India, once a member of the lost supercontinent Gondwana, broke away from it and made a solitary northward excursion and finally collided with Asia. During its long voyage, India remained isolated for 100 Ma and is expected to be characterized by stunning endemic biodiversity. But this is not recognized by the terrestrial faunal and floral content, and their distribution patterns paint no simple scenario. For example, the Inter-trappean vertebrate faunas of India, which lived during "India-in-exile", do not show any made-in-India assemblages, but rather betray a mixed biota having both Gondwanan and Laurasian affinities. These differential distribution patterns of fauna and flora, and their affinities with those of other areas, prompted many workers to envisage an array of suggestions regarding the time of India's final separation from Gondwana, the time of northward drifting and different palaeopositions during its long journey. But closer examination of the nature of the vertebrate fossil records reveals that the so-called elusive endemicity of Indian fauna during its sojourn is in fact a product of taxonomic artefact. The majority of the faunas have been described on the basis of poor fossil data, and comparisons for biogeographic correlations are made at higher taxonomic levels, which perhaps masked India's faunal distinctiveness. Yet, the biological processes that constrain biogeographical distribution operate at the species level. In this paper, we present our own data to reconstruct the palaeoposition of India in the Late Cretaceous, and to estimate the time of its northward migration. The present study is based on a newly recorded ammonite species, Placenticeras kaffrarium Etheridge from the Coniacian horizons in Bagh, central India. The species abounds in Bagh and represents a complete population structure. It resembles significantly the populations described from the coeval horizons of Madagascar and Zululand, South Africa. P kaffrarium has a stunning display of intraspecific variability represented by at least seven distinct morphotypes reported from Zululand and Madagascar. The Indian population, significantly matches the latter two populations, variant by variant and remarkably, also for the sexual dimorphs within each variant. Geographic range is a biological property of a species and ammonite species have differential distribution patterns depending on the length of larval longevity, oceanic circulation patterns and favourable environments. Placenticeras was a nektobenthic genus living in the shallowest depths of epicontinental seas, and could not cross a narrow strait wider than a few hundred kilometers. Palaeogeographic distribution patterns of all placenticeratid species during the Late Cretaceous support this view and show the wandering nature of the genus over time. However, they always exhibit a latitudinally limited distribution and are restricted mainly to the subtropics north and south of the equator. Thus, it appears that the P. kaffrarium population of Zululand, Madagascar and Bagh constitute a homogenous, single breeding population, implying geographical proximity of these areas, connected by exclusively shallow seas till the Coniacian. Other fossil records of ammonites and geophysical data also support this view. Shortly after this, India started its northward drift, By the Late Maastrichtian, India was completely isolated by a wide oceanic gap from the rest of the Gondwana fragments and the northern part of India crossed the equator. This is evident front strong endemicity of ammonite species assemblages of the northwest and southern Indian subcontinent, which constitute the most diverse communities known. (C) 2002 Elsevier Science B.V. All rights reserved.
