Bactrites
| Bactrites | ||||||||
|---|---|---|---|---|---|---|---|---|
| Temporal occurrence | ||||||||
| Ordovician to Perm | ||||||||
| 488 to 251 million years | ||||||||
| Locations | ||||||||
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| Systematics | ||||||||
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| Scientific name | ||||||||
| Bactritoidea | ||||||||
| Shimanskiy , 1951 | ||||||||
Bactrites (Bactritoidea) represent an extinct group of cephalopods that lived from the Ordovician to the Permian . They contained the ancestral forms of the also extinct ammonites and the squid .
Like the early nautiloids (Orthocerates), the Bactrites had an elongated and chambered housing with a siphon at the edge for gas exchange for static buoyancy . Another typical feature is a small, mostly round initial chamber, which is separated from the further housing by a constriction. They are likely derived from smaller Ordovician nautiloids such as Bactroceras . Possibly the oldest form of the Bactrites is Eobactrites from the deep Ordovician of Bohemia . The animal had a circular shell cross-section and a sipho that was not quite at the edge.
Systematics
The Bactrites are a typical paraphyletic group as they are the ancestors of ammonites and squid . In Karbon and Perm they also went through their own radiation . These forms became extinct at the end of the Permian. Another problem of delimitation is the derivation of the ammonites from the Bactrites, which is well documented by many transitional forms. This problem was solved differently by the different processors. While the earlier workers drew the border to the ammonites in the forms that already have a twist, newer workers draw the line at the beginning of the curvature of the housing, i.e. H. the earlier Bactrite genus Cyrtobactrites is now considered a basal form of the ammonites, as this genus already shows a first apomorphism of the ammonites (curling). Parabactrites had very close septa and is considered to be the ancestor of the Belemnites. Strictly speaking, Parabactrites already has an initial apomorphism of the Belemnoidea and should consequently already be placed with the squid.
- Ord. Bactritida
- Fam. Annulobactritidae Mapes, 1979
- Fam. Bactritidae Hyatt, 1884
- Fam. Bojobactritidae Horny, 1957
- Fam. Ctenobactritidae Shimansky, 1951
- Fam. Lobobactritidae Shimansky, 1962
- Fam. Parabactritidae Shimansky, 1951
- Fam. Sinuobactritidae Mapes, 1979
Depending on the definition of the order, the family Cyrtobactritidae Becker, 1996, is placed in the Ammonoidea or the order Bactritida.
literature
- Heinrich Karl Erben : Bactritoidea. In: Curt Teichert , Bernhard Kummel , Walter C. Sweet, HB Stenzel, William M. Furnish, Brian F. Glenister, Heinrich K. Erben , Raymond Cecil Moore , DEN Zeller (eds.): Treatise on Invertebrate Paleontology. Part K: Mollusca. 3: Cephalopoda - General Features Endoceratoidea - Actinoceratoidea - Nautiloidea - Bactritoidea. Geological Society of America et al., New York NY et al. 1964, K491-K505.
- Royal H. Mapes: Carboniferous and Permian Bactritoidea (Cephalopoda) in North America. In: University of Kansas Paleontological Contribution. Articles. Vol. 64, 1979, ISSN 0075-5044 , pp. 1-75.
- Christian Klug, Dieter Korn : The origin of ammonoid locomotion. In: Acta Palaeontologica Polonica. Vol. 49, No. 2, 2004, ISSN 0567-7920 , pp. 235-242, online .