They just didn’t like change. They kept landlines, too. And they liked country music.
Drawing a line from static cultural artifacts to “cognition” seems tenuous to me.
Representational or symbolic art indicates a huge jump in mental processes; no other species does it in the way that humans do. But maybe you are using the word cognition in some other way than we are.
I have a question regarding this reclassification,
We know that many other dinosaurs had feathers for insulation, so now Archaeopteryx is no longer unique, and it makes sense to question whether a feathered creature from that time is a “bird” or a “dinosaur” (or where it lies on that continuum between them).
But another question is whether it was capable of flight, or at least extended gliding. In many of the cases of feathered dinosaurs, they seem to have been using the feathers as insulation (or identification, or sexual signaling, or something else other than flight), because they seem to have been too heavy and lacking in wing area to be able to get off the ground.
but i think that the archaeopteryx could get off the ground. Not only is it built so that it could, but you have to consider where the fossils come from. The archaeopteryx fossils are from the Solnhofen limestone, which has extrmely fine grain, and which preserved fine details like feathers (which is how we knew about them in the first place). These were formed by the laying down on fine mud underwater. The other Solnhofen fossils are either water-dwelling creatures (jellyfish, crustaceans, crinoids, crocodiles), or else creatures that could fly over the water and fall in (beetles, dragonflies). I always assumed that the archaeopteryx fossils we found were flying or gliding over the water and crashed or died. AFAIK, none of these fossils are of land-dwellers. Granted, it’s possible that this was a tidal flat or something, and that some land-dweller wandered out into it and got stuck. But in that case I’d expect there to be more of such land-dwellers.
This suggests tome that archaeopteryx was at least a flyer or a glider, if not a “true bird”.
http://www.ucmp.berkeley.edu/mesozoic/jurassic/solnhofen.html
What’s the question?
I indicated above that I thought Archaeopteryx was probably capable of flight. Other non-avian dinosaurs like Microraptor may have been capable of flight as well. Neither feathers nor flight seem diagnostic of “birds” as a clade anymore. So whether or not Archaeopteryx could fly is not relevant to its status as a bird.
You go to the species definition war with the artifacts you have, not the artifacts you wish you had. 
Seriously, there is always the chance that absence of evidence is not evidence of absence. But we have to make conclusions based on the evidence we have. It’s quite possible that new fossil sites will yield evidence of Neanderthal representational art, but until then, our best assumption is that there is none. And it’s not like there hasn’t been a lot of looking for any.
But you don’t even need to do that. Take for example the clade of “apes”. We had no problem including humans as one of the apes rather than throwing out the concept, or restricting it to orangutans.
So if we found out that a couple of species of “birds” were really way out in left field and weren’t closely related to the other bird species at all, that doesn’t mean we need to throw out the concept of birds. After all, we didn’t throw out the concept of Mammals when we found some critters on a faraway island who laid eggs and had fur. We included monotremes as Mammals, even though if there were no extant monotremes we probably wouldn’t.
It all comes down to what we can stomach. If cladistics forced us to call a Velociraptor a bird to allow us to call all extant flying feathered creatures birds, I’d be fine with that. But if we’d be forced to call Diplodocus a bird, not so much.
Likewise, “fish” as a clade doesn’t have much use, because it would basically mean all vertebrates, and we already have a term for all vertebrates. So if “bird” included Sparrows and Diplodocuses, we already have a term for that group, the Saurischians. If “bird” included sparrows and Tyrannosaurs, though…I’d be happy to call Tyrannosaurs the world’s biggest toothiest least-feathery birds. Or maybe they did have feathers after all. My secret hunch is that Tyrannosaurs were covered with insulating coat of yellow down, much like a baby duck.
I’m re-addressing this, hopefully in a clearer manner.
Yes, it ‘ground up’ vs. ‘tree down’ is a false dichotomy. Neither one is very descriptive of the probable evolution of birds. The argument is so old that i would call the original ideas ‘romantic’. The problem I’ve seen is the attempts to justify each don’t make much sense, but it’s clear that birds started as gliders and evolved true flight.
The ‘ground up’ theories tend to imply proto-birds that jump into the air and with vigorous flapping start to fly. The justifications are sometimes ludicrous, but widely defended, such as the idea of fleeing from predators. Somehow these predators can’t jump and catch a bird at it’s most vulnerable point in flight. Other ideas are based on a running proto-bird spreading feathered forelimbs and starting to glide, just inches off the ground, and developing true flight from that posture. That would require a lengthy series of variations in physiology that have little use to the slow, short ranged glider. One of the silliest justifications for the ground up theory is the use of flapping by young pre-flight modern birds to help run up hill. I would certainly expect young modern birds to make use of their wings before they can fly, because they eventually will fly.
