Re: The Biggest Dinosaurs

[John Bois <jbois@umd5.umd.edu>]

On Wed, 20 Aug 1997, Michael wrote:

> That's an interesting point, John.  I wonder if there were other 
> reasons as well, such as predator size increasing prey size 
> increasing predator size unrelated to egg defense. 

Yes, it is very complicated.  Size changes unrelated to egg defence
undoubtedly occurred.  But pred/prey, climate, intra species competition
etc. happened in all taxa.  The question I am trying to get to is :why
dinosaurs seem to be relatively off-the-scale re size compared to mammals.
There is a stark variable.  It is nest defence.  And, among extant snakes,
among which you could assume some control of all other variables, size
depends on, I should say correlates with and dependence is an inference
which is highly likely, almost certainly, I say correlates strongly with
nest guarding vs. viviparity.

> Or did it perhaps 
> start there and escalate?  Or both?  Are they different or the same 
> mechanism (assuming they occur)?  There's no doubt that prey and 
> predator exist in everchanging equilibrium today.  

A "Just-so" sequence for snakes could be this: A snake species suffers
nest predation.  A nest-guarding mutant repels predators.  Either nest
predators grow bigger (and fuel a size-based arms race), or new predators
are alerted by frequent snake-trips to the nest.  Either way, an
evolutionary response might be to grow bigger.  Of course, with snakes,
since the whole reason for their shape is for concealment (right? I mean
for slipping into thin out-of-the-way places where predators cannot
reach) there is a fairly restricted upper limit to how big they could be.
The upper limit for dinosaurs was probably dertermined things like
mechanical stress on bones, blood pressure problems, eamount of
available forage etc. This view sees size as more of a pathology
associated with the requirement of nest defence, rather than the
crowning glory of gee whiz evolution.