Dickinsonia

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A fossil specimen of Dickinsonia costata

Artist's reconstruction of D. costata. Note that the colour is more likely to match the mud.

Dickinsonia is an ancient ovoid fossil with somewhat radial tubes from a (sometimes missing) central ridge. The ends are different, with close spaced tubes on one end and larger, more widely spaced tubes on the other. However, it is unclear whether there is an actual head and tail.

Dickinsonia somewhat resembles the Polychaete worm Spinther. It is thought by some possibly to be an annelid worm. It has also been described as a jellyfish, coral, sea anemone, and a lichen^[1]. Four species are known; Dickinsonia costata, Dickinsonia lissa, Dickinsonia tenuis, and Dickinsonia rex, the last of which can be as large as 43 cm.

The segments of Dickinsonia have been described as chambers filled with a liquid at higher than ambient pressure, analogous to a quilted air mattress. Features in a few specimens have been interpreted as evidence of logitudal muscle fibers, and a medial gut. Brian Morton argues that Dickonsonia is close to the ancestry of the chordates.^[2]

Dickinsonia is known from Ediacaran beds in both the Alice Springs and Ediacara regions of Australia, as well as Rajastan, Podolia, and the White Sea region of Russia. Dickinsonia is generally regarded as a member of the Vendazoa — a group of somewhat obscure organisms that thrived just before most of the modern multicellular animal phyla appeared. It is unclear if the Vendazoa are plants, animals, or something else entirely. Other vendazoa such as Yorgia and Marywadea somewhat resemble Dickinsonia and may be related. However its roughly bilateral symmetry suggests that it may be a Bilaterian ancestor.

Dickinsonia was originally discovered by Reg Sprigg along with other Ediacaran biota.^[3] It was named after Ben Dickinson who was then the South Australian director of Mines, for whom Sprigg worked.

Australia Post issued a 50 cent stamp featuring Dickinsonia on 21 April 2005 in a series entitled Creatures of the slime.

[edit] References

^ Retallack, Gregory J. (2004) "Death, Decay and Destruction of Dickinsonia". Geological Society of America Abstracts with Programs, Vol. 36, No. 5, p. 521 [1]
^ Dzik, Jerzy. (2000) "The Origin of the Mineral Skeleton in Chordates." in Max Knobler Hecht, Ross J. MacIntyre and Michael T. Clegg, eds. Evolutionary Biology Vol. 31. Pp. 105-46. Springer. ISBN 0306461781 [2] - URL retrieved February 10, 2007
^ Sprigg, R.C. (1947) "Early Cambrian (?) Jellyfishes from the Flinders Ranges, South Australia. Trans. Roy. Soc. S. Aust. 71: 212-224. [3]