| 词条 | Yorgia |
| 释义 |
| fossil_range = Ediacaran |image = Yorgia.jpg |image_caption = Fossil of Yorgia waggoneri | regnum = Animalia | phylum = Proarticulata | classis = Cephalozoa | familia = Yorgiidae | genus = Yorgia | species = Y. waggoneri | species_authority = Ivantsov, 1999[1] }}Yorgia waggoneri is a discoid Ediacaran, and possibly represents a transition organism between Dickinsonia and Spriggina. However, their growth form indicates that may not be the case. It has a low, segmented body consisting of a short wide "head", no appendages, and a long body region, reaching a maximum length of {{convert|25|cm|in|abbr=on}}. It is classified within the extinct animal phylum Proarticulata.[2] EtymologyThe generic name Yorgia comes from the Yorga river on the Zimnii Bereg (Winter Coast) of the White Sea, where the first specimens were found. The specific name honors the American paleontologist Ben Waggoner, who found the first specimen. MorphologyThe body plan of the Yorgia and other proarticulates is unusual for solitary (non-colonial) metazoans. These bilateral organisms have a segmented metameric body, but left and right transverse elements (isomers) are organized in an alternating pattern relatively to the axis of the body – they are not direct mirror images. This phenomenon is described as the symmetry of gliding reflection, which is a characteristic also found in the similar Spriggina. Some proarticulates (Yorgia, Archaeaspinus) demonstrate obvious asymmetry of left and right parts of the body. Yorgia’s initial isomer (on the right side, nearest the head) is the only one that extends across the median dividing left and right sides.[2][3] This lack of true bilateral symmetry, along with other considerations, has led some scientists to suspect that the organism falls in a sister group to the eumetazoa (i.e. all animals except Parazoa).[4] The integument of the dorsal side were unsegmented and covered with small tubercles, same as with Onega, Lossinia, Archaeaspinus and some Dickinsonia.[5] [6]Fossil recordImprints of the Yorgia waggoneri have been found in the rocks of Vendian period (Ediacaran) White sea region of Russia, dated around 555.5 Ma. and Yorgia sp. has been found in the Central Urals [7]of Russia and Flinders Ranges, Australia.[8] Most body imprints of Yorgia have in the past been primarily preserved on the sole of sandstone beds in negative relief. Other Yorgia fossils show internal structure in the original organism, showing two symmetrical rows of nodules, a central tube, rib-like tubes, and a semicircular shape with a hole in the circle centre positioned towards the head end. This structure has been interpreted as the impression of gonads, intestine and mouth.[9] Trace fossilsTaphonomic details revealed in Yorgia allow interpretation of the chains of positive imprints of other proarticulates as grazing traces, as opposed to trails created as organisms were swept along the sea floor by currents. In addition to Yorgia, two fossil taxa, Epibaion and Phyllozoon, seem to have produced similar grazing traces. Small groups of positive body imprints are documented for Dickinsonia costata as well and Dickinsonia cf. tenuis.[11][13] See also{{Portal|Paleontology}}
