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Ammolite comes from the fossil shells of the Upper Cretaceous disk-shaped ammonites Placenticeras meeki and Placenticeras intercalare, and (to a lesser degree) the cylindrical baculite, Baculites compressus. Ammonites were cephalopods, that thrived in tropical seas until becoming extinct along with the dinosaurs at the end of the Mesozoic era.
Fossils. Dorling, Kindersley Limited, London, 2002. A Broad Brush History of the Cephalopoda by Dr. Neale Monks, from The Cephalopod Page. Ammonite maturity, pathology and old age By Dr. Neale Monks, from The Cephalopod Page. Essay about the life span of Ammonites. Cretaceous Fossils Taxonomic Index for Order Ammonoitida
Dactylioceras was a widespread genus of ammonites from the Lower Jurassic period, [1] approximately 180 million years ago . [2] and Like many other ammonites, the genus Dactylioceras is extremely important in biostratigraphy, being a key index fossil for identifying their region of the Jurassic. It had a nearly cosmopolitan distribution during ...
Their shells had ornate ribs whose function is unknown, although some scientists have speculated that these ribs helped strengthen the animals' shells to allow them to live at greater depths where the water pressure is higher.
These ammonites lived in the Jurassic from Sinemurian to Toarcian [2] (age range: 196.5 to 182.0 million years ago). Fossils of this genus can be found in Argentina, Austria, Canada, Chile, China, France, Germany, Hungary, Italy, Morocco, Portugal, Slovakia, Spain, Tunisia, Turkey and United States.
An aptychus is a type of marine fossil. It is a hard anatomical structure, a sort of curved shelly plate, now understood to be part of the body of an ammonite. Paired aptychi have, on rare occasions, been found at or within the aperture of ammonite shells. The aptychus was usually composed of calcite, whereas the ammonite shell was aragonite.
Ammonitina comprises a diverse suborder of ammonite cephalopods that lived during the Jurassic and Cretaceous periods of the Mesozoic Era. They are excellent index fossils, and it is often possible to link the rock layer in which they are found to specific geological time periods.
Ammonites franconicus Schlotheim, 1813 Pleuroceras spinatum is a species of ammonite from the lower Jurassic , upper Pliensbachian period (189.6 ± 1.5 – 183.0 ± 1.5 Mya). Species of this genus were fast-moving nektonic carnivore.