RE: Horner's Pachy Lumpin' - Your Thoughts?

[Michael Erickson <tehdinomahn@live.com>]

Zach Armstrong wrote:

>Also, I am not sure where you are getting the spike counts (as they are not
>apparent from the quote you cite above), but _Stygimoloch_ does indeed
>apparently have four larger, prominent spikes, with three large prominent
>ones, and a (still prominent but smaller) fourth one with additional
>smaller ones, see here:
>http://upload.wikimedia.org/wikipedia/commons/8/84/Museum_f%C3%BCr_Naturkunde_Berlin._Fossil_Stygimoloch_spinifer_003.jpg

That skull is not real. It is heavily reconstructed - it bears almost no 
resemblance to the few complete (unfortunately undescribed) _Stygimoloch_ 
skulls that are known. And if you take a look at this Wikipedia article:

http://en.wikipedia.org/wiki/Stygimoloch

There's a another photo of the same skull, this time from the front. It says 
'reconstructed' right underneath it. 
 
It's a fake skull. A fake skull doesn't help much of anything.

If you read my original post, it would be apparent where I'm getting the spike 
counts. Anyway, I quote afresh from Bakker et al. 2006:

"_Stygimoloch spinifer_ is characterized by a huge spike cluster, consisting of 
3 enlarged (hypertrophied) spikes. This differs from the shorter 4 spike 
arrangement in _Dracorex hogwartsia_" (Bakker et al. 2006, page 11).

"Galton and Sues (1983) characterized _Stygimoloch spinifer_ as having 
three-to-four spikes on the squamosal. This characterization allowed them to 
include a smaller, isolated squamosal with four spikes (YPM 335), a specimen we 
here consider to be referable to _Dracorex hogwartsia_. We have been able to 
determine, based on comparison with other documented specimens of _Stygimoloch 
spinifer_ (MPM 7111 and MPM 8111), and two undescribed specimens in private 
collections, that _S. spinifer_ consistently has these enlarged spikes coupled 
with an incipient, laterally compressed dome, made up of only the frontals and 
parietal. S. spinifer lacks open supratemporal fenestrae. Moreover, these 
skulls are of the same size as the holotype of _Dracorex hogwartsia_, so we 
conclude that these differences are not the result of ontogenetic development" 
(Bakker et al. 2006, page 11).

If you read these two quotes carefully, Bakker et al. examined both two 
described (three if you count the holotype) and two undescribed specimens of 
_Stygimoloch_, and all had only three squamosal horns (or spikes, or Crazy 
Pokey Things, whatever you want to call 'em). "We have been able to determine, 
based on comparison with other documented specimens of _Stygimoloch spinifer_ 
(MPM 7111 and MPM 8111), and two undescribed specimens in private collections, 
that _S. spinifer_ consistently has these enlarged spikes...". "These enlarged 
spikes" is referring to number of the horns as well as the presence of the 
horns themselves, as is evident if you read both quotes.

It is worth noting, for the record, that five specimens (that's including the 
holotype) all with the same squamosal horn number doesn't appear to support the 
speculations that squamosal horns may have varied in number among individuals.

>We don't know, what we do know is that we *need more fossils*. Until then,
>I wouldn't reject Horner's hypothesis out of hand.

Who is rejecting it out of hand? If you read my last post, you'd have seen 
where I said:

"Hopefully, however, those who are reading this will realize that *I remain 
open-minded on this issue*: I am merely saying that Horner's going to have to 
do a *LOT LOT LOT* better than what he has done thus far to convince me that 
his interpretation is correct, and I have provided some counter-arguments for 
his claims."

Disagreeing with Horner about the data, or being of the opinion that Horner has 
thus far made a horribly weak case for his claims, or being of the opinion that 
there is currently no decent evidence to support his claims, or being of the 
opinion that there is little valid reason for accepting his claims at this 
time, or all of the above, is *not* the same as "rejecting his hypothesis out 
of hand". Rejecting it out of hand (in my understanding) would be to throw the 
idea into the metal wastebin before even considering it. That is decidedly not 
what is happening here, or with any of the "Draco-philes". As Ralph Chapman 
explained in his post, the game is still wide open at this point, and the 
majority of the burden of proof still lies with Horner - because well, let's 
face it, his hypothesis is extremely bizarre and counter-intuitive and is going 
to take heaps more evidence, especially *MORE FOSSILS* (can't emphasize that 
one enough), to demonstrate beyond reasonable doubt. That is why, among other 
things, I was dismayed to see Longrich et al. applying Horner's 
still-highly-controversial hypothesis to other taxa as if it had already been 
validated(!?!?).

