Achi news desk-
Blue whales have been considered the largest creatures to ever live on Earth. With a maximum length of almost 30 meters and weighing almost 200 tonnes, they are the undisputed heavyweight champions of the animal kingdom of all time.
Now, while digging on a beach in Somerset, UK, a team of British palaeontologists found the remains of an ichthyosaur, a marine reptile that could give the whales some competition. “It’s pretty amazing to think that huge, blue whale-sized ichthyosaurs were swimming in the oceans around what was the UK during the Triassic Period,” said Dean Lomax, a palaeontologist at the University of Manchester who led the study.
Huge jawbones
Ichthyosaurs were found in the seas throughout much of the Mesozoic era, appearing as early as 250 million years ago. They had four arms that looked like oars, vertical tail fins that extended downward in most species, and generally looked like large, reptilian dolphins with elongated narrow jaws lined with teeth. And some of them were really huge. The largest ichthyosaur skeleton to date has been found in British Columbia, Canada, measuring 21 metres, and belonging to a particularly huge ichthyosaur called Shonisaurus sikanniensis. But it seems they could go even bigger than that.
What Lomax’s team found in Somerset was a surangular, a long, curved bone that all reptiles have at the top of the lower jaw, behind the teeth. The bone measured 2.3 meters – compared to the surangular found in the Shonisaurus sikanniensis skeleton, it was 25 percent more. Using simple scaling and assuming the same body proportions, Lomax’s team estimated the size of this newly discovered ichthyosaur to be somewhere between 22 and 26 meters, which would make it the largest marine reptile ever. But there was one more thing.
When examining the sprangular, the team found no signs of the external basal system (EFS), which is a band of tissue present in the outer cortex of the bone. Its formation marks the slowing down of bone growth, which indicates skeletal maturity. In other words, the giant ichthyosaur was most likely young and still growing when it died.
Correcting the past
In 1846, five large bones were found at Cloch Aust near Bristol in south-west England. Excavated from the upper Triassic rock formation, they were called “dinosaur arm bone shafts” and were displayed in Bristol Museum, where one was destroyed by bombs during the Second World War.
But in 2005, Peter M. Galton, a British paleontologist who was then working at the University of Bridgeport, noticed something strange in one of the remaining Aust Cliff bones. He described it as an “unusual foramen” and suggested it was part of nutrients. Later studies generally continued to attribute those bones to dinosaurs but pointed to things like unusual microstructure that were difficult 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 pointed out that the morphology of the nutritional foramen, its shape, and the microstructure matched the ichthyosaur bone found in Somerset. The difference was that the EFS – a mark of mature bones – was present on the bones of Clogwyn Aust. If Lomax is correct and they are in fact part of the surangular ichthyosaurs, they belonged to a grown individual.
And using the same scaling technique used for the Somerset surangular, Lomax estimated this individual to have grown to over 30 meters in length – slightly larger than the largest confirmed blue whale.
Extinction on the horizon
“Late Triassic ichthyosaurs likely reached the known biological limits of vertebrate size. So much about these giants is still shrouded in mystery, but one fossil at a time, we will be able to unravel their secrets,” said Marcello Perillo, a member of the Lomax team responsible for examining the internal structure of the bones.
However, this mysterious beast did not last long. The swankular bone found in Somerset was buried just below a layer full of seismic and tsunami rocks that marks the start of the late Triassic mass extinction event, one of the five mass extinctions in Earth’s history. The Severnensis Ichthyotianas Lomax and his team named the species, apparently managed to reach an unbelievable size but was wiped out shortly afterwards.
The end-Triassic mass extinction was not the end of all ichthyosaurs, though. They survived but never reached similar sizes again. They faced competition from plesiosaurs and sharks who were more agile and swam much faster, and are likely to compete for the same habitats and food sources. The last known ichthyosaurs became extinct around 90 million years ago.
PLOS ONE, 2024. DOI: 10.1371/journal.pone.0300289
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