Question A Missing Link?! Birds arose from theropods? Where are the featherless fossil intermediates?

Jul 27, 2020
195
21
105
While there have been a number of threads on this topic, it remains a mystery to some of us.

Most people accept the theory that birds arose from theropod dinosaurs. But there seems to be a problem in that the fossil record does not present species of theropods that evolved bodies to accommodate flight, a prerequisite for evolving feathers to promote gliding, and later true flight. Coelurosauria is not the answer as they are also apex terrestrial bipeds, with the exception of some questionably positioned species. So please, anything with feathers is disqualified from discussion by the simple nature of these issues :

What we commonly know as theropods arose ca. 230 million years ago as an apex bipedal terrestrial predator, with a bottom heavy, top light morphology, with powerful legs, and shortened arms with three fingers. No one has derived a rational means, or reason, for how such an apex predator would evolve flight from a totally incompatible body format. Evolution requires a reason, i.e. a "driving force", for the appearance of biological traits, especially one so complicated as powered flight. The only thing a theropod had to worry about was a bigger theropod. That such animals would evolve flight seems more a flight of fantasy than of reality.

Some have referred to the transition to flight of such a terrestrial predator as the "ground-down" evolutionary sequence. If the bird-theropod relationship is correct, there should be intermediate forms in the fossil record revealing evolutionary changes in theropods to permit flight to arise. Such fossils should be trending toward a body format suitable for flight, and without feathers since flight would not yet have evolved. And these featherless theropods likely would have appeared ca. 200 mya, or earlier.

In a nutshell : Except for the reptilian features, ancient feathered "birds" do not look much at all like theropods.

Is anyone aware of fossils, prior to the appearance of feathers, that would allow such an unlikely creature as the initial bipedal terrestrial theropod to evolve flight from their poorly suited body format?

(Please, do not rain down a storm of feathered theropod stories. The question regards evidence for the transition in body formats that appears lacking in the fossil record, and almost certainly required for avian evolution to proceed.)
 
Last edited:
  • Like
Reactions: Carol Cleon
Jul 27, 2020
195
21
105
Why aren’t we looking at Ichthyornis dispar or other feathered dinosaur bones that have been found, like in northeastern China?
There certainly are some people looking at them, but the feathered fossils are not of interest in the origin of flight from therapods, which is the issue of this thread. Happy to learn of Ichthyornis dispar , thanks for that!

The question of this posting is one previous to the appearance of feathered creatures. It is about the initial evolution of the avian line, which must have arose 200 mya or more, and since everyone is calling birds theropods, the question is where are the fossils demonstrating a divergence from the standard terrestrial theropod to the avian line? There must have been a major evolutionary split, and likely much earlier than 200 mys. I have never seen any fossils which show such a dramatic change in theropods which must predate the appearance of real feathers by many millions of years.

Where are they?
 
  • Like
Reactions: Carol Cleon
Mar 19, 2020
201
22
105
In a nutshell : Except for the reptilian features, ancient feathered "birds" do not look much at all like theropods.
I'm not sure what you mean here, because those reptilian features are part of it, but body plans did not need to change as much as the adaption of nest warming tools for flight is.
 
  • Like
Reactions: Chem721
Jul 27, 2020
195
21
105
I'm not sure what you mean here, because those reptilian features are part of it, but body plans did not need to change as much as the adaption of nest warming tools for flight is.
Virtually all "therapods" look similar. Heavy lower body with massive legs and tail, and smaller upper body with very short arms. As previously noted, this body style is totally ill-suited for evolving flight. To be sure, the only chance it has of coming close to flight is falling off a cliff.

The standard therapod body format arose shortly after the P/T extinction (ca. 250 mya), and remained that way through many species all the way to T. rex, until they were all wiped out (66 mya). And yes, they and birds are both of reptilian origin. And so is a turtle. Some of these "reptiles" are simply not likely to evolve flight.

