Skip to main content Accessibility help
×
Home
  • Print publication year: 2002
  • Online publication date: August 2009

6 - Ontogeny and function of the masticatory complex in Gorilla: Functional, evolutionary, and taxonomic implications

Summary

Introduction

The classic studies of Coolidge (1929) and Groves (1967, 1970a, b, 1986; Groves and Stott, 1979), coupled with more recent investigations (Uchida, 1996, 1998; Taylor, 1998a, b, 1999, 2002), have revealed considerable variability in the cranium, mandible, and dentition among subspecies and even geographic populations of gorillas (Albrecht et al., Leigh et al., Stumpf et al., this volume). Historically, investigators have tended to emphasize the taxonomic implications of this variation (Coolidge, 1929; Groves, 1967, 1970a) and with good reason, as a well-founded taxonomy clearly forms the basis for meaningful studies in other important fields, including morphology, behavioral ecology, and genetics. While there have been some attempts to draw functional inferences from differences in craniomandibular and dental morphology among gorilla subspecies (Vogel, 1961; Groves, 1970a, b; Uchida, 1996, 1998; Taylor, 1998b, 1999, 2000), nevertheless the nature and patterning of variation in jaw form among gorilla subspecies remains unresolved.

I examine masticatory form and function in gorillas to assess whether gorilla subspecies differ predictably in morphology as a function of dietary specialization. I focus particularly on the expected pattern of morphological differentiation in Gorilla based on the degree to which these taxa differ in degree of folivory versus frugivory. I use an ontogenetic, allometric approach in an explicitly phylogenetic context to evaluate whether differences among subspecies can be principally attributed to extrapolation or truncation of inherited patterns of ontogenetic allometry (Shea, 1995), or to derived dissociations of ancestral allometries.

References
Ackermann, R. R. and Cheverud, J. M. (2000). Phenotypic covariance structure in tamarins (genus Saguinus): A comparison of variation patterns using matrix correlation and common principal component analysis. American Journal of Physical Anthropology, 111, 489–501
Albrecht, G. H. and Miller, J. M. A. (1993). Geographic variation in primates: A review with implications for interpreting fossils. In Species, Species Concepts, and Primate Evolution, eds. W. H. Kimbel and L. B. Martin, pp. 123–162. New York: Plenum Press
Antón, S. C. (1996 a). Cranial adaptation to a high attrition diet in Japanese macaques. International Journal of Primatology, 17, 401–427
Antón, S. C. (1996 b). Tendon-associated bone features of the masticatory system in Neandertals. Journal of Human Evolution, 31, 391–408
Antón, S. C. (1999). Macaque masseter muscle: Internal architecture, fiber length and cross-sectional area. International Journal of Primatology, 20, 441–462
Antón, S. C. (2000). Macaque pterygoid muscles: Internal architecture, fiber length, and cross-sectional area. International Journal of Primatology, 21, 131–156
Atchley, W. R. (1987). Developmental quantitative genetics and the evolution of ontogenies. Evolution, 41, 316–330
Atchley, W. R. and Hall, B. K. (1991). A model for development and evolution of complex morphological structures. Biological Review, 66, 101–157
Badrian, N. L. and Malenky, R. K. (1984). Feeding ecology of Pan paniscus in the Lomako Forest, Zaire. In The Pygmy Chimpanzee: Evolutionary Biology and Behavior, ed. R. L. Susman, pp. 275–299. New York: Plenum Press
Beecher, R. M. (1979). Functional significance of the mandibular symphysis. Journal of Morphology, 159, 117–130
