Spriggina

Taxobox
name = "Spriggina"
color = #taxobox colour|incertae sedis
fossil_range = Ediacaran

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image_width = 250px
image_caption = Fossil of "S. floundersi". Scale in millimetres.


image2_width = 120px
image2_caption = Sketch reconstruction
regnum = ?Animalia
unranked_phylum = ?Bilateria
phylum = ?Arthropoda
genus = "Spriggina"
genus_authority = Glaessner, 1958citation
author=Glaessner, Martin F. | year =1958
url=http://www.samuseum.sa.gov.au/Journals/TRSSA/TRSSA_V081/TRSSA_V081_p185p188.pdf
title= New Fossils from the Base of the Cambrian in South Australia.
format = Free full text
journal = Transactions of the Royal Society of South Australia
volume = 81
pages = 185–188]
species = "S. floundersi"
binomial = "Spriggina floundersi"
binomial_authority = Glaessner, 1958

Fossils of "Spriggina" are known from the Ediacaran period, around ma|550. The segmented organism reached about 3 cm in length and may have been predatory. Its bottom is covered with two rows of tough interlocking plates, while one row covered its top; its front few segments fused to form a head, which may have borne eyes and antennae.

"Spriggina"'s affinity is currently unknown; it has been classified as an annelid worm, a rangeomorph-like frond, and an arthropod, perhaps related to the trilobites. Lack of known segmented legs or limbs tends to make an arthropod classification premature.

Morphology

"Spriggina" grew to around three centimetres in length, and was approximately oblong. The organism was segmented, with no fused segments, with the segments sometimes being curved.cite journal | author = McCall | year = 2006 | doi = 10.1016/j.earscirev.2005.08.004 | title = The Vendian (Ediacaran) in the geological record: Enigmas in geology's prelude to the Cambrian explosion | journal = Earth-Science Reviews | volume = 77 | pages = 1 ] The upper surface of the organism was covered by one row of overlapping cuticular plates; the underside, paired plates.

The first two segments formed a "head". The front segment was the shape of a horseshoe, with a pair of depressions on its upper surface which may represent eyes. The second segment may have borne antennae. Subsequent segments bore annulations.

Some fossils have what may be a circular mouth at the centre of the semicircular head – although interpretation is hampered by the small size of the creature relative to the large grains of sandstones in which it is preserved. Legs are not preserved.

The symmetry observed is not exactly bilaterian, but appears to be a glide reflection, where opposite segments are shifted by half an interval. [ cite journal | author=Ivantsov, A.Y.|year= 2001 | title="Vendia" and other Precambrian "arthropods" | journal=Paleontological Journal | volume=35 | pages=335–343 ] In some specimens the body segments tilt backwards, making roughly chevron patterns; while in others they are more or less straight. There appear to be fairly complex variations between these two end members.

Fossil occurrences

"Spriggina" is known only from beds of Ediacaran age. Fossils from the Vindyhan, reliably dated to around Ma|1200|million years old, have been classified as "Spriggina",cite journal |year = 2005 | doi = 10.1016/j.jseaes.2005.06.006 | title = Ediacara fossil assemblage in the upper Vindhyans of Central India and its significance | author = De, C | journal = Journal of Asian Earth Sciences | volume = 27 | pages = 660 ] but in all likelihood represent microbial artifacts.PalAss2007|title=Resolving the great Vindyhan controversy] "Spriggina" possessed a tough, though uncalcified, body, evident from the fossils' preservation: always as a mould in the lower surface of the fossiliferous bed.

Affinity

Like many of the Ediacara biota, the relationship of "Spriggina" to other groups is unclear. It bears some similarity to the living polychaete worm "Tomopteris",cite journal
author = Donovan, S.K.
coauthors = Lewis, D.N.
year = 2001
title = Fossils explained 35: The Ediacaran biota
journal = Geology Today
volume = 17
issue = 3
pages = 115–120
url = http://www.ingentaconnect.com/content/bsc/gday/2001/00000017/00000003/art00015
accessdate = 2008-06-18
doi = 10.1046/j.0266-6979.2001.00285.x] but its lack of chaetae, along with other lines of evidence, suggests that it cannot be placed in this phylum.cite journal
author = Merz
year = 2006
doi = 10.1093/icb/icj057
title = Polychaete chaetae: Function, fossils, and phylogeny
journal = Integrative and Comparative Biology
volume = 46
pages = 481] It was also compared to the rangeomorphs, frondose members of the Ediacara biota that may represent a separate kingdom.cite journal
author = Seilacher, A.
year = 1992
title = Vendobionta and Psammocorallia: lost constructions of Precambrian evolution
journal = Journal of the Geological Society, London
volume = 149
issue = 4
pages = 607–613
url = http://jgs.lyellcollection.org/cgi/content/abstract/149/4/607
doi = 10.1144/gsjgs.149.4.0607
accessdate = 2007-06-21
format = abstract] While its glide symmetry may suggest otherwise, "Spriggina" is currently considered to be an arthropod; its resemblance to the trilobites may suggest a close relationship to this class.cite journal|url=http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_62056.htm|title ="Spriggina" is a Trilobitoid Ecdysozoan] "Spriggina" may have been predatory, and played a role in initiating the Cambrian transition. [Citation
author = McMenamin, M. A. S.
year= 2003
chapter=Origin and early evolution of predators: The ecotone model and early evidence for macropredation
editors=P. Kelley, M. Kowalewski and T. Hansen
title=Predator-Prey Interactions in the Fossil Record]

History

The genus was named after Reg Sprigg who discovered the fossils of the Ediacara Hills—part of the Flinders Ranges in South Australia—and was a proponent of their recognition as multicellular organisms."Spriggina floundersi" is at present the only generally accepted species in this genus. "Spriggina ovata" has now been moved into its own genus, "Marywadea".citation
author = Glaessner, Martin F.
year = 1976
url = http://www.samuseum.sa.gov.au/Journals/TRSSA/TRSSA_v100/TRSSA_V100_p169p170.pdf
title = A new genus of late Precambrian polychaete worms from South Australia.
format = Free full text
journal = Transactions of the Royal Society of South Australia
volume = 100
issue = 3
pages = 169–170] "Spriggia wadea" is probably a junior synonym of "Aspidella" preserved under specific conditions.

References

External links

* [http://images.google.ca/images?hl=en&q=Spriggina&btnG=Google+Search&sa=N&tab=wi Google Image Search] : "Spriggina"