New fossils could settle debate about mysterious sail-backed spinosaurs

Were the mysterious dinosaurs known as spinosaurs excellent swimmers who could dive to catch prey? Or were they “herons” who picked big fish from shallow water? Fossils of a new species of spinosaur that lived about 1,000 kilometers inland should settle the debate, the discoverers say, confirming that it was a wading bird. “Buy them 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 feet, and crocodile-like jaws. In 2025, the BBC series Walk 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 jawbone that they later realized belonged to some kind of spinosaur. Due to the covid-19 pandemic and the remote location of the site, it took years before they could return.

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

“It was a brilliant moment because we knew this was a new spinosaur, which would have a big impact on how we understand this animal,” says Sereno.

The new species, called Spinosaurus mirabilislived about 95 million years ago and grew to about 10 to 14 meters in length, the team estimates – almost as big as the best-known spinosaurus, Spinosaurus aegyptiacus. “I wouldn’t want to be near this animal because it would finish off a human being 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 centimeters high in large individuals. Based on comparisons with modern crested birds, such as the helmeted guinea fowl, the team believes the bone would likely have been covered by a keratinous sheath, making the crest at least 50 centimeters high.

The comb is too delicate to be a weapon of any kind. “Probably it was brightly colored,” says Sereno. “It’s meant to say, ‘I’m here, I’m healthy.'”

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

The answer may be that spinosaurs hunted along rivers where they needed to defend territories. “The presence of visual cues in environments like beaches or riverbanks tends to be exaggerated because that’s where you can see a mile, unobstructed, and see your competitor, or your buddy, 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 their jaw, neck and hind legs, spinosaurs came out next to waders like herons.

“It can’t swim well because it has this huge sail that makes it very unstable in water. But it can go down in 10 feet (3 meters) of water like a full adult,” says Sereno.

Then there’s the fact that it lived far inland, while most other spinosaurs have been found closer to where the sea was. No marine predator weighing more than a ton has ever moved into freshwater, says Sereno. There are river ice and dolphins, but no killer whales. “And so, I think it all plays into the same story, that these animals are mega-heron animals.”

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

“I find it quite convincing that this is a new species. If it was just the top, this could well be variation, but there are differences in the jaws and teeth as well,” says Hone.

“On face value, the fact that its 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 proposals for swimming lifestyles, which are already fraught with problems regarding the stability and propulsion of a swimming Spinosaurus.“

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