Pteraspidomorphi
| Pteraspidomorphi | ||||||||||||
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Pteraspis , living reconstruction |
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| Temporal occurrence | ||||||||||||
| Lower Ordovician to Upper Devonian | ||||||||||||
| 478.6 to 376.1 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Pteraspidomorphi | ||||||||||||
| Goodrich , 1909 |
The Pteraspidomorphi or Pteraspidomorpha are primeval jawless vertebrates (Vertebrata) that lived from the early Ordovician to the late Devonian about 479 to 376 million years ago ( mya ).
features
The fossils of this taxon show a strong armor of the head, which is formed by plates of skin bones made of aspidin . The Pteraspidomorphi inhabited the sea, mostly near the coast, but it is believed that some forms have invaded the freshwater. The skeleton is cartilaginous, only the Eriptychiida and possibly the Arandaspida show traces of calcification . Besides the caudal fin , the body has no other fins.
Systematics
The pteraspidomorphi have long been regarded as a group close to the jaw-bearing fish or jaw- mouthing fish (Gnathostomata), but the common characteristics ( synapomorphies ) of this group represent original characteristics ( plesiomorphies ) in the sense of the phylogenetic system , which they share with other groups.
Three to four subgroups are distinguished within the Pteraspidomorphi:
- The Arandaspida , also called Arandaspidida, have exclusively marine representatives. The oldest representative of Arandaspis comes from the upper Lower Ordovician from Australia . Another well-known fossil is the approximately 40 centimeter long Sacabambaspis janvieri from South America .
- The astraspida , also called astraspidida, are also exclusively marine and, like most arandaspidida, originate in the Middle Ordovician about 460 million years ago.
- The Heterostraci are the youngest group of the Pteraspidomorphi and are known from fossils from sediments of the Silurian and Devonian . The sites are in North America, Europe and Siberia.
The fourth group consists exclusively of the genus Eriptychius , known only from fragmentary remains , which, as Eriptychiida, is on a par with the others or is assigned to the Astraspida.
literature
- Hans-Peter Schultze: Pteraspidomorphi in: W. Westheide and R. Rieger: Special Zoology. Part 2. Vertebrate or skull animals. Spektrum, Munich 2004; Pages 183-184. ISBN 3-8274-0307-3 .
- Robert L. Carroll : Paleontology and Evolution of the Vertebrates , Thieme, Stuttgart (1993); Pages 29–36. ISBN 3-13-774401-6 .
- Joseph S. Nelson : Fishes of the World , John Wiley & Sons, 2006, ISBN 0-471-25031-7 .
- Oskar Kuhn: The prehistoric fish and fish , A. Ziemsen Verlag, 1967, Wittenberg.
