For the longest time, the paleontology community rejected any hypothesis that proposed dinosaurs could swim. Believed to be land predators, most renderings of dinosaur anatomy gleaned from fossils showed their bodies ending in a long, tapering tail. Now, paleontologist and National Geographic Explorer, Nizar Ibrahim, and team, have found a different kind of tail that provides conclusive proof that the 50-foot-long Spinosaurus aegyptiacus swam and hunted for food in water for long periods of time.

The newly discovered tail looks more like an oar, with an adaptation that lets its tip undulate back and forth, which scientists believe allowed the Spinosaurus to paddle inside water bodies.

The hunt for proof of swimming dinosaurs has long plagued the paleontology community. The first time they received an inkling of the Spinosaurus was when German paleontologist Ernst Stromer discovered bones in the Sahara desert in Egypt on expeditions he conducted between 1910 and 1914. He then displayed his fossil finds at the Bavarian State Archaeological Collection in Munich, one of the largest natural history museums at the time. Stromer described the Spinosaurus as resembling a Tyrannosaurus Rex, standing on its hind limbs with its back covered in spines. Soon after, however, World War II began, during which the Allied forces bombed, and subsequently destroyed, 80% of Munich, including the museum and the dinosaur bones it housed. All that remained of Stromer’s Spinosaurus research were a couple of drawings and photographs of an imagined dinosaur.

In the subsequent years, paleontologists made great headway in finding fossils that hinted dinosaurs ate fish; they even found fish scales in the ribcage of what they dubbed a “spinosaurid.” Without another Spinosaurus skeleton to examine, paleontologists settled on finding incomplete fossils that increasingly showed a group of early dinosaurs existed near shores and largely waded along the margins of river bodies to feed on fish.

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Conclusive evidence that Spinosaurus were at least semi-aquatic predators came in 2014, when Ibrahim met a local collector in Morocco who had found some spinosaur bones. Ibrahim came upon another set of bones in an Italian museum a few months later. After a bit of sleuthing, he found both sets of bones came from the same miner in Morocco, which led him to realize they belonged to the same skeleton. “It was a lot of detective work, and it was really like looking for a needle in a haystack, because I had to find this one guy who I’d only met once before to get him to show me where he had found these bones,” Ibrahim told CNN. When Ibrahim finally published his research, claiming to have found proof of the first semi-aquatic dinosaur, he faced severe pushback from peers who cast doubts upon his findings, alleging there was no conclusive proof that the two sets of bones he had found belonged to the same Spinosaurus.

Now, almost six years later, Ibrahim has published research in the journal Nature that proves the existence of an semi-aquatic Spinosaurus through a tail he found — “a propulsive structure that would have allowed this river monster to actively pursue prey in the water column,” he told Reuters — in Morocco. “This was basically a dinosaur trying to build a fish tail,” Ibrahim told National Geographic. With this new finding, Ibrahim has put to rest many of the doubts his 2014 research incited among the paleontology community, further strengthening his claim that the Spinosaurus looked and behaved more like a crocodile than it did its terrestrial counterparts.

We now know with certainty that the Spinosaurus, a meat-eating semi-aquatic predator that lived almost 95 million years ago during the Cretaceous period, “terrorized rivers and river banks,” and “may have eaten huge fish, including sharks,” Reuters reported. In addition to the tail, we now also know the Spinosaurus sported nostrils high up on its skull, dense bones that aided in buoyancy and flat-bottomed claws that complimented its semi-aquatic lifestyle.

“We believe that this discovery does indeed revolutionize our understanding of dinosaur biology,” Harvard vertebrate paleontologist and co-author of the latest research, Stephanie Pierce, told Reuters. “It just might topple T. rex,” Pierce said of the Spinosaurus, “as the most famous and exciting meat-eating dinosaur.”