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Morphometrics of the Neandertal talus.

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Morphometrics of the Neandertal Talus
JOHK G. RHOADS' AND ERIK TRINKAUS
Lkportment of Anthropology, Peabody Mccseum, Harvard University,
Cambridge, Massachmetts 021 38
KEY WORDS Talus . Morphometrics . Neandertals . Fossil
hominids.
ABSTRACT
A number of morphometric analyses of Neandertal tali since the
turn of the century have failed to reach a consensus on the functional affinities of
these fossil foot bones. 'To clarify the problem a univariate and multivariate analysis
of the available Neandertal and Skhd tali in relation to those of modern humans
was performed using nine linear dimensions and four angles. Our analysis indicates
that Neandertal tali are indistinguishable from modern human tali in the implied
locomotor capabilities and similar in overall size and proportions. The primary differences between the fossil and modern tali involve the greater articular robustness of the fossils, probably to compensate for higher levels of biomechanical stress.
The evolution of an efficient bipedal gait
among the hominids involved the development of a unique pedal morphology, one
which enables the support, propulsion and
balance of the body during a single legged
stance. This pedal structure is reflected
primarily in the hominid pedal arches and
hallucial robusticity. It is evident as well in
the hominid talus. As the central element
in the universal joint between the leg and
the subtalar skeleton, the talus must form a
stable structure with the tibia, fibula and
tarsals while conforming to the mechanical
requirements of the talocrural and subtalar
articulations. The hominid talus has, therefore, evolved as a short, high bone which
concentrates the joint reaction forces close
to the midline of the calcaneus.
Appreciation of the importance of the
talus for hominid locomotor variation and
evolution has led to the creation of numerous methods for quantifying talar morphology (e.g.,Volkov, '03-04;Martin and Saller,
'57; Day and Wood, '68; Lisowski et al.,
'74; Trinkaus, '75a) and to the detailed
description of fossil hominid tali, in particular those of the European and Near
Eastern Neandertals.
The Neandertal talus was initially
characterized as distinct from modern
human tali in ways which implied a less
AM. J. PHYS. ANTHROP., 46: 29-44.
efficient bipedal gait (e.g,, Fraipont, '12;
Boule, '11-13). Yet, recent studies of Neandertal tali (e.g., Endo and Kimura, '70;
Heim, '72; Trinkaus, '75a) have indicated
that Neandertal tali are indistinguishable
from those of modern humans in the implied locomotor capabilities. All of the differences appear to be related t o the
robustness of the tali. This robustness is
seen in the other Neandertal foot bones
(Trinkaus, '75a) and in the rest of their
postcranial anatomy (Taylor, '68; Musgrave, '70; Heim, '72; Trinkaus, '76b). Yet,
several recent multivariate analyses of
fossil hominid tali (Oxnard, '72, '73a,b,
'75a; Lisowski et al., '743 have separated
Neandertal tali from samples of modern
human tali ("Neandertal tali (Spy, Skhd)
are less like modern man than previously
thought" (Oxnard, '72: p. 12! 1, placing
them about four "standard deviation units"
from modem humans (Oxnard, '72, '75a;
Lisowski et al., '74).2 These statistical difI Current address: Department of Anthropology, Yale University, New Haven, Connecticut 06.520.
2 Recently Oxnard U 5 h , personal communication), referring to the same rnriltivariate analyses, has denicd the cxistence of a significant difference hehveen Neandertal and
modern human tali ("Thrse studirs show unequivocally that
several different Neanderthalrrs are similar to man and quite
different from non-human primattes" (Oxnard, '7%:p. 393) 1.
He does not specify the precise functional implications of his
statistical Ftatemmts.
29
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NEANDERTAL TALAR MORPIIO.\lETRICS
31
and body inertia. In response to these
habitual stresses of locomotion, the trabecular bone, through a process of microfractures and secondary formation of trabeculae, will remodel so as to concentrate
bone in the regions of maximum stress
(Pugh et al., '73). The remodeling is
reflected in the reorientation of the trabeculae and the relative increase in the
MATERIALS, MEASUREMENTS AND METHODS volume of trabecular bone, and therefore,
This analysis is based on the study by one in the shape of the bone (Ascenzi and Bell,
of us (E, T.) of the original European and '72; Lanyon, '74).
