Shark teeth, once called tongue stones or (Latin) glossopetrae mentioned are fossilized teeth of sharks. Teeth are the body parts of sharks that are best preserved as a fossil. This is because the entire skeleton of sharks, with the exception of the teeth, consisting of cartilage, which is generally not fossilises. The oldest known shark among sharks that lived about 450 million years ago, while in the North Sea Basin dating the most common shark teeth from the Eocene and the Oligocene and have an age between 40 million and 65 million years. Megalodon teeth that are between 1.5 and lived 16 million years ago, are the largest known with a maximum length of 17 cm and are very sought after by collectors of fossil shark teeth. Smaller shark teeth are in sediments of fairly deep seas rather general. At various Dutch beaches wash these fossils, especially in Zeeland and Zeeland Flanders, as in Cadzand. These teeth are mainly of Tertiary age (Eocene and Oligocene). Shark teeth were among the first fossils were correctly determined. In the 16th century, the prevailing theory that the Earth possessed an inner strength to make objects inside her to be in the likeness of live animals and plants. The Swiss naturalist Conrad Gesner (1516 - 1565), however, published in 1558 in a drawing that fossil shark teeth are compared to those of present-day species. Later, the Danish researcher Nicolas Steno would (1638- 1686) demonstrate that tongue stones that were found in the mountains, often signs of wear wore relative positions of a newly washed shark. He also discovered that the rocks in which they were found originally mild. Steno's conclusion was that tongue stone teeth of sharks were who had died long ago.