New Spinosaurus Species Discovery Fuels Dinosaur Behavior Debate

Under the central Saharan sun, paleontologist Daniel Vidal spotted a mysterious bone poking out of the ground during an excavation in Niger. It looked like a dinosaur vertebra at first. But upon further inspection, researchers realized the bone was a curved, sword-like crest that would have been attached to the skull of one of paleontology’s most oddball dinosaurs—the sail-backed predator Spinosaurus.

“It was amazing,” recalls Vidal, of the University of Chicago. “It was like a unicorn.”

Now, the researchers report the crest belonged to an entirely new species—Spinosaurus mirabilis—that roamed the area’s ancient river ecosystem some 95 million years ago in the Late Cretaceous. They published their discovery Thursday in Science. The new species adds to a heated debate over how these puzzling (and popular) dinosaurs lived and hunted in water.

Today, Jenguebi is dry and barren, with few trees and endless sand. The local Tuareg community calls the area where the fossils were found Sirig Taghat, which translates to “No water, no goat.”

Sereno was drawn to the Sahara because of a report by French geologist Hugues Faure in the 1950s of a dinosaur tooth he found in Niger and wanted to search for similar sites.

“I knew it was the needle in the haystack,” Sereno says of the remote fossil site. “It could easily have been swallowed by the sand.”

Led by a local guide named Abdul Nasser riding on a moped across the desert, Sereno and Vidal first scouted the site in 2019 and found a Spinosaurus jawbone, along with a handful of other fossils. After returning in 2022, they ultimately identified bones from three S. mirabilis individuals, along with another predatory dinosaur named Carcharodontosaurus, two long-necked sauropod dinosaurs, crocodiles, turtles, and a freshwater fish species that could reach 12 feet long.

While other spinosaurids had head crests, none were quite as dramatic as that of S. mirabilis, which the team likens to a curved blade called a scimitar. Covered in a sheath of keratin, it may have protruded even higher than the team’s skull reconstruction suggests, creating a striking silhouette with the animal’s spiny back sail.

“The shoreline is an unusual place where you can look down and see a quarter of a mile,” says Sereno. Perhaps these standout features, which are similar to the head crest of today’s helmeted guineafowl, broadcast something to potential mates or rivals. Though the researchers say, at this point, it’s unclear if there were differences between S. mirabilis males and females.

Lamanna and other outside experts agree that a display of some sort is the most likely explanation for the crest. “It's sort of signaling to other members of your species, whether it's ‘Hey, I would make a great mate,’ or ‘Get out of my territory. I'm the biggest, baddest dude on the block,’” says Lamanna.

With bones from the top and bottom of the jaw, the newly discovered Sahara specimens confirm that Spinosaurus had interlocking, cone-shaped teeth, like those seen in modern crocodiles and ancient aquatic reptiles like plesiosaurs. When the animal snagged a fish, the tooth pierced through the slippery prey, imprisoning it in place.

“Only Spinosaurus, among dinosaurs, has a fish trap,” the term for such specialized chops, says Vidal.

This “fish trap” is just one of several traits that have fueled a longstanding debate over what Spinosaurus was doing in its aquatic environments. “We know that this thing loved the water. We know it liked to eat fish,” says Lamanna. “Now we're trying to parse out exactly how it did that, and that becomes very, very challenging.”

Dinosaurs are stereotyped as landlubbers. But when researchers announced the discovery of 97-million-year-old Spinosaurus aegyptiacus fossils in Morocco's Kem Kem fossil beds in 2014, the team argued that the species spent much of its life in water—perhaps the first-known swimming dinosaur.

The idea is controversial, and part of the difficulty lies in Spinosaurus’ odd combination of features. On top of the teeth, it had a long snout, short legs for a theropod dinosaur, a six-foot sail along its back, dense bones, and a long tail capped with a fan of spines that resemble a fin or paddle. Stretching nearly 50 feet long, it also surpassed T. rex in length.

