Charnia

Charnia
Temporal range: Ediacaran, 579–555 Ma
A cast of the holotype of Charnia masoni. Metric scale.
Scientific classification
Phylum: Petalonamae
Genus: Charnia Ford, 1958
Species: C. masoni Ford, 1958
Synonyms
  • Glassnerina Germs, 1973
  • Rangea grandis Glaessner et Wade, 1966 = Glaessnerina grandis
  • Rangea sibirica Sokolov, 1972 = Glaessnerina sibirica

Charnia is a genus of frond-like Ediacaran lifeforms with segmented, leaf-like ridges branching alternately to the right and left from a zig-zag medial suture (thus exhibiting glide reflection, or opposite isometry). The genus Charnia was named after Charnwood Forest in Leicestershire, England, where the first fossilised specimen was found. It is a highly significant fossil.

The living organism was a type of life form that grew on the sea floor and is believed to have fed on nutrients in the water. Despite Charnia's fern-like appearance, it is not a plant or alga because the nature of the fossilbeds where specimens have been found demonstrate that it originally lived in deep water, well below the photic zone where photosynthesis can occur.

Diversity

Several Charnia species were described but only the type species C. masoni is considered valid. Some specimens of C. masoni were described as members of genus Rangea or a separate genus Glaessnerina:

Two other described Charnia species have been transferred to two separate genera

A number of Ediacaran form taxa are thought to represent Charnia (or Charniodiscus) at varying levels of decay; these include the Ivesheadiomorphs Ivesheadia, Blackbrookia, Pseudovendia and Shepshedia.[8]

Distribution

Charnia masoni was first described from Charnwood Forest in England and subsequently was found in Ediacara Hills in Australia,[1][9] Siberia and White Sea area in Russia[10][11] and Precambrian deposits in Newfoundland, Canada.

Discovery

Charnia masoni index fossil, New Walk Museum, Leicester

Charnia masoni[12] was brought to the attention of scientists by Roger Mason, a schoolboy who later became a professor of metamorphic petrology. In 1957 Mason and his friends were rock-climbing in Charnwood Forest, in what is now a protected fossil site in Central England. They noticed this unusual fossil, and Mason took a rubbing of the rock. He showed the rubbing to his father, the minister of Leicester's Great Meeting Unitarian Chapel, who also taught at the local university and knew Trevor Ford, a local geologist. Mason took Ford to the site; Ford wrote up the discovery in the Journal of the Yorkshire Geological Society.[13]

The holotype (the actual physical example from which the species was first described) now resides, along with a cast of its sister taxon Charniodiscus, in New Walk Museum & Art Gallery, Leicester. Decades later it came to light that Tina Negus, then a 15-year-old schoolgirl, had seen this fossil a year before the boys[14] but her geography schoolteacher discounted the possibility of Precambrian fossils.[15] Mason acknowledges, and the museum's Charnia display explains, that the fossil had been discovered a year earlier by Negus, "but no one took her seriously".[16][17] She was recognised at the 50th anniversary celebrations of the official discovery.

Significance

Reconstruction of Charnia masoni at MUSE - Science Museum in Trento

Charnia is a highly significant fossil for several reasons. Firstly, it is the first fossil that was ever described that came from undoubted Precambrian rocks. Until this point the Precambrian was thought to be completely devoid of fossils and consequently possibly of macroscopic life. Despite similar fossils being unearthed in the 1930s (in Namibia) and the 1940s (in Australia) these forms were assumed to be of Cambrian age and so were considered unremarkable at the time. Secondly, Charnia has become an enduring image of Precambrian animals. Originally interpreted as an alga (Ford), it was spectacularly recast as a sea pen (a sister group to the modern soft corals) from 1966 onwards (Glaessner). With this image of Precambrian sea pens in mind, the gates were open for the recognition of many other of the major animal groups in the Precambrian. However, this sea pen interpretation has recently been discredited,[18] [19] and the current "state of the art" is something of a "statement of ignorance".[20]

An increasingly popular theory has arisen since the mid-1980s, following the work of Adolf Seilacher who suggested that Charnia belongs to an extinct group of unknown grade that was confined to the Ediacaran Period. This theory suggests that almost all the forms that have been postulated to be members of many and various modern animal groups are actually more closely related to each other than anything else. This new group was termed the Vendobionta,[21] a clade whose position in the tree of life is unclear, perhaps united by its construction via unipolar iterations of one cell family.

The holotype is a star attraction at the New Walk Museum. A day-long seminar in 2007 devoted to Charnia called it "Leicester's fossil celebrity".[22]

Ecology

Little is known about the ecology of Charnia. It was benthic and sessile, anchored to the sea floor. According to one currently popular hypothesis, it probably lived in deep waters, well below the wave base, thus placing it out of range of photosynthesis. Furthermore, it has no obvious feeding apparatus (mouth, gut, etc.) so its lifestyle remains enigmatic. Some have speculated that it survived either by filter feeding or directly absorbing nutrients, and this is currently the focus of considerable research.[23]

The growth and development of the Ediacara biota is also a subject of continued research, and this has discredited the sea pen hypothesis. In contrast to sea pens, which grow by basal insertion, Charnia grew by the apical insertion of new buds.[20]

