Re: why larger?

["Thomas R. Holtz, Jr." <th81@umail.umd.edu>]

At 10:05 PM 2/17/97 -0500, you wrote:
>>>>Okay, I follow the logic up until this point.  Byt WHY would they be
>>>>replaced by LARGER decendants of their smaller relations?  Why "larger?"
>>
>>Cope's Law:  in any given lineage, organisms tend to increase in size
>>over time.  For example, horses and elephants.
>
>        Given, of course, exceptions due to extraordinary circumstances,
>such as dwarf mammoths and elephants that used to live on certain islands.

Oh, freaking bloody hell!!  Did NO ONE read any of the stuff I posted last
month on "Cope's Rule"?!?!?!

Shrinking (i.e., size decrease) from one species to the next is NOT an
extraordinary circumstance!!

Please read papers by MacFadden on the evolution of horses (best source is
the book Fossil Horses, with references to the appropriate work in the
literature) for a good vertebrate example.

There is no major statistical support for size increase vs. size decrease in
species-to-species transitions in horses.  The work hasn't been done on
elephants (to my knowledge), so I can't speak to that.

Stanley, Jablonski, and others give invertebrate examples.  Stanley (in
particular) and Gould (in Full House) show that a net increase in maximum
size can be due to functional/physiological "walls" to the small end of the
size spectrum, whereas the large end of the spectrum may be over.  Thus, the
maximum size of a lineage can increase even if the occurences of shrinking
from species to species equals the number of increases from species to species.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661

"To trace that life in its manifold changes through past ages to the present
is a ... difficult task, but one from which modern science does not shrink.
In this wide field, every earnest effort will meet with some degree of
success; every year will add new and important facts; and every generation
will bring to light some law, in accordance with which ancient life has been
changed into life as we see it around us to-day."
        --O.C. Marsh, Vice Presidential Address, AAAS, August 30, 1877