Journal of Human Evolution 46 (2004) 433–465

8/14/2019 Journal of Human Evolution 46 (2004) 433465

1/33

Body proportions of Homo habilis reviewed

Martin Haeuslera,b,*, Henry M. McHenrya

aDepartment of Anthropology, University of California, Davis, CA 95616, USAbAnthropologisches Institut und Museum, Universitaet Zuerich-Irchel, 8057 Zuerich, Switzerland

Received 15 October 2002; accepted 21 January 2004

Abstract

The ratio of fore- to hindlimb size plays an important role in our understanding of human evolution. Although

Homo habilis was relatively modern craniodentally, its body proportions are commonly believed to have been more

apelike than in the earlier Australopithecus afarensis. The evidence for this, however, rests, on two fragmentary

skeletons, OH 62 and KNM-ER 3735. The upper limb of the better-preserved OH 62 from Olduvai Gorge is long and

slender, but its hindlimb is represented mainly by the proximal portion of a thin femur of uncertain length.

The present analysis shows that upper-to-lower limb shaft proportions of both OH 62 and AL 288-1 ( A. afarensis)

fall in the modern human range of variation, although OH 62 also falls inside that of chimpanzees due to their overlap

in small individuals. Despite being more fragmentary, the larger-bodied KNM-ER 3735 lies outside the chimpanzeerange and close to the human mean. Because the differences between any of the three individuals are compatible with

the range of variation seen in extant hominoid groups, it is not legitimate to infer more primitive upper-to-lower limb

shaft proportions for either H. habilis or A. afarensis.

Femur length of OH 62 can only be estimated by comparison. Its closest match in size and morphology is with the

gracile OH 34 specimen, which therefore provides a better analogue for the reconstruction of OH 62 than the stocky AL

288-1 femur that is traditionally used. OH 34s slender proportions are hardly due to abrasion, but match those of a

modern human of that body-size, suggesting that the relative length of OH 62s leg may have been human-like. Brachial

proportions, however, remained primitive. Long legs may imply long distance terrestrial travel. Perhaps this adaptation

evolved early in the genus Homo, with H. habilis providing an early representative of this important change.

2004 Elsevier Ltd. All rights reserved.

Keywords: Early hominids; Limb length proportions; Humero-femoral index; Brachial index; Locomotion; Human evolution

Introduction

Homo habilis has been considered to be the

earliest member of the genus to which modern

humans belong (Leakey et al., 1964). Having a

slightly larger brain size and smaller teeth com-

pared to the australopithecines, it was thought to

* Corresponding author. Tel.: +41-1-635-54-33;

fax: +41-1-635-68-04

E-mail addresses: [email protected] (M. Haeusler),

[email protected] (H.M. McHenry).

Journal of Human Evolution 46 (2004) 433465

0047-2484/04/$ - see front matter 2004 Elsevier Ltd. All rights reserved.doi:10.1016/j.jhevol.2004.01.004


2/33

be able to make the first stone tools. The validity

and phylogenetic position of this taxon, however,

and whether its hypodigm contains one or two

species, have remained contentious since its dis-

covery (e.g., Robinson, 1965, 1966, 1972; Stringer,

1986; Wood, 1987, 1992; Lieberman et al., 1988;

Kramer et al., 1995; Wood and Collard, 1999;

Miller, 2000; Blumenschine et al., 2003; Tobias,2003). Nevertheless, phylogenetic analyses have

repeatedly associated the cranial evidence of H.

habilis, in particular that of the KNM-ER 1813

subset, referred to as H. habilis sensu stricto, with

later Homo (e.g., Wood, 1992; Lieberman et al.,

1996; Strait et al., 1997). The many intermediate

features of a recently discovered skull from

Dmanisi, Georgia (Vekua et al., 2002), further

strengthen the relationship between H. habilis and

H. erectus.

Important aspects of the postcranial mor-

phology ofHomo habilis sensu stricto, however, do

not appear to resemble later species of Homo

(McHenry and Coffing, 2000, and references

therein). Particularly conspicuous is the size of

the forelimbs relative to the hindlimbs in the

w1.8 million year old partial skeleton from

Olduvai Gorge, Tanzania (OH 62; Johansonet al., 1987; Johanson, 1989). The humerus, radius,

and ulna of this specimen seem to be long and

relatively robust compared to the neck and shaft

breadth of the femur (see Fig. 1). When the

surviving portions of the OH 62 limbs are com-

pared to the best preserved Australopithecus

afarensis specimen, AL 288-1 (Lucy), H. habilis

appears more primitive than its purported ancestor

(Johanson et al., 1987; Hartwig-Scherer and

Martin, 1991). Its reconstructed humerus length

Fig. 1. The partial skeletons of AL 288-1 (A. afarensis), OH 62, and KNM-ER 3735 (H. habilis) superimposed on the drawings byJ. Gurche of the A. afarensis skeleton (see Berger et al., 1998). The skeletal drawings are arbitrarily of identical size, although actualbody size might have differed considerably between the three specimens. Note the longer arm skeleton and more gracile proximalfemur of OH 62 compared to AL 288-1.

M. Haeusler, H.M. McHenry / Journal of Human Evolution 46 (2004) 433465434


3/33

considerably exceeds that of AL 288-1, although

humerus shaft diameters are roughly similar and

femur shaft diameters are less than those of AL

288-1. Johanson and colleagues (Johanson et al.,1987) speculated, therefore, that its humero-

femoral ratio might have been 95% or more, as

compared to values of 85% for AL 288-1, 72% for

Homo, and 100% for Pan. In contrast to the

humerus, which lacks its proximal and distal

articular ends, only a small portion of the femoral

neck and proximal shaft is preserved, and even less

is known of the proximal tibia. Korey (1990)

therefore cautioned that assuming a greater index

than that of AL 288-1 is not warranted, and also

that a value close to the human range cannot be

excluded. Yet, a second H. habilis partial skeleton,

KNM-ER 3735, despite being very fragmentary, is

also reported to possess upper-to-lower limb pro-

portions that possibly approximate those of

chimpanzees (Leakey et al., 1989).

This unexpected twist in hominid phylogeny is

further complicated by the observation that fore-

to-hindlimb joint size proportions seem to be

more humanlike in the earlier and craniodentally

more primitive A. afarensis than in the later and

craniodentally more humanlike A. africanus and

H. habilis (McHenry and Berger, 1998a).The primitive A. africanus-like body propor-

tions of H. habilis were an important factor in

Wood and Collards (1999) transferring this

taxon to the australopithecines as Australopithecus

habilis, thus concurring with other scholars who

doubted that the craniodental features of some

H. habilis specimens differed markedly from

Australopithecus , especially from A. africanus (e.g.,

Robinson, 1965; see also Blumenschine et al.,

2003). At first glance, the recent discovery of

2.5 million year old associated upper and lowerlimb bones contemporary with A. garhi with

an apparently humanlike humero-femoral ratio,

but apelike brachial length proportion, made it

seem even more unlikely that H. habilis was an

ancestor of later Homo (Asfaw et al., 1999). Their

taxonomic association is, however, not established

(DeGusta, 2003), but if they were conspecific with

A. garhi, the marked megadontia of that species

would raise further difficulties for it having been a

direct ancestor of H. habilis, whose oldest known

fossil is dated to only 0.2 million years later in time

(Kimbel et al., 1997).

The incongruencies between the cranial and

postcranial data ofHomo habilis rests, on the otherhand, almost exclusively on the length estimation

of OH 62s femur, using that of AL 288-1 as an

analogue (Johanson et al., 1987), and on the

comparison of KNM-ER 3735s shaft dimensions

with that of a single modern human and chimpan-

zee skeleton (Leakey et al., 1989). Yet, there are

many striking morphological differences between

OH 62 and AL 288-1. Not only is the OH 62

humerus longer than that of AL 288-1, it is also

slimmer, particularly distally, and even more so if

adjusted for its greater length. The same is true

for the ulna and most markedly for the femur

(Johanson et al., 1987). The overall impression,

therefore, is not of a robust skeleton, but of a

surprisingly gracile and slender one compared to

that of AL 288-1. As the craniodental characteris-

tics of OH 62 are also described as differing

considerably from those of AL 288-1 (Johanson

et al., 1987), it is doubtful whether the AL 288-1

femur is indeed a good model to estimate femur

length in this specimen.

Of all known early Pleistocene femora, the

slender OH 34 specimen from Olduvai Gorge (Dayand Molleson, 1976) is the only one to show a

remarkable morphological similarity to that of OH

62. Day and Molleson (1976: 455) wrote in the

abstract: their strange appearance resulted in

their neglect for many years. This neglect has

apparently continued.

After re-analysing shaft-proportions of the OH

62 and KNM-ER 3735 partial skeletons, the

present study will explore the usefulness of the OH

34 femur, instead of AL 288-1, as a basis to

estimate OH 62s femur length. In this context,another look will be taken at the issue of possible

abrasion of the OH 34 femur shaft.

