Archaeocydippida hunsrueckiana
| Archaeocydippida hunsrueckiana | ||||||||||||
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| Approx. 400 million years | ||||||||||||
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| Scientific name | ||||||||||||
| Archaeocydippida hunsrueckiana | ||||||||||||
| Stanley & Striker , 1987 | ||||||||||||
Archaeocydippida hunsrueckiana is only fossil obtained kind of the ctenophores (Ctenophora). It was first described in 1987 by George D. Stanley Jr. and Wilhelm Stürmer after x-rays. Their interpretation of the fossil was attacked by the paleontologist M. Otto, who even went so far asto call Archaeocydippida hunsrueckiana a non-living object. The paleontologists Simon Conway Morris and Desmond H. Collins , however, confirmed the interpretation as a comb jellyfish.
The generic name is derived from the components archeo for "old" and cydippida for the order Cydippida , the specific epithet refers to the location in the Hunsrück , a German low mountain range.
Location
The fossil was discovered during stereoradiographic examinations with X-rays in slate from the Kaisergrube near Bundenbach in the Hunsrück. It was created by replacing organic sulfur compounds with the mineral pyrite . Although it is in a worse state of preservation than the species Paleoctenophora brasseli , which comes from the same site, some details such as the comb plates of the comb ribs can be seen much better. The only known specimen of the species is now in the collection of the Bavarian State Museum.
features
The approximately 23 millimeter large specimen shows paired tentacle sheaths, from which tentacles arise that leave the body on the side facing away from the mouth. This is an essential difference to Paleoctenophora brasseli , in which the tentacles extend from the end of the mouth. The mouth itself can be identified by a slight indentation.
The characteristic feature of the comb jellyfish, the comb ribs, is clearly recognizable and enables reliable identification and analysis of the individual comb platelets from which they are composed. According to the discoverers, the number of ribs is eight, as is the case with modern species.
On the mouth side of a row of combs, rows, sometimes clumped, spherical structures can be made out, which, due to their similar shape and position, can be carefully interpreted as gonads (gonads).
Tribal history
Archaeocydippida hunsrueckiana , like the species Paleoctenophora brasseli previously described from the same site, originates from the geological period of the Devonian about 400 million years ago. Unlike some earlier finds from the Cambrian , its features such as body shape and tentacle arrangement already very clearly resemble today's comb jellyfish and is already assigned to a modern order , the Cydippida within the class Tentaculata . The discoverers even cautiously assume that a classification into the families Pleurobrachidae or Mertensiidae is possible.
Presumably, however, the Cydippida are a polyphyletic taxon , that is, they are not a natural family group that includes all descendants of their last common ancestor. Should this prove to be true, the assignment to the Cydippida would be meaningless. In particular, it would be compatible with the fact that Archaeocydippida hunsrueckiana was a lineage representative of all comb jellyfish.
literature
- C. Bartels, G. Brassel: Fossils in the Hunsrück schist, documents of marine life in the Devonian. (= Museum Idar-Oberstein. Volume 7). 1990, p. 63.
- S. Conway Morris, DH Collins: Middle Cambrian ctenophores from the Stephen formation, British Columbia, Canada. In: Philosophical Transactions of the Royal Society of London B. Volume 351, 1996, p. 279.
- M. Otto: On the question of mollusc conservation in the Hunsrück slate. In: Geol. Palaeont. Volume 28, p. 45.
- GD Stanley, W. Stürmer: A new fossil ctenophore discovered by x-rays. In: Nature. Volume 328, 1987, p. 61 ( Article text (PDF) )