How We Look at the Relationships of Taxa

Page 3
 
 

A Consensus Cladogram

What defines a clade and makes it defensible?

SYNAPOMORPHY
MONOPHYLY
 

Translating the cladogram into a classification

Once a cladogram is obtained we can make a classification.  We have already discussed how a species is defined.  Above that, the principles of grouping are clear but ranking or those groups is more ambiguous.

The grouping criterion:  Only clades can be formally recognized in the classification.
All organisms must be a part of some group.

How can a classification be derived from the cladogram above?

Hierarchy and Naming

There are two ways to look at hierarchy in classification.  The traditional Linnean system and the new clade based system.  We always name only clades now but the clade based system abandons the linnean binomial and ranking system.  Clade based naming is not widely used and it is unclear as to whether or not it will become a standard.  We will discuss the pros and cons of both in class to illustrate the differences.