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 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.

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.

A partial snout (NM QR 1788) found in 1975 on Tushielaw Farm south of Voyizane was thought to belong to Massospondylus until 2011, when it was reclassified as Heterodontosaurus.

The palaeontologist Robert Broom discovered a partial skull, possibly in the Clarens Formation of South Africa, which was sold to the American Museum of Natural History in 1913, as part of a collection that consisted almost entirely of synapsid fossils.

This specimen (AMNH 24000) was first identified as belonging to a sub-adult Heterodontosaurus by Sereno, who reported it in a 2012 monograph about the Heterodontosauridae, the first comprehensive review article about the family.

The specimen was therefore scanned at the European Synchrotron Radiation Facility in 2016, to help reveal the skeleton, and aid in research of its anatomy and lifestyle, some of which was published in 2021.

[11][12][13] In 1970, palaeontologist Richard A. Thulborn suggested that Heterodontosaurus was a junior synonym of the genus Lycorhinus, which was named in 1924 with the species L. angustidens, also from a specimen discovered in South Africa.

He reclassified the type species as a member of the older genus, as the new combination Lycorhinus tucki, which he considered distinct due to slight differences in its teeth and its stratigraphy.

[16] In spite of the controversy, neither party had examined the L. angustidens holotype first hand, but after doing so, palaeontologist James A. Hopson also defended generic separation of Heterodontosaurus in 1975, and moved L. consors to its own genus, Abrictosaurus.

A second specimen, consisting of an incomplete skull, indicates that Heterodontosaurus could have grown substantially larger – up to a length of 1.75 m (5 ft 9 in) and with a body mass of nearly 10 kg (22 lb).

The left and right upper temporal fenestrae were separated by the sagittal crest, which would have provided lateral attachment surfaces for the jaw musculature in the living animal.

Eleven tall and chisel-like cheek-teeth lined each side of the posterior parts of the upper jaw, which were separated from the canines by a large diastema (gap).

[33] In 2006, palaeontologist Xu Xing and colleagues named the clade Heterodontosauriformes, which included Heterodontosauridae and Marginocephalia, since some features earlier only known from heterodontosaurs were also seen in the basal ceratopsian genus Yinlong.

[8][3] The cladogram below shows the interrelationships within Heterodontosauridae, and follows the analysis by Sereno, 2012:[35] Echinodon Fruitadens Tianyulong Lycorhinus Pegomastax Manidens Abrictosaurus Heterodontosaurus Heterodontosaurids persisted from the Late Triassic until the Early Cretaceous period, and existed for at least a 100 million years.

The unique tooth and jaw features of heterodontosaurines appear to be specialisations for effectively processing plant material, and their level of sophistication is comparable to that of later ornithischians.

[38] In 1974, Thulborn proposed that the tusks of the dinosaur played no important role in feeding; rather, that they would have been used in combat with conspecifics, for display, as a visual threat, or for active defence.

[1][10][39] In 2000, Paul Barrett suggested that the shape of the premaxillary teeth and the fine serration of the tusks are reminiscent of carnivorous animals, hinting at facultative carnivory.

Sereno surmised that heterodontosaurids were comparable to today's peccaries, which possess similar tusks and feed on a variety of plant material such as roots, tubers, fruits, seeds and grass.

Simultaneously, Thulborn stressed that a regular tooth replacement was essential for these animals, as the supposed diet consisting of tough plant material would have led to quick abrasion of the teeth.

[7] The palaeontologists Teresa Maryańska and Halszka Osmólska supported Santa Luca's hypothesis in 1985; furthermore, they noted that the dorsal spine was strongly flexed downwards in the most completely known specimen.

[47] David Weishampel and Lawrence Witmer in 1990 as well as Norman and colleagues in 2004 argued in favour of exclusively bipedal locomotion, based on the morphology of the claws and shoulder girdle.

[22][48] The anatomical evidence suggested by Santa Luca was identified as adaptations for foraging; the robust and strong arms might have been used for digging up roots and breaking open insect nests.

Even at moderate running speeds, Heterodontosaurus would have exceeded the maximum aerobic capabilities possible for an ectotherm (cold-blooded) animal, indicating endothermy in this genus.

Heterodontosaurus had an incipient APP, and its gastralia were reduced compared to non-ornithischian dinosaurs, suggesting that the pelvis was already involved in breathing while chest contraction became less important.

As shown by the juvenile skull SAM-PK-K10487, the eye sockets became proportionally smaller as the animal grew, and the snout became longer and contained additional teeth.

[15] This hypothesis was questioned by palaeontologist Richard Butler and colleagues in 2006, who argued that the juvenile skull SAM-PK-K10487 possessed tusks despite its early developmental state.

Both formations are famous for their abundant vertebrate fossils, including temnospondyl amphibians, turtles, lepidosaurs, aetosaurs, crocodylomorphs, and non-mammal cynodonts.

The Upper Elliot Formation shows the largest known heterodontosaurid diversity of any rock unit; besides Heterodontosaurus, it contained Lycorhinus, Abrictosaurus, and Pegomastax.

The high heterodontosaurid diversity have led researchers to conclude that different species might have fed on separate food sources in order to avoid competition (niche partitioning).