Astraspis
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Astraspis ('star shield') is an extinct, monotypic genus of primitive jawless fish from the Ordovician of Central North America including the Harding Sandstone of Colorado and Bighorn Mountains of Wyoming. It is also known from Bolivia.[1] It is related to other Ordovician fishes, such as the South American Sacabambaspis, and the Australian Arandaspis.
Description
Nearly complete fossils suggest the living animals were about Script error: No such module "convert". in length. The body had a mobile tail covered with small protective plate-like scales of less than Script error: No such module "convert". and a forebody covered with plate-like scales larger than Script error: No such module "convert".. The specimen from North America (described by Sansom et al., 1997) had relatively large, laterally-positioned eyes and a series of eight gill openings on each side. The specimen was generally oval in cross-section. The protective bony plates covering the animal were composed of aspidin (chemically similar to a modern shark's teeth), covered by tubercles composed of dentine.[2] It is from these tubercles (which are generally star-shaped) that the name "Astraspis" (literally "star-shield") is derived. The histology of Astraspis desiderata was unique. Its hard tissues were made up of irregular soft tissue gaps and a basal component of spongy aspidin with extensive trabeculae. As is typical of Astraspis, the individual tubercles were composed of dentine with an enameloid cover, which contains a high density of parallel, fine-calibrated tapered tubules.
References
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- ↑ Sacabambaspis janvieri. PY Gagnier - Vertébré ordovicien de Bolivie, 1993
- ↑ Sansom IJ, Smith MP, Smith MM and Turner P (1997) "Astraspis: The anatomy and histology of an Ordovician fish" Palaeontology, 40 (3): 625–642.
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Other sources
Michael J. Benton, Vertebrate Palaeontology, 3rd edition, 2005