Proarticulata is a proposed

phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...

of extinct, bilaterally symmetrical

animals Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...

known from fossils found in the

Ediacaran The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and th ...

(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 The annelids (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecolo ...

and

arthropods Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

. This phylum was established by Mikhail A. Fedonkin in 1985 for such animals as '' Dickinsonia'', ''

Vendia ''Vendia'' is a genus of oval-shaped, Ediacaran fossils ranging from 4.5 to 12.5 mm long. The body is completely segmented into isomers, which are arranged alternately in two rows longitudinal to the axis of the body. The larger isomers cov ...

'', ''

Cephalonega ''Cephalonega stepanovi'' is a fossil organism from Ediacaran deposits of the Arkhangelsk Region, Russia. It was described by Mikhail A. Fedonkin in 1976 Name Its original genus name ''Onega'' comes from the Onega Peninsula of the White Sea ...

'', ''

Praecambridium ''Praecambridium sigillum'' is an extinct organism that superficially resembles a segmented trilobite-like arthropod. It was originally described as being a trilobite-like arthropod, though the majority of experts now place it within the Proartic ...

'' 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 Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...

, and due to possessing a clear central axis have been suggested to be stem-

bilaterians The Bilateria or bilaterians are animals with bilateral symmetry as an embryo, i.e. having a left and a right side that are mirror images of each other. This also means they have a head and a tail (anterior-posterior axis) as well as a belly and ...

. In the traditional interpretation, the Proarticulatan body is divided into transverse articulation (division) into

isomers In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. ...

as distinct from the transverse articulation segments in annelids and arthropods, as their individual isomers occupy only half the width of their bodies, and are organized in an alternating pattern along the longitudinal axis of their bodies. In other words, one side is not the direct mirror image of its opposite (''

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 ...

''). Opposite isomers of left and right side are located with displacement of half of their width. This phenomenon is described as the symmetry of gliding reflection. Some recent research suggests that some proarticulatans like ''Dickinsonia'' have genuine segments, and the isomerism is superficial and due to taphonomic distortion. However, other researchers dispute this. Displacement of left-right axis is known in bilaterians, notably

lancelets The lancelets ( or ), also known as amphioxi (singular: amphioxus ), consist of some 30 to 35 species of "fish-like" benthic filter feeding chordates in the order Amphioxiformes. They are the modern representatives of the subphylum Cephalochord ...

Morphology

Vendiamorpha

The body is completely segmented, with all isomers curved towards the posterior, and the first isomer is normally much larger than the rest. The first two isomers at the anterior dorsal end are partly fused. (e.g., ''

'', ''

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 ''Pa ...

'' and ''

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 t ...

'').

Cephalozoa

These proarticulatans are incompletely segmented, as the anterior zone is free of isomers, often making a "hairband" like appearance (example cephalozoans include ''

Yorgia ''Yorgia waggoneri'' is a discoid Ediacaran organism. It has a low, segmented body consisting of a short wide "head", no appendages, and a long body region, reaching a maximum length of . It is classified within the extinct animal phylum Proarti ...

'', ''

Andiva ''Andiva ivantsovi'' is a Vendian fossil, identified to be a bilaterian triploblastic animal in the Ediacaran phylum Proarticulata, known from the Winter Coast, White Sea, Russia. It was first discovered in 1977, and described as a new species i ...

'', ''

Archaeaspinus ''Archaeaspinus fedonkini'' is an extinct proarticulatan organism from the Late Precambrian (Ediacaran) period. Background ''Archaeaspinus'' was discovered in Zimnii Bereg, the Winter Coast of the White Sea in Russia, by A. Yu. Ivantsov in 2001 ...

'', '' Ivovicia'', '' Podolimirus'', ''

Tamga A tamga or tamgha (from otk, 𐱃𐰢𐰍𐰀, tamga, lit=stamp, seal; tr, damga; mn, tamga; ; ); an abstract Seal (emblem), seal or Seal (emblem), stamp used by Eurasian nomads and by cultures influenced by them. The tamga was normally the e ...

'', ''

Spriggina ''Spriggina'' is a genus of early bilaterian animals whose relationship to living animals is unclear. Fossils of ''Spriggina'' are known from the late Ediacaran period in what is now South Australia. ''Spriggina floundersi'' is the official fo ...

'', '' Marywadea'' and '' Cyanorus''). Some cephalozoans from the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Yorgiidae Yorgiidae is an extinct family of cephalozoans, which lived 635 million years ago. They were filter fed. Description Like most proarticulates, they present semi- bilateral symmetry. They had a discoid appearance, with the body segmented by iso ...

demonstrate pronounced asymmetry of left and right parts of the body. For instance, ''Yorgia''’s initial right isomer is the only one which spreads far towards the left side of the body. ''Archaeaspinus'' has an unpaired anterior lobe confined by the furrow to the left side only. file:Onega_stepanovi.jpg, left, Artist's reconstruction of ''

stepanovi''. file:Lossinia_lissetski.jpg, Artist's reconstruction of ''

Lossinia ''Lossinia lissetskii'' is a fossil marine organism from Precambrian strata of the White Sea area, in Russia. ''L. lissetskii'' is a member of the extinct phylum Proarticulata. Etymology The generic name refers to the Losinoe Bog (Moose Bog), n ...

