Scientists have unearthed the remains of a gigantic 200 million-year-old sea monster, which could be the largest marine reptile ever discovered.
The new creature is part of a group called ichthyosaurs, which were among the dominant marine predators during the Mesozoic era (251.9 million to 66 million years ago). The newly described species lived during the late Triassic period (251.9 million to 201.4 million years ago).
Ichthyosaurs had already reached massive sizes by the beginning of the Mesozoic, but it was not until the end of the Triassic that the largest species emerged.
While the Mesozoic is known as the age of dinosaurs, ichthyosaurs were not themselves dinosaurs. Instead, they evolved from another group of reptiles. Their evolutionary path closely mirrors that of whales, which evolved from land mammals that later returned to the sea. And like whales, they breathed air and gave birth to young.
The newly discovered ichthyosaur species was unearthed in pieces between 2020 and 2022 at Blue Anchor, Somerset in the United Kingdom. The first piece of the fossil was noticed on top of a rock on the beach, indicating that a passerby had found it and placed it there for others to examine, the researchers explain in the paper. The researchers published their results on April 17 in the journal PLOS One.
The remains of the reptile consist of a series of 12 fragments from a surangular bone, found in the upper part of the lower jaw. Researchers estimate that the bone was 2 meters long and that the living animal was approximately 25 meters long.
Researchers named the sea monster Ichthyotitan severnensis, meaning Severn giant lizardfish, named after the Severn estuary where it was found. The team believes this is not just a new species but an entirely new genus of ichthyosaur. More than 100 species are already known.
A number of rib fragments and a coprolite, or fossilized feces, have also been found in the area, but they have not been definitively attributed to the same animal.
The sediments in which these specimens were found contained rocks indicating that earthquakes and tsunamis occurred around this time, suggesting that this species lived during a period of intense volcanic activity that could have led to a mass extinction event at the end of the Triassic, according to the researchers.
A similar specimen was discovered at Lilstock, Somerset in 2016 and described in 2018. Both were found in what is known as the Westbury Mudstone Formation, less than 10 kilometers from each other. This ichthyosaur is estimated to have measured up to 85 feet (26 m) long, although the authors of the latest study estimate that it was slightly smaller.
The previous contender for the title of largest marine reptile was another ichthyosaur, Shonisaurus sikanniensiswhich measured up to 69 feet (21 m) long. S. sikanniensis appeared 13 million years earlier than I. severnensis and was found in British Columbia, making it unlikely that the new discovery represents another specimen of the previously known species.
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An equally massive ichthyosaur called Himalayasaurus tibetensiswhich may have reached a length of 49 feet (15 m), was discovered in Tibet and described in 1972. It dates from the same period, meaning it is also probably not the same species as the new discovery.
I. severnensis was probably one of the last giant ichthyosaurs, researchers say. Ichthyosaurs persisted until the Cenomanian Age (100.5 million to 93.9 million years ago) of the Late Cretaceous (100.5 million to 66 million years ago). They were eventually supplanted by plesiosaurs, long-necked marine reptiles that became extinct at the end of the Cretaceous, along with all non-avian dinosaurs.
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