Precision in Nomenclature #1 (Phalanges)


Yay! Another series, and more of a break. This time, it’s about terminology, one of my more favorite aspects of methodological science. Without knowing what to name stuff, we lapse into grunting and rude gestures, and nobody likes that. Well, I mean, I guess some of you do — perverts.

But terminology has two broad aspects, and in most cases, they are both highly useful, but you need to keep an eye on them.

1. Terminology must be concise (structure): You have to know that a term will often affect a broad range of things, while at the same time you want to keep an original concept original.
2. Terminology must be intuitive (form): You have to get nomenclature to use it, and a person who cannot grok that term will not understand it, regardless of how precisely you’ve used it. (You see what I did thar?)

This prefaces our introduction to terminology.

Phalanges are those bones or bits in your fingers and toes, and they often move around; they let you grip, maintain balance while standing, provide leverage while walking, and can be used as singalling devices. Different groups call different digits different things (like fingers, digits, or polleces). Sometimes, a system will use the same terminology, but connect the terms to different types of digits under different schemes. While this is not always a problem, it runs us afoul of point 1, and this is especially true of avian digit homology of the wing (also called “arm” or “forelimb”). There are even problems when, dealing in homology, sometimes what is originally one type of digit becomes another, and the terminology shifts (or doesn’t) when it should do the other under the argument being used (also apparent in avian digit numbering, but then this system becomes problematic when dealing with things like vertebral identity in vertebrates from fish to amphibians to reptiles to mammals).

Here I will present a scheme:

(a) The anterior and posterior limbs in tetrapods are the only motile limbs in any vertebrate that bear digits (mutants don’t count, and those are generally duplicates of standard limbs anyway and will follow the scheme for that limb);
(b) The anterior limb will be called just that (but it is also the forelimb or arm, depending on your group) and will be abbreviated AL, while the posterior limb will be called that as well (but is also a hindlimb and leg), regardless of whether you’re human, and is abbreviated PL;
(c) The manus is the digit-bearing extremity of the forelimb, and is the anterior autopodium, but when talking about the classic manus in isolation of the carpal system or limb we can also use just manus (m), and consequently the posterior autopodium is the pes (p);
(d) Bone sets between the limbs are simplistic: Carpals (C) and tarsals (T) are coordinated in some groups with metacarpals (MC) and metatarsals (MT, and are numbered using the Roman numeral system (I, II, III, etc.) with the exception of elements that do not follow a regular serial system (e.g., mammals); abbreviations labelling names of bones are capitalized, while element segments of the autopodium are not (e.g., MTII);

These terms are essential for prefacing the basic layout for phalangeal terminology, which is slightly more complex:

(e) All digits are numbered serially from the first to the last following the Roman numerals and are listed after the label “d” (e.g., dI, dII); further, all digits are listed under their autopodial designation (mdI, pdII, etc.) where “m” means manus and “p” means pes;
(f) All phalanges are numbered serially from the base to the last element of the digit, regardless of whether it ends in an ungual (“claw”) and follow the Arabic numeral system (1, 2, 3, etc.) following a dash (to separate the two numbers clearly), such that the first phalanx of the first digit is dI-1;
(g) Where left and right material is distinguished, the preface “r” and “l” followed by a dash and then by the designation is used (e.g., r-mdII-3).

The diapsid autopodium, horribly simplified. Metacarpals/metatarsals (MC and MT) in black, non-ungulate phalanges in dark gray (dI-1, dII-2, etc.), and ungulate phalanges in light gray (dIII-4u).

Finally, a graphical representation of this idea. An additional notation is used, which may or may not be useful: I apply the label “u” after the phalanx number to indicate it is an ungual, i.e., a terminal phalanx modified to bear a nail or claw. Such a phalanx is generally modified from another phalanx, termed intermediate, by the absence of a distal articulation and is usually expanded or otherwise differentially shaped.

