Sauropods were the largest animals to ever live on land. They were behemoths with long necks and equally long tails, and they needed four thick, pillar-like legs to support their massive frames. Or did they?

Back in 2007, paleontologists unearthed some bizarre sauropod tracks at a quarry near Austin, Texas. The tracks were ordinary enough, easily identifiable as sauropod footprints by their sheer size. But as more and more of the tracks were uncovered, the researchers noticed a pattern. All of the footprints were made by the front legs of the animals only, reports New Scientist.

It looked as if these dinosaurs were walking around exclusively on their front limbs. Surely a beast of this size was not capable of doing handstands?

As strange as this scene might sound, it's not unheard of. Forefoot-only sauropod tracks have been found elsewhere too, but these findings are so rare that it was easy for researchers to dismiss them. This latest discovery, however, contained at least 60 separate impressions, and none of them were made by hind legs. It was a find that demanded an explanation.

Now, finally, that explanation may have arrived. In a paper recently published in Ichnos, researchers from the Heritage Museum of the Texas Hill Country, the Houston Museum of Natural Sciences, and Purdue University provide a compelling theory that the largest dinosaurs to ever walk the land might have been semi-aquatic.

The paper, provocatively titled "Thunder lizard handstands," proposes that these tracks could be the result of the dinosaurs wading across a shallow lake or river, essentially using their front feet to "punt" across the bottom while the hind limbs floated behind.

Of course, no one seriously considered that sauropods could walk bipedally, and certainly not with their front limbs. It makes sense that such massive creatures might have taken a load off by wading through water instead of fighting gravity to trudge over land. Still, it's funny to think of these intimidating beasts doggy-paddling across a lake.

The theory is supported by the fact that all of the uncovered footprints occur at a wider distance than normal four-limbed tracks, indicating a much longer gait. This is easy to explain if the animals are imagined floating a ways between steps.

While it might be tempting to think that this means sauropods were adept swimmers, the researchers aren't ready to go quite that far. To leave tracks at all, it means the dinosaurs were still able to touch the bottom while they moved along, and their weight was heavy enough to leave deep impressions. So it's likely that this was a shallow body of water, and that the animals were probably only about shoulder deep.

Still, sauropods were probably more buoyant than their mammoth bodies might otherwise suggest. They had huge lungs, and air sacs in their bones that could have assisted with this kind of wading behavior.

More similar finds will be needed before paleontologists can say for sure that sauropods were truly semi-aquatic. It's possible that this was unusual behavior, only used sparingly by the beasts to cross rivers or other waterways, not as a regular means of locomotion. Elephants can wade through water on occasion too, but that doesn't make them semi-aquatic.

Even so, it goes to show that we've got a lot more to learn about these gentle prehistoric giants.

Bryan Nelson ( @@brynelson ) writes about everything from environmental problems here on Earth to big questions in space.

Bizarre dinosaur tracks make it look like these behemoths did handstands
Researchers think they may have clues after looking at 60 impressions of sauropod tracks.