SONGBIRDS performed their first arias in Australia more than 50 million
years ago, if the interpretation of some tiny scraps of fossilised bone found in
the back yard of a farm in Queensland are correct.
Australia has long been considered the avian equivalent of an airport lounge,
populated by travel-weary stragglers. But these fossils suggest that, far from
having a derivative bird fauna, Australia was the place where songbird species
first evolved, says Walter Boles of the Australian Museum in Sydney.
鈥淭his could have happened just after the dinosaurs went extinct,鈥� says Boles.
鈥淭hings were really moving then.鈥� Pigeons, parrots and geese are among the other
bird groups that may have had their origins in the southern hemisphere, rather
than in the north as had previously been believed, he writes in the current
issue of Emu, the journal of the Royal Australasian Ornithologists鈥�
Union (vol 97, p 43).
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The fossils include two ankle bones from a finch-sized bird, and part of a
wing bone from a creature about the size of a thrush. 鈥淓ach fragment has all the
characteristic knobs and bumps you鈥檇 expect from a songbird bone of that kind,鈥�
says Boles. 鈥淲ith bones only a few millimetres long it鈥檚 pretty difficult to say
what the whole animal would have looked like, but they were certainly well
advanced down the songbird line.鈥�
鈥淭he key thing about these fossils is their age,鈥� says Boles. According to
potassium-argon dating, the fossils are 54.6 million years old鈥攏early 25
million years older than the oldest previous known songbird fossils, dating from
the early Miocene and found in France. 鈥淭hese fossils explain why, when the
northern hemisphere has early Eocene fossils of everything from rollers to
rails, those of songbirds did not turn up until much later,鈥� says Boles.
The fossils come from the Tingamurra sediments, 160 kilometres northwest of
Brisbane. There are no other known sediments of a similar age in Australia. The
site is 鈥渢his little area in this guy鈥檚 back yard鈥�, says Boles. 鈥淥nce a year he
lets people in to start digging.鈥� The site has proven extremely rich. Apart from
the world鈥檚 oldest songbird, it has also yielded Australia鈥檚 oldest frog, bat,
marsupial and a salamander: a group of animals previously thought not to exist
in Australia. Where the farm stands now was probably once a billabong, where a
pool of highly alkaline water preserved the fossils.
鈥淭his discovery not only illustrates that all major bird groups alive today
had evolved by 50 million years ago in a very rapid diversification,鈥� says
Storrs Olson from the Bird Department at the Smithsonian Institution in
Washington DC, 鈥渋t also shows that the radiation of birds in the northern
hemisphere is a comparatively recent event.鈥�
