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Member (Idle past 1427 days) Posts: 20714 From: the other end of the sidewalk Joined: |
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Author | Topic: How do you evolve a BAT? | |||||||||||||||||||||||
RAZD Member (Idle past 1427 days) Posts: 20714 From: the other end of the sidewalk Joined: |
This is meant to be a little light-hearted, not strictly scientific (so "Is it science" is probably the best forum):
How do you evolve a BAT? First a brief history: The (currently) oldest known bat is this guy ... the 54 million year old "new" bat fossil: Which we can compare to this modern bat skeleton: And we can note certain differences (longer tail, claws on all hand fingers) and certain similarities (long finger bones, shorter hind legs that forelegs). The current thinking on bat evolution can be summarized by these two articles: (1) http://www.si.edu/Encyclopedia_SI/nmnh/batfacts.htm
quote: (2) Insectivore-like mammals, Tiny teeth and their enigmatic ownersquote: Thus we will set a starting point for our game of evolving a bat with a shrew-like animal living when the Yucatan Meteor kindly removed large predatory dinosaurs from the paths of evolution. But what is shrew-like? This is a modern tree shrew:It just finished eating an insect that it caught and held between its front paws (similar behavior to squirrels and racoons). This is a modern diving water shrew:
FIGURE 3. A diving American water shrew (Sorex palustris) (From: "Olfaction: Underwater 'sniffing' by semi-aquatic mammals" by Kenneth C. Catania, Nature 444, 1024-1025(21 December 2006), doi:10.1038/4441024a) quote: Flight evolution in birds and the "WAIR" theory: Wing-Assisted Incline Running and the Evolution of Flight - curiously the wing beating pattern is different in juvenile birds than in flying adults:
quote: That would be a transitional behavior between running and flying, one with a clear survival advantage, as well as one that is observed in existing birds as they develop from down covered arms to fully feathered wings. Curiously this behavior does not include trying to glide on the developing wings. Such flapping while falling to control descent is seen in many young birds, Wood Ducks would be an example many could be familiar with. Now the fun part begins: Stipulations: (1) Why does the bat hang up-side-down: how did this evolve and why would it be beneficial? Did this behavior evolve before flight? (2) How does the webbing between the fingers evolve? We do NOT see this formation in flying squirrels and sugargliders, probably because it interferes with other necessary use of front paws for climbing. (3) If you start with an aquatic shrew to get webbing, how do you get back in the tree and hang up-side-down, and why do you lose the rear feet webbing? (4) How does wing flapping evolve if you start with gliding? Conversly how are you going to have WAIR behavior in tree shrew? Let the games begin. Enjoy. Edited by RAZD, : moved pictures by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •
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Blue Jay Member (Idle past 2720 days) Posts: 2843 From: You couldn't pronounce it with your mouthparts Joined: |
Hi, RAZD.
I'm not a bat man ( ), but the evolution of flight is always an interesting topic, so I'll give it a little whirl.
RAZD writes: (1) Why does the bat hang up-side-down: how did this evolve and why would it be beneficial? Did this behavior evolve before flight? I'm going to go out on a limb and say upside-down hanging evolved after flight. Since bats don't have the bipedal posture to stand upright like birds, they adapted to hang. Spiders routinely hang upside from their webs, which (at least in the spiders) doesn’t require muscle tension (because they hang by their hook-like claws, I think). With the bat, it obviously requires some sort of tension in the digits, but I don’t know much about that.
RAZD writes: (2) How does the webbing between the fingers evolve? We do NOT see this formation in flying squirrels and sugargliders, probably because it interferes with other necessary use of front paws for climbing. I don’t think I have a good answer for this one. Bats do still have an unwebbed thumb, but I think that’s mostly used for climbing (probably testifying to bat ecology before flight, I would think).
RAZD writes: (3) If you start with an aquatic shrew to get webbing, how do you get back in the tree and hang up-side-down, and why do you lose the rear feet webbing? I can personally only envision the process happening in a "trees-down" direction, simply because it's ecologically the more parsimonious. Further, I think webbing is just a natural artifact of vertebrate skin stretched over bone, so I would guess that webbing could evolve in practically any vertebrate lineage that has retained long digits. Have you heard of a colugo? They are related to primates, and have the most extensive patagium of all gliding mammals (here is a really cool picture of one in flight). Their fingers are also webbed, like bats’. I think bats could have started out like a colugo, and gradually extended all or some of their fingers to improve their flight control, and eventually settled on keeping only the thumb for climbing and using the rest for flying, especially after they learned how to catch prey on the wing.
RAZD writes: (4) How does wing flapping evolve if you start with gliding? Conversly how are you going to have WAIR behavior in tree shrew? I'm going to reject WAIR in the bat’s case, simply because the bipedally cursorial adaptations of theropod dinosaurs and birds don't seem to be present in either shrews or bats. The flapping mechanism in bats isn’t all that spectacular or complex: it’s just an enlargement of the muscles and bone structures that all mammals have, except that the shoulder blades are more free to move (or something like that; it’s been awhile since I took Comparative Physiology). I could see that adaptation coming from a gliding mammal just flailing to reach a couple inches further. Edited by Bluejay, : Repeated line. Edited by Bluejay, : Fix dBCode error from a frickin' long time ago. -Bluejay/Mantis/Thylacosmilus Darwin loves you.
