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RE: Protoceratops juvies, unfenestrated parietal (repost)



Denver Fowler wrote:

<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.>

  My qualification was "relevant in _late_ ontogeny," and as such I am making a 
statement about relative _time_. Since, as you also note, as the 
"triceratopsin" group is considered paedomorphic, if it were, this is unique to 
the group among all of *Coronosauria* within *Ceratopsia*; it is as unique as 
having a character "parietal fenestrae present/not present" be effectively 
uncodable save for the complex of species lumped into *Triceratops*. This is, 
incidentally, why I put the name *Triceratops* in quotes in my last two 
replies: the assumptions made by Scannella and Horner are without respect to 
species-level distinctions, and thus the assumptions are made on a presumed and 
untested "generic" qualification. *Protoceratops andrewsi* parietal 
fenestration is as relevant as *Pachyrhinosaurus lakustai* fenestration, and is 
thus irrelevant to the particulars of late-ontogeny expression. My statement 
was also in regards to the argument that Scannella and Horner had made the infe!
rence that post-hatchling ontogeny produces the fenestrae, but this is a "duh" 
moment: The Polish-Mongolian team has made a number of discoveries of specimens 
that have been argued to merely be juvenile *Protoceratops andrewsi,* and these 
specimens have unfenestrated parietals. *Bagaceratops rozhdestvenskyi* 
especially has been questioned as an adult taxon, which is certainly testable, 
and recent taxa like *Magnirostris dodsoni* (see Makovicky & Norell, 2006, and 
Osi et al., 2010). But *Triceratops horridus* (at least) is doing something 
different, regardless of Scannella and Horner's hypothesis, and I'm not sure 
there's a whole lot of equating their ontogeny to *Protoceratops andrewsi*, 
merely distinguishing them; thus, [I do not think that] they are not "relevant 
in _late_ ontogeny."

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

  Maybe. They _are_ juveniles, and are at least protoceratopsid, but are they 
*Protoceratops*? Are they *Protoceratops andrewsi*? Are they actually? Given 
the number of distinct adult _theropod_ taxa that have been recovered from the 
Djadokhta, how certain are you that any large-bodied ceratopsian is the same 
taxon? Sure, one can make the assumption that similar taxa will have similar 
ontogenies, but the diagnosis of taxa should be done without simple assumption 
of lumping. Fastovsky et al. (2011:pg.1037) are aware of this:

"In addition to indicating their immature status, several features of the 
skull, including the relatively flat, straight snout and the short, 
parallel-sided frill, also constitute the plesiomorphic condition for 
Ceratopsia (Balanoff et al., 2008). In these features, these ceratopsians 
resemble the adults and juveniles of more basal members of this clade, like 
*Psittacosaurus* spp. (Long and McNamara, 1995; Meng et al., 2004; Zhao et al., 
2007), *Liaoceratops*, and *Auroraceratops* (You and Dodson, 2004).

"For all that, however, several characters suggest *Protoceratops* affinities 
including an eliptical antorbital fossa, median keel on the frill, small 
fronto-parietal depressions (Dong and Currie, 1983; You and Dodson, 2004), and 
hoof-shaped pedal unguals (Sereno, 2000). Within *Protoceratops*, two species 
are recognized: *P. andrewsi* (Granger and Gregory, 1923) and *P. 
hellinkorhinus* (Lambert et al., 2001). Of the characters that distinguish the 
latter from P. andrewsi-the absence of premaxillary teeth, two nasal horns, 
well-developed frontoparietal depressions, and a forwardly curved frill (You 
and Dodson, 2004)-the presence or absence premaxillary teeth has the potential 
to diagnose; the other characters are simply not well developed within these 
juvenile skeletons. In the case of the teeth, however, insufficient preparation 
precludes positive identification of the character, even presuming that at this 
juvenile stage they would have erupted. There are, however, no reas!
ons to preclude a specific assignment to *P. andrewsi*, and given the fact that 
adult *Protoceratops andrewsi* are the only ceratopsians known from Tugrikin 
Shire (Brown and Schlaikjer, 1940; Dodson, 1976; Dong and Currie, 1993; Lambert 
et al., 2001), we tentatively refer all of the individuals in MPC-D 100/530 to 
*P. cf. andrewsi*."

