A reconstruction of Smilodon, photographed at the American Museum of Natural History.

When it comes to animals, encyclopedias often present us with generalized descriptions. Where a creature lives, what color it is, what it eats, and other tidbits of information are listed to distinguish one species from another, but what is lost is an appreciation of variation. Be they genetic, anatomical, or behavioral, variations are grist for natural selection’s mill, and if you study any species in detail it becomes apparent that individuals differ considerably over space and through time.

This was true of extinct animals just as it is true of living ones. When paleontologists Wendy Binder and Blaire Van Valkenburgh looked at the wear and