First fossil evidence of Hylodesmum palaeoglutinosum from India and comments on its extinction from the subcontinent

Abstract

ABSTRACT We report for the first-time well-preserved leaflets of Hylodesmum palaeoglutinosum from the latest Neogene sediments (Rajdanda Formation: Pliocene) of Jharkhand, eastern India. Macromorphological features show that the fossil leaflet remains are identical to those of modern endemic taxon H. glutinosum (Muhl. ex Wild.) Ohashi & Mill (tribe: Desmodieae, subfamily: Papilionoideae; family: Fabaceae). This is the first authentic record of the occurrence of leaflets comparable to H. glutinosum from the Cenozoic sediments of India, and even worldwide. At present H. glutinosum does not grow in India, nor Southeast Asia, but is restricted to North America. Analysis of these fossil remains with respect to the modern distribution pattern of H. glutinosum and the physiognomic characters (including acuminate “drip tips”) of the fossil leaflets suggests that a tropical evergreen forest was growing under a warm, humid climate at the time of deposition. This interpretation agrees with earlier published qualitative climate interpretations for the area, and our recently published quantitative climatic data obtained from the study of leaf remains recovered from the same formation. Here, we discuss the possible causes of disappearance of this fabaceous taxon from the present-day vegetation of Chotanagpur Plateau area, eastern India and also comment on its extinction in India. The disappearance may be related to the gradual intensification of rainfall seasonality since the Pliocene.