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Re: Catch-22

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


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

Because you can't climb with forelimbs alone.

The hands weren't very flexible either...

>> 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.

I wouldn't say that pachyosteosclerosis* is not such a "minimal" adaptation. But more importantly, it's a _sufficient_ adaptation to keep an animal from bobbing up like a cork. Climbing, if you start from a theropod, requires more modifications. Importantly, this doesn't change if the only reason to climb a tree is to sleep in it.

* Osteosclerosis = decreased osteoclast activity leading to more massive bones with little or no marrow cavity or spongiosa. Pachyostosis = increased deposition of periosteal bone making the bones look inflated. These usually occur together (in not too small animals), but not always.

> 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.

I don't think we can take wing, leg or tail feathers as evidence for any degree of arboreality. They may all have evolved for brooding and display.