How many times have animals evolved flight?

[Argus Skyhawk]

How many times has evolution produced animals that could fly? I can think of four times myself: insects, birds, bats, and pterosaurs. Also, I can think of two gliding animals, that could transition into genuine flying ones, given a few million more years: flying fish and flying squirrels. Any other examples?

Interesting that everyone flies using the two-wings method; no one has evolved propellers or anything else.

 

[PlixTixiplik]

Those are the four groups and it seems most likely that flight evolved only a single time in each group. Flight may have been lost and reacquired in those lineages but it seems that all insects, birds, etc. descend from a single flying ancestor.

The reason that animals use wings and not propellers is similar to the reason why no animal has evolved wheels. Given the constraints of animal body plans, rotational structures are not possible because blood vessels, nerves, and so forth would twist and break (there are examples from single-celled creatures). Well, it's probably not impossible, as you could envisage ways it could happen - so suffice it to say that it's extremely difficult. Organismal evolution is constrained by the morphology of their ancestors, as they (usually) have to co-opt existing structures for new functions, so evolution of flight isn't a blank slate to find the most optimal method. It's not clear to me that propellers have substantial benefits over flapping wings anyway. The wikipedia article summarizes some of the problems with rotational locomotion in living systems.

Incidentally, flight doesn't just use two wings. Insects originally evolved to fly with four wings, like dragonflies and mayflies (the two most primitive living insect orders), and then reduced to two in more derived groups like beetles (forewings evolved into elytra, the hard beetle shell), bugs (forewings evolved into a hemelytra, also a hard shell) grasshoppers, cockroaches, or earwings (forewings evolved into stiff tegmen covering hindwings), and flies (hindwings evolved into small projections called halteres for sensing orientation).

 

[Asbo Zaprudder]

There was a theory "flying" around 20 years ago (based on examinations of various brain structures) that megabats (flying foxes) are a sister group to the primates, and so had evolved flight independently of the echolocating microbats. DNA sequencing knocked the theory on its head, and it turns out that megabats are a suborder of chiroptera after all. Pity, but there you go.

 

[scotpens]

It's interesting that aerostatic or lighter-than-air flight has never occurred naturally. Could a species evolve a biochemical process for producing sufficient quantities of a lighter-than-air gas -- hydrogen, methane, or ammonia -- to fill a large external bladder and keep the creature aloft? Such a “natural blimp” doesn't exist on Earth, but might have evolved on some other planet.

http://traveller.wikia.com/wiki/Luugiir

 

[Asbo Zaprudder]

It's interesting that aerostatic or lighter-than-air flight has never occurred naturally. Could a species evolve a biochemical process for producing sufficient quantities of a lighter-than-air gas -- hydrogen, methane, or ammonia -- to fill a large external bladder and keep the creature aloft? Such a “natural blimp” doesn't exist on Earth, but might have evolved on some other planet.

I remember a very tongue-in-cheek article from OMNI magazine back in '79 or so that proposed that dragons really existed -- based on their prevalence in many cultural traditions. They were basically floating gas bags with wings. The hydrogen was a product of reactions with the hydrochloric acid in their stomachs. Reactions with exectly what, I don't recall. Presumably, they weren't going around chomping on zinc bath tubs. All the fire breathing was due to expelled hydrogen being ignited in air in the presence of a catalyst. The reason that we don't see any dragon remains is that they imitated the fate of the Hindenburg in death.

 

[PlixTixiplik]

Although it should be feasible, with the help of symbiotic microbes, to generate hydrogen or methane, there are two limitations to blimp-style flight: generating enough lift to support a body, and a lack of maneuverability. A student asked me if a bird would float if you filled its lungs with helium (I had talked about the extensive air sac system during my bird evolution lecture) so I did some back-of-the-envelope calculations. Even though birds can be about 20% air sac (by volume), you would actually need a volume of helium 2500 times larger to lift the bird. This problem wouldn't be as difficult for an invertebrate, which would have a lower density, and there are some spiders (and some insects) that balloon on updrafts using a web (not gas-filled). But they can only do that because they are so small that the air acts as a viscous fluid.

A bigger issue would be maneuverability and the ability to avoid flying predators. Blimps aren't renowned for their flight performance and any blimp-animal would be easy pickings for a predator.

 

[Asbo Zaprudder]

Small spiders and caterpillars can paraglide using a length of silk to catch the wind.

http://news.bbc.co.uk/1/hi/sci/tech/5174012.stm

There is also the Australian "flying spider", which is reputed to be able to use flaps on its abdomen to extend its leap by gliding. However, other sources claim that the flaps are only used for mating displays, and that the reports of them being used for gliding are an urban myth.