Beecher, R. M. and Corruccini, R. S. (1981). Effects of dietary consistency on craniofacial and occlusal development in the rat. Angle Orthodontics, 51, 61–69
Beecher, R. M., Corruccini, R. S., and Freeman, M. (1983). Craniofacial correlates of dietary consistency in a nonhuman primate. Journal of Craniofacial Genetics and Developmental Biology, 3, 193–202
Biewener, A. A. (1982). Bone strength in small mammals and bipedal birds: Do safety factors change with body size?Journal of Experimental Biology, 98, 289–301
Bouvier, M. (1986 a). A biomechanical analysis of mandibular scaling in Old World monkeys. American Journal of Physical Anthropology, 69, 473–482
Bouvier, M. (1986 b). Biomechanical scaling of mandibular dimensions in New World Monkeys. International Journal of Primatology, 7, 551–567
Bouvier, M. and Hylander, W. L. (1981). Effect of bone strain on cortical bone structure in macaques (Macaca mulatta). Journal of Morphology, 167, 1–12
Brylski, P. and Hall, B. K. (1988). Ontogeny of a macroevolutionary phenotype: The external cheek pouches of geomyoid rodents. Evolution, 42, 391–395
Casimir, M. J. (1975). Some data on the systematic position of the Eastern gorilla population of the Mt. Kahuzi region (République du Zaïre). Zeitschrift für Morphologie und Anthropologie, 66, 188–201
Chapman, C. A., White, F. J., and Wrangham, R. W. (1994). Party size in chimpanzees and bonobos: A re-evaluation of theory based on two similarly forested sites. In Chimpanzee Cultures, eds. R. W. Wrangham, W. C. McGrew, F. B. M. de Waal, and P. G. Heltne, pp. 41–57. Cambridge, MA: Harvard University Press
Cheverud, J. M. (1981). Epiphyseal union and dental eruption in Macaca mulatta. American Journal of Physical Anthropology, 56, 157–169
Cheverud, J. M. (1984). Quantitative genetics and developmental constraints on evolution by selection. Journal of Theoretical Biology, 101, 155–171
Cochard, LR. (1985). Ontogenetic allometry of the skull and dentition of the rhesus monkey (Macaca mulatta). In Size and Scaling in Primate Biology, ed. W. L. Jungers, pp. 231–256. New York: Plenum Press
Cock, A. G. (1963). Genetical aspects of metrical growth and form in animals. Quarterly Review of Biology, 41, 131–190
Cole, T. M. III (1992). Postnatal heterochrony of the masticatory apparatus in Cebus apella and Cebus albifrons. Journal of Human Evolution, 23, 253–282
Coolidge, H. J. (1929). A revision of the genus Gorilla. Memoirs of the Museum of Comparative Zoology, Harvard, 50, 291–381
Corruccini, R. S. and Beecher, R. M. (1982) Occlusal variation related to soft diet in a nonhuman primate. Science, 218, 74–76
Corruccini, R. S. and Beecher, R. M. (1984). Occlusofacial morphological integration lowered in baboons raised on soft diet. Journal of Craniofacial and Genetic Developmental Biology, 4, 135–142
Daegling, D. J. (1989). Biomechanics of cross-sectional size and shape in the hominoid mandibular corpus. American Journal of Physical Anthropology, 80, 91–106
Daegling, D. J. (1990). Geometry and biomechanics of hominoid mandibles. PhD thesis, State University of New York at Stony Brook, Stony Brook, NY
Daegling, D. J. (1992). Mandibular morphology and diet in the genus Cebus. International Journal of Primatology, 13, 545–570
Daegling, D. J. (2001). Biomechanical scaling of the hominoid mandibular symphysis. Journal of Morphology, 250, 12–23
Daegling, D. J. and Grine, F. E. (1991). Compact bone distribution and biomechanics of early hominid mandibles. American Journal of Physical Anthropology, 86, 321–339
