Bactritida

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Bactriten ( Bactritoidea ) are an extinct group of cephalopods that lived from the Ordovician to the Permian. They contained the stem-forms of the also extinct ammonites and squid.

The Bactriten possessed as the early nautiloids ( Orthoceras ) is a long and chambered enclosure with one located at margins Sipho for gas exchange for the buoyancy. Typical is also a small, generally rounded top chamber, which is separated from the other housing by a constriction. They probably originate from the Ordovician nautiloid smaller as Bactroceras. Perhaps the oldest form of Bactriten is Eobactrites from the deep Ordovician of Bohemia. The animal had a circular cross section and a shell Sipho, who was not quite marginal.

System

The Bactriten are a typical paraphyletic grouping, as they are the ancestors of ammonites and squid. In Carboniferous and Permian they have also undergone an Radiation. These forms have become extinct at the end of the Permian. Another problem of demarcation is the derivative of the Ammonites from the Bactriten, and is well documented by many transitional forms. This problem was solved by different agents in different ways. While the former editor drew the border with the Ammonites in the forms that already have one turn, pull newer agents already at the beginning of the incurvation of the case, that is, the former Bactriten genus Cyrtobactrites is now regarded as a basal form of the Ammonites because this class are already showing a first apomorphy of the Ammonites ( curl ). Parabactrites had very closely spaced septa and comes as ancestor of belemnites into consideration. Strictly speaking Parabactrites has thus already a first apomorphy of Belemnoidea and would consequently are already provided to 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 is the Family Cyrtobactritidae Becker, placed in the Ammonoidea or the order Bactritida 1996.

Mya (unit) Fossil Siphon (mollusc)
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