Abstract: Previously, rhinocerotoid eggysodontines have been confined to Oligocene deposits from Europe and Asia. Here we report a new primitive Late Eocene eggysodontine, Proeggysodon qiui gen. et sp. nov., from Erden Obo, Siziwangqi, Nei Mongol, China. Proeggysodon differs from other eggysodontines in being smaller; in having two pairs of well-developed, spatulate lower incisors, non-molarized lower premolars, a more lingually aligned cristid obliqua of p4, and an angled junction between the cristid obliqua and the hypolophid of each lower molar; and in lacking buccal cingulids on the lower cheek teeth. Furthermore, we propose that eggysodontines and forstercooperes are closely related, mainly because they share the following features: large and erect canine, relatively short diastema between canine and cheek teeth, and dorsoventrally deep and anteroposteriorly abbreviated symphysis associated with nearly vertically implanted incisors. The new specimen narrows the time gap between the Early to Middle Eocene forstercooperes and the Oligocene eggysodontines. The discovery of Proeggysodon in Asia also suggests that eggysodontines dispersed from this continent into Europe after the “Grande Coupure”.

摘要： 描述了内蒙古四子王旗额尔登敖包晚始新世乌兰戈楚组(?)(中白层)的紧齿犀亚科(Eggysodontinae)一新属种：邱氏原紧齿犀(Proeggysodon qiui), 标本为破损的下颌骨。新属种与其他渐新世紧齿犀的区别在于个体较小，具有两对发育的铲形下门齿，下前臼齿没有臼齿化，p4的下斜脊更向舌侧倾斜延伸，下臼齿下斜脊与下次脊连接处呈角状，下臼齿无颊侧齿带。紧齿犀类和柯氏犀类(forstercooperes)可能有较近的系统发育关系，它们具有以下的共近裔性状：短而粗壮的大犬齿，相对短的齿隙(犬齿和前臼齿之间)，下颌联合部短而高，从而使门齿趋向直立。新标本的发现填补了早－中始新世柯氏犀类和渐新世紧齿犀类在时代上的空白，也使紧齿犀类成为欧洲始新世/渐新世之交的“大间断”之后哺乳动物群自亚洲迁入欧洲的又一例证。