So it seems clear to me that true flight emerged following successful gliding, which would be very difficult to accomplish by jumping up.
But the ‘tree down’ theories tend to have big problems also. The biggest one is the idea that an proto-bird is climbing and hopping around trees, and develops flight wings. The path from forelimbs that would be useful to tree climbing animal into bird wings seems improbable also. Forelimbs would seem to develop in favor of climbing and feeding tools, and a flying squirrel seems more of the likely result of an arboreal animal moving toward flight.
Successful gliding for birds is going to depend on initial altitude, light weight (weight to wing area ratio), strong muscles and bone structure to support gliding wings (and later flight wings), a sense of balance and coordination necessary for flight control, and strong legs to allow safe landings (unless there is an aquatic origin). These actually favor a ‘ground up’ start to the evolution of birds. And since we know that birds have evolved from ground based dinosaurs, there is undoubtedly a ‘ground up’ start.
More and more fossils and DNA analysis are showing a pre-flight origin to feathers. Insulation is a commonly accepted advantage for feathers, but they could just as easily have started as a sexual attraction, and for all we know they emerged as a mutation from poisonous glands or bards used as a means of defense. Where ever they came from, feathers would have existed before flight. Many dinosaurs were fully bipedal, and forelimbs developed in many ways. A very fast runner may have developed wing like forelimbs that were used as control surfaces enabling fast turns, which could have been a route to developing balance and coordination for gliding, and the strong legs needed for safe landing.
But once the ‘early birds’ began to glide, they would need to take advantage of any means of gaining height available, and likely would have begun to climb to gain that height. Evolution is slow, and the gradual changes to make an animal extraordinarily light, strong enough to maintain outstretched wings for extended gliding, and be able to control the wings to change the flight path. There could be many explanations for how the physiology of birds evolved from their dino ancestors. But to get the extreme adapations that birds have to enable flight would have required many generations of change that maintained advantages and survived disadvantages. And to extend the gliding capability in a useful manner, and one in which true flight evolved, proto-birds needed to gain altitude from something beyond their legs. They could have taken advantage of wind, but reliable wind with enough energy to get a heavy animal in the air without endangering it is not found that easily.
I would think the ancestors of modern birds simply used their limbs to climb up anything they could to get initial altitude. They may have dwelt on cliff faces along side water where they could glide out to grab whatever creatures lived near the surface of the water. They might have done the same over land, finding an aerial attack to be more efficient for prey that had not developed a defense against predation from above. They may have found that gliding from tree to tree was a way to avoid becoming prey and still have access to the choice food. Anything that would give them altitude for extended glides would have given the chance for the evolution of the modern bird. The extreme light weight of birds tends to make them fragile, and easily disabled by any contact, but once in the air, there were no longer predators to avoid. Variations of feathers could have extended the wing area without sacrificing additional weight. At the same time they would have diminished the utility of the forelimbs for other purposes. But again, once extended gliding existed, the longer broader feathers provide greater advantage by extending the glide capability.
That’s why I have no doubt that true flight in birds evolved from gliding, that became useful from initial climbing to gain altitude. And yes, many of the characteristics of modern birds did adapt from other purposes, undoubtedly in ground based animals.
[QUOTE=Darwin’s Finch]
Why is that preposterous? Show me a gliding animal that is/was on its way to a powered flight stroke. We already know, as noted, that many of what we think of as adaptations for flight were actually exaptations; many evolved prior, for different reasons.
[/quote]
I almost forgot about this. The answer is the Flying Fish. They have the advantage of starting their evolution from underwater ‘flight’, but in the air these fish use adjust their fins to produce lift, continue the horizontal tail motion which may add to propulsion, seem to be controlling their flight to take advantage of updrafts and wind, and at least in some accounts, flap their fins perhaps in an attempt at a flight stroke.
Let’s take htis from the top.
No, that isn’t clear at all. And as you as much as admit yourself, the little evidence we have suggests that exactly the opposite is true: birds evolved true flight, then developed the ability to glide.
In what sense is the bird at its most vulnerable point in flight? If a predator is faster than the bird then the bird will be most vulnerable on the ground.
