Heterodontosaurus is a genus of heterodontosaurid dinosaur that lived during the Early Jurassic, 200–190 million years ago. Its only known member species, Heterodontosaurus tucki, was named in 1962 based on a skull discovered in South Africa. The genus name means "different toothed lizard", in reference to its unusual, heterodont dentition; the specific name honours G. C. Tuck, who supported the discoverers. Further specimens have since been found, including an almost complete skeleton in 1966. Though it was a small dinosaur, Heterodontosaurus was one of the largest members of its family, reaching between 1.18 m (3 ft 10 in) and possibly 1.75 m (5 ft 9 in) in length, and weighing between 2 and 10 kg (4.4 and 22.0 lb). The skull was elongated, narrow, and triangular when viewed from the side. The front of the jaws were covered in a horny beak. It had three types of teeth; in the upper jaw, small, incisor-like teeth were followed by long, canine-like tusks. A gap divided the tusks from the chisel-like cheek-teeth. The body was short with a long tail. The five-fingered forelimbs were long and relatively robust, whereas the hind-limbs were long, slender, and had four toes. Heterodontosaurus is the eponymous and best-known member of the family Heterodontosauridae. This family is considered a basal (or "primitive") group within the order of ornithischian dinosaurs, while their closest affinities within the group are debated. In spite of the large tusks, Heterodontosaurus is thought to have been herbivorous, or at least omnivorous. Though it was formerly thought to have been capable of quadrupedal locomotion, it is now thought to have been bipedal. Tooth replacement was sporadic and not continuous, unlike its relatives. At least four other heterodontosaurid genera are known from the same geological formations as Heterodontosaurus.
History of discovery
The holotype specimen of Heterodontosaurus tucki (SAM-PK-K337) was discovered during the British–South African expedition to South Africa and Basutoland (former name of Lesotho) in 1961–1962. Today, it is housed in the Iziko South African Museum. It was excavated on a mountain at an altitude of about 1,890 m (6,201 ft), at a locality called Tyinindini, in the district of Transkei (sometimes referred to as Herschel) in the Cape Province of South Africa. The specimen consists of a crushed but nearly complete skull; associated postcranial remains mentioned in the original description could not be located in 2011. The animal was scientifically described and named in 1962 by palaeontologists Alfred Walter Crompton and Alan J. Charig. The genus name refers to the different-shaped teeth, and the specific name honors George C. Tuck, a director of Austin Motor Company, who supported the expedition. The specimen was not fully prepared by the time of publication, so only the front parts of the skull and lower jaw were described, and the authors conceded that their description was preliminary, serving mainly to name the animal. It was considered an important discovery, as few early ornithischian dinosaurs were known at the time. The preparation of the specimen, i.e. the freeing of the bones from the rock matrix, was very time consuming, since they were covered in a thin, very hard, ferruginous layer containing haematite. This could only be removed by a diamond saw, which damaged the specimen.
In 1966, a second specimen of Heterodontosaurus (SAM-PK-K1332) was discovered at the Voyizane locality, in the Elliot Formation of the Stormberg Group of rock formations, 1,770 m (5,807 ft) above sea level, on Krommespruit Mountain. This specimen included both the skull and skeleton, preserved in articulation (i.e. the bones being preserved in their natural position in relation to each other), with little displacement and distortion of the bones. The postcranial skeleton was briefly described by palaeontologists Albert Santa Luca, Crompton and Charig in 1976. Its forelimb bones had previously been discussed and figured in an article by the palaeontologists Peter Galton and Robert T. Bakker in 1974, as the specimen was considered significant in establishing that Dinosauria was a monophyletic natural group, whereas most scientists at the time, including the scientists who described Heterodontosaurus, thought that the two main orders Saurischia and Ornithischia were not directly related. The skeleton was fully described in 1980. SAM-PK-K1332 is the most complete heterodontosaurid skeleton described to date. Though a more detailed description of the skull of Heterodontosaurus was long promised, it remained unpublished upon the death of Charig in 1997. It was not until 2011 that the skull was fully described by the palaeontologist David B. Norman and colleagues.
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