Introduction to Primate Behavior
Date: ____________________ Start time of observation______________ End time_______________
1. Primate Name and Taxonomic classification—If more than one primate species visible, list both of them.
Primate Species #1: Common Name_________________________ Scientific Name______________________
Primate Species #2 (if applicable): Common Name___________________ Scientific name__________________
Taxonomic classification (Use Fig. 5.11 in textbook to help determine)
Sp. #1 Suborder_______________________Infraorder_________________Superfamily__________________
Sp. #2 Suborder______________________ Infraorder__________________Superfamily__________________
2. Environment. Describe the portion of the exhibit that is visible in the cam. For example, structures, trees,
ropes, open areas, rocks, etc?
3. Number of individuals (of each primate species) that were visible during your observation___________
Of those, were any juveniles present? ____________
Were you able to distinguish males and females? Describe how you were able to do so.
4. Provide a brief physical description of the primate species (both species if more than one visible). Include
information about body size, coloration, tail (or lack thereof), hands and feet, and any other distinguishing
characteristics. Note—this should come from your own personal observation; do NOT copy them from online
sources.
5. Mode of locomotion. List the types of locomotion that you observed. Categorize them according to the
descriptions in the Locomotor Adaptations section of Chap. 5.
1
6. Timed observation. Observe the primate species for 15 minutes. Use the space below to write down the
behaviors that you observe (attach extra sheets if necessary). You can use the sample ethograms to help
categorize the behaviors, but it is not required. However, your descriptions should be as detailed as possible,
and should remain unbiased. Do not anthropomorphize the primates (i.e. infer human intentions or
motivations from their actions).
2
7. How would you generally characterize the behavior of the primates you observed? Were there any
behaviors you found surprising?
8. How do you think the primates’ behavior would be different if you observed them at a different time of
day?
9. List one or two questions about the behavior of the primates that came to mind during or after your
observation.
3
.
.
EXPLORATIONS: AN OPEN INVITATION TO BIOLOGICAL
ANTHROPOLOGY
Editors: Beth Shook, Katie Nelson, Kelsie Aguilera and Lara Braff
American Anthropological Association
Arlington, VA
2019
Explorations: An Open Invitation to Biological Anthropology is licensed under a Creative Commons Attribution-NonCommercial 4.0
International License, except where otherwise noted.
ISBN – 978-1-931303-63-7
www.explorations.americananthro.org
5. Meet the Living Primates
Stephanie Etting, Ph.D., Sacramento City College
Learning Objectives
• Learn how primates are different from other mammals
• Understand how studying non-human primates is important in anthropology
• Identify different types of traits that we use to evaluate primate taxa
• Describe the major primate taxa using their key characteristics
• Understand your place in nature by learning your taxonomic classification
One of the best parts of teaching anthropology for me is getting to spend time at zoos watching primates. What I also
find interesting is watching people watch primates. I have very often heard a parent and child walk up to a chimpanzee
enclosure and exclaim “Look at the monkeys!” The parent and child often don’t know that a chimpanzee is not a monkey,
nor are they likely to know that chimpanzees share more than 98% of their DNA with us. What strikes me as significant
is that, although most people do not know the difference between a monkey, an ape, and a lemur, they nonetheless
recognize something in the animals as being similar to themselves. What people probably mean when they say “monkey”
is actually “primate,” a term that refers to all organisms classified within the Order Primates and also the subject of
this chapter. You may be wondering why a field dedicated to the study of humans would include the study of nonhuman animals.Because humans are primates, we share a wide range of behavioral and morphological traits with the
other species who also fall into this group. In Chapter 2, you learned about the nature of Linnaean classification, the
system we use for organizing life-forms. Here, we focus on the organization and diversity within the Order Primates.
The term Order Primates dates back to 1758 when, in his tenth edition of Systema Naturae, Carolus Linnaeus put humans,
“simia” (monkeys and apes), “lemurs” (lemurs and colugos), and some bats into one of eight groups of mammals. Linnaeus
was wrong in including colugos (now in Order Dermoptera) and bats (now in Order Chiroptera), but the grouping of
humans with the then-known non-human primates was significant in that by doing so Linnaeus formally recognized the
affinities between humans and these non-human taxa.In fact, acknowledgment of similarities between humans and nonhumans dates back far earlier than Linnaeus (see the Special Topic box), yet it was only more recently that we attained
the genetic data to back up our intuition.
WHAT IS A PRIMATE?
Primates are one of at least twenty Orders belonging to the Class Mammalia. All members of this class share certain
characteristics, including, among other things, having fur or hair, producing milk from mammary glands, and being
warm-blooded. There are three types of mammals: monotremes, marsupials, and placental mammals.Monotremes are
the most primitive of the mammals, meaning they have retained more ancient traits than marsupials or placental
mammals, and so, monotremes are characterized by some unusual traits. Monotremes, which include echidnas and
duck-billed platypuses, lay eggs rather than give birth to live young. Once the young hatch, they lap up milk produced
1 | Meet the Living Primates
from glands on the mother’s abdomen rather than latch onto nipples. Marsupial mammals are those, like kangaroos and
koalas, who internally gestate for a very short period of time and give birth to relatively undeveloped young. Joeys, as
these newborns are called, complete their growth externally in their mother’s pouch where they suckle. Lastly, there
are placental mammals. Placental mammals internally gestate for a longer period of time and give birth to fairly welldeveloped young who are then nursed. Primates, including ourselves, belong to this last group. Among the diversity
of mammalian orders alive today, primates are very likely one of the oldest. One genetic estimate puts the origin of
primates at approximately 91 million years ago (mya), predating the extinction of the dinosaurs (Bininda-Emonds et al.
2007). Today, the Order Primates is a diverse group of animals that includes lemurs and lorises, tarsiers, monkeys of
the New and Old Worlds, apes, and humans, all of which are united in sharing a suite of anatomical, behavioral, and
life history characteristics. Before delving into the specific traits that distinguish primates from other animals, it is
important to first discuss the different types of traits that we will encounter.
Types of Traits
When evaluating relationships between different groups of primates, we use key traits that allow us to determine which
species are most closely related to one another. Traits can be either primitive or derived. Primitive traits are those that a
taxon has because it has inherited the trait from a distant ancestor. For example, all primates have body hair because we
are mammals and all mammals share an ancestor hundreds of millions of years ago that had body hair.This trait has been
passed down to all mammals from this shared ancestor, so all mammals alive today have body hair. Derived traits are
those that have been more recently altered. This type of trait is most useful when we are trying to distinguish one group
from another because derived traits tell us which taxa are more closely related to each other. For example, humans walk
on two legs.The many adaptations that humans possess which allow us to move in this way evolved after humans split
from the Genus Pan. This means that when we find fossil taxa that share derived traits for walking on two legs, we can
conclude that they are likely more closely related to humans than to chimpanzees and bonobos.