I should also like to draw attention to the debate on the digital homology of birds, which has been shown to correspond to diapsid digital condensations in crocodilians and mammals as digits dII-III-IV, while the digits are modified as to correspond morphologically to dI-II-III. Under this scheme, regardless of the homology issue, the phalanges have the morphology and identity of dI-II-III, and that is suggested here for workers who find this post of any importance. The reason for this is that it is not actually certain where, in the development of Theropoda, the identity shift from I-II-III to II-III-IV occurs, despite recent work [1] indicating an apparent fossilized portion of the shift, which has been rebutted [2] on the basis of other homological data. I have little to say on this matter.

Note: Notation aside, terminology for phalanges is pretty cut and dry, although there are interesting corrolaries; in birds, there is a system of terms for the position and relation of the phalanges to one another, and some of these terms (such as syndactly) have been used for mammals as well. Other terms, though, are generally universal.

Pollex – This is generally used for the first manual digit, mdI, also called the “thumb” in humans. It is not generally regarded as a finger in humans (e.g., the phrase “finger and thumbs”), and is called the alular digit in birds.
Hallux – This is generally used for the first pedal digit, pdI, and also called the “big toe” in humans.
Intermediate phalanx — Any phalanx that is not terminal or an ungual, or is the first phalanx in a digit’s series.
Proximal phalanx — This first phalanx in a series of at least two; if the phalanx is by itself, it’s generally terminal.
Terminal phalanx — The last phalanx in a digital series, often modified into an ungual; in some cases, this phalanx is unremarkable, and is not ungulate in form, but just a nubbin.

[1] Xu X., Clark, J. M., Mo J., Choiniere, J., Forster, C. A., Erickson, G. M., Hone, D. W. E., Sullivan, C., Eberth, D. A., Nesbitt, S., Zhao Q.-l., Hernandez, R., Jia C.-k., Han F.-l., and Guo Y. 2009. A Jurassic ceratosaur from China helps clarify avian digital homologies. Nature 459:940–944.
[2] Vargas, A. O., Wagner, G. P. & Gauthier, J. A. 2010. Limusaurus and bird digit identity. Nature Precedings

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45 Responses to Precision in Nomenclature #1 (Phalanges)

  1. Jack says:

    I have a question about modern bird hands.
    Would the common modern bird hand be:
    1-2-1-x-x?
    I got this idea from David Marjanović here:

    http://scienceblogs.com/tetrapodzoology/2009/02/pterosaur_breathing_air_sacs.php

    • This is related to ascribing the identity of the avian digits to their position and moprhology, without having to take into account homeotic shift or identity shift. In this case, than avian digits (alular, major, minor, II-III-IV) are equivalent to theropod I-II-III, and should be regarded as such for simplicity.

  2. Jack says:

    Here is a followup question about the pterosaur hand.
    If the pterosaur pteroid is considered the thumb would the pterosaur fingers be:
    1-2-3-4-4 ?

    • This requires the pteroid to be a thumb. The best data at hand, drawn from the condition of the patagia and position of various muscle and tendon sites, argues that the pteroid, which has a distally-located site for a tendon that stretches to the shoulder, is a carpal bone; thus, the pterosaur manus would by 2-3-4-4-x. Modification of carpals or sesamoids into metacarpal or phalanx-like morphology, as occurs in some mammals, doesn’t allow the element to assume a digital identity, and in this case, the pteroid is only positioned where any other first digit would sit (if there was an identity shift). This means pterosaurs would have lost their fifth digits.

      The pteroid articulation (on a carpal) seems like a metacarpal, but then at that point that’s all it is: a modified metacarpal; if it corresponds to a digit identity, its muscle attachments would correspond to that, but the sites for muscles seem to indicate, and various soft-tissues back this up, it bore a tendon that is generally located on a carpal element or in the wrist region, but not on a digit.

  3. Jack says:

    I am familiar with the line of reasoning that you have described. My question is – IF the pteroid is the thumb, then the pterosaur hand pattern would be 1-2-3-4-4.
    And I think you are confirming that IF the pteroid is the thumb, then the pattern would be 1-2-3-4-4.

    And IF that is the case, then the elongated finger of the pterosaur, which is usually described as the 4th finger would in fact be the fifth finger.

