In an appendix to an anatomical work, written for Ferdinand Medici II, Grand Duke of Tuscany, Steno recounted his dissection of the head of a shark that recently had washed ashore. His anatomical analysis suggested that the well-known glossopetrae, or “tongue-stones,” were fossilized shark’s teeth, and lent support to the view that other fossils likewise might have formed from an organic origin. The image of the shark head, not original with Steno, became an icon for the organic origin of fossils and was frequently reprinted.