Worked example. The whale flipper and human arm have corresponding upper-arm, forearm, wrist and digit bones despite different uses. This homology supports common ancestry. A shell sequence also records past change, but an incomplete record does not establish every exact ancestor.

Optional challenge. Explain why a missing fossil does not by itself prove a lineage never existed. Adult key: Fossilisation and discovery are incomplete, so absence from a record is not proof of past absence.

What to notice. Keep the evidence sheet and schematic limbs. Note copied model features and adult explanation help.