AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 64:137-139 (1984) Does KNM-ER 1481A Establish Homo erectus at 2.0 myr BP? ERIK TRINKAUS Department of Anthropology, University of New Mexico, Albuquerque, New Mexico 87131 KEY WORDS Femora, Homo erectus, Homo habilis ABSTRACT Kennedy (1983) has proposed that the KNM-ER 1481A femur represents Homo erectus and establishes the presence of this species a t ca. 2.0.myr BP. A reconsideration of her criteria for taxonomic attribution indicates that its morphology implies only that it is a n archaic member of the genus Homo. Its geochronological position, in conjunction with its morphology, suggest that it is best referred to H. habilis. Kennedy (1983)has argued that the largely complete hominid femur from below the KBS tuff in Area 131 in Koobi Fora, KNM-ER 1481A, should be included within the taxon Homo erectus. Since KNM-ER 1481 is dated to ca. 2.0 myr BP, she concludes that H. erectus appeared in East Africa a t least 0.5 myr earlier than is generally maintained. Her discussion, however, does not take into account known patterns of femoral morphology within the genus Homo. Since attribution of the specimen to a specific taxon should consider chiefly those features that are unique to, and therefore diagnostic of, that taxon, the presence of a similar morphology in other closely related taxa would put the attribution into question. In other words, if the traits she employs to assign KNM-ER 1481 to H. erectus are found in the other recognized species of Homo (i.e., H. sapiens, since no other femora are securely attributed to H. habilis), it would no longer be justifiable to maintain it in H. erectus strictly on morphological grounds. Kennedy (1983) distinguishes KNM-ER 1481A from the femora of Australopithecus and places it within Homo primarily on the basis of proximal femoral morphology, in particular the relative size of the head, the degree of anteroposterior neck flattening, and the amount of lateral flare of the greater trochanter. She also refers to features of the diaphysis, particularly the positioning of minimum diaphyseal breadth and the amount of cortical thickening, that she claims distinguish it from those A ustralopithecus. Although aspects of her argument regarding the attribution of KNM-ER 1481 to 0 1984 ALAN R. LISS, INC Homo could be questioned, I will here accept that attribution. I will limit myself to a discussion of her placement of the specimen within H. erectus. Kennedy employs three diaphyseal features of KNM-ER 1481A to place it within H. erectus. They are “small anteroposterior shaft dimensions” (1983: p. 4311, “the point of minimum transverse shaft diameter is placed more distally than in H. sapiens” (1983: p. 431), and “extreme medullary stenosis of the shaft” (1983: p. 432). It is true, as documented by Weidenrich (1941) and Day (19711, that these features are characteristic of H. erectus femoral diaphyses. However, they do not necessarily distinguish KNM-ER 1481A from those of Middle and early Upper Pleistocene archaic H. sapiens. KNM-ER 1481A clearly has small anteroposterior (AP) diaphyseal diameters relative to those of most more recent humans (Table 11, whether one uses the measurements provided by Kennedy (1983) or by Day et al. (1975) and Leakey et al. (1978) for the specimen. Its midshaft AP diameter falls a t or slightly below the minimum values for more recent samples of archaic humans (including the H. erectus sample), its midshaft AP diameter is separate from those of early anatomically modern humans, and its proximal AP diameter is toward the lower end of the ranges of variation of all the more recent fossil human samples. However, only the comparison of KNM-ER 1481A midshaft diameter to those of early anatomically modReceived September 30,1983; accepted January 23, 1984 138 E.TRINKAUS T A B L E 1. Comparisons of the KNM-ER 1481A diaphyseal morphometrics to those o f fossil samples of the genus Homo' KNM-ER 1481A 76.4k 9.7 54.3 - 99.2 24 80.4+ 4.4 73.5 - 89.1 15 73.3 69.5 - 78.1 3 65.4 62.3 - 67.6 3 74.6 32.1k 4.3 24.9 - 41.3 24 29.7+ 4.0 22.2 - 36.0 14 27.4& 4.1 21.5 - 31.5 118.42 13.1 91.1 - 142.3 24 100.1+ 8.5 86.7 - 114.1 14 97.4k 6.8 89.6 - 106.9 70.2 21.7 X+SD Range N __ X+SD Range N X+SD Range N XkSD Range N Day et al. (1975) 26.5+ 2.8 22.0 - 33.0 24 25.6+ 7.0 21.4 - 31.0 15 23.8 19.6 - 26.8 3 23.1 22.7 - 23.3 3 23.0 Kennedv (1983) 22.0 ~ Pre-Neandertal Archaic H. sapiens4 H. erectus5 Pilastric index Meric index - Early Anat. Modern Humans' Neandertals3 Midshaft A P diaphyseal diameter (mm) Proximal AP diaphyseal diameter (mm) ~ 5 24.92 1.6 22.8 - 27.1 22.5 5 84.7+ 5.9 75.5 - 91.2 6 88.9 85.7 'Data from Day (19711, Trinkaus (1976, 1983, pers. observ.), Vandermeersch (1981), and Weidenreich (1941). 'Includes specimens from the sites of Brno, Combe-Capelle, Cro-Magnon, Grimaldi, MladeE, Paviland, PEedmosti, Qafzeh, La Rochette, and Skhul. 31ncludes specimens from the sites of Amud, Biscegli, La Chapelle-aux-Saints, La Ferrassie, Fond-de-For& Hortus, Krapina, Neandertal, La Quina, Shanidar, Spy, and Tabun. 41ncludes specimens from the sites of Ehringsdorf, Gesher Benot Ya'acov, Sedia-del-Diavolo, and Tabun. 