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Re: origin of bats/reply 2 to TMK
On Jun 20, 2008, at 4:51 PM, Jaime A. Headden wrote:
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 don’t change without
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.
Can bats open their wing while clinging with their thumbs? I don't know.
Just hazarding a guess based on pterosaurs and birds: 1) bipedal
configuration, fingers get smaller – or maybe not in the case of
bats which probably remained inverted and arboreal throughout
(Sharovipteryx, Coelophysis); 2) fingers get longer, folding
mechanism added (unnamed fenestrasaur, Velociraptor), 3) fingers (or
fingers + feathers) get much longer (eudimorphodontids,
Archaeopteryx) and become volant, no longer used for grasping,
<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 it’s 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
Of course, Drs. Martin and Feduccia, but added to the suite of
morphological characters, these add evidence to the case.
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
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.
Probably not homologous. Think "suite of characters."
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 remarkable.
Worthy of a test? Go for it.
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, I'm just giving you the cherries on top. There's so much more
in the dataset.
Jaime A. Headden