It looks like a duck, it walks like a duck, and it swims like a duck—but it’s a predatory dinosaur unlike any scientists have seen before.

A study published this week in the journal Nature has introduced the world to the Halszkaraptor escuilliei, the first amphibious dinosaur ever discovered. It’s believed to have lived some 75 million years ago in the Ukhaa Tolgod area of Mongolia’s Gobi Desert, known as a treasure trove of Cretaceous-era dinosaur bones. The unusual creature came to light in recent years after its fossil was purchased by a private French collector named François Escuillié, who contacted paleontologist Pascal Godefroit in 2015 for an expert opinion.

At first, Godefroit’s team believed that the fossil, encased in a 15-inch block of stone, was comprised of multiple skeletons glued together. Its body just didn’t make sense. The research team headed to Grenoble, France to scan the creature using a particle accelerator. Their findings, published in Nature, confirmed that it was, in fact, a very unusual dinosaur.

While the Halszkaraptor belongs to a family of predatory, mostly meat-eating, theropods, along with the Tyrannosaurus Rex and Velociraptor, it varies so significantly that it was given its own species, genus and subfamily. Equipped with distinctive sickle-shaped claws like a Velociraptor, it also has a long, flexible neck and tapering snout (like a swan). Its snout has long bones and a networks of nerves, like aquatic reptiles such as the crocodile. It also has twice the normal number of teeth of a typical dinosaur, reminiscent of fish-eating animals.

View from a 3-D rendering of the Halszkaraptor escuilliei dinosaur fossil, computed from data obtained at the European Synchrotron Radiation Facility in Grenoble, France. The creature, about 18 inches tall, had a bill like a duck but teeth like a croc’s, a swan-like neck and killer claws. (Credit: Paul Tafforeau/ESRF via AP)
View from a 3-D rendering of the Halszkaraptor escuilliei dinosaur fossil, computed from data obtained at the European Synchrotron Radiation Facility in Grenoble, France. The creature, about 18 inches tall, had a bill like a duck but teeth like a croc’s, a swan-like neck and killer claws. (Credit: Paul Tafforeau/ESRF via AP)

The strangeness doesn’t stop there. Halszkaraptor also has unusually proportioned and stubby forelimbs—not unlike those of a penguin or puffin—that appear as if they were used to swim. But while the creature might look purely aquatic, its back half is built like a land animal, with a tail and long legs. Its tail, however, wasn’t long enough to counterbalance its long neck. To balance itself, the Halszkaraptor likely stood very upright—about 45 centimeters tall—and walked on two feet.

University of Bologna paleontologist Andrea Cau, a member of Godefroit’s research team and co-author of the Nature article, believes Halszkaraptor lived in an unstable environment, where it needed to cope with cycles of both freshwater and droughts.

The unusual fossil is one of several new discoveries in recent years that have revealed to scholars a greater diversity of dinosaur lifestyles. In 2014, for example, paleontologists reconstructed the biggest of all carnivorous dinosaurs, the Spinosaurus, using evidence that the giant sail-backed creature was actually semi-aquatic. Halszkaraptor is the first fully amphibious dinosaur—at least that’s currently known.