Ammonites of the subfamily Mayaitinae Spath, 1928 from the Oxfordian of Kachchh, Western India

Abstract

A collection of 100 ammonites of the subfamily Mayaitinae Spath, 1928 (Sphaeroceratidae, Stephanocerataceae) from the Oxfordian (Upper Jurassic) of the Kachchh Basin, Western India, represents 19 morphospecies. Their study confirms most of the species originally described from the Kachchh Basin more than 80years ago, but it strongly extends the knowledge on their diagnostic features. Most species can be readily differentiated by the shape and ontogenetic development of their whorl section as illustrated by a Fourier shape analysis. The Oxfordian subfamily Mayaitinae is largely endemic to the Malagasy Gulf and adjacent regions at the southern margin of the Tethys. Finds of isolated specimens from other areas of the northern Tethys or southern Pacific are suggested to be drifted shells or misinterpretations of homeomorphic taxa. Although commonly found in the Kachchh Basin, the group has received little attention through the last decades due to their seemingly limited use in biostratigraphy. In the present study the biostratigraphic potential of a series of taxa is discussed; e.g., Epimayaites subtumidus seems to be restricted to the Stenocycloides Subzone (Bifurcatus Zone) of the Upper Oxfordian.