Bizarre Spinosaurus makes history as first known swimming dinosaur

Two Spinosaurus aegyptiacus hunt Onchopristis, a prehistoric sawfish, in the waters of a vast river system that once covered Morocco more than 95 million years ago. At the end of a dim hallway in Casablanca’s Universit√© 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. 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. “This was basically a dinosaur trying to build a fish tail,” says National Geographic Emerging Explorer Nizar Ibrahim, the lead researcher examining the fossil. Shovels scrape and pickaxes fly as crew members chip away at Morocco’s Zrigat site, where paleontologist Nizar Ibrahim and his colleagues have been excavating a Spinosaurus skeleton. 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 beland dwellers. Collectively, the findings published today suggest the giant Spinosaurus spent plenty of time underwater, perhaps hunting prey like a massive crocodile. “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. “Spinosaurus is even weirder than we thought it was.” Samir Zouhri, a paleontologist at Universit√© Hassan II, Casablanca, explores a site near Sidi Ali, Morocco, for more fossils from the time of Spinosaurus. 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. In his first publisheddescription, Stromer struggled to explain the creature’s anatomy, speculating that its oddness “speaks for a certain specialization.” He envisioned the animal standing on its hindlimbs likean off-balance T. rex, its long back bristling with spines. 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. 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. 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. 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. 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. 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. “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. “No onewas 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 QueenMaryUniversity 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. Fanned along the outcrop below, Ibrahim’s Detroit Mercy students lugged rocks in buckets made from recycled tiresand 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. 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? 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. He then walked across the lab to what looked like an elaboratelybuilt 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. 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. The finding suggests the giant Spinosaurus spent plenty of time submerged, possibly navigating rivers likea modern crocodile but on a massive scale. Crucially for Ibrahim, any fossils the team finds remain in Morocco, growing the collection that Zouhri, the Universit√© 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 worldsbeneath their feet.

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