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Re: theP-T boundary



Ron,

You wrote:

>         On the other hand, most estimates I've seen say about 95% of all
> species checked out at the end of the Permian. But the synapsids made it
> thru. In fact the land vertebrates of the lower Triassic don't look all
> that different from the Permian, do they? Granted no one group dominated the
> Permian the way dinos did the Mesozoic, but did any major land vertebrates
> cash in their chips at the P-T? How about fish? Higher plants? Was the scenery
> very different but just not as well known, or well publicized, given that
> neither the P or T is as charismatic as the Jurrasic?
> 
>         To my untutored eye, it looks as if the K-T extinction mainly
> clobbered vertebrates, while the P-T hit hardest the more species rich
> but less charismatic (to humans) inverts, especially the marine ones.
> Is this the case?

I think this may be an illusion, fostered by the fact that people
generally care more about the K-T extinction because that's when
dinosaurs cashed in their chips.  As you say, inverts and lower verts
are less charismatic than dinosaurs.  (Quick quiz: how many groups of
animals can you name off the top of your head _other than dinosaurs_
that went out for the count at the K-T border?)  

It's just not true that the Permian extinction didn't make a major
change in the land flora and fauna.  THE GREAT PALEOZOIC CRISIS (Douglas
Erwin, 1993) lists half a dozen major plant groups that either vanished
completely or went into drastic declines at the Permo-Triassic border,
clearing the way for other groups that became dominant in the Mesozoic. 
Among vertebrates, dicynodont therapsids almost disappeared, and
gorgonopsids and dinocephalians did vanish.  Temnospondyl amphibians
suffered massive losses.  Amphibs were still a significant part of the
land ecosystem in the Late Permian, but in the Triassic many of the
niches they had once held were taken over by amniotes.  All told, Erwin
estimates (p. 126) that the terminal Permian extinction (or extinctions)
claimed two-thirds of all amphibian clades and three-quarters of all
amniote clades.  

Erwin also has an interesting comment about the synapsids.  Someone
named Sloan had done some (as of 1993) unpublished studies that indicate
the synapsids suffered a series of extinction in the late Permian that
_selectively_ eliminated the most reptilian ones and preserved the most
mammal-like ones.  

As for marine life, both the P-T and K-T extinctions committed greater
mass murder among marine organisms than among land organisms.  The
Permian extinction wiped out *all* the remaining trilobites -- an entire
subphylum, gone forever.  The only extinct order of Foraminifera, the
Fusulinina, disappeared in the Permian extinction.  Tabulate and rugose
corals also disappeared completely, as did stalked crinoids and
blastoids.  Crinoids, bryozoans, brachiopods, and asteroids (starfish)
were reduced to only a few families.  Oddly, bivalve and gastropod
molluscs were relatively unaffected by the Permian extinction.
 
>         All of this raises lots of questions about what was different about
> the two events. The causes? No one has suggested ameteor strike at the P-T.

Actually, I heard recently that somebody had found an iridium anomaly
associated with the Permo-Triassic border, but in the absence of any
formal reference I have to consider that only a rumor.

-- JSW