The postcranial anatomy of Heterodontosaurus tucki has been well-described, although H. tucki is generally considered the most derived of the Early Jurassic heterodontosaurids, so it is impossible to know how many of its features were shared with other species.
The forelimbs were long for a dinosaur, over 70% of the length of the hindlimbs.
The well-developed deltopectoral crest (a ridge for the attachment of chest and shoulder muscles) of the humerus and prominent olecranon process (where muscles that extend the forearm were attached) of the ulna indicate that the forelimb was powerful as well.
There were five digits on the manus ('hand').
The first was large, tipped with a sharply curved claw, and would rotate inwards when flexed; Robert Bakker called it the 'twist-thumb'.
The second digit was the longest, slightly longer than the third.
Both of these digits bore claws, while the clawless fourth and fifth digits were very small and simple in comparison.
In the hindlimb, the tibia was 30% longer than the femur, which is generally considered an adaptation for speed.
The tibia and fibula of the lower leg were fused to the astragalus and calcaneum of the ankle, forming a 'tibiofibiotarsus' convergently with modern birds.
Also similarly to birds, the lower tarsal (ankle) bones and metatarsals were fused to form a 'tarsometatarsus.'
There are four digits in the pes (hindfoot), with only the second, third, and fourth contacting the ground.
The tail, unlike many other ornithischians, did not have ossified tendons to maintain a rigid posture and was probably flexible.
The fragmentary skeleton known for Abrictosaurus has never been fully described, although the forelimb and manus were smaller than in Heterodontosaurus.
Also, the fourth and fifth digits of the forelimb each bear one fewer phalanx bone.
The postcranial anatomy of Heterodontosaurus tucki has been well-described, although H. tucki is generally considered the most derived of the Early Jurassic heterodontosaurids, so it is impossible to know how many of its features were shared with other species. The forelimbs were long for a dinosaur, over 70% of the length of the hindlimbs. The well-developed deltopectoral crest (a ridge for the attachment of chest and shoulder muscles) of the humerus and prominent olecranon process (where muscles that extend the forearm were attached) of the ulna indicate that the forelimb was powerful as well. There were five digits on the manus ('hand'). The first was large, tipped with a sharply curved claw, and would rotate inwards when flexed; Robert Bakker called it the 'twist-thumb'. The second digit was the longest, slightly longer than the third. Both of these digits bore claws, while the clawless fourth and fifth digits were very small and simple in comparison. In the hindlimb, the tibia was 30% longer than the femur, which is generally considered an adaptation for speed. The tibia and fibula of the lower leg were fused to the astragalus and calcaneum of the ankle, forming a 'tibiofibiotarsus' convergently with modern birds. Also similarly to birds, the lower tarsal (ankle) bones and metatarsals were fused to form a 'tarsometatarsus.' There are four digits in the pes (hindfoot), with only the second, third, and fourth contacting the ground. The tail, unlike many other ornithischians, did not have ossified tendons to maintain a rigid posture and was probably flexible. The fragmentary skeleton known for Abrictosaurus has never been fully described, although the forelimb and manus were smaller than in Heterodontosaurus. Also, the fourth and fifth digits of the forelimb each bear one fewer phalanx bone.
Heterodontosauridae