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Origin of birds linked to body and limb size dissociation

From: Ben Creisler

A new online paper:

T. Alexander Dececchi & Hans CE Larsson (2013)
Body and limb size dissociation at the origin of birds: uncoupling
allometric constraints across a macroevolutionary transition.
Evolution (advance online publication (accepted articles))
DOI: 10.1111/evo.12150

The origin of birds and powered flight is a classic major evolutionary
transition. Research on their origin often focuses on the evolution of
the wing with trends of forelimb elongation traced back through many
non-avian maniraptoran dinosaurs. We present evidence that the
relative forelimb elongation within avian antecedents is primarily due
to allometry and is instead driven by a reduction in body size. Once
body size is factored out, there is no trend of increasing forelimb
length until the origin of birds. We report that early birds and
non-avian theropods have significantly different scaling relationships
within the forelimb and hindlimb skeleton. Ancestral fore- and
hindlimb allometric scaling to body size is rapidly decoupled at the
origin of birds, when wings significantly elongate, by evolving a
positive allometric relationship with body size from an ancestrally
negative allometric pattern and legs significantly shorten by keeping
a similar, near isometric relationship but with a reduced intercept.
These results have implications for the evolution of powered flight
and early diversification of birds and suggest that their limb lengths
first had to be dissociated from general body size scaling before
diversifying to the wide range of fore and hindlimb diversity present
in today's birds.