Eumetazoa Temporal range: Ediacaran–Recent PreЄ Є O S D C P T J K Pg N
A lancelet
Scientific classification
Domain:	Eukaryota
(unranked):	Opisthokonta
Kingdom:	Animalia
Subkingdom:	Eumetazoa Butschli, 1910
Phyla
Radiata (unranked) Ctenophora Cnidaria Bilateria (unranked) Orthonectida Rhombozoa Acoelomorpha Chaetognatha Superphylum Deuterostomia Chordata Hemichordata Echinodermata Xenoturbellida Vetulicolia † Protostomia (unranked) Superphylum Ecdysozoa Kinorhyncha Loricifera Priapulida Nematoda Nematomorpha Lobopodia† Onychophora Tardigrada Arthropoda Superphylum Platyzoa Platyhelminthes Gastrotricha Rotifera Acanthocephala Gnathostomulida Micrognathozoa Cycliophora Superphylum Lophotrochozoa Sipuncula Hyolitha† Nemertea Phoronida Bryozoa Entoprocta Brachiopoda Mollusca Annelida Echiura

Eumetazoa (Greek: εὖ [eu], well + μετά [metá], after + ζῷον [zóon], animal) is a clade comprising all major animal groups except sponges, placozoa, and several other obscure or extinct life forms, such as Dickinsonia. Characteristics of eumetazoans include true tissues organized into germ layers, and an embryo that goes through a gastrula stage. The clade is usually held to contain at least Ctenophora, Cnidaria, and Bilateria. Whether mesozoans and placozoans belong is in dispute.

Some phylogenists have speculated the sponges and eumetazoans evolved separately from single-celled organisms, which would mean that the animal kingdom does not form a clade (a complete grouping of organisms descended from a common ancestor). However, genetic studies and some morphological characteristics, like the common presence of choanocytes, support a common origin.^[1]

Eumetazoans are a major group of animals in the Five Kingdoms classification of Lynn Margulis and K. V. Schwartz, comprising the Radiata and Bilateria — all animals except the sponges, placozoans and mesozoans.^[2] When treated as a formal taxon Eumetazoa is typically ranked as a subkingdom. The name Metazoa has also been used to refer to this group, but more often refers to the Animalia as a whole. Many classification schemes do not include a subkingdom Eumetazoa.

Taxonomy[link]

Over the last decade, the work of developmental biologists and molecular phylogeneticists spawned new ideas about bilaterian relationships resulting in a paradigm shift.

The current widely accepted hypothesis, based on molecular data (mostly 18S rRNA sequences), divides bilateria into the following four groups: Deuterostomia, Ecdysozoa, Lophotrochozoa, and Platyzoa (sometimes included in Lophotrochozoa). The last three groups are also collectively known as Protostomia.^[3]

However, many skeptics emphasize the pitfalls and inconsistencies associated with the new data. Claus Nielsen, a professor of evolutionary invertebrate embryology at the Zoological Museum University of Copenhagen champions one of the most prominent alternative views based on morphological evidence. In his 2001 book Animal Evolution: Interrelationships of the Living Phyla, he maintains the traditional divisions of Protostomia and Deuterostomia.

Evolutionary origins[link]

It has been suggested that one type of molecular clock and one approach to interpretation of the fossil record both place the evolutionary origins of eumetazoa in the Ediacaran.^[4] However, the earliest eumetazoans may not have left a clear impact on the fossil record and other interpretations of molecular clocks suggest the possibility of an earlier origin.^[5] The discoverers of Vernanimalcula describe it as the fossil of a bilateral triploblastic animal that appeared at the end of the Marinoan glaciation prior to the Ediacaran Period, implying an even earlier origin for eumetazoans.^[6]

References[link]

External links[link]

• Bilateria. Tree of Life web project, US National Science Foundation. 2002. 6 January 2006.
• Invertebrates and the Origin of Animal Diversity
• Evers, Christine A., Lisa Starr. Biology:Concepts and Applications. 6th ed. United States:Thomson, 2006. ISBN 0-534-46224-3.
• Metazoa: the Animals
• Nielsen, C. 2001. Animal Evolution: Interrelationships of the Living Phyla, 2nd edition, 563 pp. Oxford Univ. Press, Oxford. ISBN 0-19-850681-3
• Borchiellini, C. Manuel, M., Alivon, E., Boury-Esnault N., Vacelet, J., Le-Parco, Y. 2001. Journal of Evolutionary Biology 14 (1): 171–179.
• Peterson, Kevin J., McPeek, Mark A., & Evans, David A.D. 2005. Tempo & mode of early animal evolution: inferences from rocks, Hox, & molecular clocks. Paleobiology 31(2, Supplement): 36–55.

