[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Ratites and egg predation: the pattern confirmed.



On Fri, 19 Apr 1996, Nicholas R. Longrich wrote:

>       If it is really such a battle of differential reproductive 
> success, we ought to see something similar occuring among the placentals, 
> marsupials and monotremes. We don't...If you look at the pattern, what
> we see is that placentals and marsupials coexist for long periods of
> time- millions of years

As Nick Pharris has noted, relative to each other, there may be no big 
difference between mammal groups.  Whatever their reproductive method, 
mammals, relative to dinosaurs, are stealthy!  But between each other, 
they may have only marginal, niche-dependent, advantages.

> The virginia opossum and kangaroos continue to show that it's more
> than just reproductive strategy that make you a success.

Agreed.  Advantages of this or that reproductive mode are strictly niche 
dependent.  But I would argue that, in the egg-predation ambience of the 
Cretaceous, stealthy reproduction conferred great advantage.  

>       Now take a look at the dinosaur extinction. Non-avian
> dinosaurs go completely extinct the world over in a brief span of
> time. Unlike with marsupials and monotremes, there are no island
> continents where dinosaurs hold out. The pattern appears to be the
> same the world over, unlike the extremely uneven pattern seen in
> placental/marsupial competition.

.because the diffeneces between mammals and dinosaurs are stark.

>  The pattern is completely at odds with the long term type of
> competition you see when one group edges out another.
>       Mammals did not edge dinosaurs out. You can see this because
> it is only AFTER the dinosaurs went extinct that mammals begin to
> radiate into the niches dinosaurs formerly occupied. After the K/T
> large herbivores and predators emerge, not before- the reverse of what
> your hypothesis would imply.

.No!  This _agrees_ with the non-stealthy egg theory.  Egg predation by 
mammals and others was not a battle to usurp the open-field nich of the 
dinosaurs.  It was a parasitic relationship.  And, just as a virus, 
having felled the mighty lion, does not assume kingship of the plain, 
mammals must wait out a lag period before characters advantageous in the 
open-field could be evolved.  In the meantime some mighty birds  
stepped/flew into the open niche.  But ultimately (written in what book 
of rules?) the stealthy-reproduction imperative predominated.