Eoandromeda

from Wikipedia, the free encyclopedia
Eoandromeda
Reconstruction of Eoandromeda

Reconstruction of Eoandromeda

Temporal occurrence
Ediacarium
560 to 551 million years
Locations
Systematics
Multicellular animals (Metazoa)
Eoandromeda
Scientific name
Eoandromeda
Tang , Yin , Bengtson , Liu , Wang and Gao , 2008
species
  • Eoandromeda octobrachiata

Eoandromeda is an extinct animal genus of the Ediacarium of uncertain taxonomic classification, which is characterized by eight spiral-shaped arms.

etymology

The generic name Eoandromeda is a combination of the Greek  Ἠώς or Ἕως (Éōs) 'Dawn', 'early' and the spiral galaxy Andromeda ( Ἀνδρομέδα ) in allusion to the spiral arms of the fossil. The species name octobrachiata ('eight armed') is the Latinized composition of οκτώ (októ) 'eight' and the Latin brachium - in turn derived from βραχίων 'arm'.

Occurrence

The approximately two dozen occurrences of Eoandromeda are found in Australia and the People's Republic of China . The fossilization in the Ediacara member of the Rawnsley quartzite in Australia follows the standard preservation of the Ediacara type , whereas the much more numerous fossils from the black schists of the Chinese Doushantuo Formation exist as carbonatic prints.

description

Eoandromeda octobrachiata is a circular fossil, the diameter of which can vary between 10 and 44 millimeters. Eight spiral arms extend from the center and only touch each other at their ends. The arms, which become thinner towards the end, can be segmented by ribs or furrows. Their sense of rotation can be directed either clockwise or counterclockwise. The arms of the Australian fossils are longer and more curved than those of the Chinese finds. In addition, the Australian examples are generally smaller and look kinked.

Socialization

Eoandromeda can be found in association with the following taxa:

Taxonomic position

Eoandromeda was originally interpreted as a trace fossil with similarities to Zoophycus or Spirorhaphe or as a huge, agglutinating foraminifera ( Xenophyophore ).

Since the Chinese finds received organic matter, these interpretations are invalid - the Burgess schist conservation of these fossils requires a very robust, organic starting material. The circular spiral shape suggests a relationship to fossil embryos , as they are known from the Doushantuo formation, as possible, but as long as there are no intermediate shapes, this assumption cannot be judged.

Eoandromeda has only a very superficial resemblance to echinoderms (Echinodermata), rib jellyfish (Ctenophora), cnidarians (Cnidaria) and other members of the Ediacara biota such as the triradial Tribrachidium , the tetraradial Conomedusites and the pentaradial Arkarua . This suggests that a large number of diploblastic animals had split off before triploblastic organisms appeared .

However, there is a lack of sufficient physical characteristics that would allow identification as a definite animal organism. It cannot be ruled out that Eoandromeda may also be an alga ; Algae make up the majority of the taxa present among the Doushantuo biota. Overall, however, the fossil appears to be a bit too complex for one type of algae.

Taphonomic meaning

During the Ediacarium ( Vendium ) there were two different types of multicellular cells . In contrast to previous views, the opinion is now held that these two biota are clearly different from each other:

  • Ediacara type:

The Ediacara type is composed of the Ediacara, Nama and Avalon faunal communities. It consists of Metazoa and organisms of problematic classification. Examples are Dickinsonia , Yorgia , Kimberella , Charnia , Charniodiscus , Cyclomedusa , Ediacaria , Parvancorina , Pteridinium , Rangea , Fractofusus , Tribrachidium , Hiemalora , Palaeopascichnus and others. These taxa exist as positive and negative prints on the underside of sandstone banks. The structures of the “elephant skin” and tubercles characteristic of microbe mats characterize the Ediacarara preservation, sand prints in sandstone layers mark the Nama preservation. In the Avalon Conservation, the imprints are on layers of mudstone covered by layers of ash. Finally, in the Khatyspyt conservation, the fossils are found in fine to medium-layered, bituminous tuber limestone .

  • Miaohe type:

The Miaohe type is characterized by the following algae macro fossils : Beltanelloides , Mezenia , Sinospongia , Jiuqunaoella , Grypania , Liulingjitaenia , Tawuia , Calyptrina , Cucullus and others. These fossils are formed as flat biofilms that emerged from the original organic tissue and resemble the Burgess schist conservation.

It is very problematic to compare organisms with one another that have been fossilized in two very different modes of preservation and thus transmit very different body parts. Fossil footprints reflect the outline of the body, whereas carbonaceous biofilms record the residues of organic body tissue. This is why it is so difficult to compare the two taphonomies .

Eoanadromeda is one of the few taxa in which both taphonomies are comparable. Other taxa for which this is possible are Anfesta and albumares- like fossils from the Doushantuo Formation, the taxon Beltanelloides sorichevae , which occurs in the Lyamtsa Formation off the White Sea coast in northern Russia and also in the Doushantuo Formation, and possibly also Cyclomedusa davidi from the Perevalok Formation in the central Urals .

Individual evidence

  1. a b c d e Maoyan Zhu, James G. Gehling, Shuhai Xiao, Yuanlong Zhao and Mary L. Droser: Eight-armed Ediacara fossil preserved in contrasting taphonomic windows from China and Australia . In: Geology . tape 36 (11) , 2008, pp. 867-870 , doi : 10.1130 / G25203A.1 .
  2. Ding, L. et al .: Sinian Miaohe biota . Geological Publishing House, Beijing 1996, p. 135 .
  3. Seilacher, A .: The nature of vendobionts . In: Vickers-Rich, P. and Komarower, P., The rise and fall of the Ediacaran Biota (Eds.): Geological Society of London Special Publication . tape 286 , 2007, p. 387-397 .
  4. Tang, F. et al.: Octoradiate spiral organisms in the Ediacaran of South China . In: Acta Geologica Sinica . tape 82 , 2008, p. 27-34 . doi : 10.1111 / j.1755-6724.2008.tb00321.x
  5. a b Xiao, S .; Yuan, X .; Steiner, M. and Knoll, AH: Macroscopic carbonaceous compressions in a terminal Proterozoic shale: A systematic reassessment of the Miaohe biota: South China . In: Journal of Paleontology . tape 76 (2) , 2007, pp. 347-376 , doi : 10.1666 / 0022-3360 (2002) 076 <0347: MCCIAT> 2.0.CO; 2 .
  6. a b D. V. Grazhdankin; KE Nagovitsin and AV Maslov: Late Vendian Miaohe-type Ecological Assemblage of the East European Platform . In: Doklady Earth Sciences . tape 417 (8) , 2007, pp. 1183-1187 , doi : 10.1134 / S1028334X07080107 .
  7. ^ MV Leonov: Comparative taphonomy of Vendian genera Beltanelloides and Nemiana: taxonomy and lifestyle . In: Geological Society, London, Special Publications . tape 286 (1) , 2007, pp. 259-267 , doi : 10.1144 / SP286.18 .