Hadrosaurs, like the Edmontosaurus pictured here, had a unique way of chewing that probably involved a side-to-side motion of their upper jaws, but scientists aren't sure exactly how it worked. Wikimedia Commons

Despite being dubbed duck-billed, the dinosaurs in the hadrosaur family don't swallow their food whole like ducks do. Their shovel-like jaws, unlike a bird's beak, are lined with hundreds of teeth arranged in overlapping layers, a formidable arrangement known as a 'dental battery.'

But researchers are still debating how exactly hadrosaurs employed their impressive dental equipment in chewing.

In 2009, British scientists, led by a geologist from the University of Leicester, took a very close look at the fossilized teeth of hadrosaurs. In a paper published in the Proceedings of the National Academy of Scientists, the team analyzed hundreds and hundreds of microscopic scratches on the dinosaurs' teeth and concluded that hadrosaurs' jaws moved in a way unlike those of any animal alive today.

When a hadrosaur bit down on its food, its upper jaws were forced outwards, scraping the upper and lower teeth sideways across each other to grind up plant material.

That sort of sideways motion has been a popular theory for decades, but now some scientists are questioning whether the dramatic skull movements proposed by Johns Hopkins paleontologist David Weishampel and visualized here in a video from animator David Cheney --

-- are even possible.

The Canadian Museum of Nature recently posted a video critiquing the classic side-to-side model.

We see the peculiar skull movements and disarticulations that would have had to occur in order for this original classic chewing theory to occur, the museum said in its caption for the video.

The museum's video also illustrates an alternative theory of hadrosaur chewing, in which there is still some side-to-side motion, but it's not quite as pronounced as the swinging upper jaw that some scientists have proposed.

This goes to show just how much we still have to learn about dinosaurs, Smithsonian Magazine writer Brian Switek wrote on Monday.

While hadrosaurs didn't eat like ducks, other dinosaurs gulped their food down whole, it turns out.

In a 2011 article in the journal Biological Reviews, a group of German scientists said they thought the sauropods -- long-necked behemoths like the classic Apatosaurus -- swallowed their food whole. Not chewing their food was a way for the big plant eaters to maximize their foraging efficiency. And by avoiding chewing, sauropods also avoided a lot of wear and tear on their jaws from the horsetail plants they ate, which contain a lot of silicon particles that can sand down an herbivore's teeth.