This illustration depicts a washed dish Ichthyotitan severnensis corpse on the beach.
Sergey Krasovsky
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Sergey Krasovsky
This illustration depicts a washed dish Ichthyotitan severnensis corpse on the beach.
Sergey Krasovsky
At the end of May 2020, 11-year-old Ruby Reynolds and her father Justin Reynolds drove to Blue Anchor, a coastal village in Somerset in southwest England, to look for fossils on the beach.
Upon arrival, they discovered that someone had left a piece of petrified bone at the top of the beach. It was about four inches long, which was “bigger than any piece of bone I’ve ever found,” says Justin. “So I was very excited and sat down to have a good look at it.”
Meanwhile, Ruby continued to walk along the beach, scanning the ground. She soon found a second piece of bone, half buried in a muddy slope, that was twice as long as the first – and much better preserved. “It was just laying there,” Ruby recalled. “I was just happy, really.”
Ruby and her father would later discover that they had just come across a piece of the largest marine reptile ever discovered – a giant ichthyosaur from 202 million years ago, near the end of the Triassic period.
These animals were once the dominant predators in the world’s oceans. Imagine a massive shark with a long, jagged snout, fins and four fins.
“These are reptiles that are only very, very distantly related to things like crocodiles,” says Dean Lomax, a paleontologist at the University of Bristol and the University of Manchester. And they actually resemble cetaceans, which are mammals, in key ways: “They gave birth to live young. They have devoted themselves entirely to life in the sea – they have not come out on land.’
In a study published in PLUS ONELomax, Ruby and Justin Reynolds and their colleagues describe this new species of ichthyosaur, Ichthyotitan severnensis, approximately 82 feet long. That’s twice as much as a school bus.
“There have been things in the past that we can’t even imagine,” said Kelsey Stilson, a biomechanist at the National Museum of Natural History in Paris, who was not involved in the study. “But we can get little hints. And that’s one small hint of that bigger picture’ of how life on Earth evolved.
A prehistoric puzzle
Opening of Ichthyotitan severnensis actually started almost eight years ago. Paul de la Salle, a keen amateur fossil collector, was scouring a beach at Lilstock in Somerset when he came across numerous pieces of fossilized bone. He showed them to Lomax, his longtime friend.
“They fit perfectly like an ancient prehistoric puzzle,” says Lomax. “And we can tell that it belongs to the jawbone of a reptile called an ichthyosaur that swam the seas at the time of the dinosaurs.”
But what struck Lomax was that this bone, called the supraangular, was large—over three feet long. “That suggests it’s from something unusual and something extremely large,” he says.
Lomax, de la Salle and their colleagues published a description of the specimen, but the bone was incomplete and partially eroded, so they had to leave it as it was – however painful it was to imagine what this animal might have looked like.
“What we were hoping for – fingers crossed – we were hoping that maybe more specimens would come to light in the future,” says Lomax.
A few years have passed. Then, in May 2020, Lomax received an email from Ruby and Justin Reynolds, who had just finished their trip to the Blue Anchor, with their two fossil treasures in hand. He remembers the message saying something like, “Hey Dr. Lomax – we think we’ve found another one of your giant ichthyosaur jawbones.”
Lomax downloaded the images. “Of course, they were absolutely right,” he says. “They correctly identified these sections of bone as belonging to an ichthyosaur.” Lomax was encouraged by how well Reynolds’ fossils were preserved. He organized subsequent collection trips to the beach in Somerset, which yielded additional fragments of the same jawbone.
This second copy was almost twice as full as the first. Lomax and his colleagues were now confident that it was a new species, which they named Ichthyotitan severnensis after the North Estuary in Somerset where it was discovered. He cautions that without a complete skeleton he cannot be sure of the size. The animal could have had a gigantic head and a more compact body. But if it was built like other ichthyosaurs, Lomax says it would have been massive.
“Really huge, the length of a blue whale,” he says.
This makes it the largest ichthyosaur—and therefore the largest marine reptile—ever described. In fact, Lomax says the animal may not even have been fully grown when it died.
The end of an era
The Triassic period was, in Kelsey Stilson’s words, “a really weird time.”
“Then you see the first very early mammals and the first very early dinosaurs,” they say. “It all starts right then.”
The end of the Triassic was when Ichthyotitan severnensis reigns, at a moment just before a mass extinction that consumes these animals forever.
“No marine reptile has ever reached such a gigantic size before,” says Lomax.
Not all ichthyosaurs went extinct, although those that survived and evolved during the Jurassic and Cretaceous periods were smaller. But they also disappeared about 94 million years ago, which created an opening in the ocean.
It was “a niche that had to be filled,” says Lomax, “where you eventually had mammals—including the first whales that walked on land— [make] this passage in the ocean.”
With the top perch on the food web now vacated, whales have assumed the role of dominant marine predators.
And the reptilian underwater rule was over.
