Monday, May 24, 2010

Leg Similarities (4)

More on the pterosaur tibiotarsus:
Avian-like tibiotarsi of pterodactyloids (Reptilia: Pterosauria) from the Upper Jurassic of East Africa"Tibiotarsi of Dsungaripterus brancai (Reck) (Upper Jurassic, East Africa),D. weii Young (Lower Cretaceous, China) and Puntanipterus globosus Bonaparte & Sanchez (Lower Cretaceous, South America) have a bird-like distal end with attachment areas for a transverse ligament anteriorly, lateral and medial ligamentous prominences, and an anteroposteriorly, expanded pulley-like articular surface. The M. extensor digitorum longus flexed the ankle and probably also extended the digits as in living birds and mammals. A separate tendinous slip for digit I probably passed from the M. flexor digitorum longus in a groove posteroventral to the medial ligamentous prominence. " (Peter M. Galton)
"The metamorphosis of the ankle joints of pterosaurs during development is interesting. In juvenile specimens, the proximal row consists of astragalus and calcaneum which are both reduced in length proximo-distally to become essentially only caps over the lower ends of the tibia, with the loss of the calcaneal tuber.
In adult [pterosaur] specimens, these two bones [the calcaneum and the astragalus] are fused with the tibia to form a rolling hinge joint at their distal condyles as seen in modern birds." (Sankar Chatterjee, R. J. Templin)

The shared presence of a relatively long neck with proportionally long cervical vertebrae, of an elongate tibia, and of a hinge-like ankle joint and elongate metatarsals in the foot indicate that pterosaurs, dinosaurs and a few other groups should be united in a clade which has been termed Ornithodira.

Also see these references:

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