The hind limb step cycle of Caiman sclerops and the mechanics of the crocodile tarsus and metatarsus

Abstract

Crocodiles use two distinct hind limb step cycles: an erect pattern seen in the high walk and a more sprawling lizard-like pattern. These differ in the amount of abduction of the femur and rotation of the limb elements that occurs. The sprawling step cycle of crocodiles differs from the primitive reptilian pattern in that abduction of the femur is not accompanied by a lateral rotation of the crus. The erect step cycle of crocodiles differs from that of mammals in the position of the arc described by femoral retraction and in that greater amount of rotation of the limb elements occurs. The joint between the astragalus and calcaneum in the crocodile tarsus functions as the ankle joint during locomotion. A functional mesotarsal joint is also present. This joint permits the assumption of postures seen in resting animals. Rotation of the metatarsus is a result of plan-tarflexion of each metatarsal relative to the more medial metatarsal. The lateral position of the calcaneal tuber is associated with the lateral orientation of the metatarsus during pedal plan-tarflexion. The assumption of an anteriorly oriented metatarsus by dinosaurs may have led to the loss of the calcaneal tuber.