51ncludes Olduvai OH28 and the Zhoukoudian femora. ern humans shows a significant difference (more than 2 SD from the more recent sample mean). Furthermore, if one compares meric and pilastric indexes, and hence periosteal diaphyseal proportions rather than just AP diameters, any difference between this specimen and more recent archaic human samples disappears. In fact, the meric and pilastric indexes of KNM-ER 1481A fall between those of the H. erectus sample and the Pre-Neandertal archaic H. sapiens sample and close to those of the Neandertal sample. Again, it is significantly different from more recent human fossil samples only in the midshaft comparison with the early modern human sample. It is therefore apparent that AP diaphyseal flattening was characteristic of most archaic Homo individuals. Although the H. erectus femoral diaphyses show the most extreme flattening on the average, similar AP flattening is not unusual among archaic H. sapiens. It does not align KNM-ER 1481A exlusively with H. erectus, especially since the degree of diaphyseal flattening is not known for H. habilis. As stated by Day et al. (1975), the KNMER 1481A diaphysis has its point of minimum breadth located distal to midshaft. This pattern, as noted by Kennedy (1983),is present among the H. erectus femora from Bed IV Olduvai Gorge and Locality 1 Zhoukoudian (Day, 1971; Weidenrich, 1941) and largely absent from those of anatomically modern humans (Trinkaus, 1976). However, it is also evident in most of the sufficiently complete and undistorted femoral diaphyses of archaic H. sapiens, such as Amud 1, Ehringsdorf 5, La Ferrassie 1 and 2, Gesher Benot Ya'acov 1, Neandertal 1, Spy 2, and Tabun E l . Some of these, such as Amud 1, Ehringsdorf 5, La Ferrassie 1 and 2, and Tabun E l , show the morphology clearly, whereas it is less apparent in the other femora. It is the product, as previously recognized (McCown and Keith, 1939; Trinkaus, 19761, of a buttress along the medial proximal diaphysis. In the more robust femora of archaic H. sapiens and H. erectus it extends across midshaft and thus displaces the point of minimum breadth distal to midshaft. Its presence in KNM-ER 1481A is therefore not surprising, if the specimen derives from a n archaic member of the genus Homo, but it does not align KNM-ER 1481A morphologically solely with specimens generally included within H. erectus. KNM-ER 1481A exhibits medullary stenosis, according to Kennedy (19831, a feature that has been recognized as characteristic of H. erectus femora since the work of Weiden- 139 KNM-ER 1481A AFFINITIES rich (1941).It is rare that femora of anatomically modern humans possess the extreme medullary stenosis seen in H. erectus, although a number of specimens of archaic H. sapiens approach the condition of the H. erectus femora (Weidenrich 1941; Trinkaus, personal observation). However, it should be recognized that medullary stenosis is a secondary feature of normal endosteal bone deposition in response to elevated and/or prolonged levels of biomechanical stress, a pattern which is easily promoted during development (Tschantz and Rutishauser, 1967; LiSkova and Heit, 1971; Goodship et al., 1979). Since other H. erectus postcrania, as well as external features of their femora, exhibit a level of robusticity rarely seen among H. sapiens, archaic or modern (Weidenrich, 1941; Day, 19711, it is to be expected that they would have had femoral diaphyseal hypertrophy, reflected in part by endosteal bone deposition. Similarly, the postcrania attributed to H. habilis, which are roughly contemporaneous with KNM-ER 1481, are exceptionally robust (Susman and Creel 1979; Susman and Stern 1982; Susman et al. 1983); if KNM-ER 1481 is a member of H. habilis, some hypertrophy of the femoral diaphysis (of which medullary stenosis would be a product) would not be surprising. The medullary stenosis of KNM-ER 1481A is therefore best regarded as one reflection of early hominid postcranial robusticity, rather than a specific characteristic of H erectus. It is therefore apparent that KNM-ER 1481A has morphologic features, especially of the diaphysis, that align it with archaic members of the genus Homo in general. Its morphologic affinities do not rest exclusively with H. erectus. Given its stratigraphic association at Koobi Fora with cranial remains of H habilis (e.g., KNM-ER 1470,1590,3732) and its robusticity similar to that of the slightly more recent H. habilis postcrania from Bed I Olduvai Gorge (e.g., OH 7, 8, 351, a n equally reasonable conclusion is to consider KNM-ER 1481 a s a member of H. hubilis. It does not establish the presence of Homo erectus a t ca.2.0 myr BP. Not only is Kennedy’s (1983) analysis of KNM-ER 1481A mistaken in concluding that this femur extends the origin of H. erectus to ca.2.0 myr BP, but it misses a significant implication of its morphologic similarities to the femora of H. erectus and archaic H. s a p iens. The resemblances between these femora from ca. 2.0 myr BP to the middle of the Upper Pleistocene suggest considerable stasis in the patterns, and to a lesser extent levels, of biomechanical stress through this region of hominid anatomy, a conclusion similar to that of Susman et al. (1983) in their analysis of the KNM-ER 3228 and OH 28 ilia and ischia. This implies that there was a pattern of locomotor activity characteristic of archaic members of the genus Homo not present among members of Australopithecus or anatomically modern H. sapiens. Since all of these hominids were fully bipedal, the differences probably lie in the relative frequencies and durations of various locomotor activities, activities related to the contemporaneous evolution of the hominid cultural system. LITERATURE CITED Day, MH (1971) Postcranial remains of Homo erectus from Bed IV, Olduvai Gorge, Tanzania. Nature 232:383-387. 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