Portal:Ammonoids

The Ammonoid Portal Artist's restoration of the ammonoid Asteroceras Ammonites /ˈæmənaɪts/ are an extinct group of marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs are more closely related to living coleoids (i.e., octopuses, squid, and cuttlefish) than they are to shelled nautiloids such as the living Nautilus species. The earliest ammonites appear during the Devonian, and the last species died out during the Cretaceous–Paleogene extinction event. Ammonites are excellent index fossils, and it is often possible to link the rock layer in which a particular species or genus is found to specific geological time periods. Their fossil shells usually take the form of planispirals, although there were some helically spiraled and nonspiraled forms (known as heteromorphs). The name "ammonite", from which the scientific term is derived, was inspired by the spiral shape of their fossilized shells, which somewhat resemble tightly coiled rams' horns. Pliny the Elder (d. 79 AD near Pompeii) called fossils of these animals ammonis cornua ("horns of Ammon") because the Egyptian god Ammon (Amun) was typically depicted wearing ram's horns. Often the name of an ammonite genus ends in -ceras, which is Greek (κέρας) for "horn". (see more...) Template:/box-footer Fossil shell of the parkinsoniid ammonoid Parkinsonia parkinsoni. The shell dates back to the Bajocian age (168.3–170.3 million years ago) of the Middle Jurassic epoch and is about 14.5 cm in diameter. It was collected near Evrecy, France. Photo credit: H. Zell ▼ Ammonites ► Ammonites sorted by taxa ► Ammonites sorted by geochronology A Polyptychoceras fossil ... that fossil collectors often call Polyptychoceras vancouverensis the "paperclip ammonite" or the "candy cane", due to its shape? ... that paleontologists have discovered possible Ammonoid egg fossils that may have been laid by genera like Aulacostephanus, Ceratites and Pectinatites? ... that the ammonite Hildoceras bifrons (pictured) has been used as an index fossil to help identify the age of rocks? 90px Paleontology Extinct and Endangered Species Paleozoic Belemnoids 90px 90px Brachiopods Eurypterids Graptolites Trilobites What are portals? List of portals Featured portals