Ichthyosaurs: Marine reptile tooth found in Swiss Alps is largest ever discovered

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An ichthyosaur tooth fossil with a root 6 centimetres wide is so large that it may mean that the marine reptiles were even larger than we previously thought 



Life



28 April 2022

200 million year old deposits of the precursor of the Mediterranean Sea have been preserved in the Swiss High Alps. Whale-sized ichthyosaurs came from the open sea only occasionally into shallower water.

Ichthyosaurs dominated the seas 200 million years ago

Jeannette Rüegg/Heinz Furrer, University of Zurich

Around 200 million years ago, dinosaurs roamed the land, pterosaurs took to the sky and ichthyosaurs dominated the sea. The marine reptiles were fearsome predators, with individuals ranging from the size of a small porpoise to a massive sperm whale. Now, palaeontologists have discovered the largest ichthyosaur tooth to date, suggesting these creatures were even bigger than previously thought.

Ichthyosaurs were adept hunters and swimmers that conquered nearly every aquatic corner of the globe. During their heyday of the Late Triassic and Early Jurassic periods, they took many forms, including both toothed and toothless species.

There are just a handful of ichthyosaur specimens around the world, with a giant black tooth and a collection of vertebrae and ribs from the Swiss Alps among them. Martin Sander at the University of Bonn in Germany first saw the Swiss fossils when they were unearthed more than 30 years ago, but they were shelved because new, seemingly better-quality ichthyosaur fossils were being found in British Columbia.

When Sander and his colleague Heinz Furrer at the University of Zurich in Switzerland decided to take another look at the fossils, they realised they had evidence of three of the largest ichthyosaurs to date.

Since the age of the ichthyosaurs, the planet has undergone a dramatic tectonic change, transforming what was once a shallow sea floor into jagged, rocky mountains known as the Kössen Formation. That shift transported the remains of the marine reptiles to an altitude of 2800 metres above sea level.

The crown jewel of their discovery is an ichthyosaur tooth with a root around 6 centimetres wide, which Sander says is the largest known specimen “by far”. While palaeontologists only have the bottom portion of the tooth, “these big roots usually mean there is a big crown”, says Sander. Vertebrae and rib fragments from one of the other individuals suggest that the reptile was around 20 metres in length – stretching longer than a bowling lane.

The root of the tooth found has a diameter of 60 Millimeters. This makes it the thickest ichthyosaur tooth found so far.

The root of the tooth found has a diameter of 6 centimetres

Rosi Roth/University of Zurich

Though the giant tooth infers a giant owner, Sander and Furrer aren’t sure if the tooth is from a massive ichthyosaur or a smaller one with particularly large teeth. However, they are certain that it is from an ichthyosaur. “We are fortunate in that ichthyosaurs have these strange tooth roots,” says Sander. “That grooved appearance that tells us very clearly… even with an incomplete tooth like that, there is absolutely no question of what it is.”

Journal reference: The Journal of Vertebrate Paleontology, DOI: 10.1080/02724634.2021.2046017

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