egg predation and extinction

["King, Norm" <nking.ucs@smtp.usi.edu>]

John Bois recently wrote (5/15/96; 8:03p):

>...the very thing that applies to dinosaurs AS A GROUP is the egg.  

We don't know this.

>A rapid, hopeful monster is possible.  A gradual accumulation of 
>diverse predators of eggs is more likely.

Why should we not suspect that many dinosaurs ate other dinosaur's
eggs?  Most predatory dinosaurs were big enough and "competent" enough
to eat any eggs they wanted to.  They could well have "perfected" this
predatory style way back in the Late Triassic.  In fact, I'd bet that
_Lagosuchus_-like predators (OK--_Marasuchus_) were fond of any eggs
they could find, so such predatory behavior was already programmed
into the lineage as the earliest dinosaurs emerged.

If at least some dinosaur "chicks" really were altricial, why wouldn't
the mammals just wait until they hatched to eat them, instead of
trying to gnaw through a "house?"  If all dinosaur chicks were
precocial, they were still awfully small at first--easy prey for
mammals, birds, and pterosaurs, as well as small dinosaurian
predators, snakes, lizards, crocodilians, and who knows what else.

With all of these sources of predation, the claim that it was
specifically egg eating that rather quickly became so much more of a
factor can only be made for other reasons than the evidence or logic
suggesting it.

>I did, in an earlier post, hypothesize that dinos were naive to
>mammal predation until the "moment" that mammal defences, built in
>response to dino predation, became offensive weapons.  In this sense,
>they resemble the invasions of islands where they destroy species
>which have had no time to respond (adaptively).

Why would dinosaurs have been naive to any kind of predation?  To what
kinds of predation are birds, among other animals, naive?

In what way would mammals feeding on these relatively gigantic eggs
represent a modification of defense from being eaten themselves by
dinosaurs?  Are you suggesting that mammals learned to eat just the
eggs of those dinosaurs that previously had been a threat to them?
Why would mammals ever start preying on sauropod eggs, then?

I don't think there was a "moment" when mammal defensive behavior
crossed a threshhold to become offensive behavior, even if your
scenario were correct.  It is in no way comparable to the introduction
of exotic species into isolated islands.  You're taking a situation
caused by the breakdown of geographic barriers, and claiming that a
similar barrier was broken down in the Cretaceous.  But the latter
would have involved time and behavioral barriers.  Those are faulty
analogies.  I question the scenario, anyway--it's like imagining
rabbits starting to search out and crunch up juvenile coyotes,
eventually finding that baby coyotes taste good, and becoming
pedolatransivores (a new term!).  Reminds me of a scene in a Monty
Python movie.

In any case, I thought that, except for multituberculates, the
dentition of Mesozoic mammals suggests mainly insectivory.  What known
dentition suggests they cold gnaw through eggs?  And, with respect to
your hypothesis of change from defensive to offensive behavior, what
kind of defensive behavior would tiny insectivores (or even
herbivores) most likely use to escape predatory dinosaurs?  You seem
to be suggesting that they could effectively defend themselves with
their jaws.  I doubt it!  I recently watched my dog handle a squirrel.
The squirrel did a little damage to the dog's mouth, but you should
have seen the squirrel when it was all over.  Squirrels that are still
alive use other defensive tactics.

This presumed change in Mesozoic mammal behavior is remarkable.  How
did they connect predation by dinosaurs on the prowl to the dinosaur's
eggs.  The eggs weren't a threat, so why did they start to eat EGGS?
 
If you ever expect to "sell" this idea to the scientific community,
you're going to have to get rid of all those _ad hoc_ hypotheses.

*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
Norman R. King                                       tel:  (812) 464-1794
Department of Geosciences                            fax:  (812) 464-1960
University of Southern Indiana
8600 University Blvd.
Evansville, IN 47712                      e-mail:  nking.ucs@smtp.usi.edu