AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 52:63-70 (1980)
New Estimates of Early Hominid Body Size
KAREN STEUDEL
Department of Zoology, University of Wisconsin, Madison, Wisconsin 53706
KEY WORDS
Allometry, E a r l y hominids, Body
size
ABSTRACT
Body weights for 12 early hominid specimens are estimated based
on an analysis of four variables shown to have high correlation with body size in
living Old World primates. Average size estimates of around 36 kg a r e suggested
for gracile early hominids and around 59 kg for robust early hominids. Size variation is considerably more pronounced in the robust group than in the gracile group,
suggesting substantially greater sexual dimorphism in the former.
One of the troublesome aspects ofthe study of
early horninids has been the size differences
found among the remains. The terms "gracile"
and "robust," widely used to refer to the two
major divisions within this group, emphasize
t h e obtrusiveness of t h e size difference.
Hominid paleontologistshave expressed a wide
variety of views on the implications of these
size differences in determining the adaptive
niche of each group (Brace, '72; Pilbeam and
Gould, '74; Robinson, '63). An integral part of
any study hoping to address this question is the
determination of the effects of size differences
on morphology i n primates generally, particularly in hominoids. But even with this kind of
information, the application to early hominids
requires some fairly reliable estimate of the
body size of the fossils-a difficult datum to get
given the fragmentary state of most fossil specimens. The present paper describes an attempt
to make body size estimates on early hominids.
A number of workers have previously estimated body size for early hominids (McHenry
'74, '75, '76; Lovejoy and Heiple, '70; Reed and
Falk, '77; Robinson, '72).This study attempts to
improve on previous efforts by using as estimators a series of variables found to have a
very high correlation with body size and low
standard errors across living Old World higher
primates, including man.
MATERIALS AND METHODS
The estimation of body size from fragmentary fossil specimens requires one or a few variables that can be measured in the fossils and
are known to be reliable predictors of body size.
Since body proportions in the early hominids
may well have differed both from living apes
0002-9483/80/5201-0063 $01.70 0 1980 ALAN R. LISS, INC.
and modern man, it seemed desirable to find
variables that were highly correlated with size
in primates showing a wide range of sizes and
body proportions. To arrive a t a series of predictor variables, the present study determines
the correlation between 25 individual variables
and body size for a series of Old World monkeys,
apes, and man. A variable that has a very high
correlation with size across this range of primates is likely to be effective also in the prediction of size among fossil hominoids.
Partial skeletal weight was used here to represent body size. This measure is composed of
the combined weights of skull, mandible, both
femurs, both humeri, the pelvis including sacrum, and both scapuli. These bones were chosentorepresent skeletal weight because they account for most of the total weight of the skeleton and are usually present in museum skeletal
specimens. Smaller elements, especially ribs
and phalanges, are often missing. The obvious
alternate to this would be total body weight as
measured a t the time of death. Skeletal weight
was preferred for a number of reasons. First, it
is available on a much greater range of specimens. Second, recorded weights a t time of
death sometimes seem suspicious. In the excellent Haman-Todd collection of autopsied humans in Cleveland, for example, many body
weights given were amazingly low given the
height of the individual. A number of adult
males with heights a little over 5 ' 8 had body
weights of only 104-105lbs. The photographs of
the individuals included in the file confirmed a
state of extreme emaciation. Another male of
similar height weighed 155 lbs a t death. This
type of extreme variation in nutritional level,
particularly in humans, would be a source of
63
64
KAREN STEUDEL
undesirable variation. Finally, when considering female primates, the use of body weight
raises the question of whether weight should be
measured i n lactating females, pregnant
females, or ones temporarily in neither state.
(This information is rarely included with body
weight at death of specimen in collections. Thus
using body weight at death would presumably
include females in all these states, except
perhaps advanced pregnancy, adding additional variation to size estimates.) The greater
weight of a pregnant or lactating female
is often seen as a temporarily abnormal increase, but since feral females can spend most
of their adult life in one or the other condition,
natural selection may very well result in
skeletal adjustments to this elevated body size.
Using skeletal weight avoids these difficulties.
