The reptilian order Sphenodontida (=Rhynchocephalia) is represented by only one living species of the genus Sphenodon (S. punctatus, including its junior synonym S. guntheri), popularly known as the New Zealand Tuatara; a second recent species is extinct (Daugherty et al. 1991). The nominate subspecies Sphenodon punctatus punctatus is the subject of this account. Anatomically, Sphenodon shares numerous features with other amniote groups as well as possessing its own unique characteristics. Many recent workers have regarded the Sphenodontida as the sister-group of the Squamata (snakes, lizards) (Fraser l985; Evans 1984, 1988; Gauthier, Estes and de Quieroz 1988; Gauthier, Kluge et al. 1988; Rest et al. 2003); or as advanced squamates (Whiteside l986). In contrast, cladistic analysis of sperm morphology (Jamieson and Healy 1992) suggested that sphenodontids were basal within the Amniota and were not the sister-group of squamates, only
the turtles having fewer spermatozoal apomorphies. Relationship with squamates will be re-examined in this chapter and molecular evidence for this will be briefl y discussed.