A Miocene snapshot
In the Luxi Basin of Yunnan, China, deposits of fossilized tree resin record the world of the Miocene epoch, approximately 15 million years ago. This amber formed from the sticky resin of tropical angiosperm trees belonging to the family Dipterocarpaceae. Chemical analysis of the amber reveals amyrin and amyrone-based triterpenoids, compounds characteristic of the dammar resins produced by these trees. Today, Dipterocarpaceae are dominant trees in the rainforests of Southeast Asia, but during the warmer, wetter climate of the Mid-Miocene Climatic Optimum, their range extended much farther north into what is now subtropical China.
The amber itself preserves a record of this ancient subtropical forest. The Miocene was a period when grasslands were expanding and forests dwindling globally, but the geology of Yunnan created a refuge with warm and humid conditions. The environment preserved in the Luxi amber was a seasonal, humid forest, a part of the dynamic environment that existed long after the dinosaurs vanished and well before the appearance of early humans. This region of southern China during the Miocene was a mosaic of tropical forest patches and evergreen broad-leaved forests, shaped by a more intense Asian monsoon system than exists today.
Inclusions and discoveries
The scientific value of amber comes from its ability to preserve organisms in three-dimensional detail. The Luxi Basin deposits contain a variety of "inclusions"—insects, spiders, plant parts, and other life forms that became stuck in the resin millions of years ago. These fossils provide direct evidence of the biodiversity in this Miocene ecosystem. The finds are a catalogue of the small-scale life in the forest understory and canopy.
Researchers have identified numerous species of arthropods, including ants, beetles, pseudoscorpions, and spiders, perfectly preserved within the golden-brown resin. Plant matter is also common, with fragments of leaves, flowers, and pollen grains giving a precise picture of the local flora. Fungal filaments and spores are also found, illustrating the decomposers of this ancient environment. Each piece of amber is a miniature diorama, capturing moments of life and death. These specimens allow scientists to study the physical structures of long-extinct species and understand the ecological relationships within a lost world. The existence of a Dipterocarpaceae forest in this part of China is confirmed by both the amber's chemistry and by co-occurring fossilized winged fruits from these specific trees.