An analysis of cercopithecoid odontometrics. II. Relations between dental dimorphism, body size dimorphism and diet

An Analysis of Cercopithecoid Odontometrics 1 1 . RELATIONS BETWEEN DENTAL DIMORPHISM, BODY SIZE DIMORPHISM

AND DIET DAVID POST,' SERGE GOLDSTETN ' AND DON MELNICK ' ' Department of Anthropology, Columbia University, New York, New York I0027and 'Department of Anthropology, Yale Uniuerstty, New Hacen. Connecticut 06520

K E Y WORDS Allometry . Sexual dimorphism . Odontometrics Diet . Cercopithecoids

ABSTRACT Odontometric, dietary, and body weight data were collected for a sample of 29 cercopithecoid species. Each species was assigned to one of three diet classes (frugivore, folivore, and omnivore), and indices were constructed to estimate the extent of sexual dimorphism in body weight, postcanine area and incisor width in each of the species. Analysis proceeded by means of the analysis of covariance with the dental dimorphism indices as the dependent variables. Body weight dimorphism was not significantly related to either measure of dental dimorphism across the sample, and an analysis by diet alone revealed that omnivores show significantly higher dental dimorphism than do either of the other two diet classes. The relationship between this result and theories of sexual subniche differentiation is discussed.

The question of the nature and evolution of sexual dimorphism within the living primates has been receiving increasing amounts of at tention recently, particularly from re- searchers attempting to assess and explain the extent of inter-individual morphological variability within fossil hominid populations; we agree with Wolpoff ('76a) who states that "the question of sexual dimorphism is of considerable potential importance in any attempt to reconstruct the ecology, behavior, or phylogeny of the australopithecines" (p. 579). Al- though this statement may well apply to other fossil populations, the persistent problem of the phylogeny of the South African Plio-Pleis- tocene hominids (cf. discussions in Brace, '72; Pilbeam, '72; Pilbeam and Gould, '74; Robin- son, '72; Wolpoff, '75, '76a,b) perhaps best il- lustrates the difficulty of assessing the tax- onomic affinity of any individual specimen without an estimate of the expected extent of sexual dimorphism within the population from which i t has been sampled. In part, the reason for the persistence of this particular problem is that it is difficult to evaluate the degree of sexual dimorphism in fossil populations with reference to the sampled fossil material alone; the same amount of inter-indi-

AM. J. PHYS. ANTHROP. 11978) 49: 533-544.

vidual morphological variability can often be interpreted either as the expression of a high degree of sexual dimorphism (i.e., as intra-specific variability) or as evidence for the existence of more than one biological species (i.e., as inter-specific variability). Choosing between these alternative explanations depends on one's expectations concerning the extent of inter-sexual and inter-individual variability in the population under study, those expectations influenced, in turn, primarily by studies of variability within and between living primate species. The use of the living primates as models for the evaluation of variability in fossil hominid assemblages has, as a result, been a major stimulus for research on the nature of sexual dimorphism in the primates, although the phenomenon is, of course, of in- terest in and of itself as one major aspect of the socioecology of these species (Crook, '72).

In this study we will look a t the relationship among dietary habits, dimorphism in body weight, and dimorphism in various aspects of the dentition in a sample of cercopithecoid monkeys. That different morphological features may vary with respect to the amounts of dimorphism they express within any species has not always been explicitly recognized (al-

533

534 DAVID POST, SERGE GOLDSTEIN AND DON MELNICK

though see Leut.enegger and Kelly, ’77) ; thus, for example, Brace (”72) states tha t “one of the most striking differences belween arboreal and terrestrial primates is the marked sexual dimorphism of the l a t t e r . . . with the most terrestrial forms such as baboon and gorilla groups being characterized by males which a re fully double the bulk of females” (p. 32). Even if we accept Brace’s contention tha t we should expect to find “an increasing degree of sexual dimorphism in progressively earlier hominids” (Brace, ’72: p. 311, i t is not a t all clear how such body size dimorphism would affect the amount of dimorphism expressed in other features such as jaws and teeth (which are, in fact, t he sources of t he data Brace ubes to test his hypothesis).

