This is suggested by the fact that their fossils are often found in rocks that were laid down under conditions where no bottom-dwelling life is found. Many ammonoids probably lived in the open water of ancient seas, rather than at the sea bottom. Nonetheless, a lot has been worked out by examining ammonoid shells and by using models of these shells in water tanks. Their soft body parts are practically never preserved in any detail. Jeletzkytes, a Cretaceous ammonite from the USAīecause ammonites and their close relatives are extinct, little is known about their way of life. Ancyloceratina (Upper Jurassic to Upper Cretaceous) - the heteromorph ammonites.Lytoceratina (Lower Jurassic to Upper Cretaceous). Ammonitina (Lower Jurassic to Upper Cretaceous) - includes the true ammonites.Phylloceratina (Lower Triassic to Upper Cretaceous).Ammonitida (Permian to Cretaceous) - have folded saddles and lobes, fractal patterns.Ceratitina (Permian to Triassic) - includes the true ceratites.Prolecanitina (Upper Devonian to Upper Triassic).Ceratitida (Carboniferous to Triassic) - have round saddles, serrated lobes.Goniatitina (Devonian to Upper Permian) - includes the true goniatites.Goniatitida (Devonian to Permian) - have round saddles, pointed lobes.The three orders and various suborders of Ammonoidea are herein listed from most primitive to more derived. This suture type is characteristic of Jurassic and Cretaceous ammonoids but extends back all the way to the Permian. Ammonoids of this type are the most important species from a biostratigraphical point of view. Ammonitic - lobes and saddles are much subdivided (fluted) subdivisions are usually rounded instead of saw-toothed.This suture pattern is characteristic of Triassic ammonoids and appears again in the Cretaceous "pseudoceratites." Ceratitic - lobes have subdivided tips, giving them a saw-toothed appearance, and rounded undivided saddles.This pattern is characteristic of the Paleozoic ammonoids.
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