Getting to Know Homo erectus The period from 1 million to 500,000 years ago (~1 to 0.5 Ma) is well represented in the human fossil records of Europe and Asia. Sites containing such fossils include Ceprano, Italy (~0.9 to 0.8 Ma), the TD-6 level at Atapuerca’s Gran Dolina, Spain (~0.78 Ma), Trinil, Indonesia (1 to 0.7 Ma), some parts of the Sangiran Dome, Indonesia (1.5 to 1 Ma), Lantian, China (~1 Ma), and probably Zhoukoudian, China (0.55 to 0.3 Ma). By contrast, Africa has been unusually about this part of human evolution. Three partial mandibles unearthed more than 50 years ago at Tighenif (Ternifine) in Algeria (~0.7 Ma) are similar in dental morphology to specimens from Gran Dolina (1), but the former are rarely mentioned in the literature. The question thus remained: Where are the African fossils? The recent discovery of the partial Daka skull (~1 Ma) at the Bouri site, Middle Awash, Ethiopia (2), provided part of the answer. On page 75 of this issue,Potts et al. (3) now report that the archaeologically and faunally rich site ofOlorgesailie, Kenya, has divulged its first hominid fossils: a partial frontal and more fragmentary temporal bone dated 0.97 to 0.9 Ma. Like the Daka specimen, these fragments (KNM-OL 45500) were assigned to the species Homo erectus. Potts et al. correctly assess the “Homo erectus” debate: “The entire sample of fossils from Africa, Asia, and Europe exhibits wide morphological variation that some researchers divide into multiple lineages and others place in a single, polytypic species.” They opt for the latter hypothesis and conclude that “comparison of the KNM-OL 45500 with other crania . . . illustrates that metric and qualitative similarities cut across temporal and spatial groups of fossil specimens.” Assuming that a vast array of specimens of differing morphologies constitute the same species, favorable comparisons between some of them in one or a few morphologies are expected, especially if primitive retentions and shared derived features are not sorted out. But this doesn’t clarify the question, “What is H. erectus?” One is left primarily with the traditional approach to the genus Homo: H. erectus is not H. habilis, H. heidelbergensis, or H. sapiens, whatever they are. But there is a simple and systematically valid way in which one might unpack the morphological confusion: Begin with the original name-bearer of H. erectus, the type specimen, which was discovered in the late 19th century by Eugéne Dubois at Trinil. The Trinil skull cap is distinctive in having a very low and long profile with a bluntly V-shaped occipital bulge (see the figure, panels A and B). In rear view, it is extraordinarily broad relative to its height. Its shelf-like, laterally flaring, and apparently rather thin brow ridges flow back smoothly into a gently sloping frontal plane. Near the foot of this rise, in the midline, is a pair of depressions that delineate between them an anteroposteriorly oriented “keel-like” structure. The sides of the brain case are minimally puffy. Specimens that share most of these features, but witha wide range of individual variation in their expression, come from Sangiran (panels C, D, and F). Some specimens of this substantial assemblage preserve a temporal bone (missing in Trinil) with unusual morphology: Unlike other mammals, this hominid’s intracranial sigmoid sinuses were not single, but arborized prior to draining into the jugular veins (panel E). The Trinil/ Sangiran sample also demonstrates that long-touted “H. erectus” features—very thick cranial bone, markedly puffy cranial side walls circumscribed by thick temporal lines, and pronounced midline keeling— are only variably expressed, if at all. Only the chunky Sangiran 4 specimen approaches this description (4) (panel F). Do we see any of the consistent Trinil/Sangiran H. erectus cranial features in other hominid fossils? Not in the Javanese Ngandong specimens (1 to 0.36 Ma), the Sambungmacan (1 to 0.2 Ma) or Ngawi (undated) specimens, or those from Zhoukoudian or any other Chinese site (Dali, Hexian, Jinniushan, Lantian, Maba,
Posted on: Mon, 12 Aug 2013 22:09:19 +0000