Please see the image. A cladistic approach would distinguish many of these groups (such as dimetrodon) as non-reptiles. It could redefine "reptiles" to include all, since a clade is supposed to include all of the descendants (and only the descendants) of one common ancestor.
Work Step by Step
This question is designed to have you review and understand cladistics-- start by reviewing its definition in the book. Then, after placing the information from Fig. 26.16 in place of the "birds and other reptiles" branch in Fig. 25.7, look to see if reptiles (as they were once understood) meet the definition of a clade.