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

[Dann Pigdon <dannj@alphalink.com.au>]

Quoting don ohmes <d_ohmes@yahoo.com>:

> Given the presence of easy-to-climb trees (e.g., cycads), and good reasons to
> climb them daily, but perhaps not spend all day there, I do not see where the
> terrestrial ancestry of birds necessarily speaks to a ground-up scenario.

The problem I have with the 'ground up' or 'trees down' dichotomy is that any 
creature well 
adapted to an exclusively terrestrial or arborial lifestyle (but not both)  
doesn't have much need to 
fly. An excellant runner can out-run predators and catch prey without the need 
to fly. Excellent 
climbers rarely need to survive a fall, simply because they rarely *do* fall.

However, a partially-arborial creature that spends as much time in both 
environments (hence isn't 
supremely well adapted to either) would certainly benefit from being able to 
fly, if only to survive 
frequent falls, or to evade terrestrial predators that can run a lot faster.

I don't see 'ground up' or 'trees down' to be necessarily mutually exclusive - 
in fact, I'm guessing 
that the development of avian-style (ie non-membraneous) flight would be 
stronger when both 
scenarios are in equal effect. A gliding or parachuting animal could survive 
falls (if it wasn't an 
especially good climber then falls might be relatively frequent), but passive 
flight isn't of much use 
for evading predators or chasing prey on the ground. 

Hence why I don't think that avian-style flight necessarily went through a 
gliding phase. Most 
modern gliders are primarily arborial creatures which spend as little time on 
the ground as 
possible, and tend to use their gliding abilities to move between trees. Even 
the earliest birds 
however still retained significant terrestrial abilities - and many lineages 
still do, which makes 
losing flight to become entirely terrestrial much easier for birds than it is 
for bats (and probably 
pterosaurs).

If the question is 'ground up' or 'trees down' in the origins of avian flight, 
then my answer would 
be; 'yes'. :)

-- 
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Dann Pigdon
GIS / Archaeologist              http://geo_cities.com/dannsdinosaurs
Melbourne, Australia             http://heretichides.soffiles.com
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