The most plausible explanation I have heard for the evolution of flight is that the proto-birds lived in habitats similar to the modern monsoon forest. Habitats with a dense tangle of light woody vegetation at ground level. In such an environment one of the simplest ways for a small animal to escape predators is to jump into a small branch. Even if the predator can jump the branch will no support its weight, enabling the proto-bird to leap onto another branch.
With this sort of defence mechanism the bird is never at its most vulnerable point in flight. The presence of dense ground cover makes ambush hunting very successful, so any method of escape needs to be nearly instantaneous. Running is rarely an option. On the ground the bird would be quickly overhauled and killed by predators, whereas by the simple expedient of leaping onto a branch an animal finds itself in perfect safety.
This explanation is, IMO, the most plausible for several reasons.
Firstly, it deals with all the problems you raise: the inability of climbing forelimbs to become functional wings, the needs for strong legs, good balance etc.
The second reason it is plausible is because this is *precisely *the mechanism used by almost all ground dwelling birds in similar habitats today. Chickens, tinamous, megapodes and so forth are all poor flyers, yet they all retain the power of flight because it allows them to leap onto small branches to evade predators. This is an important point o note, since it puts paid to any notion that a poorly flighted bird attempting this would be at its most vulnerable when in flight. This quite clearly isn’t true, These birds are all cumbersome flyers with very slow takeoff speeds. Yet they are all perfectly capable of using their limited flight to leap into branches.
On the contrary It is very easy to posit a series of steps by which a proto-bird with no keel-bone could develop effective short range flight through leaping onto low branches, and thence develop longer and longer flight abilities. In fact many of these steps are in use today. In contrast it is almost impossible to posit a series of steps by which a gliding animal would ever develop flapping flight. An accomplished glider remains precisely that: an accomplished glider. It has neither the need nor the mechanisms by which to ever achieve powered flight.
But this is begging the question. Flying squirrels, for example, do not “need to take advantage of any means of gaining height available”. They simply launch themselves from where they are to where they want to go. While they may climb higher to get slightly longer range, they don’t do so to any greater degree than non-flying squirrels.
What you haven’t done here is posit any reasons why these proto-birds began gliding to begin with. Flying squirrels primarily fly so they can move between widely spaced trees without exposing themselves to ground based predators. But that hardly seems like it could ever lead to powered flight. What would by the first transitional step between such gliding and powered flight? Other gliding animals glide as a way to escape predators, but once again, it’s hard to see what the pressure is to develop powered flight, or what the first step down that path would be.
The problem is that gliding animals are locked into a path: gliding. They are specialists. To achieve longer glides they develop extended glide membranes and dorso-ventrally flattened bodies. There are good reasons for that based on both physics and physiology. All living and fossil gliders exhibit those traits. That is an inevitable path. Yet birds, from *Archaeopteryx *onwards have reduced flight membranes and are laterally flattened. Exactly the *opposite *of what a gliding animal would require. IOW there is no evidence that birds could glide before they could fly, and considerable evidence against it.
So these animals climbed a cliff, glided out over the water, grabbed a fish, and then swam back to shore? That appears to make no sense at all. A creature that can glide is going to make a terrible swimmer, and the dangers of predation in the water are far higher than on land. This proposed mechanism would push heavily towards the evolution of a swimming form and heavily *against *anything remotely suited to gliding.
Can you explain how, in a world where there had been predatory Pterosaurs for 50 million years and gigantic predatory insects for 400 million years, any animal could not have a defense against predation from above?
This is one of the biggest hurdles that the evolution of flight in birds has to cope with: competition. At the time the first birds were evolving the pterosaurs were already established and diversified, occupying almost every conceivable niche in terms of size, diet and environment. Those aerial niches that the pterosaurs weren’t filling were filled by insects.
Whatever origin you propose for your proto-birds, they have to better at it than a clade which had evolved true flight 50 million years sooner. In light of that, proposals that they glided to collect food seemingly need need some rather convoluted circumstances to make them viable.
Once again, the same problems. The earliest birds and bird ancestors are almost designed as anti-gliders, since gliding becomes more efficient by increasing membrane area and flattening the body, and birds have exactly the opposite traits.
Why not? We have pretty good evidence that several of the pterosaurs were aerial predators akin to frigate birds, so why would they not prey upon birds?
That is all well and good, but what happens when the animal inevitably lands. We have a gliding animal that has, in your own words “diminished the utility of the forelimbs” for climbing or running. So we have an animal that can not yet fly or even get airborne unassisted, yet it has a greatly diminished ability to climb.
