‘Sea monster’ fossils provide clues to ichthyosaur migration 230 million years ago


Paleontologists believe they have solved a decades-old mystery: How did at least 37 school-bus-sized marine reptiles die and become enshrined in stone in what is now central Nevada about 230 million years ago? If the scientists from Smithsonian National Museum of Natural History And other institutions are correct, a fossil grave near an old silver mine represents an early example of migration, one of the most basic and deeply rooted of all animal behaviors.

The bones found at the Nevada site are from a giant ichthyosaur ShonisaurusIt resembled an enormous, shapeless dolphin. Shonisaurus According to a new study in Current Biology, an ancient version of today’s Pacific Ocean glided thousands of miles across an ocean called Panthalassa.

The discovery provides a rare window into prehistoric animal behaviors that aren’t always captured by individual fossils. This raises the possibility that further clues embedded in sediments and soils could provide a deeper understanding of the marine reptiles that inhabited the planet long before humans.

The earliest known Evidence of migration dates back more than 300 million years Bandringa sharks with long spoonbill-shaped noses and Prehistoric fish With armor plates. Today, billions of animals migrate, including species as diverse as hummingbirds and humpback whales, monarch butterflies and blue bison.

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

Traces of similar fossils found in other areas bear that out Shonisaurus They migrated to central Nevada from areas of modern-day California, Alaska, and New Mexico.

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If so, that behavior Prehistoric times can be linked Shonisaurus, the largest creature to sail the seas during the Triassic period, along with modern giants – blue whales are found today in the Gulf of California with their calves. Whales migrate to warmer waters to give birth, then move to colder waters rich in nutrients.

“Even after 200 million years, one has to wonder if the same ecological rules are at play. [whales and Shonisauruses]“said Nicholas D. Bienson, who works in the Department of Paleobiology at the National Museum of Natural History and is one of the authors of the new paper.

Not all experts in the field believe that Bienson and his colleagues have solved the mystery surrounding the superabundance. Shonisaurus The site is completely devoid of bones and any other ichthyosaurs.

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

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 at Berlin Ichthyosaur State Park West Union Canyon Forest Shonisaurus It grew to 50 feet, 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 long.

Charles L. Camp, a paleontologist at the University of California, Berkeley, first excavated alternating layers of limestone and mudstone at the site in the 1950s. He He immediately wondered what caused the large cluster Shonisaurus Skeletons.

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“He thought it might be a mass exodus,” says Neil B., as far as whales are concerned. Kelly, another author of the paper, is an assistant professor in Vanderbilt University’s Department of Earth and Environmental Sciences.

But fossil evidence rejects that hypothesis, showing that skeletons did exist Settled underwater far from shore.

Try to explain why Shonisaurus The bones were the only ichthyosaur fossils ever found at the Nevada site, becoming a feat of scientific sleuthing. The researchers combined 3D scanning and geochemistry with traditional tools such as museum collections, field notes, photographs and archival materials.

After eliminating other possibilities, they came to see migration as the most likely scenario. Testing of the sediment revealed the absence of mercury levels, which would indicate volcanic activity. Great mass destruction 252 million years ago.

The researchers were also able to rule out the possibility that a deadly algal bloom was poisoning the marine reptiles.

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

“Shonisaurus Certainly occurs elsewhere, so this species had a wide geographic range, and it is very reasonable that these large individuals traveled long distances, as most large marine vertebrates do today,” Kelly said. “We will be able to collect more data in the future that can test the hypotheses we present in the paper, including migration.”

At least two mysteries surround the ancient marine reptiles known as ichthyosaurs.

Sander of the University of Bonn says that ichthyosaurs, like sea turtles, were originally a type of land animal, but appear in the fossil record as fully blown open-sea animals. We don’t have the right rocks to show how ichthyosaurs got to sea.

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Also, when Shonisaurus Extinct at the end of the Triassic, about 200 million years ago, “small ichthyosaurs went extinct in the Jurassic and beyond, 88 million years ago in the Cretaceous,” Kelly said. It is unclear why the smaller ichthyosaurs survived and the giants did.

Benson can’t help but think that the final fate Shonisaurus A lesson for modern-day blue whales and other cetaceans, many of which are now classified as endangered.

“We want a world with these big ocean giants,” he said.

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