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Re: Gargantuavis a bird, not a pterosaur



Jaime,

In the figure of the ventral surface of the Gargantuavis pelvis by Buffetaut 
and Le Loeuff there are two non - perforate lacunae, one on each side. The 
dorsal side looks more asymmetrical, but there appear to be only two pairs of 
fused sacral ribs. In the same figure the asymmetry, matrix, and damage make 
the number of sacrals unclear, and Buffetaut and Le Loeuff acknowledged this in 
the paper. To me the caudalmost nugget looks unfused, there is a transverse 
line or crack, so it may be a caudal. Therefore there could be 9 or even 8 
sacrals. But I trust that the anatomists who have examined the fossil first 
hand know better than I do and that the best bet is that there are 10 sacrals.

But that's not the main issue. I acknowledge not only that Gargantuavis 
probably has 10 sacrals but also that it, right now, is best assigned to the 
ornithurae.

My main points are two. The first is that Gargantuavis is known only from 
fragmentary material. The second is that advanced alvarezsaurids and 
oviraptorosaurs (Gigantoraptor) converged with birds in amazing ways. If we had 
tried to identify Mononykus from just a pelvis and proximal femur wouldn't we 
have assigned it to the birds also? In fact we did assign it to birds until we 
found more basal forms.

A Nothronychus - like lineage of therizinosaurs could possibly have developed a 
pelvis with extra sacrals and more restricted lacunae. So if we ever find more 
material of Gargantuavis, and it is attached to an ostrich - sized 
therizinosaur, I won't be shocked.

But, again, with the material we have, we should assign Gargantuavis to birds.


On Jul 5, 2011, at 6:03 PM, Jaime Headden wrote:

> 
>   Jason,
> 
>   You are not noting that in a broad section of the anterior (cranial) 
> sacrum, the sacral ribs have coalesced. There are no lacunae present between 
> ribs in a sequence of about 1-2 ribs on one side, and 3 ribs on the other. 
> Perhaps this could help:
> 
> http://en.wikipedia.org/wiki/File:Gargantuavis_philoinos_pelvis.JPG
> 
>   Something that should be noted is that in therizinosauroids, the posterior 
> half of the ilium is deflected laterally, but unlike birds and rather like 
> hadrosauroids, a projection results in a broad shelf above the postacetabular 
> ala, and practically _is_ the ala. This is especially apparent in 
> *Nothronychus graffami* (UMNH VP 16420, which you show illustrated in your 
> site) where the projection is continuous with the dorsal margin and forms a 
> horizonal, flat shelf, unlike the preacetabular ala. This morphology is 
> unique within dinosaurs -- shared among several therizinosauroids, absent in 
> *Falcarius utahensis* -- and convergent with hadrosauroids. In this case, I 
> would argue that the muscle-attaching lateral surface has been deflected 
> ventrally, rather than a portion of the surface projecting outward and thus 
> preserving a part of the surface dorsally. It is particularly important, in 
> my opinion, to distinguish this pelvic morphology on the basis of implied 
> muscle attachment, by following the landmarks or inferring them from other 
> taxa, and seeing where they would go in this form; in this case, the ilium 
> deflects the muscle-bearing surface ventrad in its posterior portion, and 
> posteriad-dorsad in its cranial portion.
> 
>   As Zanno et al. (2009) note, however, the ilium is crushed dorsoventrally, 
> so perfect degrees of deflection can only be speculated about. They offer a 
> lateral view to help with their proposed recunstruction. No such view is 
> offered of the pelvis of *Gargantuavis philoinos* (MDE-C3-525), merely a 
> side-view as preserved (which is just fine).
> 
> Zanno, L. E., Gillette, D. D., Albright, L. B. & Titus, A. L. 2009. A new 
> North American therizinosaurid and the role of herbivory in “predatory” 
> dinosaur evolution. _Proceeding of the Royal Society of London, B_ 
> 276:3505-3511.
> 
> 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)
> 
> 
> ----------------------------------------
>> Subject: Re: Gargantuavis a bird, not a pterosaur
>> From: jaseb@amnh.org
>> Date: Tue, 5 Jul 2011 14:44:57 -0400
>> CC: qi_leong@hotmail.com; dinosaur@usc.edu
>> To: augustoharo@gmail.com
>> 
>> Yeah, Augusto, distortion is an important point.
>> 
>> Jaime, have you looked at the two figures, of Nothronychus and Gargantuavis, 
>> here?:
>> 
>> http://web.me.com/jasonbrougham/Site/Blog/Entries/2011/7/4_Gargantuavis_vs._Nothronychus.html
>> 
>> I don't see the differences in the lacunae that you describe, it seems more 
>> a matter of degree. Also the ilia seem to be clearly facing dorsally.
>> 
>> On Jul 5, 2011, at 2:26 PM, Augusto Haro wrote:
>> 
>>> 2011/7/5 Jaime Headden <qi_leong@hotmail.com>:
>>>> 
>>>> 
>>>> 5, The ilia face dorsal in *Gargantuavis philoinos* as they do in 
>>>> virtually all ornithothoracean birds, and in *Avimimus portentosus*; this 
>>>> face is such that the entire lateral face of ilium when viewed from above 
>>>> is visible. In therizinosauroids, this is true only for the preacetabular 
>>>> ala, but not anywhere posterior to above the acetabulum, and this is 
>>>> particularly notable because the preacetabular ala in therizinosauroids 
>>>> resemble strongly the condition of graviportal mammals is being deep, 
>>>> thick, and laterall deflected (so that the lateral face is also viewable 
>>>> from the poaterior as well as the dorsal). This doesn't happen in any 
>>>> oviraptorosaur or bird [qualifier: that I know of].
>>>> 
>>> Can it be ruled out that deformation generated the observed pattern in
>>> Gargantuavis?
>> 
>> Jason Brougham
>> Senior Principal Preparator
>> American Museum of Natural History
>> jaseb@amnh.org
>> (212) 496 3544
>> 
>> 
>                                         

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