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The possibility of lichen growth on bones of Homo naledi: Were they exposed to light?

J. Thackeray

Published 2016 in South African Journal of Science

ABSTRACT

Dirks et al report on the taphonomy of bones from the Dinaledi Chamber in the Rising Star cave complex, situated in the Cradle of Humankind in South Africa. Fossils of Homo naledi have been recovered from this chamber. An age estimate for the Homo naledi fossils, based on morphometric analyses of crania, is in the order of 2 million years, 3 although it is recognised that a younger date may apply if morphological patterns persisted for an unknown period of time. Dirks et al. state that 'some bones and teeth are dotted with black iron-manganese oxy-hydroxide deposits and coatings'. The question arises as to what factors contributed to the 'dotted' or spotty distribution of manganeseoxy-hydroxide on bone surfaces. Abiotic geological factors may account for continuous (matted) deposition of manganese oxy-hydroxide coatings in some cases, but why should these be dotted or spotted in the instance of many bones from the Dinaledi Chamber - or from other nearby sites, such as Sterkfontein? To try to answer this question, it is appropriate to refer to observations by Thackeray et al. in which we noted, firstly, that in the Cradle of Humankind, lichen can grow on certain substrates (including bone or rock) with a dotted or spotted distribution. Secondly, the spotted distribution of lichen is sometimes associated with dotted distributions of manganese oxyhydroxide on the same surfaces. The source of manganese would include dolomite and chert, 2 billion years old,relating to the shallow saline sea that existed at that time.

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