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Did the largest predator ever swim in Triassic Seas?

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  • Did the largest predator ever swim in Triassic Seas?

    A new discovery has revealed that a marine reptile that lived during the Triassic was likely the largest predator that ever lived -- being even bigger than modern Blue Whales.

    For the last couple of decades evidence for an enormous super-predator living in the oceans roughly 200 to 250 mya has been slowly amassing. Now, a series of discoveries and a re-analysis of earlier discoveries has made the case much stronger.

    Blue Whales typically reach 29 some meters in length (between 95 and 98"), but this creature, a type of ichthyosaur, measured up to 35 meters (just under 115') long, and unlike Blue Whales, ate much larger prey than krill.

    Source: Largest ever animal may have been Triassic ichthyosaur super-predator

    New fossil discoveries show predatory marine reptiles from 200 million years ago may have been bigger than today’s blue whales – and that they evolved astonishingly rapidly

    PREHISTORIC Earth was a place of monsters. There were 2.5-metre-long millipedes, flying reptiles with 11-metre wingspans and snakes that weighed over a tonne. But if it is the biggest animal of all time you are looking for, conventional wisdom says you don’t need to step back in time. The blue whale is known to reach 30 metres in length and to weigh 199 tonnes. Nothing else in more than half a billion years of animal evolution comes close, not even the largest dinosaur.

    Conventional wisdom might be wrong. The fossil record may be concealing an animal that was even bigger than a blue whale. For decades there has been a slow trickle of evidence that a truly enormous super-predator swam the seas between 200 and 250 million years ago. Now, a string of discoveries and reanalysis of previous findings has dramatically bolstered the case.

    The implications are far-reaching. We don’t know exactly what this huge animal looked like and it doesn’t even have a name. We have, however, begun to work out how such a gigantic creature could feed itself in the prehistoric seas. Confirmation that it outgrew the blue whale would tell us that we may have drastically underestimated how large toothed carnivores can grow. More than that, the discovery that such leviathans appeared shortly after the most devastating mass extinction in Earth’s history suggests we may need to rethink the factors that drive evolution on such an epic scale.

    When dinosaurs ruled the land, several groups of marine reptiles dominated …

    the seas. There were the long-necked plesiosaurs, for instance, and the mosasaurs that looked like massive crocodiles with fins. Crucially for our story, there was also a third group.

    Pioneering fossil hunter Mary Anning and her brother Joseph found the first fossils from this group in 1811 and 1812 in Lyme Regis on the south coast of England. They were described by the British surgeon Everard Home in a series of papers published between 1814 and 1820. Home was unsure how to classify the remains. In many respects they were reptilian, but in others they resembled the bones of a large fish. Over the next few decades, it became clear that the ancient animal was a reptile that lived in the sea and that it belonged to a broader group of similar animals. They were named the ichthyosaurs, meaning “fish lizards” in Greek.

    The ichthyosaurs from Lyme Regis all existed in the Jurassic period, the middle of the three geological periods in which the dinosaurs lived. But as more fossils were found elsewhere in the world, it became clear that there were also ichthyosaurs in the later Cretaceous period and in the earlier Triassic period too.

    The Jurassic and Cretaceous ichthyosaurs are all quite similar. They resemble a cross between a dolphin and a large fish such as tuna and could reach several metres in length. In January 2022, researchers including Dean Lomax at the University of Manchester, UK, unveiled the UK’s largest known complete ichthyosaur skeleton, which was 10 metres long and found in 182-million-year-old Jurassic rocks in Rutland. It was clearly an impressive apex predator, double the length of a modern great white shark. But it was still only about a third of the length of the largest blue whales.

    For larger ichthyosaurs, you have to wind the clock back to the Triassic. In 2004, the late Elizabeth Nicholls, who worked at the Royal Tyrell Museum in Alberta, Canada, and her colleague Makoto Manabe at the National Museum of Science and Nature in Japan reported a big discovery: huge fossilised ichthyosaur bones near the Sikanni Chief river in British Columbia, western Canada. They belonged to a new species, which the two researchers called Shonisaurus sikanniensis. It lived during the Triassic, about 218 million years ago, and it was enormous. With an estimated length of 21 metres, it has been recognised by Guinness World Records as the largest marine reptile of all time.

    The skeleton is “50 to 60 per cent complete”, says Lomax. “That’s your absolute largest skeleton of an ichthyosaur that is known.”

    Such large animals are rare in Earth’s history. According to Martin Sander at the Natural History Museum of Los Angeles County, California, only a handful of animal groups have evolved an estimated body mass above 20 tonnes, including the long-necked sauropod dinosaurs and the whales. The ichthyosaurs were the earliest to do so – and it is possible some of them outgrew anything that followed.

