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

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

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。

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; upperfacial 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.