In order for birds to have arose from the standard therapod body format, major changes must have occurred prior to evolving flight. The standard (universal some would say) body format simply does not permit flight, if one has a reasonably firm concept of the morphology of other flying vertebrates, and a good grasp of basic physics. Mass balance is key, as are long arms for evolving wings. Giant lower bodies and short arms are never going to make it into the air!

Again, for such changes in this standard therapod morphology to give rise to the avian line, the body format must have undergone enormous changes. And all of this must have occurred many millions of years before the evolution of flight. The driving force would likely be a change in life-style, from terrestrial to arboreal (tree dwelling). This would have allowed for the evolution of longer arms, and a diminution of the lower body. Again, these changes must have preceded the appearance of feathers and flight.

But there is no evidence for these changes in the fossil record to support such a change in body format from therapods, based on everything I have seen. What is reported is the standard terrestrial therapod line repeating through tens of millions of years, and a large number of species, all with the same body format (except those seemingly "out-of-place" birds). And why should therapods undergo such drastic change? It was an apex predator with zero pressure to change. The only thing a therapod had to worry about was a bigger therapod.

Simply put, the avian line, however it arose off the main reptilian trunk, developed a body format which evolved for flight. Clearly some reverted to a flightless status, but that is also seen in modern birds. But critically, there is no line of divergence in the fossil record to get from the bottom-heavy, top-light format of the terrestrial therapod to the stream-lined feathered format of the avian line.

Those who have studied the evolution of vertebrate flight insist that it must have arose from a climbing-glider. Such an animal most likely evolved from the terrestrial to the arboreal, and then slowly evolved into flight. Other creatures are known for this same adaptation, such as "flying" squirrels and frogs. All arose from the trees.

A Trees-Down evolution for flight is the only rational approach for the appearance of birds. The Ground-Down hypothesis, which the standard terrestrial therapods are necessarily burdened with in evolving flight, is never going to make it, for various obvious, and not so obvious reasons.



BTW, love the score:

Creationists: 0
Legitimate Science: 50 million

(Is that the final score, or just the first inning?!)
 
Last edited:
Mar 19, 2020
201
22
105
1601493181974.png
Virtually all "therapods" look similar. Heavy lower body with massive legs and tail, and smaller upper body with very short arms. As previously noted, this body style is totally ill-suited for evolving flight. To be sure, the only chance it has of coming close to flight is falling off a cliff.

The standard therapod body format arose shortly after the P/T extinction (ca. 250 mya), and remained that way through many species all the way to T. rex, until they were all wiped out (66 mya). And yes, they and birds are both of reptilian origin. And so is a turtle. Some of these "reptiles" are simply not likely to evolve flight.

In order for birds to have arose from the standard therapod body format, major changes must have occurred prior to evolving flight. The standard (universal some would say) body format simply does not permit flight, if one has a reasonably firm concept of the morphology of other flying vertebrates, and a good grasp of basic physics. Mass balance is key, as are long arms for evolving wings. Giant lower bodies and short arms are never going to make it into the air!

Again, for such changes in this standard therapod morphology to give rise to the avian line, the body format must have undergone enormous changes. And all of this must have occurred many millions of years before the evolution of flight. The driving force would likely be a change in life-style, from terrestrial to arboreal (tree dwelling). This would have allowed for the evolution of longer arms, and a diminution of the lower body. Again, these changes must have preceded the appearance of feathers and flight.

But there is no evidence for these changes in the fossil record to support such a change in body format from therapods, based on everything I have seen. What is reported is the standard terrestrial therapod line repeating through tens of millions of years, and a large number of species, all with the same body format (except those seemingly "out-of-place" birds). And why should therapods undergo such drastic change? It was an apex predator with zero pressure to change. The only thing a therapod had to worry about was a bigger therapod.

Simply put, the avian line, however it arose off the main reptilian trunk, developed a body format which evolved for flight. Clearly some reverted to a flightless status, but that is also seen in modern birds. But critically, there is no line of divergence in the fossil record to get from the bottom-heavy, top-light format of the terrestrial therapod to the stream-lined feathered format of the avian line.

