Kinematics of the escape head retraction in the common snake-necked turtle Chelodina longicollis (Testudines: Pleurodira: Chelidae)
Van Damme, J.; Aerts, P.; De Vree, F. (1995). Kinematics of the escape head retraction in the common snake-necked turtle Chelodina longicollis (Testudines: Pleurodira: Chelidae). Belg. J. Zool. 125(1): 215-235
In: Belgian Journal of Zoology. Koninklijke Belgische Vereniging voor Dierkunde = Société royale zoologique de Belgique: Gent. ISSN 0777-6276; e-ISSN 2295-0451, more
Also appears in:
Schockaert, E.R. (Ed.) (1995). Proceedings of the First Benelux Congress of Zoology, Leuven, 4-5 November 1994. Belgian Journal of Zoology, 125(1). Koninklijke Belgische Vereniging voor Dierkunde = Société royale zoologique de Belgique: Diepenbeek. 263 pp., more
Cervical movement during the fast escape head retraction in the pleurodiran turtle Chelodina longicollis were studied by means of x-ray cinematography. Radio-opaque markers were inserted near the cervical joints to allow calculations of joint rotations between the successive vertebrae expressed as a function of time and head position. Head retraction as a percentage of the extended neck configuration and angular and linear velocities were also calculated. A combination of muscular organisation and kinematics shows that the nek is divided into two functional regions, anterior and posterior to the biconvex fifth cervical vertebra respectively. Head retraction proceeds in two phases. During the first phase the animal retrackts the head very fast underneath the carapace but leaves the neck partially exposed. This phase (with exception for C3-2 and C5-4) shows no significant difference in the timing of the peak velocities. During the second phase rotations occur mainly in the proximal joints leading to the maximally retrackted configuration. Left and right head retractions are minor images. Retractions never start from a completely extended neck configuration. Initial angles always occur in C6-5 (joint between vertebrae 5 and 6) and C8-7. These joints are also the major bending sites for full retraction of the neck. Peak-velocities of these joints stronly correlate with each other but also with head retraction. When expressed as functions of head position, the rotation patterns of the proximal joints are particularly stereotyped. It is hypothesized that both initial angles and stereotypical retraction patterns are required to allow a fast (escape) retraction powered by a simple motor pattern.
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