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A joint research team has discovered a fossil belonging to a previously unknown genus and species of mammal in the Late Cretaceous (100–66 million-year-old) strata of Mongolia's Gobi Desert.

The mouse-sized animal is named Ravjaa ishiii: The species name honors Dulduityn Danzanravjaa, a revered 19th-century Buddhist monk, and the late Kenichi Ishii, former director of the Hayashibara Museum of Natural Sciences, who helped establish the Mongolia–OUS research partnership.

The work is in the journal Acta Palaeontologica Polonica. The team included researchers from Okayama University of Science (OUS) and the Institute of Paleontology and Geology, Mongolian Academy of Sciences (IPMAS).

During a joint expedition in 2019 to the Baynshire Formation, the fossil-bearing deposit in the Gobi Desert, Mongolia, the team found a one-centimeter partial lower jaw. Analysis suggested the specimen is a member of Zhelestidae, a Cretaceous mammal family.

Yet, its unusually tall molars and distinctive jaw shape differ from known relatives, and therefore the study established a new genus and species. The discovery marks the first record of a zhelestid in Mongolia, showing that the group also thrived far inland, not only along ancient coastlines as was previously inferred.

The suggested age of the Baynshire Formation corresponds to the early spread of angiosperms (flowering plants) in terrestrial ecosystems. The robust nature of the molars resembles those of seed- and fruit-eating mammals, providing an intriguing insight that early Eutherians were already exploiting resources created by flowering plants.

Tsukasa Okoshi (lead author and OUS doctoral candidate) said, "Due to the COVID-19 pandemic, the publication process took longer than expected, but we were finally able to establish the scientific importance of this specimen. We hope this research will serve as a starting point for further taxonomic studies of other small vertebrate fossils from the same site and era and will ultimately help uncover the rich biodiversity—including dinosaurs—that once inhabited the Gobi Desert during the age of dinosaurs."

Professor Mototaka Saneyoshi of OUS added, "Finding such a tiny fossil in the vast expanse of the Gobi Desert feels like a gift from the Gobi Desert. It's nothing short of miraculous."