Re: Mesozoic - the heyday of life?

[Jonathon Woolf <jwoolf@erinet.com>]

Dinogeorge@aol.com wrote:
> 
> In a message dated 97-06-11 23:06:53 EDT, jwoolf@erinet.com (Jonathon Woolf)
> writes:
> 
> << Welllll . . . . I think this kinda depends on how you define
>  "diversity."  How do you define it?  Is it the same thing as "variety"
>  (which is the word I used)?   >>
> 
> Yes. In this case, what would be the difference?

My intended meaning is that in this context "diversity" refers primarily
to matters of biology while "variety" refers to matters of ecology. 
Something like the difference between a member of the Order Carnivora
and the guild of carnivores.  If you have twenty species all of which
fill basically the same niche in basically the same way, and look
basically the same while doing it, you have a lot of taxonomic diversity
but not much ecological variety.  _Camarasaurus_ and _Brachiosaurus_
were pretty different beasties in a lot of ways, but they shared the
basic sauropod body plan and ecological niche.  Not much variety there. 
Same for, say, T-rex and _Allosaurus_ -- same basic shape, same niche,
not much variety.  OTOH, a fox and a lynx fill substantially different
niches using significantly different body plans.  That's variety.  

I look at the known dinosaurs, and I don't see a whole lot of variety
there.  (My opinion, natch, and f'sure that's all it be.)  Sure, we know
of a lot of species, genera, families, suborders, but we don't have
representatives of many different ecological guilds.  Big meat-eater,
small meat-eater, high browser, low browser, and not a whole lot of
difference in the basic body shapes used to exploit any of those
guilds.  Something like half of all known dinosaurs shared just one
basic body plan, the biped with lighter forelimbs that could be used for
walking or manipulation.  As far as we know, there weren't any aquatic
or even amphibious dinosaurs.  There weren't any arboreal dinosaurs. 
There weren't any burrowing dinosaurs.  There weren't any insect-eating
dinosaurs.  For all their success, they exploited a rather narrow range
of niches, and did it using only a very few basic forms.  As far as I
know, the mammalian Order Carnivora from weasel to otter to wolf to
sabertooth cat to bear shows a greater range of ecological variety than
any dinosaur group of similar taxonomic size and diversity.  

-- JSW