Paleozoic ammonoid biostratigraphy

The time interval between the Emsian (Early Devonian) and the end of the Permian is characterized by the rapid evolution of the Ammonoidea, and this evolution is reflected by the establishment of a detailed biostratigraphical scheme. Ammonoids are, together with the conodonts, the most important stratigraphical tools for this interval. The present time resolution in terms of ammonoid biostratigraphy is highest in the Devonian (one zone has a mean of 0.9 Ma) and in the Carboniferous (about 1 Ma), while the subdivision of the Permian is much coarser (about 2.5 Ma per ammonoid zone on average).