There are a couple of other important points about primitive and derived traits that will become apparent as we discuss
primate diversity. First, the terms primitive and derived are relative terms.This means that depending on what taxa are
being compared, a trait can be either one. For example, in the previous section, body hair was used as an example
for a primitive trait among primates. All mammals have body hair because we share a distant ancestor who had this
trait. The presence of body hair therefore doesn’t allow you to distinguish whether monkeys are more closely related
to apes or lemurs because they all share this trait.However, if we are comparing mammals to birds and fish, then body
hair becomes a derived trait of mammals. It evolved after mammals diverged from birds and fish, and it tells us that
all mammals are more closely related to each other than they are to birds or fish.The second important point is that
very often when one lineage splits into two, one taxon will stay more similar to the last common ancestor in retaining
more primitive traits, whereas the other lineage will usually become more different from the last common ancestor
by developing more derived traits. This will become very apparent when we discuss the two suborders of primates,
Strepsirrhini and Haplorrhini.When these two lineages diverged, strepsirrhines retained more primitive traits (those
present in the ancestor of primates) and haplorrhines developed more derived traits (became more different from the
ancestor of primates).
There are two other types of traits that will be relevant to our discussions here: generalized and specialized traits.
Generalized traits are those characteristics that are useful for a wide range of things. Having opposable thumbs that
go in a different direction than the rest of your fingers is a very useful, generalized trait. You can hold a pen, grab a
branch, peel a banana, or text your friends all thanks to your opposable thumbs. Specialized traits are those that have
been modified for a specific purpose. These traits may not have a wide range of uses, but they will be very efficient at
their job.Hooves in horses are a good example of a specialized trait. Horses cannot grasp objects with their hooves, but
hooves allow horses to run very quickly on the ground on all fours. You can think of generalized traits as a Swiss Army
Meet the Living Primates | 2
knife, useful for a wide range of tasks but not particularly good at any of one them. That is, if you’re in a bind, then a
Swiss Army knife can be very useful to cut a rope or fix a loose screw, but if you were going to build furniture or fix a
kitchen sink, then you’d want specialized tools for the job. As we will see, most primate traits tend to be generalized.
Primate Suite of Traits
The Order Primates is distinguished from other groups of mammals in having a suite of characteristics.This means that
there is no individual trait that you can use to instantly identify an animal as a primate; instead, you have to look for
animals that possess a collection of traits. What this also means is that each individual trait we discuss may be found in
non-primates, but if you see an animal that has most or all of these traits, there is a good chance it is a primate.
One area in which the Order Primates is most distinguished from other organisms regards traits related to our senses,
especially our vision.Compared to other animals, primates rely on vision as a primary sense. Our heavy reliance on
vision is reflected in many areas of our anatomy and behavior. All primates have eyes that face forward with convergent
(overlapping) visual fields. This means that if you cover one eye with your hand, you can still see most of the room
with your other one.This also means that we cannot see on the sides or behind us as well as some other animals can.
In order to protect the sides of the eyes from the muscles we use for chewing, all primates have at least a postorbital
bar, a bony ring around the outside of the eye (Figure 5.1). Some primate taxa have more convergent eyes than others,
so those primates need extra protection for their eyes. As a result, animals with greater orbital convergence will have
a postorbital plate or postorbital closure in addition to the bar (Figure 5.1).The postorbital bar is a derived trait of
primates, appearing in our earliest ancestors, which you will read more about in Chapter 8.
Figure 5.1 All primates have some form of bony protection around their eyes. Some have a postorbital bar only (right),
but many have full postorbital closure, also called a postorbital plate, that completely protects the back of the eye socket
(left).
3 | Meet the Living Primates
Another important and distinctive trait of our Order is that many primates have trichromatic color vision, the ability to
distinguish reds and yellows in addition to blues and greens. Interestingly, birds, fish, and reptiles are tetrachromatic
(they can see reds, yellows, blues, greens, and even ultraviolet), but most mammals, including some primates, are only
dichromatic (they see only in blues and greens). It is thought that the nocturnal ancestors of mammals benefited
from seeing better at night rather than in color, and so dichromacy is thought to be the primitive condition for
mammals.There is a lot of interest in why some primates would re-evolve trichromacy. Some theories revolve around
food, arguing that the ability to see reds/yellows may allow primates who can see these colors to better detect young
leaves (Dominy and Lucas 2001) or ripe fruits (Regan et al. 2001) against an otherwise green, leafy background. Color
vision has also been suggested to be useful for detecting predators, especially big cats (Pessoa et al. 2014). Another
theory emphasizes the usefulness of trichromacy in social and mate-choice contexts (Changizi et al. 2006).Thus far
there is no consensus, as trichromatic color vision can be useful in many circumstances. There is also the added
complication that sometimes dichromacy is more advantageous, as animals who are dichromatic are usually better at
seeing through camouflage to find hidden items like foods or predators (Morgan et al. 1992). Therefore, investigating the
evolution of color vision continues to be an interesting and ongoing area of research.
Primates also differ from other mammals in the size and complexity of our brains. All primates have brains that are
larger than you would expect when compared to other mammals of the same size. On average, primates have brains
that are twice as big for their body size as you would expect when compared to other mammals.Not unexpectedly, the
visual centers of the brain are larger in primates and the wiring is different from that in other animals, reflecting our
reliance on this sense. The neocortex, which is used for higher functions like consciousness and language in humans, as
well as sensory perception and spatial awareness, is also larger in primates relative to other animals. In non-primates
this part of the brain is often smooth, but in primates it is made up of many folds which increase the surface area. It
has been proposed that the more complex neocortex of primates is related to diet, with fruit-eating primates having
larger relative brain sizes than leaf-eating primates, due to the more challenging cognitive demands required to find and
process fruits (Clutton‐Brock and Harvey 1980). An alternative hypothesis argues that larger brain size is necessary for
navigating the complexities of primate social life, with larger brains occurring in species who live in larger, more complex
groups relative to those living in pairs or solitarily (Dunbar 1998). There seems to be support for both hypotheses, as
large brains are a benefit under both sets of selective pressures.
