Re: Life's scale reduction since the Dinosaurs

[Stan Friesen <swf@ElSegundoCA.ATTGIS.COM>]

From: swh@eatl.co.uk (Stephen Hurrell)
 > We all know that the Dinosaurs were big. What is not so generally 
 > realized is that life has been reducing in size over periods of 
 > hundreds of millions of years. 
 > 
 > There can be no doubt that this size reduction has taken place. 
 > After the extinction of the Dinosaurs a range of Supergiant Mammals 
 > approaching the size of the smaller Dinosaurs evolved. These Supergiant 
 > Mammals were superseded by Giant Mammals which were larger 
 > versions of the Mammals alive today. These Giant Mammals have in 
 > their turn died out to be replaced by a smaller scale of life.

This is an oversimplified description of the actual pattern.

What is going on is this - in a mass extinction larger animals seem
to be more susceptible than smaller ones (this is probably a corollary
of the fact that specialists are more susceptible than generalists).
Thus the 1st order mass extinction at the K-T boundary wiped out almost
land animals larget than a coyote.

Gradually, over many millions of years new species of extremely large
animals evolved.  This is also pretty much what happened after the
Permo-Triassic extinctions, with the dinosaurs being the main source
of the largest animals that time around.

Then came the Pliestocene extinctions.  As usual the biggest went first.
In the present, as the Pliestocne extinctions *continue*, aided and
abetted by human intervention, the larger animals, as usual, continue
to be hit hardest.

Thus the actual pattern is a saw-toothed one - with gradual increases
in maximum size alternating with abrupt decreases.

swf@elsegundoca.attgis.com              sarima@netcom.com

The peace of God be with you.