    I am not asking you to agree with the idea that the pteroid is the thumb. I am just saying that if it is (which I believe to be the case) then the hand pattern would be as I have described.

    • Yes, if the element were a metacarpal, the phalangeal formula would be something like 0-2-3-4-4. There would be no phalanges on digit one (the pteroid digit). If Unwin et al. [1] had that particular accepted over any other, it was not as though they rejected the others, and their support was not strong for it. Articulation of the pteroid is to a distal carpal, like a metacarpal, but not in a typical spot for a metacarpal (on the extensor margin, where various tendons providing extension of the wrist and passing to the metacarpals for extension of the first, second and third digits would be located.

      [1] Unwin, D. M., Frey, E., Martill, D. M., Clarke, J. B. & Riess, J. 1996. On the nature of the pteroid in pterosaurs. Proceedings of the Royal Society of London, B 263:45-52.

  4. Jack says:

    Here is a simpler explanation. The pteroid bone is simply the thumb metacarpal. The digit part has been lost.
    In that case the pterosaur hand pattern would be
    x-2-3-4-4.
    The x in this case just means that the digit part of the thumb has been lost but the metacarpal part is of course still there and called the “pteroid”.
    There is reference to this idea, referred as the “first metacarpal”:

    http://www.jstor.org/pss/50448

    “The nature of the pteroid, a rod-like bone projecting from the carpus in pterosaurs, has long been disputed. Three lines of evidence, morphological, developmental and histological, indicate that the pteroid is a true bone, rather than ossified cartilage. The origin of the pteroid is unclear: it may be a modified carpal, the first metacarpal, or a neomorph. “

  5. Jack says:

    I have put a reference to your point here:

    http://pterosaurnet.blogspot.com/2010/05/continued-2.html

    “The pteroid articulation (on a carpal) seems like a metacarpal, but then at that point that’s all it is: a modified metacarpal; if it corresponds to a digit identity, its muscle attachments would correspond to that, but the sites for muscles seem to indicate, and various soft-tissues back this up, it bore a tendon that is generally located on a carpal element or in the wrist region, but not on a digit.” (J. Headden)

    • You may want to hold off on citing me for that, as I’m certainly not an accredited researcher on the topic; but I am okay with it for now, with that caveat attached. Try getting a hold of S. Christopher Bennett, who has done far more work on this topic than I would think I could ever do.

      For the record, there is a decent amount of research on pteroid function and evolution, with some amount of debate on how the pteroid articulated, which influences the theories to its evolution. Bennett [1] gives a brief summary of this, and it is by the more current argument on the evolution of the pteroid itself, without calling into question the pteroid’s function or position on the carpus.

      [1] Bennett, S. C. 2007. Articulation and function of the pteroid bone in pterosaurus. Journal of Vertebrate Paleontology 27(4):881-891.

  6. Jack says:

    Since you have an interest in precision in nomenclature, how would you document a situation where the metacarpal is there, but the digit is lost?
    For example, in the situation I have been talking about, if the pterosaur thumb metacarpal is there but the thumb digit is lost would the pterosaur hand be documented as
    0-2-3-4-4?

    • Phalangeal nomenclature would only involve existing phalanges, when present. Counting digits, though, would require counting metacarpals/tarsals. In the case of some theropods and crocs, an outermost digit will be lost, but the metacarpal stays around, often serving additional functions; some sauropods lack ANY phalanges on the manus, or just have a phalanx and claw on the first manual digit (mdI) — the phalangeal formula is 2-0-0-0-0.

      So yes, if there was another pterosaur metacarpal, it would have a “digit” with no phalanges.

  7. Jack says:

    If a pterosaur hand was 0-2-3-4-4 would a modern bird be 0-2-3-x-x (where x means that both the 4th and 5th digits and metacarpals are lost)?

    My interest is in showing that the hand of a pterosaur is similar to the hand of a modern bird. And they are.