The primate visual system uses a lot of energy, so primates have compensated by cutting back on other sensory systems,
particularly our sense of smell. Compared to other mammals, primates have relatively reduced snouts. This is another
derived trait of primates that appears even in our earliest ancestors. As we will discuss, there is variation across primate
taxa in how much snouts are reduced.Those with a better sense of smell usually have poorer vision than those with
a relatively dull sense of smell. The reason for this is that all organisms have a limited amount of energy to spend on
running our bodies, so we make evolutionary trade-offs, because energy spent on one trait must mean cutting back
on energy spent on another.With regards to primate senses, primates with better vision (more convergent eyes, better
visual acuity, etc.) are spending more energy on vision and thus will have poorer smell (and a shorter snout). Primates
who spend less energy on vision (less convergent eyes, poorer visual acuity, etc.) will have a better sense of smell (and a
longer snout).
Meet the Living Primates | 4
Primates also differ from other animals in our hands and feet.The Order
Primates is a largely arboreal taxonomic group, which means that most
primates spend a significant amount of their time in trees. As a result, the
hands and feet of primates have evolved to move around in a threedimensional
environment. Primates have the generalized trait of
pentadactyly— possessing five digits (fingers and toes) on each limb. Many
non-primates, like dogs and horses, have fewer digits because they are
specialized
for
high-speed,
terrestrial
(on
the
ground)
running.Pentadactyly is also a primitive trait, one that dates back to the
earliest four-footed animals. Primates today have opposable thumbs and,
except humans, opposable big toes (Figure 5.2). Opposable thumbs/toes
are a derived trait that appeared in the earliest primates about 55 million
years ago. Having thumbs and big toes that go in a different direction from
the rest of the fingers and toes allow primates to be excellent climbers in
trees but also allow us to manipulate objects. Our ability to manipulate
objects is further enhanced by the flattened nails on the backs of our
fingers and toes that we possess in the place of the claws and hooves that
many other mammals have. On the other side of our digits, we have
sensitive tactile pads that allow us to have a fine sense of touch. Primates
use this fine sense of touch for handling food and, in many species,
grooming themselves and others. In primates, grooming is an important
social currency, through which individuals forge and maintain social bonds.
You will learn more about grooming in Chapter 6.
Animals with large brains usually have extended life history patterns, and
Figure 5.2 These drawings of the hands and feet
of different primates clearly show the opposable
thumbs and big toes, pentadactyly, flattened
nails, and tactile pads that are characteristic of
our Order.
primates are no exception. Life history refers to the pace at which an organism grows, reproduces, ages, and so forth.
Some animals grow very quickly and reproduce many offspring in a short time frame, but do not live very long. Other
animals grow slowly, reproduce few offspring, reproduce infrequently, and live a long time. Primates are all in the “slow
lane” of life history patterns. Compared to animals of similar body size, primates grow and develop more slowly, have
fewer offspring per pregnancy, reproduce less often, and live longer. Primates also invest heavily in each offspring, a
subject you will learn more about in the next chapter. With a few exceptions, most primates only have one offspring at
a time. There is a group of small-bodied monkeys in the New World who regularly give birth to twins, and some lemurs
are able to give birth to multiple offspring at a time, but these primates are the exception rather than the rule. Primates
also reproduce relatively infrequently. The fastest-reproducing primates will produce offspring about every six months,
while the slowest, the orangutan, reproduces only once every seven to nine years. This very slow reproductive rate
makes the orangutan the slowest-reproducing animal on the planet!Primates are also characterized by having long
lifespans. The group that includes humans and large-bodied apes has the most extended life history patterns among all
primates, with some large-bodied apes estimated to live up to 58 years in the wild (Robson et al. 2006).
Lastly, primates share some behavioral and ecological traits. Primates are very social animals, and all primates, even
those that search for food alone, have strong social networks with others of their species. Indeed, social networks in
primates have been shown to be crucial in times of stress and to enhance reproductive success (Silk et al. 2009). Unlike
many animals, primates do not migrate. This means that primates stay in a relatively stable area for their whole life, often
interacting with the same individuals for their long lives. The long-term relationships that primates form with others
of their species lead to complex and fascinating social behaviors, which you will read about in Chapter 6.Finally, nonhuman primates show a clear preference for tropical regions of the world. Most primates are found between the Tropic
of Cancer and the Tropic of Capricorn, with only a few taxa living outside of these regions. You can see a summary of
the primate suite of traits in Figure 5.3.
5 | Meet the Living Primates
Primate suite of traits
Convergent eyes
Post-orbital bar
Many have trichromatic color vision
Short snouts
Opposable thumbs and big toes
Pentadactyly
Flattened nails
Tactile pads
Highly arboreal
Large brains
Extended life histories
Live in the tropics
Figure 5.3 Primate Traits at a Glance: This table summarizes the suite of traits that differentiate primates from other
mammals
KEY TRAITS USED TO DISTINGUISH BETWEEN PRIMATE TAXA
When trying to place primate species into specific taxonomic groups, we use a variety of dental characteristics,
locomotor adaptations, and behavioral adaptations. Differences in these characteristics across groups reflect
constraints of evolutionary history as well as variation in adaptations.
Dental Characteristics
Teeth may not seem like the most exciting topic with which to start, but we can learn a tremendous amount of
information about an organism from its teeth. First, teeth are vital to survival. Wild animals do not have the benefit of
knives and forks, and so rely primarily on their teeth to process their food. Because of this, teeth of any species have
evolved to reflect what that organism eats and so tell us directly about their diet. Second, variation in tooth size, shape,
and number tells us a lot about an organism’s evolutionary history. Some taxa have more teeth than others or different
forms of teeth than others. Furthermore, differences in teeth between males and females can tell us about competition
over mates (see Chapter 6). Lastly, teeth preserve really well in the fossil record. Enamel is hard, and there is little meat
on jaws so carnivores and scavengers often leave them behind. Because of this, very often we find a lot of fossil jaws and
teeth, and so we need to be able to learn as much as we can from those pieces.
Meet the Living Primates | 6
If you’ve ever seen the jaws of a shark, dinosaur, or
crocodile, you were probably struck by how sharp their
teeth were and by the sheer number of teeth they had.
