Ammonites (ammonoidea) are an extinct subclass of cephalopods (squids). These are sea creatures that occurred worldwide in large numbers in the late Paleozoic and throughout the Mesozoic. They are found as fossils. Ammon have a flat spiral-shaped shell which is made up of several rooms. Each time the animal is too big for the current chamber is formed a new larger outer chamber. In this outer chamber the animal is alive, the other empty rooms further used as a means to move vertically. The ammonite separates gas in these chambers were thus regelen.Ammonieten the lift force on the shell in hundreds of species and varieties. They have almost all the same floor plan: a flat spiral shell. There still exist some exceptions: some heteromorphic species that do not spiral shell. The ammonites of size ranges from less than one centimeter to more than 2.5 meters in diameter. The closest living relatives are the Nautilidae (Nautilus). The name comes from the Egyptian god Amun, which was depicted as a man with the head of a ram. Ammonites look like the curled rams' horns that Amon was proposed. In the Roman author Pliny the Elder, we find descriptions back of fossils of these animals which he called "ammonis cornu" (horn of Ammon). Ammonites first appeared in the Late Silurian, the Permian-Triassic extinction survived with remarkably few species and came to a real flowering during the Mesozoic. At the end of this period (65 million years ago), most ammonites died out, just like the dinosaurs. Fossils from the Netherlands and Denmark, however, seem to show that the last ammonites for came to in the oldest layers of the Paleocene. The youngest known fossil of an ammonite comes from Denmark and belongs to Hoploscaphites constrictus, which until occurred approximately 65.3 million years ago, about 0.2 to 0.65 million years after the mass extinction, and possibly even a half million years longer. However, these small populations were not enough to save the last ammonites from destruction. It is thought that the ammonites became extinct because of their reproductive strategy. The boy was part of the plankton that floated to the surface. Acid rain and eclipse of the sun by dust clouds probably led to worsening conditions for the eggs and the boy to develop.