Leaf Fossils from India Hint at the Origin of Yams
The edible, starch-filled tubers of the genus Dioscorea are an important food stuff for many people. These flowering plants (Dioscoreaceae family), are often referred to as yams and several hundred species are known. These plants are widely distributed throughout warm temperate, subtropical and tropical regions, but scientists were unsure of the evolutionary history of this important group of angiosperms. However, researchers from the Birbal Sahni Institute of Palaeosciences (Lucknow, northern India), have named a new fossil species – Dioscorea eocenicus.
Two broad, heart-shaped leaf fossils unearthed at a Gurha lignite mine in Bikaner (western Rajasthan), hint that this important group of plants could have evolved on the southern super-continent of Gondwana.
One of the Broad Leaf Fossils from the Mine – Dioscorea eocenicus
Picture credit: Rakesh Chandra Mehrotra and Anumeha Shukla published (Review of Palaeobotany and Palynology)
The First Record of Dioscoreaceae from Asia
Writing in the academic journal “Review of Palaeobotany and Palynology”, the researchers describe the two leaf fossils which measure around sixteen centimetres in length. Comparative analysis with extant and extinct flowering plants led the authors to conclude that these fossils represent the first record of the Dioscoreaceae family from Asia.
Fossils representing ancient members of the Dioscoreaceae are known from Africa, Europe and America, but these Eocene fossils found on the Indian subcontinent suggest a southern hemisphere origin for this plant family and furthermore, it could mean that yams were present in the Cretaceous. Perhaps, Late Cretaceous herbivorous dinosaurs fed on their leaves and succulent, energy rich tubers.
Analysis of other plant fossils found in the same deposits, reveal that when these early yams lived, Rajasthan was a humid, tropical paradise. The climate of Rajasthan today is very different. India’s largest state is arid and it contains the Thar Desert, sometimes referred to as the “Great Indian Desert” which covers and area bigger than the whole of England and Wales.
The scientific paper: “First Record of Dioscorea from the Early Eocene of north-western India: Its Evolutionary and Palaeoecological Importance” by Rakesh Chandra Mehrotra and Anumeha Shukla published in the Review of Palaeobotany and Palynology.
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