Ichthyosaurs began to fade from our oceans around 200 million years ago in the late Triassic, but as parts of the globe folded to make what we now call the Alps, some of their remains were scooped along for the ride. The quirks of geology mean scientists have been finding prehistoric marine reptile specimens thousands of meters above sea level, and a new paper demonstrates they were fanged monsters.

Gigantic ichthyosaurs only evolved in the final chapters of these prehistoric reptiles’ time on Earth, at which point certain species grew to longer than a bowling alley and weighed more than 80 tons. However, despite their enormous size humans have found little in the way of remains for these animals. "Why that is remains a great mystery to this day," said Prof. Dr Martin Sander at the Institute of Geosciences at the University of Bonn in a statement.

However, fossilized remains retrieved in the Alps may go some way to explaining where these ocean giants have been hiding for the past ~200 million years. Is there a treasure trove of marine fossils to be found beneath the glaciers? Quite possibly.

Now, a new paper in the Journal of Vertebrate Paleontology has revisited the remains of three specimens collected between 1976 and 1990 in the Swiss Alps, 2,800 meters (9,187 feet) above sea level, to see what we can learn from these high-altitude fossils. The remains suggest that these ichthyosaurs were among the largest animals to have ever lived.

The glut of ancient remains includes ribs, vertebrae, and the largest ichthyosaur tooth ever found.

"This [tooth] is huge by ichthyosaur standards,” said Sander. “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."

However, estimate the ichthyosaur’s length from teeth alone is a tricky subject because the toothiest species are often not the biggest. This is because marine predators that need sizable gnashers will use more energy moving to hunt so are limited in their body size, while giant filter feeders can cruise along as absolute units slowly scooping up smaller prey.

Even if it was a modestly-sized ichthyosaur it would’ve been a fearsome sight at sea with the biggest teeth known to science for this group of animals. Other record-breaking finds from the Alps include the largest trunk vertebra in Europe, which gives even the 21-meter-long Shastasaurus sikkanniensis, the largest marine reptile fossil ever found, a run for its money.

As the authors continue to work to close the gap in our understanding of some of Earth’s largest marine predators, they remain optimistic that fresh insights into the life and size of ichthyosaurs are within our grasp.

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