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re: origin of bats/reply 2 to TMK
David Peters (firstname.lastname@example.org) wrote:
<Granted, certain tetrapods only need hind feet to climb (woodpeckers, etc.),
but mammals, especially Paleocene ones, would have a tough time doing the same.
So the question is, if bats were climbing using all fours, why and how would
the change to using only the thumbs and folding the other fingers under
actually work? IMHO there has to be an intermediate stage because if something
is working right (climbing hands) they donât change without intervention.>
Of course, there is always an intermediate stage. There are several
possibilities, in fact, including synchronous development of elongated fingers
and the folding mechanism, step-wise development of elongated fingers then
wing-folding, or the reverse. When climbing, the primary climbing finger can be
engaged while the rest are not, allowing them to open while attached to the
branch, which can enable lateral jumping, rotation, and flight directly
backwards from the starting (launching) position. This would be a constraint on
developing a finger/feet-only climbing style. And could develop from a
hands/feet-only climbing style.
<If you look at Ptilocercus and Nandinia, both are quadrupedal climbers, but
both hold their prey with their hands. Both enjoy inverted locomotion. Nandinia
likes to jump out of trees. Ptilocercus has a fairly naked tail. Not much, but
itâs a start.>
It is my humble opinion that you're reading too much into this argument.
There are 1) convergences in anatomy, and 2) convergences in behavior. Some
anatomical features arise from behavior, and some behaviors arise from
anatomical features. Birds lack hands, but in those with the ability to engage
other objects with their forelimbs, they might be considered to "hold things
with their hands". Hoatzins certainly hold branches this way. But they are, of
course, not mammals.
But, lets look at something else. Sloths. They enjoy a suspensory behavior.
They move fairly slowly, they climb using only a few fingers, and they have
adaptations such as reduction of the distal forelimb, torsion of the distal
hindlimb around the long axis, and fusion of the carpals. Highly derived taxa.
They also have reduced dentition, reduced mesial dentition, and often reduced
or absent premaxillae, as in bats. The anteriormost teeth are replaced forward
of the massing mesialmost teeth, and become the "first" teeth. Also as in bats.
They are eutherians, as are bats, so there's no problem comparing them to, say,
wierd-toothed animals like multituberculates. Sloths also can hang by only
their legs and use their arms to manipulate objects, as can tree anteaters
*Cyclopes*, and seem fairly comfortable doing so.
So. Are sloths very closely related to bats? The grand majority of their
physiology, biology, and evolutionary morphology tells us that, rather, NO,
they are dwarf forms of larger animals that developed from a distinct group
that did not, in fact possess much of these adaptations. The reason, it seems,
is that in adapting to an arboreal life, such as branch hanging, reduction of
dentition, enlargement of eyes and broadening of the skull, carpal fusion,
etc., are required for such a life.
I'm surprised no one has even mentioned fossa, with prehensile tails,
prehensile thumbs and a habit of carrying things. Procyonids are similarly
The fact is, certain environments provide dissimilar animals with pathways of
convergence, and arguing convergence is genetic relatedness is patently weak.
It needs to be supported, oddly enough, by the features they share that are NOT
related to their common life-style. This needs to be the priority, a-one line
of reasoning and study.
Jaime A. Headden