Extinction of conodonts just before the close of the Triassic ended almost 400 m.y. of relatively rapid evolution. Survivorship curves for conodont cohorts, based on survival of all genera that evolved during a geologic period, show the same general pattern that has been demonstrated for other fossil groups. Conodont genera survived for a mean of 30 m.y while conodont families survived for a mean of 40 m.y. The mean cohort survival was 109 m.y. but the Triassic cohort survived for less than 50 m.y. A Permian-age observer of conodont evolution would have predicted survival of conodonts at least into the Late Jurassic. Rates of evolution of conodont genera were highest during the Early Ordovician and Late Devonian. Rates were lowest during the Early Permian and Middle Devonian.--Modified journal abstract.

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