This remains one of the biggest problems in any explanation of the origin of flight in vertebrates. You only have two sets of limbs. As any set becomes better adapted for flight it necessarily becomes worse adapted for perambulation. At some point in the transition you have a limb that is incapable of flight while being almost useless for perambulation. That is the stage for which any hypothesis requires a convincing explanation.
The ground-up, direct flight hypothesis circumvents it by noting that the forelimbs of many terrestrial bird relatives were of marginal use anyway, and any additional ability to leap is only beneficial. Your hypothesis fails to address how a gliding animal that that “would need to take advantage of any means of gaining height available” is able to effectively sacrifice the ability to climb while still remaining utterly incapable of flight.
But a flying fish is in no sense “on its way to a powered flight stroke”.
As you note, the power comes entirely from the tail in the water. They have no ability at all to to generate power from their fins. Of course they adjust their membranes to produce life and take advantage of air currents. So do flying squirrels and all other gliders. That is not in any sense a powered flight stroke.
As for a claim that they “flap their fins perhaps in an attempt at a flight stroke”: Cite! The use of the word “perhaps” in the comment doesn’t give me much confidence that such a claim has any evidential basis at all.
Maybe more cognition then you think.(Science 1/15/2010)
Lemur866’s point was what I was trying to say. If it was found that extant winged flying feathered creatures came from a Tyranoraptor line, then the clade of “birds” would be expanded to include them. The genetic evidence seems to suggest that such is unlikely however.
Quoth Lemur866:
That sounds reasonable to me, too. Personally, if I had to attach a clade to the name “bird”, I’d choose the clade composed of the first feathered flier and all of its descendants. If it turned out that multiple feathery critters developed flight without one being a descendant of the other, then I might stretch it to their common ancestor (especially if that common ancestor could glide or the like). I’m not sure what the argument would be for associating the name “bird” with some other clade.
What evidence shows that? How did some non-flying animal start to fly under it’s own power in the first place? By flapping it’s arms for some reason? Maybe it was trying to cool off and became airborne. This makes no sense. Without gliding how would an animal learn to control itself in flight, or land?
Not in flight, at takeoff. There are some small birds that take off rapidly now, but do you have some sort of explanation for how a proto-bird barely able to leave the ground, with or without your magical pre-gliding ability to fly, would not be highly vulnerable?
That could be. But I don’t see why that is more plausible than a bird living on rocks, or climbing along dead trees in a swamp, or a wet rainforest.
Well now your agreeing with me that a running into flight defense would be very ineffective. But defense isn’t necessarily the reason for flight. Carnivores, herbivores, and those indecisive omnivores might have food more readily available if they could fly.
Like the young birds using their wings to go up hill, the behavior of birds who can already fly, or are losing that ability, are not at all surprising, and not indicative of the origins of flight.
Only the glider has the opportunity to develop the mechanisms and need for true flight. Control is the key to flight. From jumping to gliding an animal develops the necessary form for flight, but it requires extended glides to have a base to develop the ability for control. Without the ability to maintain orientation, sense changes in the air, change direction, and make controlled landings, a bird that leaps will… as Arthur Carlson so eloquently stated “As God is my witness, I thought turkeys could fly”.
With extended gliding, a bird could develop the bone and muscles needed to achieve powered flight. They would be necessary to extend gliding time, and control. Without extended gliding, there would be no advantage to adding the extra weight to an animal trying to stay in the air without it.
I’m quite sure flying squirrels started in trees. Aren’t you? And the range of squirrels in my limited observations is the top of trees. I don’t think the flying squirrels can get higher than that.
I didn’t claim to, because there’s no way to know why, but it seems most likely that defense or greater access to food would be the reason. Squirrels use skin spread across short limbs for flight, so conversion to powered flight would be very slow. But pterosaurs and bats developed powered flight as well, so the ‘pressure’ certainly exists. And as I keep coming back to, the transitional step between gliding and flying is control. The glider once it gains sufficient initial height for extended gliding needs to develop control to take advantage of it. Jumping from a tree or a rock to an unknown landing spot is not a tremendous defense mechanism. The snake that scared some critter out of the tree might just be launching him into the jaws of crocodile. I think access to food is a better advantage. Birds can get at fruit inaccessible to other large arboreal animals, and can get at a lot of insects in flight, and as I mentioned, target their prey from above and catch them without their approach being detected. And once in the air, even if only gliding is available, food and predators can be seen more readily. The excellent eyesight of birds may well have developed in parallel with flight ability.
