Mossosaurus and sharksander and others teeth from the Atlas Mountains of Morocco.

Shark teeth, also known as tongue stones or (Latin) glossopetrae, are fossilized shark teeth. The teeth are the body parts of sharks that are best preserved as fossils. This is because the entire skeleton of sharks, with the exception of the teeth, consists of cartilage, which usually does not fossilize. The oldest known shark teeth belong to shark species that lived about 450 million years ago, while in the North Sea Basin the most common shark teeth date from the Eocene and Oligocene and have an age between 40 million and 65 million years. Megalodon teeth, which lived between 1.5 and 16 million years ago, are the largest known with a maximum length of 17 cm and are highly sought after by fossil shark tooth collectors. Smaller shark teeth are fairly common in sediments from fairly deep seas. These fossils wash up on various Dutch beaches, especially in Zeeland and Zeeland Flanders, such as at Cadzand. These teeth are mainly of Tertiary age (Eocene and Oligocene). Shark teeth were among the first fossils to be correctly identified. In the 16th century, the prevailing theory was that the Earth possessed an inner power to transform objects within her into the likeness of living animals and plants. However, the Swiss naturalist Conrad Gesner (1516 - 1565) published a drawing in 1558 comparing fossil shark teeth with those of present-day species. Later, the Danish researcher Nicolaus Steno (1638-1686) would show that tongue stones, found in the mountains, often bore traces of wear and tear compared to teeth of a freshly washed ashore shark. He also discovered that the rocks in which they were found were originally soft in nature. Steno's conclusion was that tongue stones were the teeth of sharks that had died long ago.