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About 246 million years ago, a sea lizard with a skull the size of a grand piano died out in the ancient ocean that is now Nevada. It was an ichthyosaur, and its body was most likely the size of a modern sperm whale.

Although ichthyosaurs and whales are separated by several hundred million years, they have much in common. Both are descendants of animals that return to the sea after being on land. Both developed huge bodies that made them the largest creatures of the seas when they lived. Both were born young.

But whales had to live in the ocean for 45 million years to develop their largest body size. This new species of giant ichthyosaurs appeared just three million years after the first ichthyosaurs landed in the seas, suggesting that sea lizards had evolved extremely rapidly with large bodies. This early giant lived before the small dinosaurs. Widespread Overland; The terrestrial world would not see a giant of this size for another 40 million years, with the emergence of sauropods in the Jurassic.

A team of scientists has identified the new ichthyosaur they call Cymbospondylus youngorum and reconstructed their food web. An article published Thursday in the journal Science.

“It’s definitely a surprise,” said Benjamin C. Moon, an ichthyosaurus researcher at the University of Bristol in England who was not involved in the study. “It’s not a long time to suddenly master such large dimensions, almost only when you’re in the water.”

Lars Schmitz, a Scripps College paleontologist in California, said the ichthyosaur was first discovered in 1998 in Fossil Hill, Nev. an author of the article. “Very tiring,” said Dr. Schmitz. “Getting him off the field was a huge effort.”

Dr. According to Schmitz, the fossil’s size was modest, even half-buried—the reptile’s humerus eclipsed the rock hammer. “It makes you feel so small,” he said.

In 2015, researchers finished excavating all that was left of the ichthyosaur (skull, shoulder and arm bones) and sent the fossil for preparation at the Los Angeles County Museum of Natural History. “It was mind-blowing to see that,” said Jorge Velez-Juarbe, assistant curator of marine mammals at the museum and another author of the paper.

Based on the size of its skull, the authors estimate that the ichthyosaur likely grew to be as tall as 55 feet. Dr. Moon said that might be a bit of an overestimate and suggested the more conservative 45 to 50 feet. “It’s the same whaling field of today’s whales,” they said. “There was nothing around as big as these things.”

Ichthyosaur swam in Triassic seas soon after. Worst mass extinction in Earth’s history, which killed 81 percent of marine life. The researchers had a question: “How did it get so big?” Dr. said Schmitz.

In modern oceans, many giant whales are filter feeders that filter krill and other plankton from the plates of their mouths. But this abundance of modern plankton that made whales so large was absent when ichthyosaurs lived, suggesting that ancient oceans simply did not have enough energy to support such a large predator.

Eva Maria Griebeler, an evolutionary ecologist at the Johannes Gutenberg University Mainz in Germany and author of the paper, studied fossils collected from the Nevada region to reconstruct the food webs of the ichthyosaur’s ancient seas. Dr. Griebeler said he and other researchers consulted with teeth and stomach contents, as well as size differences between food web members, to understand who ate who. The ichthyosaur’s sharp fangs indicate that it preyed on fish and squid, and perhaps even smaller marine reptiles.

Dr. “Count the number and size of predators at the top, the number and size of their prey, and see if those numbers add up,” Moon said, explaining the model.

Dr. Griebeler’s model, ammonites alone provided enough energy to support the giants. They didn’t feed directly on ammonites, but ate other creatures that squashed crustacean cephalopods: a shorter, less diverse food web that still offers the same energy input as modern oceans. Dr. “This is surprising,” the Griebes said. “This food web has a completely different structure than existing ones.”

Lene Liebe Delsett, a paleontologist at the Smithsonian National Museum of Natural History who was not involved in the research, lauded the study’s food web model as a “first step” towards understanding the Triassic ocean environment. “There’s still a lot we don’t know about these early ecosystems,” he said.

And how did ichthyosaurs manage to balloon in as little as three million years, while whales took 45 million years? Dr. Velez-Juarbe said he couldn’t think of any other marine vertebrate that had developed large body sizes as quickly as ichthyosaurs. But the authors offer a number of possible explanations, including that the reptiles’ large eyes and endotherm may have made them better hunters. Or perhaps the mass extinction provided an opportunity to diversify life, reducing the number of competing predators.

Dr. Delsett, by A perspective accompanying new paper in science He, along with Nick Pyenson, a paleontologist at the Smithsonian, believes that research on extinct sea giants can offer insight into the conservation of whales.

“They went through a mass extinction and survived; Dr. “They experienced climate change for ichthyosaurs,” Delsett said. “It’s easier to take better care of the oceans today if you can understand marine evolution.”