Re: Radiation of species at late mid-Triassic

[Stan Friesen <swf@ElSegundoCA.NCR.COM>]

From: Pterodon@aol.com
 > Can anyone explain the extraordinary radiation of new orders of animal life
 > late in the mid-Triassic. This fruitful period spawned the earliest
 > dinosaurs, therapsids, thecodonts, pterosaurs, and perhaps even birds. 

The main cause was probably the depauperation of the fauna after the
P-Tr extinctions.  This left many open ecological opportunities
to be filled in by new forms.  Such adaptive radiations are fairly
normal when an 'empty' ecological zone is avialble to exploit.

 > This
 > remarkable diversification of higher life forms has not been
 > matched since.

Well, the radiation of mammals and advanced birds in the Paleocene and
early Eocene comes close.  To the extent it falls short fo the
mid-Triassic radiation, this is probably due to the fact that the
P-Tr extinctions were *far* more extensive than the K-T extinctions
(despite the latter being more famous).

 >    What environmental factors contributed to this, other than the
 > Permain-Triassic extinctions? 

I doubt there were any others.

The shear magnitude of the P-Tr extinctions is probably enough.
After all, the P-Tr extinctions were the largest since the end
of the Precambrian.

swf@elsegundoca.ncr.com         sarima@netcom.com

The peace of God be with you.