Similarly, Wolpoff (’76b! analyzes the extent of sexual dimorphism in the dental re- mains of the South African australopithecines; he claims tha t “the amount of dimorphism in the australopithecines is no less than gorillas in the posterior maxillary dentition, and is significantly less than gorillas towards the front” (p. 504). We will not be directly addressing this contention here; in the same study, however, he states that “the pattern suggests a great difference in female and male australopithecine body size? with the significant amount of posterior dimorphism result- ing from the fact t ha t the much larger males must masticate many more calories” (Wol- poff, ’76b; pp. 504-505). We feel tha t the use of gnathic material for a determination of body size dimorphism implicitly assumes a predic- tive relationship between measures of body size dimorphism and gnathic (dental) dimorphism whose existence, to our knowledge, has yet to be demonstrated empirically. Of course, such a relationship would be most convenient, given that most causal or functional models of sexual dimorphism deal explicitly with male- female differences in body size, while the fossil material with which to test these models consists primarily of jaws and teeth. Further- more, we certainly expect tha t a strong relationship of this kind exists (between body size dimorphism and, for example, dimorphism in postcanine area) given all tha t we know about t he allometric scaling of dental dimensions with body weight (cf. Gould, ‘75; Goldstein et al., ’78; Pilbeam and Gould, ‘74); t ha t is, we expect tha t species showing large amounts of body weight dimorphism will show corre- spondingly large amounts of dimorphism in dental proportions. We will attempt here both

to quantify this relationship and, once having done so, to use this relationship as a kind of “criterion of subtraction” (Gould, ’75) for analyzing species-specific deviations from an interspecific body weight dimorphism!dental dimorphism curve. If there is, in fact, a strong relationship between measures of these different kinds of dimorphism, the observed amount of dental dimorphism in any species (or group of species) can be compared to the amount predicted on the basis of the observed weight dimorphism, and t.he deviation (observed minus predicted) may perhaps indicate some special adaptation within tha t species (or species group). Do, for example, omnivorous species show greater lor less) dental dimorphism than one would expect on the basis of their dimorphism in body weight? We feel t ha t this approach may be more fruitful than simply comparing the extent of dental dimorphism in different species without reference to differences in body size dimorphism among them.

MATERIALS AND METHODS

This investigation is part of a larger study of primate odontometrics presented elsewhere (Goldstein et al., ’78) and, as a thorough de- scription of the methods of data collection and data analysis is presented in tha t more com- plete report we will give only a brief outline here.

Data on mean body weights, mean mesio- distal and buccolingual dimensions of all teeth for males and females of 29 cercopithecoid species were collected from pub- lished sources; in the interests of consistency (and to minimize inter-observer measurement error) the odontometric data were taken whenever possible from either Sirianni (’74) or Swindler (’76). Reliable weight estimates for primates are considerably more difficult to obtain; whenever possible, data from Kay (”73) were used.

With these data, we created several indices to measure the separate aspects of dimorphism in which we were interested. Body weight dimorphism (hereinafter abbreviated as as DMBW) for each species is defined as 100 times the natural logarithm of the ratio of mean male to mean female weight; tha t is,

Body weight dimorphism = DMBW = mean male weight

mean female weight 100 x log, )

Postcanine area dimorphism is defined as the logarithm of the male-female ratio of summed

CERCOPITHECOID DENTAL DIMORPHISM

TABLE I

535

Identificnt~on number DMBW DMIW DMPA

&?Cleb

Cercopithecus neglectus C. nictitans C. ascanius C. muna C. mitis C. cephus Cercocebus albigena C. torquatus C. galeritus Macaca nemestrina M. mulatta M. fascicularis M. arctoides M. nigra

