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Proarticulata Incertae Sedis
Proarticulata is a proposed phylum of extinct, near-bilaterally symmetrical animals known from fossils found in the Ediacaran (Vendian) marine deposits, and dates to approximately . The name comes from the Greek () = "before" and Articulata, i.e. prior to animals with true segmentation such as annelids and arthropods. This phylum was established by Mikhail A. Fedonkin in 1985 for such animals as ''Dickinsonia'', '' Vendia'', ''Cephalonega'', '' Praecambridium'' and currently many other Proarticulata are described (see list). Due to their simplistic morphology, their affinities and mode of life are subject to debate. They are almost universally considered to be metazoans, and due to possessing a clear central axis have been suggested to be stem-bilaterians. In the traditional interpretation, the Proarticulatan body is divided into transverse articulation (division) into isomers as distinct from the transverse articulation segments in annelids and arthropods, as their individua ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ediacaran
The Ediacaran ( ) is a geological period of the Neoproterozoic geologic era, Era that spans 96 million years from the end of the Cryogenian Period at 635 Million years ago, Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last period of the Proterozoic geologic eon, Eon as well as the last of the so-called "Precambrian supereon", before the beginning of the subsequent Cambrian Period marks the start of the Phanerozoic Eon, where recognizable fossil evidence of life becomes common. The Ediacaran Period is named after the Ediacara Hills of South Australia, where trace fossils of a diverse community of previously unrecognized lifeforms (later named the Ediacaran biota) were first discovered by geologist Reg Sprigg in 1946. Its status as an official geological period was ratified in 2004 by the International Union of Geological Sciences (IUGS), making it the first new geological period declared in 120 years. Although the period took namesake from the Ediacara Hills ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vendia
''Vendia'' is an extinct vendiamorph from the late Ediacaran, estimated to be around 567 - 550 Ma years old, it contains two species, ''V. sokolovi'' and ''V. rachiata'', both of which are restricted to the Ust' Pinega Formation in Northwestern Russia. Discovery and naming The first fossil materials of ''Vendia'' were found in a core from a Yarensk borehole that was collected from the Ust' Pinega Formation of the Arkhangelsk Oblast, northwestern Russia in 1963,V. V. Menner. (1963). "The Other Problematical Organic Remains". In: "Stratigraphy of the USSR: Upper Precambrian" Gos. Nauchno-Tekh. Izd., Moscow. pp. 504-507. (In Russian) and was formally described and named in 1969 as ''Vendia sokolovi''.B. M. Keller. (1969). "Imprint of unknown animal from Valdai Series of Russian Platform". In: A. Y. Rozanov and et al. (Eds.), "Tommotian Stage and the Cambrian lower boundary problem". ''Geol. Inst. Trans''. Vol. 206, p. 175. (In Russian) A Further two species were found and named i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Karakhtia
''Karakhtia nessovi'' is a species of Proarticulate from the Ediacaran period, around 555 Million Years Ago. K. nessovi is the only species in the genus ''Karakhtia''. The genus '' Haootia'' has been compared minorly to ''Karakhtia'' in the way that the fossils of ''Haootia'' superficially resemble the crumpled margins of ''Karakhtia''. Discovery and name The holotype fossil of ''Karakhtia'' was found from the Ustʹ Pinega Formation, in the White Sea of Russia, and described in 2004. The generic name ''Karakhtia'' is derived from the place name ''Karakhta River'', near to where the fossil material was found. The specific name ''nessovi'' is derived from the surname of ''L.A. Nessov'', a Leningrad paleontologist. Description ''Karakhtia nessovi'' is a Proarticulate from the Vendiidae family, growing up to in length, and like other members of its family, it has a headshield-like structure. Unlike anything seen in other Proarticulates, it features a margin with radial fol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paravendia
''Paravendia'' is an extinct genus of proarticulate vendiamorph that lived in the Ediacaran period, about 553 million years ago. It shares the Vendiidae family with ''Vendia'' and ''Karakhtia''. It is a monotypic genus, with the species ''Paravendia janae''. Description It is an animal that presents 'bilateral' symmetry, similar in appearance to the previously mentioned genus '' Vendia '', with new isomers replacing the older ones. Distribution Ediacaran of the Russian Federation (Arkhangelsk). See also *List of ediacaran genera The existence of life, especially that of animals, before the Cambrian had long been the subject of debate in paleontology. The apparent suddenness of the Cambrian explosion had no firm explanation, and Charles Darwin himself recognized the chal ... References Notes Zakrevskaya, Maria. Paleoecological reconstruction of the Ediacaran benthic macroscopic communities of the White Sea (Russia). Palaeogeography, Palaeoclimatology, Palaeoecology 15 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proarticulata Classes
Proarticulata is a proposed phylum of extinct, near-bilaterally symmetrical animals known from fossils found in the Ediacaran (Vendian) marine deposits, and dates to approximately . The name comes from the Greek () = "before" and Articulata, i.e. prior to animals with true segmentation such as annelids and arthropods. This phylum was established by Mikhail A. Fedonkin in 1985 for such animals as ''Dickinsonia'', '' Vendia'', '' Cephalonega'', '' Praecambridium'' and currently many other Proarticulata are described (see list). Due to their simplistic morphology, their affinities and mode of life are subject to debate. They are almost universally considered to be metazoans, and due to possessing a clear central axis have been suggested to be stem-bilaterians. In the traditional interpretation, the Proarticulatan body is divided into transverse articulation (division) into isomers as distinct from the transverse articulation segments in annelids and arthropods, as their individu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lancelets
