Archaeopteryx may not be a bird

[Colibri]

@TriPolar

There’s no plausible explanation for how an animal would acquire the otherwise useless set of characteristics for flight, and then suddenly leap into the air and start flying.

A lot of the adaptations useful for flight, such as feathers, thermoregulation, hollow bones, etc, clearly evolved before flight. There are a number of hypotheses for how bird ancestors may have acquired other characters that might have been used in developing flight indirectly. Certainly there are enough flightless non-avian dinosaurs with well developed feathers on the arms that we can think that they must have been using these structures for something other than flight.

It’s also testable based on enough fossil and DNA evidence, but it may be an impossible test because we may never find that much evidence.

It may be testable theoretically, but it will never be testable practically. Since all but one lineage involved are extinct, and few fossils of appropriate age preserve DNA, genetic evidence is unlikely to come into it.

All modern birds descended from flying species, and there’s no evidence of flying dinosaurs (unless you include pterosaurs, which do not seem to be the ancestors of modern birds).

Have you been reading this thread? I already cited one example of a flying non-avian dinosaur, Microraptor, twice. This would seem to indicate there were at least two, perhaps more independent acquisitions of flight within dinosaurs.

‘Ground up’ is not plausible. The justifications are things that are not ‘ground up’, or nonsense. For example, the theory that animals with wing-like feathered limbs running uphill and then taking flight are ridiculous. Long before ever flying, these animals would have been jumping and then gliding in descent, eventually gaining flight capability. That’s not ‘ground up’. The false dichotomy would be saying ‘tree down’ opposed to ‘ground up’, and excluding everything but trees as the source of initial altitude. The ‘down’ path could be from rocks instead of trees, or even jumping into the air, but there’s no plausible means of having a ground based animal starting to flap it’s arms and taking flight.

You’re just arguing semantics here. The “ground up” theory of course includes jumping up from the ground. If you want to define it some other way, go ahead, but you’re not actually addressing the existing theories.

[TriPolar]

@Musicat

Imagine this: animal is being chased by a predator. Just before the last lunge, the prey jumps up in the air, escaping the jaws. The higher it jumps and the longer it can stay up from flapping, the more successful the species and the better the flyer. That’s ground up.

So while being chased, an animal jumps into the air, slowing down it’s forward motion, flapping it’s arms and slowing down even more, and has the ability to get high enough, and move far enough, and land safely away from the predator? And then on top of that, this activity never first simply turned from a jump to a glide? The idea is preposterous. Jumping may have led to flight, but not without gliding as a precursor.

[Colibri]

@TriPolar

Jumping may have led to flight, but not without gliding as a precursor.

So what?

[TriPolar]

@Colibri

A lot of the adaptations useful for flight, such as feathers, thermoregulation, hollow bones, etc, clearly evolved before flight. There are a number of hypotheses for how bird ancestors may have acquired other characters that might have been used in developing flight indirectly. Certainly there are enough flightless non-avian dinosaurs with well developed feathers on the arms that we can think that they must have been using these structures for something other than flight.

I didn’t say quite that. I don’t think any dinosaurs had their bones reduced in weight to the point of fragility. There are certainly good reasons why the flight features would have evolved.

It may be testable theoretically, but it will never be testable practically. Since all but one lineage involved are extinct, and few fossils of appropriate age preserve DNA, genetic evidence is unlikely to come into it.

That’s what I said.

Have you been reading this thread? I already cited one example of a flying non-avian dinosaur, Microraptor, twice. This would seem to indicate there were at least two, perhaps more independent acquisitions of flight within dinosaurs.

You’re right. My statement was inaccurate. I was getting to the idea that modern birds didn’t descend from flying dinosaurs.

You’re just arguing semantics here. The “ground up” theory of course includes jumping up from the ground. If you want to define it some other way, go ahead, but you’re not actually addressing the existing theories.

It is sematics, and they matter. The ‘ground up’ theory implies flight before gliding, which remains preposterous.

[Darwin_s_Finch]

@TriPolar

There is a true dichotomy between ascending and descending, because it’s one or the other. And quite clearly it’s descending. There’s no plausible explanation for how an animal would acquire the otherwise useless set of characteristics for flight, and then suddenly leap into the air and start flying.

It’s also implausible how animals with no arboreal adaptations to speak of managed to get into those trees in the first place. Nor is it plausible that said animals would go straight for powered flight instead of, say gliding (and no, gliding is not simply a stepping stone to powered flight…) or parachuting.

Very likely, the evolutionary path taken was not simply one way or the other, but a combination of leaping, bounding, flapping, gliding, and parachuting.

If birds are dinosaurs, humans are fish.

