(CNN) — The fossils of giant, extinct marine reptiles have been found in an unlikely place: within the high altitudes of the Swiss Alps.

The fossils belong to three ichthyosaurs, and they may have been some of the largest animals that ever lived on Earth, according to a new study. The ancient creatures could reach 80 tons and 65 feet (20 meters) in length, rivaling modern sperm whales.

These “fish lizards” first appeared in the ocean about 250 million years ago, looking a bit like dolphins with elongated bodies and small heads. They emerged after the Permian mass extinction wiped out more than 95% of marine species. But by 200 million years ago, the giant ichthyosaurs were extinct and only the smaller, more dolphin-like ones lived until 90 million years ago.

A study detailing the discovery published Thursday in the Journal of Vertebrate Paleontology.

So how did the remains of massive sea creatures, including one longer than a bowling alley, end up at an altitude of 9,186 feet (2,800 meters)?

About 200 million years ago, those rock layers were the floor of a wide lagoon.

“We think that the big ichthyosaurs followed schools of fish into the lagoon. The fossils may also derive from strays that died there,” said study coauthor Heinz Furrer, retired curator at the University of Zurich’s Paleontological Institute and Museum, in a statement.

But the folding of the Alps, which began 95 million years ago when the African tectonic plate began to push up against the European tectonic plate, created piles of rock layers about 30 to 40 million years ago. The fossils were “tectonically deformed,” squashed by the tectonic plate movements that pushed them to a rock formation at the top of a mountain.

“You have to be kind of a mountain goat to access the relevant beds,” said lead study author P. Martin Sander, professor of vertebrate paleontology at the University of Bonn in Germany, in a statement. “They have the vexing property of not occurring below about 8,000 feet (2,438.4 meters), way above the treeline.”

Although these creatures once ruled the seas, fossils are rare, which has created a great mystery for paleontologists. But the remains of these ichthyosaurs have shed new light on these enigmatic, extinct creatures.

One huge tooth

The fossils belonged to three different ichthyosaurs. One was about 65 feet (20 meters) long while the other was 49 feet (15 meters) long. But the most exciting find associated with these fossils is the largest ichthyosaur tooth ever found.

“This is huge by ichthyosaur standards: Its root was 60 millimeters in diameter — the largest specimen still in a complete skull to date was 20 millimeters and came from an ichthyosaur that was nearly 18 meters (59 feet) long,” Sander said.

Scientists know that smaller ichthyosaurs had teeth, but most of the giant ones were toothless, and it was assumed they fed on cephalopods, like squid, through suction.

Giant ichthyosaurs with teeth were likely similar to sperm whales and killer whales today, using their teeth to capture prey like giant squid.

But the tooth presents a challenge because it was broken off at the crown. While researchers know it was an ichthyosaur tooth because of unique features, like the infolding of dentin in the tooth root, they can’t be sure that the size of the tooth reflects the size of the animal.

“It is hard to say if the tooth is from a large ichthyosaur with giant teeth or from a giant ichthyosaur with average-sized teeth,” Sander said.

This is because, according to researchers, being giant and being a predator (with teeth) don’t align — which is why the blue whale, which weighs 150 tons and can reach 98 feet (30 meters) long, doesn’t have any teeth. Instead, it filters out tiny creatures from the water.

Meanwhile, sperm whales, which weigh 50 tons and reach 65 feet (20 meters) in length, are hunters.

“Marine predators therefore probably can’t get much bigger than a sperm whale,” Sander said.

Giants in the mountains

The fossils were first discovered during geological mapping of the Alps between 1976 and 1990. Furrer was part of the original team that recovered the fossils from the rocks, known as the Kössen Formation, and remembers holding the fossils in his hand as a doctoral student at the University of Zurich.

Over time, the fossils were largely forgotten.

“Recently, though, more remains of giant ichthyosaurs have appeared,” Furrer said. “So it seemed worthwhile to us to analyze the Swiss finds again in more detail as well.”

Ichthyosaur fossils have been found around the world, but the remains of giant species have been concentrated in North America. Finding these specimens in modern-day Switzerland expands their range.

Previous evidence has suggested that some of them could reach the size of blue whales, the largest animal in the world.

“In Nevada, we see the beginnings of true giants, and in the Alps the end,” Sander said. “Only the medium-to-large-sized dolphin — and orca-like forms survived into the Jurassic (Period),” between 145 and 201 million years ago.

Sander wonders if there are more “giant sea creatures hidden beneath the glaciers.” But these fossils help fill a knowledge gap about the giant marine lizards.

“It amounts to a major embarrassment for paleontology that we know so little about these giant ichthyosaurs despite the extraordinary size of their fossils,” Sander said. “We hope to rise to this challenge and find new and better fossils soon.”

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