Chapter 23: Question 2

Explain how the use of a cladistic classification for the vertebrates results in important regroupings of the traditional vertebrate taxa. Why are certain traditional groupings such as Reptilia and Agnatha not recognized in cladistic usage?


A cladistic diagram shows all probable relationships of all monophyletic groups composing the phylum. Each branch in the cladogram represents a different group. Nesting brackets across the top of the the cladogram indentify the groupings within the phylum. Groups such as Reptilla and Agnatha are not recognized in cladistic usage because they do not satisfy the requirement of cladistics that only monophyletic groups are valid taxonomic entities. They are paraphyletic meaning they contain the ancestors of all members of the group but excludes some descendants of that ancestor.

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