At first, the fossil was smuggled out of Mongolia, as many dinosaurs are. It found its way to Japan, then Britain, then France. In 2015, the private collector who finally bought it contacted the paleontologist Pascal Godefroit to get his opinion on the specimen.

Godefroit’s opinion was: This is one weird dinosaur.

The creature was clearly a small predator, much like Velociraptor. Its feet even had the distinctive sickle-shaped claws that clinked across the kitchen floor in Jurassic Park. But its long neck and tapering snout resembled those of a swan. Its arms and hands also had unusual proportions—something halfway between the grasping limbs of other raptors and the flattened flippers of modern penguins. It looked like a Velociraptor that had adapted for life in the water—that is, if it was even an actual dinosaur.

“It was so strange that we suspected that it might have been a chimera—a mix of different skeletons glued together. It wouldn’t be the first time,” says Andrea Cau from the University of Bologna, who joined Godefroit’s investigation. “We had to be sure that it was a real dinosaur and not a fake.”

Since most of the animal was still encased in a 15-inch block of stone, the team took it to Grenoble, and scanned it using a particle accelerator. The scans showed that the block was a solid mass that hadn’t been assembled from separate pieces. And the parts of the skull still within it were identical to those on the outside, as were the hidden arm bones. This swan-necked, duck-snouted, almost-paddle-limbed, sickle-clawed creature was assuredly weird—but it was a real dinosaur. (Cau notes that the scans are all openly available in case any other paleontologists want to check them.)

The team called the creature Halszkaraptor escuilliei. The name’s first half, pronounced “hull-shka-raptor,” honors Halszka Osmólska, a Polish paleontologist who discovered more than a dozen Mongolian dinosaurs and has at least four species named after her. The second half honors François Escuillié, the French collector who bought the fossil, alerted Godefroit, and worked to return the poached specimen to its rightful home in Mongolia. It currently sits in Brussels and will remain there for a year or so while the team finishes studying it.

Halszkaraptor is one of the theropods—a group of mostly meat-eating dinosaurs that count Tyrannosaurus and Velociraptor among their ranks. But unlike its kin, Halszkaraptor’s odd features suggest it was a strong swimmer that perhaps chased fish underwater, much like modern cormorants do. Outside of birds, “this is the first time we see that in a dinosaur,” says Cau. (Other ancient reptiles like paddle-limbed plesiosaurs and the dolphin-esque ichthyosaurs are not actually dinosaurs.)

Like many other fish-eating specialists, Halszkaraptor had a lot of teeth in the front of its snout—more than twice the number of a typical dinosaur. “The first time I saw that, I asked my colleagues to repeat the analysis because I wasn’t convinced,” says Cau. The snout also contained branching bony chambers that would have once housed a large network of blood vessels and sensory nerves. Such features are common in modern crocodiles, giving them an exquisite sense of touch.

Halszkaraptor’s neck made up half its length from snout to hip, reminiscent of plesiosaurs, several groups of freshwater turtles, and birds like swans and herons—all of which use their long necks to catch fish. Halszkaraptor’s neck bones also had more side-to-side mobility than those of the average theropod. “That might be an adaptation to swimming, or it may indicate that the animal used rapid sweeping motions of the neck to capture some sort of small prey,” says Michael Habib, from the University of Southern California.

The arms “are the most problematic part,” says Cau, because they’re not quite like anything else. The long bones are flattened, and the fingers get progressively longer from the outside in—the opposite pattern to most theropods. They’re closest in proportion to the limbs of swimming birds like puffins, murres, and penguins. But they’re not flippers. “I prefer not to say if [Halszkaraptor] used its arms propulsively,” says Cau. “We don’t have information on the shoulder girdle, which would be important to determine if it swam like a penguin.”

Despite all these adaptations for swimming, Halszkaraptor’s back half is that of a typical landlubbing theropod. It had long legs, although it wasn’t well adapted for running. It had a longish tail, although one that was too thin to effectively counterbalance the exceptionally long neck. To compensate, Halszkaraptor probably stood upright, more so than other raptors, but not quite as erect as a penguin. Cau thinks it lived in an unstable environment, with cycles of freshwater and drought. Halszkaraptor evolved to cope with both worlds.

Halszkaraptor is the first amphibious dinosaur that we know of—and that’s strange. With mammals, you have digging moles, gliding squirrels, flying bats, swimming otters, oceangoing dolphins, running gazelles, climbing monkeys, and swinging gibbons. Where’s that diversity of lifestyles among the dinosaurs? Until recently, it seemed that aside from birds, “nearly all dinosaurs are considered to be typical ground-living animals,” says Xing Xu, a prolific dino discoverer from the Chinese Academy of Sciences. That’s surprising, given how diverse they were, and how thoroughly they dominated the planet for hundreds and millions of years.

But that view has changed in recent years, thanks to new discoveries. In 2014, scientists reimagined Spinosaurus, the sail-backed giant that menaced the cast of Jurassic Park 3, as a semiaquatic, crocodile-like fish hunter. They also revealed the complete skeleton of Deinocheirus, a “horse-headed, humpbacked dinosaur that looks like something out of a bad sci-fi movie.” A year later, Xu described Yi, a small predator which had both feathers and bat-like wings, and may have glided between trees. The year after that, another team described Limusaurus, a beaked plant eater that loses its teeth as it grows up. All of these species are theropods. And all of these differ wildly in their lifestyles, diets, physiques, and more. Halszkaraptor, the first amphibious theropod, is part of that revolution.

“It’s exhilarating and yet almost embarrassing thinking back on how typecast these beasties were just a few short decades ago,” says Lindsay Zanno, from the North Carolina Museum of Natural Sciences. In particular, “the theropod section of the dinosaur family tree continues to be in flux as specimens like this one keep popping up.”

“There’s great potential for future dinosaur-fossil hunting,” Xu adds.