For serious readers with or without a special background, the distinguished American paleontologist sorts out the evolutionary history of South American mammals, starting with the ""scant handful"" of late Cretaceous fragments and then tracing the continents' mammals' appearance, disappearance, and evolutionary radiation through three major time periods. The first began about 60 million years ago when South America was an island continent and its fauna therefore limited to just three basic stocks, which were able to develop and diversify in ""splendid isolation."" Simpson describes the fossil records and surveys known suborders and families of the three groups: marsupials (who radiated into niches which would on other continents have been occupied by placentals), xenarthrans (""strange-joint"" mammals whose descendants include armadillos, anteaters, and sloths), and ungulants (with family names like notostylop, meso-there, and hegetothere). In the second phase, about 35 million years ago, early rodents and primates arrived by island-hopping or overseas dispersal from North America or Africa; and in the third, called ""the Great American Interchange"" (beginning seven or eight million years ago), such families as canidae (dogs), ursidae (bears), felidae (cats), and cricetidae (field mice) first filtered down through the previously nonexistent Central-American land bridge. Throughout the chronological catalogue Simpson refers to such phenomena as convergent evolution, which misled early collectors to attribute common ancestry to unrelated but similar animals, and ecological replacement, whereby an ""old-timer"" is nosed out by an unrelated immigrant who takes over its niche. He does not, however, point up these concepts, or play up the ""splendor"" of the continent's unique isolation, for the general reader. With orienting time charts and a classified ""cast of characters"" his comprehensive summary will be of value to students at all levels. The subtitle notwithstanding, it is not an item for the idly curious--or for any but the most scholarly leisure-time animal-book enthusiast.