Bizarre Spinosaurus makes history as first known swimming dinosaur

Casablanca, MoroccoAt the end of a dim hallway in Casablanca’s Université Hassan II, I’ve walked into a dusty room containing a remarkable set of fossils—bones that raise foundational questions about Spinosaurus aegyptiacus, one of the weirdest dinosaurs ever discovered.

Longer than an adult Tyrannosaurus rex, the 50-foot-long, seven-ton predator had a large sail on its back and an elongated snout that resembled the maw of a crocodile, bristling with conical teeth. For decades, reconstructions of its bulky body have ended in a long, narrowing tail like the ones on its many theropod cousins.

The red-brown remains laid before me are altering that picture. These bones assemble into a mostly complete tail, the first yet found for Spinosaurus. It’s so large, five tables are required to support its full length, and to my shock, the appendage resembles a giant bony paddle.

Described today in the journal Nature, this tail is the most extreme aquatic adaptation ever seen in a large dinosaur. Its discovery in Morocco stretches our understanding of how one of Earth’s most dominant groups of land animals lived and thrived.

Delicate struts nearly two feet long jut from many of the vertebrae that make up the tail, giving it the profile of an oar. By the end of the tail, the bony bumps that help adjacent vertebrae interlock practically disappear, letting the tail’s tip undulate back and forth in a way that would propel the animal through water. The adaptation probably helped it move through the vast river ecosystem it called home—or even dart after the huge fish it likely preyed upon.

“This was basically a dinosaur trying to build a fish tail,” says National Geographic Emerging Explorer Nizar Ibrahim, the lead researcher examining the fossil.

The structure of the bones—along with state-of-the-art robotic modeling of the tail’s movement—add fresh and compelling evidence to an argument that has raged for years among paleontologists: How much time did Spinosaurus actually spend swimming, and, by implication, how close did large predatory dinosaurs ever get toward a life in the water? In 2014, researchers led by Ibrahim argued that the predator was the first confirmed semiaquatic dinosaur, a hypothesis that generated pushback from peers who questioned whether the fossil Ibrahim’s team were studying was actually Spinosaurus, or even a single individual.

By the time of Spinosaurus, 95 to 100 million years ago in the Cretaceous period, several groups of reptiles had evolved to live in marine environments, such as the dolphin-like ichthyosaurs and the long-necked plesiosaurs. But those dino-era sea monsters sit on a different branch of the reptile family tree, while true dinosaurs like Spinosaurus have long been believed to be land dwellers.

Now, with evidence from the newly analyzed tail, there’s a strong case that Spinosaurus didn’t merely flirt with the shore but was capable of full-fledged aquatic movement. Collectively, the findings published today suggest the giant Spinosaurus spent plenty of time underwater, perhaps hunting prey like a massive crocodile. “This tail is unambiguous,” says team member Samir Zouhri, a paleontologist at the Université Hassan II. “This dinosaur was swimming.”

Other scientists who have evaluated the new study agree that the tail puts some lingering doubts to rest and strengthens the case of a semiaquatic Spinosaurus.

“This is certainly a bit of a surprise,” says University of Maryland paleontologist Tom Holtz, who wasn’t involved with the study. “Spinosaurus is even weirder than we thought it was.”

Bones and bombs

The story of Spinosaurus is nearly as unusual as the newfound tail, an adventure that winds from bombed-out German museums to the Martian-like sandstone of the Moroccan Sahara.

The remains of this odd animal first emerged from the depths of time more than a century ago, thanks to Bavarian paleontologist and aristocrat Ernst Freiherr Stromer von Reichenbach. From 1910 to 1914, Stromer organized a series of expeditions to Egypt that yielded dozens of fossils, including pieces of what he would later name Spinosaurus aegyptiacus. In his first published description, Stromer struggled to explain the creature’s anatomy, speculating that its oddness “speaks for a certain specialization.” He envisioned the animal standing on its hind limbs like an off-balance T. rex, its long back bristling with spines. When the fossils went on display in Munich’s Paleontological Museum, they brought Stromer renown.

During World War II, Allied bombing prompted Stromer—a critic of the Nazi regime—to beg the museum director to move the fossils to safety. The Nazi director refused, and bombing destroyed the fossils in 1944. Drawings, photos, and descriptions in journal articles were all that remained to prove Stromer’s Spinosaurus fossils ever existed.

In the decades that followed, Spinosaurus took on a certain mythos, as generations of paleontologists found more of its close relatives across the world, from Brazil to Thailand, and tried to make sense of how they lived. Unearthed across four continents, these additional “spinosaurids” almost certainly ate fish based on their skull anatomy, tooth structures and, in one case, fish scales that were found preserved in a spinosaurid ribcage.

In the early 20^th century, paleontologists were toying with notions of aquatic dinosaurs, including one idea that large plant-eating dinosaurs lived in lagoons to help support their immense weight. But decades of anatomical research now show that dinosaurs of all shapes and sizes, even the titans among them, thrived on terra firma. The anatomy of other spinosaurids’ hind limbs strongly suggested that they, too, walked on land.

