Massive marine ichthyosaur fossils found high in the Alps

There was a time when the rocks high up in the Alps of Switzerland actually formed part of the bed of a shallow sea or lagoon far below. During that time, some 200 million years ago, animals that swam in the shallow, coastal seas, died and sank to the bottom, becoming fossilized as the sediments turned to rock. When the African and European tectonic plates collided, however, these sediments were pushed upwards and today form part of the Alps, almost 3,000 meters above Earth’s surface. 

During the geological mapping of these rocks, which are known today as the Kössen Formation, scientists unearthed some remarkable fossils high up in the Swiss Alps. These include the remains of three new ichthyosaurs that are thought to be among the largest animals ever to have lived. Details of these findings, excavated by paleontologists between 1976 and 1990, are published today in a paper in the Journal of Vertebrate Paleontology. 

Ichthyosaurs are ancient, marine-dwelling reptiles that first appeared in the fossil record around 250 million years ago. They evolved from a group of land reptiles that returned to the sea, and gradually came to resemble modern dolphins and whales as they adapted to the marine environment. Their fossils have been found in many locations around the world and represent the remains of thousands of different individuals.

The recently published findings from the Alps include details of the largest ichthyosaur tooth ever found. The width of the tooth at its root is twice the size of the tooth from a 15-meter-long ichthyosaur that previously held this record. Among the find is also the largest trunk vertebra ever found in Europe, which indicates another ichthyosaur individual that was probably at least the size of the largest marine reptile fossil known today, the 21-meter long Shastasaurus sikkanniensis from British Columbia in Canada. 

Dr. Heinz Furrer, retired curator at the University of Zurich’s Paleontological Institute and Museum and co-author of the study said he was delighted to have uncovered “the world’s longest ichthyosaur; with the thickest tooth found to date and the largest trunk vertebra in Europe!” 

Study lead author P. Martin Sander of the University of Bonn hopes that maybe there are more remains of the giant sea creatures hidden beneath the glaciers.

“Bigger is always better,” said Sander. “There are distinct selective advantages to large body size. Life will go there if it can. There were only three animal groups that had masses greater than 10–20 metric tons: long-necked dinosaurs (sauropods); whales; and the giant ichthyosaurs of the Triassic.”

Ichthyosaurs have anatomical features that resemble those of fish, reptiles and marine mammals, and their fossils have been variously identified during the past two centuries as belonging to crocodiles, humans, giant amphibious lizards and fish. Most of them were nowhere as large as the latest specimens unearthed in the Alps, but all were thought to be marine predators that prowled the world’s oceans in search of prey. 

Ichthyosaurs first emerged after the Permian extinction some 250 million years ago, when about 95 percent of marine species died out. The group reached its greatest diversity in the mid-Triassic and a few species persisted into the Cretaceous Period. Their fossils have been found mostly in North America and Europe, but also in South America, Asia, and Australia. Giant species have mostly been located in North America, so the discovery of the new oversized individuals in Switzerland represents an expansion of their known range.

Despite the abundance of ichthyosaur fossils, very little is known about the habits of these giant species. “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.”

These new specimens probably represent the last of the leviathans. “In Nevada, we see the beginnings of true giants, and in the Alps the end,” said Sander, who also co-authored a paper last year about an early giant ichthyosaur from Nevada’s Fossil Hill. “Only the medium-to-large-sized dolphin- and orca-like forms survived into the Jurassic.”

The large fossilized tooth found in the Alps could easily be identified as belonging to an ichthyosaur because of a peculiarity in its dental anatomy. “Ichthyosaurs have a feature in their teeth that is nearly unique among reptiles: the infolding of the dentine in the roots of their teeth,” explained Sander. “The only other group to show this are monitor lizards.”

Smaller ichthyosaurs typically had conical teeth, similar to those of crocodiles, but the larger specimens appear to have been toothless. The large tooth described in the current paper is only the second instance of a giant ichthyosaur with teeth. Sander suggests that these species probably fed on smaller ichthyosaurs and large fish and occupied similar ecological niches to modern sperm whales and killer whales. Indeed, the teeth are curved inwards like those of their mammalian successors, indicating a grasping mode of feeding conducive to capturing prey such as giant squid.

Apart from the fossilized tooth, the two sets of skeletal remains, which consist of vertebrae and rib fragments, have been classified in the family Shastasauridae, which contains the other ichthyosaur giants Shastasaurus, Shonisaurus, and Himalayasaurus. Comparison of the vertebrae from one fossilized skeleton suggests that the animal may have been the same size or slightly smaller than the 21-meter long S. sikkanniensis. 

The measurements are, however, probably inaccurate because the fossils have been squashed and deformed by pressure as the tectonic plates collided and the rock in which the fossils were embedded was forced from the former sea or lagoon floor to the top of a mountain.

Most ichthyosaurs are thought to have inhabited the open oceans where their large body size would have been a useful adaptation. The fact that the three individuals in the current study died in shallow coastal or lagoon waters, where their large bodies would have been a disadvantage, adds more understanding of their behaviour. “We think that the big ichthyosaurs followed schools of fish into the lagoon. The fossils may also derive from strays that died there,” suggests Furrer.

The researchers worked under taxing conditions while excavating these new ichthyosaur finds. They had to pick through frozen rocks, high up in the Alps, in order to retrieve the fossilized pieces of the marine giants and bring them down almost to sea level again for scientific processing. 

“You have to be kind of a mountain goat to access the relevant beds,” said Sander. “They have the vexing property of not occurring below about 8,000 feet, way above the treeline.”

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By Alison Bosman, Earth.com Staff Writer