Evidence is mounting that modern birds descended
from gliding, feathered non-avian dinosaurs.
Two dinosaurs could be candidates for the bottom
of the bird family tree, and each helps to reveal how feathers first evolved.
"The oldest known feathered dinosaurs would
be Anchiornis (155 million years ago) and Epidexipteryx (between 152 million
and 168 million years ago)," Yale University paleontologist Nicholas
Longrich told Discovery News. "Feathers seem to have appeared initially
for insulation. Basically they start out as down, and later are used to make
wings."
For a study published in the latest Current
Biology, Longrich and colleagues Jakob Vinther and Anthony Russell examined
fossils of Anchiornis huxley and of Archaeopteryx lithographica, a Jurassic
species that could be the world's oldest known bird.
"Where dinosaurs end and birds begin is a
bit arbitrary," Longrich explained. "There's no clear cutoff that
separates one from the other. That's the nature of evolution; things gradually
change from one thing into another."
The scientists found that the wing feathers of
Archaeopteryx and Anchiornis were similar, but not identical. The variations
between the two appear to represent early experiments in the evolution of the
wing.
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