Additionally the articular surfaces will
Near Eastern Neandertal and Skhd hominid postcranial remains (Trinkaus, '75a; ta- change in orientation and size to best
ble 1). The "Neandertals" are defined as transmit joint reaction forces while conthe Upper Pleistocene hominids from forming to the geometric requirements of
Europe and the Near East included in the the articulations. Articular cartilage is
taxon Homo sapiens neanderthalensis highly sensitive to excess pressure and
(Campbell, '65). The remains from Mug- under high impact compression may unharet es-Skhd and Djebel Kafzeh, which dergo fibrillation and degeneration (Trias,
are morphologically separate from this '61; Radin and Paul, '71). Since the presgroup (Vandermeersch, '72; Howells, '75; sure on a unit area of cartilage is inversely
Trinkaus, '76a), are considered early Homo proportional to the surface area bearing
sapiens of uncertain phylogenetic affinities the force, an increase in the total articular
surface transmitting the joint reaction
to the Neandertals.
All of the measurements were taken on forces will proportionately reduce the
the original fossil specimens except those compressive stress on the articular caron Kiik-Koba 1 (BM(NH1cast No. EM 2081, tilage. Therefore, under conditions of high
Shanidar 1 (cast No. 381,217 of T. D. joint reaction forces, an expansion of the
Stewart), and Skhd 4 (McCown and Keith, articular surface would be adaptive. TO
'39 data and PUM cast No. 603). For com- reflect the results of these processes on the
parison, samples of modern human adult talus, we have used length, physiological
tali from the Late Woodland Amerind site height and articular breadth to indicate
of Libben (collections of the Department the overall proportions of the talus, and
of Anthropology, Kent State University), trochlear length, trochlear breadth, trochthe predynastic Egyptian site of Keneh, lear height, head-neck length, articular
and the medieval Yugoslav site of Mistihalj breadth, lateral malleolar breadth and
(collections of the Peabody Museum, Har- lateral malleolar height to quantify the relative sizes of the trochlear and malleolar
vard University) were measured.
The measurements were chosen to quan- surfaces (APPENDIX).
The articulations of the talus, proximally
tify the relative proportions, articular
dimensions, and articular geometry of the with the tibia and fibula (the talocrural
hominid talus. Since the talus occupies a joint) and distally with the calcaneus and
central position between the leg and the navicular (the subtalar and mid-tarsal
subtalar skeleton, its morphology is closely joints), permit the plantarflexion-dorsiflexcorrelated with the requirements of the ion of the foot and the pronation-supinaankle and subtalar joints. Additionally, the tion of the subtalar skeleton (Hicks, '53;
talus must transmit most of the body Elftman, '60). The angles employed were
weight and reaction forces generated by chosen to quantify the articular mechanics
the tibia1 musculature, body momentum of the talus. The trochlear angle is a meaferences do not appear to reflect accurately the anatomical differences between Neandertal and modern human tali.
We have therefore collected metrical data
from all of the available Neandertal and
Skhul tali sufficiently intact for analysis (table 1) and from samples of modern human
tali and have compared them statistically.
32
JOHN C RHOADS 4ND ERIK TRINKAUS
sure of the anteroposterior wedging characteristic of recent hominid talar trochleae
(Day and Napier, '64). The wedging is necessary to accommodate the trochlea between the malleoli as the talus is abducted
and adducted on the tibia during dorsiflexion and plantarflexion (Barnett and
Napier, '52).This movement contributes to
the medial displacement of force trajectories through the foot at push-off, thereby
concentrating the stress on the stronger
medial pedal arch. The subtalar angle is an
estimate of the orientation of the subtalar
joint, the primary articulation responsible
for subtalar movement and pronation-supination of the foot (Manter, '41; Hicks, '53);
therefore limitation of movement at this
joint strengthens the foot as a lever for
locomotion. The subtalar articular axis
among the hominids is oriented more anteroposteriorly than among the pongids so
as to permit more efficient resistance to
the bending stresses on the pedal arch
(Elftman and Manter, '35;Preuschoft, '70).
On the dorsal aspect of the talus this articular orientation, as well as the mediolateral
splaying of the talus, is indicated by the
neck angle. The pedal arches are also
maintained by the limitation of movement
at the mid-tarsal joint (Hicks, '53;Elftman,
'60). Its articular stability is reinforced by
the nun-parallel orientation of the talonavicular and calcaneocuboid articular axes,
which is accentuated by the torsion of the
talar head (Elftman, '60). This feature is
measured by the talar torsion angle.
