1978 Grant-in-Aid for Scientific Research (研究課題番号: 304326

Watanabe, Tsuyoshi

Kyoto University Research Information Repository

Title Craniometrical Studies on Alouatta seniculus - from the viewpoint of sex differences and age changes -Author(s)Watanabe, TsuyoshiCitationKyoto University overseas research reports of new worldmonkeys (1979), 1: 51-57Issue Date1979URL http://hdl.handle.net/2433/198659RightType Departmental Bulletin PaperTextversionpublisherKyoto UniversityKyoto University Overseas Research Reports of New World Monkeys (1979): 51-57 Kyoto University Primate Research Institute 51 Craniometrical Studies on Alouatta seniculus - from the view point of sex differences and age changes -Introduction Tsuyoshi Watanabe Primate Research Institute, Kyoto University Craniometrical studies on South American monkeys, Platyrrhini, have been done by Schultz (1926, 1960 and 1962). The number of species studied by him was limited; the species involved are Alouattαvillosa, Ate/es geoかoyiand Cebus cαpucinus. His studies comprise mostly of the analyses of morphological variation given by sex differences and age changes. And consequently his studies gave us the basic concept about infra-specific variation on cranial morphology of the above listed species of the New World monkeys. To extend and to elaborate the Schultz’s works, I made researches on morphology ofplatyrrhines in Colombia, S.A., as a member of the Third Upper Amazon Scientific Expedition organized by the Japan Monkey Centre, from October, 1975 to March, 1976 and a member of preliminary expedition by Kyoto University, from December, 1976 to February, 1977. The data were taken from the several species. The data given by the cranial morphology of Alouatta ceniculus are analized and reported here. This species was not treated by Schultz. This study is a part of the projects to clarify the evolutionary sequences and tax onかmic problems among South American monkeys. Acknowledgments This study was supported by the grants of the Ministry of Education, Science and Culture of the Japanese Government. The field and laboratory works were cooperated by INDERENA (Institute de Desarollo de los Recursos Naturales Renovables) and Museo de Ciencia Naturales de la Universidad Nacional, Colombia, S.A .I am also deeply grateful to Dr. Jorge Hernandez and Dr. Carlos Cruz at INDERENA, and to Dr. Jesus Maria Idrobo and Dr. Gonzaro Correal at Universidad Nacional. 九faterialand Methods The number of specimens studied are shown in the Table 1. They are divided into three age classes based on the dgree of eruption of teeth; individuals with fully erupted thirs molars are regarded as Adult, individuals with fully erupted first molars but without (not erupted) permanent canie and third molars are as Age Class I, and in-dividuals without (not erupted）自rstmolars are as Age Class I. Among the specimens studied, 33 specimens are housed in INDERENA, 33 specimens are in Universidad Nacional, Colombia, and 1 specimens are in Primate Research Institute, Kyoto University, Japan. 52 Table 1. Number of Specimens Studied Age of classes Age class I Age class I Adu! t female Adult male Total Number of specimens 13 7 26 31 77 I follow Martin (1914) for the measurements of skulls. Hems of measurements are as follows: 1. Cranial length: n-i 2. Cranial breadth: average of three dimensions, po-po, greatest breadth of brain case, greatest breadth of basi-cranium 3. Bizygomatic breadth: greatest breadth between zygomatic arches 4. Postorbital breadth: smallest frontal breadth behind orbital rims 5. Base length: n-ba 6. Facial length: pr-ba 7. Middle facial breadth: zm-zm 8. Upper facial height: n pr 9. Nasal hight: n-rhi 10. Nasal breadth: greatest breadth of nasal bones 11. Interorbital breadth: smallest breadth between the medial walls of the orbits at their entrances 12. Biorbital breadth: fmo-fmo 13. Bicondylar breadth: kdl-kdl 14. Bigonial breadth: go go 15. Symphysis height: id-gn 16. Ramus height Results The means of dimensions of 16 items listed above of each sex and age class and the means of indices are shown in the Tables 2-4. The sex differences seen in each dimen-sion expressed by percentage of those of male sover those off emales are shown in the Table 5. The item of dimensions with the greatest sex difference is seen in Bigonial breadth. The foilowing is the list of items with sex di町erencein descending order. Table 2. Cranial dimensions and indices of