Some aspects of femoral morphology in Homo erectus

Some Aspects of Femoral Morphology in

G. E. Kennedy

H o m o erectus Department of Anthropoloz~,,,, University of Cali/brnia, Los Angeles, California, The available femora of' lower and middle Pleistocene hominines were 90024, U.S.A. examined osteometrically and radiographically. This fossil sample was compared with samples of Romano-British and Bushmen [~mora. The results showed distinctive internal and external morphological patterns in the Homo erectus group. This pattern consisted, in part, of very thick cortical bone, narrow AP shaft diameters and a low point of minimum shaft breadth. Where preserved, the trabeculae of the medial femoral neck showed a distinctive diffuse pattern. The Trinil lkmora showed a basically sapient pattern although they demonstrated thickened cortical bone in lhe distal shaft, The restricted distribution of this thickened cortex suggests that it may not be homologous with the generally thickened cortex seen in Homo erertus. Several hypotheses arc proposcd to explain the thickened cortex in lIomo erectus.

Received 10June 1981 and accepted 15 July 1983

Ke~,,wordr: femur, ttomo, cortex, trabeculation, X-ray.

1. Introduction

Descriptive reports of ttle femora of fossil hominines have indicated that some may demonstrate a morphological pattern distinctive from that of modern sapiens. Walkoff (1904), for example, argued that the trajectorial systems in the proximal {kmur of" the Krapina I and Spy specimens were less differentiated than in modern man. Wcidenreich (1941), in describing femora from the Lower Cave at Choukoutien, identified a morphological pattern characterized by increased cortical thickness, greater platymeria and a more distal position of minimum shaft breadth, relative to sapients. Day (1971) later identified a similar pattern in O H 28 and suggested that both the Choukoutien and Olduvai specimens should be attributed to Homo ereclus. None of these studies, howe.ver, tested the significance of characters in the tbssil specimens against the ranges of variation found in larger fossil and sapient samples. The present study has examined internal and external features of the femoral shaft in virtually all known lower and middle Pleistocene femora currently attributed to the genus Homo. This research has tocused mainly on the morphology of" the shaft which is more fl'equently preserved than the articular portions in the lower and middle Pleistocene specimens. However, despite the very small sample size, certain features of the proximal and distal articular areas have also been included where possible. 2. Methods and Materials

The primary comparative sample was composed of 100 Romano-British femora from Ancaster, England. Only complete, adult femora without obvious pathology were chosen for this study; a further criterion for selection was the inclusion with the remains of at least one-half of the os innominatum. Sexual assessment was made on f~atures of the pelvis as outlined by H a n n a & Washburn (1953) and Phenice (1969). The Ancaster sample consists of femora from 57 male and 43 female individuals. A further sample of eight Bushmen femora was also included. Because these are from incomplete and/or disassociated skeletons no assessment of sex was made for this series. These bones are also adult and Journal qfltuman Evolution (1983) 12, 587 616 0047-2484/83/070587 + 30 $03.00/0

9

1983 Academic Press Inc. (I,ondon) Limited

588

G.E. KENNEDY

w i t h o u t p a t h o l o g y . T h e A n c a s t e r a n d B u s h m e n s a m p l e s arc h o u s e d at the British M u s e u m (Natural History). T h e fossil s a m p l e is listed in T a b l e 1. All f e m o r a i n c l u d e d in this s t u d y were a n a l y s e d o s t e o m e t r i c a l l y b o t h i n t e r n a l l y a n d externally. I n t e r n a l a n a l y s i s was a c c o m p l i s h e d t h r o u g h X - r a y s , m a d e specifically for this study. W i t h the e x c e p t i o n of the two f e m o r a from the Lower C a v e at C h o u k o u t i e n only o r i g i n a l m a t e r i a l s were studied. T h e " S i n a n t h r o p u s p e k i n e n s i s " m a t e r i a l was lost d u r i n g W o r l d W a r I I b u t W e i d e n r e i c h i n c l u d e d b o t h X - r a y s a n d i n t e r n a l a n d e x t e r n a l shaft m e a s u r e m e n t s in his 1941 m o n o g r a p h . M o r e o v e r , a n excellent set of casts, m a d e by W e i d c n r e i c h , was a v a i l a b l e for this s t u d y a n d c e r t a i n o b s e r v a t i o n s a n d m e a s u r e m e n t s could therefore be a s c e r t a i n e d or verified o n this m a t e r i a l . All other X - r a y s were m a d e for this s t u d y a n d were t a k e n in s t a n d a r d i z e d a n t e r o p o s t e r i o r a n d m e d i o l a t e r a l o r i e n t a t i o n s ; the cone h e i g h t was a c o n s t a n t 90 c m a b o v e the film. K V , M A a n d e x p o s u r e time v a r i e d a c c o r d i n g to the fossilization or d c m i n e r a l i z a t i o n of the m a t e r i a l . Since a c o m p r e h e n s i v e

Fossil h o m i n i n e f e m o r a

Table 1

Gurrent

Specimen Choukoutien, Femur I Choukoutien, Femur IV* TriniI, Femur I'~ Trinil, Femurll Trinil, Femur III Trinil, Femur IV Olduvai Hominid 28

First description

taxonomic status

Date m.y.a,

Wcidenreich (1941) Weidenreich {1941)

Homo erectus

0"21 0'50

Homo erectus

0'21 0"50

Dubois (1892)

?

0.50

KaboehFm. Shaftwith Duhois(1932) core of head, 400

?

?

KaboehFm. Shaft, 320 Dubois (1932)

?

Level

Specimen size (mm)

Locus C, Layer 8 (?) Locus M, Layer 26

Shaft, 199 Shaft with inferior border of neck, 312 Kaboeh Fm. Complete, 455

Kaboeh Fm. Shaft, 315 Bed IV, WK Shaft with inferior border of neck, 290 KNM ER 737 Koobi Fora, Shaft with inferior Area 103 border of neck, 369 KNM ER803 Ileret, Shaft, Area 8-A 229 KNMER1481a KoobiFora, Complete Area 131 397

?

Reference for date Oakley et at (1975) Oakley et al. (1975) von Koenigswald (1968b)

Dubois (1932) Day (1971)

Homoerectus

? 0"50

Leakey 1971)

Homo sp.

1"5

Fitch etat. (1974)

Leakey (1972)

Homosp.

1"5

Fitchetal.

Leakey (1973)

Homosp.

>1'8

Fitchetal.

Ha~, (1976)

(I974) (1974)

* Five additiona~ femoral ti'agments have been recovered from Choukoutien; these specimens are too small to be included here. ~"Two further femora have been reported from these deposits. Trinil, Femur V (Dubois, 1939) is a small shaft fragment; Trini[, Femur VI (Dubois, 1934) is not primate (Day & Molleson, 1973).

F E M O R A L M O R P H O L O G Y IN H. E R E C T U S

589

study of the internal structure of hominid femora has not previously been made, new measurements had to be designed for this analysis; the osteometric techniques have been described (Kennedy, 19731.