Daegling, D. J. and Hylander, W. L. (1998). Biomechanics of torsion in the human mandible. American Journal of Physical Anthropology, 105, 73–87
Daegling, D. J. and Hylander, W. L. (2000). Experimental observation, theoretical models, and biomechanical inference in the study of mandibular form. American Journal of Physical Anthropology, 112, 541–551
Dodson, P. (1975). Functional and ecological significance of relative growth in Alligator. Journal of Zoology, London, 1975, 315–355
DuBrul, L. E. (1977). Early hominid feeding mechanisms. American Journal of Physical Anthropology, 47, 305–320
Emerson, S. B. and Bramble, D. M. (1993). Scaling, allometry, and skull design. In The Skull, vol. 3, Functional and Evolutionary Mechanisms, eds. J. Hanken and B. K. Hall, pp. 384–421. Chicago, IL: University of Chicago Press
Freeman, P. W. (1988). Frugivorous and animalivorous bats (Microchiroptera): Dental and cranial adaptations. Biological Journal of the Linnean Society, 33, 249–272
Garner, K. J. and Ryder, O. A. (1996). Mitochondrial DNA diversity in gorillas. Molecular Phylogenetics and Evolution, 6, 39–48
Godfrey, L. R., King, S. J., and Sutherland, M. R. (1998). Heterochronic approaches to the study of locomotion. In Primate Locomotion: Recent Advances, eds. E. Strasser, J. Fleagle, A. Rosenberger, and H. McHenry, pp. 277–307. New York: Plenum Press
Gould, S. J. (1966). Allometry and size in ontogeny and phylogeny. Biological Review, 41, 587–640
Gould, S. J. (1971). Geometric similarity in allometric growth: A contribution to the problem of scaling in the evolution of size. American Naturalist, 105, 113–136
Gould, S. J. (1975). Allometry in primates, with emphasis on scaling and the evolution of the brain. In Approaches to Primate Paleobiology, ed. F. Szalay, pp. 244–292. Basel, Switzerland: S. Karger
Gould, S. J. and Lewontin, R. C. (1979). The spandrels of San Marco and the Panglossian paradigm: A critique of the adaptationist programme. In The Evolution of Adaptation by Natural Selection, eds. J. Maynard Smith and R. Holliday, pp. 147–164. London: Royal Society
Gould, S. J. and Vrba, E. S. (1982). Exaptation: A missing term in the science of form. Paleobiology, 8, 4–15
Groves, C. P. (1967). Ecology and taxonomy of the gorilla. Nature, 213, 890–893
Groves, C. P. (1970 a). Gigantopithecus and the mountain gorilla. Nature, 226, 973–974
Groves, C. P. (1970 b). Population systematics of the gorilla. Journal of the Zoological Society of London, 161, 287–300
Groves, C. P. (1986). Systematics of the Great Apes. In Evolution, Ecology, Behavior and Captive Maintenance, ed. D. M. Rumbaugh, pp. 2–102. Basel, Switzerland: S. Karger
Groves, C. P. (2001). Primate Taxonomy. Washington, D.C.: Smithsonian Institution Press
Groves, C. P. and Stott, K. W. Jr. (1979). Systematic relationships of gorillas from Kahuzi, Tshiaberimu and Kayonza. Folia Primatologica, 32, 161–179
Harvey, P. H. and Pagel, M. D. (1991). The Comparative Method in Evolutionary Biology. Oxford, U.K.: Oxford University Press
Herring, S. W. and Herring, S. E. (1974). The superficial masseter and gape in mammals. American Naturalist, 108, 561–576
Huxley, J. S. (1932). Problems of Relative Growth. London: MacVeagh
Hylander, W. L. (1975). Incisor size and diet in anthropoids with special reference to Cercopithecidae. Science, 26, 1095–1098
Hylander, W. L. (1977). The adaptive significance of Eskimo craniofacial morphology. In Orofacial Growth and Development, eds. A. A. Dahlberg and T. M. Graber, pp. 129–170. Paris: Mouton
Hylander, W. L. (1979 a). The functional significance of primate mandibular form. Journal of Morphology, 160, 223–240
