Sometimes called Phylogenetic Systematics, the major criteria are:
1. One criterion for classification: recency of common descent.
2. The method allows only the use of specialized or derived character
states, character states that we call apomorphic (primitive characters
states are called plesiomorphic). So, in this sense, characters, or
more precisely, character states, are more heavily weighted over
others.
3. Taxa that share derived or apomorphic characters states are
said to be related. Shared apomorphic character states are called
synapomorphic, whereas shared plesiomorphic character states are
called symplesiomorphic.
4. Grouping and ranking are given simultaneously by branching points
in a diagram called a cladogram (from the Greek “clad” or “klados,”
meaning to branch).
A cladogram showing the phylogenetic relationships
of families of anglerfishes
1-6
7-9
10-11
12-13
14-17
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