Robert Musil's post on mammoths and mastodons reminded me of my last visit to Monticello in 1996 or thereabouts. One of the treasures of the collection was a mastodon jawbone Jefferson had collected, with a few grinding teeth still attached. Like most molars, these had conical bumps for grinding. To be more precise, they were bulging cones, or something between a cone and a hemisphere -- again, nothing unusual. However, unlike most molars, these had little nubs at the tip. When I saw them I couldn't help exclaiming "so that's why they're called 'mastodons'!". I had never thought about the name before, but it is obviously Greek for 'breast-tooth': mast- (as in "mastectomy") means "breast", while -odon means "tooth". It may seem odd to name a huge hairy beast after an unobtrusive feature of its dental apparatus, but I suppose that's the point that separates mastodons from the other extinct members of the order of elephants (Proboscidea).