    • Well, the evolution of the avian hand as derived from the basic tetrapod manus, a standard configuration of 2-3-4-5-x, coincides with the pterosaur hand only in deriving from a similar tetrapodan configuration. Pterosaurs retain four digits, losing one, and birds simply lose two. The evidence supports that in theropod evolution, they dhifted digit identities from I-II-III to II-III-IV, but the manus is still functionally I-II-III, and pterosaurs simply add to this. But any reduction of unecessary digits in various animals that do reduce them (some turtles, crocs, etc.) do so from an external direction (losing outer digits first). It may be presumptuous without extraordinary data to push pterosaurs into a configuration that presupposes the hands are similar to each other in their evolutionary development, beyond the typical tetrapodan digit reduction observed. It would require a (or several) functional analysis/es of digit reduction for mechanical purposes …. unless you are proposing that pterosaurs and birds are more closely related than has been typically accepted?

  8. Jack says:

    I am having trouble posting here. Is there a technical problem?

    • I am not sure. WordPress is usually good on posting.

      • Jack says:

        Thank you for working with me on the specifics of the documentation of bird hands and pterosaur hands.
        Pterosaur: 0-2-3-4-4
        Bird: 0-2-3-x-x
        And yes. Pterosaurs and birds are closely related. Modern birds developed from pterosaurs.
        For details see:

        http://pterosaurnet.blogspot.com/

        I am quite interested in your thoughts.

        • Jack says:

          For a pterosaur hand to develop into a bird hand, all that would be required is for the 4th and 5th fingers to be lost.

          • It’s not just the hand that is at issue with trying to place pterosaurs and birds together to the exclusion of any other archosaur; it’s the rest of the skeleton, including the skull. Trying to even say dromaeosaurids or such are birds to try to contradict the argument that birds and dromaeosaurs share so many features that link them ancestrally to other archosaurs is shifting a nomenclatural goalpost: the term “bird” simply encompasses what is now called Paraves. But what you’re also trying to do with what Czerckas did for a few papers, and that was try to take dromaeosaurs out of Dinosauria without absolutely any evidence, much less finding a separate and more parsimonious lineage with which to support this premise. The statement “MANIAC” (Maniraptorans are not in actuality coelurosaurs” isn’t a hypothesis of any sort, as it makes no positive argument, just dismisses one hypothesis without replacing it. This is, in short, not scientific.

          • Except that in all of pterosaur development, the manus is unchanged in its formula, and is derived further towards elongation. There is NO morphological similarity in the manus save for reduction and loss of the fifth digit and metacarpal, and this is so prevalent among Diapsida that singling out avians and pterosaurs as special for doing something lizards, crocs, turtles, and dinosaurs (not to mention frogs, salamanders, and even mammals) all do progressively. Loss of the outermost pedal digit (pdV) also occurs in nearly the same pattern as loss of the outermost manual digit (mdV), and often occurs in sync with each other. This is because the outermost digits in virtually all tetrapods are the most extraneous, and the most useful to lose to free-up developmental time, energy, and reducing costs.

  9. Jack says:

    It’s not just the hands – agreed. It is dozens of other characteristics as well.
    They are all laid out in great detail at:

    http://pterosaurnet.blogspot.com/

    If you wish to dismiss the idea, you need to address the dozens of similarities. We have nailed down the striking similarity in the hands. We have just scratched the surface.

    • My address to the idea does not require a point-counterpoint dismissal of your posts. This idea has not been supported in the scientific literature on a morphological basis without placing dinosaurs in between them (the classic Ornithodira topology), even though Bakker, for no strong reason, placed them within dinosaurs. The argument you make does not require anyone to actually try to refute it. All I might need to do is point to the various cladistic analyses of the last 20 years supporting archosaur topology, even when pterosaurs are wishy-washy in where they fall, to argue that your premise requires severe rigorous testing of THEIR theories (using their methods, or a method that is independent of personal interest, such as parsimony or logic that can be shown to produce more seemingly accurate results of their own data) before you can say your theory is better.

  10. Jack says:

    I made a typing error.
    The bird hand is 0-2-1-x-x.
    And the pterosaur hand is 0-2-3-4-4.

    • It would be better if you framed your statements in the form of an hypothesis (because of A, then B).