Material and methods

Modern comparative sample

One set of our modern comparative materials

includes 139 modern humans with an emphasis on

M. Haeusler, H.M. McHenry / Journal of Human Evolution 46 (2004) 433465 435


4/33

small-bodied individuals: 8 Neolithics from

Switzerland (Anthropologisches Institut der

Universitat Zurich and Universite de Geneve),

6 Pygmies from Ituri (Universite de Geneve),7 Bushmen, and 6 Hottentots (University of the

Witwatersrand, Johannesburg). The remainder

is housed at the Anthropologisches Institut

der Universitat Zurich (composed mainly of

European, African, and Asian individuals) and the

Hearst Museum of the University of Berkeley,

California (prehistoric Californian Indians). The

sample of 79 Pan troglodytes (28 males, 40 females,

11 of unknown sex), 46 Gorilla gorilla (28 males, 18

females), and 32 Pongo pygmaeus (15 males, 17

females) comes from the Anthropologisches

Institut der Universitat Zurich, which also includes

the Adolph H. Schultz-Sammlung and the Boesch

Collection of Ta-chimpanzees; the Zoologisches

Museum Zurich; the Naturhistorisches Museum

Basel; the Museum de lhistoire naturelle de

Geneve; the University of the Witwatersrand,

Johannesburg; and the Transvaal Museum,

Pretoria.

The chimpanzee sample consists of a large por-

tion of captive specimens (39 versus 35 wild-

collected and 5 of unknown origin). Regression

analyses of the captive and wild-collected samplesshowed that, on average, captive chimpanzees

have slightly larger cross-sections of the arm skel-

eton relative to femur shaft dimensions than do

wild animals. The lower boundaries of the ranges

of variation are, however, almost identical in the

two groups. Thus, for the purpose of this study,

combining the two groups probably has no effect

on the relative position of the fossil hominids.

Additional data for long bone lengths of 36 Pan

troglodytes, 10 Pan paniscus, 11 Gorilla gorilla, 47

Pongo pygmaeus, and 194 Hylobates sp. werederived from the records of Adolph H. Schultz,

Anthropologisches Institut der Universitat Zurich.

A further 120 Homo sapiens, 74 Pan troglodytes (22

males, 54 females), 17 Pan paniscus (9 males,

8 females), 87 Gorilla (42 males, 45 females), and

41 Pongo (17 males, 24 females) stem from

McHenrys data set (McHenry, 1972, 1974, 1978,

1992; McHenry and Corruccini, 1975, 1978;

McHenry et al., 1976). Before combining these

data sets, they were tested for equality of the slopes

and intercepts of the regression lines with an

analysis of covariance (see Sokal and Rohlf, 1995).

Fossil material

The OH 62 skeleton was studied by M.H. at the

National Museum of Tanzania in Dar es Salaam

and by H.M.M. at the Institute of Human Origins.

It is dated to w1.8 Ma and includes several

hundred skull fragments, parts of the right arm,

the proximal left femur, and a right tibial tuber-

osity (Fig. 1; Johanson et al., 1987). Measurements

of the KNM-ER 3735 skeleton were taken by both

authors at the National Museum of Kenya, Nari-

obi. KNM-ER 3735 comes from the Upper Burgi

Member of the Koobi Fora Formation and is

dated to 1.88 to 1.91 Ma (Feibel et al., 1989),

making it slightly older than OH 62. Besides more

than 50 pieces of the skull and several short

fragments of limb bones, this associated skeleton

consists of a weathered partial sacrum, distal right

humerus, proximal right radius, distal left (right,

according to Leakey et al., 1989) femoral shaft, a

tibial mid-shaft fragment, and two partial hand

phalanges.

Comparative fossil material consists of all avail-

able East and South African Plio-Pleistocenehominid long bones that are attributed to

A. anamensis, A. afarensis (including the AL 288-1

partial skeleton), A. africanus, H. habilis,

Paranthropus robustus, P. boisei, Homo sp., and

H. erectus/ergaster (called henceforth simply

H. erectus).

The OH 34 femur

The OH 34 femur is much better preserved than

that of OH 62, but it, too, has an abraded head.The trochantera major and minor, as well as the

condyles, are lacking, and the shaft is broken in the

middle (Fig. 2; Day and Molleson, 1976). It was

found by M. Kleindienst in situ in an ancient

stream channel during the 1962 excavation at

JK2 West, Olduvai Gorge, together with a frag-

ment of a slender tibia midshaft (Kleindienst,

1973). In addition, the femur is remarkably slender

and possesses a sharp pilaster and an antero-

posteriorly compressed femoral neck, which



5/33

correspond well to OH 62 (due to its fragmentarycondition, only the beginning of the pilaster can be

seen).

Another peculiarity of the OH 34 femur is its

huge foramen nutricium. Together with its slender-

ness, this has raised speculations of a possible

pathology associated with this femur, but Day and

Molleson (1976) could not substantiate this claim.

Atrophy following a neurological disease with

paralysis of the leg could have led to a comparably

thin bone. However, this can be excluded because

a radiological analysis failed to show any anomalyof the trabecula, nor is the microscopic bone

structure pathological (Day and Molleson, 1976).

Day and Molleson (1976) therefore preferred an

alternative explanation for the slenderness of OH

34: fluvial erosion unmistakably shaped the

femoral head and superior part of the neck and the

shaft bears numerous scratch marks. Accordingly,

Day and Molleson (1976) could not observe any

outer circumferential lamellar bone in a micro-

scopic study. Based on a regression formula of

shaft thickness on medullary cavity diameter thatwas derived from a British archaeological sample,

they speculated that the total thickness of the OH

34 femur at mid-shaft could have been some 6 mm

greater than it is at present. But they cautioned:

Whether this clear evidence of surface chemical

erosion and abrasion was sufficient to account for

the bizarre appearance of the bone was a different

matter. This particular issue was clouded by the

clear retention of such superficial muscle markings

as the spiral line and the supracondylar lines (Day

and Molleson, 1976: 463). Indeed, if abrasion hadconsiderably affected the circumference of the fem-

oral shaft, all projecting structures and edges

would be expected to be ground off; abrasion never

enhances these features. As on modern human

femora, the above-mentioned muscle markings

usually do not project more than fractions of a

millimeter, and thus the actual shaft diameters and

circumferences probably do not differ greatly from

the original measured dimensions. Heavy abrasion

is also contradicted by the sharpness of the lip of

Fig. 2. Anterior aspect and cross-sections of the femur fragment of OH 62 (middle) compared with that of AL 288-1 (top) and OH34 (bottom). The restored parts of OH 34 are transparent. Minimum (dashed) and maximum (continuous) estimates are shown, as wellas the maximum length and femur head estimates of Day and Molleson (1976) (dotted outlines).



6/33

the pilaster and the depression lateral to it, as well

as by the sharp-edged triangular cross-section of

the associated tibia mid-shaft fragment (every

object becomes spherical with time when exposedto the forces of moving water and sand particles,

be it wood, stone, or bone; e.g., Nawrocki et al.,

1997; Haglund and Sorg, 2002, and references

therein). Likewise, the sharpness of the edges of

the femoral foramen nutricium refutes the idea

that abrasive processes enlarged its diameterthe

edges would at least have been rounded off. More-

over, save for several grooves, pits, and micro-

scopic scratch marks, which are mainly on the

anterior aspect, the surfaces of OH 34s femur and

tibia shaft are surprisingly smooth macroscopically

compared to the femoral head and neck and other

bones subjected to extensive fluvial reworking that

we have studied. Their surfaces look as if they were

rubbed with coarse sand paper, and often lack

numerous large flakes. On the other hand, assum-

ing that polishing was responsible for the smooth

surface would require very fine-grained abrasive

particles, which are incompatible with the high-

energy fluvial environment of the site where OH 34

was found (Kleindienst, 1973). Finally, Day and

Mollesons (1976) radiographic study, together

with the distribution of the cortical thicknessrevealed by the mid-shaft break, provides no evi-

dence for a substantial asymmetrical loss of super-

ficial bone. It is, however, difficult to imagine a

simple process by which the entire circumference

was affected evenly by abrasion.

It seems more likely that the tibia fragment and

the whole femoral shaft up to the inferior margin

of the neck were embedded in sand or matrix when

water currents eroded the head and upper margin

of the neck, whereas the trochantera major and

minor and the distal femur could have been lostdue to carnivore activity before fossilization, as

suggested by the presence of several tooth marks

(see Day and Molleson, 1976). The femoral shaft

suffered thereby numerous scratch marks and lost

superficial splinters of bone, but was probably

protected from a marked reduction of its girth. On

the other hand, Day and Mollesons (1976) failure

to detect external basic lamella does not con-

clusively prove substantial abrasion because the

external circumferential lamellar bone is usually

completely resorbed in modern humans over the

age of approximately 40 years (Kerley, 1965;

Schultz, 1999)and the absence of the epiphyseal

line of the head indicates that OH 34 was fullyadult. In any case, it is unlikely that the shaft

diameter of OH 34 was affected more by abrasion

than that of OH 62. The rugged external appear-

ance and the loss of surface detail leaves no doubt

that heavy abrasion occurred in the latter specimen

(Johanson et al., 1987).

The length of the OH 34 femur can be fairly

reliably estimated since a slight swelling at the

inferior rim of the neck corresponds to the begin-

ning of the head, and the expansion of the distal

shaft and the supracondylar lines indicate the base

of the condyles. Using the distal and proximal

thirds of KNM-ER 1472, 1481, and KNM-WT

15000 as analogues in a graphical reconstruction

yields a minimum estimate for OH 34s femur

length of 375 mm, and a maximum of 392 mm. A

value close to the upper end of this range is

supported by various wax reconstructions of the

proximal and distal portions of a cast of OH 34,

which yielded femoral lengths of 385395 mm.

