RE: BAD vs. BADD (was: Re: Most popular/common dinosaur misconceptions)

[John Scanlon <riversleigh@outbackatisa.com.au>]

There've been some remarks from one or several folks disparaging an argument
attributed to one Spotila, suggesting that (A) dinosaurs probably had
temperature-dependent sex determination (TSD), so (B) sudden change in
global temperature (even if only a few degrees, if persisting for long
enough) could be a mechanism for mass-extinction by distorting sex ratio in
a large number of species simultaneously.  

I read the paper some while ago, and mainly noticed that the same argument
had been published years earlier by J.C. Rage.  But maybe that was in French
so didn't count, I dunno.  But the criticism here seems to be that Spotila
argued from dinosaurs being 'reptiles', and 'reptiles' have TSD... QED.

Now I don't recall how the argument was actually phrased, but look at it
this way.  Extant dinosaurs (Aves) don't have TSD, but all crocodilians do
(AFAIK); most if not all turtles do (and they may be derived archosaurs, or
at least much sequence evidence suggests so); Sphenodon and many (if not
all) Iguania do.  Thus, TSD characterises the three successive outgroups to
Dinosauria: i.e. it is most likely the ancestral state. It's been lost
somewhere on the line to extant Aves, but could well have been present in
all non-avian dinosaurs.  Or of course - and I'm not sure if Spotila or even
Rage explicitly noted this - an ancestor of all dinosaurs could have already
switched to GSD; maybe the 'bird vs. reptile' prejudice actually entered
here, but does not effect the rest of the argument.

Cheers,
John
 
-----------------------------------------------
Dr John D. Scanlon
Palaeontologist, 
Riversleigh Fossil Centre, Outback at Isa
19 Marian Street / PO Box 1094
Mount Isa  QLD  4825
AUSTRALIA
Ph:   07 4749 1555
Fax: 07 4743 6296
Email: riversleigh@outbackatisa.com.au
http://tinyurl.com/f2rby


> -----Original Message-----
> From: dinoboygraphics@aol.com [mailto:dinoboygraphics@aol.com]
> Sent: Friday, August 25, 2006 2:11 AM
> To: david.marjanovic@gmx.at; dinosaur@usc.edu
> Cc: pristichampsus@yahoo.com
> Subject: Re: BAD vs. BADD (was: Re: Most popular/common dinosaur
> misconceptions)
> 
> >> Long story short, as a disparity guage, the Linnean
> >> rank system tends to work very well.
> 
> >It tends not to work at all.
> 
> Actually, it works much more poorly than "not at all".  Not at all
> would imply a largely inconsequential hueristic device, but the fact
> that it doesn't in any way accurately measure disparity, but causes
> people to believe it does makes it misleading, sometimes to an almost
> vicsious degree.  I am still asked on a regular basis if a pterosaur or
> theropod with dermal insulation is still a "reptile".  Whether Spotilia
> "knew better" or not he still published and then regurgitated for the
> popular press an idea that can't even be framed when held to a
> phylogenetic framework.  Much of the resistance to dino-fuzz covered
> coelurosaurs and winged non-avian maniraptorans seems to stem from
> Linnean-style typological thinking.  The popular idea that the fossil
> record doesn't show abundant (and I mean *abundant*) transitional forms
> stems from the habbit of lumping them into existing "ranks" (after all,
> if Tiktaalik is a fish and Ventastega a tetrapod, there aren't any
> intermediate forms...!).  The fact that on this very list it was
> claimed that inner ear bones (which are likely homoplastic anyways) and
> fur makes whales, bats, and pyrotheres all mammals, while running with
> slightly less femoral excursion makes extant birds different from
> theropods, shows how badly misleading the system is.
> 
> As a gauge of disparity, the Linnean system is an absolute disaster.
> 
> Scott Hartman
> Science Director
> Wyoming Dinosaur Center
> 110 Carter Ranch Rd.
> Thermopolis, WY 82443
> (800) 455-3466 ext. 230
> Cell: (307) 921-8333
> 
> www.skeletaldrawing.com
> 
> 
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