    In 2016, at Lilstock in south-west England, Paul de la Salle at the Etches Collection Museum of Jurassic Marine Life found what Lomax calls “this massive chunk of bone”. It was 96 centimetres long. Careful examination by de la Salle, Lomax and their colleagues revealed it was part of a surangular bone from the lower jaw of an ichthyosaur. It is about 205 million years old, meaning the animal it belonged to lived close to the end of the Triassic.

    If just one part of the jaw was almost a metre long, how big was the entire animal? Lomax says we can make an educated guess. If we compare how long the surangular bone was in relation to overall body length for closely related ichthyosaurs, then by scaling up we can estimate the length of the Lilstock ichthyosaur. That gave a range of 20 to 25 metres – larger than S. sikanniensis.

    The discovery got Lomax and his colleagues thinking. About 50 kilometres along the coast from Lilstock, there is another fossil-bearing site called Aust Cliff. Between the 1840s and 1950s, five long shafts of bone were found there. They had been interpreted as limb bones from dinosaurs or other land-dwelling reptiles.

    Lomax remembered that one had “a really strange groove that runs down the side” – unusual for a limb bone, but typical of an ichthyosaur jawbone.

    The team re-examined three of the bones and concluded that, sure enough, they were pieces of ichthyosaur jaws. Some of the Aust Cliff bones appear to have belonged to ichthyosaurs even bigger than the Lilstock specimen: “30-plus metres”, says Lomax, perhaps even 35 metres.

    In other words, larger even than a blue whale. “You are starting to get out to that point of truly gigantic contender for the world’s largest animal,” he says.

    Lomax is at pains to emphasise that such numbers carry caveats. As species evolve, different body parts change size at different rates. It may be that the Aust Cliff and Lilstock ichthyosaurs had disproportionately large heads. In that case, their body lengths may not have been exceptional. Because the fossils are fragments, he says, the uncertainties are enormous.

    But he isn’t alone in entertaining the possibility that Triassic ichthyosaurs were exceptionally large. “These animals may well have been the largest that ever existed on this planet,” says Sander. “And we know next to nothing about them.”

    For Sander, the evidence for these giant ichthyosaurs has been accumulating for over a century. He points to a paper from 1878 by geologist James Hector that describes a piece of ichthyosaur vertebra 45.7 centimetres in diameter. “If that is true, then that is by far the largest ichthyosaur,” says Sander – at least as long as a blue whale and possibly longer. The bone was found in New Zealand, but frustratingly it was lost soon afterwards – possibly in the sinking of a transport ship. This means there is no way of confirming whether it really did belong to one of the world’s largest ever animals.

    The fact that the New Zealand ichthyosaur has vanished into the shadows seems curiously apt. At this stage, we know for sure that some Triassic ichthyosaurs reached 21 metres in length. We also have hints that a few grew much larger. Frustratingly, however, we lack the complete skeletons that would tell us for sure if some outgrew the blue whale.

    Growing large

    While we wait for a 35-metre ichthyosaur skeleton to show up, we can instead address some related questions – namely how and when did ichthyosaurs first evolve and why did they get so large?

    The Triassic period was bookended by mass extinctions. The Permian-Triassic event of 252 million years ago is the worst extinction event known. “We cannot overstate how devastating [it] was,” says Paige dePolo at the University of Edinburgh, UK. “Ninety per cent of the species in the ocean went extinct.” Then, about 51 million years later, came the end-Triassic extinction, which is less famous and less well understood.

    The Permian-Triassic extinction meant that, at the start of the Triassic, the oceans had been virtually stripped of animal life. The ichthyosaurs dived into this unpromising looking marine world just a few million years later. They had started out as land-dwelling reptiles, and by 248 million years ago – just 4 million years after the extinction – there were at least two types of proto-ichthyosaur: the 0.4-metre-long Cartorhynchus lenticarpus, described in 2014, and the 1.6-metre-long Sclerocormus parviceps, described in 2016.

    Ichthyosaurs didn’t stay small for long. In 2018, Lene Liebe Delsett at the University of Oslo in Norway and her colleagues described ichthyosaur remains from Marmierfjellet on the island of Spitsbergen off the north coast of Norway. Many of the bones were fragmentary, but enough remained to identify the animals as being several metres long. The remains date from the first 5 to 10 million years of the Triassic. “There were large ichthyosaurs really early,” says Liebe Delsett.

    Rapid evolution

    Then, in 2021, Sander and his colleagues reported a real whopper. They described a 2-metre-long ichthyosaur skull, plus some other bones, found at a site called Fossil Hill in Nevada. The animal, which they named Cymbospondylus youngorum, was probably 17.5 metres long. It lived 246 million years ago, a mere 6 million years after the Permian-Triassic extinction, and only 2 million years after the proto-ichthyosaurs. The implication was clear: once they had taken to the water, some ichthyosaurs got very big, very fast.

