[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Nocturnal crocs?
On Sat, 25 Aug 2001, David Marjanovic wrote:
> Hesperornithiformes, Ambiortimorphae incl. *Ichthyornis*, Enantiornithes...
> at least some of those were present late in the Maastrichtian.
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.
> Then why didn't they die out much earlier -- and evolve in the first place?
Because, until organisms existed to take advantage of these species they
were OK. So has it ever been! Otherwise the planet would still be
populated with the original species.
> 3 months?
> > > > Today,
> > > > mammals and birds (and, to a lesser extent, reps) appear to be the
> > > > 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
> > > 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 deal 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)?
> > 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.
> 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
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
> BTW, apparently ostrich males seem to be capable of quite some defense nest
> defense -- they are still alive and have lived on canid-infested continents
> as long as the canids themselves AFAIK...
True. But they are not able to do this effectively at night. Therefore,
their prime strategy is concealment (ostriches nest within a 2 sq
km. space and cannot be see by humans (Bertram, anyway) from further than
10 m. Once the nest is found it is destroyed. They suffer 90%-95%
predation to the first year.
> Wait a minute. Do you think any mammal would dare to attack a brooding
> troodontid or dromaeosaur?
Their prey, at least. And, I'm not talking about
"attack". "Stealing" would be a better adjective.