Iraqi National Journal of Earth Sciences

Abstract

Biometric invesgation of the megalospheric individuals of nephrolepidina assemblages from several sections in Kirkuk area, iraq led to recognize three morphometically defined species by the combination of two parameters. The degree of embracement of the protoconch by deuteroconch (factor A ) and number of accessory auxiliary chambers on the deuteroconch (factor C ) on the basis of generally accepted theory which is called embryonic and nepionic acceleration. The succession of these three species corresponds to the phylogenitic lineage in the European-medierranean area which started at some level in the middle part of the Oligocene and continued upward into the early Miocene. The slow numerical progress in this lineage and especially the double morphometric definition of the species limits have led to the recognition of a wide array of morphologically intermediate assemblages.