Data from: Macroevolutionary patterns in Rhynchocephalia: is the tuatara (Sphenodon punctatus) a living fossil?

The tuatara, Sphenodon punctatus, known from 32 small islands around New
Zealand, has often been noted as a classic ‘living fossil’ because of its
apparently close resemblance to its Mesozoic forebears and because of a
long, low-diversity history. This designation has been disputed because of
the wide diversity of Mesozoic forms and because of derived adaptations in
living Sphenodon. We provide a testable definition for ‘living fossils’
based on a slow rate of lineage evolution and a morphology close to the
centroid of clade morphospace. We show that through their history since
the Triassic, rhynchocephalians had heterogeneous rates of morphological
evolution and occupied wide morphospaces during the Triassic and Jurassic,
and these then declined in the Cretaceous. In particular, we demonstrate
that the extant tuatara underwent unusually slow lineage evolution, and is
morphologically conservative, being located near the centre of the
morphospace for all Rhynchocephalia.