|Phylum:||†Proarticulata Fedonkin, 1985|
|Class / Family|
Proarticulata is an extinct phylum of very early, superficially bilaterally symmetrical animals known from fossils found in the Ediacaran (Vendian) marine deposits, and dates to approximately . The name from Greek προ (pro-) = "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, Onega, Praecambridium and currently many other Proarticulata are described (see list).
The transverse articulation (division) of the Proarticulata body into isomers is 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). 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.
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., Vendia, Paravendia and Karakhtia).
Cephalozoa (preliminary name)
These proarticulatans demonstrate incomplete segmentation, as the anterior zone is free of isomers, often making a "hairband" like appearance. (example cephalozoans include Yorgia, Praecambridium, Andiva, Archaeaspinus, Ivovicia, Spriggina, Marywadea and Cyanorus. Some cephalozoans from the family Yorgiidae 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.
The dipleurozoan body is subradial, divided by isomers entirely (e.g., Dickinsonia and Phyllozoon). 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.
Proarticulata Incertae sedis
In Onega stepanovi and Tamga hamulifera all isomers are encircled by a peripheral undivided zone. In the former, the isomers remain in contact with each other, forming a raft-like region, while in the latter, the isomers are isolated from each other and do not touch. In Lossinia, 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."
List of Proarticulata
- A. parva Fedonkin, 1980
- A. ivantsovi Fedonkin, 2002
- A. fedonkini Ivantsov, 2001
- Chondroplon Wade, 1971 (possible =Dickinsonia)
- C. bilobatum Wade, 1971
- 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 et Wade, 1966
- I. rugulosa Ivantsov, 2007
- Karakhtia Ivantsov, 2004
- K. nessovi Ivantsov, 2004
- L. lissetskii Ivantsov, 2007
- Marywadea Glaessner, 1976
- M. ovata Glaessner et Wade, 1966
- O. stepanovi Fedonkin, 1976
- Ovatoscutum Glaessner et Wade, 1966
- O. concentricum Glaessner et Wade, 1966
- P. janae Ivantsov, 2001 (=Vendia janae Ivantsov, 2001)
- Phyllozoon Jenkins et Gehling, 1978
- P. hanseni Jenkins et Gehling, 1978
- Podolimirus Fedonkin, 1983
- P. mirus Fedonkin, 1983
- Praecambridium Glaessner et Wade, 1966
- P. siggilum Glaessner et Wade, 1966
- Spriggina Glaessner, 1958
- S. floundersi Glaessner, 1958
- T. hamulifera Ivantsov, 2007
- Valdainia Fedonkin, 1983
- V. plumosa Fedonkin, 1983
- V. sokolovi Keller, 1969
- V. rachiata Ivantsov, 2004
- ? Windermeria Narbonne, 1994
- W. aitkeni Narbonne, 1994
- Y. waggoneri Ivantsov, 1999
- 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
- Mikhail A. Fedonkin, James G. Gehling, Kathleen Grey, Guy M. Narbonne, and Patricia Vickers-Rich foreword by Arthur C. Clarke. (2008) "The Rise of Animals. Evolution and Diversification of the Kingdom Animalia"
- M. A. Fedonkin (1985). "Systematic Description of Vendian Metazoa". In Sokolov, B. S. and Iwanowski, A. B., eds., "Vendian System: Historical–Geological and Paleontological Foundation, Vol. 1: Paleontology". Moscow: Nauka, pp. 70–106.
- Fedonkin, M.A. (31 March 2003). "The origin of the Metazoa in the light of the Proterozoic fossil record" (PDF). Paleontological Research. 7 (1): 9–41. doi:10.2517/prpsj.7.9.
- Ivantsov, A.Y. (2001). "Vendia and Other Precambrian "Arthropods"". Paleontological Journal. 35 (4): 335–343.
- Ivantsov, A.Y. (1999). "A New Dickinsoniid from the Upper Vendian of the White Sea Winter Coast (Russia, Arkhangelsk Region)". Paleontological Journal. 33 (3): 233–241.
- Ivantsov, A. Yu (2004). "New Proarticulata from the Vendian of the Arkhangel'sk Region" (PDF). Paleontological Journal. 38 (3): 247–253. Archived from the original (PDF) on 2007-09-27.
- Ivantsov, A.Y.; Malakhovskaya, Y.E.; Serezhnikova, E.A. (2004). "Some Problematic Fossils from the Vendian of the Southeastern White Sea Region" (PDF). Paleontological Journal. 38 (1): 1–9. Archived from the original (PDF) on 2007-07-04.
- Ivantsov, A.Y. (2004) "Vendian Animals in the Phylum Proarticulata". The Rise and Fall of the Vendian Biota. IGSP Project 493. Abstracts. Prato, Italy, p. 52.
- Ivantsov, A. Yu. (April 2007). "Small Vendian transversely Articulated fossils". Paleontological Journal. 41 (2): 113. doi:10.1134/S0031030107020013.
- Ivantsov, A.Y.; Malakhovskaya, Y.E. (2002). "Giant Traces of Vendian Animals" (PDF). Doklady Earth Sciences. 385 (6): 618–622. Archived from the original (PDF) on 2007-07-04.
- Andrey Yu. Ivantsov (December 2010). "Paleontological evidence for the supposed precambrian occurrence of mollusks". Paleontological Journal. 40 (12): 1552–1559. doi:10.1134/S0031030110120105.
- Fedonkin, M. A. (2002). "Andiva ivantsovi gen. et sp. n. and related carapace‐bearing Ediacaran fossils from the Vendian of the Winter Coast, White Sea, Russia". Italian Journal of Zoology. 69 (2): 175–181. doi:10.1080/11250000209356456.
- B. M. Keller and M. A. Fedonkin (1976). "New Records of Fossils in the Valdaian Group of the Precambrian on the Syuz'ma River" (PDF). Izv. Akad. Nauk SSSR, Ser. Geol. (in Russian). 3: 38–44. Archived from the original (PDF) on 2007-09-27.
- Narbonne, G. M. (May 1994). "New Ediacaran fossils from the Mackenzie Mountains, Northwestern Canada". Journal of Paleontology. 63 (3): 411–416. JSTOR 1306192.
- Ivantsov, A. Y. (May 2011). "Feeding traces of Proarticulata — the Vendian metazoa". Paleontological Journal. 45 (3): 237–248. doi:10.1134/S0031030111030063.
- Database of Ediacaran Biota Advent of Complex Life