Culobus badius C. guereza C. polykumus C. uerus Presbytis phayrer P. johnii P. aygula P. cristatus Pygathrw nemeus Nasalis laruatus

Cercopithecus aethrups Papiu cynocephalus P. anubis P. ursinus Theropithecus gelada

11 12 13 14 15 16 20 21 22 30 31 32 33 34

50 51 52 53 60 61 62 63 64 70

10 40 41 42 43

Frugivores

46.97 6.74 49.07 0.00 36.32 1.95 24.51 4.65 34.33 1.05 41.96 2.13 29.99 9.62 93.00 0.83 62.02 4.02 28.77 6.30 36.75 2.72

-. 8.41 7.18

36.16 1 .a2

-

Folivores

40.55 1.00 40.55 6.11 29.84 4.21

5.41 ~~ 1.95 30.99 7.49 - 8.10

-4.13 0.00 15.42 5.26 - 9.53

72.96 5.13

Omnivores

25.13 6.37 60.82 10.65 49.49 13.66 19.42 12.41 49.47 -

16.14 4.74 9.07 6-88 7.95

10.53 14.43

10.25 15.62 4.42 5.19

44.53 18.44

~ 0.80

-0.17 11.47 9.38

- 1.16 3.01

- 10.14 3.17 3.03

11.17 11.08

16.25 19.39 21.68 23.35

4.51

postcanine area (the product of mean mesio- distal and mean bucco-lingual dimensions of each tooth, summed over all teeth posterior to and including the third premolar on one side of the jaw), again multiplied by 100, and incisor width dimorphism is similarly defined (incisor width being the sum of the mesio-distal dimensions of the two incisors).

Postcanine area dimorphism = DMPA =

1 mean male postcanine area

mean female postcanine area 100 x log, (

Incisor width dimoruhism = DMIW =

1 mean male incisor width

mean female incisor width 100 x log, ( ___

Thus, for all three of the dimorphism indices, a value of 0.00 indicates equal values for males and females for the variable under considera- tion; a negative value indicates a higher value for females, a positive value indicates the reverse.

The rationale for choosing these variables

(i.e., postcanine area and incisor width) is discussed in Goldstein et al. ('78); the use of these particular dimorphism indices is discussed in the APPENDIX Data from the upper jaw were used in all cases, and the value for all three indices for each species is given in table 1. It should be noted that no canine data have been examined in this study, thereby exclud- ing a series of interesting but distinct questions concerning dimorphism in this aspect of the dentition of these species (see Leuteneg- ger and Kelly, '77 for a discussion of some of these issues).

Finally, each species was assigned t o one of three diet categories (frugivore, folivore, and omnivore) as shown in table 1, following Kay's classificatory scheme (Kay, '731, but with the addition of an ominivore class. We recognize that this scheme is little more than an indica- tor of gross dietary preferences, but a t the present stage in our knowledge of primate

536 DAVID POST, SERGE GOLDSTEIN AND DON MELNICK

TABLE 2

Analysis of covariance for incisor width dimorphism

Model I I.W. Dimorphism = DMIW = Constant + (Diet effect) + B, x Body weight

dimorphism ( = DMBW) + Interaction effect (Diet x DMBW)

Source S.S

Total Reduction due to

above model Reduction due t o DMBW

and Diet Reduction due to DMBW,

adjusted for diet Reduction due to Diet,

adjusted for DMBW Reduction due to

Interactions Residuals

Model I1 DMIW = Constant + Diet effect

376.518

216.54

180.24

1.98

177.491

36.09 160.18

df M.S. F

24

5 43.267 4.862 (P<O.Ol)

3 60.081 6.753 (P<O.Ol)

1 1.98 0.223 (NS)

2 88.745 9.973 (P<O.Ol)

2 18.040 2.027 (NS) 18 8.900

Source S.S. df M.S. F

Total Reduction due to Diet Residuals

Means Frugivore: 3.486 Folivore: 3.420 Omnivore: 10.772

376.518 178.263 198.255

feeding behavior a more precise classification of a sample this large seems unabtainable (see Goldstein et al., ’78; DISCUSSION below).

