Many of our current classifications are not “natural,” in the sense that they do not reflect the evolutionary relationships among species. As an introduction to phylogenetic classification, try reclassifying the tetrapods (animals with four legs). These animals have traditionally been classified into four groups of the same rank:

Class Amphibia (frogs, salamanders, newts, etc.)
Class Reptilia (snakes, lizards, crocodiles, turtles, etc.)
Class Aves (birds)
Class Mammalia (mammals)

Reptiles possess a common ancestor with certain extinct amphibians, the birds are derived from a group of reptiles, and the mammals probably branched off before the rest of the reptiles (and birds). One hypothesis for the actual evolutionary relationships among the tetrapods is shown in the branching diagram (cladogram) shown below. In a cladogram, each line represents a lineage, and the various lineages join together to make larger clades (as in a hierarchical classification). In this diagram, we show only one characteristic for a clade (the amniotic egg), which may be useful in providing a name for the clade of tetrapods that have this characteristic.

Working with a partner, construct a hierarchical classification based purely on the clades shown in this diagram. Note that a cladogram is not a classification - you must construct a classification based on the phylogenetic data contained in the cladogram. You can assume that these groups are monophyletic - that is, they all derive from a recent common ancestor and collectively form the superclass Tetrapoda. In your classification give each clade a name, and be sure that branches farther up the tree are classified at lower (less inclusive) taxonomic ranks within the taxonomic group defined by their parent branch.

For example, a tree like this:	Might be classified like this:
	Class A Subclass B Subclass C Order D Order E

If you followed the process outlined above in making your classification, what are the major differences between your classification and the traditional classification that is usually found in textbooks, including your own? What are the advantages of your classification? What are the disadvantages? Are you concerned that your classification does not seem to be traditional?