3. Results

The Comparative Sample The Ancaster collection provided an excellent comparative series of nearly complete skeletons with little obvious pathology or post-mortem damage. A very small number of individuals of both sexes demonstrated excessively large cortical diameters. Re-examination of X-rays of these individuals (N = 3) showed changes in bone density and/or other subtle changes suggestive of pathological process but since pathology could not be positively demonstrated the individuals remained in the sample. The low within-sex standard deviations confirms the unusualness of large cortices in recent sapients. In the Ancaster males, the femoral cortex at all levels is thicker than in the females and although the ranges are large and nearly equivalent in both sexes, the low within-sex standard deviations point out the significance of the mean differences (Table 2, 4, 6). Ontogeny, as well as sex, has an effect on cortical diameters. In recent populations, cortical diameters increase through the fourth decade of life after which they show a gradual decrease largely because endosteal resorption exceeds subperiosteal apposition (Garn, 19701. Therefore, although the total shaft diameters may increase there is a gross loss of cortical tissue with age (see also Smith & Walker, 1964; Bartley & Arnold, 1965; Dewey et al., 1969; Armelagos et al., 19721. Average cortical loss after the fourth decade amounts to approximately 0"22 m m per decade in males and 0"54 m m per decade in females (Garn, 1970). Femoral head diameter is also sexually dimorphic ('Fable 15) (see also Parsons 1914, 19151. The mean Ancaster female head diameter of 43'02 m m is just within the male range (42'1-53'0 ram); the low standard deviations of 2'44 (9) and 2'56 (Cf) suggest the importance of this parameter" in sexual distinction. It would be reasonable to expect that shaft obliquity is similarly sexually dimorphic since the female pelvis (as measured by biacetabular breadth, for example) is broader and the female femur is, on the average, shorter than the male. However, the data do not bear out this supposition. Mean shaft obliquity (Table 131 is only 0.8 ~ greater in the female and the range is, in fact, smaller than for males. The product-moment values do show a negative but statistically non-significant (P = <0'05) correlation (r = - 0"04 (9) and r = - 0'09 (&) between shaft length and obliquity). Moreover, length of the head-neck axis (Table 15) does not play a significant part in shaft obliquity. In absolute terms the length of this axis is less in females, although their obliquity is slightly greater than in males. The correlation between the head-neck axial length and obliquity is again very small: r = + 0'19 (~)) and r = - 0"14 (C~). It would appear, therefore, that the broader female pelvis is biomechanically counteracted in the proximal femur by a shortened head-neck axis rather than in the shaft. All remaining measurements of the shaft show large within-sex variations and overlapping ranges and are apparently less sexually dimorphic.

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T h e inter-relationships and possible i n t e r d e p e n d e n c e betwccn certain shaft parameters is suggested by the p r o d u c t - m o m e n t correlation coefficients (Table 17). Moderate correlations in both sexes are seen between the internal a n d external parameters at the s u b t r o c h a n t e r i c a n d mid shaft levels with the length of the head-neck axis. O f particular interest are the correlations between the sub trochanteric medial cortex and transverse shaft diameter with the length of the h e a d - n e c k axis. The correlation between the medial cortical d i a m e t e r at the s u b t r o c h a n t e r i c level and the h e a d - n e c k axis is r = 0.50 ( 9 ) and r = 0'42 ( ( f ) ; both correlations are significant at the P = >0.01 levels. These values account for 25% of the variability at this level in females and 17% in males. T h e medial cortical tissue in the u p p e r shaft u n d o u b t e d l y provides buttressing and stabilization for the b e n d i n g m o m e n t s and compression associated with the neck axis, T h e fact that the lateral cortical diameters are more highly correlated with the length of the h e a d - n e c k axis at the mid shaft and subpilastric (70% of shaf't length) levels is indicative of the sapient p a t t e r n of weight t r a n s m i s s i o n p r e d o m i n a n t l y along the lateral aspect of the shaft b e g i n n i n g at or slightly above the mid-shaft level. This supposition is supported by the negative and statistically non-significant (P = <0'05) p r o d u c t - m o m e n t correlations between the medial cortex and the axial length at the lower-shaft level. Moreover, in the Ancaster sample the lateral cortex exceeds the medial cortex in thickness at the mid-shaft level. Most fossil hominines, however, show the reverse situation; this wilt be discussed below. I n the lower shaft the cortex becomes very thin in all orientations. I n the mediolateral orientation at the subpilastric level, for example, the cortex occupies only 27% ( 9 ) or 28"3% (O~) of total shaft diameter. I n the anteroposterior orientation these values become 33'4% ( ~ ) and 32"7% (O~).

Table 3

Cortical indices: subtrochanteric level

Mediolateral*

Ancaster Males = 57 Females = 4.3 Bushmen = 8 Choukoutien Femur I Femur IV Trinil Femur I Femur II Femur III Femur IV OH 28 KNM ER 737 803 1481a

Mean

S.D.

45"99 41"47 52"39

9"30 9"94 7-58

Standard error of M 1"23 i'i5

Anteroposteriort

Range

Mean

S,D.

29'6-74'6 29"6-60"9 35"9-59"2

39"57 37"80 48'96

7"62 t0-46 9,97

52'9 52.5

63'8 54.7

62"8 41,9 53'3 42.6 50"1 59"1 40.1 64"5

63.1 48"6 52'6 38'4 45-2 48.5 44"1

Standard error of M 1.01 1-59

Range 26"9-62"3 26"9-69-7 30'5-51-8

All measurements in ram. * 100 (medial + lateral cortical diameters)/Martin No. 9. 100 (anterior + posterior cortical diameters)/Martin No. 10.

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A n u m b e r of workers (Schultz, 1953;Jolicoeur, 1963; K u m m e r , 1972, for example) have noted a relationship between femoral length and various shaft diameters. I n this study external shaft p a r a m e t e r s (mid-shaft circumference and diameters in both orientations) are positively correlated with length. Correlations b e t w e c n a n t e r o p o s t e r i o r shaft diameters a n d shaft length are significant at all level in both sexes (P = >0"01). Correlations generally are lower, however, in the mediolateral orientation; in the upper shaft in the males the correlation between mediolaterial shaft diameter and length is not significant (P = <0'05) but at other levels in male and at all levels in females the p r o d u c t - m o m e n t correlations are significant (P = >0'01). While there are generally significant correlations between length and the external shaft parameters, there is very little significant correlation between length and the cortical diameters at various shaft levels. I n all cases, the correlations between length and the internal diameters are less than between length and the external diameters. Only the correlation between anterior cortices in males and shaft length are consistently significant (P = > 0"01). It might thus be concluded that this relationship indicated the presence of additional cortical mass on the anterior shaft to buttress against the b e n d i n g m o m e n t s produced by anteropostcrior shaft bowing (Table 14). This does not seem to be the case, however, since the correlations between anterior cortical diameter at mid-shaft and the height of the subtense are non-significant in both sexes (P = <0"01). It seems more likely that the b e n d i n g m o m e n t s on the anterior shaft are resolved to a greater degree by the total anteroposterior mid-shaft diameter. T h e p r o d u c t - m o m e n t correlation between this diameter and subtense height are significant: r = 0'48 ((~) and r = 0"46 (Cf).

Table 5

Cortical indices: mid-shaft level

Mediolatcral*

Anteroposteriort

Standard

Standard

error

Mean Ancaster Males (N 57) 57.66 Females (N - d-3)55-32 Bushmen(N = 8) 57.10 Choukoutien Femur I 63'3 Femur IV 65.7 Trinil Femur l 50"7 Femur II 48"1 Femur III 57.7 Femur IV 48'9 OH 28 53.8 KNM ER 737 66"5 803 43.6 1481a 73.9 =

S.D.

of M

7"83 I 1-16 10"24

1,03 1.70

error

Raugc

Mean

29.6-74.5 53"24 27-8- 75.8 49-72 't3-1 78"3 56"08

S.D.

of M

Range

7.62 1t'63 5"63

1"00 1"72

32"8-78"5 31"3-71"4 44"2-61-7

70"2 67,1 61-2 52"9 58"5 53' 1 .t5"9 6(1"4 42<) All measurements in ram. * 100 (medial + lateral cortical diameters)/(ML shaf! diameter, taken at level of maximum AP mid-shaft diameter). + t01) (anterior + posterior cortical diameters)/(maximum AP mid-shaft diameter).