To ask of these data the questions in which we were interested we chose the analysis of covariance as our statistical model, in order to assess the effects of a continuous variable (body weight dimorphism) and a categorical variable (diet) on dental dimorphism; again, many of the details of this method are discussed in Goldstein et al. ( ’78). In effect, we are asking “Can a significant proportion of the variability among species in dental dimorphism be attributed to dimorphism in body weight?”; this might be considered the most reasonable a priori hypothesis, i.e., that we can predict dental dimorphism from a knowledge of body size dimorphism alone, which in turn implies that the between-sex scaling of tooth size with body weight is approximately constant for all species in the sample (cf. AP- PENDIX). This is the implicit assumption when one tries to predict size dimorphism from a knowledge of dental dimorphism, as in the examples mentioned at the beginning of the article. If, however, size dimorphism alone cannot completely predict the extent of dental dimorphism, we might then ask “How much of

24

21 9.441 2 89.132 9.441 (P<O.Ol)

the remaining variability is due to dietary differences among these species?”, which is ac- complished by using diet as a “treatment” in the analysis.

RESULTS

Separate analyses were performed with postcanine area dimorphism and with incisor width dimorphism as our criterion (dependent) variable in the covariance analysis; the results, however, were similar enough to justify discussing both sets of results simulta- neously. Our first step in each case was to examine the “saturated” model which uses, as predictor variables, DMBW, diet, and the term representing the interaction between diet and DMBW. If this interaction term was not significant (i.e., if the within-diet-class slopes of dental dimorphism against DMBW were not significantly heterogeneous), then the interaction term was dropped (i.e., one common, within-diet-class slope was used) and the reduced model, with only diet and DMBW as pre- dictors, was examined. As can be seen in tables 2 and 3, in both cases this procedure was followed.

The next step involves an examination of the terms in this reduced model; as described

CERCOPITHECOID DENTAL DTMORPHISM 537

TABIZ 3

Analysts of coonrinnce for postranine area dimorphism

iModel I P.A. Dirnorphrsm ~ DMPA = Constant - (Diet effect) + B, X Bndy weight

dimorphism = DMBU‘I + Interaction effect (Diet X DMBWl

Source s.s df M.S. F

Total Reduction due t o

above model Iteduction due to DMBW

and Diet Reduction due to DMBW

adjusted for Diet Reduction due to Diet,

adjusted for DMBW Reduction due to

Interactions Residuals

Model I1 DMPA = Constant Diet effect

Source

1121.05

774.85

637.00

0.01

628.00

136.16 346.18

S.S.

24

5 154 97 8 058 ( P < 0 011

3 212 33 1104 l P i 0 0 1 )

1 0 01 0 001 (NS)

2 314 00 16 32 cP<0 011

2 68 082 354 iP=O06) 18 19 23

df M.S. F

Total 1121.05 24 Reduction due to Diet 636.99 2 318.50 13.817 (Pi0.01) Residuals 484.05 21 23.05

Means Frugivore: 8.702 Folivore: 4.976 Omnivore: 20.292

in Goldstein et al. (’78), the independent contribution made by each of the predictor variables towards reducing the variability of the dependent variable can be assessed, and in both cases only the diet term was significant (tables 2, 3). That is, DMBW does not “explain” a significant proportion of variability in either measure of dental dimorphism; the implication that DMBW is only weakly corre- lated with either of the latter variables is borne out quite clearly in figures 1 and 2. In neither case is the correlation coefficient significantly different from zero. Thus, within this sample (and we know of no comparable body of data for other primate species), no significant relationship exists between either aspect of dental dimorphism and dimorphism in body weight.