Hylander, W. L. (1979 b). Mandibular function in Galago crassicaudatus and Macaca fascicularis: An in vivo approach to stress analysis of the mandible. Journal of Morphology, 159, 253–296
Hylander, W. L. (1981). Patterns of stress and strain in the macaque mandible. In Craniofacial Biology, ed. C. S. Carlson, pp. 1–37. Ann Arbor, MI: University of Michigan
Hylander, W. L. (1984). Stress and strain in the mandibular symphysis of Primates: A test of competing hypotheses. American Journal of Physical Anthropology, 64, 1–46
Hylander, W. L. (1985). Mandibular function and biomechanical stress and scaling. American Zoologist, 25, 315–330
Hylander, W. L. (1986). In vivo bone strain as an indicator of masticatory bite force in Macaca fascicularis. Archives of Oral Biology, 31, 149–157
Hylander, W. L. (1988). Implications of in vivo experiments for interpreting the functional significance of “robust” australopithecine jaws. In Evolutionary History of the “Robust” Australopithecines, ed. F. E. Grine, pp. 55–83. New York: Aldine de Gruyter
Hylander, W. L. and Bays, R. (1979). An in vivo strain gage analysis of squamosal dentary joint reaction force during mastication and incision in Macaca mulatta and Macaca fascicularis. Archives of Oral Biology, 24, 689–697
Hylander, W. L. and Johnson, K. (1994). Jaw muscle function and wishboning of the mandible during mastication in macaques and baboons. American Journal of Physical Anthropology, 94, 523–548
Hylander, W.L, Johnson, K. R., and Crompton, A. W. (1987). Loading patterns and jaw movements during mastication in Macaca fascicularis: A bone strain, electromyographic, and cineradiographic analysis. American Journal of Physical Anthropology, 72, 287–314
Hylander, W. L., Johnson, K. R., Ravosa, M. J., and Ross, C. F. (1996). Mandibular bone strain and jaw-muscle recruitment patterns during mastication in anthropoids and prosimians. American Journal of Physical Anthropology, Supplement 22, 128–129
Hylander, W. L., Ravosa, M. J., Ross, C. F., Wall, C. E., and Johnson, K. R. (2000). Symphyseal fusion and jaw-adductor muscle force: An EMG study. American Journal of Physical Anthropology, 112, 469–492
Inouye, S. E. (1992). Ontogeny and allometry of African apes manual rays. Journal of Human Evolution, 23, 107–138
Janson, C. and van Schaik, C. P. (1993). Ecological risk aversion in juvenile primates: Slow and steady wins the race. In Juvenile Primates, Life History, Development and Behavior, eds. M. E. Pereira and L. A. Fairbanks, pp. 57–74. Oxford, U.K.: Oxford University Press
Jolicoeur, P. (1963). The multivariate generalization of the allometry equation. Biometrics, 19, 497–499
Jolly, C. J. (1993). The seed-eaters: A new model of hominid differentiation based on a baboon analogy. Man, 5, 5–26
Jungers, W. L. and Cole, M. S. (1992). Relative growth and shape of the locomotor skeleton in lesser apes. Journal of Human Evolution, 23, 93–106
Jungers, W. L. and Fleagle, J. G. (1980). Postnatal growth allometry of the extremities in Cebus albifrons and Cebus apella: A longitudinal and comparative study. American Journal of Physical Anthropology, 53, 471–478
Kano, T. and Mulavwa, M. (1984). Feeding ecology of the pygmy chimpanzees (Pan paniscus) of Wamba. In The Pygmy Chimpanzee: Evolutionary Biology and Behavior, ed. R. L. Susman, pp. 233–274. New York: Plenum Press
Kimbel, W. (1991). Species, species concepts and hominid evolution. Journal of Human Evolution, 20, 355–372
Klingenberg, C. P., Neuenschwander, B. E., and Flury, B. D. (1996). Ontogeny and individual variation: Analysis of patterned covariance matrices with common principal components. Systematic Biology, 45, 135–150
