Kingdom Animalia Phylum Mollusca Subclass Ammonites | Family Psiloceratidae Rank Genus | |
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Similar Ammonites, Promicroceras, Schlotheimia, Pleuroceras, Quenstedtoceras | ||
Ammonite fossile irridescente fossil ammonite irridescent psiloceras planorbis
Psiloceras is an extinct genus of cephalopod belonging to the ammonite subclass. Psiloceras fossils are commonly found at Watchet, Somerset, England. Here smooth-shelled Psiloceras planorbis (along with other species) are to be found as usually flattened fossils in the Blue Lias. Unlike most earlier ammonites, which had complex shell shapes and ornamentation, Psiloceras had a smooth shell.
Contents
- Ammonite fossile irridescente fossil ammonite irridescent psiloceras planorbis
- psiloceras planorbis an206
- Taxonomy
- Biostratigraphic significance
- Distribution
- References
psiloceras planorbis an206
Taxonomy
All Ammonites, with the sole exemption of the genus Psiloceras were wiped out at the Triassic–Jurassic extinction event (201.3 million years ago). Hence all ammonites that lived during the Jurassic and Cretaceous are descendants of Psiloceras.
Most authors assume that Psiloceras descended from the Phyllocerataceae. P. spelae is probably the earliest species of Psiloceras.
Biostratigraphic significance
The International Commission on Stratigraphy (ICS) has assigned the First Appearance Datum of the Psiloceras spela-group as the defining biological marker for the start of the Hettangian, 201.3 ± 0.2 million years ago, the earliest stage Jurassic.
Distribution
Jurassic of Argentina, Austria, Canada, China, France, Germany, New Zealand, Spain, the United Kingdom, United States
