Giant Triassic Ichthyosaur is One of Biggest Animals Ever

Thursday, April 12, 2018

Giant ichthyosaurs Shonisaurus. Image credit: Nobumichi Tamura.

According to a study released this week in the journal PLoS ONE, an isolated bone from the lower jaw of a prehistoric marine reptile found in Somerset, UK, belongs to one of the largest animals ever.


Fossil collector Paul de la Salle found the 205-million-year-old (Late Triassic epoch) specimen on the beach at Lilstock, Somerset, in May 2016.

Paleontologists Dean Lomax from the University of Manchester and Professor Judy Massare of SUNY College at Brockport identified it as an incomplete bone — called a surangular — from the lower jaw of a giant ichthyosaur.

The researchers estimate the length of this specimen’s body would have been up to 85 feet (26 m) — almost the size of a blue whale.

They also compared the specimen with several ichthyosaur species, including the largest ichthyosaur known — the shastasaurid Shonisaurus sikanniensis, which is 69 feet (21 m) long.

They found similarities between the new specimen and Shonisaurus sikanniensis which suggest the Lilstock bone belongs to a giant shastasaurid-like ichthyosaur.

“As the specimen is represented only by a large piece of jaw, it is difficult to provide a size estimate, but by using a simple scaling factor and comparing the same bone in Shonisaurus sikanniensis, the Lilstock specimen is about 25% larger,” the paleontologists said.

Other comparisons suggest the Lilstock ichthyosaur was at least 65-82 feet (20-25 m).

“Of course, such estimates are not entirely realistic because of differences between species,” Lomax said.

“Nonetheless, simple scaling is commonly used to estimate size, especially when comparative material is scarce.”

In 1850, a large bone was described from the Late Triassic (208 million years old) of Aust Cliff, Gloucestershire, UK.

Four other similarly incomplete bones were also found and described. Two of them are now missing and presumed destroyed.

They have been identified as the limb bones of several dinosaurs (stegosaurs and sauropods), indeterminate dinosaurs and other reptiles.

However, with the discovery of the Lilstock specimen, this new study refutes previous identifications and also the most recent assertion that the Aust bones represent an early experiment of dinosaur-like gigantism in terrestrial reptiles. They are, in fact, jaw fragments of giant, previously unrecognized ichthyosaurs.

“One of the Aust bones might also be an ichthyosaur surangular. If it is, by comparison with the Lilstock specimen, it might represent a much larger animal,” Lomax said.

“To verify these findings, we need a complete giant Triassic ichthyosaur from the UK — a lot easier said than done.”


D.R. Lomax et al. A giant Late Triassic ichthyosaur from the UK and a reinterpretation of the Aust Cliff ‘dinosaurian’ bones. PLoS ONE 13 (4): e0194742; doi: 10.1371/journal.pone.0194742