Lauder, G. (1982). Historical biology and the problem of design. Journal of Theoretical Biology, 97, 57–67
Lauder, G. V. and Reilly, S. M. (1990). Metamorphosis of the feeding mechanism in tiger salamanders (Ambystoma tigrinum): The ontogeny of cranial muscle mass. Journal of Zoology, London, 222, 59–74
Lovell, N. C. (1990). Skeletal dental pathology of free-ranging Mountain Gorillas. American Journal of Physical Anthropology, 81, 399–412
Lucas, P. W., Turner, I. M., Dominy, N. J., and Yamashita, N. (2000). Mechanical defenses to herbivory. Annals of Botany, 86, 913–920
Macdonald, M. E. and Hall, B. K. (2001). Altered timing of the extracellular-matrix-mediated epithelial–mesenchymal interaction that initiates mandibular skeletogenesis in three inbred strains of mice: Development, heterochrony, and evolutionary change in morphology. Journal of Experimental Zoology, 291, 258–273
Malenkey, R. K. and Stiles, E. W. (1991). Distribution of terrestrial herbaceous vegetation and its consumption by Pan paniscus in the Lomako Forest, Zaire. American Journal of Primatology, 23, 153–169
Malenky, R. K. and Wrangham, R. W. (1994). A quantitative comparison of terrestrial herbaceous food consumption by Pan paniscus in the Lomako Forest, Zaire, and Pan troglodytes in the Kibale Forest, Uganda. American Journal of Primatology, 32, 1–12
Malenky, R. K., Kuroda, S., Vineberg, E. O., and Wrangham, R. W. (1994). The significance of terrestrial herbaceous foods for bonobos, chimpanzees, and gorillas. In Chimpanzee Cultures, eds. R. W. Wrangham, W. C. McGrew, F. B. M. de Waal, and P. G. Heltne, pp. 59–75. Cambridge, MA: Harvard University Press
Martin, R. D. (1989). Size, shape and evolution. In Evolutionary Studies: A Centenary Celebration of the Life of Julian Huxley, eds. M. Keynes and G. A. Harrison, pp. 96–141. Basingstoke, U.K.: Macmillan
Mayr, E. (1982). Of what use are subspecies?Auk, 99, 593–595
McCollum, M. A. (1997). Mechanical and spatial determinants of Paranthropus facial form. American Journal of Physical Anthropology, 93, 259–273
McCrossin, M. L. and Benefit, B. R. (1993). Recently recovered Kenyapithecus mandible and its implications for great ape and human origins. Proceedings of the National Academy of Sciences U.S.A., 90, 1962–1966
Miyake, T., Cameron, A. M., and Hall, B. K. (1997). Variability of embryonic development among three inbred strains of mice. Growth, Development and Aging, 61, 141–155
Morell, V. (1999). Ecology returns to speciation studies. Science, 284, 2106
Müller, G. B. (1990). Developmental mechanisms: A side-effect hypothesis. In Evolutionary Innovations, ed. M. H. Nitecki, pp. 99–130. Chicago, IL: University of Chicago Press
Nichols, D. H. (1986). Formation and distribution of neural crest mesenchyme to the first pharyngeal arch region of the mouse embryo. American Journal of Anatomy, 176, 221–231
Oxnard, C. E. (1972). Functional morphology of primates: Some mathetmatical and physical methods. In The Functional and Evolutionary Biology of Primates, ed. R. H. Tuttle, pp. 305–336. Chicago, IL: University of Chicago Press
Oxnard, C. E. (1979). Some methodological factors in studying the morphological–behavioral interface. In Environment, Behavior, and Morphology: Dynamic Interactions in Primates, eds. M. E. Morbeck, H. Preuschoft, and N. Gomberg, pp. 209–227. New York: Gustav Fischer
Price, T. D., Grant, P. R., and Boag, P. T. (1984). Genetic changes in the morphological differentiation of Darwin's ground finches. In Population Biology and Evolution, eds. K. Wohrmann and V. Loeschke, pp. 49–66. Berlin: Springer-Verlag
