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Asymmetrical gaits of juvenile Crocodylus johnstoni, galloping Australian crocodiles

Published online by Cambridge University Press:  14 February 2002

S. Renous
Affiliation:
U.M.R. 8570 CNRS/MNHN/Universities Paris 7, Collège de France, Laboratoire d'Anatomie Comparée, Muséum National d'Histoire Naturelle, 55 rue Buffon, 75005 Paris, France
J.-P. Gasc
Affiliation:
U.M.R. 8570 CNRS/MNHN/Universities Paris 7, Collège de France, Laboratoire d'Anatomie Comparée, Muséum National d'Histoire Naturelle, 55 rue Buffon, 75005 Paris, France
V. L. Bels
Affiliation:
Centre Agronomique de Recherches Appliquées du Hainaut, HEPHO & HEPCUT, 11 rue Paul Pastur, 7800 Ath, Belgique
R. Wicker
Affiliation:
Zoologischer Garten, 16 Alfred Brehm Platz, 60316 Frankfurt-am-Main, Deutschland
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Abstract

Seven juvenile individuals of the Australian species Crocodylus johnstoni from the Frankfurt Zoological Park were filmed on high-speed video, at 250 fields s−1, whilst freely moving at various speeds in a long corridor. The sequences of locomotion were analysed to determine the various space and time parameters to characterize limb kinematics. We found that the animals use diverse patterns of asymmetrical gait, revealing great flexibility in limb co-ordination. In all these gaits, the forelimb strikes the ground first, in the couple made by diagonally opposite fore- and hindlimbs. Among these gaits, rotary gallop offers probably a high level of manoeuvrability, whereas transverse gallop resulted in a higher level of stability. Speed increase is achieved by half-bound and bound, the latter being the only gait used at velocities > 2 m s−1. Speed was increased mainly by increasing the stride length of the fore- and hindlimbs by simultaneously increasing both its components, the step and swing lengths. However, in bound, the step length of each forelimb increased more than the swing length, resulting in a stronger thrust action, whereas swing length increased more than step length for the hindlimb, causing the centre of mass to accelerate forwards during its ballistic phase. The asymmetrical gaits of crocodiles such as Crocodylus johnstoni are probably not functionally equivalent to the transitional asymmetrical gaits exhibited by lizards when building up into a bipedal run. These gaits are also not entirely equivalent to mammalian gaits, despite the use of vertical movements of the vertebral axis in these crocodiles, favouring an erect dynamic posture.

Type
Research Article
Copyright
2002 The Zoological Society of London

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