Eucycloceratin ammonites from the Callovian Chari formation, Kutch, India

Abstract

The subfamily Eucycloceratinae Spath, 1928, belonging to the family Sphaeroceratidae, is an important Indo-Madagascan faunal element and is reported here from the Callovian of Kutch, India. Previously the subfamily was considered to consist of 14 morphospecies placed in four morphogenera. The present study is based on re-examination of the type material and more than 350 new specimens, collected with secure stratigraphical control, from sections in mainland Kutch. It reveals that the subfamily includes only two highly variable monospecific genera: Eucycloceras Spath, 1924 and Idiocycloceras Spath, 1928. Dimorphism in Eucycloceratinae, which was not previously recognized, is firmly established. Cladograms have been constructed, based on numerous morphological characters, which show relationships among different subfamilies of the Sphaeroceratidae and genera of the Macrocephalitinae and Eucycloceratinae. The palaeobiogeography and evolution of the Eucycloceratinae are discussed in the light of the new data. © The Palaeontological Association.