As the length of the OH 34 femur is critical to

the estimation of OH 62s limb proportions, the

accuracy of the graphical reconstruction methodwas tested on 13 modern human femora that

were between 365 and 415 mm long. Their distal

extremities were cut off graphically at about the

same level as that of OH 34 and then reconstructed

by fitting the superimposed distal third of another

femur to the remaining shaft stumps. The thus

reconstructed femora were slightly too long

(mean deviation +2 mm, 8.7 mm, range 12 to

+13 mm).

An alternative estimate for the femur length of

OH 34 of 411432 mm was provided by Day andMolleson (1976). This is markedly longer than our

graphical and wax reconstructions, even if the

possible error in these reconstructions is taken into

account. Day and Mollesons femur length is hard

to fit to the expanding mediolateral shaft diameter

of OH 34 (see dotted outline in Fig. 2), as it would

lead to an abnormally large bicondylar breadth.

Day and Molleson based their length estimate on a

comparison with a 432 mm long modern human

femur that matched OH 34 in terms of the



7/33

position along its length of identifiable features

(Day and Molleson, 1976: 459). It was not indi-

cated whether this femur matched OH 34 in other

features such as shaft thickness, but the headdiameter of this modern femur was indicated to be

40 mm, which seems to be considerably larger than

that which can be inferred from OH 34s abraded

head remnant (if KNM-ER 1472 or 1481 are

graphically scaled down to fit the proximal femur

of OH 34, a head size of about 33 mm is predicted,

and 35 mm when KNM-WT 15000 is used as a

guideline).

Day and Mollesons second length estimate of

411 mm was based on a regression formula of

femur length on medullary cavity diameter that

was derived from a British archaeological sample,

but they cautioned: perhaps not too much weight

should be placed on these calculations (Day and

Molleson, 1976: 461).

The OH 34 femur and tibia were found in situ

by M. Kleindienst during the 1962 excavation at

JK2 West. Their exact stratigraphic provenience is

unknown, but most fossils from JK2 West are

considered to come from Bed III, except for a few

finds in Bed II (Kleindienst, 1973). However, she

cautioned (p. 189) that the complexity of the

stratigraphy in upper Bed II, Bed III, and Bed IVindicate[s] that it would have been, and still is,

difficult to precisely correlate horizons between

sites which are similar in field appearance.

The dating of Bed III (1.150.8 Ma; Hay, 1976)

suggests that OH 34 should be allocated to either

H. erectus or P. boisei. Yet, among other features,

the well-developed pilaster probably and the

slenderness of the shaft clearly oppose attribution

to the latter taxon. The only femur tentatively

assigned to P. boisei, the fragmentary KNM-ER

1500, is said to be similar to the stout femur of AL288-1 with its roundish shaft (Grausz et al., 1988).

A difference as great as that between OH 34 and

KNM-ER 1500 with respect to the proportion of

the femur shaft cross-sectional area to the recon-

structed length occurs in less than 1 of all

possible pair-wise comparisons of the modern

human sample and exceeds the range of variation

in all extant great apes (see Fig. 7). The difference

is even larger when OH 34 is compared to

KNM-ER 1463, another femur that possibly

belongs to P. boisei. In fact, its slender shaft

aligns OH 34 exclusively with modern and fossil

representatives of the genus Homo.

On the other hand, the anteroposterior flatten-ing and mediolateral broadening of the proximal

shaft in OH 34 is not as extreme as in some other

early Homo femora. It is rare in extant hominoids

to find differences in cross-sectional shape of the

proximal femur as great as those between OH 34

and the KNM-ER 737 or OH 28 femora, which

belong to H. erectus. Such extremes occur in 5%

and 3%, respectively, of all possible pair-wise

comparisons in a world-wide sample of modern

humans encompassing a large range of body-size

(cf. Table 5 and Fig. 9). Similar degrees of differ-

ence are observed in less than 3% of the gorilla

sample and 1% of the chimpanzee sample and

exceed the range of variation of orang-utans.

Moreover, an attribution of OH 34 to H. erectus,

as tentatively proposed by Howell (1978), would

lead to an extreme body size range within that

species (cf. Figs. 7 and 10), although the recent

discovery of a surprisingly small young adult H.

erectus calvaria (Leakey et al., 2003) could be in

agreement with this notion.

Furthermore, early Homo femora are said to

possess an extremely thick femoral cortex com-pared to both Australopithecus and modern

humans (Weidenreich, 1941; Day, 1971, 1978;

Kennedy, 1983a,b; Trinkaus, 1984; Ruff et al.,

1993). A radiological analysis revealed that OH 34

falls inside the range of modern humans except for

the sub-trochanteric posterior and lateral regions,

which are thinner (Day and Molleson, 1976). Yet,

this result may be different if adjusted for the small

size of OH 34. Moreover, medullar stenosis seems

to be typical mainly for later Eurasian H. erectus,

whereas the only two analysed femora of theearlier African H. erectus have a thinner cortex

and also fall in the modern human range of

variation (see Ruff et al., 1993).

In conclusion, there is no support for marked

post-mortem changes in the morphology of

OH 34. Although the current comparative sample

of early hominid femora is larger than that which

Day and Molleson had at their disposal, its mor-

phology remains unique. It differs statistically sig-

nificantly from P. boisei and H. erectus specimens,



8/33

and other pene-contemporaneous early hominid

species are unknown. The closest match is with

OH 62. Homo habilis does, however, not occur as

late as Olduvai Bed III. It is worthy of mention inthis context that the pattern of abrasion of the

fossils from the JK2 site and their recovery from

ancient stream channel sediments indicate that

they were reworked from older deposits, although

it is not known how old (Alan Walker and Michael

Day, personal communication). Nevertheless,

based on the available evidence, it seems best to

follow Day and Molleson (1976), who preferred to

refer OH 34 to Homo sp. indet.

In any case, the use of OH 34 for a comparative

analysis of the OH 62 femur is hardly less appro-

priate than the traditional reconstruction of OH 62

based on the stout AL 288-1 femur.

Measurements and analyses

All measurements were taken as described by

Martin and Saller (1957) and Knussmann (1988),

except (1) the anteroposterior diameter of the

distal humerus, which was taken at a level equal to

three capitulum heights from the distal end; (2) the

radius shaft diameters, which were taken as maxi-

mum and minimum diameters at the foramennutricium; (3) the anteroposterior diameter of the

incisura trochlearis ulnae, which was measured at

its deepest point; (4) the anteroposterior diameter

of the distal femur shaft, which was taken at a level

equal to two condylar heights from the distal

extremity; and (5) the anteroposterior diameter of

the distal tibia, which is the maximum antero-

posterior diameter at the distal extremity of the

tibia.

As the KNM-ER 3735 skeleton is very fragmen-

tary, femoral mid-shaft dimensions are probablynot measurable exactly at the original mid-shaft. A

comparison to modern human femora of similar

shaft size suggested that the proximal extremity of

the left femoral fragment of KNM-ER 3735 is

perhaps 13 cm below this level. Similarly, the

distal extremity of the OH 62 femur fragment

might be 0.5 cm above (compared to the maximum

length estimate of the OH 34 femur) or up to

4.5 cm below the original mid-shaft (compared

to the femur length of AL 288-1). Due to damage

to the OH 62 femur, however, mid-shaft

dimensions can only be taken at about 3.5 cm

proximal to the distal extremity, which means that

they could have been measured either about 4 cmtoo proximally or 1 cm too distally. The deviations

relative to mid-shaft circumference and antero-

posterior and mediolateral diameters were there-

fore recorded for a cast of OH 34 and 20 modern

human femora measured up to 6 cm above or

below mid-shaft (Fig. 3). The modern human

femora were chosen based on a mid-shaft circum-

ference of 6979 mm (KNM-ER 3735: 75 mm) and

a length of 376410 mm. In addition, as the

position of the distal end of the KNM-ER 3735

femur fragment cannot exactly be determined, the

deviation of the anteroposterior diameter of the

distal femur shaft was recorded at a point 4 or

3 times instead of 2 times the height of the

condyles from the distal extremity.

As can be seen in Fig. 3, on average the

circumference and the product of the antero-

posterior and mediolateral femur shaft diameter

change only slightly up to 4.5 cm above or below

mid-shaft. But based on the extremes, it is possible

that, for example, the original mid-shaft circumfer-

ence of KNM-ER 3735 was between 98% and

105%, or that of OH 62 between 98% and 103%, ofthe measurable circumference. No relationship of

these deviations was found with the slenderness,

development of the pilaster, or length of the

femora in the comparative sample, which is cor-

roborated by a second sample of 10 modern

human femora that measure between 366 and

460 mm in length. The pattern of the OH 34 femur

is encompassed by both modern human com-

parative samples: its shaft circumference and the

product of anteroposterior and mediolateral

diameters increase continually from 6 cm abovemid-shaft to mid-shaft, following the lower

extremes of the comparative samples. There-

after, its shaft size remains constant until 6 cm

below mid-shaft, which is similar to the average

pattern of the modern human femora.

