The exquisitely preserved longipterygid enantiornithine Rapaxavis pani is redescribed here after more extensive preparation. A complete review of its morphology is presented based on information gathered before and after preparation. Among other features, Rapaxavis pani is characterized by having an elongate rostrum (close to 60% of the skull length), rostrally restricted dentition, and schizorhinal external nares. Yet, the most puzzling feature of this bird is the presence of a pair of pectoral bones (here termed paracoracoidal ossifications) that, with the exception of the enantiornithine Concornis lacustris, are unknown within Aves. Particularly notable is the presence of a distal tarsal cap, formed by the fusion of distal tarsal elements, a feature that is controversial in non−ornithuromorph birds. The holotype and only known specimen of Rapaxavis pani thus reveals important information for better understanding the anatomy and phylogenetic relationships of longipterygids, in particular, as well as basal birds as a whole.

Key words: Aves, Enantiornithes, Longipterygidae, Rapaxavis, Jiufotang Formation, Early Cretaceous, China.

Jingmai K. O’Connor [jingmai@usc.edu ], Institute of Vertebrate Paleontology and Paleoanthropology, 142 Xizhimenwaidajie, Beijing, China, 100044; The Dinosaur Institute, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007 USA; Luis M. Chiappe [chiappe@nhm.org], The Dinosaur Institute, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007 USA ; Chunling Gao [homegcl@163.com] and Bo Zhao [zhaobo1961@163.com], Dalian Natural History Museum, No. 40 Xicun Street Heishijiao Shahekou, District Dalian, PR China.