New fossils may settle debate over mysterious sail-backed spinosaurs

Were the mysterious dinosaurs known as spinosaurs excellent swimmers capable of diving to catch prey? Or were they “herons from hell” that caught huge fish in the shallows? Fossils of a new species of spinosaur living about 1,000 kilometers inland should settle the debate, its discoverers say, confirming that it was a wading bird. “Coup de graceas far as I’m concerned,” says Paul Sereno of the University of Chicago.

The lifestyle of spinosaurs has been a controversial topic among paleontologists, due to the animal’s strange combination of features, including a large sail, enormous claws, broad paws, and crocodile-like jaws. In 2025, the BBC series Walk with the 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 jaw fragments that they later realized belonged to some kind of spinosaur. Due to the covid-19 pandemic and the remoteness of the site, it took years before they were able to return.

During their second trip, Sereno and his colleagues discovered the bones of around ten spinosaurs. Within hours of the initial discoveries, the team realized that these spinosaurs had a large crest at the top of their skull, in addition to the characteristic sail along their back.

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

The new species, nicknamed Spinosaurus mirabilislived around 95 million years ago and measured around 10 to 14 meters long, the team estimates – almost 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 reached at least 40 centimeters high in large individuals. Based on comparisons with modern birds with crests, such as the helmeted guinea fowl, the team believes the bone would likely have been covered in a keratinous sheath, making the crest at least 50 centimeters high.

The crest is too delicate to constitute a weapon of any kind. “It was probably brightly colored,” says Sereno. “It means: ‘I’m here, I’m healthy.'”

It’s thought that spinosaurs’ large sails also served for visual display, he says. “So these animals are really exposed, and the question is: why? »

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

Modern wading birds, like the great blue heron, are also extremely display-oriented, Sereno says, and other features of spinosaurs also fit the wading bird 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 appeared alongside wading birds like herons.

“He can’t swim well because he has this huge sail that makes him very unstable in the water. But he can go up to 10 feet. [3 metres] of water as an adult,” says Sereno.

Then there’s the fact that it lived far inland, whereas most other spinosaurs were found closer to the seas. No marine predator weighing more than a ton has ever moved into fresh water, Sereno says. There are river porpoises and dolphins, but no river orcas. “And so, I think it all fits the same story, which is that these animals are mega-heron type animals.”

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

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

“At first glance, the fact that the legs were not particularly short or undermuscled suggests that it was no less capable of walking and wading than any other predatory dinosaur,” says Mark Witton of the University of Portsmouth, UK. “This does not bode well for swimmers’ lifestyle proposals, which already face issues regarding a swimmer’s stability and propulsion. Spinosaurus.“

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