Limb length and shaft proportions were

analysed using bivariate regressions. This has the

advantage over indices used in other studies (e.g.,

Johanson et al., 1987; Kimbel et al., 1994;

Richmond et al., 2002) in that the effect of body



9/33

size can be separated when the variable under

study does not change proportionally (isometri-

cally) to body size (Aiello, 1981). In fact, limbproportions change nearly isometrically only in

chimpanzees (i.e., slope=1), but not in other homi-

noid species (see Table 1). Brachial and humero-

femoral indices are therefore inappropriate means

to study these proportions, especially if the body

size covers such a large range as in the comparison

of OH 62 and average-sized modern humans.

There are different methods to analyse the trend

of bivariate plots. It is often agreed that least

squares regression should be used particularly for

prediction purposes (Jungers, 1982, 1988; Martin

and Barbour, 1989; Aiello, 1992; Dagosto and

Terranova, 1992; Smith, 1994; Hens et al., 1998;Konigsberg et al., 1998), but it may produce biased

results when a case does not derive from the same

distribution as the reference sample and when

there are no clear dependent and independent

variables. Alternatives are Model II regressions. It

is, however, controversial whether the major axis

(e.g., Teissier, 1948; Olivier, 1976; Martin, 1982;

Feldesman and Lundy, 1988; McHenry, 1988;

Martin and Barbour, 1989; Formicola, 1993;

Konigsberg et al., 1998) or the reduced major axis

Fig. 3. Deviation of the (a) circumference and (b) anteroposterior and mediolateral diameters of the femur relative to mid-shaftdimensions for 20 modern human femora when measured up to 6 cm above or below mid-shaft, and (c) divergence of theanteroposterior diameter of the distal femur shaft measured at 4 and 3 times the height of the condyles compared to a point measuredat 2 times the height of the condyles. The thick black lines show the average relative deviation. (=diameter).

Table 1

Slopes of regressions of brachial and humero-femoral length proportions

Proportion/species Slope of the LSR Slope of the MA Slope of the RMA

Ulna to humerus length

Homo sapiens 0.75 (0.700.80) 0.81 (0.750.87) 0.82 (0.770.87)

Pan troglodytes 0.97 (0.901.04) 1.08 (1.011.16) 1.07 (1.001.14)

Gorilla gorilla 0.80 (0.760.84) 0.83 (0.790.87) 0.83 (0.790.87)

Humerus to femur length

Homo sapiens 0.66 (0.630.69) 0.68 (0.650.71) 0.69 (0.660.72)

Pan troglodytes 0.94 (0.861.02) 1.08 (1.001.17) 1.07 (0.991.15)

Gorilla gorilla 1.11 (1.031.18) 1.19 (1.121.28) 1.18 (1.111.25)

LSR=least squares regression, MA=major axis, RMA=reduced major axis, 95% confidence intervals in brackets.



10/33

(e.g., Rayner, 1985; Aiello, 1992; Sjvold, 1992;

Jungers et al., 1998) is preferable in determining

functional relationships between variables. In thepresent study, the major axis was favoured in most

cases, following the argument of Konigsberg et al.

(1998) and others, but all analyses were done using

all three regression techniques. To reduce the prob-

lem of extrapolating beyond the characteristic

body size for the reference sample, the present

study used a modern human sample with an em-

phasis on small-sized individuals. The major axis

produces oval prediction intervals, which cannot

be used for extrapolation. However, as in most

analyses, the major axes are almost identical to the

least squares regressions, and thus it is feasible to

use the 95% prediction limits of the latter regres-sion technique for comparing the fossils to the

ranges of variation of the modern reference

samples. In those cases where the major axis devi-

ates markedly from the least squares regression,

the slope is mostly similar to the reduced major

axis, which allows calculation of the prediction

limits accordingly (see Sokal and Rohlf, 1995).

The 95% prediction limits of the bivariate

regressions are not only useful for comparing a

specific metrical proportion of a fossil to the range

Fig. 4 (a).



11/33

of variation of the reference sample. As the fossil

specimens do not belong to any of the extant

hominoid groups, the average morphology and

their variability is unknown. More important is the

distance between a pair of fossils relative to the

slope of the regression line of an extant hominoid

group compared to the corresponding width of the

95% prediction interval. If the distance between

two fossils exceeds the width of the 95% prediction

interval, they are deemed to differ significantly

compared to the range of variation of the reference

sample. On the other hand, if the distance between

two fossils can be encompassed by the prediction

interval of a reference sample, there is no reason to

conclude that they had a different functional

anatomy.

A similar approach to examine the dissimilarity

between two fossils is the permutation test, which

Fig. 4 (b).

Fig. 4. (a) Four examples demonstrating the position of OH 62 ( Homo habilis), AL 288-1 (Australopithecus afarensis), KNM-ER 1500(P. boisei), and KNM-WT 15000 (Homo erectus) relative to modern humans and African apes. The 95% prediction limits for humanand chimpanzee data points are indicated based on least squares regressions (continuous lines); their area of overlap is shaded darker.Major axes are represented by dashed lines. Symbols for fossils with dashed lines reflect the possible effect of not measuring femurmid-shaft dimensions at true mid-shaft. The larger sized individuals of the gorilla sample lie outside the graphs frames. (b) Four otherexamples of upper-to-lower limb shaft proportions, demonstrating also the position of KNM-ER 3735 (Homo habilis).



12/33

calculates the probability of sampling proportions

as divergent as those observed between a fossil

pair within extant hominoid groups. To this end,

all possible pair-wise diff

erences between theresiduals of the reference species regression were

computed. The distance between the data points

of the fossils was calculated based on the slope of

the reference samples regression line. Finally, the

probability that the corresponding difference is

either compatible with or exceeds intra-specific

variation was inferred from a comparison with the

distribution of the permutated differences between

two points of the reference sample (see also

Grine et al., 1993; Richmond and Jungers, 1995;

Richmond et al., 2002).

In contrast to common practice, logarithmic

transformations were not employed in this present

study because an examination of the residuals

revealed no improvement of the linear regression.

In addition, it might have been illegitimate to use

95% prediction limits after logarithmic transfor-

mation (cf. Sprugel, 1983; Dagosto and Terranova,

1992).

Results

Limb shaft proportions

A comparison of the shaft diameters and cir-

cumferences of the OH 62 skeleton with those of

AL 288-1 yields a mixed picture: OH 62 has in

many respects a more massive upper limb than AL

288-1. This is true, for example, for the antero-

posterior diameter of the distal humerus shaft

and the proximal ulna and radius, whereas the

humerus is slightly more slender at the mid-shaft

and the ulna is slimmer distally (Johanson et al.,

1987). On the other hand, all diameters of OH 62sproximal femur fragment are thinner than in the

Hadar skeletons, except for the anteroposterior

sub-trochanteric diameter.

Compared to the intra-specific variation of

hominoids, however, these differences turn out not

to be significant. Upper-to-lower limb shaft pro-

portions have been analysed in modern humans,

chimpanzees, gorillas, and orang-utans by means

of regressions of humerus mid-shaft circumference,

anteroposterior diameter of the distal humerus

shaft, articular width of the distal humerus, radius

head, radius shaft, and anteroposterior diameter of

the incisura ulnae to sub-trochanteric and mid-

shaft femur diameters, femur mid-shaft circumfer-ence, and anteroposterior diameter of the distal

femur shaft. Some of these 24 pair-wise compari-

sons are represented in Fig. 4. In most cases, the

major axes are virtually identical to the least

squares regressions, except for the plots of

humerus mid-shaft circumference, radius shaft,

and radius head to femur mid-shaft circumference,

and humerus articular width, radius shaft, and

radius head to distal femur shaft, where the major

axes are similar to the reduced major axes.

Fig. 4 shows that both OH 62 and AL 288-1 fall

inside the 95% prediction interval of our sample of

modern humans, which is true for almost all

pair-wise comparisons between the upper-to-lower

limb shaft dimensions of these fossils. The only

exception is the proportion of humerus mid-shaft

circumference to sub-trochanteric femur size

(=APML diameter), in which OH 62 and, to a

slightly greater degree, AL 288-1 fall just above the

95% prediction limits for modern humans. This

departure from average modern proportions is

slightly more marked in a reduced major axis

regression. However, both fossils, and especiallyOH 62, are in the lower body size range of the

comparative modern human sample. At the edges

of the comparative samples size range, the choice

of the proper regression technique becomes more

critical and the conclusions less confident (cf.

Jungers, 1985). Nevertheless, even in a reduced

major axis regression, OH 62 still falls inside the

99% prediction limits of modern humans. If the

femur mid-shaft dimensions are corrected for

the fact that the measurement may have been

taken too far proximally, OH 62 could even fallinside the 95% prediction limits of modern

humans. In addition, in almost all comparisons,

a Swiss Neolithic female of about the same

inferred body size as OH 62 had very similar or

even slightly larger upper limb to femur shaft

proportions.

On the other hand, OH 62 falls inside the range

of chimpanzees not only for humerus mid-shaft

circumference vs. femur sub-trochanteric size, but

also for humerus distal shaft and proximal ulna



13/33

size vs. both femur sub-trochanteric and mid-shaft

size. This is because at small body sizes the ranges

for chimpanzees and modern humans overlap.

