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Re: Nocturnal crocs?
Interesting theories regarding mammal predation on nests
from all thus far. I have a couple of thoughts to add.
> 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). 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?
I don't see how your mammal predation model produces
selective bird extinction, either. It seems to me that all
avians would have problems with a massive nest predator
boom. Modern birds have many nest predators. Other birds,
lizards, snakes, small mammals: all of these
attack nestlings and eggs. 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.
There are, of course, a number of mechanisms utilized by
modern egg-layers to defend nests (otherwise losses would
be too high). These include concealment and burial, active
nest defense, mass egg laying (acceptable losses are
higher), among many others. Both nocturnal and diurnal
oviparous animal species exist today, some members of both
groups nest on the ground, and some members of both groups
nest in elevated locations. In fact, concealment, active
nest defense, and nearly any nest protection strategy
one selects can be found in both diurnal and nocturnal
oviparous animals. I honestly do not see there being a
correlation with nocturnal habits and nest survival.
Another point to consider: even if average mammal size or
abundance increased in the late Cretaceous, I doubt it
would make a significant difference regarding nest
predation compared to the fungal infections, insect
predators (like ant species), reptile predation, and bird
predation that would have been common already. I find it
hard to believe that mammal nest predation compares much
to egg losses due to fungal and bacterial infections, or
that of insects.
University of Virginia