chimpanzee study guide for artists and researchers

chimpanzee facial expression landmarks

Hello and welcome to Face the FACS‘s chimpanzee study compilation! This document is a work-in-progress passion project. There are parts left blank, because I am either still searching for the information or have not gotten around to it yet.

Want to help?

Please email me if you have any information or references to add:

I’m currently looking for more information on – Central and Nigeria-Cameroon chimpanzee subspecies.

what's in the guide?

Table of Contents

intro to chimpanzee subspecies

WHY ARTISTS SHOULD CARE: If you are creating a chimpanzee character using multiple references, knowing which subspecies you are working with can help you achieve consistency and realism. (Of course, there is no problem with deviating from realism and intentionally taking your own creative license!)

WHY RESEARCHERS SHOULD CARE: Subspecies of chimpanzees display unique behaviors and physical characteristics; classifying this sub-information may yield clearer, better organized data regarding behavior and genetics.

What is a subspecies? (And why it can be difficult to wrap your head around.)

“Distinguishing between a species and a subspecies can be difficult: most people are aware of the definition of a species, but when it comes to defining a subspecies, it can be a bit hazy and subjective.
Technically, a species is a population or groups of populations that can potentially interbreed freely within and among themselves. This is a naturally-defined concept, something which exists by itself.  Subspecies, on the other hand, are subgroups within a species that have different traits and are defined by scientists. Let’s examine this concept more closely.
. . .
A widely accepted definition for subspecies is that of Mayr and Ashlock (1991:43): ‘A subspecies is an aggregate of phenotypically similar populations of a species inhabiting a geographic subdivision of the range of that species and differing taxonomically from other populations of that species.’
. . .
As you can imagine, a subspecies is subordinate to a species. This means that while you can have a species of its own within its own genus, you can’t have a subspecies of its own. You can only define a subspecies in relation to a species — and you need at least two subspecies for the idea to make sense (else that single ‘subspecies’ would actually be the whole species). This is where things start to get even murkier.”

Read the rest of this article here.


Bonobos are not chimpanzees. They are a different species altogether.

“The bonobo (/bəˈnoʊboʊ, ˈbɒnəboʊ/; Pan paniscus), also historically called the pygmy chimpanzee and less often, the dwarf or gracile chimpanzee,[3] is an endangered great ape and one of the two species making up the genus Pan; the other being the common chimpanzee (Pan troglodytes).[4] Although bonobos are not a subspecies of chimpanzee (Pan troglodytes), but rather a distinct species in their own right, both species are sometimes referred to collectively using the generalized term chimpanzees, or chimps. Taxonomically, the members of the chimpanzee/bonobo subtribe Panina (comprised entirely by the genus Pan) are collectively termed panins.[5][6]

– Wikipedia

chimpanzee subspecies types

 Four subspecies of chimpanzees have been recognized, with the possibility of a fifth.

  • the 4:
    • Central
    • Eastern
    • Western
    • Nigeria-Cameroon

  • the possible 5th:
    • Southeastern

The content in the tabs below is in large thanks to the compiled research and information provided by the New England Primate Conservancy. I highly recommend checking out their site for more in-depth study.

chimpanzee subspecies chart

chimpanzee facial landmarks

chimpanzee facial landmark diagram
chimpanzee facial landmark diagram
chimpanzee facial landmarks diagram
groovy chimpanzee facial landmark diagram.
Click image to check out merchandise for this design 🙂

comparative primate facial landmarks

orangutan facial landmark diagram
orangutan facial landmark diagram
human landmark labels
human facial landmark diagram

chimpanzee facial actions chart

chart 1


✓  =  AU identified
  =  AU not identified, but muscle present
a  =  AU not identified and muscle absent


AU name


human FACS

chimp FACS



inner brow raiser

frontalis (medial)



outer brow raiser

frontalis (lateral)



inner brow raiser + brow raiser

frontalis (full)

full brow raise is not a single AU. It is the combination of AUs 1+2 (inner brow raiser + outer brow raiser). Thus far, separation of AUs 1 and 2 has only been recorded in humans.