Other measurements possible on the
talus are either redundant with those included here or contribute little to our understanding of talar variation. Non-metric
or discrete variations of the talus, although
they provide valuable information for the
functional interpretation of Neandertal tali
(Trinkaus, '7%), are not relevant to this
analysis.
The linear measurements were taken
with standard sliding, spreading and coordinate calipers, while the angles were measured with a protractor with a moveable
indicator. The linear measurements are
considered reliable to the nearest 0.5 mm;
the angles are reliable to the nearest whole
degree.
The computer programs used were
MULTIVARIANCE (Finn, '74) for the
multivariate analysis of variance and
covariance and the single degree of
freedom contrasts with their associated
discriminant functions, SPSS (Nie et al.,
'75) for one-way analysis of variance and
discriminant functions, D/DA (Rhoads, '73)
for distance analysis and canonical variates, and BMD (Dixon, '75) for crosschecking analysis of variance and discriminant functions. Where possible all computations were cross-checked with at least
two, and usually three, different programs.
Numerical errors are common, even in the
widely used programs, so cross-checking is
necessary.
In the statistical analyses the linear
dimensions were used directly, rather than
as indices. This simplifies interpretation of
the results, and avoids the potentially nonGaussian distributions of indices (Simpson
et al., '60).Angles have their own statistical
problems, but were included to represent
features of joint orientation otherwise
difficult to quantify. They fit a normal
model satisfactorily over the restricted
range of variation in the present samples.
Relations among the measurements
The joint variation of the dimensions of a
structure within a population deserves
careful study, both as a necessary preliminary to detailed interpretation of group differences and for its interest as a reflection
of the influences determining the form of
the structure. The talar measurements
from the modern samples were fist tested
for heterogeneity of covariance matrices.
Since there were no significant differences,
a pooled covariance matrix was computed
which provided the basis for further study
of the intrapopulational measurement relationships.
Table 2 shows that positive correlations
exist among nearly all linear measurements
except lateral malleolar breadth. The rela-
33
NEANUERTAL TALAR bIORPHOMETRICS
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34
JOHN C;. RHOADS AND ERIK THINKAUS
tionships indicated by the correlation lesser degrees of displacement (Anthony,
coefficients are moderately strong ( r = '23; Trinkaus, '7%). As this would also
0.4-0.75)but nowhere near deterministic. affect trochlear length, it is consistent with
This configuration suggests that much of the finding that the highest correlation bethe variance in the linear measurements is tween trochlear height and another talar
associated simply with the general size of dimension is with trochlear length.
the bone. Length best reflects general size,
Further details of the covariation among
since it has the highest and most generally measurements are obscured in the simple
distributed positive correlations with the correlation matrix by the association of
other linear measurements, as well as the nearly all linear dimensions with the
highest loading on the first principal com- general size of the bone. New details
ponent, which accoimts for 40% of the emerge when general size effects are restandardized variance in the measure- moved from the correlation matrix by comments and clearly represents general size. puting partial correlations holding length
Lateral malleolar breadth is conspicuous constant (table 2).
in its high variability and its low level of
When length is held constant, most of
correlation with other measurements. the other relations between variates disapSome of this is no doubt due to the pear. Trochlear dimensions are a sigdifficulties of measuring such a sinall nificant exception. Although the breadth of
dimension consistently, but variance of ob- the trochlea loses its sizable correlations
servation is not sufficient to account for when length is controlled for, suggesting
this entire pattern. It must be principally that it is largely determined by the size of
due to the relative absence of direct rela- the bone, there is a moderate residual
tionships between lateral malleolar association (partial r = 0.43) between the
breadth and the other talar measurements, height and the length of the trochlea. This
since lateral malleolar breadth is deter- supports the interpretation of the trochlear
mined by a complex biomechanical and sagittal dimensions as jointly dependent
architectural interaction of the trochlear, upon the sagittal extent of the trochlea
lateral malleolar and posterior calcaneal rather than merely upon overall size.
articular surfaces. The highest correlation
The associations of the head-neck length
of lateral malleolar breadth with another show another aspect of talar measurement
dimension, articular breadth, is tautologi- relationships. Its simple correlations are of
cal, since it is included in articular breadth a straightforward general size configuraas defined here. Lateral malleolar breadth tion (correlation with length = 0.69).The
is also weakly associated with the height of most telling of its partial correlations with
the lateral malleolar facet, which has a length removed is a slight negative one
closer but still weak pattern of association (partial r = - 0.13) with trochlear length.
with other talar dimensions.