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F r o m this d a t a it would seem that with increasing length, b i o m c c h a n i c a l stability is achieved by total cross-sectional a r e a of the shaft rather than by increasing cortical thicknesses. T h u s , the increase in cross-sectional shaft a r e a related to increasing fkmoral length is not reflected in increasing cortical diameters. T h e cancellar structures and t r a b e c u l a r systems of the p r o x i m a l femur have been described by a n u m b e r of a u t h o r s ( W a r d , 1838; Walkoff, t904; Koch, 1917, for example). K o c h (1917) identified two systems of compressive t r a b e c u l a e and three systems of tensile t r a b e c u l a e in m o d e r n sapients. T h e compressive lamellae arise from the m e d i a l aspect of the p r o x i m a l shaft. T h e first of these systems, "a", arches across the shaft with some lamellae ending in the greater t r o c h a n t e r and others following a less a r c u a t e course into the superior lateral p o r t i o n of the neck. T h e m a i o r compressive system, "b", travels in a c r a n i a d direction a n d ends at the superior surface of the head. This system shows a m a r k e d a m o u n t of r a d i o g r a p h i c density. Generally, in m o d e r n h u m a n s these two systems arc clearly diitkrentiated a n d there is no m i x t u r e of their n e i g h b o r i n g lamellae. T h e strong d i r e c t i o n a l i t y of these systems, p a r t i c u l a r l y the m a r k e d craniad orientation of group "b", leaves an area of low or m i n i m a l r a d i o g r a p h i c density in the femoral neck called W a r d ' s Triangle. Systems % " a n d "b" form the sides of the triangle with the m a i n tensile g r o u p " d " (see below) forming its base. 'vVhile a clearly m a r k e d W a r d ' s T r i a n g l e was present in all of the B u s h m e n sample, 6% of the A n c a s t c r controls did not show d i m i n i s h e d r a d i o g r a p h i c d e n s i t y in this area. In these i n d i v i d u a l s the superior lamellac of system "a" intermingle with the inferior l a m e l l a e of system " b " thus leaving no clear area between them. T h e three tensile t r a b e c u l a r systems arise from the p r o x i m a l portion of the laterat shaft. G r o u p "c" travels from the distal to the p r o x i m a l portions of the greater trochanter. T h e m a i n tensile group, "d", follows a high, arching course from the outer p a r t of the s h a • j u s t below "c" to the infkrior surface of the head. System "c" follows a more or less horizontal course across the p r o x i m a l shaft. Cortical Indices: Subpilastric level

Table 7

Mediolateral*

Mean Ancaster Males (N = 57) 28"33 Females (N = 43) 27.04 Bushmen (N= 8) 31"64 Trinil I 36"06 Trinil II 50"37 Trinil III 43"52 Trinil IV 42-40 OH 28 33"33 KNMER737 34'39

S.D.

Standard error of M

5'14 4'37 5"44

0"68 0"66 1'92

AnteroposteriorJ-

Range 2l'0-39'3 20"0-30"6 21'1-39'0

Mean

S.D.

Standard error of M

32'77 33'45 36"91 39"60 56'45 50'18 31'49 35"60 47'68

4'81 4"66 4'85

0'63 0'71 1'71

Range 26'2 38'2 24,l-43"2 27'3-41'5

All measurements in ram. * 100 (medial + lateral cortical diameters)/ML subpilastric shaft diameter). ~" 100 (anterior + posterior cortical diameters)/(AP subpilastric shaft diameter),

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Table 12

External sha~ indices: minimum breadth index*

Ancaster Males (N = 53) Females ( N = 47) Bushmen ( N = 8) Choukoutien, Femur IV Trinil Femur I Femur II OH 28 K N M ER 737 1481a

Mean

S,D.

54'67 56.10 59"81 45'5

7"60 7.41 6"72

Standard error of M

1.00 1.13

Range

42.9-74.0 44.3-70'7 50.1-75.9

47'3 48"2 44"0 45'4 35'5

All measurements in mm, * I00 (height of minimum shaft ML breadth above the infra-condylar plane)/shaft length. ~"Taken at most distal point remaining on shaft.

Table 1:3

Obliquity of femur* Standard error

Ancaster Males (N = 57) Females ( N = 4 3 ) Bushmen ( N = 8) Trinil I K N M ER 1481a

Mean

S.D.

of M

Range

10"3~ 11'1 ~ 11"0~ 12'8 ~ 13'4 ~

1.9 2.0 3.2

0"04 0'06

5"0-16"8 4.5-15.0 9.9 13,0

* Martin No. 31) (Martin & Sailer, 1957).

Table 14

Shaft bowing: height of subtense*

Ancaster Males (A'= 57) Females ( N = 43) Bushmen ( N - 8/ Choukoutien. Femur IV Trinil Femm" I Femur II KNM ER 737 1481 a

Mean

S,D,

5"92 4'50 6'64 4'50

2"24 1.79 8'30

Standard error of M

0"29 0.27

Range

1.2 8"6 1.8-13,8 5"5-10'8

5"40 4"41 5'02 5"90

All measurements in ram. * Taken on MI. X-ray: maximum height ofa subtense to a chord fi'om tile anterior subn'ochanteric to anterior popliteal levels.

601

FEMORAL MORPHOLOGY IN H. E R E C T U S

Table 15

Head diameter, length of head-neck axis Head diameter*

Length of head-neck axis~

Standard

Standard

error

Ancaster Males (N = 57) Females (N = 43) Bushmen ( N = 8) Trinil Femur I Femur II K N M ER 1481a

Mean

S.D.

of M

48'94 43'02 38"01

2'56 2"44 2'39

0'37 0"37

error

Range

42"1 53'0 39"2-49"1 35'0-41"8

41'0 44'0

Mean

S.1).

of M

Range

78"28 68"19 59'56

6'02 5"72 3'79

0"79 0'87

65'9-90"9 60'0-86'3 54"(>65'9

83"1 82,0 76"5

(est.)

All measurements in ram. * Martin No. 18 (Martin & Sailer, 1957). I- Distance fi'om periphery of head to mid-shaft axis; taken on AP X-ray.

Table 16

Neck-shaft index, head-shaft index Neck-shaft index*

Ancaster Males ( N - 57) Females (N = 43) Bushmen (,V= 8) Trinil I Trinil II KNM ER 1481a

Standard crror of M

Mean

S.D.

20'51 19.72 17.12 20'22 20'81 18"49

1"73 1'52 1'10

0"23 0"23

Head-sha~index*

Range

Mean

S.D.

16"6-25'7 16'7-23'3 15"8 18'2

12"59 12"49 1(/'98 10"14

(1"55 0"88 0"40

13"09 All measurements in mm. * 100 (length of head-neck axis)/shaft length. + 100 (head diameter)/shaft length.

