To Tommy Holmeb, age 13, of High Point, N.C., for his question:

What reptiles have survived the longest?

The reptiles set a record about 300 million years ago. They became the first backboned animals to live their entire lives on the dry land. In the modern world, the life span record is held by two of their descendants. And these old timers just happen to resemb1e their remote reptile ancestors.

Our most famous old timer is the giant turtle of the Galopagos Islands. In his balmy Pacific home near the Equator, the huge slow poke may Enjoy life for 100 years or more. Far across the Pacific, on a few ocean islands off New Zealand, lives the tuatara  the last survivor of an ancient family. The tuatara, known as the beak headed lizard, can expect to outlive even a Galopogos turtle.

So far as we know, these two old timers have the longest life spans of our sizable . Living animals. Since turtles and lizards are in the class reptilia, these life span records belong to the reptiles. The family tree of all reptiles, living or Extinct, reaches back some 300 million years. Their original ancestors shared their primitive world with assorted insects and with another group of vertebrates  the amphibians. The swampy forests of this carboniferous age have long since become buried beds of coal.

The scaly, cold blooded reptiles branched out and changed with the times. The astounding dinosaurs dominated the Earth for ages and then departed. Crawling reptiles survived as snakes, and the descendants of flying reptiles becaiiie our feathery birds. The turtles and crocodiles of today are not very different from their ancestors of 150 million years ago.

The history of the ancient reptile clan is told in fossil records. In the past, 23 species of tuataras lived in many lands. Scientists thought that these beak headed lizards had departed with the dinosaurs  until 1831. Then a last surviving species was found on lonely islands off New Zealand. They called it a living fossil.

The durable fellow is a greenish brown lizard, two feet long. His large scales are dotted with yellow, and he wears a scaly yellow crest down his spine. Fossils show that this tuatara species has survived unchanged for some 200 million years. Such sturdy endurance is a record, ever in the long lasting reptile clan.

The tuatara may borrow a burrow or dig one of his own. HE dozes in the mid day sun and frisks around at night in search of snails and crickets. Tuatara Eggs are buried in the soil and take 15 months to hatch. The youngsters wait 20 years to become mature and may live to celebrate more than 100 birthdays. When captured, these oldest surviving reptiles sett1e down in a zoo where they become tame and friendly pets.