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

["ralphchapman" <ralphchapman@earthlink.net>]

Well I guess I don't have the mental superpowers of Denver to be able to read 
into the recesses of the brains of those of us that don't immediately accept a 
new hypothesis from Horner as fact, and that we must all be incredible 
splitters and think Jack is full of crap.

Well baloney.

Not immediately accepting a hypothesis is not the same as thinking they are 
full of crap. I just have a long fetch in my experience base and know there is 
a lot more to do all the time, especially with the difficulty of dealing with 
dinosaurs. I actually think there is an excellent chance they are right-ish and 
tend to think more like Jack in this context than many others who are part of 
this debate. I just need to let things evolve and expand before I start to 
think in such sure terms and I really don't do the acolyte thing very well as I 
am always a niggler on details, etc. I don't think Jack would want me to be any 
different and, by the way, Jack is a royal pain in the butt to others and their 
new hypotheses, as he should be. No one should do a disservice to people to put 
thoughts in their head. My problems with the BANDits, for example, are not that 
they disagree with most of us and are trying to disprove something - that's 
their job - it's that they are not really trying to do a quality job of it and 
I can't stand the laziness and politics of their actions

First of all, I am probably as big a lumper as exists in this community so my 
operating assumption generally is that everything is the same unless the data 
puts a gun to my head and forces me to say it isn't - that yes that's a new or 
different taxon - and even then I am suspicious. So my personal assumption 
would be they are all the same taxon. However, they have been split up 
previously and this is the basic assumption that must be strongly countered. I 
just am not enthralled by ANY of the phylogenetic work, backed up by 
morphological/morphometric documentation, that any of these researchers have 
done - with the possible exception of Tom Williamson's stuff who I think gave 
it a nice try - and this is a big problem and not all on the researchers. It's 
not an easy problem and it won't get to a great consensus point all that 
quickly.

The problems with assuming that flat domes are immature are great and include 
Denver's last admission that there must have been a flat dome that was 
ancestral somewhere. We are not doing this in a vacuum - we know lots about how 
social tetrapods of other types have evolved and vary and can use that 
information to help us understand how to approach pachys. That the mechanism 
described by Horner et al. is a bit unusual does not help, and the fact that 
something similar was also described by basically the same researchers on other 
dinosaurs does not alleviate the effect of this. It is just another piece of 
the puzzle to test and assimilate.

But to decide to assume flat is juvenile when we have an established record of 
evolutionary studies on social tetrapods with extreme morphologies is not 
right. When comparing two specimens and one seems to have a flatter dome, the 
assumption must be that one may be more juvenile, or one might be a different 
dimorph, or it might be just variation of one taxa, or it may be a different 
taxon, or it may come from a heterochronic mechanism and a different taxon, or 
there can even be taphonomic signatures in the morphology - or wait, it might 
be one is a different morph and more juvenile and a progenetic taxon, or a 
dimorph and a different taxon, or a different taxon and in a different part of 
the variation cloud.

When the number of options is much larger than your sample size, then we just 
have another set of ideas and data to assimilate and use for further work. I 
truly appreciate Jack's work and always get a bit of a thrill when taxa get 
nuked - seeing Grine et al's work on the South African therapsid material in 
the 1970's where 20+ species of multiple genera get folded into one or two 
dimorphic species with taphonomic signatures was a gleeful day for me as I am a 
gadfly by nature. There is just a lot of work to do and we must stop thinking 
simply. See a flatter dome, sure think it might be a more juvenile form of some 
sort but function from a much more complex series of possibilities and try to 
come up with a suite of rigorous analyses that will address all these.

Ralph Chapman



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*********************************************************************

-----Original Message-----
From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] On Behalf Of 
Denver Fowler
Sent: Saturday, January 09, 2010 1:12 PM
To: DML
Subject: Re: Horner's Pachy Lumpin' - Your Thoughts?



>>>>>>>>>>>>>>>>>>>>>>>>>>
No one is suggesting that Horner et al. are full of crap 
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Not in so many words.


>>>>>>>>>>>>>>>>>>>>>>>>>
Sorry but we are nowhere near the point of work where we can suggest that all 
flat-headed pachys that are or will be found were immature 
>>>>>>>>>>>>>>>>>>>>>>>>>

Of course we are. This suggestion opens the debate; we are not at a point where 
we can falsify either hypothesis, but that is not the same thing as a 
suggestion. Some of the language bombarded at the Horner & Goodwin paper seems 
to say that it should never have been published. They present good evidence 
that the non-domed pachycephalosaurini from the Hell Creek forms are immature, 
and would have had full domes in the adult form. From this we might investigate 
whether the same case can be made for other flat-headed pachys. What is wrong 
with that?

Of course, there will eventually be some basal form that lacks a dome as an 
adult... but since the oldest pachy has a fully formed dome (Latest Santonian / 
earliest Campanian), then making the suggestion that all Late Santonian and 
younger flat-headed pachys are immature is a good hypothesis, and pretty easy 
to test.

I fail to see why, with a small dataset, taxonomic diversity is a preferable 
hypothesis over ontogeny. The argument going on here seems to be against the 
principle point of Horner & Goodwin's paper, and that is that the dome forms 
through ontogeny.