01Reading trees
Phylogenetic trees show hypothesized relationships. Nodes = common ancestors; branch tips = taxa. Two groups that share a more recent node are more closely related.
Cladograms use shared derived characters (traits that appeared in a common ancestor and are shared by its descendants). An outgroup lacks them and roots the tree.
02Molecular trees
DNA and protein data give the most reliable trees. Trees are hypotheses; they change with new data. Clades (monophyletic groups) include an ancestor and ALL its descendants.
03Notebook box
Rotating branches at a node doesn't change relationships. Read the nodes, not left-to-right order.
Worked example: In a tree where lizards and birds share a node not shared with mammals, which is the closest relative of birds? → Lizards (reptiles).