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

I have a trio of squamosal spines (nice and pointed) from a unidentified Pachy variety (lance) associated with other pachy bones still in the ground. Haven't had the time to deal with a major job like this but did reconstruct the spines nicely after sampling the site briefly. Also have found an isolated skull cap on ranch which is a museum piece. No complete skull yet but no one is working the site. The material is rare but not unknown around here. It's been there a while and will not go anywhere until an interested museum affiliated party works it. I'm busy recovering from lower back surgery so I won't be working it right away plus my little crew is busy working a tric site which is a job by itself for the next few years. 

Frank (Rooster) Bliss
MS Biostratigraphy
Weston, Wyoming
www.wyomingdinosaurs.com


On Jan 8, 2010, at 11:24 AM, 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 a fragmentary skull which could explain the differing spike counts. 

Best regards,

Zach



----- Original Message ----
From: Tor Bertin <nightimeshadow@yahoo.com>
To: dinosaur@usc.edu
Sent: Thu, January 7, 2010 9:38:50 PM
Subject: RE: Horner's Pachy Lumpin' - Your Thoughts?


Horner likewise did not attempt to explain this, from the
Bakker et al. description of _Dracorex_: "_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). If 'Draco' has
four horns, and 'Stygi' has three, then we've lost a horn
during ontogeny. This interesting quirk is not touched upon,
nowhere in Horner and Goodwin (2009) is the ontogenetic loss
of a horn mentioned.
It's possible that it's a population difference. I'm not sure what kind of sample size there is (is there more than one skull known for _Dracorex_ and _Stygimoloch_?), but if the number of spikes varied on a creature to creature basis, it wouldn't be quite so unusual.