However, due to the large intra-specific variability

of upper-to-lower limb shaft proportions in all

comparative samples, it cannot be concluded that

OH 62s limb shaft proportions are more

chimpanzee-like than those of AL 288-1. Likewise,

it would be incorrect to characterize, for example,

the Neolithic female that in many of these com-

parisons lies close to OH 62 as chimpanzee-

like due to its large upper limb shaft dimensions

relative to femur shaft size.

In fact, independent of the regression technique

used, the points of OH 62 and AL 288-1 lie

relatively close together compared to the range of

variation of extant hominoid species, with the

exception of AL 288-1s proximal ulna relative tofemur size. Consequently, there is a high prob-

ability that the differences in upper-to-lower limb

shaft proportions between OH 62 and AL 288-1

could be drawn from within any extant hominoid

group. Table 2 summarizes these probabilities. The

results for three proportions are shown, represent-

ing the smallest (humerus mid-shaft circumference

vs. femur shaft size), average (distal humerus and

radius shaft vs. femur shaft size), and largest

proportional difference within this fossil pair

(proximal ulna vs. femur shaft size). In the lattercase, the two fossils lie at opposite edges of the

modern human 95% prediction interval (cf. Fig.

4a). Consequently, differences in proximal ulna-to-

femur shaft proportions as great as those between

OH 62 and AL 288-1 are found in only 5% of

the modern human sample. In chimpanzees and

gorillas, they are, however, much more common

(20% and 28%, respectively). Although great, the

differences between the two fossils are therefore

not statistically significant.

The second H. habilis partial skeleton,

KNM-ER 3735 is considerably larger than OH 62.

For all possible comparisons of upper-to-lower

limb shaft size, it falls close to the mean of modern

humans, i.e., for anteroposterior diameter of the

distal humerus shaft, distal humerus articular

width, radius neck, and radius shaft size relative to

femur mid-shaft dimensions and anteroposterior

diameter of the distal femur (cf. Fig. 4b). Although

the original femur length of KNM-ER 3735 is

unknown, the result is not different even if mid-

shaft dimensions are maximally corrected, i.e., for

an up to 4.5 cm too distal measurement; upper-to-

lower limb proportions are still outside the range

of chimpanzees.

Similar conclusions can be drawn from upper

limb to distal femur shaft proportions. Because the

anteroposterior diameter of the femur shaft gener-ally increases when approaching the condyles

(Fig. 3c), the measurable thickness of the distal

extremity of the KNM-ER 3735 femur shaft frag-

ment is a minimum estimate, and any correction

would push upper limb to distal femur shaft pro-

portion further away from great ape proportions

(Fig. 4b).

Apart from the effect of the fragmentary nature

of the femur, it might also be possible that the

human-like upper-to-lower limb proportions of

KNM-ER 3735 partly result from the erodedcondition of its arm skeleton. An attempt was

made to take this into account, but it may be that

additional superficial bone is missing. The radius

shaft to femur mid-shaft proportion of KNM-ER

3735 would, however, only fall beyond the human

95% prediction limits and inside those of chimpan-

zees if one assumes that 3 mm are missing from the

anteroposterior and an additional 3 mm from the

mediolateral shaft diameter, and simultaneously

the femoral mid-shaft diameters are corrected

Table 2

Probabilities of sampling differences in upper-to-lower limb shift proportions as great as those observed between OH 62 and

AL 288-1 from extant hominoid groups based on the slopes of the major axis (=diameter)

Proportion Homo Pan Gorilla PongoHumerus mid-shaft circumference vs. femur sub-trochanteric size 0.89 0.98 0.92 0.70

Humerus distal shaft AP vs. femur sub-trochanteric size 0.38 0.25 0.39 0.24

Incisura trochlearis ulnae AP vs. femur sub-trochanteric size 0.05 0.20 0.28 0.14



14/33

according to the most negative deviation in

Fig. 3b. Similarly, 1.5 mm must be missing from

the anteroposterior diameter of the distal humerus

shaft if femoral mid-shaft dimensions are maxi-mally corrected, or 2 mm without correction for

the femur mid-shaft. Finally, with correction to the

femur mid-shaft, 4.6 mm must be missing from the

articular width of the distal humerus (5.8 mm

without correction). Such an extreme loss of

superficial bone can be excluded.

For comparison, Fig. 4a and b also shows the

positions of two other early hominid skeletons.

The adolescent H. erectus KNM-WT 15000 falls

close to the mean of adult modern humans for

most limb shaft proportions. Noteworthy is the

size of its distal humerus shaft relative to femur

mid-shaft size, which lies in the upper range of the

modern human variation and thus resembles the

proportion of OH 62 and AL 288-1.

Another early hominid for which limb shaft

proportions can be analysed is KNM-ER 1500,

which might represent P. boisei (Grausz et al.,

1988). Relative to sub-trochanteric femur size, its

radius shaft and proximal ulna dimensions are

much larger than those of OH 62 and AL 288-1,

although the differences between these fossils are

still within the ranges of intra-specific variation forextant hominoid groups. Compared to the distal

femur shaft, the size difference between KNM-ER

1500s and AL 288-1s radius head, however, just

exceeds the width of the 95% prediction interval of

modern humans: KNM-ER 1500 lies at its upper

limit, AL 288-1 falls just beyond the lower limit

(data not shown). The discrepancy between the

proportion of radius shaft to distal femur shaft of

KNM-ER 1500, on the one hand, and KNM-ER

3735 and AL 288-1, on the other hand, surpasses

markedly intra-specific variation in modern homi-noids (Fig. 4b). This strongly suggests that P.

boisei had different body proportions from both

H. habilis and A. afarensis.

Limb length proportions

Brachial proportions

The humerus of OH 62 is relatively well pre-

served, lacking only the proximal and distal

extremities. Its length can be estimated with only

minor error. A graphical reconstruction using

diverse modern and fossil humeri as analogues for

the missing parts suggests a maximum length of270 mm and a minimum length of 258 mm. This

compares well with the estimate of 264 mm given

by Johanson et al. (1987), but the range of the

estimates is smaller than predicted by Koreys

(1990) study. By visually aligning different com-

plete modern human humeri with damaged

humeri, where the two fragmented ends have been

masked according to the damage in OH 62, he

suggested that the standard deviation for the re-

construction is 10.5 mm. This equals about 8 mm if

scaled down to the length of OH 62. The goodness

of the match between the contours of two humeri

is, however, probably better in our graphical

reconstruction method than with Koreys tech-

nique, which might explain his larger confidence

interval. A minor factor is that he was familiar

with the OH 62 specimen only from photographs.

Nevertheless, all these values for OH 62s humerus

are considerably longer than the humerus length

of AL 288-1 (236.8 mm, Johanson et al., 1982; or

246 mm if corrected for the crushed head, see

Hausler, 2001).

Of the OH 62 radius, only a 143 mm long shaftfragment is preserved, making it impossible to

estimate its total length.

The ulna consists of four fragments. Joining

them as closely as possible yields a value of

225 mm as the minimum ulna length if the lacking

olecranon and caput ulnae are taken into

account. However, a length of approximately 245

to 255 mm is more realistic considering the differ-

ences of the individual fragments cross-sectional

diameters. This is almost the length of the large

and very robust AL 438-1a (A. afarensis) ulna,and far longer than AL 288-1, as well as the

smallest known A. africanus ulna, Stw 326 (Fig. 5).

Since the ulna in hominoids is generally roughly

5% longer than the radius, our estimate for

OH 62s ulna length also closely agrees with

Hartwig-Scherer and Martins (1991) estimate of

its radius length, for which they give a range of

210 mm (in their view a less likely value) to

246 mm. In conclusion, given the considerably

greater length, but only slightly greater shaft



15/33

thickness compared to AL 288-1, both OH 62s

humerus and ulna were probably remarkably

slender and less robust than in the Hadarspecimen.

If the value of 245 mm for OH 62s ulna length

is plotted against the mean reconstructed humerus

length, it falls close to the average brachial pro-

portion of chimpanzees (Fig. 6). Even combined

with the upper limit of the reconstructed humerus

length, the resulting brachial proportion lies out-

side the 95% prediction limit of modern humans.

The ulna might, however, also have been longer,

but the corresponding upper-to-forearm pro-

portion does not exceed the probable range of thelarge-sized A. afarensis specimens (Kimbel et al.,

1994), or that of A. africanus (Hausler, 2001) or

BOU-VP-12/1 (Hominidae gen. et sp. indet; Asfaw

et al., 1999). Rather, it is indistinguishable from

them. On the other hand, although the minimum

estimated ulna length is less likely, with a slightly

shorter ulna of 236245 mm, according to the

corresponding humerus length, OH 62s brachial

proportion would fall inside the 95% prediction

limits of modern humans.

Relative femur length

Upper limb proportions of OH 62 may there-

fore not differ from those of the australopithecines.Yet, its femur is in all measurable dimensions

considerably thinner than the AL 288-1 femur and

possesses a different morphology (Table 3 and

Fig. 2). In fact, none of the Plio-Pleistocene femora

closely matches the morphology and metrics of

that of OH 62, save for OH 34. This enigmatic

femur has been described to be surprisingly

slender, but a regression of femur shaft diameter

against femur length demonstrates that OH 34 is

not unusually slender: its reconstructed length falls

within the modern human range of variation basedon the least squares regression (Fig. 7). The major

axis is nearly identical. With the reduced major

axis regression, it approaches but is still below, the

upper 95% prediction limits for modern humans.

