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



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.