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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. 

Ronald Orenstein 
1825 Shady Creek Court
Mississauga, ON
Canada L5L 3W2

On 2011-08-11, at 1:36 AM, Tim Williams <tijawi@gmail.com> wrote:

> Jaime Headden <qi_leong@hotmail.com> wrote:
> 
>> So close! From the title: "Assessing Arboreal Adaptations of Bird 
>> Antecedents."
>> 
>> 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.
> 
>