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.
| Spriggina Temporal range: Late Ediacaran, | |
|---|---|
 | |
| Fossil of S. floundersi. Scale in millimetres | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | †Proarticulata |
| Class: | †Cephalozoa |
| Family: | †Sprigginidae |
| Genus: | †Spriggina Glaessner, 1958[1] |
| Species: | †S. floundersi |
| Binomial name | |
| †Spriggina floundersi Glaessner, 1958 | |
The organism reached 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."
The affinity of Spriggina is unknown; it has been variously classified as an annelid worm, a rangeomorph-like frond, a variant of Charniodiscus, a proarticulatan, an arthropod (perhaps related to the trilobites), or even an extinct phylum. The lack of known segmented legs or limbs, coupled with the presence of glide reflection instead of symmetric segments, suggests that an arthropod classification is unlikely despite some superficial resemblance.[3]
The genus Spriggina originally contained three different species—S. floundersi, S. ovata, and S. borealis—but S. ovata is now considered a junior synonym of Marywadea ovata,[4][5] while the phylogenetic status of S. borealis remains a subject of debate.[5]
Description
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; the segments were sometimes curved.[6] The upper surface of the organism was covered by one row of overlapping cuticular plates, the underside with paired plates.[6]
The first two segments formed a "head". The front segment had the shape of a horseshoe with a pair of depressions on its upper surface; these may have represented eyes.[6] The second segment may have borne antennae. Subsequent segments bore annulations.[6]
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.[6] Legs are not preserved.
The symmetry observed is not exactly bilaterian[6] 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.[7] Spriggina ovata has now been moved into its own genus, Marywadea.[8]
Spriggina is known only from beds of Ediacaran age. Fossils from the Vindhyan basin, reliably dated to around 1,650 million years old,[9] have been classified as Spriggina,[10] but in all likelihood represent microbial artifacts.[9]
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
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,[11] but its lack of chaetae, along with other lines of evidence, suggests that it cannot be placed in this phylum.[12] It was also compared to the rangeomorphs,[13] frondose members of the Ediacara biota that may represent a separate kingdom.[14] 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.[13] This similarity to trilobites could also be an example of convergent evolution.[15] Spriggina may have been predatory, and may have played a role in initiating the Cambrian transition.[16]
See also
References
- 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.
- "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.
- Ivantsov A.Yu. (2001). "Vendian and Other Precambrian "Arthropods"". Paleontological Journal. 35: 335–343.
- Glaessner, Martin F. & Wade, Mary (1966). "The Late Precambrian Fossils from Ediacara, South Australia" (PDF). Palaeontology. 9 (4): 599–628. Archived from the original (PDF) on 22 September 2013.
- Fedonkin, Mikhail A.; Gehling, James G.; Grey, Kathleen; Narbonne, Guy M.; Vickers-Rich, Patricia (2007). The Rise of Animals: Evolution and Diversification of the Kingdom Animalia. ISBN 9780801886799.
- 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. Bibcode:2006ESRv...77....1M. doi:10.1016/j.earscirev.2005.08.004.
- Vickers-Rich, P. Komarower, P. The Rise and Fall of the Ediacaran Biota. The Geological Society, 2007, p. 444.
- 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 29 September 2007.
- Bengtson, Stefan; Belivanova, Veneta; Rasmussen, Birger; Whitehouse, Martin (2009). "The controversial "Cambrian" fossils of the Vindhyan are real but more than a billion years older". Proceedings of the National Academy of Sciences. 106 (19): 7729–7734. Bibcode:2009PNAS..106.7729B. doi:10.1073/pnas.0812460106. PMC 2683128. PMID 19416859.
- 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.
- 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. S2CID 128395097.
- Merz (2006). "Polychaete chaetae: Function, fossils, and phylogeny". Integrative and Comparative Biology. 46 (4): 481–96. doi:10.1093/icb/icj057. PMID 21672760.
- "Spriggina is a Trilobitoid Ecdysozoan". Geological Society of America. Archived from the original on 4 July 2017.
- Seilacher, A. (1992). "Vendobionta and Psammocorallia: lost constructions of Precambrian evolution". Journal of the Geological Society. 149 (4): 607–613. Bibcode:1992JGSoc.149..607S. doi:10.1144/gsjgs.149.4.0607. S2CID 128681462. Retrieved 21 June 2007.
- Morris, S. Conway (1993). "The fossil record and the early evolution of the Metazoa" (PDF). Nature. 361 (6409): 219. Bibcode:1993Natur.361..219M. doi:10.1038/361219a0. S2CID 86276440. Archived from the original (PDF) on 4 August 2016. Retrieved 11 October 2016.
- 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.
External links
- Google Image Search: Spriggina