John Bois <jbois@umd5.umd.edu> wrote:
Not known whether Enantiornithes suffered from competition/predation from
Neornithes. Until this is known, it is impossible to say whether _any_ of
these species became extinct. Remember, what you are expecting us to
believe is a stretch: that all but a few birds became extinct without
first being endangered; and that a few lucky survivors made it
through. If a few made it through, why didn't a few more? What magic
bullet effect can account for selection among small, volant animals such
that only a couple survive throughout the entire world, even in places
which bolide is thought to have limited effect? Cracking crabs by the sea
shore strikes me as fanciful, and this is the only suggested scenario. In
other words, the extinction of birds at the K/T is only a _belief_. 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.
> 3 months?
>
> > > > Today,
> > > > mammals and birds (and, to a lesser extent, reps) appear to be the
> agents
> > > > keeping that niche empty. The question then becomes: at what time did
> > > > this first start being the case?
> > >
> > > IMHO modern mammals occupy quite closely the same niches as dinosaurs
> > > earlier (some niches for large animals being empty since we emptied them
> in
> > > the Pleistocene).
> >
> > Then why no competition?
I'm sorry, I am saying that if
mammals occupy the same niche as dinos why don't they have to d! ! ! eal with
_re-evolved_ dinosaur species?
An enduring mystery is: why didn't dinos reevolve? We've had this
discussion before. Still, we're only stabbing in the dark for an
answer. Then ask: how would a large dinosaur do trying to defend a
non-concealed nest in the middle of the Serengeti? Most have the opinion
they would do terribly. 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.
> > I'm trying to build a case for increasing pressure, summation, etc. Yes,
> > there were likely always predators, just as there are for today's
> > oviparous survivors. This doesn't mean that pressure cannot become too
> > strong for a specific reproductive strategy to withstand.
>
> But it does mean that you have to show the pressure increased... :-)
Not by myself. I'm proposing an hypothesis. I have pointed to some
suggestive evidence of size relaxation in K/T species which brings those
species into extant pred/prey ratios.But I would argue that their wasn't really any "size relaxation" in the K/T. Merely a better represented fossil record.
> That's what I mean -- don't ostriches have much better eyes? Their eyes are
> not only much larger but are _bird_ eyes, means, they have a lot more
> light-sensitive cells per area than mammals. (Apart from having 4
> color-sensitive opsins instead of 2, which is most likely irrelevant at
> night.)
Not sure of the science of this. But can cite the fact of jackal
dominance at night. Light would seem to be the only relevant variable
here. See Bertram's monograph on Ostrich reproduction (let me know for
full citation).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. And what about the Cassowary. They are a lot more dangerous birds, as was mentioned recently. Does anyone know anything of Cassowary nesting behavior?