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Re: AW: how many bird-species right after the K-T ?

> Of these, what was the largest in
> size?

There are some Atlantic Seaboard fossils about the size of a small albatross. 
Thes probably did not make it (see below), but their relatives elsewhere quite 
obviously did, and these might not have been much smaller (but your 
considerations abot the size factor still applies).

See also here: http://www.ugcs.caltech.edu/~presto/cenozoic.pdf

Oh, I forgot - there are TWO lineages that almost certainly did not made it 
through: _Laornis_ (a largish long-legged ?wader ?waterfowl 
?stork/crane/???vulture-ancestor from the Atlantic Seaboard) and an even larger 
species of ?seabird that was recently discovered on the Chatham Islands of New 
Zealand. I pondered over the image, but being no paleontologist myself I could 
only tell it has nothing to do with penguins, and probably not with anything 
else still alive either.

Both are undisputably modern birds as far as I know, and at least the latter 
definitely comes from the Mesozoic. The former also seems to; at least its 
lineage did not progress significantly into the Cenozoic.

Any other modern birds from the Cretaceous I can think off the top of my head 
make possible ancestors of lineages that survived at least to the Eocene..

(Actually, since the bulk of the ejecta of the Mexican impact was blow into the 
Northern Hemisphere air masses - and as there is no reason to think global 
atmospheric circulation back then fundamentally differed from that today, 
probably mostly were washed down again over the N Hemisphere too -, none or at 
most a bare few of the 15 or so species of modern birds that are documented 
from Cretaceous North America make likely survivors. 

As each species is representative of its individual lineage, such lineages did 
thus not make it. Also fits the fact that the candidates of prolonged 
survivorship are almost all either global pelagics or have a Gondwanan origin 
of their post-Cretaceous radiation. Even the pelagics have a S Hemisphere bias.)