河南济源中始新世似两栖犀属(奇蹄目:两栖犀科)一新种

A new species of Amynodontopsis(Perissodactyla:Amynodontidae)from the Middle Eocene of Jiyuan,Henan,China

描述了河南济源盆地中始新统聂庄组似两栖犀属(Amynodontopsis)一新种:济源似两栖犀(A.jiyuanensis sp.nov.),材料为一成年头骨。新种除了具有长头型,颅顶上凸,前颌骨和鼻骨连接,眶前窝较大并向眼眶内侧延伸,M1反前刺发育,M3后附尖强烈偏向唇侧等似两栖犀属的典型特征外,与其他似两栖犀的区别在于鼻骨较长,前颌骨鼻突在侧面向后延伸较多,与鼻骨接触面较大,上颌骨未参与构成外鼻孔边缘,鼻切迹位于犬齿后齿缺上方,上臼齿原脊和后脊相对较长,近于与外脊垂直。新种所具有的一系列原始特征表明济源似两栖犀比其他似两栖犀更原始。动物群对比显示其时代为沙拉木伦期,早于其他似两栖犀,由此推测似两栖犀属起源于亚洲并扩散至北美。

An adult amynodont skull,collected from the Middle Eocene Niezhuang Formation of Jiyuan Basin(Henan,China),is recognized as a new species Amynodontopsis jiyuanensis sp.nov.The specimen possesses the typical features of the genus Amynodontopsis,such as a dolichocephalic skull with elevated roof,premaxilla-nasal contact,large preorbital fossa extending posteriorly medial to the orbit,inner surface of anterior orbital bar concave in continuation with the preorbital fossa,antecrochet usually presented on M1,and metastyle of M3 strongly deflected labially.Amynodontopsis jiyuanensis is diagnosed by a combination of the following characters:long nasals,nasal process of premaxilla extending far back laterally below the nasal and excluding the maxilla from the border of external nares,nasal notch above the post-canine diastema,more transverse and proportionally longer protoloph and metaloph on upper molars.Comparison with known species of Amynodontopsis indicates that it is the most primitive one in the genus,due to the possession of primitive characters.Associated fossil mammals support a correlation of the strata bearing A.jiyuanensis with the Shara Murun Formation of the Erlian Basin,Nei Mongol,China,namely the Middle Eocene Sharamurunian Asian Land Mammal Age(ALMA),prior to all other known Amynodontopsis species.The earlier geologic age and primitive morphological features of A.jiyuanensis suggest that Amynodontopsis has an Asian origin in the Middle Eocene and later immigrated into North America.