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Re: Dinosaurs vs. Therapsids





Dave,
I think the best way to look at it is that therapsids got off to a pretty good start, diversified in the mid-to-late Permian, and then WHAMO---it was downhill from there.
The end-Permian extinction was the main blow. They were able to rediversify somewhat, but other reptile groups were more successful in recovering and competing with them. And they also had the added pressure of competing with their own descendants (mammals) beginning in the Upper Triassic.
Dinosaurs would have just added to their problems (not necessarily their MAIN problem), so I wouldn't give too much credit to the dinosaurs. And then the end-Triassic extinction decimated the poor therapsids again, leaving only a family or two to muddle through the Jurassic, and at least one genus hanging on into the Early Cretaceous (at least in Japan).
Their extreme bad luck started at the end of the Permian, well before dinosaurs, and I was surprised to learn that they made it to the Early Cretaceous. The only piece of good luck they had was when one therapsid clade gave rise to the mammals in the Triassic. That's the only silver lining in the sad history of therapsids during the Mesozoic.
----------Ken Kinman
********************************************************
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
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