> I've been trying to figure out this holotype stuff and I think I get
> it for species. But how the heck are holotypes chosen for a given
> genus? It all seems too  much like apples and oranges to me.

A species is based on a type specimen (by modern rules; older
publications might have a series of syntype specimens).  A genus (and
genus-level groups such as subgenera) is based on a particular type
species; a family (and family-level groups such as superfamilies,
subfamilies, tribes, etc.) is based on a particular type genus.  The
type specimen for the type species also determines the identity of the
genus; the type specimen of the type species of the type genus
determines the identity of the family.  For instance, some careless
paleontologist based a new genus of dinosaur on a species with a type
specimen that actually is a chunk of petrified wood.   Even if his
concept of the genus was based on other material that actually was
from a dinosaur, the genus belongs in the realm of paleobotany, not
vertebrate paleontology.

Of course, the decision of how much belongs in one genus before it's
too big is a subjective one.  Most people seem to agree that things
within a genus ought to share a common ancestor exclusive of other
genera, but there is debate about whether we should allow genera to
evolve form other genera (i.e., paraphyletic taxa).  For example,
there's a group of pyriform volutids in the Paleocene to Oligocene or
so, currently assigned to the genus Caricella.  Eventually they get
more fusiform and become Scaphella or Aurinia.  There are also a few
weird-looking offshoots of the Caricella group in the Eocene, such as
Santeevoluta and Voluticella.  Probably some of the "Caricella"
species are more closely related to Scaphella or Santeevoluta or
Voluticella than they are to other "Caricella" species, but they look
more similar to other "Caricella".  How should they be classified?
This issue nearly causes physical fights among systematists.

--
Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"

----------------------------------------------------------------------
[log in to unmask] - a forum for informal discussions on molluscs
To leave this list, click on the following web link:
http://listserv.uga.edu/cgi-bin/wa?SUBED1=conch-l&A=1
Type your email address and name in the appropriate box and
click leave the list.
----------------------------------------------------------------------