Sharks use revolving teeth for cutting and biting. In contrast to mammalian teeth, thesy contain the mineral fluoroapatite instead of hydroxyapatite. Like human teeth, they are highly structured to fulfil their function, starting from fluoroapatite needles that are organized in different levels to give the teeth hardness, toughness, and corrosion resistance. Teeth of a number of recent shark species has been studied with respect to their ultrastructural organization as well as their crystallographic and mechanical properties. Sharks are an old species in the evolution, and many fossilized teeth have been preserved over the past million years. We have analysed a range of them, and found that their ultrastructure was remarkably well preserved, even after million years of fossilization. This points to the fact that this structural principle has been very successful during the evolution, and that there was no evolutionary pressure to change it. For comparison, teeth of various extinct species (like dinosaurs) were analysed with the same methods. In this case, the structural organization is clearly different, as expected for taxonomically different species.