Well, sure, for certain definitions of “fish”. Humans are sarcopterygians, which are often referred to as “fleshy-finned fish”.

All modern birds descended from flying species

This has not yet been conclusively demonstrated by the fossil record.

and there’s no evidence of flying dinosaurs (unless you include pterosaurs, which do not seem to be the ancestors of modern birds).

As Colibri noted, there may well be: Microraptor, for one.
Also: pterosaurs weren’t dinosaurs.

[Darwin_s_Finch]

@TriPolar

It is sematics, and they matter. The ‘ground up’ theory implies flight before gliding, which remains preposterous.

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.

[TriPolar]

@Darwin_s_Finch

. 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.

I’ll address the first part of your question later when I have more time. But I am not arguing against flight characteristics evolving for other reasons. The opposite actually, that characteristics that had other advantages adapted to allow flight.

ETA: Also this is now in GQ, maybe this part should be in GD. What do you think?

[Colibri]

@TriPolar

I didn’t say quite that. I don’t think any dinosaurs had their bones reduced in weight to the point of fragility.

That’s not a requirement for developing flight. A few flying birds today have relatively solid bones.

There are certainly good reasons why the flight features would have evolved.

And terrestrial theropods already had most of the adaptations needed for flight.

You’re right. My statement was inaccurate. I was getting to the idea that modern birds didn’t descend from flying dinosaurs.

Since birds are dinosaurs, they clearly did. And there were other lineages of flying dinosaurs like Microraptor. Deciding at what point you call something a “bird” within the dinosaurs depends purely upon what node you choose. Neither feathers nor flight define birds as a clade.

It is sematics, and they matter. The ‘ground up’ theory implies flight before gliding, which remains preposterous.

First of all, “ground up” would not necessarily exclude some gliding. However, as Darwin’s Finch mentions, there is no reason that the acquisition of powered flight has to include a gliding stage. This is an unfounded assumption on your part. As he says, all extant gliding animals are pure gliders; they don’t have any capability to prolong their glide with a powered stroke. Nor would there seem to be much of a way to acquire one without sacrificing some of their gliding ability. Gliding and powered flight may be two alternative strategies, and it may actually be very difficult to acquire powered flight once you are on the trajectory to develop gliding capability.

The argument between “tree down” and “ground up” is far from being resolved. Years ago I was pretty skeptical of “ground up.” However, now we have a host of clearly terrestrial, clearly flightless, fast-running non-avian dinosaurs with long, well developed feathers on their forearms. They are very close to the kind of animal that could have developed flight from the ground up. On the other hand, I can’t think of any definitely arboreal feathered non-avian dinosaurs that would seem to have any gliding capability. (Microraptor could have evolved from such a form, perhaps, but it is not in the lineage of modern birds.)

[Colibri]

@TriPolar

ETA: Also this is now in GQ, maybe this part should be in GD. What do you think?

Unless this get political, I think it’s OK here for now.

[Chronos]

It looked to me that the Wikipedia article was saying that the microraptors were a result of the same evolution-of-flight event as modern birds, and it was just a question of whether microraptor descended from a two-winged ancestor like modern birds, or modern birds descended from a four-winged ancestor like microraptors.

[Cheshire_Human]

@Ludovic

But an ostrich does have feathers and flies – when it’s dead.

I have it on good authority that any live ostrich, when placed in an aircraft that is then piloted into the air, flies just as well as the human non-pilot flight crew and passengers. Naturally the pilot is more capable of flight, until one can teach the student ostrich how to work the controls.

[Blake]

@Colibri

Unless this get political, I think it’s OK here for now.

You’re only saying that because Velociraptors vote Democrat.

There, that oughta do it.

[Colibri]

@Chronos

It looked to me that the Wikipedia article was saying that the microraptors were a result of the same evolution-of-flight event as modern birds, and it was just a question of whether microraptor descended from a two-winged ancestor like modern birds, or modern birds descended from a four-winged ancestor like microraptors.

I don’t read it that way. I don’t see any definite statement that Microraptor and modern birds had a common ancestor that flew, whether two-winged or four-winged. Any resemblances between their respective flying ancestors might have been convergent.

But all this could change with the next fossil find.

[Colibri]

@Blake

You’re only saying that because Velociraptors vote Democrat.

No, I’m sure that as therapods they would have been T[sub]rex[/sub] Party.

[Polycarp]

@Colibri

No, I’m sure that as therapods they would have been T[sub]rex[/sub] Party.

Oh, come on, everybody knows they were DINOs.

[Polycarp]

@Cheshire_Human

I have it on good authority that any live ostrich, when placed in an aircraft that is then piloted into the air, flies just as well as the human non-pilot flight crew and passengers. Naturally the pilot is more capable of flight, until one can teach the student ostrich how to work the controls.

