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Re: Extinction once again (crocs)




On Sun, 18 Feb 2001, Adam Britton wrote:

> Although wetlands are today the most important nesting habitat for many croc
> species, it is not true that they are totally dependent upon them. Crocs
> require access to freshwater during nesting, which may come from a variety
> of sources including tidal rivers and their upstream areas, isolated lakes
> and pools, or even flooded patches during wet season rains.

I agree, and this is a very curious fact.  What is so important about
proximity to water?  It's not for the sake of the eggs--the eggs can be
placed in sand away from water (presumably).  Anyway, alligators building
nest mounds of vegetation could do it away from water if they wanted to.

> Some species,
> such as Australian freshwater crocodiles or Nile crocodiles, utilise sand
> banks to lay their eggs and only require that the substrate be moist close
> to water. This can provide excellent inland nesting habitat.

Well, there may be competing factors here.  Nest defense is a big deal for
Nile crocs.  So, proximity to water may also be favored so that parent
unit can be close at hand.  Anyway, all oviparous creatures (except
crocs) depend upon concealment or remote nesting. I realize that many
will defend their nest upon discovery--but they depend upon not being
discovered. How is it that this obligatory nest defense of easily
discoverable eggs works for only one taxon?  Why hasn't it evolved in
other species?  A reasonable hypothesis is that the crocs enjoy a home
field advantage over would-be nest robbers (I realize they suffer heavy
predation, anyway).  That is, predators are relatively less likely to prey
on a croc nest than (for example) a hadrosaur nest, because they are more
likely to become prey themselves.  The crocs can be waiting in ambush, can
drag unsuspecting predator into the water, shred it to bits in seconds,
etc.
Any other ideas on the value of semi-aquatic niche for this
all-but-defunct strategy, i.e., obligatory nest defense?

> I would be interested in reviewing the ideas about the Eusuchia surviving
> the K-T extinction, if anyone has any.

As above, croc nests more secure than dinosaur nests (assuming active nest
defense was the prime strategy of at least the largest dinosaurs).