Re: Faunal list (Was Re: Selective Extinction)

[Jonathon Woolf <jwoolf@erinet.com>]

Brian Choo wrote:

<snip>

> No clear trends in extinction patterns? While it's true that the trends in
> the terrestrial vertebrate biota leading up to the K-T are debatable,
> compare all of the Earth's major extinction events (where groups of at
> least order level or above are going kaput) and several factors constantly
> repeat themselves.
> 
> - Wide-ranging or cosmopolitan species are generally less severely hit.
> 
> - High latitude marine faunas less affected
> 
> - High-latitude biota migrates into low latitude regions during/immediately
> after many extinction events.
> 
> - Marine plankton always gets decimated
> 
> - Epicontinetal/continental shelf benthonic communities are harder hit than
> deepwater oceanic communities.
> 
> - Tropical marine reef ecosystems are always hit HARD:
> 
> archaeocyathid reefs in the Early Cambrian
> bryozoan reefs in the Late Ordovician
> stromatoporoid/tabular coral reefs at Frasnian/Fammenian boundary.
> diverse sponge/algae/bryozoan/brachiopod communities at end of Permian
> hexacoral reefs in Late Triassic
> rudistid bivalve reefs at the end of the Cretaceous
> 
> all of these were totally terminated.
> 
> - finally, aside from extinction events in the early Paleozoic (when there
> was nothing to kill on the land), both marine and terrestrial communities
> are always affected.

Over last weekend I read a book called NATURE'S KEEPERS, by science
writer/essayist Stephen Budiansky.  The book wasn't intended to have
anything to do with evolution or mass extinctions, but it did anyway.
<g>  One of the book's major points is how a single stimulus, repeated
many times over decades or centuries, can have profound influences on
the way animals and even whole ecosystems evolve.  Budiansky was writing
about man's influence on nature, so the example he was using was the
habit shared by many primitive peoples of periodically burning large
areas to control vegetation.  However, the same idea keeps turning up in
a lot of ecology-connected subjects.  An ecosystem is both robust and
delicate, and the wrong stimulus can bring it down in a relatively short
time.  

Brian's list of features all appear to be consistent with a substantial
cooling of world climate.  Wide-ranging species are less affected by any
major ecological disruption because in a large range, the chance of
finding a shelter area is higher.  High latitude (colder weather) faunas
do better because they can move south as the climate cools.  Deepwater
communities are less affected because to a large extent, the deep oceans
are isothermal.  Preobably nothing that's news to anybody here, but I
thought it worth saying anyway.

And one more factor that needs to be considered: in the Permian,
Triassic, and Cretaceous extinctions, among land vertebrates there was a
metabolic pattern to the survivors.  100% ectotherms like lizards and
crocs survived, though greatly diminished.  Highly endothermic animals
like mammals and birds survived, again with heavy losses.  Animals with
in-between metabolisms, like dinosaurs and dicynodont therapsids, got
the chop.  Again, that seems to be consistent with some sort of massive
climatic disruption.  Not a disruption of food supply -- endotherms need
more food than ectotherms -- but to something else.  And it had to be
global in its effects, because the extinctions are global.

Matter a'fact, it occurs to me that some sort of "reverse El Nino," a
massive cooling of tropical waters,  could have precisely those sorts of
effects.

-- JSW