AMNIOTES THROUGH MAJOR BIOLOGICAL CRISES: FAUNAL TURNOVER AMONG PARAREPTILES AND THE END-PERMIAN MASS EXTINCTION

The Parareptilia are a small but ecologically and morphologically diverse clade of Permian and Triassic crown amniotes generally considered to be phylogenetically more proximal to eureptiles (diapsids and their kin) than to synapsids (mammals and their kin). A recent supertree provides impetus for an analysis of parareptile diversity through time and for examining the influence of the end-Permian mass extinction on the clade's origination and extinction rates. Phylogeny-corrected measures of diversity have a significant impact on both rates and the distribution of origination and extinction intensities. Time calibration generally results in a closer correspondence between origination and extinction rate values than in the case of no time correction. Near the end-Permian event, extinction levels are not significantly higher than origination levels, particularly when time calibration is introduced. Finally, regardless of time calibration and/or phylogenetic correction, the distribution of rates does not differ significantly from unimodal. The curves of rate values are discussed in the light of the numbers and distributions of both range extensions and ghost lineages. The disjoint time distributions of major parareptile clades (e. g. procolophonoids and nycteroleterids-pareiasaurs) are mostly responsible for the occurrence of long-range extensions throughout the Permian. Available data are not consistent with a model of sudden decline at the end-Permian but rather suggest a rapid alternation of originations and extinctions in a number of parareptile groups, both before and after the Permian/Triassic boundary.