Harpoceras Ammonite | Germany

Harpoceras sp.
Lower Jurassic (180 MYO)
Posidonia Shale
Holzmaden, Germany

Ammonite approx. size: 3.25" x 2.5"

Plate approx. size: 4" x 3.25" x 0.75" at thickest part

This Harpoceras ammonite from the Posidonia Shale in Holzmaden, Germany has been compressed on black slate and is partially pyritized.

Ammonoids are a group of extinct marine mollusk animals in the subclass Ammonoidea of the class Cephalopoda. These mollusks, commonly referred to as ammonites, 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 vanished in 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 geologic time periods. Their fossil shells usually take the form of planispirals, although there were some helically spiraled and non-spiraled 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.[2] Often the name of an ammonite genus ends in -ceras, which is Greek (κέρας) for "horn".