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Re: flight beginnings

Jason Brougham <jaseb@amnh.org> wrote:

> You often say that the skeletal features of animals clearly predict whether 
> they are capable of arboreality
> or not.

The skeleton can provide strong predictors for ecology - terrestrial,
scansorial, arboreal, fossorial, aquatic, etc.  (This is fundamental
to the concept of ecomorphology.)

> For example, you have said that, based on the skeletons of caprinids alone, 
> we would expect
> that they are climbers. Could you state once again what those predictive 
> skeletal features are please?

Hmmm... I said that?  Goats can climb trees, without being specialized
for arboreality.  This applies to lots of tetrapods.  (Probably even
to non-avian maniraptoran theropods....)

> Also, what skeletal features of the Hyrax (Procavia) do you see as predictive 
> of arboreality?

None.  The skeletons of all hyraxes lack obvious arboreal
specializations - hyraxes are famous for this.  Yet, all hyrax species
are adept climbers, and the tree-hyraxes spend most of their time in
trees - so among hyraxes the tree-hyraxes are arboreal in the true
sense.  The excellent rock-climbing and arboreal abilities of hyraxes
are largely due to specialized adhesive foot-pads that also apparently
provide suction.

However, that's not to say that the hyrax skeleton is non-arboreal.
In general, the hyrax skeleton is well-suited to scansorial and
arboreal habits.  Their small size and high fulcrum / crouched posture
during locomotion make hyraxes highly amenable to moving around in

For small quadrupedal mammals, it is often difficult to distinguish
terrestrial vs scansorial vs arboreal based solely on the skeleton.
This is because the smaller a mammal is, the larger the obstacles and
irregularities in its terrain - so some climbing may be needed during
locomotion across a forest floor, for example.  (This is not
hand-waving on my part - this theme is well-attested in the
literature.)  From an evolutionary standpoint, switching between
terrestrial / scansorial / arboreal ecomorphologies is relatively
straightforward for small quadrupedal mammals (e.g., the tree-shrew
genus _Tupaia_ includes all three locomotor modes: terrestrial,
scansorial, arboreal.)  Hyraxes are no exception.

This ecomorphological fluidity observed for small, crouched,
quadrupedal mammals like tree-shrews and hyraxes is far removed from
the situation of erect, cursorial, bipedal theropods of any size.
Chalk and cheese.