Alouatta Dimensions & indices Head length Head breadth Bizygomatic breadth Postorbital breadth Base length Cranial index Trans, cran. fac. I. Vert. cran. fac. I. Zygo. front. I. Postorb. I. Age class I 61.99 47.68 46.06 41.12 48.14 76.73 96.58 96.04 90.17 86.42 Age class I 68.02 51.59 60.16 43.02 56.59 75.93 117.21 112.64 71.07 83.64 Adult female 71.14 52.13 65.45 41.63 61.41 73.14 126.05 121.73 63.60 80.09 Adult male 78.98 56.48 78.58 40.37 71.09 71.53 139.53 133.53 51.46 72.29 53 Table 3. Facial dimensions and indices of Alouatta Dimensions & indices Age class I Age class I Adult female Adult male Facial length 59.60 76.45 86.45 105.41 Mid. fac. height 37.45 48.65 55.54 65.89 Up. fac. height 26.68 34.02 37.26 44.39 Nas. height 14.83 18.45 19.14 22.19 Nas. breadth 6.45 8.59 9.10 11.25 Interorb. breadth 7.07 9.16 10.87 12.61 Biorb. breadth 38.07 45.31 48.85 53.51 Up. fac. index 57.50 56.36 57.33 56.63 Zygo-malar I. 81.19 81.70 84.85 83.56 Alveolar 1 123.88 135.50 141.62 148.75 Nas. I. 41.73 44.67 46.08 50.17 Interorb. I. 17.42 19.45 21.38 22.92 Fronto-fac. I. 111.50 88.50 64.50 61.78 Table 4. Mandibular dimensions and indices of Alouatta Dimensions & indices Age class I Age class I Adult female Adult male Bi-co~~t breadth 43.30 52.59 55.89 63.59 Bigoni breadth 22.30 30.02 36.20 53.85 Symphysis height 18.22 23.45 24.49 29.12 Ramus height 29.60 45.45 52.30 66.68 Zygo”・gonial index 47.96 49.36 54.68 68.83 Mand. breadth I. 51.19 56.93 63.75 84.00 Table 5. Average value and sexual dimorphism in cranial dimensions of Alouatta seniculus Dimensions Cranial I ength Cranial bread th Postorbital breadth Base length Facial length Bizygomatic breadth 恥1id.facial breadth Up. facial height Nasal height Nasal breadth Interorbital breadth Biorbital breadth Bicondylar breadth Bigonial breadth Symphysis height Ramus height Average value F /M×100 Male (n = 31) Female (n = 26) 78.98 71.14 56.48 52.13 40.37 41.63 71.09 61.41 105.41 86.45 78.58 65.45 65.89 55.54 44.39 37.26 22.19 19.41 11.25 9.10 12.61 10;87 53.51 48.85 63.59 55.89 53.85 36.20 29.12 24.49 66.68 52.30 90.07 92.30 103.12 86.38 82.01 83.29 84.29 83.94 87.47 80.89 86.20 91.29 87.89 67.22 84.10 78.43 Ramus height, Nasal breadth, Facial length, Bizygomatic breadth, Upper facial height, Symphysis height，孔1iddlefacial breadth, lnterorbital breadth, Base length, Nasal height, Bicondylar breadth, Cranial length, Biorbital breadth, Cranial breadth, Postorbital breadth. The value of the item, Postorbital breadth exceeds 100 % showing that the dimension seen in females is greater than that of males. As for the parts of skulls, the greatest sex di汀erenceis seen in the mandible, the facial part follows next to it, and the brain case shows the smallest degree in sex difference. Among the mandi-ble, the fact that the degree of sex di町erenceseen in Bicondylar breadth is small is surely correlated to the mode of development of the basicranial part of skulls with which the condyle of mandible articulates. 54 Among age changes from Age Class I to Adult Male, the differences with age are greater in Bigonial breadth and Ramus height as in sex differences. The difference with age seen in Postorbital breadth is very minor. In compared with the trend seen in sex differences, the different trends are seen in age changes of Middle facial breadth, Interorbital breadth, and Biorbital breadth. They represent the transverse dimensions of the facial part, and age changes of these are comparatively greater than sex diι ferences. According to the indices calculated, the greatest value both in age changes and sex differences is seen in孔fandibularbreadth index (Biognial breadth/Bicondylar breadth ×I 00). This indicates that the lateral development of the gonial region in compared with that of the cranial base is prominent in Adult males. Zygomatic gonial index (Bigonial breadth/Zygomatic breadth ×100) also shows greater value for both age changes and sex differences, and this indicates that the degree of development of the gonial region is prominent for facial dimension. Cranial index (Cranial breadth/ Cranial length ×100) decrees with age, and the value of it in males is smaller than that of females. These results indicate that Adult males have more dolicho-cephalic cranium than Adult females. This morphological characteristic is surely correlated Table 6. Sex differences and growth rate on indices Mand. br. Index Zygo.-gonial. I. Zygo.-front. I. Front.-orb. I. Trans. cran.