Raff, R. A., Parr, B., Parks, A., and Wray, G. (1990). Heterochrony and other mechanisms of radical evolutionary change in early development. In Evolutionary Innovations, ed. M. H. Nitecki, pp. 71–98. Chicago, IL: University of Chicago Press
Rak, Y. (1983). The Australopithecine Face. New York: Academic Press
Raven, H. C. (1950). The Anatomy of the Gorilla. New York: Columbia University Press
Ravosa, M. J. (1990). Functional assessment of subfamily variation in maxillomandibular morphology among Old World monkeys. American Journal of Physical Anthropology, 82, 199–212
Ravosa, M. J. (1991). Structural allometry of the prosimian mandibular corpus and symphysis. Journal of Human Evolution, 20, 3–20
Ravosa, M. J. (1996 a). Jaw morphology and function in living and fossil Old World Monkeys. International Journal of Primatology, 17, 909–932
Ravosa, M. J. (1996 b). Mandibular form and function in North American and European Adapidae and Omomyidae. Journal of Morphology, 229, 171–190
Ravosa, M. J. (2000). Size and scaling in the mandible of living and extinct apes. Folia Primatologica, 71, 305–322
Reilly, S. M., and Lauder, G. V. (1990). Metamorphosis of cranial design in tiger salamanders (Ambystoma tigrinum): A morphometric analysis of ontogenetic change. Journal of Morphology, 104, 121–137
Remis, M. J. (1997). Western lowland gorillas (Gorilla gorilla gorilla) as seasonal frugivores: Use of variable resources. American Journal of Primatology, 43, 87–109
Rensberger, J. M. (1973). Sanctimus (Mammalia, Rodentia) and the phyletic relationships of the large arikareean geomyoids. Journal of Paleontology, 47, 835–853
Rubin, C. T. and Lanyon, L. E. (1984). Dynamic strain similarity in vertebrates: An alternative to allometric limb bone scaling. Journal of Theoretical Biology, 107, 321–327
Ruvolo, M., Pan, D., Zehr, S., Goldberg, T., Disotell, T. R., and Dornum, M. (1994). Gene trees and hominoid phylogeny. Proceedings of the National Academy of Sciences U.S.A. 91, 8900–8904
Sarmiento, E. E., & Oates, J. (2000). The Cross River gorillas: A distinct subspecies Gorilla gorilla diehli Matschie 1904. American Museum Novitates, 3304, 1–55
Sarmiento, E. E., Butynski, T. M., and Kalina, J. (1996). Gorillas of the Bwindi-Impenetrable Forest and Virunga Volcanoes: Taxonomic implications of morphological and ecological differences. American Journal of Primatology, 40, 1–21
Schultz, A. (1930). The skeleton of the trunk and limbs of higher primates. Human Biology, 2, 303–435
Schultz, A. H. (1934). Some distinguishing characters of the mountain gorilla. Journal of Mammalogy, 15, 51–61
Seaman, M. L., Deinard, A. S., & Kidd, K. K. (1999). Incongruence between mitochondrial and nuclear DNA estimated of divergence between gorilla subspecies. American Journal of Physical Anthropology, Supplement 28, 259
Shea, B. T. (1982). Growth and size allometry in the African Pongidae: Cranial and postcranial analyses. PhD dissertation, Duke University, Chapel Hill, NC
Shea, B. T. (1983 a). Size and diet in the evolution of African ape craniodental form. Folia Primatologica, 40, 32–68
Shea, B. T. (1983 b). Allometry and heterochrony in the African apes. American Journal of Physical Anthropology, 62, 275–289
Shea, B. T. (1984). An allometric perspective on the morphological and evolutionary relationships between pygmy (Pan paniscus) and common (Pan troglodytes) chimpanzees. In The Pygmy Chimpanzee: Evolutionary Biology and Behavior, ed. R. L. Susman, pp. 89–130. New York: Plenum Press
Shea, B. T. (1985a). Ontogenetic allometry and scaling: A discussion based on growth and form of the skull in African apes. In Size and Scaling in Primate Biology, ed. W. L. Jungers, pp. 175–206. New York: Plenum Press
