Re: Cretaceous taeniodont

[Phil Bigelow <bigelowp@juno.com>]

> > > How  many species need to be
> > > above, say, one kg. before we can say predation and/or 
> competition was no
> > > longer keeping mammals small?  Would one more do it?  Two?
> >
> > Even three thousand would not do it.


> But this is a serious question.  Much is made about the explosive
> diversification of mammals _after_ the K/T.  And there is good 
> reason for
> this!  But increasing evidence of diversity--especially with regard 
> to
> niche utilization and size--before the K/T is also an important
> phenomenon.


I suspect that small islands played a large role in the evolution and
radiation of Mesozoic mammals.  If some islands lacked dinosaurs (and I'd
guess that many of them did), then the conditions would have been similar
(although by no means identical) to the conditions in the earliest
Paleocene.

So, how did these new Mesozoic mammal species spread widely if their
population was trapped on a small island?  Because of their smaller size,
mammals can "raft" over to the mainland much easier than the medium- to
large-mass dinosaurs could "raft" from the mainland to an island.  Most
typical floating debris bundles probably could support the weight of, at
most,  a Troodon- or Dromaeosaurus- size dinosaur, but only one
individual at a time.  In contrast, that same small debris bundle could
transport a breeding pair of mammals from the island to the mainland.


> My question is simply: what is the magic
> number of one kilo plus mammals that
> will make people pay attention?


Somewhere in my garage I have a Norway Rat skull that is about 8/10s the
length of a typical adult house cat skull.  A single breeding pair can
theoretically produce at least 100,000 descendants in a year.  What if
those two Norway Rats rafted over to a predator-free island?........

And you asked, does size matter?  Penthouse Magazine says YES!! (and who
are we to argue with the experts, eh my friends?).  If the amply-endowed
_Didelphodon vorax_ can thrive amongst the hungry Hell Creek dromaeosaurs
(which are still undescribed beasts, BTW), then being large and furry
probably wasn't a significant handicap in the Mesozoic.  So why were most
other Mesozoic mammals small?  My guess is that, since dinosaurs didn't
get that small, the mammals "conquered" that niche way back in the middle
Triassic, and they never let go of their conquered territory.  Perhaps
the dinosaurs *didn't* keep the Mesozoic mammals small.  Perhaps it was
the other way around:  perhaps the Mesozoic mammals kept the dinosaurs
large.  _D. vorax_ proves that Mesozoic mammals could Live Large if they
"chose" to do so.

On the other hand, how many shrew-sized flightless birds (fossil or
living) can we name?

<pb>
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