What you probably didn’t think about was that they also
only have one type of tooth, referred to as homodont. In
fact, one of the ways that mammals differ from other
organisms is that we have multiple types of teeth
(heterodont) that we use in different ways. We have
incisors, which we use for slicing; we have premolars and
molars, which we use for grinding up our food; and we
have canines, which most primates (not humans) use as
weapons against predators and each other. The sizes of
canines vary across species and can often be sexually
dimorphic, with male canines usually being larger than
those of females. Non-human primates often hone, or
sharpen, their canines by gnashing the teeth together to
sharpen the sides. The upper canine sharpens on the first
Figure 5.4 This open-mouthed Hamadryas baboon clearly
demonstrates the diastema between his upper canine and front
teeth. This space is taken up by his lower canine when he closes his
mouth.
lower premolar and the lower canine sharpens on the
front of the upper canine. As canines get larger, they require a space to fit in order for the jaws to close. This space
between the teeth is called a diastema (Figure 5.4).
As discussed before, primate taxa can vary in the numbers and forms of teeth they have.
We determine the number of each type of tooth an organism has by its dental formula.
The dental formula tells you how many incisors, canines, premolars, and molars are in
each quadrant of the mouth (half of the top or bottom). For example, Figure 5.5 shows
half of the lower teeth of a human. You can see that in half of the mandible, there are two
incisors, one canine, two premolars, and three molars. This dental formula is written as
2:1:2:3. (The first number represents the number of incisors, followed by the number of
canines, premolars, and molars). Some early fossil primates had a dental formula of
2:1:4:3, but among the living primates, none have more teeth than can be found in a 2:1:3:3
dental formula. Many have fewer teeth, however, and some have a different dental
formula on the top than they do on the bottom.
To determine the dental formula, you need to be able to identify the different types of
teeth. You can recognize incisors because they often look like spatulas with a flat, bladelike surface. Premolars and molars can be differentiated by the number of cusps that they
have. Cusps are the little bumps (which in some species can be quite sharp) that you can
feel with your tongue on the surface of your back teeth. Premolars are smaller than
Figure 5.5 This drawing shows
half of the human mandible.
With the four types of teeth
labeled, you can determine that
the dental formula is 2:1:2:3.
molars and, in primates, often have one or two cusps on them. Molars are bigger, with a
larger chewing surface, and so have more cusps. Depending on the species of primate
and whether you’re looking at upper or lower teeth, molars can have between three and
five cusps. There is even one extinct primate (Oreopithecus) who had six cusps on its
molars. Molar cusps can also vary between taxa in how they are arranged, as you will
learn more about later in this chapter. Canines are often easy to distinguish because they are usually much longer and
more conical than the other teeth. This is not always the case, however, as you will see when you read about the teeth
of lemurs and lorises.
Teeth also tell us directly about an organism’s diet. Primates are known to eat a wide range of plant parts, insects,
gums, and, rarely, meat. While all primates eat a variety of foods, what differs among primates are the proportions
7 | Meet the Living Primates
of each of these food items in the diet. That is, two primates living in the same forest may be eating the same foods
but in vastly different proportions, and so we would categorize them as different dietary types. The most common
dietary types among primates are those whose diets consist primarily of fruit (frugivores), those who eat mostly insects
(insectivores), and those who eat primarily leaves (folivores). Fewer primates are gummivores, who specialize in eating
gums and saps, so we will not discuss the adaptations for this dietary type in great detail.
Frugivores
Plants want animals to eat their fruits because, in doing so, animals eat the seeds of the fruit and then disperse them far
away from the parent plant. Because plants want animals to eat the fruit, plants often “advertise” fruits by making them
colorful and easy to spot, full of easy-to-digest sugars that make them taste good—and, often, easy to chew and digest
(not being too fibrous or tough). For these reasons, frugivores often do not need a lot of specialized traits to consume a
diet rich in fruits (Figure 5.6a). Their molars usually have a broad chewing surface with low, rounded cusps (referred to
as bunodont molars). Frugivores also often have large incisors for slicing through the outer coatings on fruit. Primates
that eat fruit tend to have stomachs, colons, and small intestines that are intermediate in terms of size and complexity
between insectivores and folivores (Chivers and Hladik 1980). They are also usually of intermediate body size between
the other two dietary types.Because fruit does not contain protein, frugivores must supplement their diet with protein
from insects and/or leaves. Some frugivorous primates get protein by eating seeds and so have evolved to have thicker
enamel on their teeth to protect them from excessive wear.
Large incisors
Bunodont molars
Intermediate complexity of digestive tract
Figure 5.6a Frugivores are characterized by large incisors, bunodont molars, and digestive tracts that are intermediate
in complexity between the other two dietary types.
Insectivores
Insects can be difficult to find and catch but are not typically difficult to chew. As a result, insectivorous primates usually
have small molars with pointed cusps that allow them to puncture the exoskeleton of the insects (Figure 5.6b). Once the
outer shells of the insects are punctured, insects are not difficult to digest, so insectivores have simple stomachs and
colons and a long small intestine. Nutritionally, insects provide a lot of protein and fat but are not plentiful enough in
the environment to support large-bodied animals, so insectivores are usually the smallest of the primates.
Meet the Living Primates | 8
Sharp, pointed molars
Simple digestive tract
Figure 5.6b Insectivores need sharp, pointed molar cusps in order to break through the exoskeletons of insects. Insects
are easy to digest, so these primates have simple digestive tracts.
Folivores
Unlike with fruits, plants do not want animals to eat their leaves. Leaves are the way plants get their energy from
the sun, therefore, plants evolved to make their leaves very difficult for animals to eat. Leaves often have toxins in
them, taste bitter, are very fibrous and difficult to chew, and are made of large cellulose molecules that are difficult
to break down into usable sugars. Because of these defenses, animals who eat leaves need a lot of specialized traits
(Figure 5.6c). Folivorous primates have broad molars with high, sharp cusps connected by shearing crests. These molar
traits allow folivores to physically break down fibrous leaves when chewing. Folivores then have to chemically break
down cellulose molecules into usable energy, so these animals need specialized digestive systems. Some folivores have
complex stomachs with multiple compartments, but all leaf eaters have large, long intestines and special gut bacteria
that can break up cellulose. Folivores are usually the largest bodied of all primates, and they spend a large portion of
their day digesting their food, so they are often less active than frugivores or insectivores.
Smaller
incisors
High, sharp
molar cusps with
shearing crests
Complex
digestive tract
Figure 5.6c In order to derive energy from leaves, folivores have smaller incisors, high, sharp molar cusps connected by
shearing crests and complex digestive tracts filled with specialized bacteria.