Wikispecies has information related to: Eumetazoa

For his grandfather, the American doctor, see Walter C. Alvarez.

This biographical article needs additional citations for verification. Please help by adding reliable sources. Contentious material about living persons that is unsourced or poorly sourced must be removed immediately, especially if potentially libelous or harmful. (April 2011)

Walter Alvarez (born October 3, 1940) is a professor in the Earth and Planetary Science department at the University of California, Berkeley. He is most widely known for the theory that dinosaurs were killed by an asteroid impact, developed in collaboration with his father, Nobel Prize winning physicist Luis Alvarez.

Biography[link]

Born in Berkeley, California, Alvarez was the son of Luis Walter Alvarez, a Nobel prize-winner in physics. His grandfather was the famed physician Walter C. Alvarez and his great-grandfather, Spanish-born Luis F. Alvarez, worked as a doctor in Hawaii and developed a method for the better diagnosis of macular leprosy. His great-aunt Mabel Alvarez was a noted California artist and oil painter.

Alvarez earned his B.A. in geology in 1962 from Carleton College in Minnesota and Ph.D. in geology from Princeton University in 1967. He worked for American Overseas Petroleum Limited in the Netherlands, and in Libya at the time of Colonel Gadaffi’s revolution. Having developed a side interest in archaeological geology, he left the oil company and spent some time in Italy, studying the Roman volcanics and their influence on patterns of settlement in early Roman times.

Alvarez then moved to Lamont-Doherty Geological Observatory of Columbia University, and began studying the Mediterranean tectonics in the light of the new theory of plate tectonics. His work on tectonic paleomagnetism in Italy led to a study of the geomagnetic reversals recorded in Italian deep-sea limestones, and he and his colleagues were able to date the reversals for an interval of more than 100 million years of Earth history.

Impact theory[link]

Alvarez and his father Luis W. Alvarez are most widely known for their discovery (with Frank Asaro and Helen Michel) that a clay layer occurring right at the Cretaceous-Tertiary (K-T) boundary was highly enriched in the element iridium. Since iridium enrichment is common in asteroids, but very uncommon on the Earth, they further postulated that the layer had been created by the impact of a large asteroid with the Earth and that this impact event was the likely cause of the Cretaceous–Paleogene extinction event.^[1]

This iridium enrichment has now been observed in many other sites around the world. And further, the very large Chicxulub crater was identified and is now regarded as the definitive evidence of a large impact. Consequently, a majority of scientists now accept the impact scenario as the most likely cause for the Cretaceous–Paleogene extinction event which occurred 65 million years ago and eliminated 75% of all species,^[2] including all non-avian dinosaurs. His book, T. Rex and the Crater of Doom, details the discovery of the Cretaceous–Paleogene extinction event.

In addition to his interest in extinction events and impacts, Alvarez has contributed to the understanding of Mediterranean tectonics, Roman geology and archeology, and the establishment of magnetostratigraphic correlations.

Big History[link]

Alvarez began teaching a course in Big History at UC Berkeley in 2006 under the title "Big History: Cosmos, Earth, Life, Humanity." ^[3] According to Alvarez, Big History is the "attempt to understand, in a unified and interdisciplinary way, the history of the Cosmos, Earth, Life and Humanity." This definition was later adopted by the International Big History Association (IBHA).^[4] Alvarez's course is open to all majors and grade levels and seeks to provide a broad understanding of the past, present and future.

Alvarez is also one of the founding members of the IBHA,^[5] presently serving on the advisory board.

ChronoZoom[link]

Alvarez's most recent contribution to the field of Big History has been the creation of a zoomable, interactive timeline in partnership with Microsoft Research called ChronoZoom.^[6] ChronoZoom is a computer-graphical approach to dealing with this problem of visualizing and understanding time scales, and presenting vast quantities of historical information in a useful way.^[7] ChronoZoom was introduced at the 97th Annual Faculty Research Lecture at UC Berkeley.^[8] Video recording of the talk.

Awards and honors[link]

Alvarez is the recipient of numerous awards and honors. He was elected a Fellow of the American Academy of Arts and Sciences in 1983, and elected a member of the National Academy of Sciences in 1991.^[9] He was awarded the 2006 Nevada Medal, the 2008 Vetlesen Prize,^[10] and the Penrose Medal from the Geological Society of America. In 2005, he received the doctorate "Honoris Causa" in Geological Sciences from the University of Siena, Italy.

Further reading[link]

• T. Rex and the Crater of Doom by Walter Alvarez ISBN 0-375-70210-5
• The Mountains of Saint Francis: The Geologic Events that Shaped Our Earth by Walter Alvarez (W. W. Norton, December 2008)
• ChronoZoom

External links[link]

• Walter Alvarez's Berkeley homepage
• ChronoZoom project homepage

References[link]