SCALE REDUCTION???

["D.W.Naish" <dwn194@soton.ac.uk>]

> 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 Mammals were superseded by Giant Mammals which were larger 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.
> Stephen Hurrell 

I disagree with this. There has not been any gradual, observable trend in size
reduction in tetrapods - true, the late Jurassic had more than its fair share
of mega-dinosaurs, but they don't then diminish gradually in size into the
Cretaceous. As for mammals, they had to evolve giant forms after the K-T event,
and thereafter do not present any kind of gradual decline. Though the biggest
land mammals, indricotheres, were around in the Oligocene, recent mammoths (up
to 10 tonnes in _Mammuthus colombi_) far outweigh the vast majority of big
mammals that lived earlier. Therefore, no gradual reduction. Recent mammals are
mostly smaller than their prehistoric ancestors due to complex global-crises
phenomena, which caused massive extinctions and population depletions.
Furthermore, a number of big animals start small, get big, get small, and get
bigger again. This seemingly relates to climatic conditions and availability of
food - not compatible with simple decrease in body size.

If such a size reduction was for real, the _Balaeonoptera_ whales would have had
to had lived and gone extinct back in the Oligocene, _Aepyornis and _Dinornis_
would have had to have died out in the Eocene and Tertiary mega-crocodiles
couldn't possibly have been around after their Mesozoic kin. 

The evolution of size is a complex, multi-faceted phenomena pending on
ecological interaction, available resources, biomechanics and genetic raw
material. Other factors, like proximity of bodies in space to Earth, spin rate,
magnetic polarity and crap like that take second place. No way is there a simple
correlation!

"It looks like a plucked ostrich!"

DARREN NAISH