They just have trouble using the flight emu-lator.

[Darwin_s_Finch]

@PlainJain

Could you expand on this a bit?

OK, now that I have time for a more detailed answer:

Starting with Theropoda, the usual cladogram (well, sequence, really) is as follows:

                     /_Aves
                    /
                   /_Avialae
                  /
                 /_Paraves
                /
               /_Maniraptora
              /
             /_Maniraptoriformes
            /
           /_Tyrannoptora
          /
         /_Coelurosauria
        /
       /_Avetheropoda
      /
     /_Tetanurae
    /
   /_Therapoda
  /

(side branches left off because they’re a pain in the ass to include using ASCII art…)

One of the earliest specimens with evidence of feathers (or their precursors) is Dilong, which falls in with Tyrannoptora. We see more developed feathers (of the “downy”-ish variety) in Sinosauropteryx (.pdf paper). Note that that paper, published in 2001, classifies Sinosauropteryx as a full-fledged (uh…heh) bird, within Aves proper; it has since been reclassified as a compsagnathid (sister group to Maniraptoriformes in the sequence diagrammed above). We find more of the same type of feathers in Shuvuuia, an alvarezsaurid (branch between Maniraptora and Paraves in the sequence).

Then we see Caudipteryx, which was preserved with a type of “contour feathers” (Caudipteryx was an oviraptorosaur, which was a sister group to Paraves). Then we have Sinornithosaurus, which had similar contour feathers, as well as “downy” feathers. Sinornithosaurus was a dromaeosaurid, which is currently a branch within Paraves.

When we get into Avialae, we get what most folks would agree are “winged dinosaurs”; these may or may not have been capable of flight, and are all closely related to modern birds at any rate. Archaeopteryx is usually found here.

So, we find unambiguous evidence of feathers (of various types) lying outside of any true bird (Aves), and even outside of known “winged dinosaurs” (Avialae), which, of course, brings me back to my original point: feathers alone do not a bird make. Way back when, prior to the discovery of Archaeopteryx, the only known animals with feathers were, of course, birds, so it was only natural that when Archie was discovered, people would look at it and say, “Huh. Bird.” The picture has changed substantially since then with the large number of extraordinary fossils coming out of China, so we can’t really look at a feathered fossil and assume “bird” anymore.

(Apologies for any mistakes in the preceding…it’s late and I’m tired…)

[Novelty_Bobble]

@TriPolar

‘Ground up’ is not plausible. The justifications are things that are not ‘ground up’, or nonsense. For example, the theory that animals with wing-like feathered limbs running uphill and then taking flight are ridiculous. Long before ever flying, these animals would have been jumping and then gliding in descent, eventually gaining flight capability. That’s not ‘ground up’. The false dichotomy would be saying ‘tree down’ opposed to ‘ground up’, and excluding everything but trees as the source of initial altitude. The ‘down’ path could be from rocks instead of trees, or even jumping into the air, but there’s no plausible means of having a ground based animal starting to flap it’s arms and taking flight.

“plausible” does not mean “equally probable”. But it certainly isn’t ridiculous.

My definition of “ground up” may differ from yours. But I can easily see how feathers and body coverings evolved for one benefit (warmth etc.) could become advantageous for another (additional thrust for climbing or predator escape) and lead, by degrees, to powered flight.

It may be that the “tree down” view is the correct one but it is far from a nailed-on certainty. Let us go where the evidence takes us eh?

[DSeid]

Is it believed that modern birds all came from one dinosaur line that split off from the other lines relatively late in the game? Is there any consideration that modern birds may be a convergent evolution of several dinosaur lines, an amalgam of older lines? Given that feathers are an old and relatively wide spread feature of dinosaur lines, and that flight was even wider spread, including non-dinosaur reptiles, it seems that in an environmental condition in which a bird like form was selected for that several lines would be likely to provide some selectable material …

(I fear my ignorance is showing, and that there is some feature common to all birds that is very unusual in other dinosaur lines, but I do not learn if I do not ask.)

[bup]

@DSeid

Is it believed that modern birds all came from one dinosaur line that split off from the other lines relatively late in the game? Is there any consideration that modern birds may be a convergent evolution of several dinosaur lines, an amalgam of older lines?

It sounds like you are suggesting that modern birds come from several lines. If that were the case, by modern cladistic definitions (things split at the most recent common ancestor), they aren’t all birds. Fear not, though, that is not the case.

The other interpretation of what you’re saying - that somehow, disparate species combined DNA into a new species - that is not correct. Species just differentiate as you move forward in time - they don’t combine.