Ischnacanthiformes
| Ischnacanthiformes | ||||||||||||
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Ischnacanthus gracilis |
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| Temporal occurrence | ||||||||||||
| middle Silurian to Upper Carboniferous | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Ischnacanthiformes | ||||||||||||
| Berg , 1940 |
The Ischnacanthiformes are a group of extinct fish from the Upper Paleozoic . The scales assigned to them date from the middle and late Silurian , the oldest more complete fossils come from the early Devonian of England and Canada. At the end of the Devonian most forms died out; few, like Acanthodops, survived to the Upper Carboniferous .
features
The Ischnacanthiformes had a longer and lighter body compared to the Climatiiformes . They had two dorsal fins, each headed by a fin spine. The fin spines of the Ischnacanthiformes were usually slender and narrow and reached deep into the body. Her scales were thin. With the exception of the primitive Ischnacanthiform Uraniacanthus from England, the Ischnacanthiforms lacked additional fin spines between the pectoral and ventral fins. The edge of the palatoquadratum and Meckel's cartilage facing the mouth was ossified and covered with teeth that had grown firmly together with the bone. The bone armor around the shoulder girdle, which is characteristic of the Climatiiformes, is absent from the Ischnacanthiformes.
Overall, the Ischnacanthiformes are little known, many of the genera described are only known from isolated jaws and tooth spirals. Most Ischnacanthiformes were unspecialized fish that fed on small organisms. Some larger and more sophisticated forms may also hunt larger prey. The largest genus of Ischnacanthiformes, the Xylacanthus found on Svalbard , was estimated to be 2 m long, but is only known from the pine.
Systematics
The Ischnacanthiformes are counted among the Acanthodii and also called "Stachelhaie" in German. They are probably the sister group of the Acanthodiformes and together with these the sister group of the bony fish (Osteichthyes) or they must be placed in the parent group of the bony fish.
literature
- Robert L. Carroll : Paleontology and Evolution of the Vertebrates , Thieme, Stuttgart (1993), ISBN 3-13774-401-6
- John A. Long: The Rise of Fishes . The Johns Hopkins University Press, 1995, ISBN 0801849926
- Joseph S. Nelson : Fishes of the World. 4th edition. John Wiley & Sons, Hoboken NJ 2006, ISBN 0-471-25031-7 .
Individual evidence
- ^ Samuel P. Davis, John A. Finarelli & Michael I. Coates: Acanthodes and shark-like conditions in the last common ancestor of modern gnathostomes. Nature 486, 247-250, (14 June 2012) doi : 10.1038 / nature11080
- ↑ Brazeau, MD 2009. The braincase and jaws of a Devonian 'acanthodian' and the origin of modern gnathostomes. Nature Vol. 457 | 15 January 2009 | doi : 10.1038 / nature07436
