PERSPECTIVES T

wo hundred and fi fty-two million years ago, the Paleozoic Era came to a cat-aclysmic close with the end-Permian mass extinction, when as much as 85 % of readily fossilizable marine species became extinct. It took 5 million years for the bio-sphere to begin to recover from the event. At least this has been the conventional view. However, on page 1118 of this issue, Brayard et al. ( 1) show that ceratitid ammonoids (see the fi gure, panel A) recovered much faster than did most other marine groups, attain-ing considerable diversity just 1 million years after the mass extinction. Moreover, these mollusks reached a peak in their diversity at the end of the Early Triassic, when the diver-sity and body size of most other groups (par-ticularly bivalves and gastropods) was still depressed ( 2). What do these data tell us about the post-apocalyptic world of the Early Trias-sic, and about the cause of the end-Permian extinction event itself? The cause of the end-Permian mass extinc-tion has long been controversial ( 3). There is increasing agreement that toxic waters deci-mated bottom communities in shallow waters, but it remains unclear whether the kill mecha-nism was hypercapnia (high CO 2 levels) ( 4)