Behavioral Adaptations
Chapter 6 is entirely dedicated to primate behavior, so only broad differences related to taxonomic classification will
be discussed here. These differences include variations in activity patterns, social grouping, and habitat use. Primate
9 | Meet the Living Primates
groups often differ in activity patterns—that is, whether they are active during the day (diurnal), at night (nocturnal), or
through the 24-hour period (cathemeral). We also see variations among primate groups in social groupings: some taxa
are primarily solitary, others live in pairs, and still others live in groups of varying sizes and compositions. Lastly, some
taxa are primarily arboreal while others are more terrestrial.
Locomotor Adaptations
Figure 5.7 An example of a vertical clinger and leaper. Note the longer legs than arms, long
lower back and long fingers and toes. This vertical clinger and leaper doesn’t have a tail, but
most have long tails as well.
Finally, primate groups vary in their adaptations for different forms of locomotion, or how they move around. Living
primates are known to move by vertical clinging and leaping, quadrupedalism, brachiation, and bipedalism. Vertical
clinging and leaping is when an animal grasps a vertical branch with its body upright, pushes off with long hind legs and
then lands on another vertical support branch (Figure 5.7). Animals who move in this way usually have longer legs than
arms, long fingers and toes, and smaller bodies. Vertical clinger leapers also tend to have elongated ankle bones, which
serve as a lever to help them push off with their legs and leap to another branch.
Figure 5.8 Here are examples of a typical quadrupedal primate. Note that the arms and legs are about the same length
and the back is long and flexible. This is a terrestrial quadruped so the arms and legs are relatively long and the tail is
shorter.
Quadrupedalism is the most common form of locomotion among primates (Figure 5.8). The term quadrupedal means
to walk on all fours. Animals that move in this way usually have legs and arms that are about the same length and
typically have a tail for balance. Arboreal quadrupeds usually have shorter arms and legs and longer tails, while terrestrial
Meet the Living Primates | 10
quadrupeds have longer arms and legs and, often, shorter tails. These differences relate to the lower center of gravity
needed by arboreal quadrupeds for balance in trees and the longer tail required for better balance when moving along
the tops of branches. Terrestrial quadrupeds have longer limbs to help them cover more distance more efficiently. You
will learn more specific anatomical features of quadrupedalism later in the chapter.
Figure 5.9 These are examples of a typical brachiator. Note the longer arms than legs, short back, and lack of a tail. You
will read about more details of their anatomy later in the chapter.
The third form of locomotion seen in primates is brachiation,
the way of moving you used if you played on “monkey bars” as
a child. Brachiation involves swinging below branches by the
hands (Figure 5.9). To be an efficient brachiator, a primate
needs to have longer arms than legs, flexible shoulders and
wrists, a short lower back, and no tail. You will learn more
about the specifics of these traits when you learn about apes
later in this chapter. Some primates move via semibrachiation. These taxa also swing below branches but do not
have all of the same specializations as brachiators. They have
flexible shoulders, but their arms and legs are about the same
length, useful because they are quadrupedal when on the
ground. Semi-brachiators also use long prehensile tails as a
third limb when swinging (Figure 5.10). The underside of the
Figure 5.10 Spider monkeys, like the one shown here, are
considered semi-brachiators who can swing below branches
but use their tails as a third limb. On the ground they move via
quadrupedal locomotion.
tail has a tactile pad, resembling your fingerprints, for better
grip.
Lastly, humans move around on two feet, called bipedalism. Some primates will occasionally travel on two feet but do
so awkwardly and never for long distances. Among mammals, only humans have evolved to walk with a striding gait on
two legs as a primary form of locomotion. To move bipedally, humans need many specialized adaptations that will be
discussed in detail in later chapters.
11 | Meet the Living Primates
PRIMATE DIVERSITY
As we begin exploring the different taxa of primates, it is important to keep in mind the hierarchical nature of taxonomic
classification (discussed in Chapter 2) and how this relates to the key characteristics that will be covered. Figure 5.11
summarizes the major taxonomic groups of primates. If you locate humans on the chart, you can trace our classification
and see all of the categories getting more and more inclusive as you work your way up to the Order Primates. What this
means is that humans will have the key traits of each of those groups. It is a good idea to refer to the figure to orient
yourself as we discuss each taxon.
Figure 5.11 This taxonomy chart shows the major groups of primate taxa. Be sure to refer back to this chart as you read through the
primate groups so that you can see how each group is related to one another.
Ways of Organizing Taxa
Our goal in taxonomic classification is to place taxa into categories that reflect their clade relationships. A clade
is a grouping of organisms that reflect a branch of the evolutionary tree, a grouping based on relatedness. Clade
relationships are determined using derived traits shared by groups of taxa as well as genetic similarities. An example
of a clade would be a grouping that includes humans, chimpanzees, bonobos, and gorillas. These taxa are in what is
referred to as the African clade of hominoids. The African clade grouping reflects the fact that humans, chimpanzees,
bonobos, and gorillas all share a more recent ancestor with each other than any of them do with other species—that
is, we are on the same branch of the evolutionary tree.We know members of the African clade are most closely related
based on derived morphological traits as well as genetic similarities. In this grouping, we exclude the orangutan, which
is considered a member of the Asian clade of hominoids.
Meet the Living Primates | 12
Figure 5.12 Grades vs. Clades: Grouping orangutans, gorillas, chimpanzees and bonobos but excluding humans is a grade
classification based on overall similarity in appearance and lifestyle among the apes. We are most interested in groupings
based on evolutionary relationships, so we use the clade classification in which humans are grouped with gorillas,
chimpanzees, and bonobos. This grouping reflects our evolutionary relationships.
In contrast, grades are groupings that reflect levels of adaptation or overall similarity and not necessarily actual
evolutionary relationships. An example of a grade would be placing orangutans, gorillas, bonobos, and chimpanzees into
a group, and excluding humans. Grouping in this way is based on the superficial similarities of the apes in being largebodied, having lots of body hair, living in tropical forests, using trees, and so on. According to these criteria, humans
seem to be the unusual ones in that we differ in our morphology, behavior, and ecology. Separating humans from the
other large-bodied apes is the system that was used historically. We now know that grouping orangutans, gorillas,
bonobos, and chimpanzees and excluding humans does not accurately reflect our true evolutionary relationships (Figure
5.12), and because our goal in taxonomic classification is to organize animals to reflect their evolutionary relationships,
we prefer to use clade classifications.
