Biostratigraphy of Triassic ammonoids

The Triassic is a turning point in the evolutionary history of ammonoids, characterized by the flourishing Ceratitida and the appearance of the first heteromorphs. Following the end-Permian mass extinction, ammonoids were among the first groups to rediversify by producing many new taxa. Already in the late nineteenth century, the still currently recognized Triassic stages and substages were introduced. The historical development of Triassic ammonoid biostratigraphy is a good example of worldwide cooperation between many geographically-diverse research groups, which initially began in Germany and the European Alps. This cooperation was then extended to North America, Transcaucasia, North Indian Margin, South China, and Russia. A renewed interest in Triassic ammonoid biozonation has occurred during the last few decades, leading to the recognition of tens of ammonoid zones spanning about 50.9 Myr (leading to an average duration for ammonoid biochronozones of about 0.74 Myr), whose correlation and definition are herein synthesized.