailed in a study published September 10 in the journal Current Biology.
The remains belong to the now extinct Longipteryx chaoyangensis. This small, but long-beaked and strong-toothed avian lived about 120 million years ago in present day northeastern China.
“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,” Jingmai O’Connor, a study co-author and the associate curator of fossil reptiles in the Field Museum’s Neguanee Integrative Research Center, said in a statement.
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“Tooth enamel is the hardest substance in the body, and Longipteryx’s tooth enamel is 50 microns thick,” added Alex Clark, a study co-author and PhD 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 is the size of a bluejay.”
Longipteryx was first discovered and named in 2000. At that time, paleontologists suggested that it likely hunted fish due to an elongated skull like the modern kingfisher. However, a number of scientists have questioned this hypothesis
“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. 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,” said O’Connor. “It just didn’t add up.”
During a visit to the Shandong Tianyu Museum of Nature in China, O’Connor noticed two Longipteryx specimens that appeared to have something in their stomachs. Paleobotanist and Field Museum associate curator of fossil plants Fabiany Herrera was able to determine that these small and round structures in the birds’ stomachs were seeds from the fruits of an ancient tree. More technically, these were flesh-covered seeds or “true fruits” that are only found in flowering plants. These lush types of plants were beginning to flourish about 120 million years ago when Longipteryx walked the earth. Longipteryx was feeding from gymnosperms, relatives of the ginkgos and conifers around today.
Longipteryx also lived in a temperate climate, so it likely wasn’t feasting on fruits all year. The team believes that it likely had a mixed diet and ate insects when fruits were not available.
Longipteryx is a member of a larger group of prehistoric birds called the enantiornithines, that were generally the size of a starling or sparrow. This discovery marks the first time that researchers have found any discernible stomach contents from an enantiornithine in China’s Jehol Biota, despite thousands of uncovered fossils 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.
However, one major question remains. What was it using its long and pointy beak and incredibly strong teeth or if not fish?
“The thick enamel is overpowered, it seems to be weaponized,” said Clark, who looked to modern birds to try to understand what Longipteryx was doing with its beak. “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.”
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Some modern hummingbirds have keratinous projections near the tip of the rostrom–another name for its beak or bill. The projections resemble what is seen on Longipteryx and these weaponized beaks are used to right one another. Weaponized beaks in hummingbirds have evolved at least seven times and allow them to compete for resources. Clark suggested the hypothesis that Longipteryx’s teeth and beak may have also been used as a weapon, potentially evolving under social or sexual selection.
The team hopes that this research can shed light on some of the other broad questions in paleontology about what stories lay beneath fossilized skeletal remains.
“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,” said O’Connor. “There are many factors that could be shaping the structures that we see.”