Only on the basis of the maximum length estimate

of Day and Molleson (1976), which has already

been shown to be unrealistic, would it fall outside

the human range of variation. Thus, its apparent

slenderness seems to be an optical illusion due to

its small size rather than a puzzle, as Day and

Fig. 5. The ulna of OH 62 compared with the contours of the Stw 326 (completed with the proximal fragment 398; A. africanus), AL288-1 (A. afarensis), and AL 438-1 (A. afarensis). All comparative specimens are from the left side and have been mirrored for thisillustration.



16/33

Molleson (1976) called it. Therefore, there is no

reason to suspect a substantial degree of abrasion

of its surface bone, of which Day and Molleson

(1976) themselves were not convinced.

Nevertheless, OH 34 is remarkably slender

when compared to the few contemporaneous

fossils. Only the subadult femur of KNM-WT

15000 has a similar robusticity, although this

Fig. 6. Plot of ulna length vs. humerus length (mm). The 95% prediction limits for human and chimpanzee data points are indicatedbased on reduced major axes (thin, long-dashed lines). Major axes (thick, short-dashed lines) are almost identical, least squaresregressions (not shown) slightly flatter. OH 62, AL 288-1, Stw 431, and BOU-VP-12/1 are shown with the most likely proportions andthe ranges of the estimates (shaded rectangles). The minimum ulna length of AL 288-1 (191 mm) results from directly joining the two

fragments, the maximum length (219 mm) is Kimbel et al.s ( 1994) estimate; the minimum humerus length was estimated by Johansonet al. (1982), whereas correcting for crushing suggests a greater length (Hausler, 2001). For the range of Stw 431 see Hausler (2001).The data points for AL 137-50 and MAK-VP-1/3 were obtained by combining these reconstructed humeri with the AL 438-1a ulna.Minimum and maximum humerus lengths of BOU-VP-12/1 correspond to the estimate of Asfaw et al. (1999) based on regressions andan anatomical reconstruction, respectively; the range of its ulna length results from the lower and upper 95% prediction limits forAfrican apes and modern humans, respectively, of the regression on Asfaw et al.s (1999) radius length.



17/33

Table 3

Comparison of some measurable dimensions of the OH 62 femur fragment with those of OH 34 and AL 288-1 (=diameter, mm)

OH 62 OH 34 AL 288-1

Femur neck ap 13.2 (12.513.5) 15.4Femur shaft sub-trochanteric ap 19.4 17.4 17.5

ml 20.1 21.2 25.3

Femur mid-shaft ap 18.7a 19.3 21

ml 19.4a 18.9 21.9

minimum 17.5a 15.6 19.9

Femur mid-shaft circumference 62a 59.5 67.5

Estimated femur length 375392 280286b

aMeasured about 3.5 cm proximal to the distal extremity.bLength estimates: 280 (Johanson et al., 1982), 281 (Jungers, 1982); after reconstruction of the crushed distal end: 283 (Schmid,

1983), 286 (McHenry and Berger, 1998b).

Fig. 7. Plot of femur length (mm) vs. sub-trochanteric femur shaft size (anteroposteriormediolateral diameter, mm2). The 95%prediction limits for human data points are indicated based on least squares regressions (continuous lines). Major axes (thick,short-dotted lines) are nearly identical, reduced major axes (thin, long-dashed lines) are steeper. The range of the estimated femurlength is given for OH 34, OH 53, AL 288-1, and the A. africanus specimens Stw 99 and Stw 121 (Hausler 2001). Length estimates forKNM-ER 1500 (P. boisei), OH 53, KNM-ER 1809 (P. boisei or H. habilis), KNM-ER 3728 (possibly H. rudolfensis), KNM-ER 993and 1463 (P. boisei or H. erectus), KNM-ER 737, 1808, and OH 28 (H. erectus) are derived from McHenry (1991). KNM-ER 1808is also corrected for pathological hyperostosis (Walker et al., 1982). KNM-ER 1472 and 1481 (possibly H. rudolfensis) and KNM-WT15000 (H. erectus) were measured on the original. The length of KNM-WT 16002 (Australopithecus sp.) was estimated byreconstruction and comparison with other fossils.



18/33

might partly be due to its young age (cf. Ruffet al.,

1994). On the other hand, the femur of KNM-ER

1808 might have been even more slender if cor-

rected for its pathological hyperostosis (Walkeret al., 1982; Rothschild et al., 1995). In any case,

the number of early Homo femora for which femur

robusticity can be inferred is very small. There are,

indeed, only two specimens that do not need a

considerable amount of estimation for determi-

nation of their length (KNM-ER 1472 and 1481).

The difference between OH 34 and KNM-ER 1481

are exceeded by 31% of the comparisons within the

modern human sample, while the difference be-

tween OH 34 and KNM-ER 1472 are exceeded by

25% of those comparisons. Owing to the paucity of

contemporaneous femora, it therefore cannot be

concluded at present that the OH 34 femur is

abnormally slim in comparison to the available

specimens. The question of whether OH 34 is an

unusual specimen remains open.

As can be seen from Fig. 7, all early Homo

specimens fall within the range of modern humans

with regard to femur length vs. shaft diameter,

whereas all australopithecines, including AL 288-1,

fall in the range of modern great apes. This indi-

cates that a general feature of australopithecines

and paranthropines was an apelike short femur,possibly not only relative to shaft dimensions, but

also relative to body size (see also Jungers, 1982,

1991). The body size-femur length relationship of

AL 288-1 and its relatives certainly deserves

another look. Yet, the present data suggest that

the shortness of the femur is hardly an effect of

small body size and the convergent regression lines

of modern humans and chimpanzees, as has

been repeatedly suggested (e.g., Franciscus and

Holliday, 1992; Vancata, 1996; Hens et al., 2000;

Holliday and Franciscus, 2001). Even if the steeperslope of the reduced major axis is preferred,

AL 288-1 falls below the range of modern humans;

only the smaller-sized KNM-WT 16002 (Australo-

pithecus sp.) would lie within the lower range of

humans.

The femoral proportion makes it likely that

KNM-ER 1809, which on geochronological

grounds alone could either belong to H. habilis,

H. erectus, or P. boisei, can be assigned to the

latter taxon. With the same logic, the slightly

younger KNM-ER 993 and KNM-ER 1463 might

belong to P. boisei rather than to H. erectus, and

OH 53 to H. habilis.

Although Fig. 7 illustrates the diffi

culty ofestimating femur length based merely on shaft

diameters, OH 62s morphological similarity to

the proximal segment of the OH 34 femur sug-

gests that a Homo model might be more appro-

priate for femur length reconstruction than an

Australopithecus model.

Another similarity between OH 62 and OH 34 is

the presence of a well-developed pilaster (a linea

aspera is absent). Interestingly, this parallels the

morphology of the left femur shaft fragment of

KNM-ER 3735. Although a pilaster is said to be

found rarely in early hominids (see references in

Ruff, 1995), it can also be found in AL 333-61,

KNM-ER 736, 737, 738, and others. It starts in

OH 62 at the same level as in OH 34 and is

identical in its degree of development to the corre-

sponding part of the latter specimen (see Fig. 2).

The pilaster usually expands over the middle third

of those femora in which it is present. Its origin

near the distal end of the preserved OH 62 femur

fragment suggests that almost two thirds of the

entire femur length are missing, and not one-half,

as it would be expected if it had the length ofAL 288-1. In the latter case, the pilaster must have

ended just after it had started. This seems unlikely,

as the biomechanical function of this buttress is to

increase bending rigidity of the femur (Pauwels,

1965; Kummer, 1978). It might therefore be nor-

mal to find exceptionally well-developed pilasters

in long and slender bones (see also Day and

Molleson, 1976).

Thus, if the OH 62 femur is reconstructed with

the length of OH 34, it results in an essentially

humanlike humero-femoral proportion (Figs. 8and 11). In fact, assuming human-like proportions,

the 95% prediction limits for the femur length

based on a humerus length of 270 mm correspond

to 354 mm and 404 mm (least squares regression),

as compared to OH 34s reconstructed length of

between 375 and 392 mm.

The associated upper and lower limb bones

from Bouri, BOU-VP-12/1 (Hominidae gen. et sp.

indet.), might also have possessed humanlike pro-

portions if the anatomical reconstruction of the



19/33

humerus and femur length by Asfaw et al. (1999) is

correct. As with the brachial proportion, limb

lengths of BOU-VP-12/1 predicted by regressions

seem to be less trustworthy because the resulting

humero-femoral proportion falls outside the range

of all extant hominoids. Thus, both intermembral

proportions might have been similar to those of

OH 62.

Discussion

Limb shaft proportions

Johanson and co-workers stated in their

original description: Even allowing for slight

exfoliation of the OH 62 femur, visual comparison

makes it obvious that this individuals femur was

Fig. 8. Plot of femur length vs. humerus length (mm). The 95% prediction limits for human and chimpanzee data points are indicatedbased on reduced major axes (thin, long-dashed lines). Major axes (thick, short-dashed lines) are almost identical, least squaresregressions (not shown) barely steeper. Shaded rectangles symbolise the ranges of the estimates for OH 62 (femur length correspondingto that of AL 288-1 and OH 34, respectively), AL 288-1 (for the humerus length cf. Fig. 6), Stw 431 (A. africanus; see Hausler, 2001),and BOU-VP-12/1 (see Asfaw et al., 1999).



