Although highly diversified in their early history,only one genus in Ochotonidae,Ochotona,survives to the present.Ochotona is generally accepted to have originated from the Middle Miocene Bellatona.During the 2006-2010 field seasons,we found Miocene localities at Damiao,Siziwang Qi,Nei Mongol,which produced rich materials of ochotonids.Of these localities,DM01 (pliopithecid locality),dated by the paleomagnetic method and faunal comparison as late Middle Miocene( ～ 12 Ma),yielded rich materials of the Bellatona-Bellatonoides-Ochotona group,and a large-sized relic form assigned to Desmatolagus moergenensis.The p3 morphology of the Bellatona-Bellatonoides-Ochotona complex conserves a similar tooth outline,but with distinct successive structures.The Bellatona form has two labial folds and no lingual fold on p3.The p3 of Bellatonoides form has one shallow anterolingual fold that is widely separated from the anterolabial fold.The p3 of Ochotona has a deep anterolingual fold that is closely connected with the anterolabial fold by a central bridge.The posterior process on M2 also shows progressive enlargement from Bellatona to Ochotona.Other cheek teeth of this complex are not distinguishable by either morphology or size.With only teeth found,we tentatively propose successive linear evolutionary relationships of the Bellatona-Bellatonoides-Ochotona complex,and Ochotona may have directly originated from Bellatonoides during the late Middle Miocene.The geological age of this fossil locality is consistent with the divergence time of Ochotona as estimated by molecular dating methods.%鼠兔科虽然是地质历史时期较为繁盛的一个门类,但现在仅有一个属(鼠兔属Ochotona).Ochotona被认为与Bellatona有密切的亲缘关系,可能是由后者衍生而来.详细描述了内蒙古大庙上猿化石地点发现的鼠兔科化石,识别出一种古老类型Desmatolagus moergenensis以及其他三个种Bellatona cf.B,forsythmajori,Bellatonoides eroli,Ochotona cf.O.lagreli.归入Bellatona,Bellatonoides和Ochotona的这三个种的p3具有相似的形态,并呈现出连续变化的特征.Bellatona的p3具有两个唇侧褶沟,但无舌侧褶沟；Bellatonoides的p3具有浅的舌侧前褶沟,但与唇侧前褶沟分开较宽；Ochotona的p3则具有深的舌侧前褶沟,与唇侧前褶沟之间仅以很窄的齿质桥连接.M2从无后突起、较小的后突起至发育的后突起,也呈现出连续变化的特征.中间颊齿则难以区分.因此,推测这三个种之间存在连续的线性演化关系,Ochotona 可能直接起源于Bellatonoides.磁性地层学与生物地层学对比结果显示该地点的年代约为12Ma,与根据分子钟推测的Ochotona的分化时间基本一致.
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