April 16, 2024

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“Sea monster” fossils provide evidence of ichthyosaurs migrating 230 million years ago


Paleontologists think they have solved a decades-old mystery: How did at least 37 marine reptiles the size of a school bus die and become embedded in stone some 230 million years ago in what is now central Nevada? If the scholars of Smithsonian National Museum of Natural History And other institutions are right, a fossil graveyard near an ancient silver mine is an early example of migration, one of the most fundamental and deeply entrenched animal behaviors.

The bones found at the Nevada site come from a giant ichthyosaur shonesauruswhich out of shape resembles an enormous dolphin. shonesaurus It glided like a barge thousands of miles across the ocean known as the Panthalassa, the ancient version of the Pacific Ocean today, to breed and generate its offspring, according to a new study in Current Biology.

The discovery offers a rare window into the behaviors of prehistoric animals, something individual fossils don’t always capture. It raises the possibility that additional clues found in sediment and soil could provide a deeper understanding of the marine reptiles that inhabited the planet long before humans.

earliest known Evidence of migration dates back more than 300 million years to antiquity Bandrenga sharks With a long spoon-shaped snout and a beak Prehistoric fish with armor plates. Today billions of animals migrate, including species as diverse as hummingbirds, humpback whales, monarch butterflies, and blue wildebeest.

Climate change may play a role in reports of larger-than-normal fish in unexpected areas. (Video: John Farrell, Brian Monroe/The Washington Post)

Evidence from similar fossils found in other regions point to this shonesaurus They migrated to central Nevada from parts of modern-day California, Alaska, and New Mexico.

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If so, this behavior prehistoric times can be linked shonesaurus, the largest ocean-traveling creature of the Triassic period, with modern giants – blue whales observed today with their calves in the Gulf of California. Whales tend to migrate to warmer waters to give birth, and then to cooler, nutrient-rich waters.

“One has to wonder if the same environmental rules apply even though there are more than 200 million years between them.” [whales and Shonisauruses]Nicholas D. said: Benson, one of the new paper’s authors who works in the Department of Paleontology at the National Museum of Natural History.

Not all experts in the field believe that Benson and his colleagues have solved the mystery surrounding the superabundance. shonesaurus Bones in situ and the absolute absence of any other ichthyosaurs.

“This study may not be the final word, but it is a good step forward,” he cautioned. Martin SanderProfessor of Paleontology at the University of Bonn, Germany, and Research Associate at the Los Angeles County Museum of Natural History.

Sander, who was not involved in the study, added, “I’m not entirely convinced. It’s a good idea but it’s very difficult to prove.”

skeletons in Berlin Ichthyosaurus State Park In West Union Canyon show that shonesaurus It grew up to 50 feet long, five times the length of a modern dolphin, and weighed about 22 tons, the equivalent of three large elephants. Their offspring were only a few feet tall.

Charles L. campD., a paleontologist at the University of California, Berkeley, was the first to excavate the alternating layers of limestone and mudstone at the site in the 1950s. he is I immediately wondered what could represent such a large group of shonesaurus skeletons.

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Kelly, one of the paper’s authors and assistant professor in the Department of Earth and Environmental Sciences at Vanderbilt University, “was thinking it might be mass strandings,” such as those involving whales.

But fossil evidence refutes this hypothesis, showing that they had skeletons He settled under the water, far from the shore.

effort to explain why shonesaurus The bones were, to date, the only ichthyosaur fossils discovered at the Nevada site and have become a scholarly achievement. The researchers combined 3D scanning and geochemistry with more traditional tools such as museum collections, field notes, photographs, and archival materials.

They have come to view migration as the most likely scenario after excluding other possibilities. Sediment testing revealed no levels of mercury that would indicate volcanic activity, which is believed to have caused the volcanic eruption The largest mass extinction 252 million years ago.

The researchers were also able to eliminate the possibility that deadly algal blooms could poison marine reptiles.

In the end, only the migration scenario seems to make sense.

“Shonisaurus.” It certainly occurs in other locations, so the genus would have had a wide geographic range, and it is very plausible that these large individuals traveled long distances, as most large marine vertebrates do today,” Kelly said. “It should be possible to collect additional data in the future that could It tests the hypotheses we present in the paper, including migration.”

At least two other mysteries still surround ancient marine reptiles called ichthyosaurs.

Ichthyosaurs, such as sea turtles, were originally terrestrial animals of some kind, said Sander of the University of Bonn, “but they appear in the fossil record as fully open ocean animals. We don’t have the right rocks to show how ichthyosaurs went to sea.”

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Also, while shonesaurus Extinct about 200 million years ago at the end of the Triassic period, “smaller ichthyosaurs survived into the Jurassic period and beyond with the entire group becoming extinct about 88 million years ago in the Cretaceous period,” Kelly said. It is not clear why small ichthyosaurs survived and giants did not.

Benson can’t help but think that the ultimate fate of L shonesaurus It holds a lesson for modern blue whales and other cetaceans, many of which are now classified as endangered.

“We must desire a world,” he said, “with huge ocean giants inside.”