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A Jurassic gliding euharamiyidan mammal with an ear of five auditory bones


Gliding is a distinctive locomotion type that has been identified in only three mammal species from the Mesozoic era. Here we describe another Jurassic glider that belongs to the euharamiyidan mammals and shows hair details on its gliding membrane that are highly similar to those of extant gliding mammals. This species possesses a five-boned auditory apparatus consisting of the stapes, incus, malleus, ectotympanic and surangular, representing, to our knowledge, the earliest known definitive mammalian middle ear. The surangular has not been previously identified in any mammalian middle ear, and the morphology of each auditory bone differs from those of known mammals and their kin. We conclude that gliding locomotion was probably common in euharamiyidans, which lends support to idea that there was a major adaptive radiation of mammals in the mid-Jurassic period. The acquisition of the auditory bones in euharamiyidans was related to the formation of the dentary-squamosal jaw joint, which allows a posterior chewing movement, and must have evolved independently from the middle ear structures of monotremes and therian mammals.


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We thank S.-H. Xie for specimen preparation; P.-F. Yin and Y.-M. Hou for computed laminography scanning of the specimens; X.-T. Zheng, X.-L. Wang, H.-J. Li, Z.-J. Gao, X.-H. Ding, and D.-Y. Sun for access to comparative specimens; N. Wong for drawing the auditory bones and animal reconstruction; D. W. Krause and S. Hoffmann for sharing data and insights on incisor identification; D. Sigogneau-Russell and Z.-X. Luo for permissions to use their published figures; and Z.-X. Luo, Z.-H. Zhou, X. Xu, G. Rougier, J. A. Schultz, A. S. Tucker, and M. Takechi for discussions. This work was supported by the National Natural Science Foundation of China (41688103; 41404022) and the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (XDB18000000).