Sorry, but I’m still waiting to hear any evidence of any animal larger than an insect developing flight without gliding. And feathers make the difference in bird wings. Broad flat feathers provide more wing area at light weight than membranes without the long extension of bones as seen in pterosaurs and bats. Flat feathers might have existed in the proto-birds before they got into the air at all. Development of longer feathers seems easier to me than extending a finger.
That may or not be the case. The earliest bird could have been aquatic, developing feathers for insulation and shedding water, and developing wings to aid in paddling or running across the water. They could actually be a ‘water up’ species in some sense. But they weren’t going to suddenly leap into the air and start flapping to stay aloft.
But my point is that the initial takeoff point isn’t very important. It was whatever was available, to use for initial altitude to glide.
I don’t think insects are worth mentioning in this regard when comparing the prey of pterosaurs and birds. We don’t know the range or extent of pterosaurs. Prey may have developed instinctual fear of attack from above or not. But attack from overhead is complicated. Modern birds know how to use the sun avoid detection by attacking with the sun behind them, and by keeping their shadow from passing over an animal on the ground. Perhaps their ancestors were also better at that than the pterosaurs. And once again, control, something that requires muscles and brains are the big factor in making predation from the air successful.
That is quite true, and makes it seem likely to me that pterosaurs and birds developed in different environments, otherwise early birds would have had a hard time surviving their distant cousins who had so much more experience.
It doesn’t seem convoluted at all. Predation and food gathering have had impact on evolution in all sorts of ways. A bird that developed flight to eat flying insects probably ate flying insects already,. A tree climber that ate fruit would have access to more fruit, not just by flying to it, but by seeing it sooner, and reaching it sooner than its competitors. A bird that attacks prey on the ground may have started by leaping on prey long before it began to fly.
You aren’t offering any evidence of that. When membranes are used as wings the evolutionary path will be different, and require longer limbs and broader membranes to increase wing area, but birds are distinctly different in having feathers. And nothing about birds makes them anti-gliders.
As I mentioned, seperate environments is the easy explanation. But whatever the explanation, it isn’t going to matter how the birds started to fly, unless you think some ground based animal suddenly leapt into the air and demonstrated the ability to outfly a pterosaur.
I’m glad you agree.
As I mentioned, that’s why tree climbing seems less likely an approach. But Archy had more utile forelimbs that may have been a climbing aid, or predation aid. And there is no doubt that birds have a line of descent through ground based dinosaurs, so in some sense ‘ground up’ is definitely true, and ‘water up’ is definitely true as well. The question though is how did the earliest birds get in the air. I haven’t seen any evidence anywhere that they did it by flapping their arms, either from ground take off, or to keep from dying when they fell out of a tree.
The flying fish is certainly on it’s way to a powered flight stroke, just not likely from it’s winglike fins, but from continued flapping of its tail after it leaves the water. And its fins have more of a controllable wing form than the membranes of a flying squirrel, who has no means of propulsion at all. Based on your reasoning, no animal could ever fly.
I didn’t make that claim, I repeated it, and wouldn’t have used the word ‘perhaps’ if it could be verified. I know next to nothing about the physiology of flying fish, but I doubt they could use their fins for a power stroke in the air. But fish already ‘fly’ in the water. It has the instincts for powered flight, and some ability to control. And unlike numerous fish that launch themselves out of the water directly towards the heads of unsuspecting boaters, Flying Fish control their glides, and have adapted to increase their ability past the point of the initial launch.
As I said at length in my previous post: lack of gliding body form in birds, well developed legs and sense of balance in birds, lack of any plausible means of transition form gliding to flight and so forth.
I explained this at length in my last post: by leaping onto branches to evade predators.
Rather than simply stating this, it would help if you could can you expand on which parts make no sense to you. For example, do you not understand how an animal in a monsoon forest could evade a predator by leaping onto a low-hanging branch? Or do you not understand how such an evasion mechanism could provide selective pressure for the evolution for the evolution of wings?
Just saying “This makes no sense” doesn’t really allow me to explain it to you.
]
A I said, by leaping onto branches. Do you not believe that an animal with proto-wings would would need to learn how to control itself in flight or how to land on branches? I suppose they could begin by just leaping into the air flapping madly and hope to crash into a leafy branch that both supports them and holds them in place, but doesn’t even that situation suggest an evolutionary pressure to learn how to steer the ascent?
Can you explain how they would be vulnerable? And can you explain why they would be “barely able to leave the ground?”