Standard error of M

(/"07 0'13

Range

10'9-13'5 10'9-13"3 10'2-11'4

602

G. E. K E N N E D Y

Table 17

Product-moment correlations, Romano-British Mediolateral shaft Males Females

Anteriorposterior shaft Males Females

0"24 0.08 -0"23 - 0" 18

0'47 0.39 0"01 0,09

-0'06 -0"40 -0"23 - 0" 18

0"22 0.08 0"02 0.34

0'08 0.08 0'11 0-30

0'23 0'12 0'12 0"25

M i d - s h a f t level M e d i a l cortex L a t e r a l cortex P o s t e r i o r cortex A n t e r i o r cortex

0"38 0"41 0'20 0' l 8

0'23 0"25 0' 16 -0"04

0'02 0"23 0'27 0"24

0" 10 -0'19 0'22 - 0" 13

0'07 0"37 0"03 0'39

0'30 0'11 0"34 0' 19

S u b p i l a s t r i c level M e d i a l cortex L a t e r a l cortex P o s t e r i o r cortex A n t e r i o r cortex

-0"14 - 0" 16 - 0 ' 17 - 0" 10

-0"11 0'05 -0'01 - 0"03

-0'16 0' 14 - 0 " 11 - 0'03

-0'34 0"09 0'29 - 0" 18

-0'02 0" 13 0"03 0"33

-0"02 0"21 -0'01 0" 17

-0.09 0.52 0.34

--0.04 0.34 (/.51

Sub t r o c h a n t e r i c level M e d i a l cortex L a t e r a l cortex P o s t e r i o r cortex A n t e r i o r cortex

Shaft obliquity Head diameter H e a d - n e c k axis

Table 18

F e m o r a l shaft length Males Females

Mahalanobis D212 values

D i s t a n c e from g r o u p m e a n Romano-British Males Females

Specimen

Trinil

T r i n i l II I[I IV

2"6 2"6 1"0

12"5 10"4 13'7

13'8 14'2 14,7

27'8 33"7 36'9

89"3 34'0 28"7 22'9

59.4 39'8 28'0 29'9

62.5 37"7 42"8 35.8

19" 1 6'3 13'5 5'5

K N M E R 737 K N M E R 1481a O H 28 C h o u k o u t i e n IV

H. erectus

The Bushmen Externally thc B u s h m e n shaft is very gracile. In the medi01ateral orientation of the u p p e r and mid shaft their m e a n is below the control* female range and at the s u b p i l a s t r i c level is within 0'5 m m of the low end of" that range. In the a n t e r o p o s t e r i o r orientation the differences are not as m a r k e d but the B u s h m e n means at all shaft levels are below the control female means. This conformation is reflected in the shaft indices which, except fbr the popliteal index, are above the control means i n d i c a t i n g a r o u n d e r shaft. T h e gracility of * T h e t e r m " c o n t r o l " refers o n l y to the R o m a n o - B r i t i s h sample.

FEMORAL MORPHOI,OGY

IN H . E R E C T U S

603

the Bushmen shaft is emphasized in the head diameter; the mean of thc eight unsexed individuals is more than four s.d. units (-4'26) below the male control means. Internally, however, the Bushmen shaft has relatively thicker cortices in both orientations in the upper shaft and in the mediotateral orientation at mid shaft. This [inding is somewhat unexpected in view of the small stature and overall gracility of the Bushmen in contrast with the robustly build Romano-British controls.

The FossilSample Lower Cave, Cho~&oulien.Weidenreich's ( 1941 ) description of the "extraordinary thickness of" the walls and the relative narrowness of the medullary canal" in the Choukoutien femora is confirmed in the context of a large comparative sample. All cortical diameters and cortical indices in the two most complete specimens (I and IV) exceed thc control combined ((3 + 9) means and, except tbr Ihe posterior cortex at mid shaft, exceed the male means as well. The antcroposterior cortical indices show the greatest differences from the control values. In the upper shaft this index has values ot"63"8 (Femur 1) and 54"7 (Femur IV) in contrast with the male control means of 39'5. Even the more gracile of these two individuals (Fernur IV) exceeds the male control means by + 1'98 standard deviations; the index tbr Femur I exceeds the male control range. At mid-shaft the cortical index in this orientation is also large. Here Femur IV, again the smallest, has an Index + 1'81 standard deviations from the male control mean while Femur I shows a distance of" +2"22 s.d. In this orientation at mid-shaft the cortex of Femur I occupies 70'2% of the total shaft diameter while the mean tbr the male controls is 53'2%. These very high indices in the anteroposterior orientation are due to a combination of absolutely large cortical values and very small external shaft diameters. In the mediotateral orientation the cortical indices deviate less from the male control means but they are. still above those values. Only the mediolaterat cortical index of Femur IV at mid-shaft exceeds one standard deviation f?om the male control mean (+ 1'02 CY s.d.). It was not possible to determine the subpilastric cortical values. The cortex on the inferior aspect of the neck remains thickened to a more proximal point than in the sapient controls. In the modern sapiens the medial cortex thins at the base of the neck while in Choukoutien IV it remains thickened to the level of the break, presumably near the base of the head. Ahhough it is not possible to estimate the total length of the neck on these two femora it is likely that such proximal buttressing of the cortex could, in part, at least, act to provide stabilization for a long femoral neck. Despite the cortical thicknesses seen in these specimens they are not robust externally. Thus, the thickened cortex is not reflected in greater external shaft size. In the mediotateral orientation at the upper shaft, for example, where the thickened cortex is very marked, the transverse shaft diameter of Femur I exactly coincides with the mean of the male controls; in Femur IV it is, in fact, below the male control means. In the anteroposterior orientation at the same level where the relative cortical thickness of Femur I is above the male control range, the total shaft diameter in the Choukoutien specimen, in fact, falls below even the female control mean. This pattern of very small anteroposterior diameters continues throughout the measurable parts of the shaft and is reflected in the shaft indices which are below the control means at atl levels. There is no pilastre fbrmation on the posterior shaf) and the linea aspera lies directly upon the shaft. The minimum breadth index (using Weidenreich's estimate of shaft length) shows that the smallest transverse diameter falls lower on the shaft in Femur IV than in the controls; the index could not be calculated fbr Femur I because of the shortness of the

604

G.E. KENNEDY

fragment. The minimum breadth index of 45"5 in Femur IV, in contrast with the control combined mean of 55'3, supports Weidenreich's suggestion that the point of least shaft breadth fell low on the Choukoutien specimens. In Choukoutien, Femur IV and all other fossil femora included here (except the pathological Trinil, Femur I where the measurements are distorted and K N M ER 803) the medial cortex at mid-shaft is thicker than the lateral cortex. The reverse situation is seen in the modern sapients included in this study. This is undoubtedly associated with tile low position of minimum shaft breadth in the fossil hominines and may reflect a differing pattern of weight transmission in the early hominine lower limb (see below). In his monograph, Weidenreich reported that the proximal femora of "Sinanthropus" demonstrated several distinctive internal features apparent on the skiagraphs. The first of these distinctions concerned the way in which the lamellae diverge from the inferior aspect of the neck. Wcindenreich stated that WalkolTs systems I and II (equivalent to Koch's (1917) systems "a" and '%" respectively) are not separate and discrete as they are in "modern" man but are "diffuse" and that because of this homogeneous dispersion of the trabcculae Ward's Triangle is absent. These distinctive characters of the trabecular systems were also said to be present in Neandertal. Weidenreich's diagram (1941) of the Chinese Femur 1 appears to confirm that tile two medial trabecular systems lack the differentiation seen in the modern controls. Ahhough the superior portion of the neck is missing in Femur IV the honmgcnous dispersion of the trabeculae in the inferior portion make it very unlikely that a clearly defined Ward's Triangle was pro'sent. However', in tile few controls (6%) which lack a Ward's Triangle the trabeculae do not show such a homogeneous dispersion in the inferior cervical area. In those control individuals the Ward's Triangle is lacking because of tile mingling of the trabeculae at the interface between svstems "a" and "b". The strong orientation of these systems apparent in the controIs is lacking (at least in the preserved portions) in this fossil specimen. Thus, in Femur I the lamellae can be seen radiating in a difthse manner from the inferior surface of" the neck. The trabecular systems appear to originate in the proximal shaft, as in the controls. OH 28. This specimen consists of most of the shaft and the inferior portion of the neck. At the subtrochanteric level, all cortical measurements, except the anterior diameter exceed the male control means. Despite the smallness of the anterior cortical diameter at this level (it is, however, above the female mean) both cortical indices at this level are above the male means. The anteroposterior cortical index exceeds that value by +0'73 s.d.; the mediolaterial cortical index exceeds it by +0.44 s.d. At mid-shaft the cortical indices fall below the control means. At this level, the lateral cortex exceeds the medial diameter as in other fbssil hominines. Externally this specimen reflects the pattern described previously fbr early hominines. Tile anteroposterior shaf't diameters are very small; at the upper and mid shaft they are below the female control means. The mediolateral diameters at both levels, however, exceed the male means rcsuhing in a very lo~ platymcric index ( - 2 ' 0 3 (3* s.d.) as in Choukoutien. The shaft flatness is even more marked at mid shaft whcrc the pilastric index is -3"15 s.d. below the male control mean. The platymeric and pilastric indices are the lowest in tile entire series and are below the control ranges. The shaft flatness is less marked at the subpilastric level where the index approaches the control values. The minimum breadth index of 44'0 using Day's (1971) reconstructed length of 456 mm is closely