~ Michael


> Date: Fri, 8 Jan 2010 15:49:34 -0800
> From: zach.armstrong64@yahoo.com
> Subject: Re: Horner's Pachy Lumpin' - Your Thoughts?
> To: tehdinomahn@live.com; dinosaur@usc.edu
>
> Michael Erickson wrote:
>
>
>
>>Zach Armstrong wrote:
>
>>> Tracy Ford, in Prehistoric Times issue #73 "How to Draw Dinosaurs-Spiky
>>>Pachycephalosaurs?" commented that there are known Pachycephalosaurus>skulls 
>>>with spikes, not nobs, which means no loss of horns nor "absorbtion"
>>>of horns is needed. One of the skulls was reported to have been found by
>>>Mike Triebold. Ford reports that the Black Hills Institute has a spiked
>>>Pachycephalosaurus skull. I am not sure if this is the same as Ford's
>>>drawing of the "Sandy Site" Pachycephalosaurus of that same issue, but a
>>>photo of the Sandy Site skull in all its spiky glory can be found here:
>>>http://www.wmnh.com/wmtr0000.htm
>>>
>>> I should also point out that in PT #75, there is a
>>>Pachycephalosaurus>skeletal done by Greg Paul that has long spikes, too. I
>>>am not sure of his>reasoning on this, but I'm sure he has a good one :)
>>>
>>> If these skulls indeed are referable to Pachycephalosaurus, that means the
>>>"Dracorex" juvenile would not have needed to lose any horns or re-absorb
>>>them at all. Also, as far as I know, Stygimoloch is only known from
>>>fragmentary skull which could explain the differing spike counts.
>
>>This is not true. For one thing, the squamosal horns of the Sandy Site 
>>_Pachycephalosaurus_ are clearly much shorter than those of 
>>_Stygimoloch_,>whose squamosal horns are about a third again as long. So 
>>there would *still* be horn-absorption to a degree not seen in any extant 
>>terrestrial tetrapod.>Second, contrary to what Zach says, a whole entire horn 
>>would also *still* have to be lost, as _Dracorex_ possesses four, 
>>_Stygimoloch_ three. From the>_Dracorex_ description_:
>
>>"We have been able to determine, based on comparison with other documented 
>>specimens of _Stygimoloch spinifer_ (MPM 7111 and MPM 8111), and>two 
>>undescribed specimens in private collections, that _S. spinifer_ consistently 
>>has these enlarged spikes coupled with an incipient, laterally 
>>compressed>dome, made up of only the frontals and parietal."
>
>>_Stygimoloch_ is *not* known only from the fragmentary type specimen. Other 
>>specimens confirm that this taxon invariably possesses three horns. 
>>In>Horner's senerio, the loss of a whole horn during ontogeny is inevitable.
>
> I don't think it is "clear" that the _Pachycephalosaurus_ horns are "much" 
> shorter than in _Stygimoloch_, the apparent difference in length may have to 
> do more with the differing proportions in the skull as a result of ontogeny 
> than anything else and I would suspect there would be individual variation in 
> length of the spikes between individuals. One should also remember that these 
> are *individuals*, maybe the _Stygimoloch_ specimen would have grown up 
> having larger spikes than average. We don't know, what we do know is that we 
> *need more fossils*. Until then, I wouldn't reject Horner's hypothesis out of 
> hand.
>
> Also, I am not sure where you are getting the spike counts (as they are not 
> apparent from the quote you cite above), but _Stygimoloch_ does indeed 
> apparently have four larger, prominent spikes, with three large prominent 
> ones, and a (still prominent but smaller) fourth one with additional smaller 
> ones, see here: 
> http://upload.wikimedia.org/wikipedia/commons/8/84/Museum_f%C3%BCr_Naturkunde_Berlin._Fossil_Stygimoloch_spinifer_003.jpg
>
> It would be interesting to know if the spikes, bumps and bosses are 
> numerically uniform across individuals of a known pachycephalosaur taxa, or 
> if there is room for variation like in many horned/spiked mammals and 
> squamates.
>
> Best regards,
>
> Zach
>
>
>
>                                         
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