Fruitadens and the Dinosaur Diet

When asked to account for why dinosaurs are so popular, psychologist Sheldon White delivered the simple answer: “Big, fierce and extinct.” Our perennial favorites—Tyrannosaurus, Triceratops, Stegosaurus, Diplodocus and so on—were all gigantic and wielded a potential for destruction unlike anything alive today. From the time that dinosaurs were first recognized by science, we have brought them back to life in art and museum reconstructions only to eviscerate each other once more. To borrow a few lines from Tennyson’s In Memoriam, we often see dinosaurs as “dragons of the prime, that tare each other in their slime.”

But a dinosaur’s ferocity lies at the intersection of anatomy and imagination. We cheer Mesozoic conflicts, but dinosaurs did not spend every waking hour trying to eat and avoid being eaten. Nor were all dinosaurs titans. The largest sauropods stretched more than 100 feet in length, but the smallest dinosaur we know of is the bee hummingbird—a minuscule avian that weighs less than two grams and is about two inches long. While not quite that tiny, there were small non-avian dinosaurs, too. One of the smallest—a Jurassic omnivore named Fruitadens haagarorum—has just received a detailed description in PLoS One.

Found in the 150-million-year-old rock of Colorado, Fruitadens lived in the shadow of Jurassic giants. The relatively puny dinosaur was only about three feet long as an adult. But the most remarkable aspect of this dinosaur is its dentition. 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. And thanks to a peculiar form called Tianyulong, we know that at least some of these dinosaurs sported a mane of bristly filaments along their backs.

Whether Fruitadens was similarly decorated—as restored in sculptures at the Natural History Museum of Los Angeles—is unknown. The rock in which the little dinosaur was found doesn’t record the intricacies of the feather-like body coverings. All we know of Fruitadens comes from the animal’s bones, and the new paper by paleontologist Richard Butler and colleagues focuses on the dinosaur’s skull.

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. But Butler and co-authors went beyond simply, giving Fruitadens a dental exam. 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. A weaker, quicker bite, the paleontologists hypothesized, indicates that Fruitadens might have been catching invertebrates as well as crushing plants in its jaws, and this represents a dietary shift from earlier, more herbivorous heterodontosaurids.

When I was introduced to dinosaurs as a child, I was often told that the entire swath of dinosaurian diversity could be divided into carnivores and herbivores. Theropods were the meat eaters, and all other dinosaurs—the sauropods and the whole ornithischian group—chewed plants. Nice and simple. And also wrong. Many theropod lineages, particularly feather-bearing coelurosaurs, shifted from carnivorous to omnivorous and herbivorous diets. And as Fruitadens shows, some ornithischian dinosaurs were probably omnivores that consumed whatever small prey they could catch. The dinosaur diet was not a simply a choice between steak or salad.

For more on Fruitadens, see Andy Farke’s post on the new paper at the official PLoS blog.

References:

Butler, R., Porro, L., Galton, P., & Chiappe, L. (2012). Anatomy and Cranial Functional Morphology of the Small-Bodied Dinosaur Fruitadens haagarorum from the Upper Jurassic of the USA PLoS ONE, 7 (4) DOI: 10.1371/journal.pone.0031556

Gould, S.J. 1991. Bully for Brontosaurus. New York: W.W. Norton & Company. pp. 94-106

Riley Black | | READ MORE

Riley Black is a freelance science writer specializing in evolution, paleontology and natural history who blogs regularly for Scientific American.