The plant-eating dinosaur Fruitadens wouldn't strike much fear into a poodle, let alone your average dinosaur. Less than a meter long and weighing under a kilogram, Fruitadens seems wholly unremarkable apart from its tininess. But just look inside its mouth.
Fruitadens is an example of a very special type of dinosaur called heterodontosaurids. These rare species were found everywhere from South Africa to England between about 200 and 140 million years ago, and they are distinctive for their fangs. These giant sharp teeth complemented their more standard set of teeth adapted for eating plants. According to the latest paleontological research, the fangs were likely used to chow down on insects and other tiny organisms, while its other teeth were used for eating plants. Brian Switek has a good explanation over at Dinosaur Tracking:
Fruitadens was a heterodontosaurid-a group of small, bipedal dinosaurs with skulls lined with several different kinds of teeth. In addition to leaf-shaped teeth suited to crushing through vegetation, heterodontosaurids also possessed a set of sharp, piercing teeth at the front of the jaw, including a set that looked like canines.
Fruitadens had the dental armament of an omnivore. The dinosaur's varied set of teeth looks best suited to gripping and puncturing insects as well as plants. After reconstructing the dinosaur's musculature, the paleontologists examined how Fruitadens would have bitten into its meals. This dinosaur, the researchers found, was capable of opening its jaws wide and delivering quick bites-a skill set different from that of its larger cousin Heterodontosaurus, which had a more powerful bite at a smaller gape.
These heterodontosaurids evolved from exclusively plant-eating ancestors, and the fangs were a specialized adaptation that allowed them to start eating meat just as effectively. Fruitadens represents another evolutionary jump towards being omnivorous, as these quick bites would have made it much better at capturing animals than earlier examples like Heterodontosaurus. For more, check out Dinosaur Tracking and the original paper at PLoS ONE.
Artist's reconstruction of Fruitaden by Smokeybjb, via PLoS ONE Blog.