EVIDENCE FOR LATE MIOCENE CENTRAL ASIAN ARIDITY NEAR THE TIBETAN PLATEAU BASED ON THE FIRST FOSSIL SKELETON OF A SANDGROUSE (AVES: PTEROCLIDAE) FROM THE LINXIA BASIN IN WESTERN CHINA

Adding to the rapidly growing avian fauna of vultures, falcons, pheasants, and ostrich from the Liushu Formation (7.25- 11.1 Ma) is a partial skeleton of a sandgrouse (Columbiformes) that is the most complete fossil of the group known, the oldest record of the group in Asia, and fills a significant temporal gap in their Neogene history. The specimen includes articulated and associated elements of the wing, shoulder girdle, vertebrae, and hind limb. The skeleton preserves a notarium of four fused vertebrae that is present also in pteroclids and columbids. The fossil’s coracoids have short shafts unlike that of stem pteroclids and columbids. The dorsal supracondylar tubercle on the humerus is elongate and differs from that of columbids. The radiale has a much less distinct groove for m. ulnometacarpalis ventralis than the condition in the sandgrouse genus Syrrhaptes. Despite occurring within the extant geographic range of the Asian endemic Syrrhaptes, it appears that the fossil is a member of the crown pteroclid clade, and also outside of crown Syrrhaptes. This pteroclid skeleton was found associated with the foot of an ergilornithine gruoid and mammalian remains, and the majority of the sandgrouse skeleton is adjacent to and in contact with a horned bovid skull roof. The mixture of articulated, semicomplete individuals, and broken, unassociated vertebrate remains in otherwise structureless fine-grained sediments parallels that seen at other localities in the Liushu Formation. That taphonomy potentially suggests flood plain deposition during a flash flood event (possibly related to the seasonal Asian monsoon).

Extant and fossil sandgrouse are known from arid habitats across Eurasia and Africa. Males of extant sandgrouse are known for their unusual use of modified breast feathers for absorbing water from permanent water bodies and transporting it long distances to supply their young. The interpretation of the Linxia Basin deposits at the northeastern edge of the Qinghai-Tibetan Plateau has been as an arid savannah habitat occupied by a diverse Hipparion fauna. The occurrence of a sandgrouse within this environmental setting reinforces the hypothesis of drying and increased aridity in Central Asia associated coincidentally with the rise of the plateau during the late Miocene.