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Re: Nocturnal crocs?
On Sat, 25 Aug 2001, David Marjanovic wrote:
> > Dinosaur diversity was probably not affected much at the K/T
> > (inasmuch as bird diversity making it through may well have
> > been greater than non-avian esxtinction).
> Dinosaur diversity was reduced to a few species of Neornithes... I don't
> understand something here.
We have no idea how many species of birds were alive at the time. We
have no evidence to suggest _any_ became extinct. I suggest the burden of
proof rests with those who would claim that what you say is true--I mean,
there is no evidence (other than negative, and birds are famously
underrepresented in the fossil record) of bird extinctions.
> > Instead, the K/T represents the
> > death of a niche--that filled by large oviparous species in terrestrial
> > locations. This niche has been practically empty ever since!
> Why should there be extra niches for _oviparous_ animals? How does this
> affect their ecology?
Let me count the ways. Just one example. A nesting dino must stay in one
place for 3 months and live off local resources.
> > 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?
> Well, *Gobiconodon* also had such a size, and *Repenomamus* (*-nus*?) was
> even larger.
> Such animals (along with LK varanoids) would have produced a selection
> pressure for better nest defense/concealment, and obviously dinosaurs
> survived this.
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.
> > Whichever sex it is, it is driven off the nest by jackals taking advantage
> > of their superior night vision.
> Jackals have better night vision than ostriches? How come?