The covariate and interaction terms, having been shown to be non-significant, can be dropped from the analysis, reducing our covariance model still further to a simple analysis of variance by diet class (the results of which are shown a t the bottom of tables 2 and 3). In both cases, the analysis yields highly significant results, and we can conclude that mean dental dimorphism differs among the three diet classes and furthermore, that this is

not due to differences in body weight dimorphism among them.

Finally,a posteriori tests were performed on these means using Scheffe’s methods of simu- lateneous confidence intervals (Guenther, ’64: pp. 57-59); for both DMIW and DMPA there is no significant difference between the frugivore and folivore means, while the omnivore mean is significantly greater than either.

DISCUSSION

Two major points emerge from the forego- ing analyses: the absence of a significant relationship between our index of body weight dimorphism and either of the dental dimorphism indices, and t h e strong relationship between these latter measures and dietary habits. In order to discuss these points, it is useful to describe the rationale behind the analyses performed above.

The statistical model we have used in these analyses was chosen because it best expressed our initial underlying biological model, which can be stated briefly as follows: we will assume that selection for increasing body size dimorphism, which could be the result of a number of factors (e.g., inter- or intra-sexual selection for large-bodied males, selection for

538

83.29

14.15

DMBW

25 01

- 4 13

DAVID POST, SERGE GOLDSTEIN AND DON MELNICK

12

53

70

22 0

60 52

030 .I0 14

63 0

40

42

52 I . I

5 1 I I I

2.73 7 42 12.10 DMlW Fig. 1 Plot of body weight dimorphism (DMBW) against incisor width dimorphism (DMIW). Correlation

coefficient r = 0.0855. P > 0.10.

83.29

54 15

DMBW

25.01

-4 13 -

70

22

4 3.1 2 II 0

50 16. .51

31

60. 32 OI5 O0 .I3

20 '52 '030

J4 .I0

40

41

42 63

53

67 _- I I . I I I I I I

4 39.06 D M PA 22.66 6.26

Fig. 2 Plot of body weight dimorphism (DMBW) against postcanine area dimorphism (DMPA). Correla- tion coefficient r = 0.0710, P > 0.10.

539 CEKCOPITHECOID DENTAL DIMORPHISM

early menarche and small body size in females, etc.) (see, for example, the recent analyses of sexual dimorphism by Clutton- Brock and Harvey 1’77: p. 221 and Clutton- Brock e t al., ’771, will inevitably result in associated size-related differences in feeding structures between males and females; hence the use of DMBW as a covariate in the original model. The use of diet as an additional independent variable is predicated to a large extent on the work of Selander and others on sexual dimorphism in birds (Selander, ’66, ’72; Grant, ’71; Rothstein, ’73). Selander has argued tha t

. . . even small sexual differences in trophic structures may have ecological significance . , . this dimorphism sometimes has ecological significance in adapting males and females t o different subniches and thereby reducing inter-sexual competition for food. However, i t is often difficult to determine the ultimate causes of ecological sexual dimorphism since sexual selection for dimorphism in body size also produces in trophic structures associated differences that secondarily result in differential niche utilization (Selander, ’72: p. 186).

Our intent, then, was to remove, insofar as this was possible, the effects of body size dimorphism on dimorphism in dental proportions and t o examine the residual variability in dental dimorphism for possible ecological correlates. Diet was chosen because it seems, at this rather gross level, an approximate indi- cator of overall species ecology. An additional reason for our use of diet as a “treatment” in the above analysis was tha t we wished to examine the hypothesis t ha t omnivorous species, feeding on a wider variety of foods than the more specialized frugivores or folivores, might show a greater degree of dental dimorphism as a consequence of the greater oppor- tunity their more catholic diet provides for the kind of inter-sexual feeding niche subdivision Selander discusses. Field data bearing on the latter portion of this hypothesis (the expected greater dietary differentiation of males and females -in omnivorous species) a re quite scan- t y (although cf. Post 1’781 and Rose “771 for a discussion of this phenomenon in two of those species, Papio cynocephalus and P. anubis ) , and generalizations at this point would be unwarranted. Whatever may be the underlying cause, however, our results do suggest tha t ominivores are significantly more dimorphic than the other diet classes in both postcanine area and incisor width. Several factors, however, mitigate against any simple or simplistic interpretation of these results:

A. The assignment of species to diet classes

is, as mentioned earlier, quite possibly subject to considerable error. More serious, perhaps, than the simple fact of missing or inadequate dietary data for some species is t he question of what precisely i t is tha t this (or any similar) dietary classification accomplishes. why, for example, are Colobus guereza and C. badius placed together in one diet class despite well- documented and important dietary differences between them (Clutton-Brock, ’75; Struhsaker and Oates, ’75)? Are their diets more similar in some sense than are the diets of C. badius and, say, Cercopithecus ascanius ? How, after all, are we to measure that similarity? To paraphrase Soule and St.ewart (’701, a young leaf petiole and a berry may place functional demands on tooth morphology and size tha t are more similar to one another than do a leaf petiole and a mature leaf, although petiole and leaf ea te rs wouId be placed together within our folivore class, distin- guished from the berry-eating frugivore. That is, hardness, or size. or structural carbohy- drate content, etc. may be more important dis- tinguishing criteria with regard to the functional demands placed on the teeth than are our criteria of chemistry and phylogeny. We bring up this point not to imply tha t such diet classifications a re not useful, but simply to inject a cautionary note into any attempt, including our own, to interpret results based on a classification scheme of this kind.

B. An additional source of error arises out of the uncertainty of our estimates of body weights, a problem discussed in some detail in Goldstein et al . (’78). We have suggested there, however, at relatively major inac- curacies (e.g., on the order of 10%) in our weight estimates a re unlikely to upset our findings significantly; figures 3 and 4 illus- t ra te one aspect of these da ta which further supports this suggestion. We have plotted, in figure 3, log male postcanine area against log female postcanine area, and the same has been done for incisor width in figure 4. The correlation coefficients are extremely high, and over 96% of the variability has been “ex- plained” in each case; this is, perhaps, surpris- ing in a sample tha t includes some species with large body weight differences between males and females (e.g., Papio anubis, Nasalis laruatus) and others with virtually no size dimorphism at all (e.g., Colubus uersus, Pres- bytis uygula). Now, in at least a heuristic, if not necessarily a causal, sense we see why there is almost no discernable relationship be-

540 DAVID POST, SERGE GOLDSTElN AND DON MELNICK

6 27

5 75

LPAMX

5.22

4 69

LPAFX Fig. 3 Plot of log postcanine area, male maxilla (LPAMX) against log postcanine area, female maxilla

(LPAFX). Correlation coefficient r = 0.9802, P < 0.01. Least-squares regression equation: LPAMX = -0.2732 t 1.0713 (LPAFX).

3.c

2.5

I W M X

.31

33, *22

'21

32. '30

41 '40

*42

3 53 L I W F X

I I 1 1

21 2.0

Fig. 4 Plot of log incisor width, male maxilla (LIWMX) against log incisor width, female maxilla (LIWFX). Correlation coefficient r = 0.9915, P < 0.01. Least-squares regression equation: LIWMX = -0.1726 + 1.0964 (LIWFX).

CERCOPITHECOID DENTAL DIMORPHTSM 54 1

: species mean o : male mean x i female rncan

log PA

loy WT

Fig. 5 Hypothetical plot of log postcanine area against log body weight. Cf. APPENDIX for details

tween body weight dimorphism and dental dimorphism in this sample; the dental dimensions of either sex are almost completely pre- dictable on the basis of the dimensions of the other sex irrespective of the relationship between their body weights, with virtually no variability remaining that could be attributed to body weight dimorphism. We certainly do not wish to minimize the problem of obtaining accurate estimates of male and female body weights for a study of this kind, but we do suggest that the information in figures 3 and 4 imply that errors in our estimates will not ma- terially affect our conclusions concerning the absence of a relationship between body weight dimorphism and dental dimorphism.

