KYODO NEWS - Aug 24, 2017 - 12:16 | Arts, All, Lifestyle

A fossilized tooth of a marsupial relative has been unearthed in southwestern Japan, boosting hopes that the trove dating back some 90 million years can unravel the evolution of mammals in Asia, a local museum said Thursday.

The fossil, the first of its kind excavated in Japan, was found in March 2014 in the town of Mifune, Kumamoto Prefecture, from a geological layer formed in the late Cretaceous period, according to the Mifune Dinosaur Museum.

The tooth measuring about 2 millimeters in length and 3 mm in width was uncovered from sandstone in the Tashiro district in Mifune. Based on the shape and size, it is assumed to be a back tooth from the upper left jaw of a carnivore that was about 10 to 15 centimeters tall.

(Mifune Dinosaur Museum)

The fossil is believed to be of an animal similar to a deltatheridium, an ancient relative of marsupials which include kangaroos and koalas that lived in Mongolia in the Cretaceous period between around 145 million years ago and 66 million years ago.

Marsupials and deltatheridiums are classified in the Metatheria group. In Asia, some Metatheria fossils have been discovered in a geological layer of the late Cretaceous period in inland areas of Mongolia and China.

(Akio Ito and Yasuko Okamoto)

Kazunori Miyata, an associate professor at the Dinosaur Research Institute of Fukui Prefectural University, said the fossil's discovery is "significant."

"It suggests the possibility that primitive marsupial ancestors were thriving on the east bank of Asia including Japan in the late Cretaceous period when dinosaurs were still dominant."

The fossil tooth will be displayed at the museum from Friday to Nov. 26.