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''Heterodontosaurus'' (meaning "different toothed lizard") is a genus of small herbivorous dinosaur with prominent canine teeth which lived in the Early Jurassic of South Africa. It was similar to a hypsilophodont in shape, and ate plants, despite its canines. ==Description== ''Heterodontosaurus'' was a small, fleetfooted ornithischian classified inside the family Heterodontosauridae. The family contains some of the smallest known ornithischians〔 – the North American ''Fruitadens'', for example, reached a length of only 65 to 75 cm.〔 ''Heterodontosaurus'' was amongst the largest known members of its family, reaching a length of between 1 to 1.75 m and weighing 1.8〔 or 10 kg.〔 Only the South African ''Lycorhinus'' might have been larger.〔〔 The skull was robustly built and triangular in side view. The front of the jaws where covered by a toothless horny beak. The upper beak was carried by the premaxilla and the lower beak by the predentary, which in ornithischians are the foremost bones of the upper and lower jaw, respectively. The eye openings were proportionally large and almost circular in shape, while the external nostril openings were small. A large spur-like bone, the palpebral, protruded backwards into the eye opening.〔 Below the eye socket, the jugal bone gave rise to a sidewards projecting horn like process. The antorbital fossa, a large depression between the eye and nostril openings, contained two smaller openings.〔 Ventrally, the antorbital fossa was bounded by a prominent bony ridge, to which the animal's fleshy cheek would have been attached. Behind the eye opening, there was the proportionally large lower temporal fenestra, which in ''Heterodontosaurus'' was egg-shaped and tilted back. The elliptical upper temporal fenestra was visible only in top view of the skull. The left and right upper temporal fenestrae were separated by a pronounced sagittal crest, which in the living animal would have provided attachment sides for the jaw musculature.〔 The neck consisted of nine cervical vertebrae, which would have followed an S-curve, as indicated by the shape of the vertebral bodies in side view: while the vertebral bodies of the anterior cervical vertebrae are shaped like a parallelogram, those of the middle were rectangular and those of the posterior showed a trapezoid shape.〔〔 The trunk was short, consisting of 12 dorsal and 6 fused sacral vertebrae.〔 The tail was long compared to the body; although incompletely known, it would probably have consisted of 34 to 37 caudal vertebrae. The dorsal spine was stiffened by ossified tendons, beginning with the forth dorsal vertebrae. This feature is present in many other ornithischians and probably countered stress caused by bending forces acting on the spine during bipedal locomotion. Different to many other ornithischians, the tail of ''Heterodontosaurus'' lacked ossified tendons, and therefore probably was flexible.〔 It had a long, narrow pelvis and a pubis which resembled those possessed by more advanced ornithischians.〔〔〔 The forelimbs were robustly built〔 and proportionally long, measuring 70% of the length of the hind limbs. The radius of the forearm measured 70% of the length of the humerus.〔 The hand was large, approaching the humerus in length, and showed five fingers equipped for grasping.〔〔 The bone in the foot and ankle were fused in a manner reminiscent of those in birds.〔〔 The second finger was the longest, followed by the third and the first finger (the thumb).〔 The first three fingers ended in large and strong claws. The forth and fifth finger were strongly reduced and possibly functionless. The phalangeal formula, which states the number of finger bones in each finger starting from the first, was 2-3-4-3-2.〔 The hindlimbs were long and gracile and ended in four toes, of which only the second, third and forth made contact with the ground. Uniquely for ornithischians, several bones of the leg and foot were fused: The tibia and fibula were fused with upper tarsal bones (astragalus and calcaneus), forming a tibiotarsus, while the lower tarsal bones were fused with the metatarsal bones, forming a tarsometatarsus.〔 This constellation can be also found in today's birds, where it has evolved independently.〔 The tibiotarsus was ca. 30% longer than the femur.〔 Following the discovery of the related ''Tianyulong'' in 2009, which was preserved with long, filamentous integuments, ''Heterodontosaurus'' has also been depicted with such structures, for example in publications by Gregory S. Paul and Paul Sereno.〔 Sereno also published a restoration of ''Heterodontosaurus'' with a hypothetical display structure located above the nasal fossa, though the function of the fossa is unknown. A similar fossa is also seen in ''Tianyulong'', ''Agilisaurus'', and ''Eoraptor''.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Heterodontosaurus」の詳細全文を読む スポンサード リンク
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