body size and the species/genus ratio

["Colette H. Adams" <cadams@hh.gpz.org>]

What I wish to achieve is an understanding of why, for example, mammals
stayed so small during most of the Mesozoic, while no dinosaur that we know
of was smaller than a ferret.  This involves a comparison of the taxonomic
groupings "dinosaur" and "mammal."  But what difference does it make what
my purpose is in asking a question about dinosaur biology?  I hope we are
not going to start trying to bully each other about which questions are
supposed to be acceptable.  Be advised that such attempts will fall on deaf
ears here.

If comparisons above the species level are in any way relevant to the
biology of living animals, it is difficult to see how they can be
irrelevant to that of extinct ones.  Higher-level taxonomy is about
something very real, namely phylogeny, relatedness.  It is true that in
many cases the groupings do not reflect this.  For example, turtles and
crocodilians are lumped together in the class Reptilia.  But few doubt that
crocodilians are much more closely related to birds than to turtles.  I
would prefer to see the four main lineages that arose from stem reptiles be
the basis for classifying reptiles and their descendants.  But this does
not change the fact that higher-level classification does to one degree or
another reflect phylogeny.

There are lots of good reasons to have a standardized nomenclature, and
that is what the ICZN is for.  None of them, however, have much to do with
science.  If this were the case, every scientific field would have a list
of "standardized" working hypotheses.  We would have this year's consensus
on whether T. rex was an obligate scavenger, and this year's consensus on
how the forelimbs of Triceratops horridus were oriented.  We would all be
able to authoritatively cite a whole plethora of currently accepted
theories.  But to what end?  It does nothing to progress science.  Our
society is full of appeals to authority, and many want to make science
another source of authority.  Scientists know better, even when we like
having our egos massaged by being cited as "authorities."

The way that credentials came into this discussion is that it was suggested
that Greg Paul did not have any "scientific" credentials.  Presumably this
is supposed to justify giving his ideas less credence.  Now we have, "the
more familiarity a worker has with a particular group, the more respectable
their position should be on matters relating to that group."  I assume we
should take the word "respectable" here to mean "able to be respected."  It
poses an interesting dilemma.  If only one person in the world has a large
amount of specialized knowledge of a particular topic, how are we to verify
its accuracy?  It is one of the problems we run into when we try to appeal
to authority.  Even worse, how are we supposed to determine how familiar a
person is with a group except by studying his work and evaluating it ON ITS
MERITS?  We have now created a vicious circle.  We have to look at the work
on its merits in order to determine whether his position is respectable, so
that we can choose whether to look at the work on its merits or not.  I
have a simple solution for those who are not lazy-minded:  just look at the
work on its merits and skip the rest.  

But enough heavy-handed elaboration of the obvious.  My point about the
number of species per genus and selective fossilization was this.  Clearly
fossilization is much more likely in some ecosystems than others.  In cases
in which there are multiple species per genus, they often occur in
different habitats.  In many cases a given habitat has only one species of
the genus.  So the selective fossilization process may tend to produce
fewer species per genus than actually occurred.  I suspect that if we look
at living species on a habitat by habitat basis, we will find a lower
species/genus ratio than if we look at the same taxonomic group globally.
This could explain the apparently low species/genus ratio amongst
dinosaurs.  This was my point and I would be interested in hearing feedback.

Best regards,

Dave