Without a new Spinosaurus skeleton to examine, the species seemed destined to remain ambiguous.

(See how paleontologists used the new Spinosaurus fossils to reconstruct a gigantic aquatic predator.)

Lost and found

Clarity would come decades later from southeastern Morocco, where thousands of artisanal miners have scoured the region’s rocks and found fossils that span hundreds of millions of years of Earth’s history. Hoping to find dinosaur remains in particular, some diggers have focused their energies on the Kem Kem beds, a sandstone formation between 95 and 100 million years old that starts 200 miles east of Marrakesh and extends 150 miles to the southwest. The rocks preserve traces of what was once a vast river system where fish the size of cars once swam. If you spot an exposed patch of the Kem Kem beds’ red sandstone on the side of a butte, you’re liable to find the mouth of a tunnel too short to stand up in, carved by local miners with a sharpened piece of rebar.

When miners come across fossils, they usually sell the bones to a web of wholesalers and exporters. This fossil mining industry provides vital income to thousands in this region, though it operates in a legal and ethical gray area. Locals dig year-round, making them almost certain to find more scientifically valuable specimens than academic paleontologists, who dig only a few weeks a year.

That’s why paleontologists get to know local diggers and frequently check their hauls. An assistant professor at the University of Detroit Mercy, Ibrahim, who is of German and Moroccan descent, travels from village to village whenever he visits Morocco, discussing locals’ latest finds in Darija, the local Arabic dialect, over steaming glasses of fresh mint tea.

On one such visit to a village outside the town of Erfoud in 2008, Ibrahim—by then a specialist in the Kem Kem beds—met a man who had found bones the scientist later realized might belong to a Spinosaurus. The encounter may as well have been fate. Ibrahim had loved Spinosaurus ever since he was a young boy growing up in Berlin.

Ibrahim’s research partners at the Natural History Museum of Milan alerted him to even more bones from the same local miner in Italy and helped secure their return to Morocco. A second trip by Ibrahim, Zouhri, and University of Portsmouth paleontologist David Martill in 2013 at last led the team to the Kem Kem outcrop where the fossils originated, and they started finding more bone fragments.

Ibrahim used these fresh fossils, previously found bones, and Stromer’s articles to attempt a fresh reconstruction of Spinosaurus. Their work, published in Science in 2014, declared the Moroccan fossils as a replacement for the original Egyptian ones lost in World War II bombings. Their reconstruction revealed the creature was 50 feet long when fully grown, longer than an adult T. rex.

The study also argued that Spinosaurus had a slender torso, stubby hind limbs, a skull shaped like a fish-eating crocodile’s, and thick-walled bones similar to those in penguins and manatees—features that pointed to some kind of semiaquatic lifestyle.

The study polarized paleontologists. Some reacted positively, convinced by the new data on Spinosaurus’s thick-walled bones. “That really sealed the deal for me,” says Lindsay Zanno, a North Carolina Museum of Natural Sciences paleontologist who wasn’t part of Ibrahim’s research team. “Bone has memory,” she adds, noting that the microstructure of bone looks different in terrestrial animals, flying animals, or animals that spend most of their time in water.

For other paleontologists, however, the evidence presented in 2014 didn’t clinch the case for an actively swimming Spinosaurus. Those researchers thought it likely that Spinosaurus, like other spinosaurids, ate fish by wading into the shallows like grizzly bears and herons. But based on the incomplete Moroccan remains, could researchers now say for certain that the prehistoric predator did more than its kin and quickly swam after aquatic prey? If so, how did it move through the water?

Still others expressed doubt that the Moroccan bones belonged to a Spinosaurus. While the newfound Moroccan bones were clearly spinosaurid, the number of spinosaurid species in North Africa was, and is, a matter of scientific debate. Did the fossil’s anatomy exactly match Stromer’s lost Egyptian creature? Or did they instead belong to a close, but distinct, relative? “No one was particularly sure quite how many species or genera we’ve got [in North Africa], and quite where any one of them is in time and space,” says Dave Hone, a paleontologist at Queen Mary University of London and a spinosaurid specialist.

Seeking to put the controversy to rest, Ibrahim and his colleagues returned to the Moroccan site, with the support of the National Geographic Society, to check for more bones in September 2018. Time was of the essence: He had heard from local contacts that commercial fossil diggers were tunneling into nearby hills for bones. Ibrahim could not risk letting the rest of what he believed to be the world’s only known Spinosaurus skeleton vanish into collectors’ curio cabinets.

Fossil bonanza

The 2018 dig started brutally. To clear tons of sandstone, the crew bought the region’s only working jackhammer. It broke within minutes. Days were so grueling that several team members were hospitalized once they returned home. But the promise of discovery kept them going, along with Nutella breaks that temporarily took their minds off the punishing work. Finally, they started finding one caudal vertebra after another from the animal’s tail, sometimes just minutes and inches apart. The team was so giddy over the bonanza, they drummed out musical beats with their rock hammers and broke into song, belting out, “It’s another caudal!” to the tune of Europe’s “The Final Countdown.”