      If you think that pterosaur hands underwent the same shift in avian digit identity (unproven) you would need to back this up with precursor fossils that show a likelihood in transitioning digit identities. We haven’t even found this for dinosaurs, despite Limusaurus, although it came close. But you must also understand that the earliest birds, especially if you consider dromaeosaurs “birds” have a digit identity of I-II-III and a phalangeal formula of 2-3-4-x-x; pterosaurs, as a group, start out with a formula of 2-3-4-4-x and reduce it to 2-3-4-3-x in some taxa (e.g., azhdarchids). Birds only reduce relative phalangeal contribution, sometimes cutting them down to just one phalanx per digit, losing the minor digit altogether, or have elaborated unguals as the second [terminal] phalanges (even when that digit is the second one), making the ungual identity irrelevant of digit identity (I wrote of this in the post to which we are in the reply section of).

      Even if you propose that the digits are II-III-IV-V (which I do not understand — it is far more likely [historically] to lose the outer than the inner dgit, evolutionarily) the phalangeal formula should be constrained according to the earliest members (as any derivative taxa can modify the digit morphology wildly: moa don’t even have a manus, and kiwi have just one actual digit!)

  11. Jack says:

    You are making this much too complicated.
    I am not saying that pterosaur hands underwent the same shift in avian digit identity. No shift is necessary.
    The bird hand is 0-2-1-x-x. There is agreement on that.
    And the pterosaur hand is 0-2-3-4-4. There is agreement on that.

  12. Jack says:

    Let me clarify.
    The MODERN bird hand is 0-2-1-x-x. There is agreement on that.
    And the pterosaur hand is 0-2-3-4-4. There is agreement on that.

    • 1. The modern avian hand varies (edit: I wrote “various” here) in its phalangeal proportions. Up to clade Aves, used here to describe all descendants of the most recent common ancestor of all living birds, as a crown clade, the basal condition is that the alular digit has one phalanx (some birds have a calcified and horn-covered claw on the end), the major digit has to phalanges (some birds modify the second or add a calcified and horn-covered claw on the end), and the minor digit has between one and two phalanges. In taxa which deviate strongly from this (hesperornithiforms and moa lose the manus entirely, kiwi have only one functional digit with a claw on the end [the major digit]) they are generally kept out for the sake of simplicity when counting digit phalanges in general. In this case, birds have a digit identity of I-II-III-x-x, a developmental identity of x-II-III-IV-x, and a phalangeal count [using digit identity] of 1-2-(1/2)-x-x [and again it can go up to 2-3-2-x-x]. In your statement it seems you are excluding the alular digit to position the first functional digit as having a phalangeal count of 2, and this is incorrect. The agreement you seem to offer so far requires workers to accept that the morphological identity is secondary to the developmental identity, but this excludes all other fossil vertebrates for which we cannot ascertain development in the first several months, as we cannot know how far back digit identity shifted in dinosaurs. You want to include dromaeosaurs in birds for somereason, and you ignore the data used to even support bird origins within dinosaurs that indicated dromaeosaurs are merely modifed theropod dinosaurs, and there is just as much information (from the same people who argued dromaeosaurs and birds are closely related) to put dromaeosaurs inside Theropoda. This is especially significant because tracking back the morphological identity of the hand in theropods presents a clear transition from a full five metacerpals (and apparent fully-five digit identity) down to four, then to three, reducing the outermost digits, We simply do not know where the avian shift occured, as it could have occured between the transition between five digits to four, or four digits to three, and this involves a hefty chunk of Theropoda. So it seems problematic to argue that “there is agreement” when the only contradictory data comes from a single working group that denies the origin of birds from dinosaurs regardless of data (they are called the BAND – birds are not dinosaurs – and often MANIAC – maniraptorans are not, in actuality, coelurosaurs; the latter involves the group that specifically argues dromaeosaurs are birds, but not dinosaurs, and it’s ludicrous in the extent to which they ignore data to support this argument).