20/33

smaller and less robust than the A.L. 288-1 femur

(Johanson et al., 1987: 208). Combined with the

evidence for a considerably longer humerus in

OH 62, they speculated that body proportions inH. habilis fell in the range ofPan. Although Korey

(1990) showed that their humero-femoral index

had such a large confidence interval that it can be

placed anywhere between gorillas and humans,

Hartwig-Scherer and Martin (1991) inferred from

upper-to-lower limb shaft and length proportions

that OH 62 displays closer similarities to African

apes than does AL 288-1. The present study, in

contrast, using a much largercomparative data set,

found that all examined upper-to-lower limb shaft

proportions of OH 62 and AL 288-1 are inside the

range of modern humans. Only in humerus mid-

shaft circumference relative to sub-trochanteric

femur size does OH 62 and AL 288-1 fall just

above the 95%, but still within the 99%, prediction

limits, for the modern human sample. This obser-

vation only illustrates that the difference between

the two fossil hominids can be encompassed within

the range of variation of a single species and is

therefore not statistically significantit does not

mean that limb shaft proportions of A. afarensis,

H. habilis, and H. sapiens cannot be distinguished

at the species level. It is therefore unimportant toknow that a certain specimen falls slightly closer to

the modern human or the chimpanzee regression

line. Indeed, for all upper-to-lower limb shaft

proportions, the average individual variation

within extant hominoid groups is greater than

between these two early hominids (see also

Richmond et al., 2002). Accordingly, it cannot be

inferred, as did Hartwig-Scherer and Martin

(1991), that one of them has more primitive limb

shaft proportions than the other.

Other reasons for the divergent conclusions ofHartwig-Scherer and Martin (1991) are their much

smaller comparative sample size and the lack of

small-bodied modern humans in their data set.

Moreover, their consolidation of chimpanzee and

gorilla data in a single African ape sample is

problematic because gorillas are not simply scaled

up chimpanzees (Shea, 1981), and they often have

different slopes and intercepts of the regression

lines (cf. Fig. 4). In addition, especially with a

sample size that covers a limited range of size, the

correlation coefficient of the regression can be low,

and the exclusive use of reduced major axis often

produces steep slopes, which obviously had a

dramatic eff

ect on the position of OH 62.However, as can be seen in Fig. 4, modern

humans and chimpanzees overlap slightly for these

proportions in the small body-size range. It there-

fore cannot be determined whether H. habilis more

closely follows human or ape proportions, unless a

larger-sized specimen is analysed. An unexpected

support for rather modern upper-to-lower limb

proportions comes from the fragmentary skeleton

KNM-ER 3735 from East Turkana, Kenya

(Leakey and Walker, 1985; Leakey et al., 1989).

Being considerably bigger than OH 62, it was

tentatively identified as a male individual (Leakey

et al., 1989). The size of the fragments suggested

that the skeletons limb proportions possibly

approximate those of chimpanzees, although the

sacrum is much smaller and shaped differently.

Nonetheless, whereas Leakey et al. (1989) stated

that the distal humerus of KNM-ER 3735 is as

large as that of their chimpanzee, they also wrote

that hindlimb dimensions are larger in the fossil.

In accordance with this observation, the few

measurements that can be taken on this partial

skeleton do not verify the claim of having limbshaft proportions that are, compared to AL 288-1,

more apelike than what can be explained by

individual variation. Indeed, even with the most

generous corrections for its incompleteness, none

of our chimpanzees approaches KNM-ER 3735 in

any of these proportions. The present re-analysis

of its humerus, radius, and femur fragments

demonstrates that its shaft proportions fall close to

the modern human mean and outside the range of

variation of chimpanzees. This has, of course,

implications for OH 62 as well. Although therelatively large humerus shaft cross-section of

OH 62 could indicate relatively higher arboreal

activity levels, the proportions of KNM-ER 3735

suggest that any behavioural differences between

H. habilis and later Homo were not so extensive

as to have had a major effect on limb shaft

proportions.

Upper-to-lower limb shaft proportions of the

KNM-WT 15000 skeleton from Nariokotome

(H. erectus) lie entirely inside the range of modern



21/33

humans. It is conspicuous only in that its relative

distal humerus shaft size resembles that of OH 62

and AL 288-1 in falling in the upper half of the

modern human distribution. As the specimen isthat of a juvenile with a skeletal age of about

1313.5 years (range 1115 years) and a dental age

of 11 (Smith, 1993; see also Ruffand Walker, 1993;

Clegg and Aiello, 1999), it is possible that some of

its limb shaft proportions are not yet those of an

adult H. erectus. At the age of 13, modern human

males have on average 12% lower humerus to

femur strength proportions at midshaft than at

17 years of age (Sumner and Andriacchi, 1996;

Ruff, 2003; Ruff, personal communication). Thus,

speculations about the functional implications of

the relatively large distal humerus shaft size must

wait until a complete enough adult H. erectus

skeleton is recovered.

Another remarkable pattern of upper-to-lower

limb shaft proportions is found in KNM-ER 1500,

which is tentatively attributed to P. boisei (Grausz

et al., 1988). Compared to the H. habilis skeleton

KNM-ER 3735 and to AL 288-1 (A. afarensis), its

radius shaft relative to femur shaft size signifi-

cantly surpasses intra-specific variation in modern

hominoids (Fig. 4b). In contrast to Grausz et al.

(1988), who proposed nearly identical body pro-portions to those of AL 288-1, this strongly

suggests that P. boisei at least possessed a con-

siderably larger forearm than either AL 288-1 or

OH 62.

Limb length proportions

Although OH 62, KNM-ER 3735, AL 288-1,

and KNM-WT 15000 do not differ significantly in

their upper-to-lower limb shaft proportions com-pared to the intra-specific variation in extant homi-

noid species, it is quite possible that they diverged

in their limb length proportions. Richmond et al.

(2002) suggested that diaphyseal dimensions are

fairly variable in hominoids and therefore do not

have great power in uncovering species-level differ-

ences in skeletal form. Indeed, in contrast to

relative shaft dimensions, the length of OH 62s

upper limb skeleton considerably exceeds that of

AL 288-1, as is well demonstrated in Fig. 1.

Brachial proportions

Length estimates for the forearm of OH 62 are

less secure. Combined with the length of the

humerus, the fragmentary ulna suggests that H.habilis had a high brachial proportion. Although

modern human proportions cannot be excluded, a

great forearm length is supported by the relatively

long radius neck of KNM-ER 3735, which is in

the range of chimpanzees (Leakey et al., 1989;

Haeusler and McHenry, 2004). Similar body pro-

portions with a relatively long forearm and an

elongated lower limb compared to humerus length

have been reported for the w2.5 million year old

associated limb bones BOU-VP-12/1 from Bouri

(Hominidae gen. et sp. indet.; Asfaw et al., 1999),

if the anatomical reconstruction is used. The

other method used by Asfaw and colleagues for

estimating its limb lengths, which is based on

regression formulas, seems to be less reliable. It

would suggest a femur length relative to humerus

length that is much greater than in modern

humans, combined with a relative forearm

length that exceeds the range of extant African

apes.

BOU-VP-12-1s brachial proportion is the

highest of all fossil hominids. It was, however,

probably not as highly derived among hominids asclaimed by Richmond et al. (2002). If the humerus

length is anatomically reconstructed, and accord-

ing to the exact length of the forearm, it does not

seem to be markedly different from those of OH

62, large-sized A. afarensis specimens, or A. africa-

nus (see Table 4). The discrepancy with Richmond

and colleagues conclusions might be attributable

to their inappropriate use of indices. Indeed, only

when the humerus length is estimated from a

regression (Asfaw et al., 1999) does the brachial

proportion of BOU-VP-12/1 lie beyond the 95%prediction limits of chimpanzees and the corre-

sponding difference to OH 62 and the australo-

pithecines is less often observed in the extant

hominoid samples (see also Fig. 6). Consequently,

the humerus length estimated by the regression

method seems much less reliable. What is more,

Asfaw et al. (1999) did not provide 95% prediction

limits for their estimate. There is therefore no

indication for unique brachial proportions of

BOU-VP-12/1 among hominids. Based on the



22/33

above evidence, it is conceivable that BOU-VP-

12/1 belonged to H. habilis, but full description

of this specimen must be awaited before further

conclusions can be drawn. So far, the Bouri post-

cranials have not been assigned to a particular

hominid genus or species. Asfaw et al. (1999)hesitated to attribute it to A. garhi, which they

discovered in the same strata (see also DeGusta,

2003). Indeed, the megadontia of A. garhi would

not easily fit to a close phylogenetic relationship

with H. habilis.