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RAZD Member (Idle past 1427 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Hey Bluejay,
I'm not a bat man ... Well, here we're just taming the shrew ...
Have you heard of a colugo? They are related to primates, and have the most extensive patagium of all gliding mammals (here is a really cool picture of one in flight). Their fingers are also webbed, like bats’. Nice picture. Colugo - Wikipedia
quote: So they share a common ancestor with tree shrews (and bats) ... but are herbivores instead of insectivores. Interesting.
Spiders routinely hang upside from their webs, which (at least in the spiders) doesn’t require muscle tension (because they hang by their hook-like claws, I think). With the bat, it obviously requires some sort of tension in the digits, but I don’t know much about that. Actually the claws at rest allow them to hang. I would go with the hanging first hypothesis, as being able to hang on to the tree would allow the shrew greater reach to grab insects from the air, as would the development of longer fingers, and webbing would add to the net effect.
I'm going to reject WAIR in the bat’s case, simply because the bipedally cursorial adaptations of theropod dinosaurs and birds don't seem to be present in either shrews or bats. Agreed that the running bit is out, however I think there may be something to the young birds furious waving of the arms to partially control descent that could apply to an animal with a webbed hand. Curiously, Wallace's Frogs don't seem to flap when they glide from tree to tree, so that doesn't necessarily develop.
The flapping mechanism in bats isn’t all that spectacular or complex: it’s just an enlargement of the muscles and bone structures that all mammals have, except that the shoulder blades are more free to move (or something like that; it’s been awhile since I took Comparative Physiology). I could see that adaptation coming from a gliding mammal just flailing to reach a couple inches further. Or perhaps trying to grab that insect out of the air while anchored to the branches, possibly up-side-down.
I think bats could have started out like a colugo, and gradually extended all or some of their fingers to improve their flight control, and eventually settled on keeping only the thumb for climbing and using the rest for flying, especially after they learned how to catch prey on the wing. I think that extensive wing aft would make flapping unproductive. One distinctive difference is that gliding seems to be limited to escape behavior - getting away from predators on one tree by gliding to another. Flight, on the other hand, could be an adaptation for predatory behavior. Enjoy, by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •
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RAZD Member (Idle past 1427 days) Posts: 20714 From: the other end of the sidewalk Joined: |
This is from the Nature article:
Abstract: Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocationNature 451, 818-821 (14 February 2008) doi:10.1038/nature06549; quote:bold color for emPHAsis. So we have a bat ancestor that is capable of quadrapedal locomotion as well as tree climbing ability, and the flight pattern is not fully developed. Here is a picture from the actual article:
Notice that the fossil is intermediate in characteristics between non-flying mammals (in general) and bats (in general), ie it is transitional by Darwin's definition. Curiously genetics is now showing bats are not necessarily descended from NyctitheriidaeBat - Wikipedia quote: Looks like another round of scientific revision is in order due to new evidence ... Modern bats have evolved since the first fossils known of bat ancestors, and when older bats are found we will know more about bat evolution - until then we can make some educated hypothesis, but that is all they are. Was there a common ancestry between sloths and bats? Or is branch hanging a just a similar behavior? Time will tell. Enjoy. Edited by RAZD, : picture by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • • |
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RAZD Member (Idle past 1427 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Hey bluejay,
They are related to primates, and have the most extensive patagium of all gliding mammals (here is a really cool picture of one in flight). Found another picture of a colugo
Now why would a gliding animal hang upside-down from a branch? It's enough to drive you batty ... Enjoy. Edited by RAZD, : photo by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •
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Blue Jay Member (Idle past 2720 days) Posts: 2843 From: You couldn't pronounce it with your mouthparts Joined: |
Hi, RAZD.
RAZD writes: Now why would a gliding animal hang upside-down from a branch? Awesome: I didn't even think about that.
ToL puts bats and colugos as sister groups, so you could be right about the "hanging-first" model. But, much of the genetic data is returning the four-way Eutherian split (Xenarthra, Laurasiatheria, Afrotheria, Euarchontoglires), which puts bats in Laurasiatheira as the relatives of Perissodactyla and the Carnivora/Pholidota, and colugos and sister to Primates within the Euarchontoglires. If this split is correct, your hanging observation may not be relevant. Edited by Bluejay, : Very bad wording. -Bluejay/Mantis/Thylacosmilus Darwin loves you.
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RAZD Member (Idle past 1427 days) Posts: 20714 From: the other end of the sidewalk Joined: |
If this split is correct, your hanging observation may not be relevant. Yet the behavior could evolve repeatedly, it could help keep the folds of skin out of the way for climbing around, and as seen above, it forms a nice cozy pouch for young. From wiki
quote: Enjoy by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •
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Blue Jay Member (Idle past 2720 days) Posts: 2843 From: You couldn't pronounce it with your mouthparts Joined: |
Hi, RAZD.
RAZD writes: Yet the behavior could evolve repeatedly... Okay, so you weren't arguing common ancestry: you were just arguing for proof-of-concept. I gotcha. -Bluejay/Mantis/Thylacosmilus Darwin loves you.
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