SCIENTISTS have had few living organisms to examine that illustrate life during prehistoric times.Mostly, they have had to depend on information fused in tablets of stone, where the great mammoths of the ice age and the collosal dinosaurs have left their calling cards. In "Living Fossil: The Story of the Coelacanth," Keith S. Thomson recounts the discovery of a fish that has given scientists clues to what life was like at the time of the pterodactyls. Through step-by-step detail, Thomson descibes the unfolding biological discovery of the coelacanth (pronounced SEEL-uh-kanth) - a fish believed extinct for 80 million years - from its first identification to zoologists' most recent expedition in 1989 when they tried to capture a live specimen. Thomson not only introduces the reader to the fish, but also to the lives and personalities of the people who have devoted their careers to uncovering the mysteries of the coelacanth and its link to history. One such is Marjorie Courtenay-Latimer, the young curator of a natural history museum in the fishing port of East London, Cape Province, South Africa. In 1938, she received a call from a Capt. Hendrik Goosen, who said he had a fish for her museum. When she got to the dock, she "saw a blue fin and pushing off the fish, the most beautiful fish I had ever seen was revealed. It was 5 feet long and a pale mauve blue with iridescent silver markings." A second coelacanth was caught in 1952, 14 years after the first, this time, off the coast of the Comoro Islands in the Indian Ocean. Since then, coelacanths have only been captured at night, off the Comores and only by the island natives. What has researchers baffled is that the Comores did not exist until approximately 5 million years ago. So where in the system of evolving ocean basins did the coalacanths live during the 65 million years since the end of the Cretaceous? And are they still there? This "living fossil," named by scientists Latimeria chalumnae to honor Courtenay-Latimer and to link it to the Chalumna River where it was found, has proved valuable to scientists in the study of evolution. Originally, the coelcanth was thought to be the immediate ancestor of land vertebrates. As its biology was studied, scientists found that it did not hold that distinction. Instead, the species is one of only four genera of living lobe-finned fishes crucial to the evolution of living organisms from the water to land that have survived prehistoric times. Even though its population size is unknown, scientists continue exploring the ocean bottoms off the Comores trying to view a live coelacanth feeding or breeding. But the desire for information may well drive a once thought extinct fish into real extinction. In Thomson's words, "Of all the endangered and threatened species in the world, Latimeria chalumnae may well be the only organism whose extinction is by scientists." "Living Fossil" is more than the story of a unique fish, it is about life, evolution, and curiosity. While the potential for losing nonscientific readers is great with such a topic, the author does a masterly job of making readers feel they are participating in each step of the half-century discovery process. He uses diary excerpts, newspaper clippings, photos, and interviews to let the story of the fish unfold through the experience of the people involved. Some sections do bog down with the biological why's and wherefore's of the fish's place in history and its relationship to other more modern fish species, its reproduction and feeding patterns. But a reader who can wade through these parts will come away with a greater understanding of how scientists approach a great scientific discovery.