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Re: Greg Paul is right (again); or "Archie's not a birdy"



Dann Pigdon <dannj@alphalink.com.au> wrote:

> The earliest bat fossils appear to be insectivores though. Perhaps when 
> predators develop flight,
> they jump straight to active flight and forgo a passive gliding phase? Or at 
> the very least, any
> passive gliding stage might be shortened (geologically speaking) by intense 
> selective pressure to
> retain the ability to persue prey (which I would imagine parachuting 
> membranes would hinder
> greatly).


Based on the inferred insectivorous habits of basal chiropterans, it's
been proposed that early fossil bats were perch-hunters that preyed
upon insects found in trees (gleaning) rather than capturing aerial
insects on the wing (hawking).  So, as with the inception of gliding
in arboreal herbivorous mammals, aerial locomotion in proto-bats might
have been directed at improved foraging over a large area rather than
aerial hunting, which required echolocation.  If the diet was rich
enough in protein and energy (as a diet in insects would tend to be,
if you eat enough of them), it could facilitate the shift to powered
flight.


> It might explain why the earliest pterosaur and bat fossils already seem to
> have 'advanced' flight adaptations.


Yes.  Another explanation (not mutually exclusive) is that the wing
developed very rapidly.  The extreme elongation of the fingers could
have occurred as a result of very few changes along a single
developmental pathway (see work by Karen Sears &c).


Don Ohmes <d_ohmes@yahoo.com> wrote:

> Is it known that bats went through no gliding phase?


Based on the shape of the wings of the basal chiropteran
_Onychonycteris_, Simmons et al. (2008) suggest that it had an
undulating flight style in which fluttering alternated with gliding,
and, therefore that _Onychonycteris_ represents a transitional stage
between gliding and continuous flapping.  So on this basis, bats (or
rather their ancestors) passed through a gliding stage.


> If bats did go through a gliding phase, then that could be rephrased as:
> 'the mammals that never made it past gliding are exclusively herbivores'. :D


That's an interesting point.  Flight is more energetically demanding
than gliding.  Although fruit bats are herbivores, their diet is
energy-rich (fruit, nectar).  The evolution of gliding in modern
gliding mammals has been associated with low-quality herbivorous diets
including leaves and plant exudates  - although fruit, nectar and
other higher-energy foods can also be sampled.  Commuting rapidly
between trees allows for more time an animal can spend foraging.





Cheers

Tim