Thursday, October 27, 2011

"Bird feathers are analogous to the wing fibers of pterosaurs,"

Here is a reference that shows the internal composition of the pterosaur wing membrane. It is quite astonishing. Check out page 241 and the pages nearby.

Page 243:
The strings cross the fibres at angles between 30° and 90°

It is astonishing, because we can see that the structure and material of feathers is already present as the actinofibrils in the membrane.
"Bird feathers are analogous to the wing fibers of pterosaurs,"

"Wellnhofer [4, 5] and Padian [6, 7], following von Zittel [8],described a system of fine structural fibers investing the wing membrane, in a pattern similar to the orientation of the feather shafts of birds and the wing fingers of bats, both principal structural elements supporting the patagium and responsible for the transmission of aerodynamic force."
The wing membrane was supported and controlled through a system of stiffened, intercalated fibers, which were oriented like the main structural elements in the wings of birds and bats.

From David Unwin's book "The Pterosaurs from Deep Time":
"...[T]he wing fibers were embedded within the patagia [wing membranes] and typically measured a little less than one-tenth of a millimetre in diameter- about twice the thickness of a human hair. In some spots unravelled fibers reveal that they were composite structures composed of at least 20 or 30 very fine strands, wound together in a helical fashion. Each strand was only a few hundredth of a millimeter across and probably made of collagen a material that is common in the skin of vertebrates".
"The actual function of the actinofibrils is unknown, as is the exact material from which they were made. Depending on their exact composition (keratin, muscle, elastic structures, etc.), they may have been stiffening or strengthening agents in the outer part of the wing.[6] The wing membranes also contained a thin layer of muscle, fibrous tissue, and a unique, complex circulatory system of looping blood vessels.[7]"
"Since they [actinofibrils] were external, they were probably epidermal structures composed of keratin as in scales and feathers."
"research has since shown that the wing membranes of pterosaurs were actually highly complex and dynamic structures suited to an active style of flight. First, the outer wings (from the wing to the elbow) were strengthened by closely spaced fibers called actinofibrils.[5] The actinofibrils themselves consisted of three distinct layers in the wing, forming a crisscross pattern when superimposed on one another."
"The brachiopatagium ("arm membrane") was the primary component of the [pterosaur] wing, stretching from the highly elongated fourth finger of the hand to the hind limbs"

"Pennaceous feathers are also known as contour feathers. This type of feather is present in most modern birds and has been shown in some species of maniraptoran dinosaurs. A pennaceous feather has a stalk or quill. Its basal part, called a calamus, is embedded in the skin. The calamus is hollow and has pith formed from the dry remains of the feather pulp, and the calamus opens below by an inferior umbilicus and above by a superior umbilicus. The stalk above the calamus is a solid rachis having an umbilical groove on its underside. Pennaceous feathers have a central shaft (or rachis) with vanes or vaxillum spreading to either side. These vanes are composed of a high number of flattened barbs, that are connected to one another with barbules.
The barbules are tiny strands that criss-cross on the flattened sides of the barbs. This forms a kind of miniature velcro-like mesh that holds all the barbs together, stabilizing the vanes."
Remiges (from the Latin for "oarsman") are located on the posterior side of the [bird] wing. Ligaments attach the long calami, or quills, firmly to the wing bones, and a thick, strong band of tendinous tissue—known as the postpatagium—helps to hold and support the remiges in place.[1]
" In ornithology, the triangular fold of skin, just back of the shoulder-joint, which runs from the side of the body to the upper posterior face of the upper arm."
"Postpatagium is the tough band of tendinous tissue that envelops and supports the quills of all the wing remiges, from elbow to wingtip. The postpatagium provides much of the elastic strength of the wing and keeps the flight feathers properly aligned and firmly attached to the wing skeleton."

This is interesting:
"I`m not sure exactly how feathers developed,but actinofibrils arranged in a pattern similar to flight feather rachis is very suggestive."

Earlier post:



  1. Let's look at the word "analogous" again.
    In ordinary English it means:
    "Comparable in certain respects, typically in a way that makes clearer the nature of the things compared."

    In evolution terminology, it has a particular meaning:
    "An analogy is a trait or an organ that appears similar in two unrelated organisms. The cladistic term for the same phenomenon is homoplasy*, from Greek for same form. Biological analogies are often the result of convergent evolution.".

    So when we see the phrase, "Bird feathers are analogous to the wing fibers of pterosaurs", the writer is expressing the opinion that bird feathers did not evolve from those fibers, even though the bird feathers and the pterosaur wing fibers (actinofibrils) are very similar.

    But the simpler explanation, which I am proposing, is that in fact, bird feathers did develop from those pterosaur wing fibers.

    *Do not confuse the word "homoplasy" with the word "homology".

