Knowra Ammonite Ammonite An ammonite was an extinct marine cephalopod whose shell was divided into chambers and usually coiled. Ammonites lived from the Devonian Period until the end-Cretaceous mass extinction.
Cephalopod : A marine mollusk with arms or tentacles, including octopuses, squids, cuttlefish, and nautiluses. Ammonites belonged to this mollusk group, alongside living and extinct relatives.
Septum (mollusc) : An internal wall separating successive chambers in a cephalopod shell. Ammonites added septa as they grew, partitioning older shell portions into chambers.
Index fossil : A fossil used to identify and correlate the age of rock layers across different locations. Rapid evolution and broad distribution made many ammonite species effective index fossils.
Ammonoidea : An extinct subclass of cephalopods that includes ammonites and several related groups of shelled forms. Ammonites are the best-known members of this broader cephalopod lineage.
Baculites : An extinct genus of Cretaceous ammonoid with a largely straight shell. Its uncoiled adult shell contrasts with the familiar spiral ammonite form.
Ammonite shell : The external, chambered shell of an ammonite, divided by internal walls called septa. Its chambers and coiling are the most recognizable features of ammonite fossils.
Siphuncle : A cord of tissue passing through the chambers of a chambered cephalopod shell. It helped regulate chamber fluid and gas, supporting buoyancy control.
Biostratigraphy : The dating and correlation of rock strata through their fossil content. Ammonite succession helps geologists divide and correlate Mesozoic marine strata.
Bactritida : An extinct group of small, straight-shelled cephalopods from the Paleozoic Era. Bactritids are among the likely ancestral groups from which ammonoids arose.
Aptychus : A paired or single calcitic plate found with some ammonoid fossils, often interpreted as part of the jaw apparatus. Aptychi preserve clues to ammonite feeding anatomy and fossil preservation.
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