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Re: Dinosaurs vs. Therapsids






From: Dave Hardenbrook <DaveH47@mindspring.com>
Reply-To: DaveH47@mindspring.com
To: dinosaur@usc.edu
Subject: Dinosaurs vs. Therapsids
Date: Tue, 15 May 2001 19:13:50 -0700

I'm preparing to give a speech on Therapsids and why the Dinosaurs
wrestled world dominion from them. My primary sources of research
are Robert Bakker's _Dinosaur Heresies_ and John McLoughlin's
_Synapsida_, which both discuss the anatomical advantages that
gave dinos the edge over our pre-mammalian ancestors.  But I've seen
a couple of web pages that say this "Competitive Displacement"
theory has fallen into disfavor.  Is this true?  Would it be wrong
to say in my speech that dinosaurs had a competitive advantage over
therapsids?  Even if a mass extinction swept away most therapsids
and opened the way for diversification of dinos (much as the K/T
extinctions turned the tables in favor of mammals), didn't dinos still
have to have the advantages Bakker and McLoughlin point out
in order to repress the diversification of mammals in the Mesozoic?



-- Dave
The therapsids were already on their way out when the dinosaurs evolved, especially in predatory niches where they had pretty much been replaced by rauischians in the mid to late triassic, although dicynodonts would still have been competitors to herbivorous dinos. The cynodonts were mostly small predators, I don't think there were any therapsid/mammalian megapredators in the late Triassic, although I may be wrong on this. Weren't the groups the early dinos were most competing with the rauisuchians and related clades?


Patrick


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