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Re: Nocturnal crocs?




On Sat, 25 Aug 2001, Morgan Churchill wrote:

>> Until
>> it is something more, something that is supported by data, the
extinction
>> hypothesis for birds must line up and take a number.

>this strikes me as very selective reasoning; you argue that thier is
>not much evidence to support a mass extinction of birds at the end of the
>Cretaceous, but you hold to a belief that a mammal egg predation
>holocaust, which if anything has even less to support it, did happen.

I have said there are no data supporting either case.  In the meantime, my
beliefs are, I would argue, as roughly supportable as yours.  My mechanism
is not a "holocaust" at all; it is a slow, steady, abiding selecetion, a
selection which operates strongly today (at least this claim is supported
if not known).  Your claim has no observable phenomena, no
precedent.  Yes, there was a bolide, but, again, what magic-bullet effect
can account for selective bird extinction.  I mean the big dinos can
starve due to no food.  What about the little birds?

>> The question then is: at what point in nest and
>> hatchling predator evolution did this first become true (if true)?

 
> Haven't they though?  the Phorushacoids of south america are pretty
>close to being a "re-evolved" dinosaur predator.  These birds not only
>competed well with mammals, but actually entered North America when the
>two continents were bridged.  Their were also the Diatrymids.

Phorusrhacids evolved amid grasses.  Grasses are an effective concealing
medium that was not available to dinos.  Diatrymids may have depended upon
wetlands, a mammalian refuge which was in short supply at the terminal
Cretaceous.

> But I would argue that their wasn't really any "size relaxation" in the
> K/T.  Merely a better represented fossil record.

Then we have competing hypotheses.  But I have positive evidence, you,
only negative.  I think this edges my hypothesis ahead of yours.  At the
very least, it keeps me in the argument!


> And Ostriches aren't anyware near as predatory as some of the
>dinosaurs.  If a modern day jackal tried to drive a dromaeosaur off a
>nest, it would be merely dinner.

Only if it could _see_ the jackal.


> And what about the Cassowary.  They are
> a lot more dangerous birds, as was mentioned recently.  Does anyone know
>anything of Cassowary nesting behavior?

This could use a whole lot of study.  There is very little work done on
the Cassowary.  I've read that they are aggressive at the nest, also that
they go into torpor.  Torpor would be a concealment strategy.  As far as I
know, the cassowary is the largest forest-nesting bird.