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



Jason Brougham <jaseb@amnh.org> wrote:


> "All ages of birds climb freely in Phylica and tussock grass to a height of 
> 1.5 m, flapping the wings to aid
> balance and probably using the well - developed wing-claw."


Not at the same time, presumably.  :-)  The only accounts of
flightless rails I have read mention that the wings are flapped as an
aid during climbing.  The use of the wing claws by rail chicks during
climbing is well attested, as I think you mentioned.


The Inaccessible Island Rail was also reported to use its wings as
brakes when jumping down sloped terrain (Hagen, 1952).


Similar behavior has been reported for the kagu: the wings are
deployed when this flightless bird is running down slopes and it
"launches" into a glide using the wings (Roots, 2006).


So we have two examples of aerial behavior (aerodynamic control,
gliding) in flightless birds, both in a completely terrestrial
setting.


> So, another report of a tiny winged theropod that is a quadrupedal climber.


They are climbing/clambering using all four limbs.  But they are a
long way from being arboreal quadrupeds (sensu stricto).


> I am not finding measurements of the manual claw curvatures of 
> Epidendrosaurus but the curvatures
> don't look weaker than in Opisthocomus.


In juvenile hoatzins (_Opisthocomus_), the feet do most of the work
during climbing.  I don't think it's a great idea to compare
scansoriopterygids too closely with hoatzins (juvenile or adult).
There's a great deal of morphospace between the two.



References

Clive Roots (2006).  "Flightless Birds", Greenwood Publishing.

Yngvar Hagen (1952)  Birds of Tristan da Cunha. Results of the
Norwegian Scientific Expedition to Tristan da Cunha 1937-1938.