From movies to museums, the most famous dinosaurs are among the largest. We like superlatives, and want to know what the biggest, fastest, and fiercest dinosaurs are. Yet, just like living animals, dinosaurs came in a variety of shapes and sizes, and a team of paleontologists has just announced, in the Proceedings of the Royal Society B, one of the smallest dinosaurs yet discovered
Named Fruitadens haagarorum, this diminutive dinosaur from the 150-million-year-old strata of western Colorado was only about two-and-a-half feet long. It was a heterodontosaurid, or a member of a group of ornithischian dinosaurs that split off early from the family tree and persisted for millions of years. It is the first time a heterodontosaurid dinosaur has been found in North America.
While many other ornithischian dinosaurs like hadrosaurs and horned dinosaurs were herbivores, though, it appears that Fruitadens was an omnivore. Like other heterodontosaurids it had at least three kinds of teeth: peg-like teeth at the front of the jaw, a single large "tusk" or canine-like tooth, and a series of leaf-shaped teeth good for shearing plants. This would have allowed it to eat a variety of foods, including meat, and its small body size probably meant that it had to.
The bodies of small animals are typically more energetically expensive than those of large ones, meaning that small animals have to find high-quality food like fruit and flesh and consume a lot of it. They cannot get by eating only relatively poor-quality food such as leaves. Such is the price of small body size, and thus Fruitadens may have been a late-surviving relic of an early radiation of small, omnivorous dinosaurs that later gave rise to more specialized plant-eating giants.