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Re: why isn't Tethyshadros insularis just a juvenile?




>The neurocentral fusion is not addressed in the vertebral descriptions, and is 
>not confirmed histologically.>
Jaime replied:
>  My understanding is that generally taken, the obliteration or 
> near-obliteration of the suture between two bones is a proxy for complete 
> fusion. This is how vertebrae have been assigned "fusion" status for the 
> past, oh, 200 years.  To histologically section -- or, perhaps >favorably to 
> the preservation of the bones, CT -- each vertebra to compare the progress of 
> true fusion would be so time consuming and perhaps annoying if it would need 
> to be done for each specimen to assure oneself of IT'S age.  This is 
> especially problematic when >vertebral fusion may not actually infere sexual 
> maturity and/or "adult" status:  It merely represents skeletal maturity, 
> which is most important in biomechanical aspects.  

Whenever you see the statement "unique combination of primitive and derived 
characters" you should consider whether or not the onotogenetic status of the 
specimen concerned has been adequately assessed, since immature dinosaurs often 
exhibit characters that make them look more basal than they really are. In this 
case, neurocentral fusion is stated as present, but not illustrated, making it 
impossible to judge whether or not this is the case. 

Moreover, Brochu (1996, JVP) describes how in crocs the neurocentral sutures of 
most caudals are closed in hatchlings, and that suture closure then proceeds 
through to the cervicals. It is not stated which neurocentral sutures are 
closed in Tethyshadros, although looking at the figured type specimen, it would 
be difficult to observe those of the cervical and dorsal series because of 
specimen orientation and rib articulations.

Regardless, in an alleged dwarf taxon, histological sectioning of limb bones 
would be the most reliable way to demonstrate maturity at small body size. Chop 
a limb, any limb, and find an EFS. 

Given the lack of named hadrosaurs from contemporaneous deposits of Europe, it 
is likely that Tethyshadros is a valid taxon. I'm no
is wrong, I'm saying that without histological analysis of limb bones a 
non-mature status for the holotype cannot be falsified.

REF
Closure of Neurocentral Sutures during Crocodilian Ontogeny: Implications for 
Maturity
Assessment in Fossil Archosaurs
Author(s): Christopher A. Brochu
Source: Journal of Vertebrate Paleontology, Vol. 16, No. 1, (Mar. 19, 1996), 
pp. 49-62


Cheers,

Jaime A. Headden

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