Structural changes in the passage Euaspidoceratiforms-Aspidoceratiforms (Aspidoceratidae, Ammonitina)

Abstract

The structural change from Euaspidoceratiforms to Aspidoceratiforms involves as a primary change the loss of the ribbing connecting both series of tubercles . This alteration must have occurred simultaneously starting from the genera Euaspidoceras and Neaspidoceras, giving rise respectively to Aspidoceras and Pseudowaagenia. Remaining observed transformations between both morphological schemes may be considered as a direct consequence of this primary change, specially with regard to the independence of both ornamental series and the obtaining of more involute schemes.