Figure 8.3Nicolaus Steno was the first to demonstrate that fossils are the remains of ancient life. (a) A portrait of Nicolaus Steno (1638–1686). [SPL/Science Source.] (b) “Tongue stones” of the type found in sedimentary rocks in the Mediterranean region, where Steno worked. [Corbis RF/Alamy.] (c) This diagram is from Steno’s 1667 book, which demonstrated that tongue stones are the fossilized teeth of ancient sharks.