Those who have studied the evolution of vertebrate flight insist that it must have arose from a climbing-glider. Such an animal most likely evolved from the terrestrial to the arboreal, and then slowly evolved into flight. Other creatures are known for this same adaptation, such as "flying" squirrels and frogs. All arose from the trees.

A Trees-Down evolution for flight is the only rational approach for the appearance of birds. The Ground-Down hypothesis, which the standard terrestrial therapods are necessarily burdened with in evolving flight, is never going to make it, for various obvious, and not so obvious reasons.



BTW, love the score:

Creationists: 0
Legitimate Science: 50 million

(Is that the final score, or just the first inning?!)
I have never liked ground down, becuase it is just not the way we see early flight adaptions today. Often, the example is given of how modern flightless birds use their wings to go faster on land (or at least in a book I just finished reading), but they had flight and lost it because adaptions for it reduced fitness for their niche. We see gliding mammals and such today flying by jumping of trees and gliding, or 'trees down'.

If a therapod that had pseudofeathers that were used to warm larger clutches of eggs (pictured in fossil below, we no that it needed some sort of feather on its arm to warm a nest this way)
1601492119415.png
Let's say, for example one of these smaller theropods with feathers nested in trees, fell out of the nest. If the mother could surrvive this fall, the eggs would not be left without a parent, and therefore not die. In other examples, faster movement gliding from tree to tree for superior hunting to slower ground based small therapods, and the fact that in the trees, they don't have to worry as much about 'the bigger fish'.
1601492933120.png
Adressing body plans such as long arms, remember, these are dinosaurs about the size of a chicken. Chickens can still hop despite thier relativly short wings in relation to weight. But, the velociraptor, a probaly non-avain dinosaur had not so short arms. The archaeopteryx has1601493362152.png
very similar arm structure to the velociraptor fossil, other than increased muscle anchors, a nessecary adaption for flight.
 

Attachments

  • Like
Reactions: Chem721
Jul 27, 2020
195
21
105
I have never liked ground down, becuase it is just not the way we see early flight adaptions today.
It must be stated out-right that you are certainly on the correct track by rejecting the ground-down concept. You are half-way to appreciating the reality of the true descent of the avian line.

If a therapod that had pseudofeathers that were used to warm larger clutches of eggs (pictured in fossil below, we no that it needed some sort of feather on its arm to warm a nest this way)
Firstly, the "pseudofeathers" you note in the first fossil are not really feathers (if you are referring to the dino-fuzz seen in some fossilized specimens). The "fuzz" results from the extrusion of collagenous fibers from the animal as it decomposed, and these fibers were fossilized (sometimes carbonized) with the remaining parts as you see them. They are not a part of the animals living morphology. This sort of thing has been seen in various fossils unrelated to birds and dinos. So pseudofeathers are not in the picture, at least not this one, if you will be so kind as to allow this for the moment.

Indeed, feathers of any kind are not yet in the story line since we are looking for fossil remains without feathers, with a morphology evolving to an arboreal climbing-glider. That is also why it is not appropriate to bring in Archaeopteryx, which has feathers, and existed ca. 80 million years after the rise of the basal bipedal therapod. So with Archaeopteryx, we are well along in the avian line - it is true flying bird with wings and feathers, but does not provide the evidence for how it arose. But one can see that it has greatly increased the mass distribution of its body plan, just as one would expect for a development leading to birds. There are other features of Archaeopteryx which are discussed later which really seal the deal, so to say.

