Archaeaspinus

Archaeaspinus was discovered in Zimnii Bereg, the Winter Coast of the White Sea in Russia, by A. Yu. Ivantsov in 2001.{{Cite journal|last=Ivantsov|first=Andrey Yu.|title=New Proarticulata from the Vendian of the Arkhangel'sk Region|journal=Paleontological Journal|volume=38|issue=3|pages=247–253|date=January 2004 |url=https://www.academia.edu/6408008|language=en}} Since then, numerous additional fossils have been attributed to the genus, mostly from that same type locality, but a small number from Flinders Ranges in South Australia as well.{{cite book|author=Mikhail A. Fodonkin, James G. Gehling, Kathleen Grey, Guy M. Narbonne, Patricia Vickers-Rich|url=https://books.google.com/books?id=KsFFIrJ8IxEC&dq=archaeaspinus+in+south+australia&pg=PA261|title=The Rise of Animals, Evolution and Diversification of the Kingdom Animalia|publisher=Johns Hopkins University Press, Baltimore|date=2007|page=261|isbn=9780801886799}}

Originally called Archaeaspis—a name already applied to a redlichiid trilobite—in 2001 by Ivantsov, it was later recombined under its current name in 2007 by the same author.{{Cite journal|last=Ivantsov|first=A. Yu.|title=Small Vendian transversely Articulated fossils|url=https://www.academia.edu/2352394|journal=Paleontological Journal|year=2007 |language=en|volume=41|issue=2|pages=113–122|doi=10.1134/S0031030107020013 |s2cid=86636748 |issn=0031-0301}} The type species, A. fedonkini, is the only species known in this genus. It appears in the fossil record between 571-551Ma.{{Cite journal|last1=Muscente|first1=A. D.|last2=Bykova|first2=Natalia|last3=Boag|first3=Thomas H.|last4=Buatois|first4=Luis A.|last5=Mángano|first5=M. Gabriela|last6=Eleish|first6=Ahmed|last7=Prabhu|first7=Anirudh|last8=Pan|first8=Feifei|last9=Meyer|first9=Michael B.|last10=Schiffbauer|first10=James D.|last11=Fox|first11=Peter|date=2019-02-22|title=Ediacaran biozones identified with network analysis provide evidence for pulsed extinctions of early complex life|journal=Nature Communications|language=en|volume=10|issue=1|pages=911|doi=10.1038/s41467-019-08837-3|pmid=30796215 |issn=2041-1723|pmc=6384941|bibcode=2019NatCo..10..911M }}

File:Photo_of_"Archaeaspinus_fedonkini"_fossil_Ivantsov_2007.png

As with other genera within the family Yorgiidae, Archaeaspinus is discoid. Much of its body segmented by up to 15 bilateral isomers. It has an unsegmented anterior end reminiscent of a head, full of what may be distribution channels. It also contains what appears to be an unpaired lobe which branches off the isomer that is furthest forward to loop within the "head" section, following the shape of the body.Ivantsov AY (2004). [https://www.monash.edu/__data/assets/pdf_file/0010/75655/ivantsov.pdf "Vendian Animals in the Phylum Proarticulata"] (PDF). The Rise and Fall of the Vendian Biota. IGSP Project 493. Prato, Italy. p. 52 This lobe, or perhaps irregular isomer, is bordered by a shallow furrow on the anterior and left edge.{{Cite journal|last=Ivantsov|first=Andrey Yu.|title=Vendia and Other Precambrian "Arthropods"|url=https://www.academia.edu/2605872|journal=Paleontological Journal|volume=35|issue=4|pages=335–343|date=January 2001 |language=en}}

The isomers are arranged in a gliding reflection symmetry, thought to have increased in size and quantity as the organism aged and grew. The dorsal side is covered with evenly spaced tubercles.

Though originally thought to have been soft bodied, it has also been suggested that Archaeaspinus had a delicate, flexible carapace ("cover tissue") covering its dorsal side.{{Cite journal|last=Fedonkin|first=Mikhail A.|date=2003-03-31|title=The origin of the Metazoa in the light of the Proterozoic fossil record|journal=Paleontological Research|volume=7|issue=1|pages=9–41|doi=10.2517/prpsj.7.9|s2cid=55178329 |issn=1342-8144|doi-access=free}}

It closely resembles Yorgia, because of the similar anterior region, and to a lesser extent Dickinsonia and other Proarticulates.

Archaeaspinus belongs to the phylum Proarticulata. Within that, its class is Cephalozoa and family Yorgiidae.{{Cite web|title=PBDB|url=https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=152324&is_real_user=1|access-date=2020-11-30|website=paleobiodb.org}}{{Cite web|title=IRMNG - Cephalozoa †|url=https://www.irmng.org/aphia.php?p=taxdetails&id=11915625|access-date=2020-11-30|website=www.irmng.org}} Until 2004 Cephalozoans were categorized within the class Vendiamorpha, so older records of the Archaeaspinus may label it a Vendiamorph.{{Cite journal|last1=Ivantsov|first1=A. Yu.|last2=Fedonkin|first2=M. A.|last3=Nagovitsyn|first3=A. L.|last4=Zakrevskaya|first4=M. A.|date=September 2019|title=Cephalonega, A New Generic Name, and the System of Vendian Proarticulata|url=http://dx.doi.org/10.1134/s0031030119050046|journal=Paleontological Journal|volume=53|issue=5|pages=447–454|doi=10.1134/s0031030119050046|s2cid=203853224 |issn=0031-0301|url-access=subscription}}

Newer analyses suggest that tissue on the ventral side of most Proarticulates, and therefore Archaeaspinus, bore cilia for feeding.{{Cite journal|last1=Ivantsov|first1=A. Yu.|last2=Zakrevskaya|first2=M. A.|last3=Nagovitsyn|first3=A. L.|date=December 2019|title=Morphology of integuments of the Precambrian animals, Proarticulata|journal=Invertebrate Zoology|volume=16|issue=1|pages=19–26|doi=10.15298/invertzool.16.1.03|issn=1812-9250|doi-access=free}}

Archaeaspinus is thought to have used an osmotrophic or filter-feeding strategy, absorbing nutrients from the microbial mat below in much the same way that Yorgia did.{{Cite journal|last1=Budd|first1=Graham E.|last2=Jensen|first2=Sören|date=2017|title=The origin of the animals and a 'Savannah' hypothesis for early bilaterian evolution|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/brv.12239|journal=Biological Reviews|language=en|volume=92|issue=1|pages=446–473|doi=10.1111/brv.12239|pmid=26588818 |issn=1469-185X|hdl=10662/8091|s2cid=39110115 |hdl-access=free}}

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Category:Proarticulata

Category:Yorgiidae