Since head-neck length is measured from
The dimensions of the trochlea have an the anterior limit of the trochlea (APPENinteresting pattern of correlations. Both DIX), the inverse variation of head-neck
the length and breadth of the trochlea length and trochlear length indicates that
show strong general size associations, but some of the variation in head-neck length
trochlear height has a lower set of correla- as it is measured is actually variation in the
tions with other linear dimensions of the distal extent of the trochlea.
talus ( r = 0.4-0.6).These correlations may
The angular measurements show only
reflect the dependence of trochlear height the weakest associations with each other
on the degree of habitual angular displace- and with the linear measurements. The
ment at the ankle, which promotes the ex- highest correlation between two angles,
tension or retreat of the articular surface 0.28 between the neck angle and the subanteriorly and posteriorly with greater or talar angle, reflects their similar anatomical
35
XEiLl UERTAL TALAR MORPHOMETRICS
bases (see above). With linear measurements the correlation of 0.23 between the
subtalar angle and trochlear height, and
correlations of neck angle with length
( - 0.20)and trochlear breadth ( - 0.21) are
high enough to mention; most of the remaining correlations involving angles are
very low. As these are too low to explain
much of the variation within populations,
talar angles clearly bear no substantial
allometric relations within populations of
modern adults. Either they poorly reflect
real structural variation (technical inadequacy), they are largely determined by
separate genetic or biomechanical influences, or the range of morphologies present in our modern samples is insufficient to
show allometry.
significance levels of the analysis of
variance contrast:
X,
-
(1/3X ,
+ 113 XL + 1/3 X,)
(11
where XN is the Neandertal mcan, and XK,
&, and X,, are the modern group means.
Program MULTIVARIANCE (Finn, ’74)
was used to compute both univariate and
multivariate versions of this “Neandertal
effect,” taking into account the differences
in group size.
The Neandertal-modern differences in
the actual measurements are physically
small and statistically non-significant at the
0.05 level for 8 of the 13 measurements (table 3). While the Neandertal sample is
small, the confidence intervals are narrow
enough to assure us that if marked differences existed they should be evident. It is
Metric comparison of Neandertal and
the functiona2 magnitude of group differmodern Homo sapiens tali
ences that is important, not whether the
The measurement means of the Nean- groups are statistically distinguishable.
dertals and the three modern groups (table Biologists often confuse the distinct issues
3) show no major differences. For most in- of biological significance and of statistical
dividual measurements the Neandertal significance; the latter is merely a measure
mean falls within the spread of means for of the state of our knowledge, a measure of
the modern groups. The means of the the completeness of our sampling. Given
Skhul talar measurements are also close to sufficiently large samples, statistically “sigthe modern means for most measurements. nificant” group differences are a foregone
When the equality of variances in the conclusion. Depending upon their genetic
groups was tested for each variate using or functional basis, to the biologist these
Bartlett’s test (Snedecor and Cochran, ’671, may signify anything, or nothing at all.
One of the statistically reliable Neanderthere was no significant heterogeneity except in trochlear length, for which the tal-modern differences is the greater laterNeandertals had a slightly elevated vari- al extension of the lateral malleolar facet in
ance due to one anomalous value (an ex- the Neandertals (increased lateral malleolar breadth), a difference in means of
ceptionally low value for Tabm C l ) .
