Hairy Museum of Natural History

Heterodontosaur Edition

These grumpy looking critters are Heterodontosaurus, the “differently-toothed dinosaur”. Unlike us mammals, who have been packing several different sizes and shapes of teeth into our mouths almost since we were sphenacodonts*, dinosaurs (and most other reptiles) generally made do with only one or two tooth styles, repeated throughout their mouths.

Tyrannosaurus, for example, had pointed, nipping teeth at the very front of its mouth with pointed, tearing teeth further back. Sauropods like Diplodocus had a row of uniform peg-like teeth for raking foliage into their mouths. Even the duckbilled hadrosaurs, who evolved a unique and efficient way to chew their food, had only one type of small, leaf-shaped tooth packed next to hundreds of teeth just like it in massive grinding surfaces.

So a little dinosaur with sharp nipping teeth, large tusks, and a row of closely packed plant-shredding teeth is just a bit unusual.

The shredding teeth (behind the cheeks in this restoration) were most likely used to process vegetation. And the nipping teeth could have worked with the slender beak at the front of the mouth to crop the greenest, freshest bits of leaves and fronds. But what about the large, fanglike tusks? One clue comes from different types of small deer that live today in the forests of Asia and Indonesia. Male muntjacs and mouse deer have sharp, tusklike canines that are used as weapons in fights over females or territory.

Heterodontosaurus seemed well equipped for such face-to-face combat. The heterodontosaur skull has prominent cheekbones that could have been used in shoving matches. The angry stare depicted here comes from a bar of bone that arched over the heterodontosaur eye socket (not unlike that seen in eagles today) that might have helped protect their eyes during scuffles.

In many of today’s tusked species, only adult males bear tusks. The same has been proposed for Heterodontosaurus. At least one tuskless heterodontosaurid skull is known, but it appears to be from a different animal (called Abrictosaurus). So the skull of Abrictosaurus could be female, juvenile, or a member of a heterodontosaur species that got along just fine without any tusks. Until more specimens are found, it is impossible to say whether or not heterodontosaur tusks were strictly a male trait. In this restoration, a slightly more colorful male stands watch over an equally-tusked female, reclining among the arid sandy dunes of an early Jurassic desert.

*The famous sphenacodont Dimetrodon is named for its two different sizes of tooth.

—Matt Celeskey.

File under: Dinosaurs, Jurassic.