 

[ThankQ]

What about the bacterial flagellum? Of course it's no good for Behe's IC argument, but if I recall my Panda Trial reading correctly, that does work as a fully rotating propeller.

 

[scotpens]

What about the bacterial flagellum? Of course it's no good for Behe's IC argument, but if I recall my Panda Trial reading correctly, that does work as a fully rotating propeller.

On a monocellular level. Rotating wheel-like structures can't exist in more complex organisms for reasons already stated upthread.

 

[YellowSubmarine]

Those are the four groups and it seems most likely that flight evolved only a single time in each group. Flight may have been lost and reacquired in those lineages but it seems that all insects, birds, etc. descend from a single flying ancestor.

I find this unlikely. The insect wings share almost nothing in common with the rest of the animals.

The wings on the pterosaurs, bats and birds all come from a common trait. But that common trait are their extremities. The actual wings are a variation of their extremities. The wings of the birds and the wings of the pterosaurs differ a lot, so I'd assume that the actual wings developed independently. The bat, the pterosaur and the flying squirrel wings might have common genetic origin to some extend, but that doesn't mean that they didn't develop independently.

On a monocellular level. Rotating wheel-like structures can't exist in more complex organisms for reasons already stated upthread.

I believe that it's more appropriate to say that they can exist, but the evolutionary development of such is unlikely. However, if the universe is swarmed with life, maybe on some planet somewhere some species did develop them.

 

[PlixTixiplik]

Those are the four groups and it seems most likely that flight evolved only a single time in each group. Flight may have been lost and reacquired in those lineages but it seems that all insects, birds, etc. descend from a single flying ancestor.

I find this unlikely. The insect wings share almost nothing in common with the rest of the animals.

The wings on the pterosaurs, bats and birds all come from a common trait. But that common trait are their extremities. The actual wings are a variation of their extremities. The wings of the birds and the wings of the pterosaurs differ a lot, so I'd assume that the actual wings developed independently. The bat, the pterosaur and the flying squirrel wings might have common genetic origin to some extend, but that doesn't mean that they didn't develop independently.

On a monocellular level. Rotating wheel-like structures can't exist in more complex organisms for reasons already stated upthread.

I believe that it's more appropriate to say that they can exist, but the evolutionary development of such is unlikely. However, if the universe is swarmed with life, maybe on some planet somewhere some species did develop them.

I think you misunderstood what I was saying - I said that each of the four flying groups seems to have evolved from a single common ancestor within that group. As I said, the evidence suggests that flight evolved four times, once in each of the four groups (i.e., birds, pterygote insects, pterosaurs, and bats are all monophyletic groups that evolved from a single ancestor that took to the air). Although their wings are homologous structures, pterosaurs, birds, and bats certainly evolved flight independently from one another.

 

[YellowSubmarine]

Oh, I misread.

Anyway, that's pretty awesome, because this can be used as evidence that where complex extraterrestrial life exists there are likely flying animals, and maybe some of them are sentient and advanced. Think about it.

 

[scotpens]

The wings on the pterosaurs, bats and birds all come from a common trait. But that common trait are their extremities. The actual wings are a variation of their extremities. The wings of the birds and the wings of the pterosaurs differ a lot, so I'd assume that the actual wings developed independently. The bat, the pterosaur and the flying squirrel wings might have common genetic origin to some extend, but that doesn't mean that they didn't develop independently.

Flying squirrels don't have skeletal wings. They have a fold or flap of loose skin between the forelimbs and hind limbs on each side, which, when the limbs are outstretched, forms a kind of paraglider or semi-airfoil. They can glide for short distances but are incapable of true flight.

Here's the skeletal anatomy of the wings of birds, bats and pterosaurs, with a human arm for comparison:

The wing structures of the three flying vertebrate classes are quite different from one another. The three outer bones of the pterosaur wing are actually an elongated fourth finger.

 

[Myasishchev]

Oh, I misread.

Anyway, that's pretty awesome, because this can be used as evidence that where complex extraterrestrial life exists there are likely flying animals, and maybe some of them are sentient and advanced. Think about it.

For the first part, almost definitely.

Of course, there are many birds that are effectively sapient already--African gray parrots, many corvids, bucorvids, and Adam Duritz, just to name a few. On the other hand, it's hard to square the technological manipulation potential that primates have with flight, since all chordate wings are modified arms. You'd need what were essentially sectopods to have alien Warren Worthingtons, and you could make an argument that sectopodalism isn't as advantageous a solution as tetrapodalism. But sapient life evolved from fliers who returned to Earth doesn't strike me as unlikely.

