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''Micraster'' is an
In the classic text '' The Science of Life'' (1931), 
''Micraster''
in the Paleobiology Database
extinct
Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of echinoids from the Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...
to the early Eocene
The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
. Its remains have been found in Africa
Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...
, Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...
, Europe
Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
, and North America
North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
. Micraster was an infaunal 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
Tube or tubes may refer to:
* Tube (2003 film), ''Tube'' (2003 film), a 2003 Korean film
* "Tubes" (Peter Dale), performer on the Soccer AM#Tubes, Soccer AM television show
* Tube (band), a Japanese rock band
* Tube & Berger, the alias of dance/e ...
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'' (1931), H. G. Wells
Herbert George Wells (21 September 1866 – 13 August 1946) was an English writer, prolific in many genres. He wrote more than fifty novels and dozens of short stories. His non-fiction output included works of social commentary, politics, hist ...
, Julian Huxley and G. P. Wells 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."
Species
* '' Micraster quebrada'' , 2023 † * '' Micraster norfolkensis'' , 2012 † * '' Micraster burgiensis'' , 1935 † * '' Micraster coravium'' , 1959 † * Micraster corangium Leske, 1778 † * '' Micraster decipiens 1878 † * '' Micraster depressus'' , 1937 † * '' Micraster desori'' , 1926 † * '' Micraster elevatus'' , 1949 † * '' Micraster ernsti'' , 2024 † * '' Micraster leskei'' , 1855 † * '' Micraster piriformis'' , 1927 † * '' Micraster subglobosus'' , 1959 † * '' Micraster trangahyensis'' , 1936 † * '' Micraster turonensis'' 1878 † * '' Micraster uddeni'' , 1953 † * '' Micraster vistulensis'' , 1950 †Sources
* ''Fossils'' (Smithsonian Handbooks) by David Ward (Page 185)External links
''Micraster''
in the Paleobiology Database
Notes