Argentine Paleontologist Marta Fernandez presents a fossil of a Ichthyosaur at the headquarters of the museum in Colunga, northern Spain, in this file picture from 2015. Picture: REUTERS/ELOY ALONSO
Argentine Paleontologist Marta Fernandez presents a fossil of a Ichthyosaur at the headquarters of the museum in Colunga, northern Spain, in this file picture from 2015. Picture: REUTERS/ELOY ALONSO

Washington — A jawbone fossil found on a rocky English beach belongs to one of the biggest marine animals on record, a type of seagoing reptile called an ichthyosaur that scientists estimated at up to 26m long — approaching the size of a blue whale.

Scientists said on Monday this ichthyosaur, which appears to be the largest marine reptile ever discovered, lived 205-million years ago at the end of the Triassic period, dominating the oceans just as dinosaurs were becoming the undisputed masters on land. The bone, called a surangular, was part of its lower jaw.

The researchers estimated the animal’s length by comparing this surangular to the same bone in the largest ichthyosaur skeleton ever found, a species called Shonisaurus sikanniensis from British Columbia that was 21m long. The newly discovered bone was 25% larger.

"This bone belonged to a giant," said University of Manchester paleontologist Dean Lomax. "The entire carcass was probably very similar to a whale fall in which a dead whale drops to the bottom of the sea floor, where an entire ecosystem of animals feeds on the carcass for a very long time. After that, bones become separated, and we suspect that’s what happened to our isolated bone."

Fossil collector Paul de la Salle, affiliated with the Etches Collection in Dorset, England, found the bone in 2016 at Lilstock on England’s Somerset coast along the Bristol Channel. "The structure was in the form of growth rings, like that of a tree, and I’d seen something similar before in the jaws of late Jurassic ichthyosaurs," he said.

Ichthyosaurs swam the world’s oceans from 250-million years ago to 90-million years ago, preying on squid and fish. The biggest were larger than other huge marine reptiles of the dinosaur age like pliosaurs and mosasaurs. Only today’s filter-feeding baleen whales are larger. The blue whale, up to about 30m long, is the biggest animal alive today and the biggest marine animal ever.

The ichthyosaur appears to have belonged to a group called shastasaurids. Because the remains are so incomplete, it is unclear whether it represents a new ichthyosaur genus or is a member of a previously identified genus, said paleontologist Judy Massare of the State University of New York College at Brockport.

The research was published in the journal PLOS ONE.

Reuters

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