Although it should be feasible, with the help of symbiotic microbes, to generate hydrogen or methane, there are two limitations to blimp-style flight: generating enough lift to support a body, and a lack of maneuverability. A student asked me if a bird would float if you filled its lungs with helium (I had talked about the extensive air sac system during my bird evolution lecture) so I did some back-of-the-envelope calculations. Even though birds can be about 20% air sac (by volume), you would actually need a volume of helium 2500 times larger to lift the bird. This problem wouldn't be as difficult for an invertebrate, which would have a lower density, and there are some spiders (and some insects) that balloon on updrafts using a web (not gas-filled). But they can only do that because they are so small that the air acts as a viscous fluid.

A bigger issue would be maneuverability and the ability to avoid flying predators. Blimps aren't renowned for their flight performance and any blimp-animal would be easy pickings for a predator.

For a heterotroph, I think blimps could be ruled out almost entirely, but I wonder if it would work for a photosynthesizer? After all, plants are easy prey for predators as well, and defenses don't need to incorporate extra weight (toxicity, symbiotic relationship with helper insects, etc., can be used reasonably cheaply).

 

[Owain Taggart]

There's a big theory going around right now due to finds in China during the last 10 years relating to feathered dinosaurs. They found evidence of feathered wings in a dinosaur with 4 wings that's a lot more bird-like than not, and there's a lot of debate about wether it's a link to the evolution of birds. It's not a Pterosaur, and in fact looks more like the fabled Pheonix. It's called the Microraptor. It actually has a bi-plane like flight model. A pretty exciting find in the dinosaur field. I currently work at a science centre (museum) at a dinosaur exhibit that takes a look at the whole feathered dinosaurs and their links to birds.

Nova on PBS had a show about it in 2008, which they just repeated earlier this week. And there will be a 6-part National Geographic mini-series coming up in November touching on the subject.

http://www.pbs.org/wgbh/nova/evolution/four-winged-dinosaur.html

http://www.youtube.com/watch?v=ZC2ebSaaVXg

http://news.nationalgeographic.com/news/2003/01/0121_030122_dromaeosaur.html

 

[Miss Chicken]

A couple of questions

Do flying fish glide rather than fly? If they only glide would they ever be likely to actually develop the ability to fly in the distant future?

 

[Robert Maxwell]

A couple of questions

Do flying fish glide rather than fly? If they only glide would they ever be likely to actually develop the ability to fly in the distant future?

They glide. They use their tails a bit like propellers, using the "wing" fins for actual gliding. I don't think they could ever fly in the sense that birds too--not enough strength in the wing fins to really accommodate that.

 

[FordSVT]

A couple of questions

Do flying fish glide rather than fly? If they only glide would they ever be likely to actually develop the ability to fly in the distant future?

They glide. They use their tails a bit like propellers, using the "wing" fins for actual gliding. I don't think they could ever fly in the sense that birds too--not enough strength in the wing fins to really accommodate that.

.... and as far as "could they in the distant future goes", evolution is rather impossible to predict. Who knows what their descendants might look like in a million years, maybe their fins will be the size of those on manta rays and they'll leap out of the water and glide or fly long distances. Hell, they might not even glide anymore, evolution doesn't always work in the direction you think it will. It does not always "advance" in the way we intuitively think it will.

 

[farmkid]

A couple of questions

Do flying fish glide rather than fly? If they only glide would they ever be likely to actually develop the ability to fly in the distant future?

They glide. They use their tails a bit like propellers, using the "wing" fins for actual gliding. I don't think they could ever fly in the sense that birds too--not enough strength in the wing fins to really accommodate that.

For fish to actually fly would require more adaptation than just stronger "wing" fins. If they were to fly, they would be out of the water for longer periods of time, so flight would also require other adaptations to deal with that, such as lungs, different skin to retain water, etc.

 

[Robert Maxwell]

A couple of questions

Do flying fish glide rather than fly? If they only glide would they ever be likely to actually develop the ability to fly in the distant future?

They glide. They use their tails a bit like propellers, using the "wing" fins for actual gliding. I don't think they could ever fly in the sense that birds too--not enough strength in the wing fins to really accommodate that.

For fish to actually fly would require more adaptation than just stronger "wing" fins. If they were to fly, they would be out of the water for longer periods of time, so flight would also require other adaptations to deal with that, such as lungs, different skin to retain water, etc.

Good point. They would basically cease to be "fish" by any stretch of the imagination.