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Re: versus mammals



> Date:          Thu, 22 May 1997 21:13:09 -0400 (EDT)
> Reply-to:      smfaust@edisto.cofc.edu
On Thu, 22 May 1997, Stephen Faust wrote:
> I may be wrong here, but didn't the mammal - like reptiles rule the world 
> before the Permian extinction and then the archosaurs ( dinosaurs ) got 
> the upper hand?
 
You are certainly right: the synapsid lineage was the first one to 
invade the real terrestrial world and radiate into small and large 
herbivores, omnivores and carnivores. 'Pelycosaurs 'in the Early 
Permian, non-mammalian therapsids in the Late Permian  dominated 
terrestrial ecosystems; diapsids were restricted to the role of small 
insectivores/carnivores (in fact quite similar to the niche of the 
Mesozoic mammals). Even after the end Permian mass extinction, 
therapsids "returned" and radiated again in medium-sized and large 
herbivores (dicynodonts and gomphodont cynodonts, some last 
therocephalians)  and small,  medium-sized and large carnivores
(carnivorous cynodonts) , but diapsids, and especially 
archosauromorphs (rynchosaurs) and true archosaurs (the 
"thecodontians") had become a signifant part by Middle Triassic times. 
In the late Triassic, therapsids ceased to dominate ecosystems 
although tritylodonts survived into Middle Jurassic times and the 
first real mammals appeared (indeed slightly later than the first true 
dinosaurs, as far as I know). There have been held lots of congresses 
and there have been written LOTS of papers and books about the 
decline of the therapsids and the rise of the dinosaurs; I think the 
most important views/ theories are 1) (proposed the first time by 
Charig I think) Archosaurs were (at that time!) superior to 
therapsids (because of their improved, semi-erect gait, because of 
their better ability to cope with arid conditions, because of their 
ability to exploit the new, higher level vegetation of conifers and 
Bennetitales (spelled correcly?)... and 2) (Benton) the Late Triassic 
witnessed one (or two) mass extinctions and dinosaurs just radiated 
first in the empty ecosystems which this caused (a bit similar to the 
explosive mammal radiation after the KT event), perhaps favoured by 
some anatomic novelties which were in those circumstances at that 
time "superior", or simply they happened to be at the right time in 
the right place.

> On Thu, 22 May 1997, John Bois wrote:
> > On Thu, 22 May 1997, Jonathan R. Wagner wrote:
> > >         You seem to be forgetting what might be the simplest explanation:
> > > dinosaurs got there the firstest with the mostest.

This is view 2, am I correct?
> > The question then becomes: Why were they and not mammals the firstest with
> > the mostest?
> >