The spread among the modern groups almost 2 mm in a dimension of about 8 mm.
throws open to question the precise mean- The overall articular breadth, measured
ing of any overall mean vector of talar across the lateral malleolar facet, the
dimensions for modern H . sapiens, except trochlea and the medial malleolar facet, is
perhaps as a rough functional Gestalt for greater by 3.4 mm in the Neandertal samstriding bipeds. Even so, it is instructive to ple. The difference in lateral malleolar
examine the univariate contrasts between breadth accounts for some of this, and
the eleven Neandertal specimens on which since the trochlear breadths of the Neanall measurements could be taken and a dertal and modern samples appear to be
common modern mean obtained b y substantially the same (observed differweighting the Keneh, Libben and Mistihalj ence of less than 0.1 mm), presumably
samples equally. Table 3 presents least there is on the order of 1 mm greater
squares estimates with standard errors and average medial extension of the medial
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37
NEANDERTAL TALAH M O R P H O ~ ~ E T H l ( 5
malleolar facet (which was not included as
an individual measurement to avoid redundancy). This supports the observations of
Gorjanovic-Kramberger (’061, Martin (’101,
Fraipont (’12) and Boule (’11-131 that the
Neandertals had enlarged malleolar surfaces.
Relative to the modern samples, the
mean length of the trochlea in the Neandertal sample is greater by 2.2 mm, and the
head-neck length is reduced by the same
amount. Since the mean overall length of
the Neandertal tali falls between the
modern means and since head-neck length
is measured from the distal edge of the
trochlea, it is likely that the apparent difference in head-neck length is merely a
reflection of the difference in trochlear
size (see above).
This entire suite of differences, both
from n priori considerations and from the
study of the covariation of measurements
within modern groups, would be expected
to reflect use-connected modeling of articular surfaces. Neandertals are seen to
differ primarily in the increased robusticity of the talocrural joint. The only remaining statistically reliable difference, a
greater physiological height of the talus
among the Neandertals, complements the
articular robustness by concentrating trabecular bone along the primary stress
paths in the talus (see above).
MULTIVARIATE RESULTS
TAB1.F 4
0 2
c;alzre~
brtween modPrn samples and hetween
modern satnples and the Neandertalr
Keneh
Lihben
Mistihalj
3.19
3.04
2.82
2.06
2.12
2.30
ble 4) shows that the Neandertal mean
vector is not much more remote from
modern group means than the modern
groups are remote from one another. The
distinctiveness of the Neandertals is even
less impressive when individual variation is
taken into account, some individual modern specimens are closer to the Neandertal
mean vector than to their own population
mean, and vice versa. (The Skhul tali were
not included in the multivariate analyses
due to the small sample size and the incompleteness of the specimens.)
This scale of individual variation must be
kept in mind when interpreting multivariate analyses. There is a further trap for the
unwary in the practice of expressing Mahalanobis distances between samples or individuals in “standard deviation units.” A
distance of three or four “standard deviation units” will sound quite remote to anyone accustomed to thinking of two standard deviations as an approximate 95%
point for the “two-tailed” comparison with
a univariate normal distribution. This apparent analogy is seriously deceptive. The
multivariate “standard deviation units” do
not correspond to the standard deviation
units of the familiar univariate case. The
univariate “distance,” (x-d)/s, between a
single specimen with measurement value r
and a sample mean %, standardized b y the
sample standard deviation s, has a null distribution (probability distribution under
the null hypothesis that the single specimen is drawn from the same normally distributed population as the sample) related
to Student’s t. Specifically, the quantity
Our analysis of individual measurements
(table 3) and our multivariate distance
analysis based on all measurements (table
4)show marked variations among modern
populations. In many individual measurements differences between modern groups
are greater than between moderns and
Neandertals. This does not imply there are
functional distinctions between modern
groups. It does indicate, however, that the
comparison of Neandertals and modern H.
sapiens must be made with a full appreciation of the amount of variation existing
both within and between modern popula(21
tions.
Inspection of multivariate distances (ta- has the Student’s t distribution with N-1
38
JOHN C. RHOADS AND ERIK TRINKAUS
degrees of freedom, where N is the size of
the sample to which the single specimen is
k i n g compared. This distribution approaches the normal as N becomes large.
