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Re: Catch-22

David Marjanovic <david.marjanovic@gmx.at> wrote:

> ...and the very long legs with very long metatarsi and insanely long shins
> of *Microraptor*. *Archaeopteryx* isn't that extreme, but still has very
> long legs for the standards of climbing birds.

Long metatarsi *might* be associated with improved aerodynamic
behavior: these basal paravians also had wings attached to the

> Bears do, however, have plenty of "adaptations" for climbing. It just so
> happens that, in terms of their evolutionary history, they aren't
> adaptations; some are mammalian plesiomorphies (like the fairly short but
> not too short limbs and their wide ranges of movement), others are probably
> exaptations. Many of these character states do not occur in the theropods
> we're talking about.

Yes, this point deserves to be hammered home: impressive limb mobility
is primitive for placentals (and likely marsupials too).

> But, you're right, neither are those of a hoatzin chick. Point taken.

However... let's not forget that juvenile hoatzins have large, grasping feet.

> Why, then, don't birds look more like *Ptychozoon*?

Because basal paravians were predominantly terrestrial bipeds?  This
doesn't appear to have changed until pygostylian birds came along.

> The babies never descend, except accidentally or to flee. In both cases,
> they simply drop uncontrolled into the river under the nest.
> The adults fly... and they don't climb much, do they?

Adults hoatzins fly poorly, but they do fly.  They have no need to
climb.  Adult hoatzins are rather sedentary birds: they spend most of
their time eating (leaves, fruit, flowers) and digesting.

BTW, a small request to David M.: Could you include the name of the
person whose message you're actually responding to?  Otherwise, it's a
little confusing - especially when you're responding to more than one
person in the body of your own message.