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




Don Ohmes wrote:


>> There is a swathe of empty morphospace available to gliders
>> who want to engage in occasional flapping. This
>> ecomorphology would put them outside the vast morphospace
>> currently occupied by flying vertebrates (birds and bats).
>
> Yes, but there is nothing to eat there now, which is why it is empty...


Isn't this contradicted by your next statement...


> I am guessing the level of competition was very important; ie, lots of fat, 
> slow bugs, and nobody faster or better positioned than _Onychonycteris_ (and 
> presumed ancestors/kin) to eat them.
>
> My personal best-guess cartoon re bat evolution has lack of competition in 
> the field of nocturnal insect-catching as a key plot element. I have been 
> places 
> where flying insect populations are large enough that one is bound to 
> encounter a few on any straight-line tree-to-tree excursion. Makes a good 
> base-line for 
> step-wise evolution...


If the areas between modern trees are literally buzzing with insects, why isn't 
this niche ripe for exploitation by an incipiently flapping, gliding 
insect-eater?


As for our ancient batty friend _Onychonycteris_... lack of echolocation might 
have made aerial hawking difficult at night.  Because _Onychonycteris_ seems to 
have been insectivorous, it may have obtained insect prey mostly by gleaning.  


> Quite correct. Acquiring prey by gliding simply isn't going to work when 
> birds are around, but commuting is always an open option if you have a job to 
> go to...


Again, an apparent contradiction.  If obligatory biped Don Ohmes can encounter 
flying insect populations in his tree-to-tree excursions (presumably 
terrestrial) - why are these same hordes of insects beyond the reach of a 
modern aerial glider?


> Also, the debate IS a dichotomy in the sense that you HAVE to start 
> somewhere. Once the ball is rolling, the dichotomy disappears, but that first 
> step is is a 
> booger...


Yes; but the "first step" is not dictated by relative ease.  Natural selection 
can only act on what's already available.  The decision about which side of 
this (alleged) dichotomy is more likely to have occurred - "ground-up" or 
"trees-down" - should be based on the ecomorphologies of those taxa closest to 
the origin of flight.  So *a priori* assumptions about which pathway is 
"easier" are utterly irrelevant, because natural selection does not have the 
luxury of making such choices.  Even if I were to concede (which I won't) that 
"trees-down" is "easier", it cuts no ice with natural selection.  As long as 
"ground-up" (or at least some kind of cursorial/terrestrial contribution to the 
origin of flight) is biophysically/biomechanically possible, there's no reason 
why it can be considered less likely than "trees-down".  


In other words, it makes no difference if gliding is "easier" than leaping 
upwards to catch insects, if the former behavior never existed in the ancestors 
of birds.  Something lead to flight, and I don't think that preconceived ideas 
of what these theropods *should* have been doing (because it's less 
biomechanically or biophysically challenging) are relevant.


Cheers

Tim



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