|1st Species||Heterodontosaurus tucki|
|Time Range||200-190 mya|
|Name Meaning||Different-toothed reptile|
|Physical Dimensions||1.7 meters long|
Heterodontosaurus is a heterodontosaurid dinosaur from the Early Jurassic of South Africa. It was named in 1962 by Alfred W. Crompton and Alan J. Charig. It was a unique ornithischian dinosaur, as it had more than one type of tooth morphology, a trait that is usually only observed in mammals.
Heterodontosaurus was, in terms of physiology, a unique ornithischian. It had a build not unlike that of the more advanced ornithopods, with a small, slender body, long legs, a long tail, a small beak in front of its mouth, and large, eagle-like brows near the top of its eyes. However, it was very different in the sense that its arms were longer than other ornithischians and bore 5 grasping fingers on each hand, and that it had long, prehensile toes, a small, yet equally prehensile dewclaw, and large, fang-like tusks just behind its beak and in front of its battery of flatter back teeth. Most of its body (excluding most of its legs and all of its beak and tail) would have been covered in short, fuzz-like feathers, with quills running down its back, its tail, and the underside of its neck.
Heterodontosaurus was an herbivore, feeding on plants low to the ground by shredding them with its beak, right before proceeding to hold them in its cheeks while grinding them with the many teeth in its back. As well as this, it was once considered to be an omnivore, preying on small animals like lizards and mammals to supplement its diet; however, due to the fact that the tusk size and position of it and its relatives varied, as well as its beak, the kinds of teeth it had, and the bone structure of its jaw, this was disproved.
The function of Heterodontosaurus' tusks remains open to debate; many theories that emerged include being used for display and for intraspecific combat, as well as for weapons for attacking small vertebrate prey to supplement a potentially omnivorous diet. The very latter has been disproved, as tusk size and position within the entire heterodontosaurid family varied greatly; as well as this, its horny beak and the many teeth in the back of its mouth were shown to be suitable for shredding leaves, it had enlarged jaw muscles for chewing, and the jaw joint was just below the battery of teeth, which would have allowed for an evenly-spread out bite from its mouth (as opposed to the scissor-like bite of theropods). As well as this, earlier research considered Heterodontosaurus to be quadrupedal due to its seemingly long arms and large claws that could boost the thrust of the hand while walking, with some suggesting that it was capable of performing a mammalian gallop when running; however, it is now considered to be bipedal, as its arms actually weren't long enough for it to perform a normal quadrupedal gait, its hands were used for grasping rather than walking, and its shoulders were not heavily built enough for quadrupedal locomotion. A recently discovered foot from a later-surviving heterodontosaurid was found to have long toe bones, as well as a dewclaw that was smaller than the other toe bones, but still capable of grasping; from this, it can be assumed that Heterodontosaurus had dexterous claws not unlike those of a modern arboreal bird, and could have perched on trees from time to time.