Science Question From a Toddler: Omnivore Dinosaur

Anyone who's watched "Jurassic Park" (and, subsequently, thought up a velociraptor escape plan) knows there were meat-eating dinosaurs. Anyone who's had to talk a child (or themselves) down from a post-"Jurassic Park" nightmare knows that most dinosaurs ate plants. But Pbryden's 4-year-old wants to know whether any dinosaurs ate both.

That sounds like just the kind of thing velociraptors would do to trick you into complacency…

That aside, the idea that a dinosaur would eat both flora and fauna makes a lot of sense. After all, birds evolved from dinosaurs. And plenty of birds are omnivorous. But what birds eat is easy to verify. We can toss a bucket full of varied grub into a pack of chickens and watch as they dine happily on everything from cabbage to, um, chicken. Paleontology doesn't really work that way (thank God). So how do scientists know what dinosaurs ate? They look to the teeth.

Today, animals that eat only plants and animals that eat only meat have very different sorts of teeth. Carnivore teeth tend to be pointy, curved and serrated–good for holding a wriggling victim and ripping through flesh. Herbivores, on the other hand, don't usually have much of an issue with their dinner escaping. Their teeth have a wider variety of shape across species–meat is more of a uniform product than plant life–and within the mouth of a herbivore you'll often find a mix of pointy-but-blunted teeth (for biting off hunks of plant) and some flat teeth (for grinding and chewing the plants). Scientists use these traits to interpret what they see in the mouths of dinosaurs.

It doesn't always work perfectly. For instance, prosauropods—a family of dinosaurs that tended to look sort of like a bi-pedal version of the more familiar long-tailed, long-necked Apatosaurus (nee Brontosaurus)—were once thought to be carnivorous, according to Emory University professor Anthony J. Martin. After all, they had serrated teeth. But later research—based on the teeth of modern plant-eating reptiles—turned up a better theory. Some herbivorous dinos had serrated teeth, but the serrations where different—more course and pointing in different directions—than the serrations on meat-eating teeth. The serrations helped animals like the prosauropods cut through thick, woody vegetation.

Because this is all a bit inexact, there's a lot of debate over whether omnivorous dinosaurs existed. In 2006, Dr. Martin wrote that there wasn't yet any real compelling evidence of omnivorous dino-diets from stomach contents or fossilized poop. Therizinosaurs—a truly weird-looking creature that walked on two legs, had a long neck, and sported a set of front claws that made it look like the improbable love-child of Edward Scissorhands, Wolverine and a sloth—is often cited as an omnivore. But it's actual diet is still unclear. There's a good chance it was just another herbivore or, possibly, an insectivore.

Heterodontosaurus is another possible candidate for the omnivorous dino crown. It's very name means "different-teeth-lizard". It might as well be called, "Wow, that's pretty freakin' weird." Heterodontosaurus has a larger variety of different types of teeth than most other dinosaurs. You'll often hear it compared to human teeth, which feature bitey, grindy and rippy options. Some scientists think that means Heterodontosaurus ate an equally varied diet. Fruitadens haagarorum, for instance, is a raccoon-sized relative of the Heterodontosaurus whose discoverers think probably dined on fruit and insects. Others, however, say that—like the prosauropods—all the heterodontosaurids were likely using their funky teeth to process plants.

The final verdict: If Pbryden's 4-year-old wants a firm answer, he or she may want to consider a career studying fossilized dinosaur poop. This is one discovery that's still waiting to happen.