Shea, B. T. (1985 b). Bivariate and multivariate growth allometry: Statistical and biological considerations. Journal of Zoology, London, 206, 367–390
Shea, B. T. (1986). Scapula form and locomotion in chimpanzee evolution. American Journal of Physical Anthropology, 70, 475–488
Shea, B. T. (1995). Ontogenetic scaling and size correction in the comparative study of primate adaptations. Anthropologie, 33, 1–16
Shea, B. T. and Coolidge, H. T. (1988). Craniometric differentiation and systematics in the genus Pan. Journal of Human Evolution, 17, 671–685
Shea, B. T., Leigh, S. R., and Groves, C. P. (1993). Multivariate craniometric variation in chimpanzees: implications for species identification in paleoanthropology. In Species, Species Concepts, and Primate Evolution, eds. W. H. Kimbel and L. B. Martin, pp. 265–296. New York: Plenum Press
Smith, R. J. (1983). The mandibular corpus of female primates: Taxonomic, dietary, and allometric correlates of interspecific variations in size and shape. American Journal of Physical Anthropology, 61, 315–330
Smith, R. J. (1993). Categories of allometry: Body size versus biomechanics. Journal of Human Evolution, 24, 173–182
Smith, R. J. and Jungers, W. L. (1997). Body mass in comparative primatology. Journal of Human Evolution, 32, 523–559
Smith, R. J., Petersen, C. E., and Gipe, D. P. (1983). Size and shape of the mandibular condyle in primates. Journal of Morphology, 177, 59–68
Spencer, M. A. (1998). Force production in the primate masticatory system: Electro-myographic tests of biomechanical hypotheses. Journal of Human Evolution, 34, 25–54
Spencer, M. A. and Demes, B. (1993). Biomechanical analysis of masticatory function–configuration in Neandertals and Inuits. American Journal of Physical Anthropology, 91, 1–20
Spencer, M. A. and Hogard, R. (2001). Biomechanics of sexual dimorphism in the anthropoid masticatory system. American Journal of Physical Anthropology, Supplement 32, 141
Takahashi, L. K. and Pan, R. (1994). Mandibular morphometrics among macaques: The case of Macaca thibetana. International Journal of Primatology, 15, 597–621
Tan, S. S. and Morriss-Kay, G. M. (1985). The development and distribution of the cranial neural crest in the rat embryo. Cell and Tissue Research, 240, 403–416
Tattersall, I. (1986). Species recognition in human paleontology. Journal of Human Evolution, 15, 165–175
Taylor, A. B. (1995). Effects of ontogeny and sexual dimorphism on scapula morphology in the mountain gorilla (Gorilla gorilla beringei). American Journal of Physical Anthropology, 98, 431–445
Taylor, A. B. (1997 a). Relative growth, ontogeny, and sexual dimorphism in Gorilla (Gorilla gorilla gorilla and G. g. beringei): Evolutionary and ecological considerations. American Journal of Primatology, 43, 1–33
Taylor, A. B. (1997 b). Scapula form and biomechanics in gorillas. Journal of Human Evolution, 34, 529–533
Taylor, A. B. (1998 a). Ontogeny and function of maxillomandibular form in Gorilla. Abstracts of Contributions to the Dual Congress 1998, 65
Taylor, A. B. (1998 b). Masticatory form and function in gorillas (G. g. gorilla and G. g. beringei). American Journal of Physical Anthropology, Supplement 26, 216–217
Taylor, A. B. (1999). Variation in masticatory form in lowland gorillas (Gorilla gorilla gorilla and G. g. graueri): An ontogenetic approach. American Journal of Physical Anthropology, Supplement 28, 262
Taylor, A. B. (2000). Tooth or consequences: Is jaw robusticity the correlated effect of increased tooth size?American Journal of Physical Anthropology, Supplement 30, 300