One final point; the slope of the regression lines in the graphs discussed above (figs. 3, 4) are slightly, but significantly, greater than unity (see regression equations in the figure captions); both male postcanine area and incisor width are increasing in this sample a t a faster rate than the corresponding female dimensions. Therefore, with increasing male

tooth size, the difference between male and female tooth size is increasing, i.e., dental dimorphism is increasing. Since as body size increases absolute tooth size also increases within this sample (Goldstein et al., ’781, this in turn implies that dental dimorphism increases as body size increases (independent of whatever relationship might exist between overall body size and body size dimorphism). In this sample, overall body size is related t o diet, the omnivores being of significantly larger mean size than the other diet classes (Anova, F = 11.011, df = 2, 22, P < 0.05) (cf. Gould, ’75; pp. 352-353 for a discussion, utilizing Levins’ concept of “grain,” of why this might be a “weak but pervasive generality” within many mammalian taxa). We expect, therefore, omnivores in this sample to show a greater amount of dental dimorphism simply as a consequence of their larger overall size. We would like to stress that this result cannot be phrased, within the context of this analysis, in causal terms; dental dimorphism increases in larger animals, but is that because those

542 DAVID POST. SERGE GOLDSTEIN AND DON MELNICK

animals are omnivores and omnivory is “responsible” for this increased increased dimorphism (as suggested by the dietary model discussed earlier), or is large size “responsible” for greater dental dimorphism, with larger species here happening to be omnivores? These alternative hypotheses generate identi- cal predictions within our present analytical model-that is, they are both compatible with our results-and therefore we cannot, at pres- en t judge which one of them is most plausible.

LITERATURE CITED

Brace, C. L. 1972 Sexual dimorphism in human evolution. Yearbook of Physical Anthropology, lfi: 31-49.

Clutton-Brock, T. H. 1975 Feeding behavior of red col obus and black and white colobus in East Africa. Folio Primat., 23: 165-207.

Clutton~Brock. T. H., and P. H. Harvey 1977 Primate social organization and ecology J. Zool.. 183: 1-39.

Clutlon-Brock. T. H., P. H. Harvey and I). Rudder 1977 Sex- ual dimorphism, socioeconomic sex ratio and body weight in primates. Nature, 2fi9: 797-800.

Crook, d. H. 1972 Sexual selection, diniorphism and social organization in the primates. In: Sexual Selection and the Descent of Man. €3. Campbell, ed. Aldine, Chlcago, pp. 231-281.

Goldstein, S.. D. Melnick and D. Post 1978 An analysis of Cercopithecoid odontometrics. I. Relations with diet, body size and body size dimorphism. Am. J. Phys. An- throp., in press.

Gould, S. J. 1966 Allometry and size in ontogeny and phylogeny. Biol. Rev. Cambridge Philos. SOC., 41: 587-640.

Geometric similarity in allometric growth: A contribution to the problem of scaling in the evolution of size. Am. Nat., 105: 113-136.

On the scaling of tooth size in mammals. Amer. Zool., 15: 351-362.

Grant, P. W. Variation in the tarsus length of birds in island and mainland reDons. Evolution. 25: 599-614.

Guenther. W. C. 1964 The Analysis of Variance. Pren- tice-Hall, Englewood Cliffs. N.J.

1971

1975

1971

Kay, R. F. 1973 Mastication, Molar Tooth Structure, and Diet in Primates. Ph.D. Thesis. Yale University.

Leutenegger, W., and J. T. Kelly 1977 Relatiomhip of sexual dimorphism in canine size and body size to social, be- havioral, and ecological correlates in anthropoidal primates. Primates, 18: 117-136.

Pilbeam. D. R. 1972 The Ascent of Man. MacMillan, New York.

