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Does KNM-ER 1481A establish Homo erectus at 2.0 myr BP0

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Does KNM-ER 1481A Establish Homo erectus at 2.0 myr BP?
Department of Anthropology, University of New Mexico, Albuquerque, New
Mexico 87131
Femora, Homo erectus, Homo habilis
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
T A B L E 1. Comparisons of the KNM-ER 1481A diaphyseal morphometrics to those o f fossil samples
of the genus Homo'
76.4k 9.7
54.3 - 99.2
80.4+ 4.4
73.5 - 89.1
69.5 - 78.1
62.3 - 67.6
32.1k 4.3
24.9 - 41.3
29.7+ 4.0
22.2 - 36.0
27.4& 4.1
21.5 - 31.5
118.42 13.1
91.1 - 142.3
100.1+ 8.5
86.7 - 114.1
97.4k 6.8
89.6 - 106.9
Day et al. (1975)
26.5+ 2.8
22.0 - 33.0
25.6+ 7.0
21.4 - 31.0
19.6 - 26.8
22.7 - 23.3
Kennedv (1983)
H. sapiens4
H. erectus5
Early Anat.
Midshaft A P
Proximal AP
24.92 1.6
22.8 - 27.1
84.7+ 5.9
75.5 - 91.2
'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-
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
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