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Re: Protoceratops juvies, unfenestrated parietal (repost)



----- Original Message -----

From: Jaime Headden <qi_leong@hotmail.com>
 > In "Triceratops," Scannella and Horner infer the fenestrae open _only_ 
during adulthood, discretely classifying a "young adult" above the "subadult" 
stage which acheived adult size and frill characteristics, no fenestrae, but 
are not "old adult" which is reserved for specimens ascribed to *Torosaurus 
latus* and *gladius*. 

Yes. Triceratops ontogeny is not identical to Protoceratops.

> The relative size of the fenestrae in the parietals in *Protoceratops 
> andrewsi* do not appear, in this small sample, to be relevant in _late_ 
> ontogeny, which was Scannella and Horner's argument for "Triceratops." 

Not relevant? Of course they are relevant. Protoceratops parietal fenestration 
through ontogeny sets a precedent, especially as Proto is a more basal taxon. 
Regardless of whether or not you agree with trike-toro synonomy, most people 
accept that Triceratops is paedomophic (in many aspects of its morphology). 
This at least is consistent with retention of unfenestrated parietal until late 
in ontogeny.

>  Based on the photo below, the skulls of these juveniles appear to be about 
>50mm, so smaller than the smallest specimen Dodson sampled, and thus the 
>assertion that fenestrae appear "somewhere post-hatching ontogeny" can be 
>true, 

"can be true"? If these little dinosaurs are indeed Protoceratops, then it IS 
true.

>but the arguments for any sort of comparison is problematic. 

Ah "problematic". Fenestrae open through ontogeny in Protoceratops. Maybe we 
should just ignore these specimens because they are so much of a problem.

>Why did the frill open up so extremely late in *Triceratops horridus* or 
>*prorsus* ontogeny? 

Why did Triceratops have a solid frill at all? Why have brow horns? why 
elongate the rostrum? why start developing a big nasal or? Why morphology? For 
Triceratops: differential paedomoprhism (more prevalent) and permorphism. 
Heterochrony. That's where we are right now. 

>But it certainly wasn't the same timing as *Protoceratops an
rewsi*, 

Different species have different growth trajectories. Protoceratops developing 
fenestrae ontogenetically shows that the tendency/ability to do so was present 
in a more basal ceratopsian. Sorry that this rocks your world so badly you 
choose to ignore it.

Does Avaceratops have fenestrae? Does Brachyceratops have fenestrae? Can we 
know? Is parietal thinning in these taxa indicative of incipient fenestrae? 
Fenestration is 1:0, present or absent; what would incipient fenstrae look 
like? how would you code it?  Is extreme parietal thinning different from 2 
inch thick solid frill? why? How many complete parietals exist for Triceratops? 
How many are incomplete? How many of those incomplete specimens are 
conveniently broken where the fenestrae (incipient or otherwise) would be? When 
do fenestrae form in ceratopsids? in the egg? through ontogeny? Protoceratops 
says through ontogeny.