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Re: Predator relationships



Michael wrote:
> 
> > But what about _Acinonyx_pardinensis_, as well as
> > _Miracinonyx_inexpectatus_ and _M._trumani_?  _A._pardinensus_ was
> > unquestionable a cheetah, but was half again as large as the modern
> > cheetah; estimates are that it could run as fast or faster than the
> > modern form.  The same holds with the _Miracinonyx_ species.  Prey
> > species would be abundant in Africa, but competition with lions and
> > hyenas might be a much stronger mitigating factor; it's hard for those
> > guys to grab tommys, after all, so that may be the only prey animal the
> > cheetah can get away with grabbing on a regular basis.
> 
> Don't know.  I'll try to see if anyone knows.  Cheetahs now occupy a
> certain niche.  They cannot compete for larger prey nor with the
> other competitors.  I haven't studied the playing field 20-2mya.
> They are likely remnants of a large worldwide population that evolved
> before modern felids and were basically supplanted by them.  Those
> left may be pockets of small gene pools.

By the references I have, the modern cheetah and its close relatives
(_Acinonyx_ and _Miracinonyx_) are relatively recent offshoots from a
line closer to _Felis_ than to _Panthera_.  Many of the traits that look
like plesiomorphies, such as the non-retractile claws, are actually
"re-derived" features.  I think the right term for that is "secondarily
derived features," but I'm not sure.  In any case, cheetahs are a
relatively recent line of cats, not a relic.  

Modern cheetahs face two major problems: their extreme specializations
for speed, and the fact that they live in an extremely predator-heavy
ecosystem.  Their timidity is a survival trait.  A cheetah is kept fed
by its feet.  Even a minor injury can be deadly for a lone-hunting
animal that depends on speed.  Cheetahs are so reluctant to fight for
any reason that a female cheetah will abandon her cubs rather than fight
for them, something that as far as I know is unique among carnivores,
and uncommon in mammals of all groups.  

That said, I find myself questioning the entire logic of using the
Serengeti as a model for dinosaur interactions.  The Serengeti is unique
among modern ecosystems in that it has _five_ carnivores of roughly
equivalent size and predatory skill that go after many of the same prey
animals: cheetah, lion, leopard, spotted hyena, and African wild dog. 
In other parts of the world, either there's one top predator, or the
predators divvy up the available prey base either by habitat or by prey
species.  But lion, leopard, hyena, and wild dog all chase pretty much
the same prey species, and cheetahs occasionally will hit calves of
wildebeest, impala, or other antelope as well as their favored Tommy
gazelles.  Would any dinosaurian ecosystem likely have such an odd
confluence of competing predators?

-- JSW