Re: Life's scale reduction since the Dinosaurs

[ornstn@inforamp.net (Ronald Orenstein)]

>Darren then went on to sight the biggest of the land animals: mega-dinosaurs, 
>indricotheres, recent mammoths and recent mammals. Arguing 
>all the time that there has NOT been any reduction in the 
>scale of life.
>
>If I plot the weights of these animals in their time periods I get
>something like (very roughly)
>
>80 MYA      - Mega-dinosaurs     up to about 75 tonnes
>40 MYA      - Indricotheres      about 30 tonnes
>3 MYA       - recent mammoths    about 10 Tonnes
>Present Day -                    Max. weight about 6 Tonnes
>
>I would have thought the trend was obvious (although there is 
>probably considerable scope for improvement in the accuracy of 
>the dates and weights)

I'm sorry, but I still don't see a trend.  Your data is highly selective; I
could as easily select data to show just the opposite.  The largest Jurassic
dinosaurs were considerably bigger than the largest Triassic dinosaurs (or
anything else living on land in the Triassic).  Indricotheres, which lived
in the Oligocene, were considerably larger than any mammal living prior to
that time (including the 30-odd million years since the K/T); furthermore,
indricotheres do not represent a general global trend but an isolated group
of extremely large mammals found only in central Asia. One large mammal
living in the Oligocene, far bigger than anything before or since, hardly
constitutes a trend (you would not say that there has been a general
tendency for humans to get shorter these days because nobody is as tall as
the Cardiff Giant). I would think (without checking) that if you looked at
(say) the ten largest land mammals known from each of the Paleocene, Eocene,
Oligocene, Miocene, Pliocene and Pleistocene and compared the results you
would be more likely to see a trend (if any) towards increasing size, not
the reverse.

In fact when you look at individual lineages you often find that the trend
was precisely the opposite through most of their evolutionary history - eg
from smaller to larger (consider deer, horses, titanotheres, toxodonts,
giant ground sloths, litopterns, diprotodonts etc - all of whose largest
members arose late in their evolutionary history.  The loss of many of these
forms in the very recent past appears to be an isolated phenomenon - in
effect, a mass extinction.

Your example of dragonflies really doesn't apply.  For one thing, giants
like Meganeura belong to an extinct group and are not the ancestors of
modern dragonflies - they didn't get smaller, they died out.  Further, some
have speculated that with the evolution of flying vertebrates the niche for
giant predatory insects has been filled to such an extent that the rise of
creatures like Meganeura may be precluded.

May I suggest that you let go of your idea long enough to stand back from it
and judge it as though someone else had brought it to you?
--
Ronald I. Orenstein                           Phone: (905) 820-7886 (home)
International Wildlife Coalition              Fax/Modem: (905) 569-0116 (home)
Home: 1825 Shady Creek Court                  Messages: (416) 368-4661
Mississauga, Ontario, Canada L5L 3W2          Internet: ornstn@inforamp.net
Office: 130 Adelaide Street W., Suite 1940    
Toronto, Ontario Canada M5H 3P5