An international team of paleontologists discovered a previously unknown species of ancient mammal, named Ravjaa ishii, in Mongolia's Gobi Desert.
The fossils of Ravjaa ishii were unearthed in the Baynshire Formation, one of the Gobi Desert's fossil-rich ancient rock layers. The discovery was made during a joint expedition in 2019 by researchers from Okayama University of Science and the Institute of Paleontology and Geology of the Mongolian Academy of Sciences.
Ravjaa ishii is characterized as a small, fast-moving mammal with a slender build, roughly the size of a modern mouse. It belongs to the family Zhelestidae, a group of ancient mammals that lived during the Cretaceous period, approximately 100 to 66 million years ago.
This marks the first time fossils from the Zhelestidae family have been found in Mongolia, altering previous understandings of the geographical distribution of these animals. It was previously believed that Zhelestidae inhabited mainly coastal regions. However, the discovery of Ravjaa ishii indicates that these mammals also evolved far inland on the continent.
The unique morphology of the fossil, particularly the distinct shape of the jaw and the high-crowned molar teeth, sets Ravjaa ishii apart from other known members of the Zhelestidae family. These distinguishing features allowed scientists to classify it as a separate genus and species, demonstrating the diversity of early mammals in the region.
The dental structure of Ravjaa ishii suggests that the animal fed on seeds and fruits. The diet coincides with the era of the flourishing of angiosperms, or flowering plants, reflecting how early mammals may have begun to exploit new food resources that emerged with the evolution of these plants.
"The publication process was delayed due to the pandemic, but we are glad that we can now show the scientific value of this tiny find," said Tsukasa Okoshi, a graduate student at Okayama University of Science and the lead author of the study, according to Kompas. The diminutive size of the fossil—specifically, a lower jaw fragment measuring only one centimeter in length—made its discovery all the more remarkable.
Professor Mototaka Saneyoshi expressed his amazement at the find. "Finding such a tiny fossil in a huge desert is almost a miracle. A real gift from the Gobi," he said, according to Kompas. The meticulous work required to locate such a small specimen highlights the dedication of the research team.
Mongolian researchers Dr. Kh. Tsogtbaatar and B. Mainbayar also participated in the discovery, contributing to Mongolia's rich history of paleontological finds. The species name Ravjaa ishii honors Dulduityn Danzanravjaa, a renowned 19th-century Buddhist monk, and Kenichi Ishii, the former director of the Hayashibara Museum of Natural Sciences who played a key role in establishing the Mongolia-Okayama University of Science research partnership.
The Baynshire Formation, where the fossil was found, is estimated to be contemporaneous with the early spread of flowering plants in terrestrial ecosystems. The timing suggests a possible link between the evolution of flowering plants and the dietary adaptations of early mammals like Ravjaa ishii.
The discovery enriches the understanding of Mongolia's prehistoric fauna and biodiversity during the age of dinosaurs. It opens new avenues for exploring how ancient mammals adapted to changes in Earth's ecosystems, particularly the emergence of new food sources.
It also offers fresh information on the characteristics and geographical distribution of Cretaceous mammals. By revealing that Zhelestidae mammals inhabited continental interiors, the find challenges previous notions that they were confined to coastal areas.
"Tsukasa Okoshi hopes this research will pave the way for further taxonomic studies of other small vertebrate fossils from the same site and era," reported Kompas. The potential for uncovering more about the diverse life forms that existed during the Late Cretaceous period is substantial.
The structure of the teeth of Ravjaa ishii not only indicates its diet but also provides insights into the adaptive strategies of early mammals. This aligns with the hypothesis that mammals of the Eutheria group began to exploit new resources that became available with the evolution of flowering plants.
The article was written with the assistance of a news analysis system.