A new species of Eogruidae (Aves: Gruiformes) from the Miocene of the Linxia Basin, Gansu, China: Evolutionary and climatic implications

Despite having one of the most robust fossil records within core-gruiform birds (rails, cranes, and allies), the biogeographic history of Gruidae (cranes) and key drivers of diversification within this group remain largely unknown. The Eogruidae of Eurasia represent some of the earliest known crane-like fossils. Here, we present description of a new species represented by a well-preserved specimen of a foot from the late Miocene (7–6.5 mya) Liushu Formation of Linxia Basin, Gansu, China. It is the only eogruid fossil that has been found in this formation and is the first eogruid known from northwest China. Linxia Basin is located along the margin of the northeastern Tibetan Plateau, which allows for new insight into Miocene dispersal of the Eogruidae and potential climatological and geological connections. It is also the first specimen with an associated tarsometatarsus and nearly complete phalanges, including a claw, which provides further morphological information on this taxon. Referral of the new specimen to Eogruidae is based on extreme reduction of the trochlea of metatarsal II, which is most similar to the condition present in the eogruid subclade traditionally termed Ergilornithidae.

Methods
The specimen was scanned using x-ray microtomography (225 Micro CT) at the Key Laboratory of Vertebrate Evolution and Human Origins. The specimen is housed in the collections of the Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China. The raw data has been uploaded as TIFFs. The data has been segmented in Aviso and these segments are available as .stl files. .avi movies of the CT Data are also available.