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| Ravjaa ishiii Okoshi, Takasaki, Chiba, Natori, Saneyoshi, Takahashi, Kodaira, Hayashi, Ishigaki, Mainbayar & Tsogtbaatar, 2025 |
Numerous exquisitely preserved mammal fossils unearthed from Upper Cretaceous strata in the Gobi Desert of Mongolia have played a key role in understanding Mesozoic mammalian evolution. These splendid mammal fossils have been recovered mainly from the Baruungoyot and Djadokhta formations, but only two fragmentary remains of mammals have been collected from the underlying Bayanshiree Formation. Here we report a new species of Zhelestidae, Ravjaa ishiii gen. et sp. nov., based on a new mammal specimen recently discovered from the Bayanshiree Formation at the Bayan Shiree locality. The new specimen is represented by a well-preserved partial right dentary with the distal portion of an ultimate premolar and the first to the third molars. The gross observation and the phylogenetic analyses demonstrate zhelestid affinities: the subequally tall protoconid and metaconid, closely approximated hypoconulid and entoconid. Zhelestidae was widely distributed from Eurasia to North America in the Late Cretaceous but has not previously been recovered in the abundant Late Cretaceous mammalian fauna of Mongolia. This species represents the first zhelestid from the Mongolian Upper Cretaceous strata and contributes to further understanding of their paleobiogeographic and ecological insights.
Key words: Mammalia, Eutheria, Cretaceous, Bayanshiree Formation, Mongolia.
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| . Holotype of the zhelestid eutherian mammal Ravjaa ishiii gen. et sp. nov. (MPC-M 100s/001) from the Upper Cretaceous Bayanshiree Formation, Dornogovi, Mongolia. Right mandible in labial (A), occlusal (B) and lingual (C) views. Photographs (A1–C1) and 3D model (A2–C2) produced from a CT scan. |
Mammalia Linnaeus, 1758
Theria Parker and Haswell, 1897
Eutheria Gill, 1872
Zhelestidae Nessov, 1985a
Genus Ravjaa nov.
Etymology: Derived from the 5th Noyon Khutugt lama of the Gobi,
Dulduityn Danzanravjaa, the famous Buddhist scholar who was deeply
respected by people in the Dornogobi region, where this specimen was
unearthed. Given that the genus name “Ravjaa” originates from the
personal name of a male figure, it should be considered masculine.
Ravjaa ishiii sp. nov.
Etymology: In honor of Ken-ichi Ishii, the director of Hayashibara
Museum of Natural Sciences, Okayama, Japan, for his leading role
in the Japanese team of the Mongolia-Japan joint expedition, which
tremendously contributes to Mongolian paleontology.
Holotype: MPC-M 100s/001, partial right dentary with a distal portion
of the ultimate premolar, damaged m1, and well-preserved m2–3.
Type locality: Bayan Shiree, located approximately 25 km southwest of
Dzüünbayan, Dornogovi, Mongolia.
Type horizon: Cenomanian–Santonian, Upper Cretaceous, Bayanshiree
Formation.
Diagnosis.—A zhelestid eutherian that differs from all
other zhelestids in: the faint coronoid crest of the dentary
with the shallow masseteric fossa, the concave dorsal alveolar margin of the dentary, the complete absence of the
labial mandibular foramen, and the significantly high m2
crown that reaches approximately 70% of the height of the
horizontal ramus directly below it on labial view.
Tsukasa Okoshi, Ryuji Takasaki, Kentaro Chiba, Masahito Natori, Mototaka Saneyoshi, Akio Takahashi, Shota Kodaira, Shoji Hayashi, Shinobu Ishigaki, Buuvei Mainbayar, and Khishigjav Tsogtbaatar. 2025. New Late Cretaceous zhelestid mammal from the Bayanshiree Formation, Mongolia. Acta Palaeontologica Polonica. 70 (1); 193-203. DOI: doi.org/10.4202/app.01213.2024