FEMORAL M O R P H O L O G Y IN H . E R E C T U S

605

equivalent to the figure for Choukoutien IV and reflects, again, the distal shaft constriction characteristic of the early hominines. The linea aspera lies fiat on the posterior surface of the shaft without a pilastre as in the Choukoutien femora and K N M ER 803 (see below). K N M ER 737. O f primary interest in this specimen is the great thickness of the cortex throughout the shaft and especially at the inferior aspect of the neck. Radiographically, the appearance of the cortical tissue in the inferior region of the neck shows the same thickened proximal extension seen in the Choukoutien specimens. The trabecular patterns of the inferior neck cannot be observed. The medial cortical diameter in the subtrochanteric region is the second largest in the entire fossil series and exceeds the control range (+ 1-33 C5 s.d.; + 3'61 9 s.d.). The mediolatcral cortical index at this level is +1"40 standard deviations above the male mean. At mid-shaft the medial cortical diameter is again very large (+1'79 O* s.d.); it is exceeded only by Choukoutien, Femur I and K N M ER 1481a (see below). The mediolateral cortical index at this level exceeds the male mean by +1" 12 standard deviations. As in other fossil hominines, the medial cortex at mid shaft exceeds the lateral. Externally, the upper and mid-shaft are narrow anteroposteriorly as in other early hominines. The rather large mediolatcral diameter in the upper shaft has prevented the platymeric index from being very low ( - 0 ' 8 0 CY s.d.). The pilastric index, however, is very low (-9.80 Cf s.d.) and is below the control ranges. In comparison with the controls the shaft narrows considerably in both orientations at the subpilastric level. This is reflected in the low minimum breadth index ( - 1"21 Cf s.d.) which closely approximates the figure for Choukoutien Femur IV; it is very near the low end of the control ranges. The transverse narrowness of the lower shaft is fbund in other early hominines and is distinct from the supracondylar expansion seen in the controls. This specimen differs from the Choukoutien, K N M ER 803 and O H 28 femora in having a moderate pilastre on the posterior surface. In modern sapients the pilastre is surmounted by a double-lipped linea aspera. On K N M ER 737 the linea aspera begins as a double crest proximally but in its middle portion apparent surface erosion of the bone has reduced this to a single, sharp line (see also Day & Leakey, 1973). K N M ER 803. This is a very fragmentary shaft specimen. Internally, the specimen is not robust. However, the subtrochanteric measurements, taken at the most proximal point remaining on the shaft, undoubtedly do not reflect the maximum cortical values in that area. Nevertheless, the cortical diameters are also small at mid-shaft; the anterior" and lateral diameters are below the male means while the posterior and medial diameters are below the female means as well. The cortical indices at both levels and in both orientations are also below the female mean except for the anteroposterior cortical index at the upper level which is above the male mean (+ 0'59 s.d.). Externally, all anteroposterior shaft measurements are blow the male mean resulting in platymeric and pilastric indices which are also below the means for both sexes. Thus, in the very few' quantifiable features remaining on this individual the external resemblances are close to the other early hominines. Internally, however, the shaft is more gracile than in other members of this group. The internal gracility of this specimen cannot be due to juvenile status since other bones with fused epiphyses are known from the same individual.

606

G.E. KENNEDY

K N M ER 1481. This is a complete fkmur showing erosion of the peripheral cancellous hone on the head and medial condyle. A complete anatomical description of this specimen can bc fbund in Day et aL (1975), Internally, heavy mineralization has resulted in poor X-ray visualization in the head, neck and distal shaft; details of the trabecular systems are not visible. In tile anteroposterior orientation, however, visualization of the upper and mid-shaft was clear. In the upper shaft the medial cortex is the thickest in the fossil series and is above the male control range ( + 2 ' 0 9 (2)* s.d.). The mediolateral cortical index for the upper shaft shows that, relative to shaft diameter, this femur is the thickest specimen in the fbssil series (+ 1"99 C~ s.d.). It is of interest that the very large medial cortex is not associated with a very long h e a d - n e c k axis, indicating again that variability at this position in the fbssils is only partly due to the length of this axis. The relative and absolute thickness of the cortex of this femur is even more marked at mid-shaft. At this level, the medial cortex is very thick indeed; it is equivalent to Choukoutien I in being thc thickest in tile fossil series and approaches the high values of Choukoutien IV and K N M ER 737 very closely. This value is just within tile male control range but is above the f'emalc range. Mcdiolaterally at mid-shaft the cortex occupies nearly three-quarters of the shaft (73'9%) while in the male controls it occupies, on the average, just over half ( 5 7 6 % ) . A1 mid-shaft, the medial cortex exceeds the lateral in thickness. Despite the very large cortical diameters, the external dimensions of the bone are at all levels and orientations, below the male means. In all but the transverse diameter- in the upper shaft the dimensions for K N M ER 1481a are also below the female means. T h e anteroposterior diameters are below the male control ranges throughout the shaft. The very small anteroposterior diameters arc reflected in the low shaft indices. The platymeric index of 70"2 is below both control means but within their ranges. The lower shaft lacks the transverse expansion seen ir~ the controls. Because of the very small mediolateral shaft diameter (-2"52 Cf s.d.), the subpilastric index is below the female control range yet within the male range. Moreover, the popliteal index in the tbssil (93"0) is more than three standard deviations (+3.48 CY s.d.) above the male control mean and is beyond that range; it is, however, within the female range. This shape, reflecting a very distal constriction of the shaft, is also seen in the low m i n i m u m breadth index ( - 2 ' 5 2 C5 s.d.) which is below both the male and female ranges. This index is the lowest in the entire series. T h e head diameter is estimated at 44 ram; although surface erosion makes this a m i n i m u m value, the true diameter cannot have been much, if any, greater. T h e head-shaft index is slightly above the male control mean (+ 0.90 C~ s.d.). This is rather different from the situation in Trinil 1 where the same index is more than four standard deviations below the male mean. The head-neck axis is not absolutely long in this individual, it is less than one standard deviation below the male control mean. However, the neck-shaft index is rather high (+ 1"16 O~ s.d.) reflecting the fact, relative to shaft length, the neck axis is somewhat longer than the average controls. This is one of the very few fossil hominines in which shaf't obliquity can be accurately determined. Shaft obliquity in this specimen, (13'4~ is above the control means but only + 1"63 standard deviations above the male mean.

