INTRODUCTION

The Late Tithonian is characterised by a strong provincialism of ammonites. The provincialism is so marked that the Upper Jurassic terminology varies in distinct regions e.g., Portlandian in England, Volgian in Arctic Region and Tithonian in Tethyan and Indo-Pacific regions. The top of the Jurassic may be distinguished from north to south into different realms/provinces like Boreal, Mediterranean and Tethyan, respectively (Callomon 1981a, 1981b). Genus level analysis using different co-efficient methods show persistence of endemism even among the provinces during the Tithonian (Riccardi 1991; Bardhan et al. 2007).

In the present work we have redescribed one of these Late Tithonian endemic genera, Umiaites, from Kutch. The genus was based on incompletely preserved rare specimens first described by Spath (1931), who was known for his characteristically brief and subtle descriptions. Moreover, Umiaites had not been illustrated and was misspelled in the Treatise (Arkell et al. 1957). Therefore, it is very difficult to compare specimens from other areas with such endemic taxa. The present study redescribes Umiaites based on additional specimens along with the types and their precise stratigraphic occurrences. This information allows a better understanding of ontogeny and intraspecific variability within the Umiaites population of Kutch, makes it possible to synonymize the two species of Spath (1931), and describes them herein as Umiaites rajnathi, which has priority.

Umiaites is similar to Proniceras both morphologically (see also Wright et al. 1996) and stratigraphically. Its early stage corresponds well with the adult stage of Proniceras, which is a lappeted microconch (e.g., see Imlay, 1939, pl. 18, figs. 5 and 6). It is shown here that these two nominal genera meet many criteria to form a dimorphic pair, Umiaites as macroconch and Proniceras as microconch.