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.
“This could have happened just after the dinosaurs went extinct,” says Boles.
“Things were really moving then.” 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’
Union (vol 97, p 43).
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. “Each fragment has all the
characteristic knobs and bumps you’d expect from a songbird bone of that kind,”
says Boles. “With bones only a few millimetres long it’s pretty difficult to say
what the whole animal would have looked like, but they were certainly well
advanced down the songbird line.”
“The key thing about these fossils is their age,” says Boles. According to
potassium-argon dating, the fossils are 54.6 million years old—nearly 25
million years older than the oldest previous known songbird fossils, dating from
the early Miocene and found in France. “These 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,” 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 “this little area in this guy’s back yard”, says Boles. “Once a year he
lets people in to start digging.” The site has proven extremely rich. Apart from
the world’s oldest songbird, it has also yielded Australia’s 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.
“This discovery not only illustrates that all major bird groups alive today
had evolved by 50 million years ago in a very rapid diversification,” says
Storrs Olson from the Bird Department at the Smithsonian Institution in
Washington DC, “it also shows that the radiation of birds in the northern
hemisphere is a comparatively recent event.”