Skeleton of the Megatherium, an extinct giant ground sloth, and Mastodon giganteus, or the American mastodon, Mammut americanum. Lithograph by an unknown artist from Dr. F.A. Schmidt's "Petrefactenbuch," published in Stuttgart, Germany, 1855 by Verlag von Krais & Hoffmann. Dr. Schmidt's "Book of Petrification" introduced fossils and palaeontology to both the specialist and general reader.