Artist's reconstruction of the dinosaur Natovenator polydontus, from the Cretaceous period, which had a streamlined body similar to that of diving birds and lived about 72 million years ago in the current Gobi desert in Mongolia.
(Photo: Yusik Choi/Handout/Reuters)
(CNN) --
A new study has found evidence that at least one species of dinosaur may have been an expert swimmer, diving into the water like a duck to hunt its prey.
The study, published in
Communications Biology
on December 1, describes a newly discovered species, the
Natovenator polydontus
.
This theropod, or hollow-bodied dinosaur with three fingers and claws on each limb, lived in Mongolia during the Late Cretaceous period, between 145 and 66 million years ago.
Scientists from Seoul National University, the University of Alberta and the Mongolian Academy of Sciences collaborated on the work.
The researchers noted that Natovenator had streamlined ribs, like those of diving birds.
"Its body shape suggests that the Natovenator was a potentially swimming predator, and that the streamlined body evolved independently in separate lineages of theropod dinosaurs," the authors wrote.
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The Natovenator specimen is very similar to Halszkaraptor, another dinosaur discovered in Mongolia, which scientists believe was likely semi-aquatic.
But the Natovenator specimen is more complete than the Halszkaraptor, making it easier for scientists to see the streamlined shape of its body.
Both the Natovenator and the Halszkaraptor likely used their forearms to propel themselves through the water, the researchers explained.
David Hone, a paleontologist and professor at Queen Mary University of London, told CNN that it's hard to say exactly where the Natovenator falls on the spectrum, whether it's entirely terrestrial or entirely aquatic.
But the specimen's arms "seem to be quite good at moving in the water," he said.
Hone participated in the review of the Communications Biology study.
In addition, the Natovenator had dense bones, essential for animals that dive below the surface of the water.
As the authors wrote, it had a "relatively hydrodynamic body."
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The next step, Hone said, would be to model the dinosaur's body shape to help scientists understand exactly how it might have moved.
"Was he paddling with his feet, a bit doggy style? How fast could he go?"
Subsequent investigations will also need to look at the environment in which the Natovenator lived.
The specimen was discovered in the Gobi desert in Mongolia, but there is evidence that lakes and other bodies of water existed in the desert in the past.
"There's a real question of, 'Okay, you've got a swimming dinosaur in the desert, what is it swimming in?'" he said.
"Finding the fossil record for those lakes is going to be difficult, but sooner or later we may well find one. And when we do, we may find many more of these objects."
Nizar Ibrahim, Senior Lecturer in Palaeontology at the University of Portsmouth, whose research work has included findings indicating that Spinosaurus was likely semi-aquatic, told CNN he is still not entirely convinced by the study's conclusions.
He argued that a more rigorous quantitative analysis would have made the findings more convincing.
"I would have liked to see, for example, a really robust depiction of bone density, the osteohistology of the animal, within a larger data set," he said.
"Even the anatomy of the ribs, if they had put that into a bigger picture, the big data set, it would have been helpful."
The "anatomical evidence is less direct" for a swimming Natovenator than for a swimming Spinosaurus, he said.
And, like Hone, he's also curious as to exactly what waters the Natovenator might have swum into.
"The environment in which this animal was found in Mongolia is exactly the opposite of what you would expect for a water-loving animal," he said.
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But he hopes the study can help open the door to broader ideas about dinosaur behavior.
Until now, dinosaurs were considered strictly terrestrial, but evidence is mounting to suggest that at least some species spent as much time in the water as they did on land.
"I'm sure there will be many, many more surprises," Ibrahim said.
"And we'll find that dinosaurs were not only around for a long time, but also, you know, they were very diverse and very good at invading new environments."
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