Re: Catch-22

[K Kripchak <saurierlagen1978@gmail.com>]

Don, Anthony, Tim,

Thanks for responding and sorry it took so long to reply. Life interfered.

Anyway, Don and Tim... I get what both of you are saying, and
appreciate the responses. Yes, of course, I know this is a very
complicated issue, hence the reason why the topic is often revisited,
but no concrete conclusions are ever nailed down. Part of the reason
for this, I believe, is that discussions always seem to turn to the
feet.

So, maybe I should beat the dead horse with this question:

What about the forelimbs? Why is so much attention focused on the
feet, and the hands almost completely ignored?

Kris


On Fri, Nov 25, 2011 at 1:05 AM, Tim Williams <tijawi@gmail.com> wrote:
> K Kripchak <saurierlagen1978@gmail.com> wrote:
>
>> The chatter in the recent “11th Specimen of Archaeopteryx” discussions
>> concerning capabilities and traits (or lack thereof) for climbing (NOT
>> “perching”) in theropods/basal birds reminded me that there is still
>> an 800-lb gorilla in the room wearing a pink t-shirt that is one size
>> too small with "Catch-22" scrawled across it in Air Force Blue...
>> There’s an obvious question that still hasn't received good,
>> convincing, direct answers...
>
>
> I'm so sorry about that.  We really try and do our best here.
>
>
>> Were theropods/basal birds up in the trees BEFORE they possessed the
>> MODERN traits we currently use to define a bird as being arboreal?
>
>
> Undoubtedly.
>
>
>> If the answer is yes; what were those traits that allowed them to
>> climb into the trees?
>>
>> If the answer is no; WHY did selection favor characteristics for an
>> arboreal lifestyle when theropods/basal birds were cursorial?
>
>
> That's just it: the question you raised doesn't appear to have a
> simple yes/no answer.  If it did, this thread would have ended a long
> time ago (to the relief of many, I don't doubt).  There are some
> characters pertaining to the pes of taxa such as _Microraptor_ and
> _Archaeopteryx_ that *might* have been involved in scansorial or
> arboreal behavior.  Characters like a lower hallux, and elongated
> penultimate phalanges, for example.  But these characters might
> equally have been the product of allometry, or involved in predation.
> If so, they still might qualify as incipient arboreal characters, if
> they were the raw material upon which more derived taxa (which were
> presumably volant) constructed a specialized arboreal pes.
>
>
>> Whales, before getting wet, didn't just decide to lose their hind
>> limbs, sprout flukes, and head for the sea, right?
>
>
> Right.  IMHO stem-cetaceans provide a good analogy, because raoellids
> and pakicetids have both been interpreted as terrestrial quadrupeds
> that headed to water only occasionally, such as a refuge, or to feed
> on fish.  Raoellids and pakicetids show minimal adaptations to an
> amphibious/aquatic lifestyle.  The limb bones of both groups are
> pachyostotic ('osteosclerotic'), a trait that has been tied to
> increased submersion by these animals, with the heavier bones
> providing ballast.  In all other respects, the postcranial skeletons
> of these stem-cetaceans are thoroughly terrestrial and cursorial.
>
>
> To return to theropods, it is possible that the ambiguous scansorial
> characters seen in the pes are indeed nascent arboreal characters in
> otherwise dedicated  terrestrial/cursorial animals.  I tend to think
> so.  But I admit that this assertion comes from viewing these
> characters through the prism of what came after.  Arboreality had to
> start somewhere, and the elaborate plumage suggests to me that the
> paravian integument had a big headstart on the osteology.
>
>
>
>
>
> Cheers
>
> Tim
>
>
>
>>
>> Kris
>>
>>
>> PS: Bit of trivia for you literary types/WWII buffs... Anyone catch
>> the reason for the "Air Force Blue" reference? ;-)
>>