page_title: Heterodontosaurus
section_title: Locomotion and metabolism
hierarchical_section_title: Heterodontosaurus / Palaeobiology / Locomotion and metabolism
caption_attribution_description: Limbs of Heterodontosaurus tucki from the Lower Jurassic Upper Elliot and Clarens formations of South Africa. Reconstructions based on an adult skeleton (SAM-PK-K1332). Right forearm, carpus and manus (A), right distal tarsals and pes (B). Abbreviations: I-V digits I-V ce centrale dc1-5 distal carpals 1–5 dt3, 4 distal tarsal 3, 4 fo foramen mc1, 4, 5 metacarpal 1, 4, 5 mt1-4 metatarsals 1–4 ol olecranon ph phalanx pi pisiform ra radius rae radiale ul ulna ule ulnare un ungual.
context_page_description: 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 honors 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 and possibly 1.75 m in length, and weighing between 2 and 10 kg. 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.
context_section_description: Although most researchers now consider Heterodontosaurus a bipedal runner, some earlier studies proposed a partial or fully quadrupedal locomotion. In 1980, Santa Luca described several features of the forelimb that are also present in recent quadrupedal animals and imply a strong arm musculature: These include a large olecranon (a bony eminence forming the uppermost part of the ulna), enlarging the lever arm of the forearm. The medial epicondyle of the humerus was enlarged, providing attachment sites for strong flexor muscles of the forearm. Furthermore, projections on the claws might have increased the forward thrust of the hand during walking. According to Santa Luca, Heterodontosaurus was quadrupedal when moving slowly but was able to switch to a much faster, bipedal run. 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. In 1987, Gregory S. Paul suggested that Heterodontosaurus might have been obligatorily quadrupedal, and that these animals would have galloped for fast locomotion. 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. 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.
  Most studies consider dinosaurs as endothermic (warm-blooded) animals, with an elevated metabolism comparable to that of today's mammals and birds. In a 2009 study, Herman Pontzer and colleagues calculated the aerobic endurance of various dinosaurs. 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.
caption: Diagrams showing hand and foot bones of specimen SAM-PK-K1332
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