The mixosaurs had developed a stabilizing fin on the back (like the dorsal fin of a fish) — a swimming aid present in all later ichthyosaurs. But they did not have the typical fishlike tail, with 2 equal lobes, that made their later relatives such powerful swimmers.
In mixosaurs, the end of the backbone was not bent sharply down into the tail, as it was in later ichthyosaurs; instead, the vertebrae were extended upward, probably to support a low fin on top of the tail.
name: Mixosaurus time: Middle Triassic locality: Asia (China and Timor, Indonesia), Europe (Alps), North America (Alaska, Canadian Arctic and Nevada) and Spitsbergen size: 3 ft 3 in/1 m long Mixosaurus seems to have been intermediate in appearance between the early, primitive ichthyosaurs, as exemplified by Cymbospondylus (above), and the later, more advanced types. For example, Mixosaurus had a fishlike body with a dorsal fin on its back, and probably also the beginnings of a fin on the top of its tail.
Its limbs were transformed into short paddles, the front pair being longer than the hind pair. Each paddle consisted of 5 toes, which were greatly elongated by the addition of many small bones (hyperphalangy). The long, narrow jaws were equipped with sharp teeth, adapted for catching and eating fish.
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