Introduction
Bradshaw rock art of northern Australia enjoys continuing controversy concerning which community painted them and how to interpret the images (Reference RoyRoy 2002). The keen observation and accurate depictions of the natural world shown here, as well as the extraordinary longevity of the stains used, all tend to support the side of the controversy that posits a distinct cultural entity. We describe a painting unmistakably depicting flying foxes with features not found in bats presently found in Australia. Thermoluminescence dating of the fossilised remains of a wasp nest overlying the art suggests an ice age migration to Australia, either of the bats or of the artists who painted them, a more likely scenario biologically than younger dates. The bat depictions were found on a sandstone wall protected by overhangs, near Kalumburu (14.30°S; 126.64°E; and see Figure 4), amongst other walls showing characteristic Bradshaw art (Reference WalshWalsh 2002). The depiction shows eight roosting megabats (flying foxes, Family Pteropodidae, sub-Order Megachiroptera) hanging from a slender branch, or more likely, a vine (Figures 1 and 2). Each bat has a distinctive white facial stripe and pale belly (Figure 3).
White-striped flying foxes depicted in Bradshaw rock art at Kalumburu, in the Kimberley of Western Australia.
Extension, to the left, of the same depicted group of shown in Figure 1, with which there is some overlap.
Diagnostic features of a megabat (flying fox, Family Pteropodidae, Sub-Order Megachiroptera) in a rock art depiction: 1. Flexed head on neck (cf. extended head on neck of microbats); 2. Simple, complete ears lacking a tragus, the extra, central process found in microbat ears; 3. Elongated, dog-like face. A linear white jugal stripe (arrow) is not found in any living Australian megabat, but is found in four different species of megabat from Sulawesi, Maluku and Phillipines.
Distribution (in red) of extant stripe-faced megabats in Sulawesi and Maluku (also Phillipines, not shown) in relation to the depicted rock art in the Kimberley of Australia (Kalumburu). Potential migration routes from these sites during the last glacial maximum are shown to the east or west of the Banda Sea.
The indelible inks used in Bradshaw art penetrate more than a millimetre into the sandstone but have resisted all attempts so far to date them directly, with a number of different estimates of their age (Reference MichaelsonMichaelson & Ebersole 2000). A fossilised wasp nest overlying this kind of art has been dated using luminescence at 17 500 BP, a time during the last ice age (Reference RobertsRoberts et al. 1997) and therefore in keeping with an ice age scenario for the migration of this bat from Asia to Australia along the then continuous belt of lowland forest. Since the art must have preceded the wasp nest by an indeterminate time, its creation may have taken place even closer to the glacial maximum (20–25 000 BP) than to the shorter estimate given by luminescence.
Discussion
Identification of the animals depicted as pteropodids is unmistakeable because of their elongated faces, simple ears and flexed head posture (which all contrast with the smaller, insect-eating microbats). The depictions are likely to be of medium-sized megabats rather than larger Pteropus spp. because of the slightly bunched roosting posture. None of Australia's eight species of megabats has white facial markings. Worldwide there are six such species, two in Africa and four in the islands off Southeast Asia (Reference NovakNovak 1999). The two African species, Scotonycteris and Casinycteris, have irregular white markings, unlike the depiction, and Pteropus personatus from Maluku has a dorsal extension of the white stripe giving a patch above the eye, which is also inconsistent with the painting. This leaves Styloctenium wallacei, from Sulawesi, S. mindorensis from Mindoro in the Phillipines, and Neopteryx frosti from Maluku for consideration. All are medium-sized and show a distinctive white jugal stripe as seen in the painting, and all are fruit eaters in lowland forest. Styloctenium has an additional, separate, supra-ciliary white stripe, that may be invisible in profile views, but has a pale belly like the depictions, unlike Neopteryx (Reference EsselstynEsselstyn 2007). On balance, Styloctenium is the most likely model living genus for the depicted ancient species, which latter may nevertheless be extinct worldwide. If the Kimberley white-faced flying foxes were derived from, or the same species as, one of these white-faced flying foxes from Sulawesi or Maluku, they (or those who painted them) could have taken either of two possible routes to Australia during the ice age (Figure 4): 1. On the eastern side of the Banda Sea, an island-hopping route would provide access to the New Guinea floodplain, which was continuous with the NW Australian floodplain at that time; 2. a route to the west of the Banda Sea would have involved a 60–70km crossing of the Timor Sea, a feasible journey for flying foxes, which are known to cover this distance in a single night (Tidemann & Nelson 2004). The medium-sized flying fox, Pteropus scapulatus, crossed the Tasman Sea from Australia to New Zealand, a journey of 1000km (Reference NovakNovak 1999).
Much debate concerns whether past mammal extinctions were caused by human hunting pressure or by climate change. Human influence is unlikely to explain the present case completely, since the mobility of megabats is proof against even more sophisticated technologies than would have been available to the 'Bradshaw culture'. The demise of the Kimberley white-faced megabats is therefore most likely to have resulted from the marked climatic and ecological changes that followed the end of the ice age, such as the reduction of floodplains and forests.
Acknowledgements
Jacob Esselstyn and Kristofer Helgen provided valuable discussion about the possible identity of the depicted flying foxes. AM found the flying fox art. This note is dedicated to the memory of the late Grahame Walsh, who has made enormous contributions to a better understanding of Bradshaw art.