I got a taste for the site’s challenges, and the rush of discovery, when I joined the team in July 2019 for a return expedition. The 117-degree heat and arid winds wicked liters of water from my body as we chipped our way through an outcrop marbled like bacon. Fanned along the outcrop below, Ibrahim’s Detroit Mercy students lugged rocks in buckets made from recycled tires and scoured the debris for even the tiniest flecks of bone.

By the end of the next day, we’d found several Spinosaurus fossils, including foot bones and two dainty caudal vertebrae that would have formed the tip of the dinosaur’s tail. When the fruits of all this labor were at last laid out on tables back in the Casablanca lab, Ibrahim and his colleagues knew they had something truly remarkable.

By the end of 2018 alone, the dig team had uncovered more than 30 Spinosaurus tail vertebrae. Crucially, some of the tail bones neatly match up with illustrations of more fragmentary spinosaurid tail vertebrae that Stromer published in 1934, bolstering the case that a spinosaurid species living in Cretaceous North Africa ranged from Morocco to Egypt. In addition, Ibrahim and his team haven’t found any duplicate bones at the Moroccan site—a clear sign that the fossils belong to just one individual, an extremely unusual occurrence in the Kem Kem beds’ rough-and-tumble riverbeds.

Made for water

With the creature’s nearly complete tail now in hand, Ibrahim and his colleagues are more confident than ever that Spinosaurus was a swimmer—an assertion they’ve started putting to the test in the lab.

In February 2019, Ibrahim contacted Stephanie Pierce, curator of vertebrate paleontology at Harvard’s Museum of Comparative Zoology, with a question: Could she help him test how much thrust a dinosaur’s tail would generate in water? Though digitally modeling animal motion is one of her specialties, Pierce knew that answering the question required dynamic, real-world experiments. She and her colleague George Lauder, a fish biologist, agreed to join the team.

Nearly six months after the Harvard duo joined Ibrahim’s team, I walked into Lauder’s lab, a room whirring with ventilation and the fans of overworked computers. Lauder, sitting at a workbench, reached for an orange plastic sheet—the laser-cut outline of a Spinosaurus tail—and attached it to a metal rod. He then walked across the lab to what looked like an elaborately built fish tank and mounted the tail inside a tangle of metal beams hanging from the ceiling.

The device is a robot called the “Flapper,” which dangles beneath a water flume whose flow speed Lauder can control with exquisite precision. Studded with lights, cameras, and sensors, the ensemble can precisely track the aquatic movements of a swimming animal or a swimming robot—and the forces they impart as they move.

As I watched, Lauder lowered the Flapper into the water, and the plastic model Spinosaurus tail attached to it sprang to life with a motion meant to mimic a swimming alligator. With each flap, a shadow rushed across the tail—and data streamed into Lauder’s computers. The Flapper recorded the forces imparted by the tail, reflecting how well it would have propelled Spinosaurus through water.

Pierce and Lauder’s results, which are included in the Nature paper, show that the tail of Spinosaurus delivers more than eight times the forward thrust in water than the tails of the non-spinosaurid theropods Coelophysis and Allosaurus—and does so twice as efficiently. The finding suggests the giant Spinosaurus spent plenty of time submerged, possibly navigating rivers like a modern crocodile but on a massive scale.

That conclusion sets Spinosaurus apart from other water-loving dinosaurs described since 2014, including species that may have lived like geese or turtles. The more Lauder talks about a paddle on the rear of a predator up to 50 feet long, the more his eyes widen at the unprecedented nature of the discovery. “It’s unbelievable!” he says.

In future experiments, Pierce and Lauder say that a modified version of the Flapper trials could test a 3D model of the tail, or even a full-body model of the updated Spinosaurus, which would help clarify how the dinosaur’s six-foot-tall dorsal sail affected its swimming. To achieve that dream, though, Ibrahim wants to incorporate every last scrap of bone he can, which is why his team returned to the desert in the height of summer 2019 for more digging.

Some of the fossils I saw them find on that expedition will soon help test another aquatic feature of Spinosaurus: its possibly webbed feet. With more bones in hand, researchers can finally reconstruct the dinosaur’s whole foot to help test how widely Spinosaurus splayed its toes.

Crucially for Ibrahim, any fossils the team finds remain in Morocco, growing the collection that Zouhri, the Université Hassan II paleontologist, oversees in his Casablanca lab. The hope is that someday, these bones and the scientists studying them will seed Morocco’s first national museum of natural history—and inspire people across North Africa to dream of the lost worlds beneath their feet.

“What I want to do is build a home for Spinosaurus,” Ibrahim says. “This is going to become a symbol—an icon—of African paleontology.”