      2. You are the only person I have seen who has argued that the pterosaur hand is “0-2-3-4-4.” The last, wing-bearing digit in pterosaurs various in the number of phalanges without there being much of a phylogenetic signal. The agreement, therefore, among pterosaur researchers is that the digit identity is I-II-III-IV-x and that the phalangeal count is 2-3-4-(3/4)-x. I am not sure of anyone who argues otherwise (in the literature, so I have no idea what agreement you speak of). If this is an issue of semantics, i.e., that it doesn’t matter which position you place the particular digit in, then perhaps we can come to a bit of a better grounding, as I argued in this post that phalangeal count can be irrespective of digit identity when the digit identity is morphologically identical to another position (that no shift would occur).

  13. Jack says:

    Let’s begin with the pterosaur hand.
    I should have said that if the pteroid is the first metacarpal then the count would be 0-2-3-4-4.
    Would you agree?

    • IF — BIG “if” — then, yes. It isn’t likely, but the phalangeal count could be that. Try this extension to birds, though: 2-3-2-x-x. There is NO comparative similarity.

      • Jack says:

        We are in agreement that IF the pteroid is the first metacarpal then the pterosaur hand is 0-2-3-4-4. (You think this possibility is unlikely. I would say that it is more likely than any competing hypothesis, but let’s move on to the bird hand.)

        You have the bird hand as 2-3-2-x-x.
        If we take the alula as the thumb then the hand would be 0-2-1-x-x. The alula is the metacarpal and the digit is lost.
        Why do you say it is 2-3-2-x-x?

        • Hopefully I will get around to digital variation and apply the terminology to it to give you a clear idea of some of the things you’re talking about and seem to be confusing:

          1. The avian alula corresponds to the first functional digit of tetrapods, which is called a pollex. In hominoids and general English parlance, this is called a “thumb.” It’s still the first functional digit (mdI). Because this structure contains between 1-2 phalanges in all but polyphalangeal animals such as most sauropterygians, the typical pollecial phalangeal count is 2: mdI-1 and mdI-2. In birds, the pollex is called the alula or the alular digit, has between one and two phalanges, and when the second is present, it is a claw. When it is lost, the metacarpal remains, and is called an alular metacarpal, which correspond to mdI, regardless of the present of a digit. Note that (as I say in the post and so far this being the third time in the comments) even when there is a shift in digit identity, digit morphology indicates analogy to the first digit of tetrapods, making the alula or pollex mdI regardless of the shift.

          2. Did I not previously recount the phalangeal counts of birds from both a morphological and historical perspective? Take gulls, which have a single alular phalanx (mdI-1), two major phalanges (mdII-1 and II-2) and a potential claw (mdII-3), and generally one minor phalanx (mdII-1) with a possible expression of an additional one [in modern birds — but more prevalent among fossil non-Neornithes] (mdIII-2). But this is just in Neornithes (aka, “modern birds”). In older, fossil lineages, a secure 2-3-2-x-x count is known in, for example, Cathayornis yandica. Going even further back, Archaeopteryx lithographica has a phalangeal count of 2-3-4-x-x. This is the condition through which birds of modern form must derive (the “basal condition,” if you will). You cannot use a derived end-product andf adequately compare it to basal taxa without using other basal taxa as a starting point, especially when they are different. This is a fallacy.

          3. You completely ignored my argument about the pteroid position as a rejection of its homology as a metacarpal, didn’t you? We do not agree because there is no evidence for the identity of the element as a metacarpal OR phalanx. While there is a suggestion that it is a metacarpal, so far this is based on the shrugged-shoulder uncertainty of researchers who have not been able to determine what element the pteroid derives from. Not only can I not state with certainty that it is NOT a metacarpal, despite a hefty amount of data to argue it isn’t, YOU cannot state with certainty that it can be a metacarpal, from which you try to assert digit identity shifts in birds and pterosaurs are shared. And een were that to be the case, you can’t rule out convergence of a similar process that occurs throughout Tetrapoda. And note something important in addition to all this: when digit identity shifts, as was indicated for birds, the metacarpal identity shifts WITH it; it is, in fact, the metacarpal identity that controls the digit development and its identity. If pterosaurs have a first metacarpal without phalanges, but birds lack a metacarpal I (based on the Tetrapoda base plan and ignoring my terminology shift), how exactly do they indicate the same condition?