Suborder Strepsirrhini
The Order Primates is subdivided into Suborder Strepsirrhini and Suborder
Haplorrhini, which, according to molecular estimates, split about 70–80 million
years ago (Pozzi et al. 2014). The strepsirrhines include the groups commonly
called lemurs, lorises, and galagos (Figure 5.14). Strepsirrhines differ from
haplorrhines in many ways, most of which involve retaining primitive traits from
the last common ancestor of primates. All of the traits discussed below are
primitive traits, but strepsirrhines do have two key derived traits that evolved
after they diverged from the haplorrhines. The two derived traits are the
grooming claw (Figure 5.13), which is on the second digit of each foot, and the
tooth comb (or dental comb), located on the lower, front teeth (Figure 5.15). In
Figure 5.13 The foot of a ring-tailed lemur
showing its grooming claw on the second
digit.
13 | Meet the Living Primates
most strepsirrhines, there are six teeth in the toothcomb—the four incisors and
the two canines. Other than the tooth comb, the teeth of strepsirrhines are fairly
simple in not being particularly large or distinctive relative to haplorrhines.
Figure 5.14 (Clockwise from top right) sifaka, black-and-white
ruffed lemur, loris, galago, slender loris, mouse lemur, aye-aye,
and ring-tailed lemur.
Compared to haplorrhines, strepsirrhines rely more on nonvisual senses. Strepsirrhines have longer snouts than
haplorrhines and get their name because they all have wet noses (rhinariums) like cats and dogs. The long snout and
rhinarium reflect strepsirrhines’ greater reliance on olfaction relative to haplorrhines. Indeed, many strepsirrhines use
scent marking, rubbing scent glands or urine on objects in the environment to communicate with others. Additionally,
many strepsirrhines have mobile ears that they use to locate insect prey and predators. As discussed earlier, there
are trade-offs in sensory systems, so while strepsirrhines have a better sense of smell than haplorrhines, their visual
adaptations are more primitive. Strepsirrhines have less convergent eyes than haplorrhines, and therefore all have
postorbital bars whereas haplorrhines have full postorbital closure (Figure 5.1). All strepsirrhines have a tapetum
lucidum, a reflective layer at the back of the eye that reflects light and thereby enhances the ability to see in low-light
conditions. It is the same layer that causes your dog or cat to have “yellow eye” when you take photos of them with the
flash on. It is thought to be primitive among mammals as a whole.
Meet the Living Primates | 14
Strepsirrhines also differ from haplorrhines in some aspects of their ecology and
behavior. The majority of strepsirrhines are solitary, traveling alone to search for
food, although some taxa are more social. Most strepsirrhines are also nocturnal and
arboreal. Strepsirrhines are, on average, smaller than haplorrhines, and so many
more of them have a diet consisting of insects and fruit, with few taxa eating
primarily leaves. Lastly, most strepsirrhines are good at leaping, with several taxa
specialized for vertical clinging and leaping. In fact, among primates, all but one of
the vertical clinger leapers are in the Suborder Strepsirrhini.
Strepsirrhines can be found all
across the Old World: in Asia,
Africa, and on the island of
Madagascar (Figure 5.16). The
Suborder
Strepsirrhini
is
divided into two groups: (1) the
lemurs of Madagascar and (2)
the lorises, pottos, and galagos
of
Africa
molecular
and
Asia.
estimates,
By
Figure 5.15 The lower front teeth of a
ring-tailed lemur showing a tooth
comb. Note that there are six teeth in
the tooth comb, four incisors and two
canines. The teeth that superficially
look like canines are actually
premolars.
these
two groups split about 65 million years ago (Pozzi et al. 2014).
Figure 5.16 Geographic distribution of living
strepsirrhines. Lemurs live only on the island of
Madagascar, while their relatives the lorises and galagos
live across Central Africa and South and Southeast Asia.
Lemurs of Madagascar
Madagascar is an island off the east coast of Africa, and it is roughly the size of California, Oregon, and Washington
combined. It has been separated from Africa for about 130 million years and from India for about 85 million years, which
means it was already an island when strepsirrhines got there approximately 60–70 million years ago. Only a few mammal
species ever reached Madagascar, and so when lemurs arrived they were able to flourish into a variety of forms.
The lemurs of Madagascar are much more diverse
compared to their mainland counterparts, the lorises and
galagos. Malagasy strepsirrhines display a variety of
activity patterns. While many species are nocturnal,
plenty of others are diurnal or cathemeral. They range in
body size from the smallest of all primates, the mouse
lemur, some species of which weigh a little over an ounce
(Figure 5.13), up to the largest of all strepsirrhines, the
indri, which weighs up to about 20 pounds (Figure 5.17).
Lemurs
include
species
that
are
insectivorous,
frugivorous, and folivorous. A couple of members of this
group have specialized in more unusual diets for
primates. These include the gummivorous fork-marked
lemurs as well as bamboo lemurs, who are able to
Figure 5.17 Indris, the largest of the lemurs. These folivorous lemurs
are vertical clingers and leapers and live in pairs.
metabolize the cyanide in bamboo. The most unusual lemur is the aye-aye, which you can see depicted in Figure 5.13.
This nocturnal lemur exhibits traits not seen in any other primate, including having rodent-like front teeth that grow
continuously and a long-bony middle finger that it uses to fish grubs out of wood. It has a very large brain compared to
other strepsirrhines, which it fuels with a diet that includes bird’s eggs and other animal matter. Based on genetic
estimates and morphological studies, it is believed that aye-ayes were the first lemurs to separate from all of the other
15 | Meet the Living Primates
strepsirrhines and so have been evolving on their own since around the time strepsirrhines got to Madagascar (Matsui
et al. 2009).
Lemurs are also diverse in terms of behavior. Many Malagasy strepsirrhines are solitary foragers, but some live in pairs,
others in small groups, some in larger groups, and some, like the red-ruffed lemur, are now known to live in complex
social groups that are unlike what we see in any other primates (Vasey 2006). It is also among the lemurs that we see
some of the best vertical clingers and leapers. Many lemurs are quadrupedal, but even the quadrupedal lemurs are quite
adept at leaping. Malagasy strepsirrhines also exhibit a few unusual traits. They are highly seasonal breeders, often
mating only during a short window, once a year (Wright 1999). Female ring-tailed lemurs, for example, only come into
estrus one day a year for a mere six hours. Malagasy strepsirrhines are also unusual in that females are socially dominant.
In most primates, males dominate females because they are typically larger and exhibit greater aggression, but in lemur
groups, males and females are usually the same size and females have priority access to resources over males.
