Quantifying the equatorial climate shifts in the Indo-Burma range using late Eocene–early Oligocene leaf fossils

The late Eocene–early Oligocene geological time span saw significant Antarctic glaciation, which played a crucial role in shaping global climate patterns and influencing regional climates and ocean circulation changes. In this study, we quantitatively reconstructed the climate of a low latitude site using fossil leaf morphological traits recovered from the Laisong Formation (late Eocene–early Oligocene) of the Indo-Burma range. The Climate Leaf Analysis Multivariate Program was used to quantify the climate, suggesting a mean annual temperature of 25.3 ± 2.3 °C and a cold month mean temperature of 19.2 ± 3.5 °C. The length of the growing season extended throughout the year, with a mean annual precipitation of 244.2 ± 64.3 cm, showing clear rainfall seasonality between rainy summers (130 ± 40 cm) and dry winters (21.7 ± 9.8 cm). The study further reveals that high rainfall in the low latitude region resulted from the northward migration of the intertropical convergence zone due to Antarctic glaciation. • CLAMP analysis of fossil leaves from late Eocene–early Oligocene of the Indo-Burma Range. • Reconstructed MAT of 25.3 ± 2.3°C and CMMT of 19.2 ± 3.5°C indicate warm and humid conditions. • MAP 244.2 ± 64.3 cm, 3-WET 130 ± 40 cm, 3-DRY 21.7 ± 9.8 cm, highlighting pronounced rainfall seasonality. • CCA suggests adaptation to Indonesian-Australian monsoon (I-AM) system, influenced by the seasonal ITCZ migration.