The Oldest Fossil Evidence of Alstonia (Apocynaceae) from India and its Implication

Six well-preserved early Eocene leaf fossils documented here have an affinity with the extant genus Alstonia (Apocynaceae). They come from the Gurha opencast lignite mine (Palana Formation), western Rajasthan, NW India. We determined their taxonomic position by detailed morphological comparisons with similar modern and fossil specimens. The leaf fossils have elliptic-oblanceolate laminae, cuneate bases, acute apices, stout primary veins, intramarginal secondary venation, numerous parallel secondary veins, some secondary veins with a bifurcate nature, and intersecondary veins. We name the fossil leaves Alstonia sp. and they provide evidence that Alstonia, a tropical rainforest element, was present in India during the early Eocene. These fossil leaves represent the earliest reliable fossil record of Alstonia. We discuss the biogeographic and palaeoclimatic implications of our findings.