Lorises, Pottos, and Galagos of Asia and Africa
Unlike the lemurs of Madagascar, lorises, pottos, and galagos live in areas where they share their environments with
monkeys and apes, who often eat similar foods. Lorises live across South and Southeast Asia, while pottos and galagos
live across Central Africa. Because of competition with larger-bodied monkeys and apes, mainland strepsirrhines are
more restricted in the niches they can fill in their environments and so are not as diverse as the lemurs of Madagascar.
All strepsirrhines in Africa and Asia are nocturnal and solitary. Their body sizes
don’t range as greatly as the lemurs, and neither do their diets. For the most part,
the diet of lorises, pottos, and galagos consist of fruits and insects. A couple of
species eat more gum, but overall the diet of this group is fairly narrow when
compared to the Malagasy lemurs. Lorises and pottos are known for being slow,
quadrupedal climbers, moving quietly through the forests to avoid being detected
by predators (Figure 5.18). Because they are not fast moving, these strepsirrhines
have developed alternative defenses against predators. Lorises, for example, eat a
lot of caterpillars, which makes their saliva slightly toxic. Loris mothers will then
bathe their young in this toxic saliva, thus making the babies unappealing to
predators. In comparison to the slow-moving lorises and pottos, galagos are
active quadrupedal runners and leapers that scurry about the forests at night.
Galagos make distinctive calls that sound like a baby crying, which has led to their
nickname “bushbabies.” Figure 5.19 summarizes the key differences between
these two groups of strepsirrhines.
Figure 5.18 This slow loris, like all others
in this taxonomic group, is solitary and
nocturnal, with a diet heavy in insects
and fruit.
Meet the Living Primates | 16
Lemurs
Geographic range
Madagascar
Lorises, Pottos and Galagos
South and Southeast Asia
Central Africa
Activity patterns
Diurnal, nocturnal or cathemeral
Nocturnal
Dietary types
Insectivore, frugivore or folivore
Insectivore, frugivore
Social groupings
Solitary, pairs, or small to large groups
Solitary
Forms of locomotion
Vertical clinger leapers, quadrupedal
Slow quadrupedal climbers and active
quadrupedal runners
Figure 5.19 Strepsirrhini at a glance: This table summarizes the key differences between the two groups of strepsirrhines.
Suborder Haplorrhini
When the strepsirrhini and haplorrhini split from one another, strepsirrhines retained more primitive traits (those likely
present in the last common ancestor), while haplorrhines became quite different, developing many derived traits. Thus,
all of the traits discussed below are considered derived traits.
As mentioned earlier, the visual systems of haplorrhines are more developed than those of strepsirrhines. Many
haplorrhines are trichromatic and, with one exception that will be discussed shortly, all have full postorbital closure
(Figure 5.1). This increase in bony closure around the eye protects the more convergent eyes that haplorrhines possess.
Haplorrhines also evolved to have a fovea, a depression in the retina at the back of the eye containing concentrations of
cells that allow us to see things very close up in great detail. The heavier reliance on vision over olfaction is also reflected
in the shorter snouts ending with the dry nose (no rhinarium) of haplorrhines. All but two genera of living haplorrhines
are active during the day, so this group lacks the tapetum lucidum which is so useful to nocturnal species. On average,
haplorrhines also have larger brains relative to their body size when compared with strepsirrhines.
The Haplorrhini differ from the Strepsirrhini in aspects of ecology and behavior as well. Haplorrhines are generally
larger than strepsirrhines, and so we see many more species that are folivorous and frugivorous, and fewer that are
insectivorous. This dietary difference is reflected in the teeth of haplorrhines, which are broader with more surface
area for chewing. The larger body size of this taxon also influences locomotion. Only one haplorrhine is a vertical
clinger and leaper. Most members of this suborder are quadrupedal, with one subgroup specialized for brachiation. A
few haplorrhine taxa are monomorphic, meaning males and females are the same size, but many members of this group
show moderate to high sexual dimorphism in body size and canine size. Haplorrhines also differ in social behavior.
All but two haplorrhines live in groups, which is very different from the primarily solitary strepsirrhines. Differences
between the two suborders are summarized in Figure 5.20.
17 | Meet the Living Primates
Suborder Strepsirrhini
Rhinarium
Longer snout
Sensory
adaptations
Eyes less convergent
Post-orbital bar
Tapetum lucidum
Mobile ears
Dietary
differences
Suborder Haplorrhini
No rhinarium
Short snout
Eyes more convergent
Post-orbital plate
No tapetum lucidum
Many are trichromatic
Fovea
Mostly insectivores and frugivores, few folivores
Few insectivores, mostly frugivores and folivores
Mostly nocturnal, few diurnal or cathemeral
Only two are nocturnal, rest are diurnal
Almost entirely arboreal
Many arboreal taxa, also many terrestrial taxa
Social
groupings
Mostly solitary, some pairs, small to large groups
Only two are solitary, all others live in pairs, small to very
large groups
Sexual
dimorphism
Minimal to none
Few taxa have little/none, many taxa show moderate to
high dimorphism
Activity
patterns and
Ecology
Figure 5.20 Suborders at a glance: This table summarizes the key differences between the two primate suborders.
Suborder Haplorrhini is divided into three infraorders: Tarsiiformes, which includes the tarsiers of Asia; Platyrrhini,
which includes the New World monkeys of Central and South America; and Catarrhini, a group that includes the Old
World monkeys and apes of Asia and Africa, as well as humans. According to molecular estimates, tarsiers split from the
other haplorrhines close to 70 million years ago, and platyrrhini split from catarrhini close to 46 million years ago (Pozzi
et al. 2014).
Meet the Living Primates | 18
Infraorder Tarsiiformes of Asia
Today, the Infraorder Tarsiiformes
includes only one genus, Tarsius
(Figure 5.21). Tarsiers are smallbodied
primates
that
live
in
Southeast Asian forests (Figure 5.22)
and possess an unusual collection of
traits that have led to some debate
about their position in the primate
Figure 5.21 Tarsiers are the only living
representatives of this Infraorder.
taxonomy.
They
considered
members
are
widely
of
the
haplorrhine group because they
share several key derived traits with
monkeys,
apes,
and
Figure 5.22 Tarsiiformes can be found in
tropical forests of Southeast Asia.
humans,
including dry noses, a fovea, not having a tapetum lucidum, and having eyes that are close together. Tarsiers also have
some traits that are more like strepsirrhines and some that are unique. Tarsiers are the only haplorrhine that are
specialized vertical clinger leapers, a form of locomotion only otherwise seen in some strepsirrhines. Tarsiers actually
get their name because their ankle (tarsal) bones are elongated to provide a lever for vertical clinging and leaping.