Relative femur length

Whereas Jungers (1988) estimated OH 62s

length to be slightly shorter than that of AL 288-1,

Johanson and Shreeve (1989: 286) wrote: But

based on the distances calculated between anumber of different anatomical landmarks, we

could estimate the femur was slightly longer than

Lucys, somewhere between 300 and 330 milli-

meters, or roughly a foot long. This makes the

OH 62 femur 20 to 50 mm longer than that of

AL 288-1, yielding equivalent body proportions

in these two hominids. There are, however, no

landmarks preserved on the distal end of OH 62s

femur fragment on which such a calculation

could be based. Thus, the only way to estimate

OH 62s femur length is by a comparison with

other hominid femora.

If a modern human femur lacking its distal half

is reconstructed by comparison with a another

femur, Korey (1990) found that its length can be

estimated with an accuracy (i.e., a standard devia-tion) of3.05 cm if the mean diameters of the two

femora differed by no more than 2 mm. Scaled to

the length of the AL 288-1 femur, the accuracy of

OH 62s length estimate would probably be within

about 2 cm. However, as demonstrated in Fig. 7,

the femur of australopithecines has, like that of

great apes, a different length to girth ratio than

that of modern humans. This suggests that the

actual range for the estimate of OH 62s femur

length might be much greater than assumed by

Korey.In fact, not only do the humerus, ulna, radius,

and craniodental morphology and proportions dif-

fer considerably between OH 62 and AL 288-1

(Johanson et al., 1987), but the morphology and

proportions of the proximal femur diverge quite

markedly as well, suggesting that there might be

better analogues for reconstructing the fragmen-

tary femur of OH 62. Both the humerus and ulna

of OH 62especially if adjusted for their greater

lengthare much more slender than those of

Table 4

Probabilities of sampling differences in ulna-to-humerus length proportions as great as those observed between pairs of fossils

from extant hominid groups based on the slope of the major axis

Fossil pair Homo Pan Gorilla PongoOH 62AL 288-1 min. 0.02 0.03 0.02 0.18

OH 62AL 288-1 max. 0.92 0.43 0.90 0.62

OH 62AL 137-50 0.23 0.47 0.36 0.66

OH 62MAK-VP-1/3 0.63 0.73 0.82 0.84

OH 62BOU-VP-12/1 anatomical rec. 0.09 (0.010.28) 0.01 (0.000.06) 0.09 (0.010.28) 0.10 (0.010.38)

OH 62 max.BOU-VP-12/1 rec. by regression 0.03 (0.000.10) N/A (N/A 0.00) 0.02 (0.000.10) 0.04 (0.010.09)

AL 137-50BOU-VP-12/1 anatomical rec. 0.42 (0.080.89) 0.05 (0.000.23) 0.41 (0.070.87) 0.23 (0.060.46)

AL 137-50BOU-VP-12/1 rec. by regression 0.18 (0.020.47) 0.00 (N/A 0.04) 0.17 (0.020.45) 0.09 (0.020.20)

MAK-VP-1/3BOU-VP-12/1 anatomical rec. 0.14 (0.020.40) 0.00 (N/A 0.03) 0.13 (0.010.38) 0.07 (0.010.17)

MAK-VP-1/3BOU-VP-12/1 rec. by regression 0.04 (0.000.16) N/A (N/A 0.00) 0 (0.000.15) 0.02 (0.000.06)

N/A signifies that an equally large difference was not observed in the comparative sample. OH 62: brachial proportions are based

on a humerus length of 270 mm and an ulna length of 245 mm. BOU-VP-12/1: humerus length according to the anatomical

reconstruction or the regression-based estimate (Asfaw et al., 1999); ulna length corresponds to the mean estimate of anall-hominoid-regression of ulna to radius length; upper and lower 95% prediction limits in brackets. AL 288-1: directly joining the

two ulna fragments combined with a humerus corrected for crushing of the head yields the minimum brachial proportion

(Hausler, 2001); the maximum proportion is based on Kimbels et al. (1994) estimate. AL 137-50 and MAK-VP-1/3: the brachial

proportions were obtained by combining the reconstructed humeri with the AL 438-1a ulna.



23/33

AL 288-1. It is therefore conceivable that the

remarkably thin femur was originally relatively

long as well.

The only known Plio-Pleistocene femur that

matches the OH 62 fragment in morphology and

metrics is the OH 34 femur. Although its geologi-

cal age might be more than 650,000 years younger

than OH 62 (not taking into account reworking of

the deposits at JK2), this is much less of a discrep-

ancy than the ca. 1.4 million years between OH 62

and AL 288-1. Critical for the use of this specimen

as an analogue for estimating femur length of

OH 62 is the issue of its abnormal slenderness

raised by Day and Molleson (1976). Considering

the entire body of evidence, there is no unambigu-

ous support for substantial abrasion of the femoralshaft. Apart from numerous superficial scratches,

the idea that abrasion affected the morphology of

OH 34 is contradicted by the retention of fine

muscle markings and sharp edges of the foramen

nutricium and pilaster. Only the head and neck are

clearly abraded. With respect to the ratio of vari-

ous shaft diameters to femur length, it falls within

the range of modern humans. Moreover, due to

the dearth of contemporaneous early Homo

femora, it cannot be concluded that its robusticity

exceeds their range of variation. There is thereforeno conclusive objection against using this femur

instead of AL 288-1s to estimate femur length of

OH 62. With this approach, an essentially human-

like humero-femoral proportion is indicated for

Homo habilis.

Alternatively, presuming the same femur length

as that of AL 288-1, the humero-femoral propor-

tions of OH 62 would fall close to the lower

95% prediction limits for chimpanzees (Fig. 8).

However, only if the upper limit of its humerus

length estimate is simultaneously assumed does the

resulting difference between the humero-femoral

proportions of the two specimens become rare in

extant hominoids, i.e., it is observed in less than

5% of the sample (see Table 5). This contrasts with

the results of Richmond et al. (2002), who con-

cluded that the difference between OH 62 and AL

288-1 significantly exceeds the variation in extant

hominoid species. This discrepancy is partly due to

their use of indicessince humero-femoral pro-

portions do not change isometrically with body

size (cf. Table 1), the use of indices can yield

misleading results (Aiello, 1981). Another factor

that explains a minor part of this discrepancy is

their use of estimates for AL 288-1s humerus and

femur length that do not make allowance forcrushing (237 mm and 280.5 mm, vs. 246 mm and

286 mm, which we prefer, see Table 5).

Further support for a femur that is humanlike

in being long relative to its girth in H. habilis

comes from the KNM-ER 1472, 1481, and 3728

femora. Their robusticity is close to the mean of

modern humans (Fig. 7). If they are correctly

assigned to H. rudolfensis, and if H. habilis

sensu stricto had a femur as short as claimed by

Johanson et al. (1987) and Hartwig-Scherer and

Martin (1991), it would follow that these closelyrelated species, which some scholars do not

recognize as different species at all, showed major

differences in relative hindlimb proportions.

On the other hand, Ruff (1995) states that the

OH 62 proximal femur differs from other early

Homo specimens but might resemble P. boisei

(KNM-ER 1500) and other australopithecines

in having a nearly circular cross-sectional shaft

morphology. Cross-sectional shape is, however,

slightly positively allometricmajor axes and

Table 5

Probabilities of sampling differences in humero-femoral length proportions as great as thoses observed between AL 288-1

(corrected for crushing) and various short-legged variants of OH 62 from extant hominid groups

Femur and humerus length estimates for OH 62 Homo Pan Gorilla PongoFemur length=AL 288-1, lower limit for humerus length (258 mm) 0.17 0.21 0.50 0.61

Femur length=AL 288-1, mean humerus length (264 mm) 0.08 0.10 0.32 0.44

Femur length=AL 288-1, upper limit for humerus length (270 mm) 0.03 0.04 0.21 0.30

Femur length=300 mm, upper limit for humerus length (270 mm) 0.12 0.29 0.65 0.72

Femur length=AL 288-1 (uncorrected), mean humerus length (264 mm) vs. AL 288-1 (uncorrected) 0.02 0.04 0.20 0.28



24/33

reduced major axis are nearly identical [slopes for

modern humans 1.13 (95% confidence limits 1.051.23) and 1.09 (1.001.18)], indicating that smaller

specimens such as OH 62 and OH 34 have a more

circular proximal shaft cross-section than larger

individuals (Fig. 9). Figure 9 also shows that,

compared to the modern human regression line,

the 11 A. afarensis proximal femora possess,

on average, a slightly wider mediolateral shaft

diameter relative to the anteroposterior shaft

diameter (but see Ruff, 1995, 1998; Ruff et al.,

1999). An even wider proximal shaft diameter is

exhibited by specimens attributed to H. rudolfensis

and H. erectus (Ruff

, 1995). They all cluster closeto the upper limit of the range of variation for

modern humans. Yet, based on the relatively

restricted range of variation compared with

other fossil and extant hominoid groups, this

could in part be an artefact due to failure of

taxonomic recognition of specimens that have a

proportionally smaller mediolateral diameter.

On the other hand, the P. boisei proximal

femur KNM-ER 1500 lies almost on the regression

line of modern humans with respect to its

Fig. 9. Bivariate plot with reduced major axes (long dashed lines) and major axes (short dashed lined) of sub-trochanteric mediolateralvs. anteroposterior diameter (mm) for modern humans, chimpanzees, gorillas, orang-utans, and early hominid fossils. Least squaresregressions (not shown) are flatter. The inner and outer dotted lines repres

Documents

Journal of Human Evolution 46 (2004) 433–465