New fossils may settle debate over mysterious sail-backed spinosaurs

Were the mysterious dinosaurs known as spinosaurs excellent swimmers that could dive to catch prey? Or were they “hell herons” that plucked huge fish from shallow waters? Fossils of a new spinosaur species that lived around 1000 kilometres inland should settle the debate, say its discoverers, confirming that it was a wader. “Coup de grâce, as far as I’m concerned,” says Paul Sereno at the University of Chicago.

The lifestyle of spinosaurs has been a contentious topic among palaeontologists, due to the animal having a strange combination of features, including a large sail, huge claws, broad feet and crocodile-like jaws. In 2025, the BBC series Walking With Dinosaurs depicted them as aquatic hunters.

In 2019, a local guide took Sereno’s team to a remote desert site in Niger, where they found fragments of jawbones that they later realised belonged to some kind of spinosaur. Because of the covid-19 pandemic and the remote location of the site, it was years before they could return.

On their second trip, Sereno and his colleagues found bones from around 10 individual spinosaurs. Within hours of the first finds, the team realised these spinosaurs had a large crest on top of their skulls, in addition to the characteristic sail along their backs.

“It was a glorious moment because we knew that this was a new spinosaur, something that would have a major impact on how we understand this animal,” says Sereno.

The new species, dubbed Spinosaurus mirabilis, lived around 95 million years ago and grew to about 10 to 14 metres in length, the team estimates – nearly as large as the most famous spinosaur, Spinosaurus aegyptiacus. “I wouldn’t want to be near this animal, because it would finish off a human in about 3 seconds,” says Sereno.

S. aegyptiacus also had a crest, but that of the new species is much larger – the bony part of the skull crest would have been at least 40 centimetres high on large individuals. Based on comparisons with modern birds with crests, such as the helmeted guineafowl, the team thinks the bone would probably have been covered by a keratinous sheath, making the crest at least 50 centimetres high.

The crest is too delicate to be a weapon of any kind. “Probably it was brightly coloured,” says Sereno. “It is meant to say, ‘I am here; I am healthy.’”

It is thought that the large sails of spinosaurs were also for visual display, he says. “So, these animals are really into display, and the question is, why?”

The answer could be that spinosaurs hunted along rivers where they needed to defend territories. “The prevalence of visual cues in environments like beaches or riversides tends to be exaggerated because it’s there that you can look a mile, obstruction-free, and see your competitor, or your mate, much more easily than [in] a typical land environment,” says Sereno.

Modern waders, such as the great blue heron, are also extremely display-oriented, Sereno says, and other characteristics of spinosaurs also fit the wading hypothesis. When his team plotted a range of animals on a graph based on the relative length of the jaw, neck and hind limbs, spinosaurs came out next to waders like herons.

“It can’t swim well because it’s got this huge sail that makes it very unstable in water. But it can go into 10 feet [3 metres] of water as a full adult,” says Sereno.

Then there’s the fact that it lived far inland, whereas most other spinosaurs have been found nearer to where seas were. No marine predator weighing over a tonne has ever moved into freshwater, says Sereno. There are river porpoises and dolphins, but no river orcas. “And so, I think it’s all playing to the same story, that these animals are mega-heron-type animals.”

“The paper really confirms a lot of the consensus that has been building for these animals,” says David Hone at Queen Mary University of London. “They are not super swimmers or deep divers, but much more like a heron or stork, wading into water to catch prey, predominantly fish.”

“I think it’s fairly convincing that this is a new species. If it was just the crest, this could well be variation, but there are differences in the jaws and teeth too,” says Hone.

“At face value, the fact that the legs weren’t particularly short or undermuscled suggests that it was no less able to walk and wade than any other predatory dinosaur,” says Mark Witton at the University of Portsmouth, UK. “This doesn’t bode well for proposals of swimming lifestyles, which are already floundering with issues concerning the stability and propulsion of a swimming Spinosaurus.“

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