This result, however, does not apply
where more than one variate is involved. In
the general p-variate multinormal case, the
Mahalanobis L I Z distance can he represented as:
uz = (TC-x)‘S-’(ir-x)
13)
which is the squared Euclidean distance
between the sample mean vector x and the
individual specimen’s measurement vector
x in the metric defined by the sample variance-covariance matrix S . It has a null distribution related to Hotelling’s T2, so that
(4)
is distributed as Hotelling’s P w i t h param-
eters p and N-p-1. This distribution may be
transformed to the more commonly tabulated F distribution by using the expression,
15)
(All of the above equations are special
cases of well known results in distribution
theory, for which proofs can be found in
Rao, ’65).As N becomes large in relation to
the number of variates, the null distribution of DZ between an individual and a
sample approaches a chi-square with p
degrees of freedom. So the Euclidean distance between the individual specimen
and the sample does not have a simple relation to the normal distribution, but rather
its square is asymptotically chi-square distributed with a number of degrees of
freedom equal to the number of measurements on which it is based. It is the matter
of degrees of freedom which invalidates
the analogy to the normal deviate.
For example, the Euclidean distance between the Spy 2 talus and the pooled
modern sample in Day and Wood’s (’68)
multivariate analysis of primate tali is 3.36
in “standard deviation units.” A normal
deviate of 3.36 would have a very low
probability. However, a proper approxi-
mate comparison is of L I Z = (3.3612 = 11.3
to a chi-square variate with seven degrees
offreedom. A distance from the population
mean vector this great or greater will occur
in about 12% of the individuals in a
multivariate normal population. (This
figure is obtained using the chi-square approximation; using the exact distribution
will give an even higher probability.) So
these multivariate “standard deviation
units,” when referred to the proper scale,
indicate that the Spy 2 talus is closer to the
modern mean in that study than are many
modern tali. Similarly, the multivariate distances obtained in the present study, based
on a larger measurement set, indicate extensive population overlap.
Standard coefficients of the individual
measurements on the canonical variates
proved disappointing in the evaluation of
the morphological bases of the multivariate distinctions. In general, unless the
group differences have an especially simple mathematical form, the composition of
the canonical variates is some occult function of the particular groups one chooses to
include. The usual analysis yields canonical
variates which discriminate maximally
among all the groups, with a democratic
lack of regard for which differences may
be particularly interesting under the investigator’s hypotheses. Thus in the present
study, a traditional canonical variates analysis gave a typically unintelligible combination of measurements differentiating
the modern groups mixed in with the
Neandertal-modern distinction.
We wished to separate the overall multivariate among-group variation into portions for (1) the Neandertal-modern distinction, and (21 modern interpopulation
variation. This was done by setting up a
multivariate analysis of variance with a
single degree of freedom contrast opposing
the Neandertals to all the modern groups
(the multivariate analogue of the “Neandertal effect” used in the univariate
analyses), and two orthogonal contrasts
reflecting the variation between modern
groups. A canonical variate associated with
just the Neandertal-modern contrast was
YEANDER I i L -14 L \I{
39
\IC)RPHOhlFTHIC~
TALILb 5
Standardized camniccil tjariute coefficient5
Nrandertal-modern conNedndert,ll-rn~Jdc.rI,
trast. with covariance
djustrrient for length
contrast
Length
Physiological height
Trochlrar length
Trochlear height
Head-Neck length
Articular breadth
Trochlear breadth
Lat. rnalleolar breadth
Lat. malleolar height
- 0.08
0.59
0.57
- 0.43
- 0.76
0.46
0.36
0.2:
- 0.14
Trochlear angle
Neck angle
Torsion angle
Subtalar angle
- 0.29
0.06
- 0.20
- 0.14
~
~
computed using the MULTIVARIANCE
program (Finn, '74). It showed differentiation of the Neandertals on the basis of increased malleolar widths, greater trochlear length and corresponding lesser headneck length, and greater physiological
height (table 5 ) . Thus a canonical variate
was obtained having an interpretation consistent with the univariate results, even
though the traditional overall canonical
variates had no clear anatomical interpretation.
The Neandertal mean for talar length is
quite close to a central value of modern
man (table 31, so it appears that the
multivariate distinction between the Neandertals and the modern samples is not due
in any large measure to simple relations of
the linear measurements to overall size (table 5). This notion was further tested by
performing a multivariate analysis of
covariance, controlling for length. With
this model, that part of the between-group
variation in other measurements accounted
for by their linear correlation with the controlled variable is removed from the
multivariate comparison.
