EVOLUTION: Disappearing in Stages

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Science  28 Jan 2000:
Vol. 287, Issue 5453, pp. 549a
DOI: 10.1126/science.287.5453.549a

The extinction at the end of the Triassic is one of the five largest in the geologic record. It marked the demise of conodonts, a common but enigmatic index fossil seen through the Paleozoic, as well as other marine fauna; on land, the dinosaurs emerged to dominate Mesozoic ecosystems in its aftermath. The best-dated large extinctions, those at the end of the Permian (the largest such event in the geologic record) and at the end of the Cretaceous, seemed to have occurred extremely rapidly (within no more than a few hundred thousand years) and apparently in response to catastrophic environmental changes. The end-Triassic extinction has been less well resolved, in part because it is mostly recorded in continental rock sections.

Carter et al. now provide dates for the extinction in a marine section in the Queen Charlotte Islands off western Canada. The ages from uranium-lead dating imply that the extinction of conodonts and other marine organisms occurred just a little less than 200 million years ago. In contrast, the accepted dates on the extinction of terrestrial faunas are up to about 1 million years older (and most time scales have placed the end of the Triassic several million years earlier still), which implies that the extinction proceeded in stages. This time period in the geological record also corresponds with voluminous basaltic magmatism, which also occurred during the end-Permian and end-Cretaceous extinctions.—BH

Geology 28, 39 (2000).

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