Spriggina
| Spriggina Temporal range: Ediacaran, around 555 Ma |
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| Fossil of S. floundersi. Scale in millimetres. | |
| Scientific classification | |
| Kingdom: | Animalia |
| (unranked): | Bilateria |
| Phylum: | ?Proarticulata |
| Family: | Sprigginidae |
| Genus: | Spriggina Glaessner, 1958[1] |
| Species: | S. floundersi |
| Binomial name | |
| Spriggina floundersi Glaessner, 1958 |
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Fossils of Spriggina are known from the Ediacaran period, around 550 million years ago. 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, Proarticulata, and an arthropod, perhaps related to the trilobites. Lack of known segmented legs or limbs may make an arthropod classification premature.
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[edit] 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.[2] The upper surface of the organism was covered by one row of overlapping cuticular plates; the underside, paired plates.[2]
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.[2] The second segment may have borne antennae. Subsequent segments bore annulations.[2]
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.[2] Legs are not preserved.
The symmetry observed is not exactly bilaterian,[2] 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 end members.
[edit] Fossil occurrences
Spriggina is known only from beds of Ediacaran age. Fossils from the Vindyhan, reliably dated to around 1,200 million years old,[4] have been classified as Spriggina,[5] but in all likelihood represent microbial artifacts.[4] Spriggina possessed a tough, though uncalcified, body, evident from the fossils' preservation: always as a mould in the lower surface of the fossiliferous bed.
[edit] 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,[6] but its lack of chaetae, along with other lines of evidence, suggests that it cannot be placed in this phylum.[7] It was also compared to the rangeomorphs,[8] frondose members of the Ediacara biota that may represent a separate kingdom.[9] 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.[8] Spriggina may have been predatory, and played a role in initiating the Cambrian transition.[10]
[edit] 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.[1] Spriggina floundersi is at present the only generally accepted species in this genus. Spriggina ovata has now been moved into its own genus, Marywadea.[11] Spriggia wadea is probably a junior synonym of Aspidella preserved under specific conditions.
[edit] See also
[edit] References
- ^ a b 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. http://www.samuseum.sa.gov.au/Journals/TRSSA/TRSSA_V081/TRSSA_V081_p185p188.pdf
- ^ a b c d e f McCall (2006). "The Vendian (Ediacaran) in the geological record: Enigmas in geology's prelude to the Cambrian explosion". Earth-Science Reviews 77: 1. doi:10.1016/j.earscirev.2005.08.004.
- ^ Ivantsov, A.Y. (2001). "Vendia and other Precambrian "arthropods"". Paleontological Journal 35: 335–343.
- ^ a b {{{author}}} (2007). "Resolving the great Vindyhan controversy". In Budd, G.E.; Streng, M.; Daley, A.C.; Willman, S.. Programme with Abstracts. 51. Palaeontological Association Annual Meeting. Uppsala, Sweden. http://downloads.palass.org/annual_meeting/2007/palass2007_programme_abstracts.pdf.
- ^ De, C (2005). "Ediacara fossil assemblage in the upper Vindhyans of Central India and its significance". Journal of Asian Earth Sciences 27 (5): 660. 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. http://www.ingentaconnect.com/content/bsc/gday/2001/00000017/00000003/art00015. Retrieved 2008-06-18.
- ^ Merz (2006). "Polychaete chaetae: Function, fossils, and phylogeny". Integrative and Comparative Biology 46 (4): 481. doi:10.1093/icb/icj057.
- ^ a b Spriggina is a Trilobitoid Ecdysozoan. http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_62056.htm.
- ^ 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. http://jgs.lyellcollection.org/cgi/content/abstract/149/4/607. Retrieved 2007-06-21.
- ^ McMenamin, M. A. S. (2003). "Origin and early evolution of predators: The ecotone model and early evidence for macropredation". In P. Kelley, M. Kowalewski and T. Hansen. Predator-Prey Interactions in the Fossil Record
- ^ Glaessner, Martin F. (1976). "A new genus of late Precambrian polychaete worms from South Australia." (Free full text). Transactions of the Royal Society of South Australia 100 (3): 169–170. http://www.samuseum.sa.gov.au/Journals/TRSSA/TRSSA_v100/TRSSA_V100_p169p170.pdf
[edit] External links
- Google Image Search: Spriggina