Even modern birds can leap just as fast as a chicken can fly. The only difference is how high they can go. Numerous species of animals including frogs, crickets and macropods today escape predators by leaping onto tree branches.
Since we know that leaping into tree branches is a viable means of escaping predators for animals in the 50-50, 000 gram range, and we know that birds of monsoon forests escape predators by flying into tree branches what makes you think that an animal that can leap and has a limited ability to extend that leap through the use of proto-wings would be in any way vulnerbale?
I really don’t understand this. Do you dispute that animals can successfully evade predators by leaping into overhead tree branches? Or do you believe that having wings capable of increasing the height or control of such leaps would somehow make them more vulnerable?
Rocks: The areas of rock are tiny. Monsoon forest equivalents covered over 40% of the Earth’s and area at the time that birds evolved. Suitable rock surfaces maybe one trillionth of a percent. That make sit much less plausible. However an animal occupying a niche equivalent to rock wallabies isn’t implausible. It is simply less plausible. Rock wallabies certainly do exhibit this type of behaviour, leaping upwards onto overhanging rocks faces to evade predators. They are also well described as leaping onto overhanging tree branches where these are available.
The point to note is that this is still a ground-up evolution of flight. Rock wallabies are still terrestrial animals that leap from the ground into the trees/rock faces. They are not arboreal animals that leap down to the ground.
Dead trees in a swamp: The problem with this is that if you are already in a tree you are, by definition, already being chased by an aboreal predator. As such leaping upwards is less unlikely to be successful than leaping sideways. There is a reason why no arboreal animals today leap upwards to avoid predators.
Rainforest: If you had ever been in a rainforest the answer would be obvious. Rainforests, almost by definti0on, have little understory. The nearest branch is most likely 20 metres overhead. There is simply no evolutionary starting point for an animal that evades predators by leaping.
Running, yes. Leaping =/= running.
It can’t be disputed that animals that can fly have more food available. The problem is that you haven;t explained how a gliding animal that is at the first proto-flight stage could have more food available. No known gliding animal has more food available than its non-gliding relatives so it is not immediately obvious that gliding doe in fact provide more food.
If you can explain how it could then please do so.
Nor did I ever suggest so. You have totally ignored what I clearly stated. I used the behavior of birds who can already fly to prove that leaping into trees to evade predators is a viable defence for birds. This specifically because of your claim that such a defence could not be viable
But turkeys *can *fly. That is really all I need to say to that. The rest is a total non-sequitur.
Why does it require extended glides to develop the ability for control? Do pole-vaulters, for example, not have the ability to control their motion because they are not airborne for extended periods? It seems to me that if an animal can glide for an extended period then it has less need to develop control than an animal that can only remain ariborne long enough to reach a single pre-chosen target.
One again though, how? I asked oyu this above, and your answer is simplky to restate it as fact.
How could an accomplished glider “develop the bone and muscles needed to achieve powered flight”. What is a plausible first step that would enable a flying squirrel or basilisk lizard to “develop the bone and muscles needed to achieve powered flight”?
Why would they be necessary? Why couldn’t those things be increased by change sin membrane structure, body shape or behaviour?
Let me get this straight.
You are saying that if adding an extra 100 ounces grams of weight allows a wallaby to leap an extra 12 inches vertically then “there would be no advantage to adding the extra weight” because the wallaby can not glide?
That seems to be what you are saying, but it is so preposterous that I assume that I have misunderstood you. Can you please clarify?
And? The issue is your claim that gliding animals “need to take advantage of any means of gaining height available”, not whether gliding animals live in trees. You haven;t even tried to address the actual issue, instead making this trite and irrelevant observation that squirrels live in trees.
Then you lack both the observational and theoretical knowledge to incorporate flying squirrels into your hypothesis. They quite frequently launch themselves from tree trunks. They certainly do not invariably launch from the tops of trees, as your hypothesis demands.
The issue isn’t whether they can get higher than that. The issue is whether their is height available that they do not use. Whether, in order for gliding to be effective the animals “need to take advantage of any means of gaining height available”.
Since they quite clearly do not “need to take advantage of any means of gaining height available”, we can conclude that this part of your hypothesis is fully falsified.
Making assertions about the likelihood of why something happens is premature when you are unable to even explain how it *could *happen.
But this is a blatant non-sequitur, and it’s turtles all the way down. You know that birds must have could have evolved from gliding animals because you know that pterosaurs and bats evolved from gliding animals.