Researchers have interpreted this confusing blend of features in different ways, debating whether the animal was predisposed to swim, dive, or wade and whether it ambushed, chased, or scavenged prey. While some researchers think of Spinosaurus like an ancient Nile crocodile submerged and lying in wait for prey, others think it hunted more like a monstrous version of a heron, wading along riverbanks and plunging its head below the surface to snag a snack.

Ibrahim and his colleagues have suggested that S. aegyptiacus’ heavy bones were optimized for buoyancy, as in a manatee or a penguin, and that its tail could have propelled the animal after prey underwater. Sereno and others have co-authored papers that dispute those interpretations.

So how does the newly discovered Spinosaurus add to the debate?

Hundreds of miles from what would have been the closest ocean, Jenguebi is also the farthest inland that a Spinosaurus has turned up. The team argues that finding the new species in riverbank sediments suggests that it lived in the forests that lined the banks, along with the long-necked dinosaurs nearby. They say that adds further fuel to the idea that it waded in the water.

Other Spinosaurus fossils come from tropical river delta ecosystems closer to the coast, though Ibrahim notes that those environments would not have been drastically different from the inland river.

Sereno and his team also compared the skull, neck, and back leg traits of the new species and its relatives with those in a variety of dinosaurs, birds, crocodiles, and other reptiles, and looked for patterns in the animals’ feeding behaviors. Their analysis suggests that both Spinosaurus species aligned more closely with wading birds—like herons and storks—than crocs.

“I think the argument is coming together functionally and from the fieldwork that these were giant, heron-like animals displaying and clamping down on fish,” says Sereno.

“These wading birds have extremely long legs. They have really light bodies, which is completely the opposite of what we see in Spinosaurus,” he says.

Long legs allow the birds to avoid splashing and surprise prey—something that would have been tough for a dinosaur weighing more than 13,000 pounds. Low bone density allows the birds to tread more lightly. Ibrahim argues that the bone tissue issue is “kind of like the dinosaur in the room, so to speak.”

Spinosaurus’ size also meant that it probably couldn’t be picky about hunting strategies in order to capture enough prey to survive. When you’re that big, “to a certain extent, you've got to be an opportunist,” says Thomas Holtz Jr., a paleontologist at the University of Maryland, College Park, who was not affiliated with the study.

Chemical evidence from teeth shows Spinosaurus mostly ate fish, but it also preyed on other dinosaurs. While this could indicate more terrestrial proclivities, it could also point to a river predator chasing after land animals as they try to cross the waterway or come to drink.

Lamanna is hedging his bets: “What if it's doing both? What if it's wading sometimes? What if it's getting into the water and swimming around some? The common denominator is ambush, whether that was from shore or from the water.”

Though he’s skeptical that it could swim quickly, chasing after prey underwater over short distances doesn’t seem out of the question. “I don’t think anyone really believes Spinosaurus was the dinosaur answer to a dolphin or tuna,” says Lamanna. “I certainly don’t.”

Whether Spinosaurus is a “heron from hell” or a “river monster,” only more bones can decide. Until paleontologists find a more complete skeleton from snout to tail, ideally belonging to a single individual, “I think we're going to continue to be surprised by the details of Spinosaurus,” says Holtz.

Spinosaurus has long suffered from an incomplete picture. Discovered in the 1910s, the first fossils that paleontologists excavated were destroyed when the Allies bombed Munich in World War II.

New finds are on the horizon. Sereno says he has uncovered an unidentified spinosaurid in Brazil. At the same time, Ibrahim hints that his team is analyzing some new Spinosaurus finds that suggest that “if anything, the animal was even more aquatic than we previously thought.”

Ideally, more bones would provide a better understanding of the animal’s front limbs, shedding light on their role in movement and capturing prey. Finding a young Spinosaurus specimen could also reveal how the animal’s odd features changed over its life.

But for now, Holtz likens paleontologists’ efforts to decipher how the dinosaurs lived based on scant evidence to a famous parable in which blind scholars encounter an elephant for the first time. One touches the trunk and proclaims it a snake. Another touches a leg and proclaims it a tree trunk. “Only in this case, the elephant's been blown to smithereens,” Holtz says.