The Tangled Tree: A Radical New History of Life

by David Quammen

Eleven major lineages began the ascent. Eight of those came to dead ends—meaning, they went extinct. Trilobites, ammonites, ichthyosaurs, and plesiosaurs had all suffered such ends, leaving no descendants of any sort. One lineage rose through the eons without splitting, without tilting, like a beanstalk—meaning that it persisted through time, unchanged. That’s much the way horseshoe crabs, sometimes called living fossils, have survived relatively unchanged (at least externally, so far as fossilization can show) over 450 million years. The other two lineages, dominating the diagram, branched often and spread horizontally—as well as climbed vertically. Their branching and horizontal spread represented the exploration of different niches by newly evolved forms. So there it all was: evolution and the origins of diversity.