Arthrodira
| Arthrodira | ||||||||||||
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| Temporal occurrence | ||||||||||||
| Lower Devon to Upper Devon | ||||||||||||
| 419.2 to 358.9 million years | ||||||||||||
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| Scientific name | ||||||||||||
| Arthrodira | ||||||||||||
| Woodward , 1891 |
The Arthrodira (Arthrodiriformes) (from gr. Άρθρον, árthron "joint" and δειρή, deiré, "neck, neck") are the youngest group of the extinct Placodermi , fish-like, heavily armored vertebrates from the Devonian . They appeared in the Lower Devonian and survived until the end of the Devonian ( Famennium ). They were obviously active and predatory swimmers who ate larger, nectonic prey. About 130 genera have been described so far.
features
The older forms of Arthrodira had a long, largely connected head and trunk armor made of large bone plates. Head and torso armor were movable against each other. There were small openings for the pectoral fins. The torso armor reached down to the anus.
In younger forms, the torso armor was reduced to a clasp that only covered the front back. The border between head and body armor runs at an angle of about 45 °. The head was relatively small, the eyes sat sideways, the mouth was terminal. It could be raised in a pair of joints opposite the torso armor (shoulder girdle) (see fish skull ).
The caudal fin was heterocercous , mostly pectoral , small abdominal , a dorsal fin and a small anal fin were present.
Some arthritis became very large. Homostius and Heterostius reached a length of 5 to 6 m, the filter feeder Titanichthys was 5 to 8 m long and Dunkleosteus even 6 to 10 m. The well-researched Coccosteus , however, only reached a length of 40 centimeters.
Fossils of the Arthrodiren Incisoscutum ritchiei indicate internal fertilization (by means of clasps ), pregnancy and viviparity as in sharks .
literature
- Hans-Peter Schultze: Placodermi , page 197. In Wilfried Westheide , Reinhard Rieger : Special Zoology Part 2: Vertebrae and Skull Animals , 1st edition, Spectrum Academic Publishing House
- Joseph S. Nelson : Fishes of the World. 4th edition. John Wiley & Sons, Hoboken NJ et al. 2006, ISBN 0-471-25031-7 .
- Robert L. Carroll: Paleontology and Evolution of the Vertebrates . Thieme, Stuttgart 1993, ISBN 3-13774-401-6 .
- John A. Long: The Rise of Fishes . Johns Hopkins University Press, 1995, ISBN 0801849926 .
Web links
- Arthrodira on Palæos
Individual evidence
- ↑ according to Pape 1880, Greek Wb.
- ↑ Samuel J. Coatham, Jakob Vinther, Emily J. Rayfield and Christian Klug: Was the Devonian placoderm Titanichthys a suspension feeder? The Royal Society Publishing, May 2020, doi: 10.1098 / rsos.200272