International Journal of Primatology

, Volume 34, Issue 1, pp 115–129

OrangFACS: A Muscle-Based Facial Movement Coding System for Orangutans (Pongo spp.)

  • Cátia C. Caeiro
  • Bridget M. Waller
  • Elke Zimmermann
  • Anne M. Burrows
  • Marina Davila-Ross

DOI: 10.1007/s10764-012-9652-x

Cite this article as:
Caeiro, C.C., Waller, B.M., Zimmermann, E. et al. Int J Primatol (2013) 34: 115. doi:10.1007/s10764-012-9652-x


Comparing homologous expressions between species can shed light on the phylogenetic and functional changes that have taken place during evolution. To assess homology across species we must approach primate facial expressions in an anatomical, systematic, and standardized way. The Facial Action Coding System (FACS), a widely used muscle-based tool for analyzing human facial expressions, has recently been adapted for chimpanzees (Pan troglodytes: ChimpFACS), rhesus macaques (Macaca mulatta: MaqFACS), and gibbons (GibbonFACS). Here, we present OrangFACS, a FACS adapted for orangutans (Pongo spp.). Orangutans are the most arboreal and the least social great ape, so their visual communication has been assumed to be less important than vocal communication and is little studied. We scrutinized the facial anatomy of orangutans and coded videos of spontaneous orangutan behavior to identify independent movements: Action Units (AUs) and Action Descriptors (ADs). We then compared these facial movements with movements of homologous muscles in humans, chimpanzees, macaques, and gibbons. We also noted differences related to sexual dimorphism and developmental stages in orangutan facial morphology. Our results show 17 AUs and 7 ADs in orangutans, indicating an overall facial mobility similar to that found in chimpanzees, macaques, and gibbons but smaller than that found in humans. This facial movement capacity in orangutans may be the result of several, nonmutually exclusive explanations, including the need for facial communication in specialized contexts, phylogenetic inertia, and allometric effects.


Communication Facial expressions Facial morphology FACS Orangutans Primates 

Supplementary material

10764_2012_9652_MOESM1_ESM.mpg (4.6 mb)
Online Resources 1 (mpg fileVideo example of Action Unit 1+2 – inner and outer brow raiser. (MPG 4724 kb)
10764_2012_9652_MOESM2_ESM.mpg (1.2 mb)
Online Resources 2 (mpg fileVideo example of Action Unit 4 - glabella lowerer. (MPG 1184 kb)
10764_2012_9652_MOESM3_ESM.mpg (1.6 mb)
Online Resources 3 (mpg fileVideo example of Action Unit 6 - cheek raiser. (MPG 1636 kb)
10764_2012_9652_MOESM4_ESM.mpg (832 kb)
Online Resources 4 (mpg fileVideo example of Action Unit 9 – nose wrinkler. (MPG 832 kb)
10764_2012_9652_MOESM5_ESM.mpg (3.3 mb)
Online Resources 5 (mpg fileVideo example of Action Unit 10 - upper lip raiser. (MPG 3366 kb)
10764_2012_9652_MOESM6_ESM.mpg (366 kb)
Online Resources 6 (mpg fileVideo example of Action Unit 12 - lip corner puller. (MPG 366 kb)
Online Resources 7 (mpg file

Video example of Action Unit 16 - lower lip depressor. (MPG 2870 kb)

10764_2012_9652_MOESM8_ESM.mpg (24.7 mb)
Online Resources 8 (mpg fileVideo example of Action Unit 17 – chin raiser. (MPG 25282 kb)
10764_2012_9652_MOESM9_ESM.mpg (5 mb)
Online Resources 9 (mpg fileVideo example of Action Unit 18 – lip pucker. (MPG 5092 kb)
10764_2012_9652_MOESM10_ESM.mpg (364 kb)
Online Resources 10 (mpg fileVideo example of Action Unit 22 - lip funneler. (MPG 364 kb)
10764_2012_9652_MOESM11_ESM.mpg (978 kb)
Online Resources 11 (mpg fileVideo example of Action Unit 24 - lip presser. (MPG 978 kb)
10764_2012_9652_MOESM12_ESM.mpg (278 kb)
Online Resources 12 (mpg fileVideo example of Action Unit 28 - lips suck. (MPG 278 kb)

Copyright information

© Springer Science+Business Media New York 2012

Authors and Affiliations

  • Cátia C. Caeiro
    • 1
    • 2
  • Bridget M. Waller
    • 2
  • Elke Zimmermann
    • 3
  • Anne M. Burrows
    • 4
    • 5
  • Marina Davila-Ross
    • 2
  1. 1.Departamento de Biologia AnimalFaculdade de Ciências da Universidade de LisboaLisboaPortugal
  2. 2.Department of PsychologyUniversity of PortsmouthPortsmouthUK
  3. 3.Institute of ZoologyUniversity of Veterinary Medicine HannoverHannoverGermany
  4. 4.Department of Physical TherapyDuquesne UniversityPittsburghUSA
  5. 5.Department of AnthropologyUniversity of PittsburghPittsburghUSA

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