Frank Johnston, age 10, of Rexdale, Ontario, Canada, for his question:

Do we know when snakes originated?

All the living animals have family trees that branch hack, back into the dim past. We can study their remote ancestors from the fossil remains they left buried in the ground. From these records, we suspect that snakes began arriving on earth about 100 million years ago.

The snakes are cold blooded reptile cousins of the lizards, and the reptile clan is one of the oldest in the world. Their ancestors left the ancient seas and learned to cope with life on the dry land more than 200 million years ago. There they thrived and prospered. They branched out in countless assorted shapes and sizes and s pread out to occupy most of the land in the world. The dinosaurs were weird reptiles that dominated life on earth for more than 100 million years. Some types took to the air and became the ancestors of the flying birds. The snaky reptiles began to take shape as the long Age of Reptiles began to decline.

The evidence for this is gathered from a long series of reptile fossils. ' But fossil remains .never tell all they know. We find them in spotty locations and it is reasonable to suppose that countless extinct species left no fossil records at all. All our 3,000 modern snakes are descended from reptile ancestors that had legs. And several types are believed to have converted to the legless form at different times. Each type seems to have made the conversion by similar stages.

The ancestors of the world's first snakes are thought. to. be burrowing lizards who lived more than 100 million years ago. Their burrowing way of life made their legs useless and nature detests useless extras. Through uncountable generations, the legs of the burrowing lizards became smaller. At last their children were born without any begs at all and these new arrivals were the world's first snakes.

Nature gradually removes useless extras from forms of life but she also donates new extras to cope with changing conditions. As the legs of the old reptiles dwindled, they depended more and more on their jaws to grab and devour their food. So with nature's help, they gradually developed special jaws with stretchable joints. The lower jaw bone of the first real snake already had two separate halves, joined by a strong band of elastic muscles. He also had learned to travel without legs by wriggling his snaky body from side to side. Along with other legless lizards that we suspect developed later, he was very much like some of the non poisonous snakes of the modern world.

Some of the early snakes were boas that grew bigger than their modern descendants. We have found fossil remains of ancient snakes that were 35 and SO feet long. These legless monsters snaked around the world 40 to 60 million years ago. A fossilized fang almost two inches long may or may not have belonged to another type of ancient snaky monster.

The poisonous snakes were not among the first arrivals of 100 million years ago. Their fangs are complicated equipment that took many ages to perfect. Nevertheless, the poisonous snakes have been here a very, very long time. The fossil remains of an ancient cobra, complete with fangs, were found in France. Scientific dating of the fossils and the rocks around it proved that the cobra lived about 20 million years ago. He was not much different from the cobras of the modern world.