ammonoids are group extinct marine mollusc animals the subclass ammonoidea class cephalopoda |
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| navigate by keyword : although amazing ammonites ammonoidea ammonoids ancient animals cephalopoda chambers class closely coleoids commonly creature cuttlefish dividing excellent extinct form forms fossil fossilized fossils found general genus geologic group helically index joint jurassic layer link living marine mollusc molluscs more nature nautiloids nautilus nonspiraled octopuses old oldest outer particular period periods phragmocone planispirals possible referred related rock separate septa shape shell shelled shells siphuncles some species specific spiral spiraled squid subclass sutures take time usually wall walls |
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| Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids octopuses, squid, and cuttlefish than they are to shelled nautiloids such as the living Nautilus species. 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 nonspiraled forms. |
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