The Nature of Petroglyphs

The so-called Bradshaw paintings of Australia’s Kimberley region have always been a bit of an enigma. Called gwion gwion by the contemporary Wanjina Wunggurr Wilinggi people who are acknowledged traditional owners of the Kimberley lands, the Bradshaw paintings are thought to be some of the oldest rock paintings on the continent, depicting animals and plants that lived between 46,000 and 70,000 years ago�and yet in many of the works the pigments remain bright, the figures still sharply delineated. In a notice published in the December 2010 issue of Antiquity, University of Queensland archaeologist Jack Pettigrew and a team of his researchers report that pigmented fungi and bacteria appear to have colonized the painted areas of the ancient artworks, preserving them by replacing the faded paints with their own vibrant, perpetually-renewed hues.

The fungi inhabiting the Bradshaw paintings, Pettigrew suggests, belong to the Chaetothyriales, which the paper describes as “an extremely conservative group of rock-adapted fungi that replicate without hyphae by cannibalising their predecessors in situ“�a pretty neat trick for a fungus living on exposed stones in an arid climate. (The team recovered DNA from rock art throughout the region, but the genetic analysis has not been reported.) Resident bacteria may be cooperating by providing carbohydrates in exchange for water conserved by the fungi. The colonies might once have fed on pigments used by the ancient artists, but any trace of such materials are long gone by now; instead, the team hypothesizes, the paints etched the rock surface, dissolving silicates in a way that created a suitable microenvironment for the fungi. Preferring the etched stone to the unprepared rock surface, generation upon generation of the fungi have been feeding upon one another without coloring outside the lines. [via BBC]