Date: July 18, 2016
Source: Queen's University
Research by post-doctoral fellow
Alexander Dececchi challenges long-held hypotheses about how flight first
developed in birds. Furthermore, his findings raise the question of why certain
species developed wings long before they could fly.
Dr. Dececchi, a William E. White
Post-Doctoral Fellow in the Department of Geological Sciences and Geological
Engineering, used measurements from fossil records and data from modern birds
to test the evolutionary explanation for the origin of birds. Dr. Dececchi and
his colleagues determined that none of the previously predicted methods would
have allowed pre-avian dinosaurs to take flight.
"By disproving the idea that
the predicted models led to the development of flight, our research is a step
towards determining how flight developed and whether it can evolve once or
developed multiple times in different evolutionary lines," he says.
Dr. Dececchi and his colleagues
examined 45 specimens, representing 24 different non-avian theropod species, as
well as five bird species. After determining some critical variables from the
fossils -- such as body mass and wing size -- they used measurements from
living birds to estimate wing beat, flap angle and muscular output.
These values were used to build a
model for different behaviours linked to the origins of flight such as vertical
leaping and wing-assisted incline running (WAIR) -- a method of evasion for
many ground-based modern birds that has become a favoured pathway towards the
origin of flapping flight in the paleontological literature. They also tested
if any species met the requirements to take-off from the ground and fly under
their own power.
"We know the dimensions and
we know how modern birds muscles and anatomy work," Dr. Dececchi says.
"Using our model, if a particular species doesn't reach the minimum
thresholds for function seen in the much more derived birds -- such as the
ability to take off or to generate a certain amount of power -- it's safe to
say they would not have been able to perform these behaviours or fly."
The researchers found that none
of the behaviours met the criteria expected in the pathway models. In fact,
they found that almost all the behaviours had little or no benefit, outside of
those species which evolved right before the origin of birds. When looking at
WAIR specifically -- the method that has been touted as an explanation for some
early wing adaptations -- the researchers found that it only was possible in a
handful of large winged, small bodied species such as Microraptor, but found no
evidence to suggest its use was widespread.
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