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Re: Fwd: Aw: RE: Arboreal Theropods: The prize at the bottom of the cracker jack box

Ronald Orenstein <ron.orenstein@rogers.com> wrote:

> Take a look at photos of herons or storks in trees - usually they do not 
> grasp, or curl their toes around, the
> branch but let them dangle on either side (see, e.g., 
> http://www.123rf.com/photo_4360674_isolated-shot-of-
> black-white-open-bill-stork-bird-anastomus-oscitans.html).

The birds of today certainly make perching and roosting look easy.
Even many birds where the feet are not specialized for perching (=
grasping branches) can sit or roost in trees.  Ron's stork is a good
example.  Don's turkey can roost on a thick branch, without always
using its hind toe (hallux).

However, birds have re-worked their bauplan compared to their theropod
ancestors.  When standing, a bird is in a permanently 'crouched'
position, with the thighs tucked under the body and the knees near to
the body's center of mass.  This was quite a profound morphological
shift compared to the ancestral theropod condition, where the center
of mass was around the hips.  If a non-avialan theropod adopted the
same posture as a perching/roosting bird, it might render the body
very unstable (especially considering the relative length of the
hindlimb).  If not, and non-avialan theropods adopted an entirely
different stance when roosting, then extant birds offer a poor analog
for this hypothetical behavior in non-avialan theropods.

I don't know if the derived avialan bauplan/posture makes balancing on
a narrow substrate 'easier' or not.  But either way, it makes it
challenging to extrapolate the arboreal locomotor abilities of birds
to those of non-avialan theropods.