Trinil, Femur I. This femur demonstrates a remarkable osteophyte originating on the

F E M O R A L M O R P H O L O G - Y IN H. E R E C T U S

607

proximal medial surface of the shaft; this probably represents myositis ossificans (see Day & Molleson, 1973). X-rays show that tile medullary cavity at the level of the growth is irregular but not significantly narrowed. The cortex shows irregular opacification and uneven borders throughout the entire posterior and medial shaft beginning at approximately the level of the base of the greater troehanter and extending to a point 165 mm above the horizontal condylar plane, the anterior and lateral cortices do not, however, show these features except at the level of the exostosis. The unevenness involves both the endosteal and periosteal borders of the cortex; the posterior cortex shows irregular thickening throughout the length of the shaft and this thickening continues into the area just superior to the condyles themselves. In non-pathologic fossil and recent specimens, the cortex thins at a considerably more proximal level and it is possible that this particular condition of the cortex in Trinil, Femur I is related to the pathologic processes active in the bone. A further interesting aspect of the radiographic appearance of this femur is the presence of linear areas of vertically oriented increased density along the eortico-rnedullary boundary, extending the entire length of the shaft; this may be due to some post-mortem mineralization phenomenon but was not seen elsewhere in this study. Trabecular system "b" shows a high degree of radiographic density, as in the controls. The medial cortex, however, remains thickened up to the base of the head as in Choukoutien, Femur I, whereas in the controls it thins distal to this point. Mineralization of the bone does not permit visualiation of the area of Ward's Triangle nor the pattern of the trabccutar dispersion from the medial aspect of the neck. The head diameter of this specimen is below the mean for the Ancaster females ( - 0 ' 8 2 s.d.) and is below the male range. In view of the demonstrated dimorphism of femoral head size in the controls it seems probable that Trinil, Femur I is that of a female. Moreover, the head-shaft index for Trinil I is more titan two standard deviations ( - 2 ' 6 7 s.d.) below the female mean, confirming that, relative to shaft length, the head size is also below expected values. T h e length of the head-neck axis is above both the male (+ 0.80 s.d.) and femah: (+ 2"60 s.d.) Ancaster means. Therefore, in terms of absolute axial length 95"5% of the Ancaster females can be expected (if Trinil I is indeed a female) to have a shorter head-neck axis. However, relative to shaft length, axial length is not exceptional in the, fossil. The neck-shaft index shows that this specimen is only + 0"32 s.d. above the female mean and is equivalent to the male mean. Therefbre while the head-neck axis is absolutely long in Trinil I, relative to shaft length it is not. External diameters of the shaft and radiographs of this specimen have been measured; this data can be fbund in the tables. These measurements, however, must be regarded with a high degree of caution in view of the extent of the shaft pathology. The very large lateral and posterior cortical diameters at the mid shaft, for example, should not be unduly emphasized. It is fortunate that there exists three other relatively complete femora from the Kaboeh deposits in J a v a on which to base a discussion.

Trinil, FemurH. This is an extremely long, yet gracile bone. At an oblique distance of 400 m m from the head the shaft shows no evidence of lateral expansion for the condyles. Its total oblique length has been estimated to be 500 mm (Weidenreich, 194l) or 460 m m (Day, 1971). Despite its length, the bone is not robust internally in the upper and mid shaft. Only the anteroposterior cortical index in the upper shaft exceeds the male control mean (+1'18

608

G.E. KENNEDY

s.d.). This situation changes at the subpilastric level, however, where a combination of small external diameters and large cortices has produced the highest subpilastric cortical indices in this study. In Trinil II, the anteroposterior diameters throughout the shaft are below the male control means but the bone is also very narrow in the mediolateral orientation, relative to the controls, so tl'iat the shaft is nearly round at all levels below the subtrochanteric level. In the upper shaft, the platymeric index is nearly equivalent to the male controls. In the mid-shaft, the medial cortex is thicker than the lateral. The minimum breadth index is below both control means (-0.84 O~ s.d.; - 1 ' 0 6 ~ s.d.) indicating that minimum mediolateral shaft constriction occurred below in the shaft mid-point. Although the margins of the head are eroded, the length of the head-neck axis is estimated to be a minimum of 82 mm long. This figure is within one standard deviation of the male controls and is, thus, within that range. The neck-shaft index is very close to the control values (+0'17 O* s.d., +0"71 9 s.d.) again confirming that the proportion of neck length to shaft length does not vary significantly in the fossil Trinil hominines from the controls.

TriniI, Femur III. This, too, is an extremely long bone and probably nearly equivalent with Femur II in total length. Internally, this specimen is robust; in tile anteroposterior orientation throughout the shaft the cortical indices are above the male control means. While these values are within one standard deviation of those figures in the upper and mid-shaft, at the subpilastric level the cortical index for Trinil I I I is 3'61 standard deviations above the male mean and is above that range. The mediolateral cortical indices are only slightly larger than the male control means in the upper and mid-shaft but again at the subpilastric level this value becomes very large, exceeding the male control mean by 9.95 standard deviations. Thus, both Trinil II and I I I share a shaft conformation which is relatively gracile internally and externally in the upper and middle levels but which, in the lower shaft, very narrow external diameters combine with very robust cortical dimensions. At mid-shift, the medial cortex is thicker than the lateral, as in Femur II. Externally the shaft shows rather narrow anteroposterior diameters relative to the male', controls. As in Trinil II, Trinil I I I also shows the rather small mediolateral shaft diameters so that the shaft indices are near the control values. Although a precise determination of the position of minimum shaft breadth relative to total shaft length is not possible, this point would appear to [:all below the shaft mid-point. Trinil, Femur I K This is a more flagmentary specimen than the other Trinil femora. Internally, the medial cortical diameters are above the male means at all levels, but the cortical indices are all near the male control means. Externalh at upper and mid-shaft the specimen shows anteroposterior flattening with diameters below the male control means. The mediolateral values, however, remain near the control means resulting in external shaft indices below the controls but above the Choukoutien and Olduvai values. As in the other Trinil femora, the medial cortex at mid-shaft is thicker than the lateral.

4. Statistical Analyses In the multivariate analyses the Romano-British (sexes separate) formed the largest comparative group while the Bushmen (unsexed) formed a smaller sapient comparative group. Trinil II, I I I and IV were treated as a group because they have long been regarded

609

F E M O R A [ , M O R P H O L O G Y IN H . E R E C T U S

as having been derived from a single locality and levcl within the Kaboeh tbrmation (but see below). Because of the severe pathological distortion of its shaft, Trinil I was not entered into the multivariate analyses. A Homo erectus "group" consisted of O H 28, K N M ER 737, K N M E R 148ta and Choukoutien IV; the very fiagmentary specimens, K N M ER 803 and Choukoutien I, were not entered since too few parameters were present and would therefore have severely limited a muhivariatc analysis. Multivariate analyses were made using B M D P7M, a program using stepwise discriminant function analysis. This program includes a distance statistic (Mahalanobis's D 9) and canonical variable analysis. The multivariate analysis entered twelve variables of the internal and external shaft; these variables were included because they could be obtained on all included specimens. A bivariatc plot of the first two canonical axes is presented in Figure 1. Figure 1. Canonical axes I and 9. Romano British: males (I), tkmales (K]); Bushmen (O); Trinil (A); Homo erectus (*).

