A tarsometatarsus from the upper Eocene Na Duong Basin—the first Palaeogene fossil bird from Vietnam

Knowledge of the Palaeogene avifauna of East Asia is scarce, and only a few fossils have been described thus far. A tarsometatarsus from the upper Eocene Na Duong Basin represents the first Palaeogene fossil bird from Vietnam. The fossiliferous sediments in the Na Duong Basin originated from an aquatic ecosystem but also yielded terrestrial animal and plant remains suggesting a dense forest habitat surrounding an ancient lake. In accordance, the Na Duong Basin tarsometatarsus is compared with extant aquatic, terrestrial and arboreal bird species, but because of diagenetic compression and fragmentary preservation, it is difficult to classify the bone. Nevertheless, the specimen exhibits a distinctive morphology and is potentially referable to an endemic neognath unknown from other Palaeogene localities outside of Vietnam.