The lizardlike eosuchians are thought to be close to the ancestry of the later, advanced diapsid reptiles, many of which survive today in the form of snakes and lizards (see p. 86—89).
Eosuchians first appeared in Late Permian times, and continued until the middle of the Triassic. They are grouped into 4 families, all of whose members were apparently confined to southern and eastern Africa, and Madagascar. The family Tangasauridae contains 2 representative members (beloiv).
name: Thadeosaurus time: Late Permian locality: Madagascar size: 2 ft/60 cm long
The tremendously long tail of the land-living Thadeosaurus measured about 16 in/40 cm — making up two-thirds of the animal's total length. The 5 clawed toes of each foot were greatly elongated, and so arranged that the longer toes were on the outside. This had the advantage of allowing most of the toes to remain in contact with the ground as the foot was lifted, and so give a strong push off the surface with each step taken. The sternum, or breast bone, was massively developed, to help increase the stride of the forelegs.
name: Hovasaurus time: Late Permian locality: Madagascar size: 20 in/50 cm long
The most striking feature of this aquatic lizardlike reptile was its tail. Not only was it twice the length of the rest of the body; it was also deep and flattened from side to side. Each of the tail vertebrae was extended above and below the midline. The result was a tail that formed a broad, stiff paddle, allowing Hovasaurus to swim efficiently.
Another unusual feature of Hova-saurus is the mass of pebbles found in the abdominal cavities of most of the specimens recovered. Evidently, these reptiles swallowed stones as ballast, to help them sink quickly in the water when diving for their fish prey, or to keep them submerged when feeding.
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