[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: "Flight theory has legs"

Graydon (oak@uniserve.com) wrote:

<All of which is very *pedal*, though; those locomotor modes are
extensions of flat surface locomotion.>

  As in chameleons, fully quadrupedal. Their ancestors, as indicated by
agamids and other iguanians, are sprawling-climbers. A similar functional
consideration is given to the prolacterifom? *Megalancosaurus* (Renesto,
1994, 1999), with a nearly veritcal leg stance despite having an ankle and
wrist indicating ancestry with sprawlers [based on some in prep work].

<I think they're plausible as slow climbing postures, but implausible as a
typical locomotor posture because they involve a very limited range of the
available range of motion in the limbs.>

  I cannot see how speed is relevant here. Locomotion is locomotion. the
two- and three-toed sloths are "lethargic" animals that are nonetheless
very functional and capable in their environment, and even slower on a
tree trunk or the ground; their ancestors were graviportal

<Something that did that a lot would have different limbs.>

  Would you care to elaborate on these features? That a quadrupedal,
long-clawed, grapsing animal has not been found does not mean that it is
not possible to be found at Liaoning from known fossil material. Many Old
World monkeys and several New World ones, as well as lemuriforms, have
limb organizations similar to those posted at various times on this list.
Other climber-walkers with functional grasping/locomotory adaptations in
the limbs include the jungle cats, esp. jaguars, renowed for their prowess
in the lower canopy and on the ground.

<You did, but you're talking about manual ungual substrate contact; there
isn't any difference other than stress load between walking up a tree
trunk and walking on the ground.>

  Actually, considering the functional adaptations in the phalanges of
many primates and birds, as in work from Yoder, scansorial primates,
analyses of the scansorial *Eomaia*, etc., the best data is not in the
claw but the praeungual hand. Opposing digits, elongate penultimate
phalanges, curved penultimate phalanges, on occassion and rather telling
the presence of an extensor and/or flexor tubercle on the dorsal/ventral
phalangeal margins (respectively), occur in scansorial birds, primates,
sciuromorphan rodents, and *Eomaia*, along with some other reptiles that
have other features relating to an arboreal life style. In climbing
animals, the claws are either strongly curved, or at the expense of this
the phalanx is bowed. There are other considerations. One of my functional
perspectives on flight origin tends to involve the features relating to a
climbing function, and I've talked on this off and on over the last three
years or so.

<We can, too, but we have very different shoulder anatomy with lots of
brachiating ancestors in it.>

  We have a rotatable scapula, a free strut-like clavicular struture, a
condylar proximal humerus with a free glenoid margin. Hotzin chicks, in
spite of lacking these features, do just fine.


Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

Do you Yahoo!?
SBC Yahoo! DSL - Now only $29.95 per month!