Paleozoic Ammonoids: Historical Pathways of the Development of Morphological Diversity

Abstract

The history of Paleozoic ammonoids can be subdivided into two large intervals: Devonian and Carboniferous–Permian. There were two major evolutionary pathways: changes in the external shell morphology and changes in the suture, a character observed only in cephalopods. Almost all major shell types and ornamentation appeared at early stages of the evolution of the subclass Ammonoidea (archaic diversity). The suture in ancient taxa in this group was represented by virtually all known types, except for the complexly dissected suture lines of the “Mesozoic type” that appeared only at the end of the Paleozoic. During the time of the subclass’s existence, Devonian morphotypes recurrently appeared in different orders. The senile diversity was associated with the diversification of exotic taxa at the end of the Ammonoidea evolution.