Description
- Eutrephoceras dekayi
Hoploscaphites sp. - Cretaceous Age
- Pierre Shale
- Glendive, Montana
Ammonite: any of a subclass (Ammonoidea) of extinct cephalopods especially abundant in the Mesozoic age that had flat spiral shells with the interior divided by septa into chambers
Ammonites are an group of marine animals of the subclass Ammonoidea in the class Cephalopoda. They are excellent index fossils, and it is often possible to link the rock layer in which they are 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”). Their name came from their spiral shape as their fossilized shells somewhat resemble tightly-coiled rams’ horns.