I /

[

I

I~

I

[

I

I

I

I

On the first canonical axis, H. erecl~s lies at one limit of tile group dispersion while the Romano-British males and the Trinil group are placed very close together; the Romano-British Females and the Bushmen are grouped well away from these groups on this axis with the B u s h m e n placed at the opposite limit of dispersion. Two parameters of the mid-shaft have contributed most significantly to this dispersion: M L external shaft diameter and medial cortex. T h e separation of H. erectus on this axis then reIlects their broad mid shaft breadths, internally and externally, in contrast with the smaller diameters at this level in the comparative sapicnts (male and t~malc Romano-British and the Bushmen) and in the Trinil group. Sixty-five percent of the total dispersion occurs on this first axis. On the second axis, the H. erectz~s sample again Falls as an outlier; howc'vcr, thc Trinil group here falls away from the comparative sapient vectors and is placed about mid-way to the H. ereclus centroid. Dispersion on the second axis is duc largely to thc greater cortical thickness in the distal shaft in the Trinil and H. erectus samples, particularly the lateral

610

G,E, KENNEDY

cortex at the subpilastrie level. Eighty-nine percent of the total dispersion occurs along these first two axes. Figure 2 shows a mathematically simpler method of demonstrating the pattern of group differences occurring in the external femoral shaft. As pointed out above, the Homo erectus shaft is characteristically flattened throughout its lengttl and shows a low point of m i n i m u m shaft breadth. Thus, although shaft indices were not entered into the multivariate analyses, shaft shape is neverthelcss significantly different between early and rccent hominines. T h e two recent sapient groups (Romano-British and Bushmen) reach their highest index values (i.e. greatest roundness) at mid shaft; m i n i m u m shaft breadth (the "waist") also occurs at this level. Below this level the shaft widens transversely and lower index values occur. H. erectus, on the other hand, continues to broaden in the mid-shaft region and the highest shaft index (and the "waist") occurs at thc subpilastric level. T h e Trinil femora show a fully sapient pattern in shaft shape at the upper, mid and sub pitastric levels. Howc'ver, their distal shaft is rounder than in the sapient controls and they show very high popliteai index values. This is true in Trinil femora I and II in which the popliteal index can definitely be ascertained and is probably true of'Femur I I I where a reasonable estimation of the. Index can be obtained. Figure 2. Femoral indices. Romanc>British ( Trinil (. . . . ); llomo erectus ( ).

); Bushmen (

9 );

105 I00 95 90 85 80 75 70

?::

L

/

Piatymedc index

Pilastric index

2

Subpilastric index

Popliteal index

Mahalanobis's D 2 scores, when assumed to shqw a multivariate normal distribution, can be treated as X2 values with the degrees of freedom equal to the n u m b e r of included variables (Brown, 1977). Table 18 shows these distance values using the same twelve variables. In this arralysis, the probability of any of the three Trinil specimens being included within the Homo erectus group is very small (P = <0'01) while the probability of" their being included within tile Romano-British group is much higher (P = >0"50). The three Trinil individuals all show very small D 2 values from a Trinil centroid and this is a strong indication of their intra-group morphometric affinity. K N M ER 1481a, on the other hand, shows a very small distance (D 2 = 6'3) from the H . ereclus centroid with a probability o f P = - 0"90 of inclusion within that group. O f particular interest in the D 2 values is that

FEMORAL

MORPIIOLOGY

I N II. E R E C T U S

611

while K N M ER 1481a and Choukoutien probably represent the oldest and youngest H. ereclus specimens in the sample respectively, they show very similar distances fl'om a H. ereclz~s centroid. This would seem to indicate t h a t at least in the lemur gradual

morphological change was not occurring in this taxon either through time or space. 5. D i s c u s s i o n The data rcported here indicate that the femora of fossil hominines currently attributed to the taxon, H. erecius, were characterized by an anatomical and metric pattern which was distinctive from modern sapients both internally and externally. Externally, the thmur of the Homo erectus group (Choukoutien I, IV, O H 28, K N M ER 737,803, and 1481a) shows sevcral differences from the controls. In terms of the shape of the upper and middle shaft, they arc flatter than tile controls. Whih: this flatness is less pronounced in the proximal shaft it is very accentuated at mid-shaft where tire mean H. erectus pilastric index is 2"4 S.D. below the" control male mean. Thc low platymcric and pilastric indices of the early group reflect, in part, the fact that the upper and mid-shaft is narrower in the antcroposterior orientation while remaining close to or exceeding the male control means in the transverse values. O H 28 and K N M ER 737, in fact, have very broad transverse diameters at both levels but their indices remain low because of" the very narrow anteroposterior diameters. The low position of minimum shaft breadth is one of the most consistent and obvious distinctions of the extcrnal fcmoral shaft in the fossil group and is rcflectcd, furthermore, in the internal structure of the bone. At mid shaft in the controls the lateral cortex is thicker than the medial, apparently reflecting the fact that in modern sapients weight is transferred from the medial to the lateral aspect of the shaft at or slightly above the mid-point. Therefore, greater lateral cortical thickness at mid-shaft may reflect its greater role in weight transmission. In the early hominines, however, the medial cortex remains thicker than the lateral to a more distal point. It is likely that this morphological contbrmation reflects a different pattern of weight transmission in the lowe.r limb of the early group with weight being transl~rred to the lateral aspect of the shaft at a more distal position than in the controls. This might be eflEcted in several ways. For example, a low- degree of shaft obliquity could reflect a more vertically oriented femur resulting in a more distal transmission point. However', in the two early hominines in which shaft obliquity can be measured it is greater, rather than less, than the control means. The length of the head-neck axis could also be a factor in a lower transfer point but this varies little throughout the samples; moreover, as pointed out above, the controls show no significant correlation between obliquity and axial length. The distal shaft corrstriction in H. ereclus is retlected in other ways. The transverse diameters at the subpilastric level in this early group are below the male control means and the transverse shaft diameter at the supra condylar (popliteal) level remain remarkably small. Theretbre, the gradual lateral expansion seen in the sapient lower shaft appears to be absent in the early group. Although the popliteal index can only be definitely determined in a single H. erectus individual (KNM ER 1481a) that value is beyond the range of the sapient controls. This is further indication of the very round and narrow distal shaft in this group. One of the most consistent and remarkable internal characters of the Homo ereclus femora is the great thickness of the cortex. Although the sapient controls display a wide range of variation, the cortices of this fossil sample were, in general, thicker both absolutely and

