May 23, 2024

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The largest marine reptiles ever found can rival the size of blue whales

The largest marine reptiles ever found can rival the size of blue whales

Blue whales are the largest creatures to ever live on Earth. Reaching a maximum length of about 30 meters and weighing about 200 tons, they are the all-time heavyweight champions of the animal kingdom.

Now, while digging on a beach in Somerset, UK, a team of British paleontologists has found the remains of an ichthyosaur, a marine reptile that could give whales some competition. Dr Dean Lomax, a paleontologist at the University of Manchester who led the study, said: “It is quite remarkable to think that giant blue whale-sized ichthyosaurs were swimming in the oceans around the UK during the Triassic.

Giant jaw bones

Ichthyosaurs were found in the seas during much of the Mesozoic Era, appearing 250 million years ago. They had four paddle-like limbs, vertical tail fins extending downward in most species, and generally looked like large reptilian dolphins with narrow, elongated jaws lined with teeth. Some of them were really huge. The largest ichthyosaur skeleton to date was found in British Columbia, Canada, measuring 21 meters long, and belonged to a particularly massive ichthyosaur called Schonisaurus sikanensis. But it looks like they could get even bigger than that.

What Lomax's team found in Somerset was a rectangular, long, curved bone that all reptiles have in the upper part of the lower jaw behind the teeth. The length of the bone is 2.3 meters, compared to the rectangular bone found in Schonisaurus sikanensis The skeleton was 25 percent larger. Using a simple scale and assuming the same body dimensions, Lomax's team estimated the size of this newly discovered ichthyosaur at between 22 and 26 metres, making it the largest marine reptile ever. But there was something else.

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By examining the rectangular shape, the team found no signs of the external foundation system (EFS), which is a strip of tissue found in the outer shell of the bone. Its formation represents a slowdown in bone growth, indicating skeletal maturation. In other words, the giant ichthyosaur was likely young and still growing when it died.

Correction of the past

In 1846, five large bones were found on the Aust Cliff near Bristol in southwest England. Excavated from the Upper Triassic rock formation, they have been called “dinosaur limb bone shafts” and are on display at the Bristol Museum, where one of them was destroyed by bombing during World War II.

But in 2005, Peter M. Galton, a British paleontologist then working at the University of Bridgeport, noticed something strange in one of the remaining Aust Cliff bones. He described it as “Unusual foramen” He suggested it was a feeder corridor. Later studies generally continued to attribute these bones to dinosaurs but pointed to things like Unusual microstructure It was hard to explain.

According to Lomax, all this confusion was because the Aust Cliff bones did not belong to dinosaurs and were not parts of limbs. He noted that the shape, shape and microstructure of the nutrient foramen match the ichthyosaur bone found in Somerset. The difference was that EFS – a marker of mature bone – was present on the Aust Cliff bones. If Lomax is right and they were indeed parts of the ichthyosaur's peripheral form, then they belong to an adult individual.

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Using the same sizing technique applied to the Somerset oblong whale, Lomax estimated that this developing individual was more than 30 meters long, slightly larger than the largest confirmed blue whale.

Extinction looms

“It is likely that Late Triassic ichthyosaurs reached the known biological limits of vertebrates in terms of size. Much remains unknown about these giants, but one fossil at a time, we will be able to To reveal their secrets.

But this mysterious monster did not last long. The rectangular bone found in Somerset was buried under a layer filled with seismic and tsunami rocks that mark the beginning of the end-Triassic mass extinction event, one of five mass extinctions in Earth's history. the Ichthyotic severnensisas Lomax and his team called the species, probably managed to reach incredible size but were wiped out soon after.

However, the mass extinction at the end of the Triassic was not the end of all ichthyosaurs. They survived but never reached similar sizes again. They faced competition from plesiosaurs and sharks that were more agile and swam much faster, and they likely competed for the same habitats and food sources. The last known ichthyosaurs became extinct about 90 million years ago.

PLOS ONE, 2024. DOI: 10.1371/journal.pone.0300289