If one is constructing a phylogeny of reptiles using DNA sequence data, which taxon (birds, mammals, amphibians or fish) might be suitable to use as an outgroup?

Answer: If one is constructing a phylogeny of reptiles using DNA sequence data of birds, mammals, amphibians or fish, the suitable outgroup to be used are mammals due to the time of divergence from other group of organisms.

Explanation: Phylogeny is used to determine evolutionary relationship between items or organisms. A phylogenetic tree is a graphical illustration of phylogenetic relationship. In phylogeny, an outgroup represent an organism that is more distantly related to other group of organisms.

In a phylogenetic tree, outgroup stands alone. It shows that the time of divergence of that particular organism is far from other group of organisms. Outgroup is used to root a tree and sometimes represent a group that is more ancestral on a tree.

It should be noted that differences in the DNA sequences of the organisms under consideration will determine which organism will serve as the outgroup.