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Re: mammal mystery

On Sun, 16 Feb 1997, Larry wrote:

> Thriving is precisely what increasing size means.  Animals living in an 
> environment that can support greater size get bigger.  It's been a simple 
> fact since the Paleozoic. 

I have argued that the trend to large size in dinos was a response to the
need to defend nests (since big animal's nests are easily discoverable
they are forced to into a strategy of defence) and that bigness was more
of a pathology than an indicator of "thriving".  This is a hypothesis
which may or may not be true.  In any case I believe the size of animals
is a much more complex issue than your "simple fact". 

> Can you be serious?  A "group of species" is referred to as a "genus." Do 
> you mean that elephants are doomed because there are no mouse-sized 
> elephants?  Are we doomed because there are no mouse-sized hominids?

I refer you to DinoGeorge's post on this subject.  The "group of species"
was sloppy.  I meant groups like mammals, lizards, dinosaurs. Anyway,
there are many reasons why small members of a clade might enhance its
regenerative power: quick generation time allowing much genetic
"experimentation", large numbers allowing the same, genetic "experiments"
being easier to carry out on small things (for example, live birth would
seem difficult to initiate in big animals because of surface area/volume
considerations), stealth and its attendant immunity to novel predators...

> Many, many dinosaurs were not bipedal.  Even assuming they were, what's 
> your point?

Dinosaurs were  primitively bipedal.  Quadripedal dinosaurs
evolved secondarily as a means of support for big animals.  In
other words there were no quadripedal dinosaurs in the niche occupied by
small mammals.  Small bipedal dinos were at a disadvantage to small
mammals.  A low-to-the-ground animal in close cover moves about more
stealthily and more quickly.  Also mammalian stealthy reproduction would
have given them a reproductive advantage.  But perhaps all of this is
looking at it backwards.  Couldn't you make the case that dinosaurs
_escaped_ the close-cover niches with adaptations of agility, and speed.
Their disappearance from these niches was the price they paid for 
subsequent domination of open-field and arboreal niches.