Archive image from page 20 of Differential growth in three ichthyosaurs Differential growth in three ichthyosaurs : Ichthyosaurus communis, I. breviceps, and Stenopterygius quadriscissus (Reptilia, Ichthyosauria) differentialgrow00mcgo Year: 1973 Fig. 10 Outline drawings of the tails of two specimens of Stenopterygius quadriscissus illustrating that the aspect ratio of the tail increases during ontogeny, a. Length of body 62 cm (from Hauff, 1953, pi. 9a). b. Length of body 304 cm (from Hauff, 1953, pi. 9b). ward) than that of the lower lobe (upward). The forward propulsive thrust was therefo
Archive image from page 20 of Differential growth in three ichthyosaurs Differential growth in three ichthyosaurs : Ichthyosaurus communis, I. breviceps, and Stenopterygius quadriscissus (Reptilia, Ichthyosauria) differentialgrow00mcgo Year: 1973 Fig. 10 Outline drawings of the tails of two specimens of Stenopterygius quadriscissus illustrating that the aspect ratio of the tail increases during ontogeny, a. Length of body 62 cm (from Hauff, 1953, pi. 9a). b. Length of body 304 cm (from Hauff, 1953, pi. 9b). ward) than that of the lower lobe (upward). The forward propulsive thrust was therefore accompanied by a net downthrust. The line of action of the epicaudal downthrust was at right angles to the axis of the tail ( the axis about which the upper lobe was deflected), and can be resolved into vertical and horizontal components (Fig. 9a). If the angle of the tail bend is increased the vertical component decreases (Fig. 9b). Thus the net downthrust of the ichthyosaur tail is inversely proportional to the angle of the tail bend. The caudal downthrust, acting behind the centre of gravity, would be compensated by a downthrust in front of the centre of gravity produced by the pectoral fins. The attitude of the body could be adjusted by changing the angle of attack of the paired fins, and probably also by altering the force applied by the tail. Parenthetically it may be noted that while the animal was swimming on the surface the epicaudal lobe would be largely clear of the water so that the tail would not produce a downthrust. Diving could then be initiated by the negative inclination of the pectoral fins, and once the tail was again submerged the horizontal swimming attitude could be restored. FUNCTIONAL SIGNIFICANCE OF THE TRENDS OCCURRING IN THE TAIL AND DORSAL FIN Three trends occur during ontogeny: an increase in the relative areas of the caudal fin and dorsal fin, and a weak trend towards an increase in the angle of the tail bend. The exponential growth of the
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