Possibly because the author started out as an artist rather than as a scientist this is one of the better written books I've seen in this series, even before you get to Anton's fine drawings and paintings. If nothing else Anton wants to quash certain popular notions regarding the fitness of these creatures, noting that the sabertooth body plan has emerged independently several times over the millennia and so it cannot be a fluke. As for why they periodically went extinct the argument is that these animal thrived best in certain ideal climates that favored their hunting style of close-combat ambush and that at the opposite ends of temperature extremes existence became too unforgiving; highly recommended. ( )