|
''Vernanimalcula guizhouena'' is an acritarch dating from ; it was between 0.1 and 0.2 mm across (roughly the width of one or two human hairs). ''Vernanimalcula'' means "small spring animal", referring to its appearance in the fossil record at the end of the Marinoan Glaciation and the belief upon discovery it was an animal. The ''Vernanimalcula'' fossils were discovered in the Doushantuo Formation in China. This formation is a ''Konservat-Lagerstätte'', one of the rare places where soft body parts and very fine details are preserved in the fossil record. The ''Vernanimalcula'' fossils were interpreted as showing a triploblastic structure, a coelom, a differentiated gut, a mouth, an anus, and paired external pits that were believed possible sense organs, making it the earliest known member of the Bilateria (animals with bilateral symmetry, at least as embryos). The appearance of ''Vernanimalcula'' so early in the fossil record was believed to have had important implications if it were really bilaterian. The radiation of animals into many phyla would have occurred before any animal became much larger than microscopic size, making the sudden appearance of many animal phyla in the Cambrian explosion an illusion and merely represented a (geologically) sudden increase in size and the development of easily fossilised body parts by species in existing phyla.〔(Supporting Online Material from ''Science'' magazine. ) - accessed October 17, 2005〕〔( Article on Vernanimalcula in ''Astrobiology Magazine'' ) - accessed October 15, 2005〕〔( Article on Vernanimalcula in ''Scientific American'' ) - accessed October 15, 2005〕 The description of ''Vernanimalcula'' as bilaterian has been strongly challenged. Other workers (Bengtson, Budd and co-workers) in the field have repeatedly claimed that ''Vernanimalcula'' is largely a taphonomic artefact generated by phosphate growth within a spherical object such as an acritarch, and thus ''Vernanimalcula'' was not even an animal, let alone a bilaterian. Chen ''et al.'' initially defended their interpretation of ''Vernanimalcula'' against the claims of Bengtson and Budd.〔Chen, Jun Yuan, Paola Oliveri, Eric Davidson and David J. Bottjer. 2004. Response to Comment on "Small Bilaterian Fossils from 40 to 55 Million Years Before the Cambrian". At () - Retrieved June 20, 2007〕 Petryshyn ''et al.'' examined additional fossils resembling ''Vernanimalcula'' and concluded that the fossils are "likely biogenic in nature." == See also == * Snowball Earth * ''Spriggina'' * ''Kimberella'' 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Vernanimalcula」の詳細全文を読む スポンサード リンク
|