Japan's 86-Million-Year-Old Amber Trapped an Insect Whose Family Now Lives Only in Africa

In Kuji, a coastal city in Iwate Prefecture in northern Japan, people still dig amber out of rock laid down about 86 million years ago, when dinosaurs walked the region. Inside one small piece, scientists found a predatory insect from a family that today survives only in sub-Saharan Africa.

The age comes from the rock around the amber. Kuji amber sits in the Tamagawa Formation of the Kuji Group, and a 2018 study in Cretaceous Research dated zircon crystals from its volcanic layers to about 85.9 million years, in the Santonian stage of the Late Cretaceous. That is some 20 million years before the asteroid impact that ended the age of the dinosaurs.

According to the Japan Science and Technology Agency, the amber is fossilized resin from trees of the Araucaria family, relatives of today's monkey puzzle tree. Dinosaur fossils sometimes turn up where it is mined. The famous ambers of the Baltic coast and the Dominican Republic, by contrast, formed long after the dinosaurs had vanished.

The insect in question was dug up in 2006 by Kazuhisa Sasaki, then director of the Kuji Amber Museum. For years it was filed as a praying mantis. In 2018, entomologists Hiroshi Nakamine and Shûhei Yamamoto took a closer look and described it in ZooKeys as a new genus and species of thorny lacewing, Kujiberotha teruyukii, the first of its family ever found in Japan or anywhere in East Asia.

Thorny lacewings have grasping front legs that look a lot like a mantis's, which explains the mix-up. The Kuji specimen has the longest front thigh of any fossil in its subfamily, about 1.9 millimeters, against a previous record of about 1.14 millimeters, and more than 50 segments in each antenna. Its name honors Teruyuki Kagawa, a kabuki and film actor famous in Japan for his love of mantises.

The living members of the family Rhachiberothidae are just 13 species in three genera, all from sub-Saharan Africa. The fossil record shows 15 extinct genera, a sign that the group was far more diverse in the Cretaceous and spread across much more of the planet than it is now.

The lacewing is not alone. Kuji amber has also yielded a fossil moss, described in The Bryologist in 2013, and in 2025 researchers from Waseda University, Fukui Prefectural University and the University of Tokyo reported seven tiny parasitic wasps, six of them trapped together in a single piece. The same rock layers have produced more than 3,000 vertebrate fossils from 30 species, including dinosaur teeth, turtles and crocodilians.

People prized this amber long before paleontologists did. A 1974 infrared analysis published in Nippon Kagaku Kaishi traced amber beads from two ancient burial mounds in Nara and Kyoto prefectures to Kuji, evidence of trade between northern and central Japan in the sixth century. A national research project later concluded that ancient Japan relied on Kuji amber, which lost ground to glass beads after the Heian period.

Today the Kuji Amber Museum, run by a local amber company, calls itself the only museum in Japan devoted to amber, and it holds the lacewing's holotype. The ZooKeys authors note that more than 800 insect inclusions from Kuji were still waiting for formal descriptions.

Sources: ZooKeys (2018); Cretaceous Research (2018); The Bryologist (2013); Nippon Kagaku Kaishi (1974); Science Japan, JST (2025); Science Japan, JST (2023); KAKEN, Japan amber beads project; Kuji Amber Museum. Cover: Kujiberotha teruyukii in Kuji amber, Nakamine and Yamamoto, CC BY 4.0_Figure_2.jpg).