A now-classic -- and still provocative -- study of the 600 million-year-old fossils found in the Burgess Shale of British Columbia. Gould argues that the fossils are so distinctive that they represent a possible jumping off point for what could have been a completely different course for the evolution of life on Earth. An intriguing look at a heated scientific debate, and an eloquent account of paleontology.  (CND86, $16.95)