Wednesday, October 20, 2010

October 20, 2010 : Astraspis (Extinct)


Astraspis ('star shield') is an extinct genus of primitive jawless fish from the Ordovician of Central North America and Bolivia (Gagnier, 1993) . It is related to other Ordovician fishes, such as the South American Sacabambaspis, and the Australian Arandaspis.

Astraspids are hypothesized to have been about 200mm in length. They are supposed to have had a mobile tail covered with small protective plates (<1mm) and a head region covered with much larger plates (>>2mm). The specimen from North America (described by Sansom et al., 1997) is to have had relatively large, lateral 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 modern shark's teeth), covered by tubercles composed of dentine. It is from these tubercles (which are generally star-shaped) that the name 'Astraspis' (literally "star-shield") is derived.

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