Paleoctenophora brasseli
| Paleoctenophora brasseli | ||||||||||
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| Temporal occurrence | ||||||||||
| Devon | ||||||||||
| Approx. 400 million years | ||||||||||
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| Systematics | ||||||||||
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| Scientific name | ||||||||||
| Paleoctenophora brasseli | ||||||||||
| Stanley & Striker , 1987 |
Paleoctenophora brasseli is an extinct ctenophora - type that is in shale rock of the Hunsrück received. The generic name is made up of the components paleo for "old" and ctenophora , the scientific name of the rib jellyfish; the specific epithet brasseli refers to the fossil collector Günther Brassel, in whose holdings the species was discovered.
George D. Stanley and Wilhelm Stürmer first described the species in 1983 in the science journal Nature . Their interpretation was attacked by M. Otto, who Palaeoctenophora brasseli for remains of brachiopods held -shells, by paleontologists Simon Conway Morris and Desmond H. Collins, however, confirmed.
The only known specimen is now in the Bavarian State Collection.
features
The find examined by stereoradiographic examinations with X-rays reveals a biradial-symmetrical, egg-shaped body structure. Paleoctenophora brasseli measured accordingly from the mouth to the side facing away from the mouth about 1.3 centimeters, in the cross-section, however, 0.9 centimeters.
Opposite the side of the mouth, which is recognizable by a slight notch, small, granular structures can be made out, which are regarded as the remains of a statolith , which is part of the equilibrium organ at the end remote from the mouth in modern jellyfish. From this side facing away from the mouth, in Paleoctenophora brasseli seven to eight strip-shaped structures run radially outwards, which can easily be identified as rows of ridges, which, as in today's animals, probably served for locomotion. Most lose themselves after a short distance, while the longest is visible over about three quarters of the body length.
Two protruding structures can be seen on the long side: The former, short and relatively thick, presumably rested in an internal pocket and is rated as a tentacle drawn into the tentacle sheath; the second is five centimeters long and quite thin, but has numerous transverse threads. It is interpreted as an outstretched tentacle filled with tentils .
It cannot be said with certainty whether finely divided dark matter inside the fossil is to be regarded as a remnant of muscle fibers and the internal digestive system.
Location
The species was found in shale, which is assigned to the lower Devonian and comes from the Hunsrück near Bundenbach . During fossilization , organic sulfur compounds were replaced by pyrite , i.e. iron sulfide.
Tribal history
The species already shows all the characteristics of the comb jellyfish known today and therefore does not shed any light on the phylogenetic development of the group. Due to the presence of tentacles arising in sheaths, it is formally placed in the class Tentaculata and the order Cydippida , similar to the species Archaeocydippida hunsrueckiana known from the same formation . The latter, however, is presumably para- or even polyphyletic, so it does not include all descendants of the last common ancestor of the group. In the latter case, membership in the taxon Cydippida would be meaningless and would only express the already known fact that Paleoctenophora is an extinct comb jellyfish.
literature
- Bartels, C., Brassel, G., Fossils in the Hunsrück Slate, Documents of Marine Life in Devon , Museum Idar-Oberstein, 7 , page 63
- Conway Morris, S., Collins, DH, Middle Cambrian ctenophores from the Stephen formation, British Columbia, Canada , Philosophical Transactions of the Royal Society of London B, 351 , 1996, p. 279
- Otto, M., On the question of mollusc conservation in the Hunsrück schist, Geol. Palaeont. 28 , page 45
- George D. Stanley Jr., Wilhelm Stürmer, The first fossil ctenophore from the Lower Devonian of West Germany , Nature, 303 , 1983, p. 518