Songbirds Escaped From Australasia, Conquered Rest of World
MINNEAPOLIS / ST. PAUL (7/19/2004) -- That male cardinal singing his
heart out in your backyard has ancestors that left the neighborhood
of Australia 45 million years ago. A comprehensive study of DNA from
songbirds and their relatives shows that these birds, which account
for almost half of all bird species, did not originate in Eurasia, as
previously thought. Instead, their ancestors escaped from a relatively
small areaustralasia (Australia, New Zealand and nearby islands) and
New Guineabout 45 million years ago and went on to populate every
other continent save Antarctica. The study, led by Keith Barker of
the University of Minnesota Bell Museum of Natural History, will be
published online this week in the journal Proceedings of the National
Academy of Sciences.
The birds in question belong to the group called Passeriformes, or
perching birds. It includes all songbirds, such as robins, cardinals,
blackbirds, house sparrows, house finches and crows. The group is further
divided into birds that must learn their songs true songbirds) and those
with the innate ability to sing the correct song. True songbirds account
for 4,580 of the 6,000 known Passeriformes species. (There is a total of
9,702 known species of birds.) The true songbirds are currently divided
into two groups: Passerida (3,477 species, among them many familiar
backyard species) and Corvida (1,103 species, including crows and ravens).
The two groups of true songbirds were thought to have separate
origins. The Corvida originated in Australasia, but the Passerida
were thought to have arisen separately, in Eurasia. The Passerida
then supposedly spread from Eurasia to Africa, Australasia and the New
World. But in examining the DNA sequences of two genes in all but one
family (a closely related group, such as crows and jays or warblers)
of passerine birds, Barker and his colleagues made a startling discovery.
It was thought that the Passerida arose in Eurasia about 40 million years
ago, said Barker. But we found that these birds fall into a group within
the Corvida. That means all songbirds trace their origins to Australasia
and New Guinea.
The Passerida differ from the Corvida because the Passerida somehow made
it out of Australasia and New Guinea and onto the Asian mainland long
before the Corvida, Barker said. Asia and Australasia are carried on
separate plates in the Earth crust, and for many millions of years those
plates were far apart. Around 45 million years ago, the ancestors of the
Passerida dispersed to Asiaver more than 600 miles of open ocean--long
before these two plates approached one another. For some reason, however,
ancestors of the Corvida didn make it until about 25 million years later,
or 20 million years before today. At that time, Asia and Ausstralia were
much closer to each other, and island chains that could have allowed
the Corvida ancestors to island hop to the mainland appeared, Barker said.
There are many endemic Corvida birds on the Indonesian island of Lombok
but very few on Bali, the next island to the west, said Barker. And,
sure enough, the line separating the Asian plate from the Australasian
plate runs between Bali and Lombok.
Working with Barker were colleagues from the Natural History Museum of
Geneva, Switzerland; and the American Museum of Natural History in New
York. The study was funded by the Chapman Fund of the American Museum
of Natural History and the National Science Foundation (NSF). Barker
and Scott Lanyon, director of the University of Minnesota Bell Museum,
are currently working with NSF support on a study of cardinals and
their relatives, which include tanagers, blackbirds, warblers and New
World sparrows.
http://www.ur.umn.edu/unsreleases/find.php?ID=1763&from=umnnews
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