Evidence of triplinerved cinnamon from the Siwalik (middle Miocene) sediments of Darjeeling foothill and its biogeographic implication: Asian perspective

Abstract

Abstract Cinnamomum Schaeffer (avocado family Lauraceae), commonly known as a cinnamon tree, is a highly diverse, economically important evergreen element of tropical and sub-tropical regions of the world. In the present work, we have recovered six compressed leaf remains similar to modern leaves of Cinnamomum from the lower part of the Siwalik strata (middle Miocene) of Darjeeling foothills, eastern Himalaya. The recovered fossil specimens are characterized by an elliptic to the ovate lamina, acute to short acuminate apex, round to acute base, and basal as well as suprabasal acrodromous type of primary venation. Based on preserved architectural features, Siwalik fossil leaves are confidently placed under the genus Cinnamomum. However, the recovered Siwalik specimens cannot be traced up to the species level due to a lack of satisfactory macromorphological features (especially tertiary veins) and epidermal anatomy and are designated here as morphotypes. The evidence of current Siwalik specimens and earlier-reported fossil species similar to thermophilic Cinnamomum in appreciable number from other Siwalik localities (Darjeeling, Uttarakhand, and Nepal) suggests that Cinnamomum was a common Siwalik element and the existence of tropical, warm and humid climatic conditions during the Siwalik sedimentation. This finding also represents an important source of data for understanding the evolution, diversification, and paleobiogeographic history of Cinnamomum from an Asian perspective in deep time.