Biometric Study of Heterostegina from the Chattian of Kachchh, India

Biometric study is carried out on a rich assemblage of the genus Heterostegina from the basal part of the holostratotype of the Waiorian stage, Kachchh. The assemblage is from a level between the last occurrence level of Nummulites fichteli Michelotti and the first appearance of miogypsinids and Globigerinoides primordills Blow and Banner and can be dated as Chattian. The assemblage consists of a single homogenous population of Heterostegina (Vlerkina) borneensis Van der Vlerk. Published data together with our present results suggest that (1) there is an overall drop in the mean value of the size of the protoconch from Heterostegina (Vlerkinu) in the Chattian to Hererostegina (Heterostegina) in the Middle Miocene and, thereafter, a slight increase in protoconch size in the Recent; (2) the mean number of operculine chambers increases from the Chattian to the Burdigalian and (3) the mean height of the first whorl drops gradually from the Chattian to the Recent.