Where is your evidence that pterosaurs and bats evolved from gliding animals. The fact is that the origins of flights in pterosaurs and bats are even more problematic than in birds. You certainly can’t use some foregone conclusion on their origins to support the origins in birds.
Gliders have control. Flying squirrels and flying phalangers are able to execute 180 degree turns in their glides. Phalangers can be trained to land on on a matchbox from 20 metres away.
Does this not meet your definition of control? Or, are you arguing that sugar gliders are capable of powered flight?
I am getting the impression that you believe that gliding animals just jump into the air and move in a straight line and hope they land somewhere safe.
Yes, because birds can fly.
Can you name single gliding animal that has access to more food than its non-gliding relatives? Can you even give a hypothetical example of how it might be possible for gliding to provide access to more food in a world which is home to some 700 species of pterosaurs?
Cite! Seriously. How are food and predators more visible to a squirrel gliding than a squirrel walking along a branch?
Evidence for this claim please.
Almost certainly. But since it must have done so regardless of how that flight evolved i don;t see the relevance. Are you suggesting that a hawk that evolved from a terrestrial ancestor would have worse eyesight?
Argument form ignorance.
We have no “evidence” of any animal developing flight in any way at all. We also have no evidence of any animal developing flight *with *gliding. We simply have no evidence.
What we have are competing hypotheses. Some of these, like ground up, match the known observations and leave no questions unanswered. Others, like you gliding hypotheses. have huge numbers of questions which you are unable to answer. Questions such as: How can an animal transition from being a successful glider to powered flight? What is the first step that is evolutionarily advantageous? Why do early birds show none of the features universal to gliding animals?
All of which is true, and all of which equally applies no matter what evolutionary path avian flight took. So it doesn’t support a ground up origin and it doesn’t answer the question I asked.
To achieve longer glides, gliders develop extended glide membranes and dorso-ventrally flattened bodies. There are good reasons for that based on both physics and physiology. All living and fossil gliders exhibit those traits. That is an inevitable path. Yet birds, from *Archaeopteryx *onwards have reduced flight membranes and are laterally flattened. Exactly the opposite of what a gliding animal would require. How do you explain that?
Regardless of whether the membranes are feather, exoskeleton, fin or skin, accomplished gliders must have those traits.
So why do birds have exactly the opposite traits? A ground up origin explains this perfectly because birds were never gliders. A gliding origin needs to have some sort of explanation for it. An explanation that you are unable to give.
But you posited an animal that, and I quote, “dwelt on cliff faces along side water where they could glide out to grab whatever creatures lived near the surface of the water.”
So which is it? Did it dwell on cliff faces and glide out over the water, or did it “develop wings to aid in paddling or running across the water”?
Either hypothesis has some major problems, and you can’t avoid them by positing that the other may be correct.
And my point is that the initial take-off point is in fact critical. All the take-off points that you have proposed seem practically impossible. That’s not an insignificant flaw in a scientific hypothesis
Given that the insects at the time were larger than many modern birds and occupied the niche of small aerial predator, they are vitally important.
No, but we do know that it extended form 20 grams to over 100 kgs, and that the prey covered fish, carrion, vegetation, other pterosaurs and insects. While we don’t know, and never will know, the full extent, we do know that they seem to have occupied every major aerial niche available.
Since your hypothesis relies on prey having no instinctual fear of attack from above, this is hardly an insignificant point
So your hypothesis relies on the very first proto-birds. Birds that could only glide and not fly, having this ability? Whereas other archosaurs that had been flying for 50 million years weren’t as good at it?
And you don’t see the problem with this?
So you are claiming that pterosaurs had less control of their flight than the very first proto-birds, birds that could only glide and not fly?
Can you explain how that could possibly be?
Right, so what is this different environment?
The ground-up origin addresses this issue neatly: the environment was tangled jungle where flight was useless in obtaining food. Only terrestrial foraging was viable and the proto-birds occupied a niche very similar to chickens or cassowaries. This excluded the pterosaurs which were very poorly adapted to terrestrial foraging, while simultaneously providing a major evolutionary impetus towards developing flight. The ground up hypothesis neatly explains both observations in one locale.
You claim that your tree-down gliding-originated hypothesis is more credible, yet it is utterly unable to address this very basic question, along with many others.
How can you consider a hypothesis more credible when it is less able to explain the observations?
Right. But this doesn’t go any way towards addressing the actual issue I raised. Birds had to compete with pterosaurs, which were also eating fruit and also eating insects as well as actively preying on flying animals of bird size.
