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RE: A Perspective on Cope's Rule



With Respect to Jaime Headden's commentary on Cope's Rule, I believe he made
two points:

1. There is a selection (discovery) bias, and I would include also a
preservational bias favoring the discovery of large fossil remains, i.e.,
remains from large animals.

2. Small animal lineages give rise to larger animals over time (Cope's
Rule).

If we look at the size extremes, the smaller animals tend to reach sexual
maturity faster, produce more litters, and have larger litters. A given
small animal is likely to produce one or two orders of magnitude more
offspring in its life than the largest animals. The smallest animals evolve
at one or two orders of magnitude faster pace than the largest animals.

What is left out in Commentary 2 (above) is the fate of the majority of the
small animal offspring, do they continue without size increase, or are they
driven to extinction by a few in the lineage that acquire larger size? Based
on fossil evidence I've acquired, the small animal lineage continues -- and
continues to be poorly preserved and overlooked. However, it is the small
animal population within the lineage that possesses most of the benefit of
high evolution rates and thus higher genetic diversity.

The subgroup that goes on to increasing size rapidly experiences
evolutionary stasis by virtue of higher sexual maturity, fewer litters and
smaller litters. That portion of the lineage that does not acquire the size
trait (stays small), continues to evolve at a rapid pace. Hence, when the
inevitable extinction event occurs, the large animals lack the genetic
diversity to cope (no pun intended). The small animals, with the diversity
to cope, are the seeds for the next expression of Cope's Rule.

In a sense, Cope's Rule describes a deterministic process that starts with a
body plan developed in the high-evolution, perpetually surviving, rarely
preserved, small animal ensemble. The question I have, when does most of the
evolution occur, before or after the activation of Cope's Rule. I think
before. This would be consistent with the notion of punctuated evolution,
wherein the small animals evolve at incredible rates (which are just normal
for them)to fill the well preserved, large animal niches. If there is
evolutionary continuity, as assumed by cladistic systematics, then I
hypothesize most of the body plan development and "continuity" occurs in the
small animal gene pool that tends to survive from extinction event to
extinction event. Thus, the notion of parsimony as a guiding principle in
evolutionary study needs to be re-examined, since it's application is only
justified when applied to chracter sets that represent a continuity of
states of derivation. I'm suggesting, parsimony applied across extinction
events is not justified given the lack of small animal representation in the
fossil record. I'm also suggesting that "convergent" evolution is far more
common than suspected, and results from extinction events that return life
over and over to the same perpetually underlying, fast-evolving, gene pool.

Regards,

Michael Milbocker, PhD

-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
Jaime A. Headden
Sent: Thursday, January 06, 2005 9:30 PM
To: Dinosaur Mailing List
Subject: A Perspective on Cope's Rule


Based on the differentiation of animals to geography, space, and Cope's
Rule, I figured I'd plop this idea out here for commentary:

  Give ourselves an ecology of allosaurs, apatosaurs, othnieliines, and
some tiny mammal, say *Foxraptor.* These animals show a clear size
delineation, and a neccesity of spacial requirements without overlap: an
allosaur cannot occupy the same space as an apatosaur (unless it's
consuming it), for example.

  In a given area, large animals take up more space and are thus less
common in concentration than smaller animals: A thousand foxraptor in the
space of an apatosaur.

  Cope's Rule predicts that a trend to increase size is present in
biology, and in a lineage, smaller animals will tend to become larger. But
it is possible this is a selection bias. We will tend to find larger
animals because of the access to larger animals than smaller in an area,
given the ecology of Ngorogoro Crater or the exposure at Como Bluff. Thus
we will more easily see larger animals and a replacement over smaller
animals because of the access to smaller animals will be less obvious or
less inherent in fact.

  Hmm ... food for thought?

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making
leaps in the face of adversity, that a simple skip is so hard to do.  We
should all learn to walk soft, walk small, see the world around us rather
than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)




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