Section 17.2 Guide to Classification Using Evolutionary Relationships

Check each task by aligning organisms with shared ancestors shown on branching diagrams, not by surface similarity. Traits that appear once and persist across branches carry more weight than features that arise independently.

Use cladograms to trace lineage splits: a node marks a common forebear, while derived features define each branch. For example, the presence of an amniotic egg separates reptiles, birds, and mammals from amphibians.

Prioritize genetic evidence such as DNA sequence similarity and conserved proteins when conflicts appear between anatomy and lineage charts. Molecular data often resolves placement errors caused by convergent features like wings or fins.

Confirm group placement by checking whether all members share the same recent ancestor on the diagram. If one taxon falls outside that node, it belongs elsewhere despite visual resemblance.