We were interested in trying to
understand
how the early ancestors of birds
survived the mass extinction event
that wiped out non-avian dinosaurs
about 66 million years ago
and we discovered
by working with paleobotanists
that it's likely that forests worldwide were
devastated by the asteroid impact
that eliminated the non-avian dinosaurs
and, in line with that observation,
we infer that only ground-dwelling birds
were likely to have survived the mass extinction event.
So we think that all
living lineages of birds
that are adapted to life in the trees
only moved into the trees
after the K-Pg mass extinction event,
once global forests had rebounded
from the asteroid impact.