Adressing body plans such as long arms, remember, these are dinosaurs about the size of a chicken.
Regarding the smaller sized therapods. It really has no advantage to evolving flight. The mass imbalance and short arms still exist, and there is no way around it. An albatross and a hummingbird are prime examples of how size should not be part of these considerations. Unless you have developed the correct morphology, all notions that even small therapods could evolve into birds requires the same intermediate forms. Where are they, of any size? The smallest terrestrial bipedal therapod has no more likelihood of evolving flight than T. rex., unless there are featherless fossil intermediates to demonstrate the divergence.

the archaeopteryx has very similar arm structure to the velociraptor fossil, other than increased muscle anchors, a nessecary adaption for flight.
This is true, but the velociraptor lived around 75 mya, about 75 million years AFTER the appearance of the first flying birds, and I do not recall any of their fossils having feathers. So it is difficult to consider it as evidence for a link to the avian line, and probably represents convergent evolution. For the velociraptor, longer arms provided more efficient hunting skills, a definite evolutionary advantage. A similar body form allowed more rapid movements, again, better hunting skills. But it still comes about 125 million years after the ORIGIN of the avian line, so there is little chance that it is related (unless it is a flightless relative).

It should be pointed out, going back to the archaeopteryx fossils, that it has three highly extended digits on its forearms, obviously for the accommodation of feathered wings. Since it is believed to be a true bird, the development of these fingers would be conserved all the way to modern birds. And this is where there is a major problem for the therapod line.

Feduccia et al. (1) and others have observed the development of these three fingers of modern birds during embryogenesis. In various species, it is confirmed that these three flight digits arise from the primordial pentadactyl (five-fingered) hand by reducing digits I and V. This means its flight digits are II, III, and IV. It is without doubt by anyone that therapods have reduced their pentadactyl hand to three fingers by reducing digits IV and V.

This is an observation which cannot be lightly dismissed, as there is no way you can reverse such a reduction as seen in all therapods since their very beginning. Some who don't like this problem have suggested means by which mutations could have occurred to allow a "frame-shift" in the digit development to get therapods back into the game, but that is highly unlikely. To end that controversy, it simply needs to be pointed out that modern birds do not need any mutation to clearly demonstrate the origin of their flight digits. Only the therapod origin concept requires such special pleading.

It should also be pointed out that it is nearly impossible to determine the origin of these digits in adult fossils, and the loss of digits I and V in modern birds is seen only fleetingly in its earliest stages of embryogenesis. And no one previously debated the origin of the therapod digits until the results of Feduccia et al. were established beyond any doubt. And they have the photographs to prove it!

Therapods have digits I, II and III in their forearms, reducing IV and V during embryogenesis. Anyone with knowledge of developmental biology will tell you this is a real problem for the origin of birds from therapods.

There are other aspects which create rather large problems for the notion that birds arose from therapods. But I will let you or others reply to these recent comments and see where it takes us.

1. https://en.wikipedia.org/wiki/Alan_Feduccia
 
  • Like
Reactions: hellopunyhumans
Jul 27, 2020
195
21
105
ahem. ever hear of a TYPICAL pterosaur. did NOT have feather. out
Aside from their reptilian origin and capability for flight, pterosaurs are in no way related to birds or therapods.

Hopefully, that is "out" and gone, with the same erroneous simplicity.
 
Jul 27, 2020
195
21
105
wow. no way. really???? oh darn
It is appreciated that we keep the commentary on the topic.

Thank you for your interesting posts.

However, since you brought them up:

The pterosaurs were certainly amazing creatures. They arose from a related stem line ca. 230 mya. But they were a group of flying reptiles which evolved independently of birds. As such, they provide no direct evidence for avian evolution. It does provide us with a new topic to investigate - pterosaurs if you are up for it. They lasted for over 150 million years! And they almost certainly evolved flight from elevated positions, apparently also denying the ground-down notion for the evolution of flight.

But this thread is supposed to be about bird-brains, and those of a feather flocking together.......and where birds really came from.
 
