Thalassodraco etchesi

Artist’s impression of Thalassodraco etchesi

Megan Jacobs/Baylor University

A newly identified ancient reptile that looks like a cross between a dolphin and a shark is unusual enough to be classified as part of a new animal group. It lived 150 million years ago and probably dived deep in the sea to capture squid and other slippery prey.

The reptile, dubbed Thalassodraco etchesi, had enormous eyes and a large rib cage, suggesting it had great lung capacity and the ability to see in dark ocean depths. It is an ichthyosaur, a group of extinct marine reptiles, but as it is much smaller than other species and has other distinguishing features, researchers have classified it in its own genus.

The species was identified from an exceptionally well-preserved fossil found near Kimmeridge Bay in the UK. The name is derived from Thalasso for sea in Greek, draco for dragon in Latin and etchesi in honour of the amateur collector who discovered the fossil in 2009, Steve Etches.

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“People have been excavating ichthyosaurs in this area for 200 years, but finding a new species – let alone a new genus – is very rare,” says Megan Jacobs at Baylor University in Waco, Texas.

Jacobs and her colleague David Martill at the University of Portsmouth, UK, took high-resolution photographs of the fossil. Their analysis revealed an unknown, long-mouthed reptile with a shark-like tail and dorsal fin that lived entirely underwater and would come up for air like dolphins do, Jacobs says.

Only one side of the fossil’s jaw is visible, and the upper part is better preserved than the lower. From this quarter jaw, the pair counted about 50 small, smooth teeth, suggesting the animal had 200 such teeth, unlike most other late Jurassic ichthyosaurs, which usually had a smaller number of large, robust teeth. The tiny teeth probably acted as “cages” to trap prey such as a squid, says Jacobs.

The animal also had strong ligaments across its neck, back and ribs that might have also attached to the bony nodules on its head, making for a stiff head and body. Its eyes were particularly wide for its skull, and its rib cage was notably broad. Even so, Thalassodraco etchesi would have measured only about 2.5 metres long – quite small compared with most other ichthyosaurs from the same epoch, says Jacobs.

Journal reference: PLoS One, DOI: 10.1371/journal.pone.0241700

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