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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 (davidpeters@att.net) 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 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. 

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, climbing, walking.

<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 in behavior.

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 mammals.

Red herring.

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.

Red herring.

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.



  Cheers,

  Jaime A. Headden




David Peters
davidpeters@att.net