  14. Jack says:

    The pteroid may be the first metacarpal.

    http://www.jstor.org/pss/50448

    “The nature of the pteroid, a rod-like bone projecting from the carpus in pterosaurs, has long been disputed. Three lines of evidence, morphological, developmental and histological, indicate that the pteroid is a true bone, rather than ossified cartilage. The origin of the pteroid is unclear: it may be a modified carpal, the first metacarpal, or a neomorph. “

    • Yes, I cited this earlier. In fact, I provided several refs on pteroid position and posture to you.

      There are issues with the pteroid being anything like a metacarpal or a phalanx, and the first of these is that in any articulation scheme, it will not be articulated in such a way as to favor metacarpal identity. In the scheme of Bennett [1], the pteroid articulates to the posterodorsal surface of the preaxial carpal, posterior and proximal to the sesamoid fovea for the major extensor tendon of the wing digit; in Unwin et al.’s scheme [3], the pteroid articulates to the sesamoid on the end of the preaxial carpal. In the more “conventional” theory of pteroid articulation [2,4] the pteroid articulates on the proximal radiale/radial syncarpal (Peters [2] puts this variably along the radiale/radial syncarpal) and is oriented medially and proximal to the preaxial carpal (which is present in all pterosaurs). Even Unwin et al. [3] put the pteroid proximal to the preaxial carpal.

      Beyond this, the distal end of the pteroid [1], if not the entire pteroid [2,4] was encased in ligaments or a tendon that passed medially to the shoulder, a feature similar to some carpal structures in bats and birds, but not associated with metacarpals or phalanges, and especially not with their distal ends. There is no morphological or associative tissue to suggest that the pteroid is derived from a phalanx or a metacarpal, and even when Unwin et al [3]. mention this in their abstract, they do this to describe it historically: The paper discards the idea; I suggest you read it.

      [1] Bennett, S. C. 2007. Articulation and function of the pteroid bone of pterosaurs. Journal of Vertebrate Paleontology 27(4):881-891.
      [2] Peters, D. 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29(4):1327-1330.
      [3] Unwin, D. M., Frey, E., Martill, D. M., Clarke, J. B.& Riess, J. 1996. On the nature of the pteroid in pterosaurs. Proceedings of the Royal Society of London, B 263(1):45-52.
      [4] Wilkinson, M. T., Unwin, D. M. & Ellington, C. P. 2006. High lift function of the pteroid bone and forewing of pterosaurs. Proceedings of the Royal Society of London, B 273(1):119-126.

  15. Jack says:

    You say again and again things like:
    “from which you try to assert digit identity shifts in birds and pterosaurs are shared.”

    But I have said again and again that I am not asserting digit identity shift in either bird or pterosaur. It is not necessary in the pterosaur to bird hypothesis.

    The idea of the pterosaur-to-modern-bird hand development, does not require an additional hypothesis like a digit identity shift.

    If the pterosaur pteroid is taken as the first metacarpal, then the pterosaur hand is 0-2-3-4-4 and the development to the modern bird hand is straightforward including the loss of two fingers and the fusing of some other fingers. The alula is the continuation of the pterosaur first metacarpal.

    No significant structural changes (or shifts) are required.
    I am presenting the idea that pterosaurs developed into modern birds.
    And as far as the hand, goes it is more parsimonious then the theropod-to-bird alternative. (And it is more parsimonious in any other area we choose to look at.)

    Does that help?

  16. Jack says:

    But you do not have to even go to the site
    Just consider this:

    The idea of the pterosaur-to-modern-bird hand development, does not require an additional hypothesis like a digit identity shift.

    If the pterosaur pteroid is taken as the first metacarpal, then the pterosaur hand is 0-2-3-4-4 and the development to the modern bird hand is straightforward including the loss of two fingers and the fusing of some other fingers. The alula is the continuation of the pterosaur first metacarpal.

    No significant structural changes (or shifts) are required.