The main drawback in the use of skeletal
weight as a size estimator is differences in the
means of preparation of the skeleton which affect the amount of fat remaining in the bones
and hence their weight. This is difficult to control since precise data on preparation (other
than the use of dermestid beetles versus chemicals and so on) are often lacking. In my data the
greasiest bones were in the Haman-Todd collection. Bones from the other institutions
seemed very comparable to one another. My
samples of chimpanzees and gorillas include
significant numbers from both the HamanTodd collection (23 and 28 individuals, respectively) and from other collections (16 and
17 individuals). Yet ranges of variation in
skeletal weight for these taxa are not unusually high even when compared to H. sapiens, a
species with relatively little sexual dimorphism and one in which all individuals are from
a single (Haman-Todd)collection (see Figures 2
or 4 for illustration). The range of variation in
logskeletal weight was 2.4S2.75 inH. sapiens,
2.363.58 in Pan, and 2.53-2.97 in Gorilla. I
would thus expect that while differences in
skeletal preparation will be a source of error
tending to lower the correlation coefficients
and the standard errors of the estimates, the
magnitude of this variation is not a problem in
the data used here.
The species included in the study and their
sample sizes are given in Table 1. Nonhuman
primates are from the wild. The specimens
measured are housed in the following collections: Anthropologisches Institut, Zurich;
British Museum (Natural History), London;
Field Museum, Chicago; Haman-Todd Collection, Cleveland Museum of Natural History;
Museum of Comparative Zoology, Harvard;
and the Smithsonian Institution, Washington,
D.C.
TABLE 1
Macaca sp.
Nasalis laruatus
Presbytis cristatus
Papio sp.
Colobus sp.
Cercopithecus mitis
Pan troglodytes
Gorilla gorilla
Pongo pygmaeus
Hylobates lar
Homo sapiens
Total
9
d
18
12
17
11
3
15
4
4
11
2
24
25
9
16
12
14
6
15
20
13
16
19
286
All twenty-five variables studied were
measured by the author using sliding calipers.
Only those variables chosen because of their
value as size estimators are discussed here. The
allometric relationships of the remaining variables will be discussed separately. Skeletal
weights were measured to the nearest tenth of a
gr-.
All linear variables were transformed to
logarithms; in the case of skeletal weight, the
log of the cube root of the raw measurement was
used for comparison with the otherwise linear
data. Each variable was then plotted against
body size as represented by skeletal weight
over all species, and corresponding least
squares regression and linear correlation
analyses were performed and standard errors of
the estimates calculated for each variable.
Those variables that were found to be good
predictors of size were then used to estimate
body size for those fossil specimens for which
measurements of one or several of the sizerelated variables were possible. The following
cranial specimens were taken as examples of
the gracile early hominid, Homo africanus: Sts
5, Sts 17, and Sts 19. Crania taken to represent
the robust type, Paranthropus robustus, include: SK 11,SK 46, SK 48, SK 52, SK 79, TM
1517a, and KNM-ER 406. Femoral specimens
included KNM-ER 815 and KNM-ER 738 as
representatives of the gracile type, and OH 20,
SK 82, and SK 97 as representatives of the
robust type. The taxonomic assignments of the
femoral specimens are based on the author’s
study of the original material. One questionable specimen, KNM-ER 736, sometimes considered a possible example of a robust early
hominid is also plotted, but its taxonomic assignment is very questionable. Measurements
of the fossil specimens were taken by the author
at the National Museums of Kenya, Nairobi;
Transvaal Museum, Pretoria; and the Department of Anatomy, University of the Witwatersrand, Johannesburg.
EARLY HOMINID BODY SIZE
65
for gracile and robust early hominids, the range
of size variation seen within each taxon, and a
Of the twenty-five variables included, many comparison of the size values predicted by difhad a considerable correlation with body size, r ferent estimators on particular specimens.
For all four estimators, gracile early hom> 0.8. But even a t this fairly high level of correlation much of the variation is non-size-related, inids fall with female chimps and orangs,
giving lower confidence to any predictions. often toward the smaller end. This is true for all
Since several of the variables had correlations five specimens on both cranial and the one
with size greater than 0.95, it was decided to femoral dimension. A considerable amount of
use only these for prediction. Plots of these confidence in these estimates seems warranted
highly correlated variables against body size when the size values of Sts 5 as predicted by
revealed that in some cases the sample of mod- several different estimators are compared. Sts
ern man fell nicely along the regression line, 5 is the only gracile hominid on which several
but just above or just below the ape values. estimators could be used. In two graphs Sts 5
Since we are dealing with fossils that may be falls with the smallest female apes with values
intermediate between these groups and may be of 2.39 and 2.34. In the third, bizygomatic
more similar to man, it seemed wise to elimi- breadth, Sts 5 (at 2.47) is closer to average Pan
nate these variables also. These variables were or Pongo females. Thus these predictors agree
closely in their several estimates of the body
then chosen that satisfied these criteria-high
correlation with size, low standard errors, and size of the one individual. The size estimates for
modern man not deviating from the pattern of different gracile specimens also tend to cluster
ape variation. These were palate breadth, r = very near one another in all cases, suggesting
0.96, bizygomatic breadth, r = 0.98; orbital that the overall size variation in this taxon was
width, r = 0.97; and circumference of the femur not very great.
takenjustbelow the lesser trochanter, r = 0.98.
