- belonging or pertaining to the Rhynchocephalia, an order of lizardlike reptiles that are extinct except for the tuatara.
- a rhynchocephalian reptile.
- of, relating to, or belonging to the Rhyncocephalia, an order of lizard-like reptiles common in the Mesozoic era but today represented only by the tuatara
- any reptile belonging to the order Rhyncocephalia
