Astraspis ('star shield') is an extinct, monotypic taxon 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.[Sacabambaspis janvieri. PY Gagnier - Vertébré ordovicien de Bolivie, 1993] It is related to other Ordovician fishes, such as the Sacabambaspis, and the Arandaspis.
Description
Nearly complete fossils suggest the living animals were about in length. The body had a mobile
tail covered with small protective plate-like scales of less than and a forebody covered with plate-like scales larger than . 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
bone plates covering the animal were composed of
aspidin (chemically similar to a
shark teeth), covered by
tubercles composed of
dentine.
[Sansom IJ, Smith MP, Smith MM and Turner P (1997) " Astraspis: The anatomy and histology of an Ordovician fish" Palaeontology , 40 (3): 625–642.] 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.
Other sources
Michael J. Benton,
Vertebrate Palaeontology, 3rd edition, 2005
External links
