¿ìè¶ÌÊÓƵ

How many bird lineages escaped unscathed when a giant
asteroid wiped out the dinosaurs 65 million years ago? The prevailing wisdom has
been that most archaic groups of birds went the way of the dinosaurs and a few
survivors were responsible for today’s diversity of birdlife. But work by two
New Zealand scientists, Alan Cooper from the University of Wellington and
David Penny from Massey University, indicates that far more avian
lineages survived the devastation at the Cretaceous-Tertiary (K-T) boundary than
is generally believed (Science, vol 275, 21 February). Cooper and Penny
used differences in the DNA of modern birds as a “molecular clock” to determine
the age of each lineage. They believe that many modern birds originated in the
Early Cretaceous about 130 million years ago and that at least 21 lineages,
including parrots, wrens, and penguins, survived the mass extinction at the K-T
boundary. The work is controversial. Ornithologist Alan Feduccia from the
University of North Carolina says that the molecular clock is based on fossil
records of birds which may be misidentified.