Ichthyotitan severnensis lived in the Triassic seas around 202 million years ago and might have measured more than 25 m (82 feet).

Ichthyotitan severnensis. Image credit: Gabriel Ugueto.

Ichthyosaurs are dolphin-like marine reptiles known from hundreds of fossils from the time of the dinosaurs.

These creatures ranged in size from less than one to over 20 m (65 feet) in length.

All gave birth to live young at sea, and some were fast-swimming, deep-diving animals with enormous eyeballs and a so-called warm-blooded physiology.

“Ichthyosaurs first evolved during the early Triassic period around 250 million years ago,” said Dr. Dean Lomax from the University of Bristol and the University of Manchester and his colleagues.

“Within a few million years, some ichthyosaurs had evolved to reach at least 15 m (49 feet) long, and by the Late Triassic (roughly 200 million years ago), the largest ichthyosaurs had evolved, including the newly-described Ichthyotitan severnensis.”

“This reign didn’t necessarily last long, however. While some species of ichthyosaur continued to roam the oceans for millions of years, these ‘giant ichthyosaurs’ are believed to have gone extinct during the Triassic-Jurassic extinction event 200 million years ago — and this unique group of marine reptiles never again reached such a gargantuan size.”

Two fragmentary jaw bones of Ichthyotitan severnensis were collected from the uppermost Triassic Westbury Mudstone Formation in Somerset, the United Kingdom.

Based on the length of the fossils, the new species may have been a whopping 25 m long, or twice the length of a city bus.

“In 2018, my team studied and described the giant jawbone and we had hoped that one day another would come to light,” Dr. Lomax said.

“The new specimen is more complete, better preserved, and shows that we now have two of these giant bones — called a surangular — that have a unique shape and structure.”

“It is quite remarkable to think that gigantic, blue whale-sized ichthyosaurs were swimming in the oceans around what was the United Kingdom during the Triassic period.”

“These jawbones provide tantalizing evidence that perhaps one day a complete skull or skeleton of one of these giants might be found. You never know.”

The discovery of Ichthyotitan severnensis is described in a paper in the journal PLoS ONE.


D.R. Lomax et al. 2024. The last giants: New evidence for giant Late Triassic (Rhaetian) ichthyosaurs from the UK. PLoS ONE 19 (4): e0300289; doi: 10.1371/journal.pone.0300289

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