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Jawbone fossil found in Somerset belongs to giant sea monster

11 April 2018

Dinosaurs may hog the Mesozoic spotlight, but some of the neatest finds of recent note in paleontology come from under the sea: a very pregnant ichthyosaur and the partial remains of another that was a supersized specimen (think blue whale territory).

De La Salle declared that, at first, the piece of maxillary bone seemed to him like a rock or something similar but after he acknowledged a channel and a bone arrangement in the sample, he immediately considered that his onto something big there. Ichthyosaurs are mammoth marine reptiles that roamed the oceans along with the dinosaurs and preyed on prehistoric squid and fish.

The bone fragments of the long-extinct predator were spotted on the beach at Lilstock, Somerset, in May 2016, and together they measure about 96 centimetres, said the report in the journal PLOS One. "I also contacted Dr. Ramues Gallois, a geologist who visited the site and determined the age of the specimen stratigraphically".

The jawbone specimen found in Lilstock, Somerset, was a large but incomplete jawbone, which comes in five fractured pieces and preserved in three dimensions. The bone would have made up only a portion of the entire skull.

Researchers estimated the animal's length by comparing the surangular with the same bone in the largest ichthyosaur skeleton ever found - a species called Shonisaurus sikanniensis from British Columbia that was 21 meters (69 feet) long.

Based on their comparison, the Lilstock ichthyosaur is most likely between 20 to 25 meters or 67 to 82 feet. They found out that their bone was 25 percent deeper than that of the Shonisaurus sikanniensis.

Though the earliest ichthyosaurs were more slithery sorts, as they evolved they developed a basic built-for-speed body shape while at the same time diversifying into different species that specialized in various niches (although determining exactly how many species of ichthyosaur there were remains a point of contention). "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. On top of that, la Salle may have solved a long-standing mystery about similar bones found in the UK. Two of them are now missing and presumed destroyed. However, they were able to use a scaling factor to determine the size of the ichthyosaur.

Paleontologist Dean Lomax, of the University of Manchester, said: "This bone belonged to a giant". If it is, by comparison with the Lilstock specimen, it might represent a much larger animal.

However, paleontologists won't know for sure until more fossil remains are uncovered that would shed light on what a complete giant early Mesozoic ichthyosaur from the United Kingdom actually looked like.

Jawbone fossil found in Somerset belongs to giant sea monster