"Of or relating to the diapsid reptile order Rhynchocephalia (infraclass Lepidosauromorpha), which comprises such superficially lizard-like forms as the modern tuataras (genus Sphenodon) and various Mesozoic fossil forms, known collectively as beak-heads", Mid 19th cent. From scientific Latin Rhynchocephalia, order name (A. Günther 1867, in Philos. Trans. (Royal Soc.) 157 626; from rhyncho- + ancient Greek κεϕαλή head + scientific Latin -ia, after Rhynchocephalus, genus name) + -an.[rhynchocephalian etymology, rhynchocephalian origin, 英语词源]