612

(~.S. KSNNSnV

reiative to total shaft diameters, than in the controls. While some ofthc individual cortical diameters in the early hominine sample can be duplicated in the control samples, the total pattern of great cortical robusticity throughout the shaft in the fossils cannot. Other research on cranial and post cranial elements from fossil hominines, particularly from the Middle Pleistocene, indicates that such thickened cortical tissue may, in fact, be a general anatomical characteristic of the early group. The cranial bones of many Middle Pleistocene hominines, for example, appear to have been characterized by thickened inner and outer tables [see Wcidenreich, 1943 (Choukoutien); Woo, 1958 (Ordos); Woo & Peng, 1959 (MaPa); Woo, 1965, 1966 a,b (Lantian); Weiner & Campbell, 1964 (Swanscombe); Sartono, 1971; Jacob, 1973 (Sangiran); Conroy, et al., 1978 (Bodo); Vlcek, 1978 (Bilzingsleben); Kennedy, unpubl. ( O H 9)]. The Choukoutien tibiae, although not yet comprehensively studied, also appear to have had thick cortices and narrow medullary canals (Woo & Chia, 1954; Chia, 1975). Radiographic examination of the hominine ulna from Bed II, Olduvai Gorge ( O H 36), demonstrates a very restricted medullary canal in comparison with a small sapient sample (Kennedy, unpubl.). In other features, however, the tkmur of these early honinines is similar to that of the controls. Head size can be measured in only one individual from this fossil group; in K N M ER 1481a head size is below the male mean (-1"9 O~ s.d.) and just above the female mean (+0'40 9 s.d.). However, when head size is examined relative to shaft length it appears that K N M ER 1481a has a head-shaft index slightly above the control means: (+0"68 9 s.d.; +0'90 O~ s.d.). Therefbre, in this very early hominine the proportion of head size to shaft length does not differ significantly from that of the controls. The early hominine femur shows very slight anteroposterior bowing of the shaft and in this they also resemble the controls. The greatest subtense height in the early group is found in K N M ER 1481a yet this exceeds the male control mean by only 0"02 mm. The chronologic and taxonomic associations of the group of femora f?om Trinil have long been the subject of debate and thus their relationship with the Homo erectus cranial and dental material fi'om the Kaboeh Formation at that locality has remained uncertain. Until the present time the best documented provenance ofTrinil II, I I I and IV was a box in the Rijksmuseum voor Paleontologic in Leiden, labeled "Trinil" (Dubois, 1932) but their true stratigraphic provenance has remained controversial (von Koenigswald, 1968b). Ahhough Bergman & Karsten (1952) fbund "good concordance" between the fluorine levels of the various bones from the Trinil locality, Day & Molleson (1973) have asserted, on the basis of more recent and complete chemical analyses, that the contemporaneity of the Trinil materials is unproven. They state that " . . . if" the rigorous criteria that are demanded in modern excavations were applied to all of the Trinil material subsequent to the calotte and Femur I, it would all be rejected as of doubtful provenance and unknown stratigraphy" (Day & Molleson, 1973, p. 130). Recent investigations at the Trinil locality (Bartstra, 1982) has shown that Day & Molleson were, in fact, correct in expressing caution about the temporal associations of the Trinil specimens. Bartstra (1982) has shown that Upper Pleistocene levels do exist at the localitv excavated bv Dubois and that the f~tunal material, including the hominine specimens, could represent materials from a broad and mixed temporal zone. Externally and internally, the Trinil specimens show a full>-sapient pattern in the upper and mid-shaft. It is only at the subpilastric level that thex demonstrate a distinctive morphological pattern. This distinctive pattern, consisting of thickened cortex and narrow

FEMORAL MORPttOLOGY IN H. ERECTUS

61 3

external shaft diameters is well summarized in the cortical indices at the subpilastric level. These indices for the Trinil sample, in both orientations, exceed even most of the I-I. ereclus values. It would seem then that while H. erectus shows general cortical robusticity in the femur, the Trinil specimens show only regional or localized robusticity. The distal cortical thickness in the Trinil sample may therefore have a different etiology than it does in the earlier group. Thus, although Trinil II, I I I and IV share some morphological tEatures with the H. erectus group, particularly their large cortical diameters and high cortical indices in the distal shaft it was demonstrated in the statistical analyses that their overall morphological pattern clearly allies them with the sapicnts. Moreover, the close morphometric association between the Trinil specimens, particularly well demonstrated in D 2 values, strongly suggests that they were drawn from a single population. The position is less clear for Trinil I and it would perhaps be wise to withhold taxonomic judgement because of the severe shaft pathology. Only three individuals within the entire fossil sample yielded reliable standard length measurements, yet even within this very small sample there was high variability. Oblique length and stature estimates, assuming body proportions like those of modern H. sapiens, are given in Table 19.

Table 19

Oblique length and stature estimates Stature estimates (cm)

Trinil I Trinil II K N M E R 1481a

Oblique femur length (mm)

White male

Black male

455 500 392

172"2 + 3'94 181'5 + 3"94 156'4+3'94

168"8 + 3'91 177'2 + 3'91 154-5_+3.91

Precise length estimates are not possible [br Choukoutien IV; Weidenreich estimated the total oblique length of this specimen as 402"5 mm (1941) thereby giving an estimated reconstructed stature of 158"3 cm (white male) and 156'2 (black male) (stature formulae: Trotter & Gleser, 1952).

6. Summary Although the spccimens within the early (i.e. Homo ereclus) group extend over a broad area of space and time they present a homogeneous pattern of femoral morphology. Even though their features may differ somewhat because of sex, regional variation and possibly time they, nevertheless, share a distinctive and consistent morphological pattern. That pattern consists of marked medullary stenosis due to absolute and relative increase in cortical bone throughout the shaft, craniad extension of the cervical cortex, medial cortex thicker than the lateral at mid-shaft, small anteroposterior shaft diameters and a low position of minimum shaft breadth combined with a narrow and round lower shaft conformation. Significant elements of this pattern have previously been identified in the Choukoutien specimens and in O H 28, specimens which have been attributed to Homo erectus (see Day, 1971). Since all members of the early group share, at least in the preserved remains, this

614

G,E. KENNEDY

distinctive suite of c h a r a c t e r s it seems p r o b a b l e that K N M E R 1481a, 737 and 803 should also be a t t r i b u t e d to Homo erectus. It is of great interest that the earliest specimen in this series, K N M E R 1481a, shows a clear and well defined suite of H. erectus femoral characters. O n the basis of this evidence there can be no d o u b t that the first a p p e a r a n c e of this taxon precedes ca. 2 m.y.a. A l t h o u g h the T r i n i l femora d e m o n s t r a t e a few characters, p a r t i c u l a r l y in the lower shaft, similar to those in H. erectus, their overall p a t t e r n unequiw)cably allies them with the sapient c o m p a r a t i v e groups. It m a y be that the characters of the distal shaft which they share to some degree with H. erectus are, in part, primitive retentions but it is also possible that they represent i n d e p e n d e n t acquisitions by isolated, insular populations. Thus, while the H. erectus f~mora a p p e a r to have been c h a r a c t e r i z e d by generalized, thickened cortex the Trinil s a m p l e d e m o n s t r a t e s significantly thickened cortex only in tile distal shaft. I n view of the differing total p a t t e r n of cortical robusticity in the two groups, the tatter e x p l a n a t i o n m a y be s o m e w h a t more plausible. Moreover, the close metric association a m o n g the Trinil i n d i v i d u a l s on all analyses strongly suggests that they were d r a w n from a single population. T h e large cortical d i a m e t e r s characteristic of the H. erectus individuals are not reflected or r e p e a t e d in large external shaft diameters. Therefore, the cortical robusticity seen in H. ereclus femora is not simply a maniti~station of overall femoral robusticity, T h e n a r r o w e r external shaft d i m e n s i o n s suggest that the a d d i t i o n a l cortical mass present in H. ereclus a p p e a r s to occur largely if not entirely at the endosteal surface. Since it seems unlikely that either b i o m e c h a n i c a l or atlometric factors are solely responsible for this " a d d i t i o n a l " bone (relative to H. sapiens) it m a y be, therefore, that the large cortices are due to either excess apposition or r e d u c e d resorption rates at this surface. Sew:ral tentative hypotheses explaining these large cortical d i a m e t e r s are then possible. I f they are due to excess apposition they m a y reflect neotenous retention of j u v e n i l e or adolescent growth rates. As G a r n (1970) has d e m o n s t r a t e d , it is d u r i n g the adolescent growth phase that m a j o r bone apposition occurs at the cndosteal surface. I f they are duc, on the other hand, to d e l a y e d bone resorption at the endosteal surface then a d i e t a r y explanation, p e r h a p s related to cyclical c o n s u m p t i o n of" low-calcium foods, such as meat, alternating with h i g h - c a l c i u m vegetable foods is possible (see M a c l n t y r e , 1968). T h e extra cortical mass in H. ereclus, could, in this case, reflect a r e c u r r e n t h y p o c a l c e m i c challenge at the endosteal surface the response to which was a delay in bone resorption. Finally, it m a y reflect a heritable tbrm of m e d u l l a r y stenosis, T h e s e hypotheses, at present very tentative, will be explored in more d e p t h elsewhere. References

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