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



The paper "Cranial Anatomy and Diagnosis of Stygimoloch spinifer 
(Ornithischia:Pachycephalosauria) with Comments on Cranial Display Structures in
Agonistic Behavior Cranial Anatomy and Diagnosis of Stygimoloch spinifer 
(Ornithischia:Pachycephalosauria) with Comments on Cranial Display Structures 
in Agonistic Behavior. Mark B. Goodwin, Emily A. Buchholtz, Rolf E. Johnson 
.Journal of Vertebrate Paleontology, Vol. 18, No. 2  (Jun. 15, 1998), pp. 
363-375 says in its abstract, "the shelf is ornamented by three to four large, 
low-angle horns and multiple clusters of smaller bony nodes." The image of the 
squamosal spike cluster of specimen MPM 8111 shows bases of four large spikes 
on the left squamosal. 

Interestingly, Bakker et. al (2006) never refer to Goodwin et. al. (1998) when 
referring to squamosal spike counts.

I think your very, very careful quoting of Bakker et. al's (2006) words to try 
and cite support for only three spikes is not a very strong (or rigorous) 
argument.  Bakker et. al (2006) do indeed diagnose _Stygimoloch_  as having 
only three hypertrophied squamosal spikes, and conveniently refers specimen YPM 
335 to _Dracorex_  in order to maintain that. 

Another relevant quote from Goodwin et. al. (1998): "UCMP 131163 has at least 
four large horns on the squamosal while the type specimen and YPM 335
have one central horn surrounded by smaller secondary horns and nodes. The wide 
range of anatomy in ornamentation suggests extensive individual variation." It 
is interesting that UCMP 131163 is diagnosed as having four large horns on the 
squamosal, whilst YPM 335 (which Bakker refer to _Dracorex_) is considered to 
be similar to the type specimen of _Stygimoloch_ in horn anatomy which would 
argue against Bakker et. al's refferal of YPM 335 to _Dracorex_. Furthermore, 
like I said before, Goodwin et. al. do indeed support "extensive individual 
variation" in regards to these features, so I think all the hubbub about 
differing spike counts is not terribly relevant.

To me your arguments against individual variation, arguments for strict spike 
counts in _Stygimoloch_ and _Dracorex_, as well as (in your view) the need for 
spike re-absorption in light of the foregoing evidence are not very strong. In 
order for argument to have any support at all, you must falsify Goodwin et. 
al's (2006) diagnosis of _Stygimoloch_, which would entail original, 
peer-reviewed, published research on your part (or someone else's) or a 
subsequent paper since Goodwin et. al's (2006) that shows their above diagnosis 
was in error in order to show support for your view. Until then, I will 
continue to accept Horner's overall conclusion regarding this topic.

Best regards,

Zach

----- Original Message ----
From: Michael Erickson <tehdinomahn@live.com>
To: Dino List <dinosaur@usc.edu>
Sent: Sat, January 9, 2010 11:03:58 AM
Subject: RE: Horner's Pachy Lumpin' - Your Thoughts?


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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