ORIGINATION AND EVOLUTIONARY DYNAMICS OF THE END-PERMIAN POST-EXTINCTION RECOVERY INFERRED FROM LONGEVITIES OF TRIASSIC BIVALVE SPECIES

Analyses on origination rates and longevities performed on 2000+ Triassic bivalve species obtained from the Paleobiology Database (PBDB) provides insight into the evolutionary dynamics of the end-Permian mass extinction and subsequent biotic recover during the Early and Middle Triassic. Species-level data on Triassic bivalves following the end-Permian extinction reveal longevities exhibit a strong positive skew in temporal durations of fossil species and follow a lognormal distribution. The median duration of bivalve species durations across the entire Triassic is approximately 9 Ma. Although bivalve species longevity is negatively correlated with time of first appearance from the end-Permian event, those originating in the Early Triassic exhibit significant greater variability and are shorter-lived (median duration = 5.2 Ma) than species originating in the Middle Triassic (median duration = 13.5 Ma). Species originating in the Late Triassic are also short-lived (median duration = 5.1 Ma) due to the range termination by the end-Triassic extinction event. Stage-level cohort survivorship curves through the Triassic reveal uniform concavity but a less severe slope for Early Triassic cohorts than subsequent cohorts. These survivorship curves, however, are difficult to interpret given the short half-life of most Triassic species. Edge effects of the end-Triassic extinction on species longevity are likely significant given the duration of Triassic stages and the stratigraphic range of species. These data, although contrary to patterns of generic longevity, support the hypothesis that species originating during the interval of high turnover during the Early Triassic exhibit shorter stratigraphic ranges than those originating later in the recovery.