A freshwater ecosystem once existed in the Rajasthan desert: evidence from a fossil of the aquatic herb Nelumbo

Abstract

Nelumbonaceae encompasses aquatic plant lineages that represent major components in the modern tropical wetland ecosystems of India. The group is characterized by its distinctive reproductive receptacle incorporating in situ fruitlets and vegetative organs that are well-represented in the fossil record. Unusually, though, no Nelumbo reproductive fossils have yet been identified from the Cenozoic of India. Here, we report the first such fossil reproductive organ from the aquatic perennial herb Nelumbo, which was recovered in the lower Eocene Palana Formation at the Gurha lignite mine in Rajasthan, western India. The fossil preserves an aggregate fruit with 28 indehiscent, apocarpous and globose to oblong fruitlets embedded within an accrescent receptacle, and a single small central cavity or apical remains of a stigma in each fruitlet. Comparisons with extant and extinct Nelumbo species support attribution to Nelumbo sp. Our unexpected discovery of a fully aquatic plant in the Rajasthan Basin during the early Eocene indicates that a freshwater ecosystem existed there ca 55 ± 10 million years ago; this contrasts starkly with the arid climatic conditions predominant in Rajasthan today. Raman Patel† [ ramanpatel2142@gmail.com ], Department of Geology, Hemvati Nandan Bahuguna Garhwal University, Srinagar, 246174 Uttarakhand, India Ashif Ali† [ aashifli0011@gmail.com ], Palaeobotany, Palynology, and Plant Evolution Laboratory, Department of Botany, Sidho-Kanho-Birsha University, Ranchi Road, Purulia-723104, India Rajendra Singh Rana [ rajendra.rana1@gmail.com ], Department of Geology, Hemvati Nandan Bahuguna Garhwal University, Srinagar, 246174 Uttarakhand, India Mahasin Ali Khan* [ khan.mahasinali@gmail.com ], Palaeobotany, Palynology, and Plant Evolution Laboratory, Department of Botany, Sidho-Kanho-Birsha University, Ranchi Road, Purulia-723104, India.