Sep 26, 2020
31
3
55
ahem. gaps in the fossil record are the NORM. because the form of the original question was Rhetorical, finding a decent perch is not a certainty. i, therefore, choose to attempt to provoke 'broader' thought. have you seen michael cremo's research; in the 90s. there is plenty of documentary, and physical, evidence to suggest that tool-using humans were present, Millions of years ago. thus, over-confident reliance on the story told by the fossil record, for any purpose, is not recommended.
View: https://www.youtube.com/watch?v=DKfGC3P9KoQ

if humans have been around so long, why are we, still, stoopidly prone to superstition/religion, war, etc. this is not a rhetorical question.
i have seen one, incomplete and not wholly accurate, theory of cometary bombardment. see YD impact theory. of the many gaps in the theory, one is a failure to contemplate how a major influx of co2 at ground level would affect the ecosphere. comets are NOT water/h2o.
any major cometary bombardment would result in a 'new normal' level of atmospheric co2. the affects of a cometary bombardment would linger longest, in the ( N/S) hemisphere, where the impacts occurred. any evidence of (such) impacts will tend to 1) progress from west to east and 2) happen at the Same Latitude. if interested, see the latitude of the carolina bays and the seafloor pits, off the coast of california. d
malta
bull creek texas
View: https://www.youtube.com/watch?v=8ZVigtZpgiI

 
Jul 27, 2020
195
21
105
there is plenty of documentary, and physical, evidence to suggest that tool-using humans were present, Millions of years ago.
It would be difficult to imagine a more irrational comparison to the evolution of birds from therapods than the evolution of tools in humans. It is simply an irrational proposition.

Your best bet would be to start a thread of your own, with all these notions and see if anyone wishes to discuss them. None of them provide any value whatsoever to this thread.

Your cooperation in this regard would be appreciated by all who wish to stay on topic, and not bring in totally unrelated aspects to the thread.
 

Gringoz

BANNED
Oct 3, 2020
79
3
55
It would be difficult to imagine a more irrational comparison to the evolution of birds from therapods than the evolution of tools in humans. It is simply an irrational proposition.

Your best bet would be to start a thread of your own, with all these notions and see if anyone wishes to discuss them. None of them provide any value whatsoever to this thread.

Your cooperation in this regard would be appreciated by all who wish to stay on topic, and not bring in totally unrelated aspects to the thread.
All these threads come back to the same point, which is what came first, dna or the animal that needs it to exist. The best analogy is what came first computers or computer code...........................
 
Jul 27, 2020
195
21
105
This is all very true, but still has nothing to do with the topic of this thread.

Perhaps you should start a thread regarding "The best analogy is what came first computers or computer code"? You would likely get a lot of interest.
 

Gringoz

BANNED
Oct 3, 2020
79
3
55
This is all very true, but still has nothing to do with the topic of this thread.

Perhaps you should start a thread regarding "The best analogy is what came first computers or computer code"? You would likely get a lot of interest.
All these threads come back to the same point, which is what came first, dna or the birdbrainl that needs it to exist.
 
Jul 27, 2020
195
21
105
There is another reason to reject the ground-down concept for therapods evolving flight from its standard bottom-heavy, top-light incompatible mass distribution, which eliminates such a form from directly evolving flight morphology.

It should seem obvious to those pondering the notion of the evolution of powered flight that there is much more involved than simple morphology. Clearly there are changes required which must control the "flight surfaces", and this must require a highly evolved neuro-muscular coordination for flight stabilization and capabilities within the brain and muscles of the evolving flyer.

Thus the biological aspects of powered flight requires the co-evolution not only of body plan, but also of the brain's control over those body parts involved in flight. The animal must be able to deal with landings and take-offs, high winds and wind-shear, avoiding other flying predators, and a host of aspects which are required to reliably control flight, gliding, attitude and other aspects. These are only likely to co-evolve with a climbing-glider, from the trees-down, rather than a therapod, from the ground-down. There is no rational approach for evolving such neuro-muscular evolutionary changes from a ground-down evolutionary sequence leading to flight. It is simply not possible.
 

ASK THE COMMUNITY

Latest posts