Secure estimates for the body size of the
The positions of individual fossil specimens robust early hominids are more difficult to obfor which each measurement was available tain since values estimated for a single speciwere then added to the regression line based on men vary much more than in the case of Sts 5.
the extant species, indicating the predicted size Three robust specimens were suitable for makof each fossil. Those fossils that had several of ing two or more measurements: S K 48,
the predicting dimensions available have sev- KNM-ER 406, and TM 1517(a). For TM
eral independent estimations of their size. 1517(a), in which both palate breadth and
Skeletal weight estimates (in logarithms) for bizygomatic breadth could be measured, the
the fossils are as follows: for palate breadth - Sts agreement was quite close. In both cases this
17 2.39, Sts 5 2.39, SK 48 2-44, SK 112.33, SK specimen fell with male Pongo, though in one
79 2-40, SK 52 2-46, SK 46 2-46, TM 1517(a) case a t the top end of this group and in the other
2-59, and KNM-ER 406 2-54. Standard error of case toward the lower end. SK 48 and KNM-ER
the estimate for this relationship gives a 95% 406, however, varied quite a bit more (compare
confidence interval of 2 0.234 about each Figures 1-3). The former specimen has size esvalue. Estimates based on bizygomatic breadth timates ranging from female chimp or orang to
are: Sts 5 2.47, Sts 19 2-50, SK 48 2.67, TM male orang; whereas the latter is estimated
1517(a)2.74, and KNM-ER 406 2.94. The 95% between average-sized orang to large male
confidence interval here is i 0.162. Estimates gorilla. One is left to decide, therefore, which of
based on orbital width are: Sts 5 2-34, SK 48 these estimates seems most secure. This is dis2-45, and KNM-ER 406 2.77, with a 95% confi- cussed below.
In spite of difficulties encountered in arrivdence interval of 0.211.Femoral circumference
gives the following estimates with a 959 confi- ing a t estimates of absolute size, there seems to
be a consistent tendency for the size values of
dence interval of 0.172: KNM-ER 736 2.81,
KNM-ER 815 2.47, KNM-ER 738 2-47, OH 20 the several robust specimens determined by
2.64, SK 82 2-59, and SK 97 2-64. For compari- each estimator to vary much more widely than
son the average values for skeletal weight in do values among gracile specimens. The only
departure from this comes from the femoral
comparable living hominoids are 2.50 and 2.45
for male and female Pan, 2-85 and 2-64 for estimates in which neither group shows very
Gorilla, 2.66 and 2.47 forPongo, 2-64 for men, wide variation, unless KNM-ER 736 is considand 2-56 for women. The graphs of each vari- ered to belong to the robust type, a point which
able versus size and the positions of the fossil is by no means clear, in which case the robust
form would show much greater variation of this
specimens are shown in Figures 1-4.
There are three aspects of these data which dimension also. Based on palate breadth the
are particularly interesting: the size estimates robust specimens vary from a value just below
RESULTS
66
KAREN STEUDEL
1.6
1
1.8
2.0
2.2 2.4
SIZE
2.6
2.8
3.0
I
l-
a
a
w
cr
rn
a
z
0
I-
0
(3
>
N
-
m
2
1 . 5 t 1 1 1 ' ~ " ' ~ ' ~ ' i ' " 1 1 ' ' i 1 1 ' 1 ' 1 ' i
1.6
1.8 2.0 2.2
2.4
2.6
2.8 3.0
SIZE
Figs. 1-4. The relationships between four skeletal variables (palate breadth, bizygomatic breadth, orbital
width, and femoral circumference) and size ( = partial skeletal weight). In each figure the cluster of points in the
lower size range represents various monkeys and gibbons. 2 = Gurillu, Y = Pongo, = Pun, = H . supiens, X =
Pupzo.The sample sizes of many species have been reduced for these plots to make individual symbols legible.
