Drastic changes in Carboniferous ammonoid rates of evolution.

Abstract

Evolutionary rates permit four phases of ammonoid diversity development in ammonoids to be recognized during the Carboniferous: (A) Tournaisian, (B) Visean (excl. up.V3c), (C) Namurian A and B (incl. up.V3c), (D) Namurian C - Stephanian. All periods except C have a horotelic survivorship distribution, but different absolute rates; A and C are characterized by the predominance of short-lived, partly (C) tachytelic genera (longevity about 4 Myr, B of long-lived (about 12 Myr), and D by the prevalence of both intermediate and long-lived genera (about 4 Myr). Causal explanations for this evolutionary pattern are discussed.-Author