First record of Dioscorea from the early Eocene of northwestern India: Its evolutionary and palaeoecological importance

Abstract

The Dioscoreaceae is a monocotyledonous family belonging to the order Dioscoreales. It includes two other families, the Burmanniaceae and the Nartheciaceae. Dioscoreaceae is the largest family of this order comprising 650–700 extant species included in four genera, which are widely distributed throughout warm temperate, subtropical and tropical regions. It is a pantropical family with a disjunct distribution. A new fossil species, Dioscorea eocenicus Mehrotra and Shukla, is described from the early Eocene sediments of Bikaner district (northwestern India). The campylodromous venation (having nine primary veins), disposition and course of tertiary veins, and other attributes of the fossil show its affinity with the modern genus Dioscorea of the family Dioscoreaceae. The origin, evolution, and diversification of the family have always been a matter of concern as different views and theories exist. This is the first fossil record of the family Dioscoreaceae from Asia. To date, fossils belonging to the family Dioscoreaceae have been retrieved only from Europe, Africa, and America. The present fossil from the Indian subcontinent, along with earlier recorded fossils of the family Dioscoreaceae provides new opportunities to trace the presence of Dioscorea (yams) in Gondwana since the Cretaceous. The presence of humid tropical forest in the region during early Eocene time has been interpreted based on this and other described fossils from the Gurha lignite mine.