Ammonoidea

Ammonoidea is an extinct subclass of cephalopod mollusks, best known for species with chambered, coiled shells. Its members lived in marine environments from the Devonian Period until the end-Cretaceous extinction.

Cephalopoda: Cephalopoda is a class of mollusks that includes octopuses, squids, cuttlefish, and nautiluses. Ammonoids belong to this class and share its basic body plan.
Ammonoid suture: An ammonoid suture is the line where a shell septum meets the outer shell wall. Its pattern is a major feature used to classify ammonoids.
Devonian Period: The Devonian Period lasted from about 419 to 359 million years ago. The earliest ammonoids appeared during this period, around 400 million years ago.
Goniatitida: Goniatitida is an extinct order of ammonoids, especially diverse during the Paleozoic. Its relatively simple suture patterns characterize many early ammonoid fossils.
Cretaceous–Paleogene extinction event: The Cretaceous–Paleogene extinction event occurred about 66 million years ago and eliminated many species worldwide. All surviving ammonoid lineages disappeared during this extinction.
Ammonoid shell: An ammonoid shell is a chambered external shell divided by walls called septa. Its chambers and coiling define the most familiar ammonoid fossils.
Suture pattern: A suture pattern is the visible outline formed where internal shell walls meet an outer shell. Ammonoid suture patterns changed through time and vary among major groups.
Bactritida: Bactritida is an extinct order of small, mostly straight-shelled cephalopods. Bactritids are widely regarded as close ancestors of ammonoids.
Ceratitida: Ceratitida is an extinct order of ammonoids that flourished mainly during the Triassic Period. Its characteristic suture patterns distinguish many Triassic ammonoids.
Index fossil: An index fossil is a fossil used to identify and correlate geological strata of a particular age. Ammonoid fossils evolved rapidly and spread widely, making them useful for dating rocks.

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