67
EARLY HOMINID BODY SIZE
2.5I
2 .o
I
t-
n
5
1.5
-I
a
m
1.0
c
0
*
3
SIZE
3*0
t
W
KNM-Enb
7 2 C
I J U
KNM-ER 738 8
KNM-ER 815
O&
4
I
I
1.6
I
I
I '
1.8
I
' I i 1 ' I
2.0
'
1
2.2
SIZE
'
1
'
2.4
1
'
1 " " " '
2.6
2.8
3.0
68
KAREN STEUDEL
TABLE 2 Size estimates for individual fossil specimens'
Robust specimens
TM 1517(a) Average male orang
SK 48
Averagelarge female orang
ER 406
Large male orang
SK 46
Average female orang
OH 20
Slightly smaller than average male orang
SK 82
Slightly smaller than average male orang
SK 97
Slightly smaller than average male orang
SK 11
Small female orang
SK 79
Female orang
Gracile specimens
Female orang
ER 815
ER 738
Female orang
Sts 5
Small female orang
Sts 19
Large female orang
Sts 17
Average female orang
I
For comparison, Napier and Napier '67 give average hody welght
estimates for living apes a s f o l l o w x d a n d ?Pan 49 kg a n d 41 kg,
respectively ( N = 7 ) ; 69 kg and 37 kg f o r d a n d OPongo cN = 91; and
160 kg and 92 kg f o r d a n d ? Gorrlla tN = 21).
the smallest female orang to male orang,
whereas the two gracile specimens, Sts 5 and
Sts 17, are very close t o each other. Of course in
this case the relatively small range among
gracile specimens could well be due to the small
sample size (N = 21, but other dimensions show
the same pattern. For bizygomatic breadth Sts
5 and Sts 19 fall close together, whereas the
robust estimates vary from the size of female
gorillas to a value just above the largest male
gorillas. Values based on orbital width also
suggest a wide size range for robust early
hominids, varying from a value with female
orangs and chimps t o a value between the largest male orangs and the smallest male gorillas.
Thus it seems reasonable to conclude that the
range of size variation in robust early hominids
was considerably greater than that among
gracile early hominids. In the former group,
variation in size seems comparable to that seen
in modern orangs, the apes showing greatest
sexual dimorphism; whereas in the latter
group, the variation seems to be no greater
than that in modern chimps, perhaps considerably less. For comparison, Napier and Napier
('67) give values for female body weight as percentage of male body weight as 54% and 83% for
Pongo and Pan, respectively.
DISCUSSION
Before one is able t o draw conclusions about
the absolute body size of robust early hominids,
consideration must be given to the differences
in size values assigned to SK 48 and KNM-ER
406 by their several estimators. Since the size
estimates for each specimen varied considera-
bly between estimators, one must decide where
in this range the actual size of the specimens is
most likely to lie. It appears that the difficulty
is not with the estimators themselves, since all
three estimates on Sts 5 agree very closely. The
nonagreement in size estimates here is a
problem unique to the robust early hominids.
On reflection, I suppose that this should not be
very surprising. When the relationship between a variable and size has been determined
over a particular series of animals, predictions
based on that relationship cannot safely be extended to animals that differ substantially
from this series in the characteristics of that
variable, a point alluded to by Gingerich ('77)
and Reed and Falk ('77). Yet the marked dietary specializations of robust early hominids
have been remarked on by a number of authors,
especially Robinson ('61, '72) and Du Brul('77).
Since two of the predictor variables used here
measure traits closely related to dietary habits,
it seems probable that these traits do not show
the same proportions with respect to size seen
in dietarily less specialized primates and hence
are less accurate estimators for this specialized
taxon.
For this reason, in determining the weights
of the robust specimens, I am inclined to weight
more heavily those variables that are not so
functionally tied t o diet. Orbital width seems t o
be the cranial estimator that is least likely to be
influenced by adaptive factors that would differ
in a more extreme herbivore from dietarily less
specialized primates. In my estimates of robust
hominid body weights, therefore, I will place
most reliance on orbital width and femoral circumference. Even with this adjustment, however, one cannot have as much confidence in the
values for the absolute size of particular robust
specimens as one can for gracile specimens.
With this in mind, the following estimates of
robust hominid absolute body size are
suggested. Since TM1517(a) has only palate
breadth and bizygomatic breadth available as
size estimators, one cannot rely on non-dietrelated variables. Fortunately in this case the
two estimates agree fairly closely. The specimen falls with small male orangs in one case
and large male orangs in the other, suggesting
that an overall size value of average male orang
would not be far off. SK 48 falls with female
orangs on both orbital width and palate
breadth. The estimate for bizygomatic breadth,
sorting this specimen with male orangs, is
probably an overestimate. The conspicuous
flaring of the zygomatic arches of robust early
hominids recognized by most workers (e.g., Du
69
EARLY HOMINID BODY SIZE
Brul, '77; Leakey et al., '71; Robinson, '62)
causes this dimension to be relatively larger
than in any other primate considered here.