-fac. I. Postorb. I. Vert. cran.-fac. I. Nas. I. Interorb. I. Alve 1.I. Cran. I. Zygo.-mal. I. Up. fac. I. Alouatta seniculus +31.77 +25.88 -10.99 -17.07 +10.69 - 9.74 + 9.69 + 8.88 + 7.20 + 5.03 - 2.20 - 1.52 - 1.22 Macaca fuscata + 5.52 十11.45- 7.37 - 3.19 十 8.28+ 0.31 - 8.84 + 0.27 + 1.49 - 5.93 - 0.93 Growth rate of Aluoatta 十64.09+43.52 -42.93 -44.59 十44.47-16.35 +39.04 +20.22 十31.57+20.08 - 6.78 + 2.93 - 1.51 Table 7. Sex differences and growth rate on dimensions Bigonial Br. Ramus Ht. Nas. Br. Fae. Lg. Bizyg. Br. Up. fac. Ht. Symph. Ht. 恥lid.fac. Br. Interorb. Br. Base Lg. Nas. Ht. Bi-condyl. Br. Cran. Lg. (n-i) Biorb. Br. Cran. Br. Postorb. Br. Alouatta seniculus +48.76 十27.50+23.63 +21.93 +20.06 十19.14十18.91+18.64 十16.01+ 15.76 +13.32 +13.78 +11.02 + 9.54 十 8.34- 3.03 Macacafuscαtα 十13.70十 7.95十 3.37+14.70 +12.85 + 11.66 十16.73十 7.55+ 9.63 + 6.10 +13.59 十 8.18+ 3.63 + 7.55 + 4.27 十 4.45?????? ????????? ???????????????? ? ? ????????????????『????????????????，，???????? ??????????55 with the well-developed nuchal crest of Adult males. Upper facial index (Upper facial height/Bizygomatic breadth ×100) which shows the relative development of the facial part along vertical and transverse dimensions indicates no age changes and sex differences. The Table 6 shows the amounts of age changes and sex differences introduced by mdices. The amounts of sex differences are shown by percentage of the relative diι ferences between males and females over Adult females. The amounts of age changes are shown by percentage of the relative changes from Age Class 1 to Adult male over Age Class I. For comparison, sex differences seen in Japanese monkeys (Macaca .fuscata) reported by us (Ikeda & Watanabe, 1966) are tabled. The Table 7 also shows the data of dimensions as in the Table 6. Discussion The greatest sex differences and age changes seen in skulls of Red Howler monkeys (Alouatta seniculus) are seen in the mandibular part, especially in gonial region. The greater development of gonial region in Adult males of Howler monkeys is surely correlated with the greatest development of the hyoid. This characteristic development of the hyoid is seen among the species of this genus in general. The lateral and ventral developments of gonial region indicate the relationships with the development of the hyoid. However, Hill (1962) reported the variation of the degree of the develop-ments of the hyoid among the species of the genus Alouatta. Unfortunately, Schultz (1926, 1960 and 1962) did not mention about the differences in the mandible. The problems about the functional relationships between the mandible and the hyoid remain unsolved, and to solve the problems, extensive comparisons of morphology among species and the studies from the view points of comparative and functional morphology are needed. As seen in Cranial index and Upper facial index, the differences of the degree of development of length and breadth of the parts of brain case and facial region are minor among age classes. However, Alveolar index which indicates the degree of prognathism of the facial part varies from one age class to another. Moreover, the observation of skulls shows that the angle between the facial part and the cranial part which indicates the differences in the orientation of the development varies among age classes. To analyse the growth of the skull as a whole of Alouatta seniculus, the measurements of various angles given by the projection methods and of the curvature of the dental row are necessary. As for the difference in weight between males and females, Alouatta seniculus and Macacafuscata show almost no differences. But the former shows greater differences in cranial morphology between males and females. The greater differences between A. eniculus and M.