Inoceramen
Inoceramen | ||||||||||||
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Inoceramus cuvieri |
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Temporal occurrence | ||||||||||||
Lower Permian to Upper Cretaceous | ||||||||||||
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Systematics | ||||||||||||
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Scientific name | ||||||||||||
Inoceramidae | ||||||||||||
Gable , 1852 |
The Inoceramen (Inoceramidae) are an extinct family of mussels (Bivalvia), which belongs to the order Pteriida within the Autolamellibranchiata . It was an exclusively marine group of mussels. The oldest Inoceramen are known from the Lower Permian , the last species became extinct at the Cretaceous-Tertiary border (KT impact).
characterization
The housings of the Inoceramen are always more or less equivalently, weakly to strongly unevenly. As a rule, the left flap is significantly more arched than the right flap. The housing shape is variable, but mostly round to oblong-oval. The front wing (the pteriida) can still be relatively large, but also almost missing. In contrast, the rear wing is always present, but it is very different in size. Usually only concentric growth strips or ribs are present, rarely radial ribs. The relatively thick shell consists of an inner layer with aragonitic , mother-of-pearl microstructures and an outer, calcitic and prismatic layer. Under less favorable conservation conditions, the aragonitic layers can be dissolved away and the calcitic layer can disintegrate into individual prisms. The lock is largely reduced, lock teeth are missing in almost all species. The anterior sphincter is usually more or less significantly reduced. The ligament is wide and has several ligament pits. Most forms have a byssus . Individual types of Inoceramen can be considerably large (2 to 3 m in length!).
Way of life
The Inoceramen were an exclusively marine group of mussels that were mostly attached to hard parts on the sea floor with the help of organic byssus . They were apparently tolerant of low-oxygen environments (finds in black shale suggest this). But they are also found in a variety of other habitats from the shelf areas to the coast. A symbiosis with chemotrophic bacteria is being discussed for some species. The species were mostly widespread, sometimes even cosmopolitan and in the Upper Cretaceous only characteristic for relatively short periods of time.
Index fossils
Inoceramen are important key fossils , especially in the Upper Cretaceous , due to the brief occurrence of certain species in geologically measured periods of time and their extensive geographical distribution . Inoceramus crippsi occurs in the Cenomanium , I. labiatus and I. lamarcki are conductive in the Turonium . The end of the turonium is defined by the onset of Cremnoceramus rotundatus .
Systematics
- Superfamily † Ambonychioidea Miller, 1877 and
- Family † Inoceramidae Gable, 1852
- Inoceramus Sowerby, 1814
- Birostrina Sowerby, 1821
- Cremnoceramus Cox, 1969
- Mytiloides Brongniart, 1822
- Family † Inoceramidae Gable, 1852
and about 20 other genera. The system is z. Sometimes very inconsistent. Many genera are viewed by some authors as just sub-genus of Inoceramus or are rejected entirely.
literature
- Michael Amler, Rudolf Fischer & Nicole Rogalla: Mussels. Haeckel library, Volume 5. Enke Verlag, Stuttgart 2000, ISBN 3-13-118391-8 .
- Erle G. Kauffman, Peter J. Harries, Christian Meyer, Tomas Villamild, Claudia Arangod and Glenn Jaeckse: Paleoecology of giant Inoceramidae (Platyceramus) on a Santonian (Cretaceous) seafloor in Colorado . Journal of Paleontology, 81: 64-81, 2007 ISSN.