    At first glance this appears to be a shockingly fast pulse of evolution. For comparison, the whales seem to have taken tens of millions of years to evolve from land-dwelling animals to ocean giants. But given that the ichthyosaurs were living immediately after a period of profound ecological upheaval, perhaps we shouldn’t be too shocked. “I suspect one of the key reasons for [their rapid evolution into giants] is simply because nobody else was doing that,” says Lomax. It may be that such a rapid shift was possible because the Permian-Triassic mass extinction reduced diversity in the oceans, creating an opportunity for gigantic animals to evolve, which the ichthyosaurs seized.

    If so, it means there is more than one way to evolve into a giant. A more fertile ocean is a known route. “The conventional explanation for gigantism in modern whales is that the cooling of the Earth resulted in an increased productivity, at least in certain places of the ocean, and this is why, when Earth entered the glacial cycle, whales could become bigger,” says Sander. That isn’t what happened in the Triassic.

    That said, being large may have carried a similar benefit for Triassic ichthyosaurs and today’s whales. “Nobody can eat you, which is a great advantage,” says Liebe Delsett. When it comes to how such large animals feed themselves, we can get some insight by considering today’s whales, which fall into two groups. Toothed whales like the sperm whale, which grow to lengths of 20 metres, are top predators: they hunt squid and other large prey in the deep sea. But the largest species, like blue whales, have no teeth. They are filter feeders that sift huge quantities of tiny plankton and krill from the water.

    There is a reason why toothless filter-feeders can grow larger. Most marine ecosystems depend on phytoplankton, “primary producers” that obtain energy from sunlight and convert it to sugars, like green plants on land. Small animals eat the phytoplankton, then larger animals eat the small animals, and so on. Food chains can only have so many steps, though, because at every stage nutrients are used up fueling the metabolism of the animals in question.

    The result is that a big animal will get the most energy if it bypasses a long food chain and eats phytoplankton or microscopic animals in huge quantities. The alternative – chasing down and eating larger animals – just won’t provide enough energy to sustain a truly enormous animal.

    But it seems ichthyosaurs had the potential to grow enormous even if they had teeth and hunted like a sperm whale rather than filter fed like a toothless blue whale. When describing the 17.5-metre-long C. youngorum, Sander’s team did some calculations to see how the Triassic oceans could have supported huge ichthyosaurs. It turns out that these oceans had quite short food chains, possibly because so many species had been recently wiped out in the Permian-Triassic extinction. The seas were teeming with ammonites – molluscs with coiled shells – and eel-like conodonts. Many of these animals had body sizes in the range of tens of centimetres, but being close to the bottom of the food chain, they would have supplied the ichthyosaurs with ample nutrition without the need for filter feeding.

    “It used to be thought there was an upper limit for the ichthyosaurs because the primary producers that characterise our [modern] oceans hadn’t evolved yet,” says dePolo. That is no longer the case, she says. However, their large size may ultimately have been their downfall.

    There is evidence that giant ichthyosaurs survived until the end of the Triassic. In 2018, Lomax and his colleagues described a single bone of Wahlisaurus massarae, another big species from the Triassic-Jurassic boundary, although exactly how large is still unclear. In April 2022, Sander and his colleagues described a 10-centimetre-long ichthyosaur tooth from the Swiss Alps. It came from an animal that Sander says may have been about 20 metres in length and lived at the very end of the Triassic.

    Then came the end-Triassic extinction, which seems to have been caused by massive volcanic eruptions. At the time, all the continents were joined together in a single supercontinent called Pangaea, and as it started to break up huge volcanoes formed. Ichthyosaurs were one of the worst affected groups. Almost all the lineages died out, with only a few relatively small forms surviving into the Jurassic. The giant ichthyosaurs were no more.

    It isn’t clear why they vanished, but dePolo tentatively suggests their proposed diet of ammonites and conodonts may have been a factor. “Conodonts went extinct at the Triassic-Jurassic boundary, and there was a big turnover of ammonites,” she says. The giant ichthyosaurs may have been doomed by their size, which demanded huge food intakes. This would indicate gigantic animals are particularly vulnerable to mass extinction events – a pattern that appears to be playing out again in the modern world, where larger mammals and birds are projected to fare worse this century than smaller ones.

    That said, dePolo emphasises that the diet explanation is just a hypothesis. “The late Triassic is a confusing place,” she says. The fossil record of the second half of the Triassic is “abominable”, says Sander, with relatively few good sites, so it is hard to tell what was happening.

    Whatever the exact chain of events, we now know that the end-Triassic extinction was far more significant than its obscure reputation might suggest. It wiped out a group of extraordinary gigantic animals – the world’s first “super-predators”, according to Lomax.

    Enormous dinosaurs would rise and fall in the Jurassic and Cretaceous, the whales would begin their evolutionary journey later, in the Eocene. But it is just possible that the largest animals Earth has ever seen were the Triassic ichthyosaurs. We will know for sure only when they finally swim out of the shadows.


    © Copyright Original Source

    ETA: Hmm... I used Google cache to access the story but for some reason Google does not let me list that but instead insists on giving the regular url.

    Last edited by rogue06; 01-06-2023, 09:24 AM.

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