A 99-million-year-old ecosystem
In the Hukawng Valley of northern Myanmar, deposits of fossilized tree resin, known locally as burmite, contain an unparalleled record of a mid-Cretaceous forest. U-Pb (uranium-lead) radiometric dating of zircon crystals found within the amber-bearing layers confirms its age to be approximately 98.8 million years old. This places the amber squarely in the Cenomanian age, a time when dinosaurs still dominated the landscape. The resin is thought to have been produced by coniferous trees, possibly from the Araucariaceae family, in a humid, tropical coastal environment.
The chemical composition of burmite classifies it as a Class Ib amber, and it is Harder than the more common Baltic amber. This amber preserves a snapshot of an entire lost ecosystem with three-dimensional fidelity. The diversity of life is immense, with over 2,800 species described as of 2023. Inclusions range from fungi and the earliest examples of flowering plants to a vast array of arthropods like insects, spiders, and millipedes. The detail is so exceptional that even parasitic mites on a dinosaur feather have been identified.
Prehistoric vertebrates in resin
The Hukawng Valley amber is most famous for its rare vertebrate inclusions. The 2016 discovery of a 37-millimeter-long feathered tail from a non-avian theropod dinosaur provided the first direct look at dinosaur plumage in 3D. The tail segment contains eight vertebrae and shows feathers with a chestnut-brown upper surface and a pale or white underside. Unlike modern flight feathers, their structure suggests they were more ornamental.
Other significant finds include nearly complete hatchling birds from an extinct group called the Enantiornithes, which lived alongside dinosaurs. These specimens show details of the feathers, skin, claws, and even the external ear opening. In 2018, four specimens of the earliest known tropical frog, Electrorana limoae, were described. These tiny frogs, measuring only about 2.2 cm long, confirm that this group of amphibians inhabited wet tropical forests at least 99 million years ago. The amber has also yielded the oldest known fossil of a baby snake, a new species named Xiaophis myanmarensis.