So how does a proto-bird which can glide but not actually fly manage to compete with the master flyers in the initial stages of the development of flight. As you admit yourself, early birds can not have been in a niche where they were competing with pterosaurs. Under your tree-down gliding hypothesis, what was that niche?
Since ground up answers this question, and tree down does not, doesn’t that alone make ground up the more compelling hypothesis?
Just clarify this for me: you are requesting evidence that birds are not dorso-ventrally flattened?
How are birds distinctly different? Why would a bird not be a better glider if it ere dorso-venrtrally flattened and with a more complete membrane surface? What difference doe sit make what the membrane is made out of?
I honestly do not understand what you are saying here. Are you arguing that 200cm^2 of feather membrane would not give better gliding ability than 100cm^2? Or that a bird would not be a more effective glider if it were dorso-ventrally flattened?
In short, you keep saying that birds are different. Explain how they are different. Different laws of physics?
As I already told you, the lateral flattening and incomplete membrane systems makes them anti-gliders.
It is no explanation at all. How can you have a “seperate environment” from globally distributed aerial animals?
It isn’t going to matter? The whole thread is devoted to that one single issue. The goddamn thread is about how the birds started to fly. How can you say that it isn’t going to matter. It’s the central point.
Once again, you totally failed to address the issue. The ground-up hypothesis addresses the issue. The tree-down does not. Agreeing that the issue exists doesn’t add credibility to your tree-down hypothesis. It weakens it because you agree that the issue exists yet are able to explain how it is compatible with a tree-down hypothesis.
Well, no, you never mentioned that at all. You explicitly stated that “your gliding-bird “would need to take advantage of any means of gaining height available”
Since you now admit that tree climbing was unlikely (and by extension rock climbing even less likely), how precisely did this bird “take advantage of any means of gaining height available”?
And as I have repeatedly said, we have no evidence for anything. We only have competing hypotheses. The ground up hypothesis addresses all the questions. Your tree down gliding hypothesis seems unable to address any of them
So how exactly is it more plausible?
Cite!
Seriously, I calls bullshit on this. You presented this as fact, please provide the evidence.
Cite!
So it’s baseless, unattributed hearsay and can thus be dismissed out of hand in GQ.
Good to know.
Perhaps a better way of restating the “ground up” vs “trees down” dichotomy would “cursorial origin” vs “arboreal origin”; indeed, that’s the original debate that has since been transformed into the ground vs trees argument.
Given the fossil record we currently have, a cursorial origin is pretty much undisputed - that is, we know flying birds evolved from ground-dwelling cursorial dinosaurs. Several studies have failed to find any arboreal adaptations among those dinosaurs closest to birds (e.g., maniraptorans). As such, current evidence disfavors the arboreal hypothesis. Many adaptations involved the current flight stroke (e.g. , the semilunar carpal found in the wrists of birds, which allows them to fold their wings against the body when not in use) were already present in maniraptorans (though there are some who believe maniraptorans to have actually evolved from fliers and were thus secondarily flightless).
Of course, as I mentioned previously, the evolutionary pathway to powered flight in birds was unlikely to have been completely linear; there could have been leapers, climbers, flappers, divers, etc. along the way, each gradually adding to the suite of adaptations necessary for powered flight.
[Hijack]Do scientists distinguish humans from great apes? I thought we were apes.[/hijack]
Isn’t that what Lemur866 said?
Interesting.
See, this is something I’ve always had trouble with. “We have no evidence of Neanderthal symbolic thinking” would (before this discovery anyway) have been a valid statement under oath in court, but that isn’t the same as saying “they lacked cognition,” and its understood necessary corollary, “which sprang full-blown into homo sapiens sapiens out of nothing,” which sounds like the theory of spontaneous generation, to me.
Yes, I should not have said there is “no” evidence, but rather that there is some evidence, although not fully accepted. One paper published by one person isn’t generally going to change the consensus. And nobody said that anything “sprang fully-blown… out of nothing.”
The fact is, Neanderthal sites are notable for their lack of symbolic art. Modern human sites are notable for the inclusion of symbolic art. And that extends into the entire tool kit of the two populations-- one is varied and dynamic, the other is standardized and static. And that latter applies to very early Sapiens sites, too, implying that there was some change within the Sapiens line that did not occur in the Neanderthal line.
When we found out that chimps make tools, no one expected to find a chimpanzee automobile hidden in the juggle.
Oh, yeah. I read ‘include’ as ‘exclude.’