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Re: Catch-22



On 11/24/2011 7:23 AM, K Kripchak wrote:

If the answer is yes; what were those traits that allowed them to
climb into the trees?

Primarily claws, especially on the fore-limbs, and small size (arbitrary number = < 1kg) -- long toes, too.

As climbing down is actually more difficult than climbing up, and typically involves a long jump, or series of jumps, in vertical-climbers like cats -- feathers that serve to slow descent velocities when jumping out of trees are also useful, even when not yet incorporated into wings.

Which reminds me -- has anyone seen video of a juvenile hoatzin *descending*? Can't find a thing online...

Further --

As to why would they climb -- only food acquisition (foraging) and refuge come to mind.

Barring special cases like date palms, efficient foraging in a tree (even herbivory) requires movement through the entire tree, and even from tree-to-tree -- and negotiating/exploiting smaller flexible (and smooth) branches requires grasping ability that can be readily seen in the bones.

So arboreal foraging can be ruled out as a primary lifestyle in Archie-type animals.

Avoiding the negativity that accrues to those who "hide under the shrubbery" (e.g., ants, mites, and predators) by using a suitable tree as a sleeping place/refuge does not require grasping ability, "mammalian flexibility" or anything other than minimal climbing ability -- and suitable trees abound in most environments.

Therefore, however annoying it may be -- there are no selective pressures to further specialize the pes in vertically-climbing animals that merely roost in trees and forage/display/nest on the ground -- contra intuitive "evolutionary" arguments that roosting "is a locomotor activity" that inevitably results in a reversed hallux, even in the face of daily selective events that conserve the optimized cursorial foot.

Hence the lifestyle leaves little or no evidence in the bones of cursorial animals beyond an apparent ability to climb (or fly).

Ground foraging tree-roosting (GFTR) animals are not to my knowledge traditionally or appropriately classified as arboreal, contra the posts implying that they are. Indeed, the American Wild Turkey cannot even be said to be scansorial, as they have no climbing adaptations whatsoever, and in fact cannot climb.

Unlike Archie and his ilk -- at least on that we have consensus. Archie could climb well enough to roost.