''Micraster'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus of echinoids from the Late Cretaceous to the early Eocene. Its remains have been found in Africa, Antarctica, Europe, and

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 ...

. Micraster was an

infauna Fauna is all of the animal life present in a particular region or time. The corresponding term for plants is ''flora'', and for fungi, it is '' funga''. Flora, fauna, funga and other forms of life are collectively referred to as '' biota''. Zoo ...

l echinoid living in a burrow below the sediment surface. The test is clearly bilateral and there is a deep anterior groove to take in water containing organic particles to the mouth. The tube feet keep a supply of nutrient-laden water moving into the burrow. The anus has a waste tube behind it.

Continuous evolution

In the classic text ''

The Science of Life ''The Science of Life'' is a book written by H. G. Wells, Julian Huxley and G. P. Wells, published in three volumes by The Waverley Publishing Company Ltd in 1929–30, giving a popular account of all major aspects of biology as known in the 1 ...

'' (1931), H. G. Wells,

Julian Huxley Sir Julian Sorell Huxley (22 June 1887 – 14 February 1975) was an English evolutionary biologist, eugenicist, and internationalist. He was a proponent of natural selection, and a leading figure in the mid-twentieth century modern synthesis. ...

and

G. P. Wells George Philip Wells FRS (17 July 1901 – 27 September 1985) was a British zoologist and author. A son of the author H. G. Wells, he co-authored, with his father and Julian Huxley, ''The Science of Life''. A pupil at Oundle School, he was in t ...

use Micraster as an example of a fossil whose continuous evolution can be traced over some 10 million years through 450–500 feet of chalk beds of the Late Cretaceous. They point out: :"During this long period the fossil Micrasters are so abundant that hundreds of thousands can be collected and a gradual evolution can be traced as we pass upward. The changes are apparently trivial. There is a slow alteration of shape from rather flattened to rather arched, and from rather elongated to about as broads as long. The mouth creeps steadily forward, its distance from the front border of the lower surface decreasing from about a third of the body-length in the early types to a sixth in the latest, on a total length of fifty to sixty millimetres ... though the changes involved are small, they are absolutely continuous, the urchins found at one level grading quite imperceptibly into those of the rest; a single specimen, indeed, may show characters of one "species" in some of its tube-feet, characters of another in the rest." Micraster bajo

Species

* ''

Micraster norfolkensis ''Micraster'' is an extinct genus of echinoids from the Late Cretaceous to the early Eocene. Its remains have been found in Africa, Antarctica, Europe, and North America. Micraster was an infaunal echinoid living in a burrow below the sediment s ...

'' , 2012 † * ''

Micraster burgiensis ''Micraster'' is an extinct genus of echinoids from the Late Cretaceous to the early Eocene. Its remains have been found in Africa, Antarctica, Europe, and North America. Micraster was an infaunal echinoid living in a burrow below the sediment s ...

'' , 1935 † * ''

Micraster coravium ''Micraster'' is an extinct genus of echinoids from the Late Cretaceous to the early Eocene. Its remains have been found in Africa, Antarctica, Europe, and North America. Micraster was an infaunal echinoid living in a burrow below the sediment s ...

'' , 1959 † * ''

Micraster decipiens ''Micraster'' is an extinct genus of echinoids from the Late Cretaceous to the early Eocene. Its remains have been found in Africa, Antarctica, Europe, and North America. Micraster was an infaunal echinoid living in a burrow below the sediment s ...

1878 † * ''

Micraster depressus ''Micraster'' is an extinct genus of echinoids from the Late Cretaceous to the early Eocene. Its remains have been found in Africa, Antarctica, Europe, and North America. Micraster was an infaunal echinoid living in a burrow below the sediment s ...

'' , 1937 † * ''

Micraster desori ''Micraster'' is an extinct genus of echinoids from the Late Cretaceous to the early Eocene. Its remains have been found in Africa, Antarctica, Europe, and North America. Micraster was an infaunal echinoid living in a burrow below the sediment s ...

'' , 1926 † * ''

Micraster elevatus ''Micraster'' is an extinct genus of echinoids from the Late Cretaceous to the early Eocene. Its remains have been found in Africa, Antarctica, Europe, and North America. Micraster was an infaunal echinoid living in a burrow below the sediment s ...

'' , 1949 † * ''

Micraster gappi ''Micraster'' is an extinct genus of echinoids from the Late Cretaceous to the early Eocene. Its remains have been found in Africa, Antarctica, Europe, and North America. Micraster was an infaunal echinoid living in a burrow below the sediment s ...

'' , 1925 † * ''

Micraster leskei ''Micraster'' is an extinct genus of echinoids from the Late Cretaceous to the early Eocene. Its remains have been found in Africa, Antarctica, Europe, and North America. Micraster was an infaunal echinoid living in a burrow below the sediment s ...

'' , 1855 † * ''

Micraster piriformis ''Micraster'' is an extinct genus of echinoids from the Late Cretaceous to the early Eocene. Its remains have been found in Africa, Antarctica, Europe, and North America. Micraster was an infaunal echinoid living in a burrow below the sediment ...

'' , 1927 † * ''

Micraster subglobosus ''Micraster'' is an extinct genus of echinoids from the Late Cretaceous to the early Eocene. Its remains have been found in Africa, Antarctica, Europe, and North America. Micraster was an infaunal echinoid living in a burrow below the sediment s ...

'' , 1959 † * '' Micraster trangahyensis'' , 1936 † * ''

Micraster turonensis ''Micraster'' is an extinct genus of echinoids from the Late Cretaceous to the early Eocene. Its remains have been found in Africa, Antarctica, Europe, and North America. Micraster was an infaunal echinoid living in a burrow below the sediment ...

'' 1878 † * ''

Micraster uddeni ''Micraster'' is an extinct genus of echinoids from the Late Cretaceous to the early Eocene. Its remains have been found in Africa, Antarctica, Europe, and North America. Micraster was an infaunal echinoid living in a burrow below the sediment ...

'' , 1953 † * '' Micraster vistulensis'' , 1950 †

Sources

* ''Fossils'' (Smithsonian Handbooks) by David Ward (Page 185)

External links

''Micraster''
in the Paleobiology Database

Notes

Spatangoida Prehistoric echinoid genera Cretaceous echinoderms Prehistoric echinoderms of Africa Extinct animals of Antarctica Prehistoric echinoderms of Europe Prehistoric echinoderms of North America {{paleo-echinoidea-stub