A small fossil found in Mongolia’s Gobi Desert has unveiled a new species of early mammal, believed to have existed approximately 90 million years ago. This discovery is significant as it enhances understanding of the earliest relatives of placental mammals.
The specimen was extracted in 2019 from the Bayanshiree Formation, a site known for its scarcity of mammalian fossils compared to other locations in the region. Its rarity makes this find particularly noteworthy, occurring in a field largely dominated by more extensively documented fossil layers.
Called Ravjaa ishiii, this species is classified within the Zhelestidae family, an early group of eutherian mammals, which are ancestors to modern placental mammals. These small, mouse-sized creatures coexisted with dinosaurs and occupied ecological spaces that researchers are still working to comprehend.
The fossil itself comprises a mere 1-centimetre jaw fragment, including the tip of a premolar and three molars. Despite its size, this fragment contains enough anatomical detail to classify it as a new genus and species. Researchers, including Tsukasa Okoshi, highlighted that the well-preserved fossils from this era in Mongolia have been crucial to understanding mammalian evolution during the Mesozoic era.
Notably, the dental features of Ravjaa ishiii are distinctive; its molars are unusually tall and robust, setting it apart from known relatives. This suggests that early eutherians began to exploit resources linked to the rise of flowering plants during the Cretaceous period, indicating a shift in dietary habits even as dinosaurs maintained ecological dominance.
Beyond its anatomy, Ravjaa ishiii holds evolutionary significance as the first identified zhelestid specimen from the Bayanshiree Formation, representing a potential ancestral link that may date back to the transition between Early and Late Cretaceous periods. Experts like Professor Mototaka Saneyoshi remarked on the remarkable chance of discovering such a tiny fossil within the vast desert landscape.
Test Your Understanding
How much do you know?