Taylor, A. B. (2002). Masticatory form and function in the African apes. American Journal of Physical Anthropology, 117, 133–156
Taylor, A. B. and Ravosa, M. J. (1999). Ontogeny and function in the evolution of African ape masticatory form. American Journal of Primatology, 49, 183
Terborgh, J. W. (1983). Five New World Primates: A Study in Comparative Ecology. Princeton, NJ: Princeton University Press
Thompson, D. W. (1942). On Growth and Form. London: Cambridge University Press
Turnbull, W. D. (1970). Mammalian masticatory apparatus. Field Museum of Natural History Fieldiana: Geology, 18, 149–356
Tutin, C. E. G., Ham, R. M., White, L. J. T., and Harrison, M. J. S. (1997). The primate community of the Lopé Reserve, Gabon: Diets, responses to fruit scarcity, and effects on biomass. American Journal of Primatology, 42, 1–24
Uchida, A. (1996). Craniodental Variation among the Great Apes, Peabody Museum Bulletin no. 4. Cambridge, MA: Harvard University Press
Uchida, A. (1998). Variation in tooth morphology of Gorilla gorilla. Journal of Human Evolution, 34, 55–70
Schaik, C. P. and Noordwijk, M. A. (1986). The hidden costs of sociality: Intra-group variation in feeding strategies in Sumatran long-tailed macaques (Macaca fascicularis). Behaviour, 99, 296–315
Velhagen, W. A. and Roth, V. L. (1997). Scaling of the mandible in squirrels. Journal of Morphology, 232, 107–132
Vermeij-Keers, C. and Poelmann, R. E. (1980). The neural crest: A study on cell degeneration and the improbability of cell migration in mouse embryos. Netherlands Journal of Zoology, 30, 74–81
Vinyard, C. J. and Ravosa, M. J. (1998). Ontogeny, function, and scaling of the mandibular symphysis in papionin primates. Journal of Morphology, 235, 157–175
Vogel, V. C. (1961). Zur systematischen Untergliederung der Gattung Gorilla anhand van Untersuchungen der Mandibel. Zeitschrift für Säugetierkunde, 26, 1–12
Ward, S. C. and Molnar, S. (1980). Experimental stress analysis of topographic diversity in early hominid gnathic morphology. American Journal of Physical Anthropology, 53, 383–395
Ward, S., Brown, B., Hill, A., Kelley, J., and Downs, W. (1999). Equatorius: A new hominoid genus from the Middle Miocene of Kenya. Science, 285, 1382–1386
Watts, D. P. (1984). Composition and variability of mountain gorilla diets in the central Virungas. American Journal of Primatology, 7, 323–356
Watts, D. P. (1998). Seasonality in the ecology and life histories of mountain gorillas (Gorilla gorilla beringei). International Journal of Primatology, 19, 929–948
Wolff, J. (1870). Ueber die innere Architectur der Knochen und ihre Bedeutung für die Frage vom Knochenwachsthum. Archives für pathologische Anatomie und Physiologic und für kulinische Medizin (Virchows Archiv), 50, 389–453
Wrangham, R. W. (1986). Ecology and social evolution in two species of chimpanzee. In Ecology and Social Evolution: Birds and Mammals, eds. D. L. Rubenstein and R. W. Wrangham, pp. 352–378. Princeton, NJ: Princeton University Press
Wrangham, R. W., Chapman, C. A., Clark-Arcadia, A. P., and Isabirye-Basuta, G. (1996). Social ecology of Kanyawara chimpanzees: Implications for understanding the costs of great ape groups. In Great Ape Societies, eds. W. C. McGrew, L. F. Marchant, and T. Nishida, pp. 45–57. Cambridge, U.K.: Cambridge University Press
Yamagiwa, J., Maruhashi, T., Yumoto, T., and Mwanza, N. (1996). Dietary and ranging overlap in sympatric gorillas and chimpanzees in Kahuzi-Biega National Park, Zaire. In Great Ape Societies, eds. W. C. McGrew, L. F. Marchant, and T. Nishida, pp. 82–98. Cambridge, U.K.: Cambridge University Press