[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Gargantuavis a bird, not a pterosaur



Jaime, one last point about Gargantuavis. 

Andrea Cau sent me a message to say that he recovered Gargatuavis as a basal 
ornithuromorph in his analysis.

But the pelvis morphology of Gargantuavis is different - more advanced - than 
many basal ornithuromorphs, and I suspect it is going to have to be specialized 
no matter what Gargantuavis is.

A sacrum that is fused into a  broad sheet with missing (fused) intervertebral 
foraminae is not reported in basal Ornithurae like Apsaravis, Yixianornis, or 
Ichtyornis. They all have normal sacral ribs and wide open intervertebral 
foraminae.  (PS  you were using "lacuna" but I think that "foramen" is the 
usual term. Correct me if I'm wrong.). Patagopteryx has a highly fused pelvis. 
It looks like there are intervertebral foramina in every location but most of 
the sacral ribs are missing, and there are large cracks between the sacrum and 
both ilia, that make the exact morphology unclear.

But my point is this. If Gargantuavis is a basal ornithuromorph, then its 
pelvis is specialized relative to other basal ornithuromorphs and even basal 
ornithurines. If it is a non - avian dinosaur this is also true. 

Jaime, did you suspect that Gargantuavis was a more derived bird? Does anyone 
know where we can find Cau's cladogram to see what apomorphies he relied on 
when he found that Gargantuavis is a basal form?


On Jul 6, 2011, at 11:11 AM, Jason Brougham wrote:

> 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
> 
> 

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