The space-time relationship of taxonomic diversity and morphological disparity in the Middle Jurassic ammonite radiation

Abstract

The Middle Jurassic ammonite radiation (from the late Aalenian to the end of the mid-Bathonian) is traced using combined analyses of morphological disparity and taxonomic diversity. The global signals of disparity and diversity are compared. These signals are then broken down by paleogeographical provinces to detect any heterogeneity in the radiation. An examination of the global signals reveals three biodiversity crises (discordances between signals) where morphological disparity grows while taxonomic diversity declines. The subdivision of the signals indicates the radiation was heterogeneous between provinces: the global signal is an aggregate of signals from each province. The three biological crises have different paleogeographical signatures: the first is visible in a few provinces only while the other two are visible in most provinces. First-order crises can be distinguished from second-order ones by studying the number of paleogeographical provinces affected.