Re: Cretaceous taeniodont

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

On Wed, 7 Apr 2004, Tim Williams wrote:

> I agree that, for a mammal, being big (or at least bigGER) may have been an
> advantage.  But I'm still not hooked on the idea that mammals got bigger
> because there was a relaxation in predatory constraints.  This implies that
> predatory theropods somehow 'let down their game" in the Cretaceous,
> allowing mammals to get larger and more visible.

I am arguing for the following scenario: predators of small mammals may
have been excluded from some habitats by predation on themselves.  _If_
bird species and pterosaurs were reduced by predatory birds--and I
believe the predation hypothesesis explains at least pterosaur dcline
better than competition--it is feasible that they could also threaten or
make life miserable for terrestrial (or arboreal?) dinosaurs.

>A _Microraptor_ or _Sinosauropteryx_ might go for a shrew-sized mammal in
a
> heartbeat, but would baulk at pouncing on a mammal the size of a badger or
> wolverine.  Of course, the theropods could get bigger too, and so on...

If size gave immunity from predation, why didn't this fuel an arms race as
it seems to have done in dinosaurs.  IMHO dinosaurs play a way better game
in the large arena--body plan-wise.

>  But
> these sort of two-way interactions undermine the simplistic notion that
> increased body size in mammals is an unambiguous indicator of success in
> these furballs.

I think we're talking not so much about simple bragging rights for size,
but for the ability to enter wider niches.  Broader niche exploitation
_is_ an indicator of stronger competitiveness since other organisms could
just as well occupy them.