For more than 300 years paleontologists have operated under the assumption that the information contained in fossilized bones lies only in the size and shape of the bones themselves. It was thought that when an animal dies under conditions suitable for fossilization, inert minerals from the surrounding environment eventually replace all the organic molecules—such as those that make up cells, tissues, pigments and proteins—leaving behind what is essentially a “cast” of the once living bones, now composed entirely of mineral.