Portrait (upper left) of the French anatomist Georges Cuvier (1769-1832) who defined the anatomical procedures necessary to reconstruct extinct animals such as Megatherium (top) from the evidence of fossil bones. The tiny jaw (seen through the magnifying glass) was brought to Cuvier's attention by William Buckland (foreground left), professor of geology at Oxford University. This mammalian jawbone was found in deposits containing a large dinosaur's toe-bone, which indicated that mammals had existed in more ancient times than anyone had previously supposed.