A 100-Million-Year-Old Crime Scene
In the area around Jinju, South Korea, fragments of fossilized tree resin, or amber, preserve a detailed snapshot of a Cretaceous ecosystem. These amber pieces originate from the Jinju Formation, a geological layer deposited in a lakeside environment between 106 and 112 million years ago during the Early Cretaceous period. The formation is primarily composed of black shale and sandstone, which has proven ideal for preserving an incredible diversity of life. The paleoenvironment was a warm, arid, subtropical area with coniferous trees that produced the resin responsible for these remarkable fossils.
The amber preserves small organisms, trapping small organisms and preserving them with microscopic fidelity. While the Jinju Formation is also famous for its extensive dinosaur trackways, the amber provides a different kind of record, capturing the smaller, often overlooked inhabitants of the dinosaur's world. Discoveries range from plants and ostracods to a wide array of insects and spiders. Each piece of amber, often found as a small, isolated fragment, records the local food webs and ecological relationships of this ancient period.
Prehistoric Parasites and Prey
The most significant finds from Korean amber relate to parasites and their hosts. While Burmese amber has yielded a tick grasping a dinosaur feather, related finds help show this ancient parasitic relationship. An extinct species of tick, Deinocroton draculi ("Dracula's terrible tick"), was found in amber from a similar period. One specimen was engorged with blood, having swollen to eight times its normal size. Other specimens were found with the fossilized hairs of skin beetle larvae, insects known today for infesting nests and feeding on discarded feathers and skin. This evidence suggests these ticks inhabiting the nests of feathered dinosaurs.
The Jinju deposits also reveal other creatures from the Cretaceous undergrowth. Fossils of the extinct spider family Lagonomegopidae have been found in the local shale. Unusually, the preservation contains a reflective structure in their large eyes called a tapetum, a feature seen today in nocturnal hunters like wolf spiders. This is the first time this feature has been found in a fossil spider. Other inclusions from the Jinju Formation and its shales include click beetles, such as the 47.8 mm Megalithomerus magohalmii, the largest fossil elaterid ever found.