南京1号直立人头骨与肯尼亚KNM-ER 3733人类头骨化石的形态比较

KNM-ER 3733人类头骨化石的年代为距今1.78百万年,1975年发现于肯尼亚。Walker和Leakey注意到这具头骨与周口店直立人的在脑颅形态上很相近,但二者在年代上相差大约1百万年,故认为直立人形态在这1百万年期间是稳定的。长期来此观点缺乏更多的人类化石证据来支持。1993年在中国发现了南京1号人类头骨化石。该头骨与KNM-ER 3733头骨一样兼具脑颅和面颅,且都属于成年女性个体,但南京1号人类头骨化石的年代比KNM-ER 3733人类头骨化石的要晚大约1百万年。因此,南京1号人类头骨是目前所知的可用来验证直立人头骨形态是否在1百万年期间保持稳定的唯一合适的人类头骨化石材料。形态比较表明,这两个人类头骨化石的脑颅虽然在眶上圆枕上沟的发育程度、眶后收缩的程度、额骨横向隆起的程度、角圆枕和乳后突的发育与否、顶骨形状以及骨壁厚度的表现上有所差异,但有更多的形态性状显示出相近。这些相近表现在脑颅的长、宽、高值上;颅容量上;脑颅的低矮性上;脑颅最大宽之位置上;额骨、顶骨、枕骨之矢弧值的比例上;眶上圆枕的纤细上;顶骨的大小和矢向扁平性上;颞线位置和颞鳞顶缘的形状上;枕鳞的低宽形状上;上枕鳞与下枕鳞之间的转折形状和比例上;枕骨圆枕和枕骨圆枕上沟的发育程度上等。这两具头骨的面颅虽然有同属突颌型的面角、皆发育有鼻骨间嵴、两鼻骨组成的上部宽度与下部宽度皆差别很大,但有更多的形态性状显示出差别。这些差别表现在面型上、颜面上部扁平度上、眶形和眶型上、上颌额突外侧面的朝向上、鼻骨横向隆起程度上、鼻梁外突程度上、鼻型上、颧骨下缘外展程度上、颊高上、颧上颌下缘的形状上、上颌颧突基部的位置上以及颧结节的位置上等。因此,南京1号头骨与KNM-ER 3733头骨之间在脑颅上显示出较多的相近性状,在面颅上则显示出较多的相异性状。脑颅方面的相近性状大多具有分类上的鉴别价值。这两个头骨脑颅形态的相近支持把KNM-ER 3733头骨鉴定为"直立人"的观点;也提示了南京1号头骨的脑颅似乎保持着1百多万年前的"祖先"形态。如果直立人的某些成员在至少1百万年期间保持着形态稳定的话,则这种形态上的稳定主要是表现在脑颅形态上。这两具头骨的面颅形态上较大差异的意义,目前尚不清楚。

A Morphological Comparison of Two Homo erectus Crania: Nanjing 1 and KNM-ER 3733

KNM-ER 3733,a remarkably complete cranium found in 1975,bears a striking resemblance to the Homo erectus specimens from Zhoukoudian that are very much younger in age,and on this basis Walker and Leakey hold the view that Homo erectus was a morphologically stable human species over a span of at least a million years.This view needs to be tested.A morphological comparison shows that the calvaria of Nanjing 1 resembles KNM-ER 3733 in the following features: cranial length;porion height;supramastoid breadth;cranial capacity;low cranial profile in lateral view;position of the maximum cranial breadth;frontal,parietal and occipital having a share in the sagittal cranial arc;a gracile supraorbital torus;smaller size and sagittal flatness of the parietal;higher position of temporal lines;form of upper margin of temporal squama;low,wide and strongly flexed occipit;ratio of lower to upper scale lengths of occiput;and expression of occipital torus and supratorus sulcus.In contrast,the calvariae differ in the development of supratoral sulcus of the frontal;postorbital constriction;flatness of frontal squama in the transverse plane;expression of angular torus and retromastoid process;shape of the parietal;and expression of cranial vault thickness.The facial skeleton of Nanjing 1 differs from that of KNM-ER 3733 in upper-facial shape;upper-facial flatness;orbital shape and index;facing of lateral surface of frontal process of maxilla;roundness of nasals in transverse plane;nasal roof projection;nasal index;eversion of the lower border of malar bones;cheek height;form of inferior zygomatic-maxillary margin;position of the base of zygomatic process of maxilla;and position of malar tubercle.Nanjing 1 resembles KNM-ER 3733 in other facial features,which cover facial angle,internasal keeling,and nasal bone proportions.In conclusion,the Nanjing 1 is similar to KNM-ER 3733 in most features of the calvaria,but very different in most features of the facial skeleton.The morphological similarity in the calvariae is diagnostic and supports the claim that KNM-ER 3733 belongs to Homo erectus.In addition,this similarity suggests an anatomical stability of some members of Homo erectus in calvaria morphology over a span of at least a million years.Unfortunately,the significance of the differences in facial skeleton of these crania is uncertain.