Tertiary leaf fossils of Semecarpus (Anacardiaceae) from Li Basin, Northern Thailand

Abstract

Two leaf compressions preserved by pyritization were collected from the lacustrine deposits in Li basin, Northern Thailand which was considered to be Late Oligocene to Early Miocene. Besides features described in previous leaf architectural studies, a detailed study of marginal venation patterns of modern leaves was important in establishing the relationship between the fossil and the living species. After this analysis, they were assigned to Semecarpus paleocurtisioides. This fossil fi nding, together with the pattern of modern distribution, helps to propose a land on the west of Wallace’s line as the possible origin of the genus. In addition, these leaf fossils and fossil leaves of the genus Mangifera previously described suggest that northern Thailand is an area with a long history of evolution and diversifi cation of the family Anacardiaceae and these two genera.