Palorbitolina lenticularis, An Index Taxon from Tethyan Basin and its Biometric Factors from the Kopeh-Dagh Basin, NE Iran

Among the subfamily Orbitolininae, Palorbitolinalenticularis Blumenbach, 1805 is a common facies marker prevailed in shallow marine deposits of the Tethys during Late Barremian-Early Aptian time span. This speciesis a eurytopic taxon having the high ability of adaptation to wide range of environmental conditions. This study is based on measurements on embryonic chamber and test diameter of Palorbitolinalenticularis. The specimens were collected from three surface sections which are arranged in east-west direction.Our data show that, depth of environment controls the diameter of embryonic chamber and size of the test. Furthermore, size of embryonic chamber increases through time during the Late Barremian to Early Aptian.