人属先驱种的系统位置——头面骨关键性状的比较研究

人属先驱种(Homo antecessor),是根据西班牙阿塔普尔卡Gran Dolina洞穴堆积中发现的人类化石厘定的。出产人类化石的地层年代测定距今约90万年到78万年之间。之所以定为先驱种,是因为最初研究者认为这个西班牙的古人类群是较晚的海德堡人(H. heidelbergensis)和尼安德特人的共同祖先(H. neanderthalensis),而在非洲和欧洲发现的海德堡人则已被认为是现代人的直接祖先。目前对先驱种的争论还没有明确的结论。之所以会形成这种局面,与"先驱种"模式化石的生物学年龄和保存状况有极大的关系。本文对当初厘定"先驱种"的头骨和面骨的11个特定性状做了一个系统的回顾,尤其是和各类南方古猿(Australopithecus和Praeanthropus),最早的人属成员能人种(H. habilis)和鲁道夫种(H. rudolfensis),人属匠人种(H. ergaster),以及人属直立人种(H. erectus)面部梨状孔周边和上颌骨功能区的特征的比较研究。这11个头面骨的特征包括:1)眶下骨骼的冠状面朝向、2)犬齿窝的存在、3)上颌骨下缘外侧端向下的转折切迹、4)弧状颧骨下缘、5)梨状孔外侧上颌骨的转折和朝向、6)梨状孔外缘和颧骨起点的相对位置、7)梨状孔下缘鼻棘和侧棘的位置和组合形态、8)颧骨和上颌骨结节、9)类现代人的骨表面重塑模式、10)突出的鼻骨、和11)颞骨的上凸的颞鳞上缘。结果表明"先驱种"的头面骨的定性特征没有特异性,其组合与周口店的直立人面部基本形态也非常相似,因而作者倾向于认为"先驱种"就是直立人种的欧洲变异群体。所谓"人属先驱种"可能只是广义的人属直立人种(H. erectus sensu lato)欧洲代表。目前的化石材料显示欧洲和亚洲的直立人种是非洲匠人种的演变而来。

A comparative study of the craniofacial features defining ‘Homo antecessor’

The establishment of the new species ‘Homo antecessor’ was mainly based on the remains of an immature individual ATD6-69, found at the TD6 litostratigraphic unit (LU) of the Gran Dolina site in the Sierra de Atapuerca—Burgos, northern Spain1], along with cranial, mandibular and dental traits from other fossil hominid specimens recovered in the same level. TD6 LU was initially dated about 0.78 Ma2] using ESR-U-series; but recent redatings, employing TL and IRSL methods, suggest that its age is between 0,9-0,95 Ma. It seems that there is general consensus that TD6 LU corresponds to Marine Isotope Stage (MIS) 25. TD6-69 specimen, a partial face with R P3, M1, and germs of M2 and M3; and L I2-M1, was found in the so-called “Aurora stratum”, ~1.5 m below the Brunhes–Matuyama (B–M) geomagnetic boundary. This “stratum” was in fact, an excavation area of only 6 m2 for archaeological test pit purposes. There is no real basis, from an earnest stratigraphic point of view, to consider such sedimentary level as a new litostratigraphic unit and, therefore, “Aurora stratum” should be take into account as an informal archaeo-sedimentary small area whose name was established to gain public attention from the media.