    FOR FUN:
    When a pterosaur wing is reactin',
    Are its actinofibrils contractin'?
    Spreading rays are arrayed
    When its fingers are splayed,
    But their fibers? They're not really actin.
    (AK-tih-noh-FIE-brihl) The arm membrane (brachiopatagium) of a pterosaur wing was composed of several layers of fibers called actinofibrils. One might wrongly infer from the name that they were made of the actin muscle protein. They weren't; the name derives instead from their radiating pattern.

  2. In the bird it should be noticed that feathers extend from the ulna, the carpometacarpus and a few from the fused digits.

    In the pterosuar, the actinofibrils in the membrane extend from the ulna, the 5th finger metatacarpal and the 5th finger.

    I believe that is correct. Any input on that specific question?

  3. In addition, in the bird a few feathers extend from the alula and in the pterosaur the propatagium is supported by the pteroid.

  4. It's really quite amazing how similar the pterosaur wing is to the bird wing. It almost makes me wonder if Pterosaurs developed directly into primitive birds while maniraptors developed into their own separate lineage from pterosaurs.

  5. Holy Pterror is probably being sarcastic. But even as sarcasm it is confused.
    I am proposing that pterosaurs developed into primitive birds.
    Maniraptors (eg. dromaeosaurids, enantiornithes, ichthyornithes etc.) are primitive birds.

    And then those primitive bird lines developed into modern bird lines.

  6. I am not being sarcastic. I have been following your research for quite some time and it paints a very vivid and clear picture of pterosaur to bird development. You're doing great work. Keep it up!

  7. Hello Holy Pterror.
    I have suggested the following:
    In the bird it should be noticed that feathers extend from the ulna, the carpometacarpus and a few from the fused digits.

    In the pterosuar, the actinofibrils in the membrane extend from the ulna, the 5th finger metatacarpal and the 5th finger.

    Is what I am saying correct?

  8. It sure seems like it.

  9. The thing that throws people off in seeing the similarity of the pterosaur hand to the bird hand is of course the long 5th finger that the pterosaur has.
    But if that 5th finger is dramatically shortened or lost we can see that the hands are very similar. And we have seen that the fibers in the membrane are very similar to feathers.

    The progression is from pterosaur to primitive bird to modern bird.

  10. It is difficult to do a comparison of the pterosaur fingers to the fingers of modern birds because the fingers of modern birds are fused (and potentially some have been lost).

    The easy part is the pteroid relationship to the alula.
    But the relationship of the other fingers is mote difficult.

    The bird's fused fingers potentially include fingers 2 through 5. (The thumb is the first digit).

    It would be VERY helpful to know what the unfused bones are of bird embryos. Then we would know which fingers exist within the fused material.

    And related to this is the carpometacarpal which includes the fused metacarpals.
    How many metacarpals are fused together there? Were any metacarpals lost?

  11. Putting together a few ideas:

    If we work with the idea that ratites are the result of neoteny then what we see in their hands may give us an idea of what primitive birds in the lineage to modern birds may have been like.
    The following is significant:
    Digit II claws are rarer but are present in some neornithines (like some ratites, juvenile waterfowl and flamingos), so might also be primitive for the clade. It's sometimes said that cassowaries have a particularly large claw on digit II that they use as a weapon (Stettenheim 2000). Indeed, like other ratites, they do have such a claw,"

    This can lead to the conclusion that dromaeosaurids with that large claw on the second digit may be the ancestor of modern birds as I have proposed. The large claw is there in the early stages of the embryo but does not get expressed. (However it gets expressed in the ratites due to neoteny).

  12. Out of curiosity, what are your thoughts regarding bats vis a vis pterosaur to bird development? Perhaps they fit in somewhere as, like pterosaurs, bats fly and have a wing membrane.

    I would be interested in hearing your analysis of the subject

  13. Hello Holy Pterror.
    I have not researched the bat. If you would like to do that, we could do that together.
    What are your thoughts?

  14. Holy Pterror, if you want to analyze the bat just set up a blog on* and present your thoughts. I would be delighted to contribute. But I do not want to get sidetracked on this site. So I will not be saying more here.

    * It is free and very easy.

  15. Here's an interesting paper that might be of some help. It compares the wing membrane of bats and pterosaurs to the wings of birds.

    I am beginning to think more and more that bats are somewhere in the pterosaur lineage. Perhaps Pterosaurs developed into bats and a bat subgoup developed into a dromaeosaurid group that later developed into birds?

    Or perhaps a bat subgroup broke off from pterosaurs and went on their own lineage. Though the similarities of flight and wing membranes between pterosaurs and bats and later pterosaurs and birds make this idea somewhat hard to digest.

  16. Holy Pterror, if you would like to discuss the bat then set up a blog and I will be delighted to contribute.

  17. Holy Pterror, I appreciate your further posts but I will not be posting them here.
    Set up your own blog. It is easy and free.
    I will be delighted to contribute.

  18. This is interesting:
    "I`m not sure exactly how feathers developed,but actinofibrils arranged in a pattern similar to flight feather rachis is very suggestive."