Cephalopods
| Cephalopods | ||||||||||||
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Recent octopus |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Neocephalopoda | ||||||||||||
| Lehmann & Hillmer , 1980 | ||||||||||||
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The new cephalopods (Neocephalopoda) are a species-rich group of cephalopods , to which today's squids (Coleoidea) also belong, as well as the † ammonites (Ammon's horns, Ammonoidea), the † bactrites (Bactritoidea) and some groups of the † straight horns (Orthoceratoidea) ).
The first reliable representatives of the new cephalopods are known from the Ordovician . No initial stages of housing are known from the oldest cephalopods (from the Upper Cambrian ); d. This means that one also has no evidence of early development. These are "traditionally" placed with the cephalopods; but without any real evidence. It is regarded as the sister group of the cephalopods (Palcephalopoda). The division of cephalopods into cephalopods and new cephalopods reflects the phylogenetics of today's cephalopods, in which the many species of inner-shelled cuttlefish (Coleoidea) contrast with the few species of pearl boats (genera Nautilus and Allonautilus ), i.e. H. Represent sister groups. The inclusion of the many fossil groups in these two groups would completely break the concept of the pearl boats (genera Nautilus and Allonautilus ) and the squid (Coleoidea). Therefore, Lehmann & Hillmer (1980) suggested dividing cephalopods into Palcephalopoda (“ Nautilus / Allonautilus line” = cephalopods) and Neocephalopoda (“Coleoidea line” = new cephalopods), each including the fossil groups. The inclusion of the ammonites (Ammonoidea) in the new cephalopods by U. Lehmann also resulted from the findings of the remains of the rasp tongue (radula) among the ammonites. It has 9 elements per transverse row and is thus similar to the rasping tongue of the squid; in contrast to the rasp tongue of the pearl boats, which has 13 elements per transverse row.
characterization
The new cephalopods (Neocephalopoda) are characterized by a moderately yolk-rich development compared to the old cephalopods . The hatchlings are or were usually only a few millimeters in size. Compared to most other groups of molluscs (Mollusca), the development of the cephalopods can also be described as yolk-rich, and the individual development is direct, i.e. without a larval stage. Another criterion of the cephalopods is the mineralization mode of the first shell that is still formed in the egg. The first housing is created organically and then mineralized as a whole. This happens through the storage of the mineral aragonite in the form of prismatic structures. The further growth of the housing after hatching from the egg shell takes place through growth at the front edge of the housing. As a result, the embryonic housing stands out from the later juvenile housing by slightly different coloring (in good condition) and the absence of any growth strips. Usually it is more or less clearly constricted from the second chamber. The siphon line is thin and predominantly organic. From the cephalopods, however, groups have repeatedly formed again, which in turn have developed an extremely yolk-rich development on a secondary basis (for example cuttlefish, some deep-sea octopods, † Arionoceratidae). Sparse finds of rasp tongues in the cephalopods indicate that they had a rasp tongue with 9 elements per transverse row (like the squid). An older synonym of Neocephalopoda is Angusteradulata Lehmann, 1967.
system
The basal cephalopod group, the † Ellesmeroceratoidea, is traditionally placed with the cephalopods. However, intact initial stages have not yet become known, and the early individual development of this group is therefore unknown. Due to the development tendency, however, it is to be expected that the individual development was only moderately yolk-rich and that this group can possibly be counted among the new cephalopods. The cephalopods would then be a paraphyletic group and stage group.
- Cephalopods (Palcephalopoda)
- New cephalopods (Neocephalopoda)
- † Bactrites (Bactritoidea) (parent group of ammonites and squid)
- † Ammonites (Ammonoidea)
- Octopus (coleoidea)
- † Straight horns (Orthoceratoidea) (parent group of the Bactrites and the other groups)
Individual evidence
- ↑ Lehmann, Ulrich & Gero Hillmer 1980. Invertebrates of prehistoric times: Guide to systematic palaeontology. XI, 340 pp. - Stuttgart, Enke-Verlag.
literature
- Engeser, Theo (1990): Phylogeny of the fossil coleoid Cephalopoda (Mollusca). Berlin Geoscientific Treatises, Series A, 124: 123-191, Berlin.
- Lehmann, Ulrich (1968): Stratigraphy and ammonite formation of the Ahrensburg glacial sediments from the Lias epsilon (Unt. Toarcium). Messages from the Geological State Institute Hamburg, 37: 41-68, Hamburg.
- Kröger, Björn (2004): Revision of Middle Ordovician orthoceratacean nautiloids from Baltoscandia. Acta Palaeontologica Polonica, 49: 57-74, Warsaw.