See also

References

  1. 1 2 Glaessner, M.F.; Wade, M. (1966). "The late Precambrian fossils from Ediacara, South Australia" (PDF). Palaeontology. 9 (4): 599.
  2. ↑ Germs, G. J. B. (1973). "A reinterpretation of Rangea schneiderhoehni and the discovery of a related new fossil from the Nama Group, South West Africa". Lethaia. 6 (1): 1–10. doi:10.1111/j.1502-3931.1973.tb00870.x.
  3. ↑ Narbonne, G.M.; Gehling, J.G. (2003). "Life after Snowball: the oldest complex Ediacaran fossils" (PDF). Geology. 31: 27–30. Bibcode:2003Geo....31...27N. doi:10.1130/0091-7613(2003)031<0027:LASTOC>2.0.CO;2. Archived from the original (PDF) on 2004-10-31.
  4. ↑ Narbonne, G.M.; Laflamme, M.; Greentree, C.; Trusler, P. (2009). "Reconstructing a lost world: Ediacaran rangeomorphs from Spaniard’s Bay, Newfoundland". Journal of Paleontology. 83 (4): 503–523. doi:10.1666/08-072R1.1.
  5. ↑ M. Laflamme; G. M. Narbonne; C. Greentree; M. M. Anderson (2007). "Morphology and taphonomy of an Ediacaran frond: Charnia from the Avalon Peninsula of Newfoundland". Geological Society, London, Special Publications. 286 (1): 237–257. Bibcode:2007GSLSP.286..237L. doi:10.1144/SP286.17.
  6. ↑ Hofmann, H. J.; O'Brien, S. J.; King, A. F. (2008). "Ediacaran Biota on Bonavista Peninsula, Newfoundland, Canada". Journal of Paleontology. 82 (1): 1–36. doi:10.1666/06-087.1.
  7. ↑ Brasier, M.D.; Antcliffe, J.B.; Liu, A.G. (2012). "The architecture of Ediacaran Fronds". Palaeontology. 55 (5): 503–523. doi:10.1111/j.1475-4983.2012.01164.x.
  8. ↑ Liu, A. G.; McIlroy, D.; Antcliffe, J. B.; Brasier, M. D. (2010). "Effaced preservation in the Ediacara biota and its implications for the early macrofossil record". Palaeontology. 54 (3): 607–630. doi:10.1111/j.1475-4983.2010.01024.x.
  9. ↑ Nedin C.; Jenkins R.J.F. (1998). "First occurrence of the Ediacaran fossil Charnia from the southern hemisphere". Alcheringa. 22 (3/4): 315–316. doi:10.1080/03115519808619329.
  10. ↑ Grazhdankin, Dima (2004). "Patterns of distribution in the Ediacaran biotas: facies versus biogeography and evolution" (PDF). Palæobiology. 30 (2): 203–221,. doi:10.1666/0094-8373(2004)030<0203:PODITE>2.0.CO;2.
  11. ↑ Grazhdankin, D. V.; Balthasar, U.; Nagovitsin, K. E.; Kochnev, B. B. (2008). "Carbonate-hosted Avalon-type fossils in arctic Siberia". Geology. 36 (10): 803–806. Bibcode:2008Geo....36..803G. doi:10.1130/G24946A.1.
  12. ↑ Ford, T.D. (1958). "Precambrian fossils from Charnwood Forest". Yorkshire Geological Society Proceedings. 31 (3): 211–217. doi:10.1144/pygs.31.3.211.
  13. ↑ Mason, Roger. "The discovery of Charnia masoni" (PDF). University of Leicester. Retrieved 5 April 2016.
  14. ↑ Ford, Trevor. "The discovery of Charnia".
  15. ↑ Negus, Tina. "An account of the discovery of Charnia".
  16. ↑ Mason, Roger. "The discovery of Charnia masoni" (PDF). University of Leicester. Retrieved 5 April 2016.
  17. ↑ "In April 1957, I went rock-climbing in Charnwood Forest with two friends, Richard Allen and Richard Blachford (‘Blach’), fellow students at Wyggeston Grammar School, Leicester. I was already interested in geology and knew that the rocks of the Charnian Supergroup were Precambrian although I had not heard of the Australian fossils. Richard Allen and I agree that Blach (who died in the early 1960s) drew my attention to the leaf-like fossil holotype now on display in Leicester City Museum. I took a rubbing and showed it to my father, who was Minister of the Great Meeting Unitarian Chapel in East Bond Street, taught part-time at University College (soon to be Leicester University) and thus knew Trevor Ford. We took Trevor to visit the fossil site and convinced him that it was a genuine fossil. His publication of the discovery in the Journal of the Yorkshire Geological Society established the genus Charnia and aroused worldwide interest. ... I was able to report the discovery because of my father’s encouragement and the enquiring approach fostered by my science teachers. Tina Negus saw the frond before I did but no one took her seriously."
  18. ↑ Antcliffe, J.B.; Brasier, M.D. (2007). "Charnia and sea pens are poles apart". Journal of Geological Society. 164 (1): 49. doi:10.1144/0016-76492006-080.
  19. ↑ Gary C. Williams. "Aspects of the Evolutionary Biology of Pennatulacean Octocorals".
  20. 1 2 Antcliffe, J.B.; Brasier, M.D. (2008). "Charnia at 50: Developmental Models for Ediacaran Fronds". Palaeontology. 51 (1): 11–26. doi:10.1111/j.1475-4983.2007.00738.x.
  21. ↑ SEILACHER, A. 1984. Late Precambrian and Early Cambrian Metazoa: preservational or real extinctions? 159–168. In HOLLAND, H. D., TRENDAL, A. F. and BERNHARD, S. (eds). Patterns of change in Earth evolution. Springer Verlag, New York, NY, 450 pp.
  22. ↑ "Leicester’s fossil celebrity: Charnia and the evolution of early life" (PDF). University of Leicester. Retrieved 5 April 2016.
  23. ↑ Narbonne

For pictures of Charnia, see:

An article on the discovery of Charnia masoni:

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