Re: Primates and proavians (was Re: [RE: A glider?])

["Tim Williams" <twilliams_alpha@hotmail.com>]

Richard W Travsky wrote:

>  Feduccia was referring to sakis, not sifakas. From p. 97:
>
>  "Among New World primates, which lack prehensile tails, there are
>  numerous semi-aerial adaptations, and the sakis of the genus  Pithecia 
> are
>  notable among them. Pithecia monachus, known locally as volador  flier),  
> has a long body, with moderately long arms and legs, and its pelage, or 
> body hair, is a distinctlve long, rather coarse, grizzled blackish fur.
> Sakis prefer mature moist forest.... where they frequently glide in flying 
> squirrel fashion."

The paper I was referring to discusses the Madagascan sifaka:

Feduccia, A.  Aerodynamic model for the early evolution of feathers provided 
by _Propithecus_ (Primates, Lemuridae).  Journal of Theoretical Biology. 
1993; 160 (2) 159-164.


> >  Feduccia compares their gliding abilities to those of sifakas (they are
> >  apparently a lot better at it) and includes photos of both.


As for "gliding" in sakis (_Pithecia_) and sifakas (_Propithecus_), I wonder 
if their behavior qualifies as _true_ gliding (lift > drag), or is simply 
parachuting.  Both are important types of aerial locomotion, and they do 
grade into each other.  However, gliding and parachuting are often confused, 
even in scientific literature.  (For example, flying frogs do not glide, 
they parachute.  Flying squirrels and other patagial gliders, on the other 
hand, are capable of true gliding.)

Also, if the extra hair on the bodies of sakis and sifakas (especially on 
the arm) result in *no* net increase in the horizontal distance travelled, 
then they do not qualify as gliding surfaces.  For the sifakas (according to 
Feduccia), the brachial "mat" of hair helps the animal to steer in the air, 
allowing a more comfortable and accurate landing when leaping from trees.  I 
think this is a nice way for theropods to have evolved wings.

Hey, I'm quoting Feduccia's research in *support* of a scenario for the 
origin of flight in theropods.  Somebody pinch me!


Tim


------------------------------------------------------------

Timothy J. Williams

USDA/ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163

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