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Re: Faunal list (Was Re: Selective Extinction)



>"Peter Von Sholly" wrote:
>> An old and often asked question about the final dinosaur extinction is why
>> certain animals went and others didn't.<snippage>
>
>There is no clear trend in extinction patterns, except for the following
>points noted by Laurie Bryant (1989), and many others since her work:
>
>1) Aquatic vertebrates faired relatively well across the bounday.
>
>2) Mammals got clobbered, but still some very different taxa
>got across unscathed (multi's, metatherians and eutherians squeaked by).
>
>3) Big land verts. *all* went caput.
>
>4) Most small land verts. went belly-up too.
>

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.

Of course, the weird thing about extinction events is the fact that some
groups can pass them by with relatively fewer casualties while others can
bypass one event with few losses only to get trashed later on. (Good
examples are dinosaurs (which got through the Triassic event with few
hitches) and Devonian marine fish which went through the big
Frasnian-Fammenian event with few losses then got creamed at the end of the
Fammenian).

Cheerio
Brian Choo