Date Published: February 21, 2011
Publisher: Hindawi Publishing Corporation
Author(s): Debra R. Bolter.
The physical growth patterns of crested langurs and vervet monkeys are investigated for several unilinear dimensions. Long bone lengths, trunk height, foot length, epiphyseal fusion of the long bones and the pelvis, and cranial capacity are compared through six dental growth stages in male Trachypithecus cristatus (crested langurs) and Cercopithecus aethiops (vervet monkeys). Results show that the body elements of crested langurs mature differently than those of vervets. In some dimensions, langurs and vervets grow comparably, in others vervets attain adult values in advance of crested langurs, and in one feature the langurs are accelerated. Several factors may explain this difference, including phylogeny, diet, ecology, and locomotion. This study proposes that locomotor requirements affect differences in somatic growth between the species.
The fundamentals of growth and development are important in primate evolutionary studies. Primates have a protracted period of immaturity compared to other animals, and immature individuals must survive this prolonged life period before reproductive adulthood. When considering a life history perspective, natural selection acts on immature individuals first through survival, when mortality is quite high; only when an individual successfully navigates the long infant and juvenile stages does reproduction become a selective force. Emphasis on primate survival through immaturity and life history theory began in the 1980s and has become a major focus for primate researchers: we assess basic demographic variables like group composition and age at reproductive maturity, establish age-cohorts, follow changes in individuals as they mature, investigate patterns of sexual dimorphism, examine the influence of ecological and locomotor constraints, and explore maturity disassociations among body systems [1–16]. In order to determine the life history parameters for extinct species, paleontologists and paleoanthropologists must understand growth and development (e.g., [17–21]). Evolutionary theorists use displaced developmental events (from ancestor to descendant) to elucidate patterns of adaptations (heterochrony) or shifts in multidimensional, shape features (allometry) (e.g., [22, 23]). A new term, sequence heterochrony, has been applied to investigations of the shift in developmental sequences from ancestor to descendants—a way to confer change (evolution) without novel traits (e.g., [24, 25]).
Thirty-three male Trachypithecus cristatus (17 immature, 16 adult) were wild shot in the 1937 Asiatic Primate Expedition (A.P.E.) in North Boreno under the direction of Adolph Schultz and assisted by Sherwood Washburn (cf ). Ten years later Washburn collected 35 male Cercopithecus aethiops (13 immature, 22 adult) in Uganda over a 35-day period. Individuals for each population span all immature age classes, although the sample sizes are small.
This study offers a focused comparison between two Old World monkeys to establish growth patterns in several unilinear body dimensions. Further detailed studies on primate growth are required to ascertain which sequence reflects the ancestral condition of the Cercopithecoidea, and therefore this study precludes a heterochronic analysis (cf. ). Likewise, as multidimensional shape changes are not being investigated, allometric scaling cannot be applied to these data.
This study on dental and skeletal growth of vervet (cercopithecine) and langurs (colobine) monkeys under natural conditions provides a first step in proposing connections between body growth patterns and locomotion. By focusing on postcranial (e.g., long bone, tail, and body mass) as well as cranial (dentition) features, it is possible to connect maturity to behaviors that are essential for survival, especially foraging, traveling, and locomotion and therefore provide a more holistic and integrated view of growth and development. Phylogeny, diet and ecology, as well as locomotion may also influence timing and patterns of growth within a species and more information on growth and development in wild monkeys as well as longitudinal growth data on captive animals will help interpret the contribution of each variable. This approach may also be useful in interpretations of immature fossils, especially in the case of bipedal locomotion and early hominin ancestors.