If it walks like a duck and swims like a duck, it might be a dinosaur. Scientists have discovered a flippered theropod dinosaur that appears to have spent much of its life in water.
The fossil of Halszkaraptor escuilliei, described in the journal Nature, reveals a strange dinosaur that defies paleontologists' expectations: one that mixes the traits of theropod dinosaurs with those of aquatic or semi-aquatic birds and reptiles today.
"The first time I saw the fossil I was shocked," said lead author Andrea Cau, a paleontologist at the Geological and Palaeontological Museum Giovanni Capellini in Italy. "It was so unexpected and bizarre."
H. escuilliei lived some 75 million years ago, during the Cretaceous Period. It was a theropod, a largely carnivorous group of dinosaurs whose members included Tyrannosaurus rex and the ancestors of all living birds.
H. escuilliei, called Halszka for short, was part of the dromaeosauridae, a group of feathered theropods that included velociraptor and that were not birds or bird ancestors, but closely related to them. While no feathers survived on this specimen, Halszka probably sported plumage and it had a somewhat birdlike bill that was still not a true beak (in part because it housed several teeth).
Halszka had a long, swanlike neck, was the size of a goose, and it probably spent much of its time in lakes and rivers eating small fish, crustaceans and small animals such as lizards, Cau said. In this dino-eat-dino world, its predators may have included fellow theropods like velociraptor.
This fossil, which is still partly embedded in rock, was originally poached from Mongolia, passing through several private collections before a French fossil dealer acquired it in 2015 and donated it to the Royal Belgian Institute of Natural Sciences. It quickly struck researchers as an oddball.
"We're used to thinking of dromaeosaurs in the context of the classic raptors -- velociraptor and Deinonychus and Utahraptor, because we now know they're totally feathered and so forth -- as sort of knife-footed murder-birds," said Thomas Holtz Jr., a vertebrate paleontologist at the University of Maryland in College Park who was not involved with the study.
But this new fossil, he said, is one "weird ... looking dromaeosaur."
This dinosaur did have a curved sickle-like claw on the second toe of the foot that is typical of dinosaurs like velociraptor, but it was not especially long and probably wasn't used that much for hunting, Holtz said. Meanwhile, its "arms" were small and appeared to have been modified for use as flippers, which could have helped it paddle through the water.