Thus a size approximately that of a female
orang seems most likely-though perhaps one
on the large side-if one does not wish to discount the bizygomatic breadth estimate completely. KNM-ER 406 is consistently very
much larger than SK 48 on all shared dimensions. Orbital width, probably the most reliable
cranial estimator for robust hominids, puts the
size of this specimen as about that of a small
male gorilla. The bizygomatic breadth estimate, larger than the largest male gorilla, is
almost certainly a n overestimate for the reasons given above. The remaining variable gives
a lower estimate. Taking these into account, a
size similar to that of a largish male orang
seems reasonable.
SK 48 is not the smallest robust hominid as
indicated by these data. Specimens SK 11and
SK 79 are both somewhat smaller, whereas S K
46 and SK 52 seem to be only slightly larger.
TM1517(a)and KNM-ER 406 are both substantially larger than the former group. This very
considerable variation between specimens contrasts sharply with the similarity in size of the
gracile specimens. It seems indicated that the
range of size variation in the robust specimens
was much greater than that among the gracile
specimens, akin to that seen in modern orangs.
Since among primates size variation is usually
closely related to sexual dimorphism, it would
seem that the robust hominids must have
shown considerable sexual dimorphism. This
conclusion based on present size estimates is
consistent with the general appearance of great
size variation among robust specimens in both
the South African and East African collections
(Leakey, '72; McHenry, '74; Robinson, '62).
To reach final estimates on the absolute sizes
of the early hominid groups, the estimates here
can be compared with those made by other authors using other methods and specimens.
Robinson ('72) has estimated the body weight of
a female H . ufricanus as approximately 2&25
kg based on Sts 14. He makes a more tentative
suggestion of around 80 kg as a n average for
Purunthropus. The figure of 2&25 kg for H .
ufricunus seems t o be a little on the low side
compared to my data; however if Sts 5 is indeed
a male and Sts 14 is a female, as Robinson ('72)
has suggested, our estimates may be mutually
consistent. Since Sts 5 falls with small female
apes, a weight estimate might be around 32-35
kg. Females of this taxon might be expected to
be somewhat smaller. Since all the other
gracile specimens studied here are as large or
larger than Sts 5, however, my data do not
support the existence of gracile specimens of
the smaller size range. On the other hand,
McHenry ('75) estimates the size of Sts 14 as
about 27 kg based on the vertebrae only, corroborating Robinson's view of the small size of
that specimen. Using the same estimator,
McHenry ('75) suggests a size of around 36 kg
for the robust specimen SK 3981. This fits well
with my estimates of the size of the smaller
robust individuals. My data also lead me to see
the average size for Purunthropus as a little
smaller than the average suggested by Robinson. In the present data the smaller robust
crania (females?) tend to fall with average
female orangs and chimps (average = 41 kg,
according to Napier and Napier, '671, whereas
the larger crania fall with male orangs (69 kg,
as estimated by Napier and Napier, '67). All
included femoral specimens, however, are also
in the male orang range. So an average of 57-60
kg would seem reasonable. McHenry ('76) also
has some size estimates based on fossil femurs,
although his multiple correlation coefficientfor
his several variables was only 0.68. His estimate of 43 kg for KNM-ER 738 is in reasonable
accord with predictions from the present study.
His estimates of 50 and 53 kg for SK 82 and SK
97, respectively, however, seem low compared
to my results, which suggest a figure of around
70 kg. It is possible that my results slightly
overestimate body weight because of the quadrupeds included. But even so these robust specimens fall with average-sized H . sapiens in my
results and with small H . supiens in McHenry's. The higher correlation with size of
my circumferential measurement (r = 0.98)
gives me greater confidence in my figures. So a
size of 6 5 7 0 kg for the individuals represented
by the robust femurs seems a good estimate.
CONCLUSIONS
Average size estimates of around 36 kg for
gracile early hominids and around 59 kg for
robust early hominids are suggested. The range
of variation seen here between specimens of
each taxon suggests substantially greater sexual dimorphism among robust than among
gracile hominids. A level of sexual dimorphism
similar to that of modernPongo is suggested for
the former and a level akin toPun for the latter.
Absolute size estimates of robust specimens are
less consistent than those of gracile specimens.
It is suggested that this is due to greater deviation by the robust types from the patterns seen
in the reference series of living species.
70
KAREN STEUDEL
ACKNOWLEDGMENTS
I would like to thank Dr. J. T. Robinson for
helpful criticisms of the manuscript and Ms.
Cheryl Hughes for preparing the figures. The
data were gathered with the financial support
of National Science Foundation grant GS42706.
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