Re: Nocturnal crocs?

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

----- Original Message -----
From: "John Bois" <jbois@umd5.umd.edu>
To: "Michael Bruce Habib" <mbh3q@cms.mail.virginia.edu>
Cc: "Dinosaur Mailing list" <dinosaur@usc.edu>
Sent: Sunday, August 26, 2001 2:41 PM
Subject: Re: Nocturnal crocs?


> On Sun, 26 Aug 2001, Michael Bruce Habib wrote:
>
> > I don't see how your mammal predation model produces
> > selective bird extinction, either.
>
> It doesn't.  My prediction is that that neornithine birds outcompeted

Hardly, I mean, _how_? 0 known Mesozoic neornitheans were living in trees...

> (or preyed) enantiornithines;

Totally impossible. For this you need birds of prey suddenly breaking loose
over the world, and even then this would surely not selectively eliminate
all non-neornithean Pygostylia.
...which include not just Enantiornithes but Hesperornithiformes,
*Ichthyornis*...

> and that this has nothing to do with the
> boundary.

Just _happened_, like all other K/T extinctions, to coincide exactly with
it...

> Indeed, I would argue that recent findings in Antarctica
> support that position (i.e., old birds were already absent from large
> areas of the planet--though I recognize other scenarios are possible).
>
> > Tree and cliff nesting does not
> > stop egg predation. In fact, all oviparous species today,
> > be they crocs, birds, lizards, snakes, or turtles, suffer
> > significant amounts of nest predation.  These are
> > acceptable losses.  Predation of nests does not, and
> > probably did not, drive species rapidly into extinction.
>
> Nesting sites are selected in order to _reduce_ predation.  When predation
> load on such sites increases, losses become "unacceptable".  Such has been
> the case with increased predation in the Pothole region of Canadian
> Prairie, on Arctic islands opened up to foxes by trappers (these have
> reduced goose populations to point of collapse--now recovering due to
> extirpation of predators).

Islands with a newly introduced predator. See, exactly what did not happen i
n Maastrichtian NA. There the big mammals evolved in place (which includes
Asia east of the Turgay Strait).

> [...] birds on islands [...] only have to face similar-sized birds,

May I repeat: "???"

> > I honestly do not see there being a
> > correlation with nocturnal habits and nest survival.
>
> My argument is limited to only one oviparous class: a parent who, like
> most/many crocs uses active defense as its _prime_ strategy (in other
> words, it doesn't even attempt to conceal and is therefore constantly
> discovered).  In such a case, the ability of the predator to see at night
> is a significant advantage over a parent who cannot.

And not one nonavian dinosaur hid its nest? Or what am I misunderstanding
here?

> I agree that these sources of loss arre significant.  I argue
> _summation_, increased predation load to unacceptable levels.  As
> evidence I cite a) extant big egg layers which suffer 90% to 95% losses
> (ratites) and which remain in the black curtesy of a concealing medium not
> available to similarly-sized non-avians;

Dense forest: cassowaries, kiwis and moa. Available to lots of K dinosaurs.

> b) inability of larger species to
> become viable other than on islands with low predator density.

*Titanis*, *Bullockornis*, *Dromornis* (biggest of all), *Gastornis*... what
about those who were predators amongst lots of predatory mammals and land
crocs?