'' feeding on surface algae. In ''

stepanovi'' and '' Tamga hamulifera'' the zone containing the isomers is encircled by a peripheral, undivided zone. The ''

''s isomers are connected to each other, forming a body resembling a rubber raft; the ''

''s isomers are separated from each other, and do not touch. In ''

'', the center undivided region has no visible isomers, instead having the lobe-like isomers emanate from the periphery of the undivided region as "transverse articulations."

Dipleurozoa

The dipleurozoan body is subradial, divided by isomers entirely (e.g., '' Dickinsonia'' and ''

Phyllozoon ''Phyllozoon''(lit. "Leaf animal" in greek) is an Ediacaran imprint that resembles a proarticulatan and has been interpreted as a feeding trace. It usually occurs in long chains of imprints formed, presumably as the organism that made it moved. ...

''). ''Dickinsonia'' juveniles show undivided anterior areas but these regions were reduced in the course of ontogeny, and in the adult stages ''Dickinsonia''-like proarticulates changed so radically that they became almost indistinguishable from isomers.

List of Proarticulata

Body fossils

*'' Armillifera'' Fedonkin, 1980 :''A. parva'' Fedonkin, 1980 *''

'' Fedonkin, 2002 :''A. ivantsovi'' Fedonkin, 2002 *''

'' Ivantsov, 2007 (=''Archaeaspis'' Ivantsov, 2001) :''A. fedonkini'' Ivantsov, 2001 *''

'' Ivantsov ''et al.'', 2019 :''C. stepanovi'' (Fedonkin, 1976) *'' Chondroplon'' Wade, 1971 (possible =''Dickinsonia'') :''C. bilobatum'' Wade, 1971 *'' Cyanorus'' Ivantsov, 2004 :''C. singularis'' Ivantsov, 2004 *'' Dickinsonia'' Sprigg, 1947 :''D. costata'' Sprigg, 1947 :''D. lissa'' Wade, 1972 :''D. menneri'' Keller 1976 (=''Vendomia menneri'' Keller 1976) :''D. tenuis'' Glaessner & Wade, 1966 *'' Ivovicia'' Ivantsov, 2007 :''I. rugulosa'' Ivantsov, 2007 *''

'' Ivantsov, 2004 :''K. nessovi'' Ivantsov, 2004 *''

'' Ivantsov, 2007 :''L. lissetskii'' Ivantsov, 2007 *'' Marywadea'' Glaessner, 1976 :''M. ovata'' Glaessner & Wade, 1966 *''

Ovatoscutum ''Ovatoscutum concentricum'' is one of many enigmatic organisms known from the Ediacaran deposits of the Flinders Ranges, Australia, and the White Sea area in Russia, dating around 555 Ma. Etymology The generic name ''Ovatoscutum'' is derived fr ...

'' Glaessner & Wade, 1966 :''O. concentricum'' Glaessner & Wade, 1966 *''

'' Ivantsov, 2004 :''P. janae'' Ivantsov, 2001 (=''Vendia janae'' Ivantsov, 2001) *''

'' Jenkins & Gehling, 1978 :''P. hanseni'' Jenkins & Gehling, 1978 *'' Podolimirus'' Fedonkin, 1983 (=''Valdainia'' Fedonkin, 1983) :''P. mirus'' Fedonkin, 1983 (''Valdainia plumosa'' Fedonkin, 1983) *''

'' Glaessner & Wade, 1966 :''P. siggilum'' Glaessner & Wade, 1966 *''

'' Glaessner, 1958 :''S. floundersi'' Glaessner, 1958 *''

'' Ivantsov, 2007 :''T. hamulifera'' Ivantsov, 2007 *''

'' Keller, 1969 :''V. sokolovi'' Keller, 1969 :''V. rachiata'' Ivantsov, 2004 *? ''

Windermeria ''Windermeria aitkeni'' (named after Windermere, British Columbia, Canada) is a Precambrian organism from the Blueflower Formation of Sekwi Brook North, in the Northwest Territories of Canada. Only one specimen has been found. ''Windermeria' ...

'' Narbonne, 1994 :''W. aitkeni'' Narbonne, 1994 *''

'' Ivantsov, 1999 :''Y. waggoneri'' Ivantsov, 1999

Trace fossils

*''

Epibaion ''Epibaion'' is a trace fossil imprint of the Ediacaran animals of the phylum Proarticulata, which became extinct in the Precambrian. Imprints often occurring in chains, that is interpreted as a feeding trace; some chains terminate in a body foss ...

'' Ivantsov, 2002 :''E. axiferus'' Ivantsov, 2002. :''E. waggoneris'' Ivantsov, 2011. This is a trace of ''Yorgia waggoneri'' :''E. costatus'' Ivantsov, 2011. This is a trace of ''Dickinsonia costata''

References

External links

Database of Ediacaran Biota
Advent of Complex Life {{Taxonbar, from=Q2566978 Animal phyla Vendobionta

Morphology

Vendiamorpha

Cephalozoa

Dipleurozoa

List of Proarticulata

Body fossils

Trace fossils

See also

References

External links