Re: Definitions

["Mickey Mortimer" <Mickey_Mortimer11@msn.com>]

Jean-Michel Benoit wrote-

> Hello dear listmembers
> thanks to some of you HP's, I start to have a faint idea of cladistics (
> I'm going through slowly, slowly . .).  Just one point : I've read one
> could define a clade node-based or stem-based. What's the difference? Is
> there one better than the other ( I hope my question doesn't sound silly

A node-based definition is-
"all descendents of the most recent common ancestor of A and B"
Basically, anything in the smallest clade containing both A and B.
A stem-based definition is-
"all taxa more closely related to A than to B"
One type isn't better than the other, but I like different types of
definitions for different groups.  For many clades, I like a stem-based
definition.  This allows more primitive members to be found in the future
and still belong to the clade, eliminating the need to make up new taxa for
them and making referring to them easier.  Some groups were originally
conceived as showing a specific relationship between two taxa (eg.
Allosauroidea = Sinraptor + Allosaurus), so I like node-based definitions
for these.  It all depends.

Mickey Mortimer