References1. ^{{cite journal | author = Ivantsov, A.Y. | year = 1999 | title = A New Dickinsonid from the Upper Vendian of the White Sea Winter Coast (Russia, Arkhangelsk Region) | journal = Paleontological Journal | volume = 33 | issue = 3 | pages = 233–241 | url = https://www.academia.edu/2604893}} {{Taxonbar|from=Q141203}}2. ^1 {{cite journal |author= Ivantsov, A.Y. |year= 2001 |title= Vendia and Other Precambrian "Arthropods" |journal= Paleontological Journal |volume= 35 |issue= 4 |pages= 335–343 |url= https://www.academia.edu/2605872}} 3. ^1 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. 4. ^{{cite journal |author1=Buss, L.W. |author2=Seilacher, A. |lastauthoramp=yes |year= 1994 |title= The Phylum Vendobionta: A Sister Group of the Eumetazoa? |journal= Paleobiology |volume= 20 |issue= 1 |pages= 1–4 |issn= 0094-8373 |jstor=2401145|doi=10.1017/S0094837300011088 }} 5. ^{{cite journal | author = Ivantsov, A. Yu. | author2 = Zakrevskaya, M. A. | author3 = Nagovitsyn, A. L. | year = 2018 | title = Morphology of the covers of Proarticulata (Ediacaran Metazoa) | journal = Ist Palaeontological Virtual Congress. Book of Abstracts. | pages = 65 | url = https://www.uv.es/everlab/PUBLICACIONES/1stSVP%20BOOK%20OF%20ABTRACTS.pdf}} 6. ^{{cite journal | author = Ivantsov, Yu. A. | author2 = Zakrevskaya, M.A. | author3 = Nagovitsyn, A.L. | year = 2019 | title = Morphology of integuments of the Precambrian animals, Proarticulata | journal = Invertebrate Zoology | volume = 16 | issue = 1 | pages = 19–26 | url = https://www.researchgate.net/publication/332098715_Morphology_of_integuments_of_the_Precambrian_animals_Proarticulata | doi = 10.15298/invertzool.16.1.03}} 7. ^{{cite journal | author = Grazhdankin, D. V. | author2 = Maslov, A. V., Mustill, T. M. R. | author3 = Krupenin, M. T. | year = 2005 | title = The Ediacaran White Sea Biota in the Central Urals | journal = Doklady Earth Sciences | volume = 401 | issue = 6 | pages = 784–788}} 8. ^{{cite journal | author = Droser, M. | author2 = Gehling, J. | author3 = Jensen, S. | year = 2006 | title = Assemblage palaeoecology of the Ediacara biota: The unabridged edition? | journal = Palaeogeography, Palaeoclimatology, Palaeoecology | volume = 232 | pages = 131–147 | url = http://earthscience.ucr.edu/docs/Droser_et_2006.pdf | doi = 10.1016/j.palaeo.2005.12.015 | issue = 2–4 }} 9. ^{{cite journal | author = Dzik, Jerzy | year = 2003 | title = Anatomical Information Content in the Ediacaran Fossils and Their Possible Zoological Affinities | journal = Integrative and Comparative Biology | volume = 43 | issue = 1 | pages = 114–126 | url = http://icb.oxfordjournals.org/cgi/reprint/43/1/114.pdf | doi = 10.1093/icb/43.1.114 | pmid = 21680416}} 10. ^{{cite journal|last1=Fedonkin|first1=Mikhail A.|title=The origin of the Metazoa in the light of the Proterozoic fossil record|journal=Paleontological Research|date=31 March 2003|volume=7|issue=1|pages=9–41|doi=10.2517/prpsj.7.9}} 11. ^1 {{cite journal | author = Ivantsov, A.Y. | author2=Malakhovskaya, Y.E. | year = 2002 | title = Giant Traces of Vendian Animals | journal = Doklady Earth Sciences | volume = 385 | issue = 6 | pages = 618–622 | url = http://vend.paleo.ru/pub/Ivantsov_et_Malakhovskaya_2002-e.pdf }} 12. ^{{Cite journal| issn = 0031-0301 |journal = Paleontological Journal |year= 2011| volume= 45| issue= 3| pages= 237–248| doi=10.1134/S0031030111030063| title = Feeding traces of proarticulata—the Vendian metazoa| last1 = Ivantsov| first1 = A. Yu.}} 13. ^{{cite journal | author = Retallack, G.J. | year = 2007 | title = Growth, decay and burial compaction of Dickinsonia, an iconic Ediacaran fossil | journal = Alcheringa: An Australasian Journal of Palaeontology | volume = 31 | issue = 3 | pages = 215–240 | url = http://www.informaworld.com/index/781217204.pdf | doi = 10.1080/03115510701484705 }} 2 : Cephalozoa|White Sea fossils |
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