Abstract: Application of CT (computed tomography) scanning technology to the study of tooth morphology of mylagaulids makes better understanding the tooth structure of high-crowned mylagaulids. Two genera and species from the early Middle Miocene Halamagai Formation in northern Junggar Basin ofXinjiang are recognized: Tschalimys ckhikvadzei Shevyreva, 1971, the senior synonym of Sinomylagaulus halamagaiensis Wu, 1988 and Simpligaulus yangigen. et sp. nov. Both taxa undoubtedly belong to the subfamily Promylagaulinae. The integrated lithological, paleontological and paleomagnetic studies on sediments of the Late Oligocene through Late Miocene in the northern Junggar Basin of Xinjiang demonstrate that Halamagai Formation is fluvial-lacustrine sediments formed during the time coincident to the Mid-Miocene Climatic Optimum. T. ckhikvadzei and S. yangi probably inhabit the humid and warm regions with forests and densely vegetated thickets as the living mountain beaver Aplodontia rufa does. These mylagaulids are probably immigrants or the descendants of the immigrants from west North America.

摘要： 新疆准噶尔盆地北缘铁尔斯哈巴合中中新世早期哈拉玛盖组下部地层中产出3枚高冠的圆齿鼠牙齿化石，归属2属2种。CT断层扫描技术的研究结果表明，其中哈拉玛盖中国圆齿鼠Sinomylagaulus halamagaiensis Wu, 1988应是奇氏察里圆齿鼠Tschalimys ckhikvadzei Shevyreva, 1971的晚出同物异名，另一种为杨氏简圆齿鼠(新属新种)Simpligaulus yangi gen. et sp. nov., 这两属种都应归入原圆齿鼠亚科。对新疆准噶尔盆地北缘晚渐新世至晚中新世地层的岩石、古生物和古地磁综合研究表明，哈拉玛盖组是中中新世全球气候最佳期暖湿气候条件下的沉积物。推测Tschalimys ckhikvadzei和Simpligaulus yangi的生活习性与现生山河狸相似，居住在湿润的森林和稠密的灌丛地带，中亚的原圆齿鼠类有可能是由北美西部迁徙而来。