Among the listed taxa, "presence of skull" (marked at the deepest node) is best classified as
- A
A synapomorphy of birds and lizards only
- Bcheck_circle
A symplesiomorphy (shared ancestral character) for these taxa
- C
An autapomorphy of lampreys
- D
A homoplasy
Explanation
A trait inherited from an ancestor and shared across all included taxa is a symplesiomorphy - useful as evidence of common ancestry but not for resolving relationships within the group.