Pteraspidiformes
| Pteraspidiformes | ||||||||||||
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| Temporal occurrence | ||||||||||||
| late Silurian to Upper Devonian | ||||||||||||
| 427.4 to 358.9 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Pteraspidiformes | ||||||||||||
| Berg , 1940 |
The Pteraspidiformes are an order of about 25 genera of extinct, fish-like, armored vertebrates that occurred from the late Silurian to the late Devonian .
features
The Pteraspidiformes were of variable body shape. There were elongated, spindle-like shapes as well as dorsoventrally flattened ones that had the shape of a frying pan. The head and front body were completely surrounded by a shell made of bone plates. A characteristic feature of the group is the dorsal shield, which consisted of five individual plates, pineal, rostral and spinal plates and two orbital plates in which the eye sockets were located. The eyes were reduced and could also be missing. The sides protected the branchial and cornual plates, the underside a single ventral plate. The branchial plate could be extended to lateral keels. There were some smaller plates (oral plates) around the mouth opening. The back of the body was protected by strong, roof-tile-like overlapping scales. The bone plates showed a ornamentation of concentrically arranged ridges of dentin passed (dentin) and sawn edges had (except for the psammosteidae).
There were no paired fins, dorsal and anal fins, but the fish had a fan-shaped, laterally flattened and almost symmetrical caudal fin. Lateral spines, which occurred in some forms, may have had a stabilizing effect. A dorsal spine was also often present. The Pteraspidiformes probably swam by snaking sideways movements of the back of the body. The weight of the bone armor made them awkward and likely spent much of their life lying on the ground or buried in the sediment.
Internal system
Within the Pteraspidiformes, five subgroups are distinguished, which Nelson has the rank of families.
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Anchipteraspididae , Late Silurian to Early Devonian of North America
- Genera: Anchipteraspis , Rachiaspis , Ulutitaspis
- Protaspididae, early Devonian of North America
- Genus: Cyrtaspidichthys = Protaspis
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Protopteraspididae , Early to Middle Devonian of North America, Svalbard & Russia
- Genera: Doryaspis , Protopteraspis
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Psammosteidae
- Genera: Drepanaspis , Psammolepis , Pycnosteus
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Pteraspididae , early Devonian
- Genera: Errivaspis , Pteraspis , Rhinopteraspis , Unarkaspis
literature
- Michael J. Benton : Paleontology of the vertebrates. 2007, Verlag Friedrich Pfeil, Munich (2007), page 61, ISBN 3-89937-072-4 .
- Robert L. Carroll : Paläontologie und Evolution der Vertbeltiere , Thieme, Stuttgart (1993), page 31-32, ISBN 3-13774-401-6 .
- Joseph S. Nelson : Fishes of the World . John Wiley & Sons, 2006, pp. 29-30, ISBN 0-471-25031-7 .
- Hans-Peter Schultze: Pteraspidomorphi Page 184 in: Wilfried Westheide & Reinhard Rieger: Special Zoology Part 2: Vertebrae and Skull Animals , 1st edition, Spectrum Academic Publishing Heidelberg • Berlin, 2004, ISBN 3-8274-0307-3 .
Web links
- Philippe Janvier. 1997. Heterostraci. in The Tree of Life Web Project
- Palaeos: Pteraspidiformes
- The Paleobiology Database: Pteraspidiformes