Timing the end-Triassic mass extinction: First on land, then in the sea?

The end-Triassic marks one of the five biggest mass extinctions, but curren t geologic time scales are inadequate for understanding its dynamics. A tuf f layer in marine sedimentary rocks encompassing the Triassic-Jurassic tran sition yielded a U-Pb zircon age of 199.6 +/- 0.3 Ma. The dated level is im mediately below a prominent change in radiolarian faunas and the last occur rence of conodonts. Additional recently obtained U-Pb ages integrated with ammonoid biochronology confirm that the Triassic Period ended ca. 200 Ma, s everal million years later than suggested by previous time scales. Publishe d dating of continental sections suggests that the extinction peak of terre strial plants and vertebrates occurred before 200.6 Ma. The end-Triassic bi otic crisis on land therefore appears to have preceded that in the sea by a t least several hundred thousand years.