Huge new ichthyosaur, one of the largest animals ever discovered in the Alps


The habitat and animals that have been found with giant ichthyosaurs. Credit: Heinz Furrer

Paleontologists have discovered sets of fossils depicting three new ichthyosaurs that may have been among the largest animals to ever live, reports a new paper in the peer-reviewed Journal of Vertebrate Paleontology.

Unearthed in the Swiss Alps between 1976 and 1990, the find includes the largest ichthyosaur tooth ever found. The width of the tooth root is twice as large as any known aquatic reptile, with the previous largest belonging to a 15-meter-long ichthyosaur.

Other incomplete skeletal remains include Europe’s largest trunk vertebra which shows another ichthyosaur rivaling the largest marine reptile fossil known today, the 21-meter-long Shastasaurus sikkanniensis from British Columbia, Australia. Canada.

Dr. Heinz Furrer, co-author of this study, was part of a team that recovered the fossils during geological mapping of the Kössen Formation in the Alps. More than 200 million years ago, rock layers still covered the seabed. With the folding of the Alps, however, they had found themselves at an altitude of 2,800 meters.

Now a retired curator at the Paleontological Institute and Museum of the University of Zurich, Dr Furrer said he was delighted to have discovered “the longest ichthyosaur in the world; with the thickest tooth found so far. day and the largest trunk vertebra in Europe”.

And lead author P. Martin Sandler, from the University of Bonn, hopes “maybe there are more remains of giant sea creatures hiding under the glaciers.”

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

These monstrous 80-tonne reptiles patrolled Panthalassa, the global ocean surrounding the supercontinent Pangea during the Upper Triassic, around 205 million years ago. They also made inroads into the shallow Tethys seas on the eastern side of Pangea, as the new findings show.

Ichthyosaurs first appeared following the Permian extinction event around 250 million years ago, when some 95% of marine species disappeared. The group reached its greatest diversity in the Middle Triassic, and a few species persisted into the Cretaceous. Most were much smaller than S. sikanniensis and the similar-sized species described in the article.

Roughly the shape of contemporary whales, ichthyosaurs had elongated bodies and erect tail fins. Fossils are concentrated in North America and Europe, but ichthyosaurs have also been found in South America, Asia, and Australia. The giant species have mostly been unearthed in North America, with rare finds from the Himalayas and New Caledonia, so the discovery of other mastodons in Switzerland represents an expansion of their known range.

Huge new ichthyosaur, one of the largest animals ever discovered in the Alps

Heinz Furrer with the largest ichthyosaur vertebra. Credit: Heinz Furrer

However, so little is known about these giants that there are only ghosts. Tantalizing evidence from the UK, consisting of a huge toothless jawbone, and New Zealand suggests some of them were the size of blue whales. An 1878 paper credibly describes an ichthyosaur vertebra 45 cm in diameter from there, but the fossil never arrived in London and may have been lost at sea. Sander notes that “it represents a “A major embarrassment to paleontology that we know so little about these giant ichthyosaurs despite the extraordinary size of their fossils. We hope to meet 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,” says Sander, who also co-authored a paper last year about an early giant ichthyosaur from Fossil Hill in Nevada. “Only medium to large dolphin and orca forms survived into the Jurassic.”

While the smallest ichthyosaurs generally had teeth, most known gigantic species appear to have been toothless. One hypothesis suggests that rather than grabbing their prey, they fed by sucking. “The large eaters among the giants must have fed on cephalopods. Those with teeth likely fed on smaller ichthyosaurs and large fish,” Sander suggests.

Giant marine reptiles at an altitude of 2,800 meters

Martin Sander and Michael Hautmann examine the layers discovered on the southern slope of Schesaplana, on the border between Graubünden and Vorarlberg. Credit: © Jelle Heijne/University of Bonn

The tooth described by the article is only the second example of a giant ichthyosaur with teeth, the other being the 15-meter-long Himalayasaurus. These species probably occupied similar ecological roles as modern sperm whales and killer whales. Indeed, the teeth are curved inwards like those of their mammalian successors, indicating a mode of prehension feeding conducive to the capture of prey such as giant squid.

“It’s hard to tell if the tooth is from a large ichthyosaur with giant teeth or a giant ichthyosaur with medium-sized teeth,” Sander ironically acknowledges. Because the tooth described in the article was broken off at the crown, the authors were unable to confidently assign it to a particular taxon. However, a peculiarity of the dental anatomy allowed researchers to identify it as belonging to an ichthyosaur.

“Ichthyosaurs have a feature in their teeth that is almost unique among reptiles: the folding of dentin in the roots of their teeth,” says Sander. “The only other group to show this are the monitor lizards.”

Giant marine reptiles at an altitude of 2,800 meters

The root of the found tooth has a diameter of 60 millimeters. This makes it the thickest ichthyosaur tooth found to date. Credit: © Rosi Roth/University of Zurich

The two sets of skeletal remains, which consist of one vertebra and ten rib fragments, and seven associated vertebrae, have been assigned to the family Shastasauridae, which contains the giants Shastasaurus, Shonisaurus and Himalayasaurus. Comparison of vertebrae from one set suggests that they may have been the same size or slightly smaller than those of S. sikkaniensis. These measurements are slightly distorted by the fact that the fossils were tectonically deformed, that is, they were literally crushed by the movements of the tectonic plates whose collision led to their displacement from an ancient seabed. on top of a mountain.

Known as the Kössen Formation, the rocks from which these fossils derive were once found at the bottom of a shallow coastal area – a very wide lagoon or shallow basin.

This adds to the uncertainty surrounding the habits of these animals, whose size indicates their ability to reach the depths of the ocean. “We believe that large ichthyosaurs followed schools of fish into the lagoon. The fossils may also be from wandering animals that died there,” Furrer suggests.

“You have to be a kind of mountain goat to access the beds concerned,” laughs Sander. “They have the vexing property of not occurring below about 8,000 feet, well above the tree line.”

“95 million years ago, the northeastern part of Gondwana, the African plate (of which the Kössen Formation was a part), began to push against the European plate, ending in the formation of very complex stacks of different rock units (called ‘napkins’) in the Alpine orogeny about 30 to 40 million years ago,” says Furrer. This is how these intrepid researchers found themselves digging into the frozen rocks of the Alps and bringing pieces of ancient sea monsters back almost to sea level to enter them into the scientific archives.

Fish-like marine reptile buried in its own fat in southern Germany 150 million years ago

More information:
Late Triassic giant ichthyosaurs from the Kössen Formation of the Swiss Alps and their paleobiological implications, Journal of Vertebrate Paleontology (2022). DOI: 10.1080/02724634.2021.2046017

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