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Re: flight beginnings

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

> I suppose today the closest thing to an at least partially bipedal arboreal
> mammal (other than apes or humans) would be a tree kangaroo, not exactly a
> small animal. I've always assumed that if a tree kangaroo can manage in a
> tree a maniraptorian of similar size would have no trouble at all.

I take your point - but I respectfully disagree.  Tree kangaroos
(_Dendrolagus_ spp.) are actually quite specialized for life as an
arboreal quadruped.  This is not true for any maniraptoran.

The reason why tree kangaroos don't get much street cred as arboreal
animals might be because they look quite ungainly when up in the trees
- especially compared to other arboreal marsupials (such as phalangers
and possums).  Phalangeroid marsupials are primitively arboreal, and
the macropod (kangaroo) branch include terrestrial bipeds that evolved
from these arboreal quadrupeds.  The tree kangaroos are secondarily
arboreal, having evolved from terrestrial macropods - which is why
tree kangaroos appear less comfortable in trees than their primitively
arboreal cousins.  But tree kangaroo skeletons are certainly quite
specialized for arboreality (especially the limb elements).

Dececchi and Larsson (2011; PLoS ONE 6(8): e22292.
doi:10.1371/journal.pone.0022292) explicitly singled out the
tree-kangaroos as being poor analogs for hypothetical arboreal
theropods, and accordingly devote a whole section to tree kangaroos:
"Are Tree Kangaroos good analogues for bird antecedents?" (Answer: A
resounding 'No').  Dececchi and Larsson directly refute the recurring
myth (e.g., Chatterjee and Templin, 2004) that the skeletons of tree
kangaroos lack arboreal features (aside from recurved pedal claws).
They provide a list of arboreal characters and indices in
_Dendrolagus_, absent from their terrestrial relatives.

Other workers agree that tree kangaroos have quite a number of
arboreal characters that are lacking in fully terrestrial macropods
(e.g., Flannery et al., 1995 Mammalia 59: 65-84)  The same arboreal
characters in the forelimb and hindlimb (especially the hindfoot) are
also apparent in the fossil macropod _Bohra_ (e.g, Prideaux &
Warburton, 2009; Records of the Western Australian Museum 25:
165-179), a close relative of _Dendrolagus_.