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Re: K/T extinction (forams and birds)




David,
I don't know enough about forams to know how many species or genera survived K/T. But I can say that a minimum of about 60-70 genera survived, because about 60-70 families of forams survived. I would guess probably at least a hundred genera and perhaps several hundred species of forams survived. Of course, many of those may have been devastated to the point of near extinction. By comparison, the number of foram families that went extinct in the Cretaceous was probably only 6-10, and even some of those may have gone extinct before K-T. In any case, forams as a group did a lot better than any vertebrate group that I know of.
Forams are small and have large populations, so you can kill off 99.999% of the individuals and still have large sustainable populations of many species (I would guess benthic species did better than planctonic species). In my opinion, foram diversity would have suffered far less than the higher organisms that heavily depended on them for food. Don't know much about ammonites and what they ate, but perhaps this was a factor in their extinct(?). Bacterial diversity was probably affected little if at all at generic and higher levels.
There was probably some aspect of freakish luck in some cases of what survived---Gondawana land vertebrates certainly had the edge over those in North America (what a great time to be in Antarctica or Australia. But this becomes less important as you go to sea (especially the deeper sea) and the farther down food chains you were. Tiny decomposers like bacteria are the most immune to bollide disasters except for particular species dependent on a particular host that went extinct.
----Been a long day & time for bed, Ken
******************************************************
From: "David Marjamovic" <David.Marjanovic@gmx.at>
Reply-To: David.Marjanovic@gmx.at
To: "The Dinosaur Mailing List" <dinosaur@usc.edu>
Subject: Re: K/T extinction (forams and birds)
Date: Tue, 15 May 2001 22:33:43 +0200

> Forams were not wiped out. Class Foraminiferea actually came
through
> K/T almost unscathed in terms of ordinal diversity. Order Involuntinida
> (which made it through the Permian extinction) apparently did not make it
> through K/T (but who knows, it may be found in the early Paleozoic
someday).
> But most Cretaceous foram orders made it through and are still with
us
> today: Monothalamida, Allogromiida, Astrorhizida, Haplophragmiida,
> Spirillinida, Miliolida, Lagenida, Robertinida, Globigerinida, Buliminida,
> Cassidulinida, Nonionida, Plaorbulinia, Asterigerinida, Discorbida, and
> Rotaliida. Sadly, Order Orbitoidida made it through K/T, but only made
it
> to the Eocene.


How many species of these orders survived? 1? 2? 100?

Still not a single crown-group placental has turned up from the LK AFAIK,
which might mean that only one species survived (casts additional doubt on
NA marsupials being outcompeted by invading placentals). From biogeographic
and phylogenetic considerations, 3 species at minimum must probably have
survived (the ancestors of Xenarthra, Afrotheria and "Boreoeutheria" [ = the
rest]). (If we don't accept the molecular clock estimates, that is; I
don't.) However, this is surely a minimum because even in NA alone more
species of marsupials and multituberculates survived.


> (disaster doesn't seem like strong enough
> word for K/T--- a ghastly time to have been alive, especially on land).

It was even worse, IMHO. More tomorrow.
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