Yorgiidae
{{Short description|Extinct species of disc-shaped organism}}
{{Automatic taxobox
| fossil_range = {{fossil range|571.0|551.0}} Ediacaran
| image = Yorgia.jpg
| image_caption = Fossil of the type species, Yorgia waggoneri
| taxon = Yorgiidae
| authority = Ivantsov, 2001
| subdivision_ranks = Genera
| subdivision =
- † Yorgia
- † Archaeaspinus
- † Ivovicia
- † Praecambridium ?
}}
Yorgiidae is an extinct family of the class Cephalozoa, which is a part of the wider phylum Proarticulata.{{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}} They lived from around 571 to 551 Ma.
Description
Image:Photo_of_"Archaeaspinus_fedonkini"_fossil_Ivantsov_2007.png
Like other relatives within the phylum Proarticulata, their body plan consists of isomers arranged in a glide symmetry, meaning they do not have true bilateral symmetry. As with other cephalozoans, their initial right isomer extends right across the body, forming a distinctive 'head', whilst they have a unique feature with their initial left isomer extending slightly to the right side and into the initial right isomer.
This is most prominent in the genus Archaeaspinus, with it having an unpaired left lobe/isomer within its 'head' region, forming a distinctive question mark-like shape.
Distribution
Genera of the family Yorgiidae are most commonly found in the Ust' Pinega Formation and Central Urals of Russia,{{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}} as well as the Flinders Ranges of South Australia.{{cite journal |last1=Droser |first1=Mary L. |last2=Gehling |first2=James G. |last3=Jensen |first3=Sören R. |title=Assemblage palaeoecology of the Ediacara biota: The unabridged edition? |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |date=March 2006 |volume=232 |issue=2–4 |pages=131–147 |doi=10.1016/j.palaeo.2005.12.015|bibcode=2006PPP...232..131D }}
Taxonomy
Yorgiidae includes the following genera:
- † Archaeaspinus Ivantsov, 2007 (synonym of Archaeaspis)
- † Archaeaspinus fedonkini Ivantsov, 2001
- † Yorgia Ivantsov, 1999
- † Yorgia waggoneri Ivantsov, 1999
- † Ivovicia Ivantsov, 2007
- † Ivovicia rugulosa Ivantsov, 2007
- † Praecambridium (?) Ivantsov, 1999
- † Praecambridium sigillum (?) Ivantsov, 1999
Due to the rather small size of known Praecambridium specimens, and the large grain size of the matrix they are commonly found in, the placement of Praecambridium within family Yorgiidae is tentative, as its hard to discern certain details in such small specimens, although most reconstructions show similarities with juvenile Yorgia, and may even be a larval stage. A more recent study also suggested that Praecambridium may a juvenile, and possibly a juvenile of another cephalozoan Spriggina, which occurs in the same beds as Praecambridium.{{cite journal |last1=Ivantsov |first1=A. Yu. |title=Small Vendian transversely Articulated fossils |journal=Paleontological Journal |date=April 2007 |volume=41 |issue=2 |pages=113–122 |doi=10.1134/S0031030107020013|bibcode=2007PalJ...41..113I }}
Andiva was previously assigned to the family Yorgiidae, although a recent study removes it from the family, but still placed within the class Cephlazoa.{{cite journal |last1=Dzik |first1=J. |title=Anatomical Information Content in the Ediacaran Fossils and Their Possible Zoological Affinities |journal=Integrative and Comparative Biology |date=1 February 2003 |volume=43 |issue=1 |pages=114–126 |doi=10.1093/icb/43.1.114|pmid=21680416 }}
See also
{{portal|paleontology}}
References
{{Reflist}}
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