ルscataare seen in the developments of the mandibular and the nasal parts. Schlutz (1962) gave the mean values of sex di百erencescalculated by the measurements of 14 items. According to him, the mean value of Alouatta villosa is +IO.I; Cebus capucinus, +6.7; Ate/us geoffroyi, +0.7. These values indicate that in compared with the other genera of South American monkeys, the genus Alouatta has greater differences in cranial morphology depending on sexes. To compare the results given by Alouatta villosa studied by Schlutz with those given by A. seniculus studied by me, among 8 items in common, Postorbital breadth and Interorbital 56 Table 8. Average value and sexual dimorphism in foot length in the Platyrrhini Genus n Average value of foot length Ffおf×100Sαrguinus Male 13 65.50 mm 102.67 Female 12 67.24 Callithrix 恥1ale 4 64.25 95.92 Female 6 61.63 Cα/lice bus Male 23 93.15 96.15 Female 16 85.56 Aotus Male 6 86.83 101.35 Female 4 88.01 Pithecia 恥1ale 7 124.71 95.06 Female 9 118.56 Saimiri 恥1ale 3 85.67 Female 3 82.00 95.72 Cebus Male 24 126.58 97.17 Female 16 123.00 Alouattαvilosa Male 22 147.23 96.32 Female 26 141.81 Alouatta seniculus 恥fale 4 138,75 90.99 Female 4 126.25 Lagothrix 恥1ale 4 148.50 95.40 Female 6 141.67 Brαchyteles 恥1ale 4 177.75 97.05 Female 2 172.50 Ate/es 恥1ale 15 178.93 104.12 Female 26 186.31 breadth of A. villosa show greater di汀erencesaccording to sexes. However, the other items, Cranial length, Cranial breadth, Base length, Bizygomatic breadth, Facial length and Upper facial height seen in A. seniculus show greater di町erencesdepending to sexes than those of A. villosa. According to the data (Table 8) of length of hind feet given by Hill (1957, 1960 and 1962), the sex di百erencesof A. senivulus are greater than those of A. villosa. According to Malinow et al. (1966), the sex differences of A. caraya in the length of hind feet are greater than those of A. seniculus. It is safely concluded that among the skulls of Platyrrhini, the genus Alouatta shows the greatest sex di汀erencesin cranial morphology. Among the genus Alouatta, the sex di百erencesseen in A. seniculus are obviously greater than those of A. villosa. Accord-ing to the data of the length of hind fet, the sex differences seen in A. caraya are the greatest. 1 have hypotheses on possible correlation between the sex differences men-tioned above and the di百erencesin mode of life of these species. This problem is out of scope for the present paper. This problem will be discussed in a separate paper. But only the following point must be mentioned here; the phenomenological correlations between the sex differences and the types of social organization, especially troop size among three species of the genus Alouatta mentioned above. Conclusions From above discussion, the following points are concluded; 1. Among three parts of cranial skeleton of Alouatta seniculus, namely, facial, brain case, and mandibular parts, both age changes and sex di百erencesseen in mandi-bular part are the greatest and those of brain case part are the smallest. 2. As for mandibular part, the degree of lateral and ventral development of gonial 57 region in Adult males is prominent, and consequently it gives the greater sex differences and age changes. 3. Based on the relation between length and breadth of brain case part given by Cranial index, the brain case of Adult males is developed to having dolicho-cephalic type. This development is probably resulted by the greater development of nuchal crest in Adult male. 4. Based on the relation between length and breadth of facial part given by Upper facial index, the age changes and sex di町erencesare not observable. 5. The relative position of three parts of cranial skellton varies according to age. But the detailed studies have not been done as yet. 6. To compare three species of the genus Alouatta, A. seniculus, A. villosa, and A. caraya, the greatest sex differences are seen in A. caraya, and A. sem・cu/us,A. VI・llosafollow that species in descending order. REFERENCES Hil, 0., 1957. The Primates, Vol. II. Edingburgh Press, Edingburgh. , 1960. The Primates, Vol. IV. Edingburgh Press, Edingburgh. 一一一一一一，1962.The Primates, Vol. V. Edingburgh Press, Edingburgh. Ikeda, J. & T. Watanabe, 1966. Morphological Studies of MacacaルscataIII-Craniometry .ーPrimates, Vol. 7. Malinow, et. al., 1966. The Growth Studies of Alouatta caraya. Primates Vol. 7. Martin, R., 1914. Lehrbuch der Anthropologie. Jena. Schultz, A, H . 1926. Studies on The Variability of Platyrrhine Monkeys. J. Mammal. 4. 一一一一一一， 1960.Age Changes and Variability in The Skulls and Teeth of The Central American Monkeys Alouatta, Cebus, and Ate/es. Proc. Zool. Soc. London, 133. , 1962. Metric Age Changes and Sex Differences in The Primate Skulls. Zeit. Morph. Anthrop. 52・3.

Craniometrical Studies on Alouatta seniculus - from the view point of sex differences and age changes -

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Craniometrical Studies on Alouatta seniculus - from the view point of sex differences and age changes -

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