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Re: Senter 2006, Confuciusornis, and humeral mobility



The discussion of alvarezsaur forelimbs brings me back to the discussion Jamie 
and I had regarding the proper definitions of terms like "reduced", 
"hypertrophied", and  "incrassate".

As I read the literature on alvarezsaurs I noticed that digit 1 is called 
"hypertrophied" by Chiappe, Norell, and Clark in Mesozoic Birds (2002. pg. 
105), even though it is about 1/6th the length of the  ancestral condition (in 
Haplocheirus). It is longer relative to the ulna, but at least four times 
shorter relative to the overall body length. Xu et al.:

 (Xu, Xing; Sullivan, Corwin; Pittman, Michael; Choiniere, Jonah N.; Hone, 
David W.E.; Upchurch, Paul; Tan, Qingwei; Xiao, Dong; Lin, Tan and Han Fenglu 
(2011). "A monodactyl nonavian dinosaur and the complex evolution of the 
alvarezsauroid hand". Proceedings of the National Academy of Sciences 108 (6): 
2338–2342. doi:10.1073/pnas.1011052108.) 

use similar language:

"Adaptation to a specialized function can lead to hypertrophy
of some digits and reduction or loss of others (34). The highly
modified manus of derived alvarezsauroids, in which digit II
significantly widens and lengthens and acquires a large trenchant
ungual..."

This, despite the fact that  basal alvarezsaurs like  Haplocheirus and 
Patagonykus have much larger hands in absolute measurements, and relative to 
their body sizes,  than either  Linhenykus or the most derived alvareszsaurus, 
Mononykus and Shuvuuia. Patagonykus may have a smaller ungual than Linhenykus  
relative to some unmentioned standard, like the ulna.

Jaime, did you ever find a formal definition of "hypertrophied" or "reduced"? I 
think we agreed that these terms are only meaningful relative to some other 
measurement, and that the referent should be given clearly.

But I must just mention  that my use of the term hypertrophied to describe 
Confuciusornis' PH II 1 seems to be consistent with its use by Xu, Chiappe, 
Norell, and Clark. They never give the referent skeletal element against which 
to judge, and didn't you suggest that it should always be assumed to be the 
ancestral state? You suggested that I actually meant "incrassate", but I've 
never seen this term in the work of those four authors. 

-Jason


On Mar 30, 2011, at 9:22 AM, Jaime Headden wrote:

> 
> Jason Brougham wrote:
> 
> <When I initially was so bold as to blatantly state that Confuciusornis' 
> second manual digit is not reduced, it was in the context of a discussion 
> about function - specifically the possible flexion of this finger during the 
> flight stroke. [...] I believe you had mentioned the lack of extensor pits 
> and I thought your observations were along that same train of thought.>
> 
>   On a purely mechanical level, I equate physical mobility in a phalangeal 
> joint to a few things, as I think Senter's work on manus flexibility (Bonnan 
> and Senter, 2007; Senter and Parrish, 2006; Senter and Robins, 2005; Senter, 
> 2005, 2006 [two papers], and 2007) shows:
> 
> 1. Arc of the interphalangeal and metacarpo-phalangeal joint, which limits 
> the range of motion in general to the highest degree of arc.
> 2. Presence of bony "stops," usually in the form of "tongues" and the extent 
> of an extensor or flexor pit (a phalanx typically has a longer flexor process 
> anchoring to the flexor tendons on the ventral surface than the extensor, 
> dorsal process; the extensor process fits into a dorsal extensor pit, which 
> is inferred the limit of its motion [disarticulation is ruled out as 
> unobservable], while flexor pits are rare -- the bone should just stop the 
> phalanx from curving further).
> 3. Indications of cartilage (mottled and wrinkled surface texture), 
> indicating how far the flexion or extension of the phalanges can move.
> 
>   Extensor pits thus indicate greater realms of motion, while longer tongues 
> on the phalanges, associated themselves with greater curvature of the 
> proximal phalangeal joint. The former appear lacking in *Confuciusornis 
> sanctus*, while the latter are present (this is clear in both GMV-2132 and in 
> Paul's figuring of the manus of the bird in _Dinosaurs of the Air_). A short 
> flexor process is present in GMV-2132, and it appears raised and 
> perpendicular to the phalanx -- it would imply to me a strong leverage point, 
> and thus high flexibility; but the distal joint lacks such a process, and the 
> joint, regardless of the flexor extend of the distal condyles, appears flat 
> based on the proximal mdII-2 morphology ... but this is again based on a 
> single specimen, and it is crushed. I took the lack of pits and the latter 
> morphology to imply a lack of flexibility, but I overstated my case (I really 
> do not have a high sample-size, here).
> 
> <I assumed that you meant that it was reduced in a developmental/functional 
> way - as the third digit is in the hand of Cathayornis or Longipteryx. [...] 
> You were instead talking about reduction from the ancestral state. In that 
> case, I agree that comparison to Archaeopteryx is best. But you are also 
> equating hypertrophy to length, and there we do disagree.
> 
> <The humerus of the ostrich, for example, is much longer, proportional to the 
> ulna and manus, than in the flying ancestor of ratites, yet it still must be 
> described as reduced, mustn't it?>
> 
>   I think I get where you're going with this, but I am not talking about 
> reduction in a conceptual sense in any other than mathematical terms. I would 
> not call the humerus of the ostrich reduced if I were to compare it directly 
> only to the basal flighted paleognath [setting aside the suggestion that 
> various paleognath "families" may all be convergently flightless (Harshman et 
> al., 2008)], and were I to use a bird with a relatively longer humerus 
> (picking a non-limb element or measure in comparison). That's the thing: 
> taken on their own, without regard to developmental processes and projections 
> of an artificial evolutionary cline, picking two taxa, relegating one to the 
> baseline, results in only one of three results: the second taxa is reduced 
> from, is in agreement with, or is increased from the baseline. That I picked 
> *Archaeopteryx lithographica* as a baseline can be of evolutionary concern, 
> but I did so because it ran the potential of being the most stable baseline I 
> could provide (having multiple and potentially ontogenetic proportions to 
> compare), and because it could also be evolutionarily more useful than almost 
> anything else. It's high degree of familiarity doesn't hurt, either.
> 
> 
> 
> Jason also wrote separately:
> 
> 
> 
> <The humerus of a hummingbird is also shorter, relative to the manus,
> or relative to the humeral width, or relative to the culmen to vent 
> length, than the ancestral condition, but can we say it is reduced? 
> Instead it seems to me it is specialized, sporting exaggerated 
> processes, and even more high - performance than the ancestral 
> condition.>
> 
> 
> 
>   Regardless, a reduction in any relative length is "reduction." Note 
> that "reduction" must be relative to a typical baseline, but that 
> baseline can be anywhere; and it can be across a series, such that an 
> evolutionary lineage can result in a "reduction" _overall_ or in just 
> one element towards the end. The _purpose_ of a part, or rather 
> functional allowances it possesses or has lost from an earlier state, is
> irrelevant when all we are doing is assessing proportions and terms 
> relating to them (including diameter for the "hypertrophy" metric).
> 
> Back from the original post, Jason again:
> 
> <So I suggest a truce. If using diameter alone is, let's say, grossly 
> incorrect, then using length alone must be as well.>
> 
>   Truce met, and I agree. I like to be comprehensive in what my proportions 
> _mean_ and how they relate to the systems in which they operate for me to use 
> them (one reason I do not like seeing proportion characters in phylogenetic 
> analyses), which I guess makes me a better biomechanist than a 
