记临夏盆地维氏大唇犀—牙齿异常个体(英文)

临夏盆地已知的大唇犀(Chilotherium属)共有3种,C.primigenius,C.anderssoni和C.wimani。其中,C.wimani是临夏盆地晚中新世三趾马动物群中的优势种类,在临夏盆地的柳树组中部和上部的各个化石地点均有出土,时代为晚中新世中期。该种下颌主要特征表现在联合部强烈地横向扩展和i2巨大且内刃上翻。本文所述标本为一件带畸形牙齿的C.wimani亚成年下颌,年龄约9岁,个体中等大小,其特征与C.anderssoni相差较大,而与C.wimani完全一致。其畸形之处表现在左、右两侧的p4为异常状态,并且在左侧还保留有dp4。左p4前后内外倒转,且下三角座仅为一锥形牙尖形态;右p4不仅内外反转,而且下三角座完全退失。这件标本从病因来看,左dp4的滞留很可能是左p4牙胚的不正常发育造成的,而左、右p4的畸形生长很可能是生物体遗传因素和营养不良共同造成的。C.wimani的数量庞大,种间和种内竞争都很激烈。牙齿的畸形影响了上下牙的咬合状况,在环境恶劣、竞争激烈的情况下,功能劣势是致命的。

A DENTAL PATHOLOGICAL DEFORMITY OF CHILOTHERIUM WIMANI FROM THE LINXIA BASIN OF GANSU, CHINA

Chilotherium wirnani is the dominant species in the late Miocene Hipparion fauna of the Linxia Basin.A sub-adult mandible belonging to C.wimani is described here.The unusual characters of this mandible are the retention of left dp4 and the morbid state of left and right p4.The left p4 exhibits anterior-posterior and labial-lingual reversion and the trigonid of this tooth is strongly tapered.The right p4 shows not only anterior-posterior reversion,but also the,absence of trigonid.The retention of the left dp4 is induced likely by the abnormal growth of the left p4 germ,while the deformity of the left and right p4 may be caused by hereditary factors and/or malnutrition.The non-adaptive malocclusion would result in disadvantage in competition,and this functional disadvantage would be fatal under the likely condition of the harsh Late Miocene Linxia environment.