Monday, 17 October 2016

Evidence for Lichen on the bones of Homo naledi contested.

Homo naledi, a new species of Hominin was described in 2013 from a series of complete skeletons found in the Dinaledi (Rising Star) Chamber at the Maropeng Cradle of Humankind World Heritage Site. The presence of a large number of articulated skeletons in a deep subsurface chamber was considered indicative of organized burial practices by the species, which was surprising as anatomically Homo naledi was considered close to the earliest members of the genus Homo or even later members of the genus Australopithicus, species thought unlikely to have had advanced burial customs. Earlier this year (2016) Francis Thackeray of the Evolutionary Studies Institute at the University of the Witwatersrand published a paper in the South African Journal of Science in which he contended that a mottled pattern of manganese dioxide seen on the surface of the bones could be the product of the action of photosynthetic Lichens, and therefore possibly indicate that the cave had been exposed at to the surface at the time when the bones were laid down.

In a second paper published in the South African Journal of Science on 28 September 2016, Patrick Randolph-Quinney of the School of Forensicand Applied Sciences at the University of Central Lancashire, and the Evolutionary Studies Institute and School of Anatomical Sciences at the University of the Witwatersrand, Lucinda Backwell and Lee Berger, also of the Evolutionary Studies Institute at the University of the Witwatersrand, John Hawks again of the Evolutionary Studies Institute at the University of the Witwatersrand and of the Department of Anthropology at the University of Wisconsin-Madison, Paul Dirks and Eric Roberts, also of the Evolutionary Studies Institute at the University of the Witwatersrand and of the Department of Geoscience at James Cook University, Godwin Nhauro once again of the Evolutionary Studies Institute at the University of the Witwatersrand and Jan Kramers of the Department of Geology at the University of Johannesburg, refute Thakeray's Lichen theory, and instead put forward an alternative explanation for the mottling on the bones of Homo naledi.

 Patterns of mineral staining affecting tibia U.W. 101-996. Note the distribution of manganese (black) and iron (yellow-red) oxides around the circumference of the shaft. Randolph-Quinney et al. (2016).

Randolph-Quinney et al. do not dispute that Lichens grow in the vicinity of the Maropeng location, nor that they absorb manganese from the rocks, nor that they redeposit excess manganese on the rock surface, forming a mottled black pattern. However they do observe that they are not the only organisms to act in this way, noting that chemotrophic Bacteria are well known to secrete both manganese and iron oxides in this way, often resulting in a mottled pattern in old bones, and indeed in the case of older specimens, turning the fossils completely black. Notably, such Bactria do not require light in order to carry out this process (unlike photosynthetic Lichens). This has two main implications; firstly the chamber does not have to have been exposed to light, as Bacteria will quite happily grow in the dark, and secondly the mottling should have a random distribution upon the bones, as to a pattern induced by a photosynthetic Lichen, which would by concentrated on the upper, exposed surface, a distribution which is indeed seen on the bones of Homo naledi.

Randolph-Quinney et al. also make a further observation, that such Bacteria induced manganese oxide mottling will be concentrated along and soil surface the bones were embedded in creating a 'tifde mark', as Bacteria are better able to absorb minerals from the environment along such boundaries. Such 'tide marks' can be seen on the bones of Homo naledi.

 Specimen U.W. 101–419 Cranium A(1) displaying tide lines of mineral staining which extends across different vault fragments. Tide lines mark a contact boundary between the bone surface and surrounding sediment, and indicate the resting orientation of the bone during precipitation of the stains. Randolph-Quinney et al. (2016).

See also...

http://sciencythoughts.blogspot.co.uk/2016/09/an-osteogenic-tumour-in-198-million.htmlAn osteogenic tumour in a 1.98-million-year-old Australopithicine from Malapa Cave, South Africa.                                      Neoplasmic tumors are areas of localized tissue growth where cellular proliferation occurs without the oversight of the bodies growth control...
http://sciencythoughts.blogspot.co.uk/2016/09/evidence-of-lichen-growth-on-bones-of.htmlEvidence of Lichen growth on the bones of Homo naledi.                                                  In 2013 scientists in South Africa described the discovery of a remarkable new Hominin species in the Dinaledi Cave System in Gauteng State, South Africa (part of the Maropeng Cradle of Humankind...
http://sciencythoughts.blogspot.co.uk/2016/08/malignant-osteosarcoma-in-17-million.htmlMalignant Osteosarcoma in a 1.7 million-year-old Hominin Metatarsal from Swartkrans Cave, South Africa.                                  Malignant Cancers are the biggest singe killer of...
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