The prehistory of Koalas: apostles vs fossils
Professor Michael Archer holds BA (Princeton), PhD (Univ. Western Australia) FRZSNSW. He is currently Dean of the Faculty of Science at the University of New South Wales. For further information about Professor Archer see the University of New South Wales web site.
This article appears with the kind permission of Professor Archer and the Australian Museum.
Geologist Ian Plimer (University of Melbourne) is the latest in a long line of scientists who have had a go at publicly exposing the frontal-lobotomising brain virus that lurks below the crust of Creation 'science'. All of us hoped that the pseudoscience used by this religion to mislead people into parting with their money would be held up to public examination in the trial of Australian 'Arkeologist' Allen Roberts. Unfortunately, the trial devolved instead around relatively mundane matters such as breach of copyrightof which Roberts was convicted. Call me naive, but I cannot see why a minister of religion who uses deceit to solicit money to fund an expedition to find Noah's Ark should be any less liable to legal action than a con man who solicits money to get his budgie's teeth capped. Failure of the Federal Court to accept responsibility for protecting a gullible public from parasites of this kind has cost Ian Plimer heaps including his house and now court costs. Worse, it sends a signal to all snake oil merchants waiting in the wings, from fork-benders to faith-healers, that deceit has the Federal Court's seal of approval as a legitimate method for soliciting money.
What do Creation 'science' and the prehistory of Koalas have to do with one another? In reality, nothing rational, but in the eyes of Creation 'scientists', plenty. They tell us that God popped Koalas into being along with everything else in one divinely creative week, some 10,000 years ago. After a brief period of benevolence, Adam and Eve's disappearing apple trick led to a corrupted creation and an infuriated Creator. As things went from bad to worse God declared that all except two of every living thing would be drowned by zillions of tonnes of floodwater from somewhere. The lucky two of everything, including two of all their parasites and disease organisms, were shoe-horned into the Ark to bob about on the floodwaters for a year. Presumably on the passenger list were at least two very prolific gum trees to provide the half tonne of leaves a healthy pair of Koalas would need to survive. At the end of the cruise, the floodwaters, which had been deep enough to cover Mount Everest, went away to somewhere and the Ark settled on top of Mount Ararat in Turkey. (As support for the truth of this legend, 'Arkeologist' historian Allen Roberts claims to have identified the remains of the Ark on the slopes of Mount Araratin the form of what geologist Ian Plimer has shown to be a very large pile of dried mud.) After the Ark landed, everything from dinosaurs to Dodos disembarked onto the flood-devastated Earth and slipped, flopped, flapped or swam unerringly to appropriate parts of the globe, leaving no trace of their passage along the way. The two Koalas with their prolific gum trees then crossed the barren lands and oceans (all 'flesh' not in the Ark had been destroyed by the flood) to re-establish in Australia where they have lived happily ever after. Charming story, but it is this story that Creation 'scientists' want taught as science in schools throughout the world.
Fortunately, there are more testable sources of understanding about the origin of Koalas: the sciences of molecular biology, anatomy and palaeontology. Molecular biology and anatomy both demonstrate that, of living marsupial groups, Koalas are most closely related to wombats. Although Koala fossils are rare, one of the first Tertiary mammals found in Australia was Perikoala palankarinnica. Teeth and jaw fragments of this leaf-eating cousin of the living Koala were found in 1953 in 24 million-year-old deposits in central Australia. In the years that followed, tonnes of central Australian fossil 'dirt' were processed and the number of kinds of fossil Koalas grew to six.
Karen Black did her Honours research on the fossil Koalas of Riversleigh. One of them appears to be the most 'primitive' Koala yet known. Another, named Nimiokoala greystanesi, is so strange that it took Karen months to convince herself that it was a Koala rather than a member of some new bizarre group. Unlike all other Koalas, its molar teeth had enormously high, sheep-like cutting blades. Although this 'Koaleep' clearly ate plants, it is most unlikely that these were gum leaves. Homing in on the origins of the living Koala, Riversleigh also hosted the hip-pocket-size Litokoala kanunkaensis, previously only known from South Australia. Of all early Miocene (23 - 16 million-year-old) Koalas, this one is probably most closely related to Phascolarctos, the genus that contains the living Koala (P. cinereus). Even closer to modernity is a single, larger tooth from Riversleigh's late Miocene (ten to five million-year-old) Encore Site which may represent the first appearance of a species of Phascolarctos. Cundokoala yorkensis, a giant Koala more than twice the size of the living species, was first found in a Pliocene (five to two million-year-old) deposit in southern Australia. If accounts of soggy modern Koalas falling out of trees after days of soaking rain are true, no animal in its right mind would have camped in the wet under a gum tree laden with 'drop bears' this size.
Looked at overall, the fossil record suggests Koalas have markedly declined in diversity, with at least six species known from the late Oligocene, four from the early Miocene, two from the middle Miocene, one from the late Miocene, two from the Pliocene and one from the Pleistocene/Holocene. This trend is uncomfortably similar to that of the ill-fated thylacines and as such it does not auger particularly well for the long-term future of Koalas.
However, this worry is to some extent off-set by the fact that the modern Koala is significantly more common in its preferred habitat than any of the fossil koalas appear to have been. How could this have happened? We have speculated that at least one of the rare Koalas in Australias ancient rainforests began to specialise on the equally rare gum trees, which in turn were specialists, as most gums are today, on nutrient-deficient soils within the rainforest. After Australia's climates began to deteriorate, from about 12 million years ago, nutrient-deficient soils increased, forests opened up and the gums began a spectacular rise to dominance. And lounging on their limbs, grinning like lucky lottery winners, were the Koalas whose fortunate ancestors had bet on gums.
Lucky they may be, but there also may have been a cerebral downside to munching toxin-laden gum leaves for millions of years. Odd as it sounds, neurobiologists have found that the Koala's brain fails to fill more than 60 per cent of the space available in its skull. Perhaps Koalas and the Creation 'scientists' who would pull Koalas out of an Ark in Turkey do have something in common after all.
See Koalas for more information on this Australian arboreal marsupial and mascot of Australian Skeptics.