Astraspis

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Astraspis
Astraspis desiderata

Astraspis desiderata

Temporal occurrence
Ordovician
470 to 443.4 million years
Locations
  • North America (Colorado, Arizona, Oklahoma, Wyoming, and Quebec)
Systematics
Neumünder (Deuterostomia)
Chordates (chordata)
Vertebrates (vertebrata)
Pteraspidomorphi
Astraspida
Astraspis
Scientific name
Astraspida
Berg , 1940
Scientific name of the  genus
Astraspis
Walcott , 1892

Astraspis (= "star-covered tank") is a genus of extinct, fish-like, armored vertebrates and known from fossils from marine sediments of the Ordovician . The group's fossils were discovered as early as the 19th century. They were the first vertebrate fossils from the Ordovician to the discovery of the Arandaspida in the 1970s.

features

In the case of Astraspis , the head and the front trunk, which was oval in cross-section, were protected by a dorsal and ventral shield and a series of branchial shields in between. Both shields consisted of numerous mushroom-like, star-shaped or polygonal platelets (tesserae) made of aspidin , which were covered in the center with large tubercles made of dentin , which in turn had a cap made of translucent tooth enamel . The bone shields are relatively thick and consisted of three layers, a lower lamellar layer , a central spongy layer, which is permeated by vessels, and the superficial tubercles, each of which had a pulp delimited by dentin-like substance . The central tubercle indicates the point from which the ossification originated in juvenile specimens. They grew through the accumulation of other, smaller tubercles. The dorsal shield had strong longitudinal ridges. Between the branchial shields were eight (Benton) or ten gill openings. The bone armor shows signs of local dissolution and new formation. This could indicate injuries and subsequent healing processes. The rear trunk was protected by rhombic scales and ended in a rounded caudal fin. Paired fins, dorsal and anal fin were missing. The eyes were sideways. A sideline system is in place. It lies in pits in the bone shields. The internal anatomy of the animals is unknown.

Systematics

Astraspis is assigned to the Pteraspidomorphi and was initially placed within the Heterostraci within this group because of the acellular structure of the large dorsal and ventral shields . Since these had only one outer gill opening per head side, but astraspis up to ten, they are now placed in the taxon Astraspida (Astraspidiformes near Nelson). Two species have been described, Astraspis desiderata and Astraspis splendens . Some authors also count the genus Eriptychius from the Harding sandstones on the edge of the Rocky Mountains (Middle Ordovician) to the Astraspida (otherwise Eriptychiida) , which is known only from a few fragmentary remains .

literature

  • Michael J. Benton : Paleontology of the vertebrates. 2007, ISBN 3-89937-072-4 .
  • Robert L. Carroll: Paleontology and Evolution of the Vertebrates , Page 30, Thieme, Stuttgart (1993), ISBN 3-13774-401-6 .
  • Joseph S. Nelson : Fishes of the World . John Wiley & Sons, 2006, ISBN 0-471-25031-7 .
  • Hans-Peter Schultze: Pteraspidomorphi Page 183 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

Commons : Astraspis  - collection of images, videos and audio files