Heterodontosaurus

Heterodontosaurus gets its name from its teeth—"different toothed lizard"—because its mouth contained three distinct types. It lived during the Early Jurassic, between 200 and 190 million years ago, and is the best-known member of the Heterodontosauridae family, a basal group within the ornithischian dinosaurs. The only recognized species, *Heterodontosaurus tucki*, was named in 1962 after a skull turned up in South Africa; the species name honors G. C. Tuck, who backed the expedition that found it. More specimens followed, including a nearly complete skeleton unearthed in 1966.

Though small, this dinosaur was among the largest in its family. It could reach 1.18 to maybe 1.75 meters in length and weighed between 2 and 10 kilograms. Its skull was long, narrow, and triangular from the side, with a horny beak covering the front of the jaws. The upper jaw held small, incisor-like teeth, then long, canine-like tusks, separated by a gap from chisel-shaped cheek teeth. The body was short, the tail long. Its five-fingered forelimbs were long and sturdy, while the hind limbs were long, slender, and ended in four toes.

Despite those big tusks, *Heterodontosaurus* is thought to have been herbivorous or at least omnivorous. It was once considered capable of walking on all fours, but scientists now believe it was bipedal. Unlike its relatives, its tooth replacement was sporadic, not continuous. At least four other heterodontosaurid genera come from the same rock formations.

The first specimen, the holotype (SAM-PK-K337), was dug up during a British–South African expedition to South Africa and Basutoland (now Lesotho) in 1961–1962. It came from a mountain about 1,890 meters high, at a site called Tyinindini in the Cape Province’s Transkei district. The find was a crushed but nearly complete skull; any associated body bones mentioned in the original description were missing by 2011. Paleontologists Alfred Walter Crompton and Alan J. Charig described and named it in 1962. Because the specimen wasn’t fully prepared when published, only the front of the skull and lower jaw were described, and the authors called it a preliminary account. At the time, few early ornithischians were known, so the discovery was important. Preparation took ages because the bones were coated in a hard, thin, iron-rich layer containing haematite, which had to be cut away with a diamond saw, damaging the fossil.

In 1966, a second specimen (SAM-PK-K1332) turned up at the Voyizane locality in the Elliot Formation of the Stormberg Group, on Krommespruit Mountain at 1,770 meters elevation. This one included both skull and skeleton, with bones still in their natural positions and little distortion. The postcranial skeleton got a brief description in 1976 from Albert Santa Luca, Crompton, and Charig. Its forelimb bones had already been discussed in a 1974 article by Peter Galton and Robert T. Bakker, who saw the specimen as evidence that Dinosauria was a natural group—most scientists then thought the two main orders, Saurischia and Ornithischia, weren’t directly related. The full skeleton description came in 1980. SAM-PK-K1332 remains the most complete heterodontosaurid skeleton known. A promised detailed skull description never appeared before Charig died in 1997; it was finally published by David B. Norman and colleagues in 2011.

Other specimens assigned to *Heterodontosaurus* include a juvenile skull front (SAM-PK-K10487), a partial maxilla (SAM-PK-K1326), and a left maxilla with teeth and nearby bones (SAM-PK-K1334), all from Voyizane in 1966–1967, though the juvenile wasn’t identified as *Heterodontosaurus* until 2008. A partial snout (NM QR 1788) found in 1975 on Tushielaw Farm was thought to belong to *Massospondylus* until 2011. Paleontologist Robert Broom discovered a partial skull, possibly in South Africa’s Clarens Formation, that was sold to the American Museum of Natural History in 1913 among mostly synapsid fossils. That specimen (AMNH 24000) was first identified as a sub-adult *Heterodontosaurus* by Sereno in a 2012 monograph. The same review also classified a partial postcranial skeleton (SAM-PK-K1328) from Voyizane as *Heterodontosaurus*, though in 2014 Galton suggested it might belong to the related genus *Pegomastax*.