Spriggina

Spriggina is a genus of early bilaterian animals whose relationship to living animals is unclear. Fossils of Spriggina are known from the late Ediacaran period in what is now South Australia. Spriggina floundersi is the official fossil emblem of South Australia.[2] It has been found nowhere else. The organism reached about 3–5 centimetres (1.2–2.0 in) in length and may have been predatory. Its bottom was covered with two rows of tough interlocking plates, while one row covered its top; its front few segments fused to form a "head".

Spriggina
Temporal range: Late Ediacaran, 555 Ma
↓
Fossil of S. floundersi. Scale in millimetres.
Scientific classification
Kingdom: Animalia
Phylum: †Proarticulata
Genus: †Spriggina
Glaessner, 1958[1]
Species:
†S. floundersi
Binomial name
†Spriggina floundersi
Glaessner, 1958

Spriggina's affinity is currently unknown; it has been variously classified as an annelid worm, a rangeomorph-like frond, a variant of Charniodiscus, a proarticulatan, or an arthropod perhaps related to the trilobites, or even an extinct phylum. Lack of known segmented legs or limbs, and glide reflection instead of symmetric segments, suggest an arthropod classification is unlikely despite some superficial resemblance.[3]

Description
S. floundersi, life restoration at MUSE - Science Museum in Trento
Cast of S. floundersi at Houston Museum of Natural Science

Spriggina grew to 3–5 centimetres (1.2–2.0 in) in length, and was approximately oblong. The organism was segmented, with no fused segments, with the segments sometimes being curved.[4] The upper surface of the organism was covered by one row of overlapping cuticular plates; the underside, paired plates.[4]

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.[4] The second segment may have borne antennae. Subsequent segments bore annulations.[4]

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.[4] Legs are not preserved.

The symmetry observed is not exactly bilaterian,[4] but appears to be a glide reflection, where opposite segments are shifted by half an interval.[3] 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 extremes.

Discovery and naming

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.[1] Spriggina floundersi is at present the only generally accepted species in this genus. The specific name "floundersi" refers to amateur South Australian fossil hunter Ben Flounders.[5] Spriggina ovata has now been moved into its own genus, Marywadea.[6]

Spriggina is known only from beds of Ediacaran age. Fossils from the Vindhyan, reliably dated to around 1,200 million years old,[7] have been classified as Spriggina,[8] but in all likelihood represent microbial artifacts.[7]

Spriggina possessed a tough, though uncalcified body, evident from the fossils' preservation: always as a mould in the lower surface of the fossiliferous bed.

Classification
Digitally enhanced image of a Spriggina fossil

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 and Amphinomidae,[9] but its lack of chaetae, along with other lines of evidence, suggests that it cannot be placed in this phylum.[10] It was also compared to the rangeomorphs,[11] frondose members of the Ediacara biota that may represent a separate kingdom.[12] While its glide symmetry may suggest otherwise, Spriggina is considered by some other researchers to be an arthropod; its superficial resemblance to the trilobites may suggest a close relationship to this class.[11] This similarity to trilobites could also be an example of convergent evolution.[13] Spriggina may have been predatory, and may have played a role in initiating the Cambrian transition.[14]

See also

References
  1. Glaessner, Martin F. (1958). "New Fossils from the Base of the Cambrian in South Australia" (PDF). Transactions of the Royal Society of South Australia. 81: 185–188. BHL page 41001421. Archived from the original (PDF) on 29 September 2007.
  2. "FOSSIL EMBLEM OF THE STATE OF SOUTH AUSTRALIA" (PDF). The South Australian Government Gazette. Adelaide: Department of the Premier and Cabinet. 2017 (8): 509. 16 February 2017. Retrieved 6 July 2017.
  3. Ivantsov A.Yu. (2001). "Vendian and Other Precambrian "Arthropods"". Paleontological Journal. 35: 335–343.
  4. McCall (2006). "The Vendian (Ediacaran) in the geological record: Enigmas in geology's prelude to the Cambrian explosion". Earth-Science Reviews. 77 (1–3): 1–229. doi:10.1016/j.earscirev.2005.08.004.
  5. Vickers-Rich, P. Komarower, P. The Rise and Fall of the Ediacaran Biota. The Geological Society, 2007, p. 444.
  6. Glaessner, Martin F. (1976). "A new genus of late Precambrian polychaete worms from South Australia" (PDF). Transactions of the Royal Society of South Australia. 100 (3): 169–170. Archived from the original (Free full text) on 2007-09-29.
  7. Budd, G. E.; Streng, M.; Daley, A. C.; Willman, S., eds. (2007). "Resolving the great Vindhyan controversy" (PDF). Programme with Abstracts. Palaeontological Association Annual Meeting. 51. Uppsala, Sweden.
  8. De, C (2005). "Ediacara fossil assemblage in the upper Vindhyans of Central India and its significance". Journal of Asian Earth Sciences. 27 (5): 660–683. doi:10.1016/j.jseaes.2005.06.006.
  9. Donovan, S. K.; Lewis, D. N. (2001). "Fossils explained 35: The Ediacaran biota". Geology Today. 17 (3): 115–120. doi:10.1046/j.0266-6979.2001.00285.x.
  10. Merz (2006). "Polychaete chaetae: Function, fossils, and phylogeny". Integrative and Comparative Biology. 46 (4): 481–96. doi:10.1093/icb/icj057. PMID 21672760.
  11. "Spriggina is a Trilobitoid Ecdysozoan". Cite journal requires |journal= (help)
  12. Seilacher, A. (1992). "Vendobionta and Psammocorallia: lost constructions of Precambrian evolution". Journal of the Geological Society. 149 (4): 607–613. doi:10.1144/gsjgs.149.4.0607. Retrieved 2007-06-21.
  13. "The fossil record and the early evolution of the Metazoa" (PDF). Archived from the original (PDF) on 2016-08-04. Retrieved 2016-10-11. Cite journal requires |journal= (help)
  14. McMenamin, M. A. S. (2003). "Origin and early evolution of predators: The ecotone model and early evidence for macropredation". In P. Kelley; M. Kowalewski; T. Hansen (eds.). Predator-Prey Interactions in the Fossil Record.
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