The end-Permian mass extinction removed more than 80% of marine genera.
Ammonoid cephalopods were among the organisms most affected by this
crisis. The analysis of a global diversity data set of ammonoid genera
covering about 106 million years centered on the Permian-Triassic
boundary (PTB) shows that Triassic ammonoids actually reached levels of
diversity higher than in the Permian less than 2 million years after the
PTB. The data favor a hierarchical rather than logistic model of
diversification coupled with a niche incumbency hypothesis. This
explosive and nondelayed diversification contrasts with the slow and
delayed character of the Triassic biotic recovery as currently
illustrated for other, mainly benthic groups such as bivalves and
gastropods.