    • You may not be getting what I’m trying to go for: One cannot simply posit their similarities on the basis of a “what if?”. The pteroid is likely not a metacarpal, and trying to shoehorn it in requires a great deal of evidence you’ve not presented. And there is NO relation to the avian manus: the avian alula is formed from a phalanx, the first one of a mdI (and occassionally with an mdI-2). That’s JUST for “modern” birds. Basal ones have a fully developed first digit as in Archaeopteryx (you seem to have glossed over this point), and it bears NO similarity to a so-called first metacarpal in pterosaurs, except that actual digit-bearing first metacarpal (non-pteroid!) in pterosaurs. So I am trying to figure out why you AREN’T arguing a digit shift when your premise REQUIRES one.

  17. Jack says:

    There is considerable evidence that the pteroid bone is the first metacarpal. That evidence is on the site.
    I did not want to cover that again here.
    My interest in this discussion was looking at the progression from that pterosaur configuration through to modern birds.
    You look upon Archaeopteryx as a basal bird. As you can see, I am taking a different point of view. The point of view that modern birds developed from pterosaurs.
    You have said:
    “And there is NO relation to the avian manus: the avian alula is formed from a phalanx, the first one of a mdI (and occassionally with an mdI-2).”
    (I appreciate you using your very helpful nomenclature).
    I have a few chores right now but will get back to you about the avian manus.

    Best wishes.

  18. Jack says:

    I have simplified the discussion here. The actual progression is from rhamphorhynchus, through pterodactyloidea, through primitive birds (such as enantiornithes and dromaeosauridae etc), through to neornithes. So the interesting subject is to follow the hand transitions from earliest pterosaur through to modern bird.

    • We’re quickly running out of ground to cover. On the sole topic of phalangeal homology relative to identity, you wish to argue here on your theory. I’m somewhat ok with that, but the comments in this post alone are you repeating yourself without presenting any data, and me shaking my head while presenting data. I do not think this conversation is going anywhere. The wealth of phylogenetic analysis so far contradicts your premises, and this includes the attempt to homologize the pterosaurian pteroid with the avian first “metacarpal.” This is, as they say, an extraordinary claim, and as the saying goes further, it requires extraordinary evidence.

      So, for the moment, I am going to ask you not to comment to this post further. I’d really rather not lock this post from comments.

  19. Jack says:

    Here is a picture (Fig 5) of a primitive bird (Hongshanornis longicresta)

    http://www.pnas.org/content/102/52/18998.full

    You can see that what they call the “alular digit” is the metacarpal. It articulates with the small carpal at the proximal end.

    This is exactly the same pattern in the pterosaur and in the modern bird.

    I am interested in working with you on this. (But only if you are interested of course).

  20. Jack says:

    Here is a good picture but unfortunately does not answer the basic questions about the alula:

    http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1696302/pdf/canvetj00433-0015.pdf

  21. Jack says:

    In a discussion like this it is easy to be so caught up in the tiny details that we overlook the big picture.
    Without regard to whether the pteroid is a metacarpal or a 1st phalange the fact is that the pterosaur and the primitive bird and modern birds all have the same basic configuration. No significant structural change is required to transition from the pterosaur hand to the primitive bird hand (eg. enantiorithes, dromaeosaurid) to the modern bird hand.

    That is the fundamental point I am making. No identity shift is required.

  22. Jack says:

    Figure 1 of this article is helpful:

    http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1560000/

    And

    Description: “Fore-limb and hind-limb compared. H., Humerus; R., radius; U., ulna; r., radiale; u., ulnare; C., distal carpals united to carpo-metacarpus; CC., the whole carpal region; MC.I., metacarpal of the thumb; I., phalanx of the thumb; MC.II., second metacarpus; II., second digit; MC.III., third metacarpus; III., third digit. F., femur; T.T., tibio-tarsus; Fi., fibula; Pt., proximal tarsals united to lower end of tibia; dt., distal tarsals united to upper end of tarso-metatarsus (T.MT.); T., entire tarsal region; MT.I., first metatarsal, free; I.-IV., toes.”

  23. Jesus Christo says:

    Jack is the pedophile Doug Dobney of Peterborough Canada.

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