Lori Randall, age 10, of Des Moines, Ia., for her question:

What kind of animal is the ichthyosaur?

This ancient swimmer is no longer a native of the planet Earth. We have only the fossil bones and a few teeth to prove that he once existed. These remains, however, tell the experts all about him, his size and shape, where he lived and what he ate and even how he was born.

The seas of our modern world are populated with playful porpoises and delightful dolphins. They are the small cousins of the great ocean going whales that include the biggest animals that ever lived in our world. In the long story of life on Earth, these charming creatures are newcomers. There were no whales or dolphins or porpoises 100 million or even 60 million years ago.

But the old Earth had her watery oceans and the ancient seas were populated with streamlined swimmers that were rather like our dolphins and whales. One of them was the ichthyosaur. He was not, however, related to our whales or dolphins or their ancestors. He was a dinosaur of the mighty lizard clan that dominated the animal life on Earth for more than 100 million years.

The ichthyosaur said goodbye to the Earth with the rest of the dinosaurs some 60 million years ago, and no one knows for sure why all these mighty dinosaurs departed in such a hurry. His remains were found by modern fossil experts and he was given his fancy name millions of years after he had gone. The first part of his name means fish and the second part tells us that he was a lizard of the stupendous dinosaur clan.

His fossil skeleton, all complete, has been found in sedimentary rocks that were deposited on the floors of ancient seas. He was a streamlined fellow built for fast swimming and he often measured 10 feet from his pointed nose to his tapering tail. His long jaws were crammed with rows of sharp teeth. In at least one fossil specimen, the contents of his last meal were preserved with him. Like our modern dolphin, the ancient ichthyosaur seems to feed on fish, squid and octopus.

The dinosaurs were all cold blooded lizards and all the land and marsh dwellers hatched from reptile-type eggs. The ichthyosaur, however, gave birth to live babies. The female kept the eggs inside her body until they were ready to hatch. In one fossil specimen, the little skeletons of six unborn babies were preserved with the body of their mother.

The dinosaurs began their long reign at the start of the Mesozoic era of Earth's history, about 185 million years ago. At that time, they were small and medium size land dwelling lizards. Through the ages, they grew bigger and their descendants took on many strange shapes and forms. Several groups deserted the land and adjusted themselves to the seas where life was easy and food plentiful. One of these fellows was the fish lizard of the genus ichthyosaurus, now extinct.