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Re: theP-T boundary
> This set me to thinking about how I made that error. The K-T is
> only the second greatest mass extinction in earth's history, dwarfed by
> the Permo-Triassic (P-T). And yet on land at least, the scenery didn't seem
> to change that much.
> 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?
> 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.
> The two theories I am familiar with are massive volcanism and the
> to-soda-pop theory (CO2 bubbling up from the ocean floor) This last would
> explain a greater effect on marine life.
There is large consensus about the mass extinction that occurred in
marine faunas at the PT boundary (or better said: the PT boundary has
been drawn at the major extinction event that is documented in
marine sediments), the latest thought and theories being summarized
However, concerning terrestrial faunas, the case is indeed not that
clear. Most studies have focused on the excellent, continuous
accumulation of Permian through Jurassic sediments in the Karoo
Basin, and some authors (especially Gillian King and Roger Smith)
state that faunal diversity was already declining during the last
stages of the Permian, which they linked with increasing aridity and
a change from the typical Permian Glossopteris flora via an
intermediate flora to the typical Triassic Dicroidium flora.
Moreover, at different localities in South Africa, a 20 to 60m thick layer has
been identified where Lystrosaurus specimens occur together with
typical the Permian Dicynodon. And several 'transitional' faunal
assemblages are known: the upper Guodikeng (or something) fauna in
China where Lystrosaurus occurs with the Dicynodon like Jimusaria and
Striodon, the Viazniki fauna of Russia, where Archosaurus is found
together with large therocephalians and dicynodonts, and recently,
Lystrosaurus is identified in the Madumobina formation of Zambia,
which is dominated by typical Permian forms as Diictodon, Oudenodon,
Dicynodon and Procynosuchus.
Although the Lowest Triassic Lystrosaurus fauna is indeed an
impoverished one and lacks large species, several lineages have crossed
the PT boundary: therocephalians were still a significant part of the
Lystrosaurus fauna (scaloposaurs, moschorhinids and bauriamorphs
survived), galesaurid cynodonts such as the well known Thrinaxodon
are also known from Upper Permian strata (Cynosaurus), Lystrosaurus
is clearly related to the Permian Dicynodon trigonocephalus,
Kombuisia is an (albeit poorly know) dicynodont which is clearly
"Permian like" (probably related to Emydops) but is found in the
Cynognathus zone, and the Triassic kannemeyerid dicynodonts may have
descended from a Pristerodon-like ancestor which survived the PT. The
anapsid Owenetta is both found in Permian and Triassic strata. The
capitosaurid temnospondyl Uranocentrodon, formerly thought to be a
typical Lower Triassic genus, is probably Upper Permian.
Gorgonopsians did vanish however, but they were already less diverse in the
Uppermost Permian, being represented mainly by large forms such as
Dinogorgon and Rubidgea from South Africa and Sauroctonus and
Inostrancevia from Russia. Dinocephalians were already gone from the
end of the Kazanian/Tapinocephalus assemblage zone, quite long before
the end of the Permian...
According to this 'gradualist' scenario, decreasing faunal diversity
and extinction of many typical Permian taxa (at least in the Karoo)
was linked to a north movement of Gondwana, a fall in base-level and
ground water, climatic deterioration with increasing aridity and less
periodical rainfal, and a change from a Glossopteris and horsetail
(Schizoneura/ Phyllotheca) dominated flora to a "tougher" Dicroidium flora.