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In an ancient temperate forest in what is now Oregon, an insect burrowed deep into a sandbar near a stream. There, in a damp burrow, she laid dozens of elongated eggs, about 50 in total. Despite his careful work in building this underground nursery, none of the eggs hatched. Instead, the eggs, enclosed within a pod, fossilized into a stony, mineralized mass. And now, 29 million years later, they constitute a record of insect reproduction that could be unlike anything paleontologists have seen before.
Recently, micro-CT scans of the egg case revealed not only that it was millions of years old, but also that it was likely created by a grasshopper. The eggs and general construction of the nest closely resemble the eggs and pods of modern grasshopper species. This newly documented knowledge offers a clearer picture of that ancient ecosystem, confirming that grasshoppers were present and thriving there, and that some types of grasshoppers were burying their eggs underground.
Insect eggs are extremely rare in the fossil record, and intact egg cases are even rarer. This is likely the only fossilized grasshopper egg pod on record and offers insight into their reproduction dating back to the Oligocene epoch (33.9 million to 23 million years ago), researchers reported Monday in the journal Parks Stewardship Forum. .
“This work is exciting because such exceptional preservation provides unique insights into one of the least understood life stages of insects, particularly in the geological past,” said study lead author Jaemin Lee, an evolutionary ecologist and doctoral student. at the University of California, Berkeley. he told CNN in an email.
intact fossilization
What makes this fossil even more notable is that it was found in a habitat that is not typically conducive to fossilization, said study co-author Dr. Nick Famoso, director of the paleontology program and museum curator at the Monument. National John Day Fossil Beds. The site, located in Mitchell, Oregon, is under the management of the National Park Service.
Delicate fossils like this specimen are usually preserved in lake deposits along with plant matter. These places tend to be anoxic or oxygen-poor and relatively static, Famoso explained. There, fossils can form in peace, untouched by currents or bacteria. But millions of years ago, a river or stream passed through this place. However, the conditions surrounding this egg pod were right for it to remain buried and fossilize undisturbed in near-perfect conditions, despite the dynamic environment of the water flowing nearby, Famoso said.
The eggs of this fossil stand out for their preservation, “both individually and in groups,” said paleobiologist Dr. Ricardo Pérez-de la Fuente, deputy director of research at the Museum of Natural History at the University of Oxford in the United Kingdom, in a statement. . email.
“They are the first to be recognized as belonging to orthoptera (grasshoppers and their relatives) in the fossil record, which is noteworthy,” said Pérez-de la Fuente, who was not involved in the research.
“The work also represents an important step towards formalizing the description of the immature states of insects, more specifically those of eggs,” said Pérez-de la Fuente. This branch of science, known as ootaxonomy, “can provide fundamental data on the evolution, behavior and ecology of insects in ancient times, but which tend to be neglected in paleontological studies.” What’s more, she added, the pod and eggs may offer clues about the environment where they were fossilized.
The eggs had an unusual curvature.
Christopher Schierup, director of collections for the National Park Service, discovered the egg case at the fossil beds in July 2012. Schierup was conducting a routine visual survey of the site when he discovered the object, which was embedded in a piece of rock that had rolled down the hill, Famoso recalled.
“It didn’t require any tools to get it out of the ground,” he said. Schierup wrapped the object in toilet paper “and carefully returned to the visitor center where our laboratory is located,” Famoso added.
Based on analysis of the fossil’s surface, the researchers initially thought they had found a group of ant eggs. But Famoso was skeptical, since its curvature differed from the curves of ant eggs and pupae. His suspicions were corroborated by Lee, who first saw the object in 2022 during a visit to the John Day Fossil Beds. They took the sample to the University of Oregon’s Knight Campus in Eugene, where study co-author Angela Lin, director of the Central X-ray Imaging Research Center, performed micro-CT scans.
“That’s when we discovered that there was a layer of protein that held everything together,” Famoso said. It wasn’t just a cluster of eggs: it was a type of underground egg pod called an ootheca, with the eggs cradled by a protective layer that had mineralized into a stony crust.
“Currently, only two groups of insects produce underground egg pods,” Lee said. These are grasshoppers (order Orthoptera, suborder Caelifera) and heels (order Mantophasmatodea).
Radial arrangement
On the surface, 28 ellipsoid eggs were visible, each measuring no more than 0.18 inches (4.65 millimeters) long and 0.07 inches (1.84 millimeters) wide (this is comparable to eggs of modern grasshoppers, although the size of the eggs can vary depending on the species). ). The scans revealed more than two dozen more eggs buried in the matrix in four or five layers, arranged in a radial pattern. Some of the eggs were hollow, while others had filled with sediment, the study authors reported.
“The mineralization that we could see in each of the eggs made it very clear that it was a fossilization structure,” Famoso said.
Because fossil insect eggs are so rare, there were not many specimens available for comparison. Lee then consulted a global insect egg database, which contains more than 6,700 living species, to identify the eggs in the fossil pod.
“I compared the defining characteristics of the eggs, including the size, length-to-width ratio, and curvature of individual eggs to those of living ones,” he said. “These large, elliptically curved eggs in a large clutch (~50 eggs total) are unknown from any other living group of insects other than grasshoppers and locusts.”
This unusual find provides a never-before-seen view of reproduction in ancient relatives of modern grasshoppers. The virtually pristine specimen also speaks to the level of preservation of the national park’s fossil beds, Famoso added.
“Just being able to see that internal structure and really adequately describe what these things look like was really exciting for us,” Famoso said. “There is simply nothing like this in the fossil record anywhere that we know of.”
Mindy Weisberger is a science writer and media producer whose work has appeared in Live Science, Scientific American, and How It Works magazines.
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