The distinctions among the modern
groups were substantially reduced b y this
adjustment. On 13 measurements without
covariance, the Fvalue for the multivariate
0.40
0.38
0.38
- 0.55
0.32
0.23
0.27
- 0.12
First canonicd n r iatr hetween modern
gi-onps attrr controlling for length
0.41
- 0.63
0.16
~
~
- 0.28
- 0.06
- 0.20
- 0.14
0.24
0 4-3
0.62
0.11
0.10
- 0.11
- 0.31
- 0.17
0.28
~
heterogeneity among modern groups was
7.64 (on 26 and 240 degrees of freedom, p
< 0.0001).On the other 12 measurements
with length as a covariatc, this was
reduced to 4.88 (on 24 and 270 degrees of
freedom, p < 0.0001). So overall size was
responsible for a considerable part of the
between-group variation in modern tali. Of
the remaining between-group variation,
78% was associated with a canonical variate clearly interpretable as reflecting
trochlear size (table 5 ) . This recalls a similar pattern in the within-group variation
and is further evidence for trochlear size
being in some measure determined separately from overall size of the talus.
The covariance adjustment for length
had a quite different effect on t h e
multivariate distinction between Neandertal and modern tali. The Neandertal-modern distinctness was greater for the other
twelve measurements with length as a
covariate (I;= 5.90 on 12 and 135 degrees
of freedom, p < 0.0001)than it was for all
thirteen measurements without covariance
( F = 5.46 on 13 and 135 degrees of
freedom, p < 0.0001). Thus, with a
covariance adjustment to simulate equal
overall size of Neandertal and modern tali,
they were less alike than without this adjustment. Therefore, the difference may
40
JOHN G. HHOADS AYD ERIK TRINKAUS
be attributed to a true distinction of shape
rather than merely size. The covariance
adjustment did not change the pattern of
the canonical variate associated with the
Neandertal-modern distinction (table 5 ) .
Implications of the Neandertal talar
metrics
The morphometric analyses of the Neandertal tali presented, univariate and
multivariate, show the Neandertal tali to
be largely overlapping the ranges of variation of the modern human samples. The
only differences involve a relative enlargement of the talocrural articular surfaces,
especially the trochlea and lateral malleolar surface, and a slightly greater physiological height. These differences can all be
related to the postcranial robustness characteristic of the Neandertals.
The relative increase in talocrural articular surface area represents an adaptation
to exaggerated joint reaction forces associated with high activity levels. Since an increase in articular dimensions would
reduce the stress per unit area of the joint
surface, the large dimensions of the Neandertal trochleae would be an adaptive response to the conditions of habitually high
joint reaction force undoubtedly present
on the Neandertal lower limbs (as inferred
from their general postcranial robustness).
The relative increase in the physiological
height of Neandertal tali is a related
phenomenon; it concentrates bone capable
of absorbing and transmitting large joint
reaction forces below the trochlea and between it and the calcaneal surfaces of the
talus.
The enlargement of the malleolar surfaces of Neandertal tali appears to be correlated with the increase in joint reaction
force across their trochleae. With high activity levels the lateral shear stress at the
ankle would increase with trochlear joint
reaction force, thereby placing greater
stress on the medial and lateral malleoli.
This is especially true at heel-strike, when
the downward movement of the fibula
stabilizes the talocrural joint but also increases joint reaction forces (Weinert et al.,
'73). An adaptive response would be the
circumferential enlargement of the malleoh, via trabecular remodeling (Piigh et al.,
'731. It is not possible to assess directly the
robustness of the Neandertal fragmentary
malleoli. The dimensions of the talar
malleolar surfaces, however, demonstrate
that they were indeed accentuated. This
does not support the contention of Bode
('11-13) and others that the Neandertal
fibulae supported a greater proportion of
the body weight than among modern
humans. Due to their architectural positions relative to the talar neck and the posterior calcaneal surface respectively, the
medial and lateral surfaces are limited in
the extent to which they can extend distally by the dorsoplantar dimensions of the
talus. They must also provide appropriately positioned grooves for the long flexor
tendons. The enlargement of the malleoli
and the corresponding malleolar surfaces
of the talus to compensate for large joint
reaction forces must therefore be primarily
medial and latcral. The greater articular
breadth of the Neandertal tali therefore
correlates with the expansion of their
trochlear surfaces, since both are related
to higher levels of stress at the talocrural
joint.
None of the angles employed showed
any significant differences between the
Neandertal and modern samples (table 3).