> phylogeneticist. To paraphrase the Bard, "The context's the thing."
> 
> Bonnan, M. F. and P. Senter. 2007. Were the basal sauropodomorph dinosaurs 
> *Plateosaurus* and *Massospondylus* habitual quadrupeds? _Special Papers in 
> Palaeontology_ 77:139-155.
> Harshman, J., Braun, E. L., Braun, M. J., Huddleston, C. J., Bowie, R. C. K., 
> Chojnowski, J. L., Hackett, S. J., Han K.-l., Kimball, R. T., Marks, B. D., 
> Miglia, K. J., Moore, W. S., Reddy, S., Sheldon, F. H., Steadman, D. W., 
> Steppan, S. J., Witt, C. C. & Yuri T. 2008. Phylogenomic evidence for 
> multiple losses of flight in ratite birds. _Proceedings of the National 
> Academy of Sciences, Philadelphia_ 105(36):13462-13467.
> Senter, P. 2005. Function in the stunted forelimbs of *Mononykus 
> olecranus* (Theropoda), a dinosaurian anteater. _Paleobiology_ 31:373-381.
> Senter, P. 2006. Forelimb function in *Ornitholestes hermanni* Osborn 
> (Dinosauria, Theropoda). _Palaeontology_ 49:1029-1034.
> Senter, P. 2006. Comparison of forelimb function between *Deinonychus* and 
> *Bambiraptor* (Theropoda: Dromaeosauridae). _Journal of Vertebrate 
> Paleontology_ 26:897-906.
> 
> Senter, P. 2007. Analysis of forelimb function in basal ceratopsians 
> (Dinosauria: Ornithischia). _Journal of Zoology_ 273:305-314.
> Senter, P. and J. M. Parrish. 2006. Forelimb function in the theropod 
> dinosaur *Carnotaurus sastrei,* and its behavioral implications. _PaleoBios_ 
> 26(3):7-17.
> Senter, P. and J. H. Robins. 2005. Range of motion in the forelimb of the 
> theropod dinosaur *Acrocanthosaurus atokensis,* and implications for 
> predatory behaviour. _Journal of Zoology_ 266:307-318.
> 
> Cheers,
> 
> Jaime A. Headden
> The Bite Stuff (site v2)
> http://qilong.wordpress.com/
> 
> "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
> 
> 
> "Ever since man first left his cave and met a stranger with a
> different language and a new way of looking at things, the human race
> has had a dream: to kill him, so we don't have to learn his language or
> his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 
> Backs)
> 
> 
> 
> 
> 
> ----------------------------------------
>> Date: Tue, 29 Mar 2011 21:21:28 -0400
>> From: jaseb@amnh.org
>> To: qi_leong@hotmail.com
>> CC: jaseb@amnh.org; dinosaur@usc.edu
>> Subject: RE: Senter 2006, Confuciusornis, and humeral mobility
>> 
>> Hi Jaime,
>> 
>> Yes I did misunderstand your notation. I took your use of Md for Mc. My
>> apologies.
>> 
>> Now let's get to our real misunderstanding.
>> 
>> When I initially was so bold as to blatantly state that Confuciusornis'
>> second manual digit is not reduced, it was in the context of a discussion
>> about function - specifically the possible flexion of this finger during
>> the flight stroke.
>> 
>> I assumed that you meant that it was reduced in a developmental/functional
>> way - as the third digit is in the hand of Cathayornis or Longipteryx. I
>> thought you were suggesting that it was reduced perhaps because it
>> received less of the mechanical stress (stress placed on it by muscular
>> tension, force directed through it by loaded feathers, etc.) that induces
>> modeling and haversian remodeling. I believe you had mentioned the lack of
>> extensor pits and I thought your observations were along that same train
>> of thought.
>> 
>> You were instead talking about reduction from the ancestral state. In that
>> case, I agree that comparison to Archaeopteryx is best. But you are also
>> equating hypertrophy to length, and there we do disagree.
>> 
>> The humerus of the ostrich, for example, is much longer, proportional to
>> the ulna and manus, than in the flying ancestor of ratites, yet it still
>> must be described as reduced, mustn't it? So perhaps the converse can be
>> true as well: that a bone can be shorter yet more robust, more voluminous,
>> thicker - walled, perhaps more densely reinforced by internal trabeculae,
>> with large flanges that probably support the follicular ligaments of
>> primary feathers, and therefore more functional importance overall. I am
>> not saying that I have evidence of most of these features in the case of
>> PhII-1 of Confuciusornis, but all are possible.
>> 
>> When considering functional reduction or function - related hypertrophy,
>> the distinctness of the articular processes and muscle insertion points is
>> probably also key. Again, in fig 39 of Chiappe et al. 1999 I see that the
>> proximal end of Ph II - 2 is much broader than any other penultimate
>> phalanx, and the distal end of Ph II - 1 seems correspondingly broad. Both
>> show large condyles.
>> 
>> I agree that it would be nice to see more specimens. And I'm not certain
>> that the second digit could flex powerfully, it just looks possible to me.
>> I am looking at the two specimens preserved in IVPP V 11374 (Fig. 173 in
>> The Jehol Fossils, Academic Press (Elsevier) 2003). They show also that
>> the proximal PhII 2 and distal PhII 1 are very broad, though perhaps
>> flattened.
>> 
>> But I certainly do concede that the second digit of Confuciusornis is much
>> shorter, proportional to the other fingers, than it is in Archaeopteryx.
>> Sorry to put you to so much trouble measuring so many specimens when I
>> meant to concede that point without hesitation. And I am fascinated by
>> your observation about the ungual of digit II sitting in a bowl-like
>> cotylus.
>> 
>> So I suggest a truce. If using diameter alone is, let's say, grossly
>> incorrect, then using length alone must be as well.
>> 
>> Thank you for this stimulating exchange. You are a most knowledgeable
>> anatomist and patient in explaining your points.
>> 
>> -Jason
>> 
>> 
>> 
>> 
>                                         

Jason Brougham
Senior Principal Preparator
American Museum of Natural History
jaseb@amnh.org
(212) 496 3544