''Astraspis'' ('star shield') is an extinct genus of primitive

jawless fish Agnatha (, Ancient Greek 'without jaws') is an infraphylum of jawless fish in the phylum Chordata, subphylum Vertebrata, consisting of both present (cyclostomes) and extinct (conodonts and ostracoderms) species. Among recent animals, cyclostomes ...

from the

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...

of Central

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

including the Harding Sandstone of

Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of t ...

and

Bighorn Mountains The Bighorn Mountains ( cro, Basawaxaawúua, lit=our mountains or cro, Iisaxpúatahchee Isawaxaawúua, label=none, lit=bighorn sheep's mountains) are a mountain range in northern Wyoming and southern Montana in the United States, forming a nort ...

Wyoming Wyoming () is a U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the south ...

. It is also known from

Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...

.Sacabambaspis janvieri. PY Gagnier - Vertébré ordovicien de Bolivie, 1993 It is related to other Ordovician fishes, such as the

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...

n ''

Sacabambaspis ''Sacabambaspis'' is an extinct genus of jawless fish that lived in the Ordovician period. ''Sacabambaspis'' lived in shallow waters on the continental margins of Gondwana. It is the best known arandaspid with many specimens. It is related to ...

'', and the

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

n ''

Arandaspis ''Arandaspis prionotolepis'' is an extinct species of jawless fish that lived in the Ordovician period, about 480 to 470 million years ago. Its remains were found in the Stairway Sandstone near Alice Springs, Australia in 1959, but it was not ...

''.

Description

Nearly complete fossils suggest the living animals were about in length. The body had a mobile

tail The tail is the section at the rear end of certain kinds of animals’ bodies; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals, r ...

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) is to have had relatively large, laterally-positioned

eyes Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conve ...

and a series of eight

gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...

openings on each side. The specimen was generally

oval An oval () is a closed curve in a plane which resembles the outline of an egg. The term is not very specific, but in some areas (projective geometry, technical drawing, etc.) it is given a more precise definition, which may include either one or ...

in cross-section. The protective bony plates covering the animal were composed of aspidin (chemically similar to modern shark's

teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

), covered by

tubercles In anatomy, a tubercle (literally 'small tuber', Latin for 'lump') is any round nodule, small eminence, or warty outgrowth found on external or internal organs of a plant or an animal. In plants A tubercle is generally a wart-like projection ...

composed of

dentine Dentin () (American English) or dentine ( or ) (British English) ( la, substantia eburnea) is a calcified tissue of the body and, along with enamel, cementum, and pulp, is one of the four major components of teeth. It is usually covered by ena ...

.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.

References

Other sources

Michael J. Benton, ''Vertebrate Palaeontology'', 3rd edition, 2005

External links

Palaeos Palaeos.com is a web site on biology, paleontology, phylogeny and geology and which covers the history of Earth. The site is well respected and has been used as a reference by professional paleontologists such as Michael J. Benton, the professor of ...

Pteraspidomorphi
Pteraspidomorphi genera Ordovician jawless fish Late Ordovician animals Ordovician fish of North America Prehistoric fish of South America Fossils of Bolivia Fossil taxa described in 1892 {{ordovician-animal-stub