The talar neck angle, the one considered
by Boule ('11-131 to differentiate the
Neandertals most clearly, is virtually identical in the modern and fossil samples. The
differences in the trochlear angle and torsion angle means, which are lower among
the Neandertals, are overshadowed by the
great variation in both modern and fossil
samples.
The measurements of the limited sample
of Skhd tali (tables 1, 31 are aligned with
those of the Neandertals rather than of
modern humans for most of the cases
where a statistical difference exists between the fossil and modern tali. In some
cases, such as physiological height and
trochlear length, the Skhd mean is situated further from the modern means than
KEAhDERThL TAL.AR MORPHOMETRICS
the Neandertal one, but the relative shortening of the head-neck length of the
Neandertals is not present. Although these
measurements do not support the supposed
phylogenetic alignment of the Skhul
hominids with modern H. sapiens rather
than with the Neandertals (Stewart, ’60;
Howells, ’701, they are nonetheless in
agreement with the robustness of portions
of the Skhul postcranial skeletons bctween
that of the Neandertals and of modern
humans (McCown and Keith, ‘391.
CONCLUSIONS
The Neandertal and Skhul hominid tali
appear to be largely indistinguishable from
those of modern Homo sapiens. The only
consistent differences can be referred to
the articular and structural reinforcement
of the bone to absorb habitually high levels
of joint reaction force at the talocrural and
subtalar articulations.
Furthermore, this analysis demonstrates
the need in all such studies to evaluate
carefully the suitability of statistical techniques, the relative contributions of the
various measurements to the statistical differences between the samples, the true
statistical significance of the distance
statistics, and most importantly, the underlying biological significance of the
quantitative differences.
ACKNOWLEDGMENTS
We would like to thank the many individuals who made original specimens
available for study. This research was supported by Wenner-Gren Grant 2979 and
N. I. H. Grant 5 TO1 GM01938. Drs. S. J.
Gould, W. W. Howells, D. Pilbeam, C. E.
Oxnard and A. C. Walker provided helpful
comments, and to them we are most grateful.
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NEANDERTAL TAIAR VORPHOMETRICS
APPENDlX
Talur measurements
Length (M-1) 1
From the M. flexor hallucis longus groove to the most anterior point 011 the head measured parallel to the sagittal axis of the trochlea.
Physiological height (M-31)
From the most dorsal point on the trochlea to the most dorsal point on the posterior calcanoal
surface measured perpendicular to the sagittal axis of the trochlea in a dorsoplantar direction.
Trochlear length (M-4)
Maximum length of the trochlear articular surface on the midline mcasured parallel to the
sagittal axis of the trochlea.
Trochlear height (M-6)
From the chord defined by the Trochlear Length to the highest point on the midline sagittal
axis of the troclllea measured in the sagittal plane of the trochlea.
Head-neck length (M-8)
From the anterior median edge ofthe trochlea to the furthest point on the head measured parallel to the long axis of the head and neck.
Articular breadth (M-2b)
From the lateral edge of the lateral inalleolar surface to the medial edge of the mcdial malleolar surface measured perpendicular to the sagittal plane of the trochlea.
Trochlear breadth (M-5)
From the mid-lateral edge of the trochlea to its mid-medial edge measured perpendicular to
the sagittal plane ofthe trochlea.
Lateral malleolar breadth (M-7a)
From the lateral edge of the trochlea to the lateral edge of the lateral malleolar surface measured perpendicular to the sagittal plane of the trochlea.
Lateral malleolar height
From the dorsolateral edge of the trochlea to the lateral edge of the lateral inalleolar surface
measured parallel to the sagittal plane of the trochlea in a dorsoplantar direction.
Trochlear angle
The angle between the medial edge of the trochlea and the lateral edge of the trochlea measiired in thc horizontal plane.
Neck angle (M-16)
The angle between the sagittal axis of the trochlea and the long axis (sagittofrontal)ofthe head
and neck measured in the horizontal plane.
Torsion angle (M-17)
The angle between the long axis of the navicular articulation (medioplantar to laterodorsal)
and the horizontal plane of the trochlea measured in thr: frontal plane.
Subtalar angle
The angle between the sagittal axis of the trochlea and the midline axis across the mcdial and
posterior calcaneal surfaces measured in the horizontal plane.
I
(M - no.) refers to the number of the equivalent measurement in Martin and Saller 157).
43
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