Re: Birds as dino-killers

["David Marjanovic" <david.marjanovic@gmx.at>]

Phew, last e-mail for today, and it's just quarter past 5 PM...

> On Sun, 2 Sep 2001, David Marjanovic wrote:
>
> > _BACKGROUND_
>
> _Background extinction_ is a concept of limited value.  The idea comes (I
> think) from background radiation, the relatively constant amount of
> radiation that reaches the planet.

While it definitely doesn't come from there, it is rather similar in that
really something dies out all the time.

>Biological extinction is not at all
> like this.  Each extinction has a unique set of circumstances.

...which I don't doubt.

> There is no _rate_ for this.

There appears to be one, according to what I've read... can someone help me?

> The concept of mass extinctions grading into
> "background" extinctions is a topic of discussion among
> extinctionologists--actually, paleo-ecologists.  As in everything else in
> ecology, there are no black and whites--just clines.

Mass extinctions aren't included in normal ecology.
Known mass extinctions don't grade into background extinctions AFAIK.

> > > If birds could do this to pterosaurs, they
> > > must also be able to cause trouble for small to medium-sized non-avian
> > > dinosaurs.
> >
> > which were able to hide their nests in dense forest undergrowth,
something
> > the large LK pterosaurs were unable to do.
>
> Again, the ability of these creatures to be able to hide is in
> doubt.  Turkeys on the NA continent can do it--but they can also fly to
> escape predation--this is a margin of survivability not possessed by
> non-avian dinosaurs--and this margin is very small.

Running is also an option.

> This suggests an
> upper-limit for this strategy, a limit only exceeded by the cassowary in
> Australia/NG.  Also, why couldn't smaller pterosaurs hide?

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

> > > If it is true that there was a reduction in the diversity
> > > of these size ranges among dinosaurs,
> >
> > Yes, if... any numbers available? :-)
>
> I would love to know the status of this question.  I know that late
> Cretaceous species of theropods, ornithopods, ceratopsians, and
> ankylosaurs (?), were the largest known for their clades.  However...

...what we need here is counting small species.

> > In which case we need a LK bird capable of opening eggs. What could that
be?
> > *Ichthyornis*? :-/
>
> 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?

> > Which, of course, assumes that there was a size increase among
> > end-Maastrichtian mammals of the world...
>
> Right.

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