crocodilians, slid back to the less competitive and sluggish life of the sea. 
The pterosaurs were unique even among the odd specimens which the early 
ages developed from the initial reptiles, for they were winged animals with 
wing spans as great as twenty feet. Gigantic flesh-eating monsters such as 
the tyrannosaurs (tyrant reptiles) developed, some of which were almost 
fifty feet long, twenty feet high and weighed thirty tons. The Tyrannosaurus 
would stand on his massive hind legs and use his clawed forearms and great 
teeth to tear his prey to pieces. It was the heyday of such dinosaurs as the 
Brontosaurus or thunder lizard, the largest monster ever discovered, which 
weighed as much as thirty-five tons. They were strict vegetarians and con¬ 
sumed about five thousand pounds of green fodder daily. Despite their great 
bulk these peanut-brained goliaths were easy victims for the more ferocious, 
though smaller, flesh-eating animals. 
Then, perhaps due to climatic changes and their lack of adaptability, 
most of these gigantic reptiles disappeared. A few, however, evolved into 
different forms, and to them can be traced the ancestry of virtually all living 
reptiles, birds and mammals. 
In size, if in nothing else, the reptilian descendants of those gargantu- 
ans, are quite inferior. The longest reptiles today, such as the crocodiles 
and the pythons, do well to attain a length of thirty feet; even these are 
diminutive alongside the extinct dinosaurs, some of which grew to more than 
three times that length. The trunkback or leathery turtle, largest of living 
reptiles, seldom exceeds half a ton in weight and only averages an overall 
length of six feet. 
Modern reptiles are described and classified as follows: 
CLASS: 
REPTIL1A — the reptiles comprise about five thousand living 
species of crocodilians, tuataras, lizards, snakes and turtles. All 
are backboned animals breathing air by means of lungs. They 
have four-chambered hearts and a variable body temperature that 
generally corresponds with the temperature of the surrounding 
air or water. Protection is afforded by a covering of scales or 
plates. All have ribs and teeth, except the tortoises, whose jaws 
are armed with sharp, horny sheaths. Most of them have long tails. 
Reptiles reproduce by means of internal fertilization and lay 
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