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In Brief December 2010/January 2011

Mats and flaps - Joe McCall unearths more hidden gems from the geological literature…

Geoscientist 20.12 December 2010/January 2011

Frozen mammoths


Joe McCallKevin Campbell of the University of Manitoba has studied the blood of the extinct mammoth, using bacteria reprogrammed with 43,000 year old mammoth DNA1. There were specific changes, adaptations from the blood of elephants, which allowed the mammoth to survive the most brutal Arctic ice-age winters. Mammoths originated in Africa and migrated through Western Europe and Siberia, across the Bering Strait to North America, then down towards South America 2. They originated 7.6-6.7 million years ago and migrated no earlier than two million years ago3. The last dwarf mammoths (two metres high instead of nearly three) died out – possibly as a result of human hunting) on Wrangel Island, Siberia only 3700 years ago2. The mammoth possessed two adaptations in its blood, to make sure haemoglobin could release oxygen at low temperatures. Reindeer and musk oxen have such special adaptations to the cold too, but they are different.

Mammoth remains are frequently dug up in the Upper Thames gravels which form four terraces close to my home in the Cotswolds. These deposits of ice-sheet outwash were deposited in tundra conditions. I am a little worried by the suggestion that other features of mammoths are similar adaptations to that of the blood 3. Claudine Cohen’s excellent book2 on mammoths seems to suggest that there exists general agreement with Depéret and Mayet (1923) 4, who argued that the conclusion (by Darwin and Gaudry) that ‘normal mammoths acquired fur by migrating to a colder climate’ is wrong. Depéret and Mayet concluded that hairless mammoths would have died from cold or quickly migrated southwards again. The Beresovka Mammoth, excavated north of Magadan in 19012, also possessed an anal flap, which would have prevented it from passing frozen faeces, presumably a rather painful process; and the same was found in a baby mammoth excavated in 1977 in the same region.

Did the mammoths of Africa have furry coats (many African mammals do still)? Was the furry coat an adaptation to the cold or were the original mammoths of Africa already fur-coated and therefore pre-adapted? The anal flap is an obvious advantage in the extreme cold, but was there enough time during the migration of mammoths through Western Europe (where it was certainly very cold at that time) to Siberia, for natural selection to operate? Natural selection would surely work on an occasional mutation that developed selective advantage in the changed conditions. The blood adaptation does not worry me, but I am unsure about both the fur and flaps. It seems to be too easy to refer all these features to adaptation when the mammoths migrated to the frozen north.

References

  1. http://www.msnbc.msn.com/id/36916619/ns/technology_and_science-science/ 
  2. Cohen. C. 2002. The fate of the mammoth: fossils, myth and history. University of Chicago Press, Chicago & London; 297 pp
  3. Wayman, E. 2010. Woolly mammoth’s blood uniquely suited to the arctic.Earth 55(8); 10.
  4. Depéret, C. and Mayet, L. 1923. Monograph des elephants Pliocènes d’Europe et de l’Afrique du Nord. Annales de l’université de Lyon (42); 91-224.

The first eukaryotes


Early lifeI have been looking into the question of the fossil evidence for eukaryote protists first appearing on Earth, after the initial period from ~3800Ma when the first protozoa (cyanobacteria) were the sole life forms and by photosynthesis gave rise to the oxygenic atmosphere. My search was related to an article that I am writing entitled ‘Are we alone? The evolution factor in the context of the exoplanet-proliferated universe’ which I intend to aim for the meeting of the Meteoritical Society in Greenwich in 2011. I concluded, on reading the literature, that:

“There is no agreement among scientists as to when exactly unicellular eukaryote protists, with organelles developed: 3200Ma, 2300Ma, 1200Ma and even 900Ma have been suggested: some unicellular protists occasionally developed multicellular forms, and multicellular life seems to have developed from them (the kingdoms of animals, plants and fungi): protists adopted both asexual and sexual reproduction, and the latter required the initiation of DNA etc., a complex mechanism with the double helix, but there seems to be no evidence as exactly at what time in the geological record this happened”.

Coincidentally there has now been a discovery in Franceville, SE Gabon, in rocks of the Francevillian Group, which are confidently dated at 2.1Ga. There is confirmation from a known 13C excursion, the Lomagundi excursion. The flattened dish-like fossils are found within a black shale unit, in a marine delta environment following a rapid burial event. Sulphate-reducing bacteria decomposed them to pyrite, leaving a durable mineralised impression1. About 250 fossils 10-120 mm long were recovered. Though they could be a bacterial mat, the authors of the article describing them, Albani et al.2, used high resolution X-ray tomographic scans to reveal complex internal 3-D structure. They say that they are not bacterial colonies – they do not know of any other colony in the Precambrian fossil bacteria. These organisms are almost certainly multicellular eukaryotes – i.e., possessing organelles and DNA. They are believed to have lived in the sea 20-30m down and breathed oxygen. If this identification is correct, and evidence of steranes, chemical biomarkers of eukaryotes, was obtained supporting this identification, they appeared long before the first filamentous algae (eukaryotes) at 1.6Ga. They post- dated the Great Oxidation event at 2.4Ga, so could readily obtain oxygen.

This discovery is obviously of critical significance. The fossil record prior to the Ediacara soft bodied fossils4 (Neoproterozoic, ~600Ma onwards, just into the Cambrian) is so patchy that any discovery of fossils in the earlier Proterozoic rocks is important.

References

  1. Rowan, C 2010. How do we know Gabon’s ‘multicellular’ fossils are 2.1 billion years old? http://all-geo.org/highlyallochthonous/2010/07/how-do-we-know-gabons-multicellula
  2. Albani, A, Bergstrom, S, Canfield, D et al. 2010. Large colonial organisms with co-ordinated growth in oxygenated environments 2.1 ?ã Gyr ago. Nature 466(7302), 100-104.
  3. Complex organisms 2.1 billion years. http://www.scienceknowledge.org/2010/08/12/complex-organisms-2-1-billion-years/
  4. McCalll, G J H 2006. The Vendian (Ediacaran) in the geological record: Enigmas in geology’s prelude to the Cambrian explosion. Earth Science Reviews 77, 1-229.