Re: Birds as dino-killers

[John Bois <jbois@umd5.umd.edu>]

On Sun, 2 Sep 2001, David Marjanovic wrote:
> Mass extinctions aren't included in normal ecology.
> Known mass extinctions don't grade into background extinctions AFAIK.

I don't believe "mass extinction" has a definition--apart from lots of
things becoming extinct.  One person's mass extinction may be another's
not-so-mass extinction.  For example, I show my students a graph of
species diversity vs. geological time--the K/T extinction really doesn't
stand out from many smaller extinctions.  And they _never_ guess that htis
is the one in which the dinos bit it.

> There were no small adult pterosaurs during the entire LK AFAIK, anyway not
> in the Maastrichtian.

Why not?

> > Egg-opening plays second fiddle to hatchling snatching as a predatory
> > tactic in bird on big bird predation.
> 
> Sorry, my error. However, incredible lots of birds and mammals are
> occasional nest raiders today, so much that nests in trees are anywhere from
> safe. Yet birds show no sign of decline. What is happening here?

Could you entertain the hypothesis that many song bird species are in
steep decline due to crow predation on nests and chicks?

> So I repeat:
> "and that *Gobiconodon* and *Repenomamus* somehow failed to have similar
> effects." How?

I predict--but don't know--that sizes for latest Cretaceous mammals were,
on average, increasing.  John Alroy has data on this.  I've tried to read
his graphs but they are not that clear.  They appear to show an increase
up to the K/T.  He is fighting the idea that mammals diversity exploded
pre-K/T.  As such, he is really only interested in macro size increase.  I
might e-mail him.  Increase from mouse to mink size is not really
macro--and so is not an area of much interest to him.  But, inasmuch as it
pushes size above nest and hatchling predation-threshold size, it is
interesting to me!