brow lowerer

procerus, depressor and corrugator supercilii

procerus present and functions to pull down brows at glabella. ds and c unclear. brows are seen to lower (p or ds) but not knit (c)


upper lid raiser

orbicularis oculi

muscle present and au6 identified


cheek raiser

orbicularis oculi

muscle present and au6 identified


 lid tightener

orbicularis oculi

difficult to identify this subtle action due to morphology and colouration of eye area and eye movements
(scroll for OZEL NOTE AU7)


lips toward each other

orbicularis oris

not readily identifiable due to less eversion and contrast of lip margins


nose wrinkler

lev. labii sup. alaeque nasi

muscle present and AU9 clearly identifiable, action may

also recruit procerus


upper lip raiser

levator labii superioris

muscle present and AU10 clearly identifiable, capable of independent action


nasolabial furrow deepener

zygomaticus minor

possible incipient muscle, absence of cheek fat would make action difficult to detect if present


lip corner puller

zygomaticus major

muscle present and AU12 clearly identifiable, capable of independent action


sharp lip puller

levator anguli oris

muscle poorly developed, lack of cheek fat would make action difficult to detect if present




muscle present but AU14 not clearly identified, perhaps due to lack of cheek fat


lip corner depressor

depressor anguli oris

muscle present and capable of independent action but AU15 not yet seen independently


lower lip depressor

depressor labii inferioris

muscle present and AU16 clearly identifiable as independent action


chin raiser


muscle small but distinct and independent action seen. absence of chin boss means cues to AU17 differ in the chimpanzee.


lip pucker

incisivii labii, orbicularis oris


muscles not clearly identified. puckering of lips not clearly identified in chimpanzees


 lip stretch


risorius not present. similar action seen likely to be due to platysma action (AU 21)  (scroll for OZEL NOTE AU20)


neck tightener

platysma myoides

muscle present but AU21 may be more difficult to

identify due to hair covering neck and jaw


lip funneler

orbicularis oris

muscle present and AU22 clearly identifiable,
chimpanzees may have more independent movement in upper and lower lips than humans


lip tightener

orbicularis oris

not readily identifiable due to less eversion and contrast of lip margins


 lip presser

orbicularis oris

muscle present and AU24 clearly identifiable


lips parted

depressor labii inferioris/levator labii superioris/orbicularis oris



jaw drop

nonmimetic muscle



mouth stretch

nonmimetic muscle



lips suck

orbicularis oris

muscle present andAU28 identifiable


nostril compressor

depressor septi nasi, nasalis

nasalis muscle present but not differentiated. AU38 and AU39 not seen in chimpanzees


eye closure

orbicularis oculi




orbicularis oculi


source for chart 1:
Caeiro, C.C., Waller, B.M., Zimmermann, E. et al. OrangFACS: A Muscle-Based Facial Movement Coding System for Orangutans (Pongo spp.). Int J Primatol34, 115–129 (2013).
**Yes, this study was on orangutans, but it hosted a cross-species comparison chart with information on chimpFACS.

chart 2

chimpFACS - AUs for chimpanzees by S-J Vick , B. M. Waller, L. A. Parr, M. Smith Pasqualini & K. A. Bard (2007) A Cross Species Comparison of Facial Morphology and Movement in Humans and Chimpanzees Using FACS . Journal of Nonverbal Behavio r, 31: 1-20

source for chart 2:  Vick, Sarah-Jane & Waller, Bridget & Parr, Lisa & Pasqualini, Marcia & Bard, Kim. (2021). S-J Vick , B. M. Waller, L. A. Parr, M. Smith Pasqualini & K. A. Bard (2007) A Cross Species Comparison of Facial Morphology and Movement in Humans and Chimpanzees Using FACS . Journal of Nonverbal Behavior, 31: 1-20.


OZEL NOTE AU7 – lid tightener: Though it has not been documented in official chimpFACS or chimpanzee studies, I’ve personally observed and documented the lid tightener action in chimpanzees. See action here.)

OZEL NOTE AU20 – lip stretcher: As indicated by chart 2 and the research of Rui Diogo, the risorius muscle has been found to be present in some chimpanzees. These conflicting findings parallel the risorius muscle’s inconsistent presence in humans. It is one of the most variable facial muscles and has been reported absent in human cadavers at drastically different rates, depending on the study.

related posts