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Re: Avian flight stroke origin
This raises a point that I still do not understand. Why is it assumed that
arboreality and terrestriality are such vastly different ways of life that
entire lineages can be assumed to have been one or the other, when living
birds, mammals, reptiles etc clearly show that this is not the case? In birds
alone we have genera containing both highly arboreal and purely terrestrial
species (eg Coracina, whose members are mostly arboreal but which includes the
terrestrial Ground Cuckoo-Shrike C. maxima), families such as Corvidae with
secondarily-terrestrial genera like Podoces, etc.
It can be objected that these are much better fliers than maniraptorids, and
that getting into a tree does not require special climbing adaptations if you
can fly there. In that case, what about (say) squirrels, which range similarly
from the ground to the treetops and include gliding species. If a marmot and a
flying squirrel can be close relatives, why can't dromaeosaurids (say) have
included a similar mixture?
Further, as I have said here before, a number of birds, including particularly
the cracids, can shift back and forth between trees and the ground with ease,
and others feed on the ground and nest in trees (including such unlikely
tree-dwellers as ducks). Could there have been tree- or cavity-nesting
dinosaurs? We'd be unlikely to find fossil evidence on the point.
Also, even flightless or near-flightless species of birds can get up into a
tree without having climbing-adapted front limbs. It's quite amazing to see the
ability some birds have of getting around in trees by simply jumping from
branch to branch, and if the trees have limbs near the ground they can reach
the canopy in this way too. A good example might be the Kokako (Callaeas
cinerea) of New Zealand, which is a fairly weak flyer (and, oddly for a
passerine, a folivore), but which is almost if not entirely arboreal; it tends
to leap upwards and fly/glide downwards.
1825 Shady Creek Court
Canada L5L 3W2
On 2011-08-11, at 1:36 AM, Tim Williams <firstname.lastname@example.org> wrote:
> Jaime Headden <email@example.com> wrote:
>> So close! From the title: "Assessing Arboreal Adaptations of Bird
>> AVIAN antecedents. It would have been so beautiful!
> It's not just the alliteration that falls short. I also found myself
> disagreeing with quite a few of the conclusions in the paper.
> Nevertheless, it's pleasing to see Dececchi & Larsson (2011) refute
> the hypothesis that the ancestors of birds were specialized for
> arboreality. That's always good to see, because this is the central
> plank of the BANDit's scenario-driven approach to the evolution of
> avian flight. Dececchi & Larsso single out the splayed, quadrupedal
> posture of "four-winged" gliding theropods for special criticism.