Pilbeam, D. R.. and S. J. Gould 1974 Size and scaling in human evolution. Science, 186: 892-901.

Post, D. 1978 The Feeding and Ranging Behavior of the Yellow Baboon (Papio cynocephalusj. Ph.D. Thesis, Yale University.

Robinson. J. T. 1972 Early Hominid Posture and Locomo- tion. University of Chicago Press, Chicago.

Rose, M. D. 1977 Positional behavior of olive baboons (Papio anubis) and its relationship to maintenance and social activities. Primates, 18: 59-116.

Rothstein, S. I. 1973 Relative variation of avian morphological features: relation to the niche. Am. Nat., 107: 796-799.

Selander, R. K. 1966 Sexual dimorphism and differential niche utilization in birds. Condor, 68: 113-151.

1972 Sexual selection and dimorphism in birds. In: Sexual Selection and the Descent of Man. B. Campbell, ed. Aldine. Chicago, pp. 180-230.

Sirianm, J. 1974 Dental Variation in African Cerco- pithecidae: A Morphological, Metric. and Discriminant Analysis. Ph.D. Thesis. University of Washington.

Soule, M., and B. R. Stewart 1970 The “niche-variation” hypothesis: a test and alternatives. Am. Nat., 104: 85-97.

Swindler. D. 1976 The Dentition of Living Primates. Academic Press, New York.

Struhsaker, T. T., and J. F. Oates 1975 Comparison of the behavior and ecology of red colobus and black-and-white colobus monkeys in Uganda: a summary. In: Socioecology and Psychology of Primates. R. Tuttle, ed. Mouton, The Hague, pp 103-124

Wolpoff, M. 1975 Human Paleontology W H Freeman, San Francisco.

1976a Some aspects of the early evolution of early hominid sexual dimorphism. Current Anthropology, 17: 579-596.

1976b Primate models for australopithecine sexual dimorphism. Am. J. Phys. Anthrop.. 45: 497-510.

CERCOPITHECOID DENTAL DIMORPHISM 543

APPENDIX

We would like to briefly present our reasons for choosing the particular dimorphism indices used in the above analyses. Assume that the interspecific scaling of tooth dimension (e.g., postcanine area) against body weight can be expressed by means of the following allometric power function:

where PA, = mean postcanine area for species i, males and females pooled, WT, = mean body weight for species i, males and females pooled, and K , and (1 are empirically determined con- stants (cf. Gould, '66, '71; Goldstein e t al., '78). Therefore, utilizing the familiar transforma- tion of this equation,

Assume further that the intraspecific allometric curve between these two variables has some different slope, /3, and that this slope is a constant for all species in the sample (fig. 5). We can then express the mean postcanine area of the males and females of species i as follows:

PA, = K I X (WT1IU

log, (PA,) = K~ + a x (log,(WT,I)

log,(MPA,l = ( K ~ t u X (Iog,(WT,ji) + /3 X (log, (MWT,) -log,(WT,))

log,(FPA,) = ( K ~ + a x (log,(WTi)j) + p X !log,(FWT,) -log,(WTi))

where MPA, = mean male postcanine area,

MWT, = mean male body weight, species i FPAi = mean female postcanine area, species i,

FWTi = mean female body weight, species i.

species i,

and

By subtraction, log, (MPA,) -log,(FPA,) =

/3 X (log,(MWTi) ~ /3 X (log,(FWT,I,

or, log, (MPAJFPA,) = /3 X log,(MWTi/FWT)

By definition, this matter equation reduces to DMPAi = /3 X DMBW,.

In other words, the use of these particular dimorphism indices leads us to expect, if our assumptions (which we felt were not unrea- sonable a priori) are correct, a close linear relationship between body weight dimorphism and dental dimorphism; the presence or absence of such a relationship in these data then becomes a test of these assumptions.

Documents

An analysis of cercopithecoid odontometrics. II. Relations between dental dimorphism, body size dimorphism and diet