Between fluffy early birds, the largest land animals to ever walk the Earth and beachball-sized toads that ate baby dinosaurs, the pre-historic world was full of strange creatures. Now, palaeontologists have uncovered a bizarre new species of dinosaur that seems to blend together a swan, a penguin, a crocodile and a Velociraptor.

The new species has been named Halszkaraptor escuilliei, and its remains were found at Ukhaa Tolgod in Mongolia. Alive about 75 million years ago, Halszkaraptor belonged to the wider group known as theropods, two-legged carnivorous dinosaurs that ruled at the top of the food chain for some 160 million years.

But this creature seems to be made up of a weird mishmash of different animals. It has a long, swan-like neck, flippers on its forelimbs and sickle-shaped claws on its feet, like its cousin Velociraptor. From those features, the palaeontologists infer that Halszkaraptor was an amphibious predator.

"The first time I examined the specimen, I even questioned whether it was a genuine fossil," says Andrea Cau, lead author of the study. "This unexpected mix of traits makes it difficult to place Halszka within traditional classifications."

To learn more about it, the researchers used synchrotron multi-resolution X-ray microtomography to peer inside the fossil without damaging it. That process scans the bones and reconstructs a three-dimensional image of the skeleton. The first step was to determine that the weird mix of body parts actually belonged to a single animal, and wasn't just a jumbled pile of old bones from a whole menagerie.

Sure enough, the data revealed that Halszkaraptor was a creature every bit as bizarre as it seemed. The team was able to infer from the scan that the animal would have waddled on land like a duck, used its flippers to propel itself through the water like a penguin and used its long neck to forage and hunt like a swan.

The synchrotron scan also allowed the scientists to observe unusual features hidden inside the rock and bone, which would have been impossible to see otherwise.

"Our analysis demonstrated that numerous teeth, which are not visible externally, are still preserved inside the mouth," says Vincent Beyrand, co-author of the study. "We also identified a neurovascular mesh inside its snout that resembles those of modern crocodiles to a remarkable degree. These aspects suggest that Halszka was an aquatic predator."

Armed with that information, the researchers were better able to place Halszkaraptor on the dinosaur family tree. Not only was a new species named, but a new group dubbed Halszkaraptorinae was added to the family of dromaeosaurs, commonly known as raptors. Conveniently enough, several other theropods which previously defied classification were found to be closely related to Halszkaraptor, and so were placed into the new group.

"When we look beyond fossil dinosaurs, we find most of Halszkaraptor's unusual features among aquatic reptiles and swimming birds," says Cau. "The peculiar morphology of Halszkaraptor fits best with that of an amphibious predator that was adapted to a combined terrestrial and aquatic ecology: a peculiar lifestyle that was previously unreported in these dinosaurs. Thanks to synchrotron tomography, we now demonstrate that raptorial dinosaurs not only ran and flew, but also swam!"

The research was published in the journal Nature.

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