To a palaeontologist, a gap in the fossil record is an unanswered question and an invitation to keep looking. To a creationist, it is more often treated as a convenient space in which to insert a supernatural explanation. The difficulty for creationism is that scientists have an inconvenient habit of finding the missing evidence, whereupon the gap becomes smaller, the evolutionary history becomes clearer, and creationists must quietly move their supernatural explanation somewhere else.
A particularly neat example is provided by a paper just published in Australian Zoologist by Timothy J. Churchill, Michael Archer, Suzanne J. Hand and Roy M. Farman. As Churchill explains in an article in The Conversation, a handful of tiny fossil jaws from north-western Queensland has supplied a previously missing opening chapter in the evolutionary history of Australia’s most diverse family of marsupial predators.
The family Dasyuridae contains almost 80 living species, including Tasmanian devils, quolls, dunnarts, planigales and antechinuses. They range from insect-eaters weighing only a few grams to the much larger Tasmanian devil, and occupy environments extending from the tropical rainforests of New Guinea to Australian deserts, grasslands and alpine woodland. Yet, despite this modern diversity, their early fossil history had remained frustratingly obscure.
Molecular studies indicated that dasyurids had diverged from their closest relatives millions of years before the earliest unambiguous fossils then known. Almost all accepted dasyurid fossils were younger than about five million years, leaving what palaeontologists call a “ghost lineage”: a branch whose existence was indicated by evolutionary relationships, but whose earlier fossil representatives had not yet been found. The animal once thought to fill that gap, Barinya wangala, was subsequently shown to belong to an entirely different family of peculiar, probably snail-eating marsupials called malleodectids.
Creationists sometimes present such gaps as evidence against evolution, apparently assuming that unless every organism that ever lived has obligingly become fossilised, been exposed at the surface and been discovered, the evolutionary history can be dismissed. But incompleteness is not inconsistency. Fossilisation is rare, suitable rocks are unevenly distributed, and tiny, fragile animals are especially unlikely to leave recognisable remains. Evolution nevertheless predicted that earlier dasyurids had existed. The question was whether any of them would eventually be found.
The new species, named Miyumba chrisdickmani, is known from six partial lower jaws recovered from Early Miocene deposits in the Riversleigh World Heritage Area on Waanyi Country. It lived about 23 million years ago and probably weighed only about 30 grams, making it comparable in size to a modern antechinus or large dunnart. It is now the oldest confirmed member of Dasyuridae, extending the family’s recognised fossil history by more than five million years.
Its significance, however, lies in much more than its age. The teeth of Miyumba possess a particular arrangement in which the third lower premolar is smaller than the first and second. This appears to be a shared derived characteristic, or synapomorphy, identifying dasyurids as a natural evolutionary group. At the same time, Miyumba retains several ancestral dental features expected in an animal close to the base of that group’s family tree.
That combination is precisely what evolutionary theory predicts: an early member of a lineage should possess the defining innovations inherited by its descendants while retaining features inherited from more distant ancestors. It should not look exactly like a modern Tasmanian devil, quoll or dunnart because those specialised forms had not yet evolved. Nor should it be unrelated to them. It should display a mosaic of ancestral and newly evolved characteristics — and that is exactly what Miyumba does.
































