title: Within arm's reach: Measuring forearm length to assess growth patterns in captive bonobos and chimpanzees.
abstract: Bonobos and chimpanzees are known to differ in various morphological traits, a dichotomy that is sometimes used as an analogy for evolutionary splits during human evolution. The aim of our study was to measure the forearm length of immature and adult bonobos and adult chimpanzees to assess the extent of age-related changes of forearm length in bonobos and sex-dimorphism in bonobos and chimpanzees.
  
  
  
  As a proxy of somatic growth we measured forearm length of captive bonobos and chimpanzees ranging in age from 1 to 55 years. Measures were taken from subjects inserting their arms into a transparent Plexiglas® tube, a novel technique facilitating repeated measures of nonanesthetized apes in captivity.
  
  
  
  Measures from adult females (>12 years) showed that bonobos exceed chimpanzees in terms of forearm length and that sexual dimorphism in forearm length is pronounced in chimpanzees, but not in bonobos. Forearm length increased significantly with chronological age in bonobos. Validation tests revealed that the device generates useful data on morphometric dimensions.
  
  
  
  In most primates, sexual dimorphism in body size is male-biased and the differences in forearm length in chimpanzees follow this trend. Given that males of the two species did not differ in forearm length, the absence/presence of sexual dimorphism of this trait must be due to differences in somatic growth in females. Our novel method offers an alternative to obtain morphometric measures and facilitates longitudinal studies on somatic growth. Am J Phys Anthropol 161:37-43, 2016. © 2016 Wiley Periodicals, Inc.
authors.affiliation: Department of Primatology, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany.
authors.forename: Verena
authors.initials: V
authors.lastname: Behringer
authors.affiliation: Royal Zoological Society of Antwerp, Centre for Research and Conservation, K. Astridplein, Antwerp, Belgium.
authors.forename: Jeroen M G
authors.initials: JM
authors.lastname: Stevens
authors.affiliation: Skeletal Biology Research Centre, Animal Postcranial Evolutionary Lab, School of Anthropology and Conservation, University of Kent, Marlowe Building, Canterbury, Kent, UK.|Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany.
authors.forename: Tracy L
authors.initials: TL
authors.lastname: Kivell
authors.affiliation: Skeletal Biology Research Centre, Animal Postcranial Evolutionary Lab, School of Anthropology and Conservation, University of Kent, Marlowe Building, Canterbury, Kent, UK.
authors.forename: Johanna
authors.initials: J
authors.lastname: Neufuss
authors.affiliation: Department of Primatology, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany.
authors.forename: Christophe
authors.initials: C
authors.lastname: Boesch
authors.affiliation: Department of Primatology, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany.
authors.forename: Gottfried
authors.initials: G
authors.lastname: Hohmann
mesh_terms: D000818:Animals; D005260:Female; D005542:Forearm / Q000033:anatomy & histology* / Q000254:growth & development; D008297:Male; D019974:Pan paniscus / Q000033:anatomy & histology* / Q000254:growth & development*; D002679:Pan troglodytes / Q000033:anatomy & histology* / Q000254:growth & development*; D015203:Reproducibility of Results; D012727:Sex Characteristics
keywords: apes; longitudinal data; morphometric measures; sexual dimorphism; somatic growth