  Unable to distinguish the species by morphology (assuming the morphology is 
consistent that young), the authors use _locality_ to presume identity. The 
authors use "cf." as a label to suggest their uncertainty on this, and this is 
almost certainly a label of convenience.

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

  I think I covered this above: The "problem" is that they open _at different 
times_ between *Triceratops horridus* (say, using Scannella and Horner's 
hypothesis) and *Protoceratops andrewsi* (using Fastovsky et al's) -- since the 
opening through ontogeny is not understood throughout *Ceratopsia* it is 
"problematic" to assume one's ontogeny says anything about the other's. It is 
also a concern that juveniles are problematic when attempting to identify 
_species_, when similar species will have juveniles that are largely 
indistinguishable morphologically.

<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.>

  Yes, it would be great to get an answer to the first question. Why indeed? I 
won't delve into the conflicts surrounding whether or not heterochrony is 
useful in this regard, when we lack the refined degree of analysis that 
observing living organisms provides.

<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.>

  I completely understand how you got this from what I said, the borderline 
misrepresentation notwithstanding. That there are _other_ ceratopsians with 
parietal fenestrae should indicate that it is present in, at the least, their 
common ancestor. That adults of *Protoceratops andrewsi* have parietal 
fenestrae should be the relevant data. _Of course_ they open ontogenetically, 
as the basal condition _lack_ them (e.g., *Psittacosaurus* spp.), and the 
_inferrence_ is that there will be a point at which they will open in 
descendants. That those _times_ are different in different taxa is my point. 
How is the earlier timing relevant in *andrewsi* compared to *horridus* when we 
don't understand the timing in an intermediate?

<Does Avaceratops have fenestrae? Does Brachyceratops have fenestrae? Can
 we know?>

  Are those taxa "real"? Are they ontogenetic stages of other, known taxa? Can 
we know? Should we value juvenile or subadult taxa as holotypes when that level 
of uncertainty towards diagnostic characteristic exist?

<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.>

  Something tells me you're trying to compare the ontogeny versus biomechanical 
reduction model of Tanke and Farke. You're also trying to say, it seems, that 
only one model can be true, for the whole of ceratopsians. What if 
chasmosaurine ceratopsids developed fenestrae early, and in one lineage, closed 
them, which then opened up under biomechanical resorption at extreme age? Can 
both models truly, _truly_ be true? It's not the most _parsimonious_ argument 
when taken on the face of it, but it might be just as accurate. And as I said 
before, maybe it varies across taxa, so that one taxon is no accurate model for 
another. It would be a mistake then to presume that the fenestrae of 
*Torosaurus latus* are homologous to those of *Protoceratops andrewsi*, if they 
arise under biomechanical conditions that can differ across even closely 
related taxa.

Fastovsky, D. E., Weishampel, D. B., Watabe M., Barsbold R., Tsogtbaatar K. & 
Narmandakh P. 2011. A nest of *Protoceratops andrewsi* (Dinosauria, 
Ornithischia). _Journal of Paleontology_ 85(6):1035-1041.
Makovicky, P. J. & Norell, M. A. 2006. *Yamaceratops dorngobiensis*, a new 
primitive ceratopsian (Dinosauria: Ornithischia) from the Cretaceous of 
Mongolia. _American Museum Novitates_ 530:1-42.
Ősi, A., Butler, R. J. & Weishampel, D. B. 2010. A Late Cretaceous ceratopsian 
dinosaur from Europe with Asian affinities. _Nature_ 465:466-468.
Tanke, D. H. & Farke, A. A. 2007. Bone resorption, bone lesions and extra 
cranial fenestrae in ceratopsid dinosaurs: a preliminary assessment. pp.319-347 
in Carpenter (ed.) _Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs_. 
(Indiana University Press, Bloomington.)

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: Fri, 11 Nov 2011 19:14:04 +0000
> From: df9465@yahoo.co.uk
> To: dinosaur@usc.edu
> Subject: 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.