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RE: Campbell's even crazier than a MANIAC? (archeopteryx climbing)

Quoting Anthony Docimo <keenir@hotmail.com>:

> > >Quoting Tim Williams <twilliams_alpha@hotmail.com>:
> >
> > > Maybe the success of predatory mammals vs predatory birds has more to do
> with
> > > teeth, rather than bipedality vs quadrupedality.
> > Quoting Dann Pigdon:
> > 
> > My guess is that reproductive strategies may have given the mammals an
> advantage. Birds can try 
> > to defend a nest, but if they instead choose to run away then their eggs
> remain 'sitting ducks'. A 
> > pregnant sabre-tooth however could run away with it's precious unborn (but
> not un-borne!) cargo 
> > safely inside it. 
>  Don't pregnant mammals run slower than non-pregnant mammals?

Not much slower. A pregnant antelope or equid can still run pretty fast. 

I wonder how far into a pregnancy extant lions continue to be involved in 
hunts? Given how small 
lion cubs are relative to the mass of the mother, I'm guessing even a 'heavily' 
pregnant sabre-
tooth could have outrun anything that dared to chase it.

>  A duck can abandon its nest to a predator, and lay more eggs later in the
> year and-or the next year.  Unless the mammal is a marsupial or monotreme, a
> pregnant mammal can't do that and live.

Laying eggs requires a lot of a bird's resources, and some birds only have a 
limited breeding 
season. Sometimes they only get one shot at it. Often a secondary clutch layed 
late in the season 
is doomed from conception, since migratory adults will leave when they have too 
regardless of 
whether their chicks are ready to migrate with them. Many a penguin or flamingo 
chick hatched 
late in the season has been left for dead despite being perfectly healthy.

Most small to medium-sized mammals have gestation periods of only a few weeks 
to a few months 
(human gestation is unusually long for a species of our size range, due to the 
requirements of 
brain development). If a pregnant mammal loses it's unborn due to stress (like 
having to run a lot) 
it can often become sexually receptive again soon after. Given that failed 
flight in a pregnant 
mammal will result in the death of the unborn AND the parent, they tend to work 
pretty damn hard 
not to be caught! I suspect there were few predators that would have chased a 
pregnant sabre-
tooth in the first place - whereas unguarded terror bird eggs or hatchlings 
would have been an 
attractive meal to many predators. 

There must be advantages to being able to carry about your unborn offspring 
(otherwise we'd all 
still be pouchless monotremes). Even some reptiles and fish have opted for live 
birth, essentially 
carrying their eggs around with them internally. It's generally a lot harded to 
chase down a 
pregnant animal than it is to chase down an egg - unless of course it's down a 
steep slope. :-)


Dann Pigdon
GIS / Archaeologist              http://geo_cities.com/dannsdinosaurs
Melbourne, Australia             http://heretichides.soffiles.com