The lancelets ( ), also known as amphioxi (: amphioxus ), consist of 32 described species of somewhat fish-like benthic filter feeding chordates in the subphylum Cephalochordata, class Leptocardii, and family Branchiostomatidae. Lancelets diverged from other chordates during or prior to the Cambrian period. A number of fossil chordates have been suggested to be closely related to lancelets, including ''Pikaia'' and ''Cathaymyrus'' from the Cambrian and ''Palaeobranchiostoma'' from the Permian, but their close relationship to lancelets has been doubted by other authors. Molecular clock analysis suggests that modern lancelets probably diversified much more recently, during the Cretaceous or Cenozoic. They are of interest to Zoologists as lancelets contain many organs and organ systems that are homologous to those of modern fish. Therefore, they provide a number of examples of possible evolutionary exaptation. For example, the gill-slits of lancelets are used for feeding only, an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Taphonomy
Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek language, Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientist Ivan Yefremov, Ivan Efremov to describe the study of the transition of remains, parts, or products of organisms from the biosphere to the lithosphere. The term taphomorph is used to describe fossil structures that represent poorly-preserved, deteriorated remains of a mixture of Taxon, taxonomic groups, rather than of a single one. Description Taphonomic phenomena are grouped into two phases: biostratinomy, events that occur between death of the organism and the burial; and diagenesis, events that occur after the burial. Since Efremov's definition, taphonomy has expanded to include the fossilization of organic and inorganic materials through both cultural and environmental influences. Taphonomy is now most widely defined as the study of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glide Reflection
In geometry, a glide reflection or transflection is a geometric transformation that consists of a reflection across a hyperplane and a translation ("glide") in a direction parallel to that hyperplane, combined into a single transformation. Because the distances between points are not changed under glide reflection, it is a motion or isometry. When the context is the two-dimensional Euclidean plane, the hyperplane of reflection is a straight line called the ''glide line'' or ''glide axis''. When the context is three-dimensional space, the hyperplane of reflection is a plane called the ''glide plane''. The displacement vector of the translation is called the ''glide vector''. When some geometrical object or configuration appears unchanged by a transformation, it is said to have symmetry, and the transformation is called a symmetry operation. ''Glide-reflection symmetry'' is seen in frieze groups (patterns which repeat in one dimension, often used in decorative borders), wallpa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chirality
Chirality () is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is distinguishable from its mirror image; that is, it cannot be superposed (not to be confused with superimposed) onto it. Conversely, a mirror image of an ''achiral'' object, such as a sphere, cannot be distinguished from the object. A chiral object and its mirror image are called '' enantiomorphs'' (Greek, "opposite forms") or, when referring to molecules, ''enantiomers''. A non-chiral object is called ''achiral'' (sometimes also ''amphichiral'') and can be superposed on its mirror image. The term was first used by Lord Kelvin in 1893 in the second Robert Boyle Lecture at the Oxford University Junior Scientific Club which was published in 1894: Human hands are perhaps the most recognized example of chirality. The left hand is a non-superposable mirror ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Segmentation (biology)
Segmentation in biology is the division of some animal and plant body plans into a linear series of repetitive segments that may or may not be interconnected to each other. This article focuses on the segmentation of animal body plans, specifically using the examples of the taxa Arthropoda, Chordata, and Annelida. These three groups form segments by using a "growth zone" to direct and define the segments. While all three have a generally segmented body plan and use a growth zone, they use different mechanisms for generating this patterning. Even within these groups, different organisms have different mechanisms for segmenting the body. Segmentation of the body plan is important for allowing free movement and development of certain body parts. It also allows for regeneration in specific individuals. Definition Segmentation is a difficult process to satisfactorily define. Many taxa (for example the molluscs) have some form of serial repetition in their units but are not conventi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isomer (Proarticulata)
Isomer (Greek ''isos'' = "equal", ''méros'' = "part") is an element of transverse body articulation of the bilateral fossil animals of the Phylum Proarticulata from the Ediacaran (Vendian) period. This term has been proposed by Andrey Yu. Ivantsov, a Russian paleontologist from the Laboratory of the Precambrian organisms, Paleontological Institute, Russian Academy of Sciences. Morphology Proarticulatan isomers are distinct from the segments of the Annelida and Panarthropoda, as each of these elements occupies only half of width of a body and are organized in an alternating pattern relatively to the axis of the body. In other words, although proarticulatans are bilaterally symmetrical, one side is not the direct mirror image of its opposite. Opposite isomers of left and right side are located with displacement of half of its width. This phenomenon is described as the symmetry of gliding reflection.M. A. Fedonkin (1985). "Systematic Description of Vendian Metazoa". In Sokolov, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bilaterians
Bilateria () is a large clade of animals characterised by bilateral symmetry during embryonic development. This means their body plans are laid around a longitudinal axis with a front (or "head") and a rear (or "tail") end, as well as a left–right–symmetrical belly (ventral) and back (dorsal (anatomy), dorsal) surface. Nearly all bilaterians maintain a bilaterally symmetrical body as adults; the most notable exception is the echinoderms, which have pentaradial symmetry as adults, but bilateral symmetry as embryos. With few exceptions, bilaterian embryos are triploblastic, having three germ layers: endoderm, mesoderm and ectoderm, and have complete digestive tracts with a separate mouth and anus. Some bilaterians lack body cavities, while others have a Pseudocoelomata, primary body cavity derived from the blastocoel, or a secondary cavity, the Coelomata, coelom. Cephalization is a characteristic feature among most bilaterians, where the sense organs and central nervous system ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
