Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)

[Tim Williams <twilliams_alpha@hotmail.com>]

Jim Cunningham wrote:


>> There is a strong selective advantage for an arboreal animal to evolve
>> some sort of parachute or gliding system to prevent injury from falling or
>> to conserve energy by leaping from tree to tree instead climbing all the
>> way down and back up a tree trunk, or cliff face: this is made obvious by
>> the large number of arboreal creatures that have evolved in this way.
>
> This is quite true. How many of them seem to be developing the ability for
> powered flight?


Excellent point, Jim.  Patagial gliding has evolved at least nine times in 
mammals alone - by colugos (Dermoptera), in several rodent groups (Eomyidae, 
Gliridae, Petauristinae, Anomaluridae), in at least three lineages of 
phalangeriform marsupials (Petauridae, Acrobatidae, Pseudocheiridae), and in 
_Voluticotherium_ (the oldest known example).  Patagial gliding also been 
proposed for paromomyids (e.g., _Plesiadapis_), but the supporting evidence has 
been disputed.  (It's also been suggested that modern sifakas, _Propithecus_, 
can glide, using small patagial membranes in combination with trailing forearm 
hair - but this is controversial.)


So if bats evolved from patagial gliders, this represents (at best) one 
instance out of ten in which gliding transitioned to powered flight in mammals. 
 Not great odds.  Further (as you say) none of the extant gliders show any 
evidence of incipient flapping ability.  



> Since many improvements in parachuting and/or gliding ability don't lead
> toward the direction of powered flight, doesn't that create problems for
> your scenario?



If gliding did lead to flight in the ancestry of bats, it's clear that 
exceptional circumstances were involved.  So much for this route being "easy".  
 ;-)



Cheers

Tim
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