Wood B A, Abbott S A, Uytterschaut H
Department of Human Anatomy and Cell Biology, University of Liverpool.
J Anat. 1988 Feb;156:107-39.
The subocclusal morphology of 168 permanent mandibular premolars (N = 77) and molars (N = 91) of Plio-Pleistocene hominids has been investigated. The taxonomic allocation of the teeth, which represent at least 46 individuals, was based on nondental evidence. Specimens were allocated to one of two major taxonomic categories, (EAFROB or EAFHOM), East African Homo erectus (EAFHER), or their taxonomic affinity was regarded as 'unknown' (N = 17). Information about the root system was derived from radiography and direct observation. Morphometric data were in the form of nine linear and two angular measurements based on eighteen reference points. Root form was also assessed using a scheme which recognised four classes of root morphology. Data were compared using both univariate and multivariate techniques, including Principal Component and Canonical Variate analysis. Posterior probabilities derived from the latter were used (in a two-taxon design model) to assess the affinities of the 'unknown' specimens. The variation in hominid mandibular premolar root form was interpreted as two morphoclines, based on the presumed primitive condition of the P3 (with mesiobuccal and distal roots, 2R: MB and D) and P4 (with mesial and distal root, 2R: M and D) root systems. One trend apparently leads towards root reduction (i.e. P3 = 1 R; P4 = 1 R), and the other to root elaboration (i.e. P3 and P4 = 2R: M and D). The extreme form of the latter is the 'molarisation' of the premolar roots seen in EAFROB. Despite major differences in root form there was relatively little taxonomic variation in root metrics, except for a more robust distal root system in EAFROB. Molar root form showed little interspecific variation except for M2 in which the roots in EAFROB were larger and more robust, with differences in root height being greater for the distal than for the mesial roots. Root form and metrics enable four of the 'unknown' specimens (KMN-ER 819, 1482, 1483 and 1801) to be tentatively allocated to EAFHOM, and a single specimen, KMN-ER 3731, to EAFROB. Published assessments of the root morphology of the 'robust' australopithecines from Swartkrans suggest that the premolar root form of Australopithecus (Paranthropus) robustus is not obviously intermediate between the presumed ancestral condition, and the 'molarised' mandibular premolar root systems of Australopithecus (Paranthropus) boisei.
对168颗上新世 - 更新世原始人类的恒下颌前磨牙（N = 77）和磨牙（N = 91）的咬合下形态进行了研究。这些牙齿至少代表46个个体，其分类归属基于非牙齿证据。标本被归入两个主要分类类别之一，即东非直立人（EAFROB或EAFHOM）、东非直立人（EAFHER），或者其分类亲缘关系被视为“未知”（N = 17）。关于根系的信息来自X射线摄影和直接观察。形态测量数据以基于18个参考点的9个线性测量和2个角度测量的形式呈现。还使用一种识别四类根形态的方案来评估根形态。使用单变量和多变量技术（包括主成分分析和典型变量分析）对数据进行比较。从后者得出的后验概率用于（在双分类设计模型中）评估“未知”标本的亲缘关系。基于P3（有近中颊根和远中根，2R：MB和D）和P4（有近中根和远中根，2R：M和D）根系的假定原始状态，原始人类下颌前磨牙根形态的变异被解释为两条形态渐变群。一种趋势显然是朝着根减少（即P3 = 1R；P4 = 1R）发展，另一种趋势是朝着根细化（即P3和P4 = 2R：M和D）发展。后者的极端形式是在东非直立人中看到的前磨牙根的“磨牙化”。尽管根形态存在重大差异，但根测量指标的分类变异相对较小，除了东非直立人的远中根系更粗壮。磨牙根形态除了M2外种间变异较小，在M2中，东非直立人的根更大且更粗壮，远中根的根高差异比近中根更大。根形态和测量指标使4个“未知”标本（KMN - ER 819、1482、1483和1801）能够暂时归入东非直立人，以及一个标本KMN - ER 3731归入东非直立人。对来自斯瓦特克朗斯的“粗壮型”南方古猿根形态的已发表评估表明，粗壮南方古猿（傍人）的前磨牙根形态在假定的祖先状态和鲍氏南方古猿（傍人）的“磨牙化下颌前磨牙根系”之间并非明显处于中间状态。