Tarsiiformes are also small, with most species weighing between 100 and 150 grams. Like strepsirrhines, tarsiers are
nocturnal, but because they lack a tapetum lucidum, tarsiers compensate by having enormous eyes. In fact, each eye of
a tarsier is larger than its brain. These large eyes allow enough light in for tarsiers to still be able to see well at night
without the reflecting layer in their eyes. To protect their large eyes, tarsiers have a partially closed postorbital plate
that is somewhat intermediate between the postorbital bar of strepsirrhines and the full postorbital closure of other
haplorrhines (Figure 5.23). Tarsiers have different dental formulas on their upper and lower teeth. On the top, the dental
formula is 2:1:3:3, but on the bottom it is 1:1:3:3. Other unusual traits of tarsiers include having two grooming claws on
each foot and the ability to rotate their heads around 180 degrees, a trait useful in locating insect prey. The tarsier diet
is considered faunivorous because it consists entirely of animal matter, making them the only primate not to eat any
vegetation. They are also only one of two living haplorrhines to be solitary, the other being the orangutan. Most tarsiers
are not sexually dimorphic, like strepsirrhines, although males of a few species are slightly larger than females.
Two alternative classifications have emerged due to the
unusual mix of traits that tarsiers have. Historically,
tarsiers were grouped with lemurs, lorises, and galagos
into a suborder called Prosimii. This classification was
based on tarsiers, lemurs, lorises, and galagos all having
grooming claws and similar lifestyles (e.g., small,
nocturnal, more leaping locomotion, diet heavy in insects,
more solitary). Monkeys, apes, and humans were then
separated into a suborder called the Anthropoidea. These
suborder groupings were based on grade rather than
clade. Today, most people use Suborders Strepsirrhini
and Haplorrhini, which are clade groupings based on the
derived traits that tarsiers share with monkeys, apes, and
humans (e.g., more postorbital closure, fovea, no tapetum
Figure 5.23 Skull of a tarsier showing very large eye sockets and
partially closed postorbital plates.
lucidum, dry nose). The Strepsirrhini/Haplorrhini dichotomy is also supported by the genetic evidence that indicates
tarsiers are more closely related to monkeys, apes, and humans (Jameson et al. 2011). Figure 5.24 summarizes the unusual
mix of traits seen in tarsiers.
19 | Meet the Living Primates
Like Strepsirrhini
Like
Haplorrhini
Unique
Very small
Almost full PO
closure
Nocturnal
Two grooming
claws
Highly
insectivorous
2:1:3:3/1:1:3:3 dental
formula
Solitary
Do not eat
vegetation
Vertical clingerleapers
Little/no sexual
dimorphism
More
convergent eyes
No tapetum
lucidum
No rhinarium
Can rotate their
heads nearly 180
degrees
Genetic
evidence
Fovea
Figure 5.24 Tarsiers at a glance: Tarsiers have a mix of traits that lead to debate about their classification. Some of their
traits superficially resemble strepsirrhines, but they share many derived traits with haplorrhines. They also possess
unique characteristics that are unlike any other primates.
Infraorder Platyrrhini of Central and South America
The platyrrhines, also commonly called New World monkeys, are the only
non-human primates in Central and South America (Figure 5.25) and so, like
the lemurs of Madagascar, have diversified into a variety of forms in the
absence of competition. Infraorder Platyrrhini get their name from their
distinctive nose shape. “Platy” means flat and “rhini” refers to noses and,
indeed, New World monkeys have noses that are flat and wide, with nostrils
that are far apart, facing outward, and usually round in shape (Figure 5.26).
This nose shape is very different from what we see in catarrhines, the group
that includes Old World monkeys, apes, and humans.
On average, Platyrrhini are smaller
and less sexually dimorphic than
catarrhines,
Figure 5.25 Geographic distribution of the
platyrrhines across Central and South America.
New World monkeys are the only naturally
occurring non-human primates in the
Americas.
retained
and
the
they
more
have
primitive
primate dental formula of 2:1:3:3.
Platyrrhines are also all highly
arboreal, whereas many Old World
monkeys
and
apes
spend
significant time on the ground. The New World monkeys also differ in having
less well-developed vision. This is reflected in the wiring in the visual system
of the brain but also in their polymorphic color vision. The genes that enable
Figure 5.26 A capuchin monkey
demonstrating a typical platyrrhine nose
shape with round nostrils pointing outward
on a flat nose.
individuals to distinguish reds and yellows from blues and greens are on the X
Meet the Living Primates | 20
chromosome. Different genes code for being able to see different wavelengths of light so to distinguish between them
you need to be heterozygous for seeing color. In New World monkeys, each X chromosome carries the genes for seeing
one wavelength. This means that male platyrrhines (having only one X chromosome) are always dichromatic. Female
platyrrhines can be dichromatic (if they are homozygous for the same version of the color vision gene) or trichromatic (if
they are heterozygous) (Kawamura et al. 2012). We currently know of two exceptions to this pattern among platyrrhines.
Owl monkeys, which are nocturnal, are monochromatic, meaning that they cannot distinguish any colors. The other
exception are Howler monkeys, which have evolved to have two color vision genes on each X chromosome.This means
that both male and female howler monkeys are able to see reds and yellows. As we will discuss, all Old World monkeys,
apes, and humans are trichromatic.
Platyrrhines include the smallest of the monkeys, the marmosets and tamarins (Figure 5.27). These small monkeys, all
of which weigh less than 1 kilogram, live in cooperative family groups, wherein usually only one female reproduces and
everyone else helps carry and raise the offspring. They are unusual primates in that they regularly produce twins. The
diet of marmosets and tamarins largely consists of gums and saps, so these monkeys have evolved claw-like nails that
enable them to cling to the sides of tree trunks like squirrels as well as special teeth that allow them to gnaw through
bark. They also have one fewer molar than other platyrrhines, giving them a dental formula of 2:1:3:2.
The largest of the platyrrhines are a family that include spider monkeys, woolly spider monkeys, woolly monkeys, and
howler monkeys (Figure 5.28). This group of monkeys can weigh up to 9–15 kg and have evolved prehensile tails that
can hold their entire body weight. It is among this group that we see semi-brachiators, like the spider monkey (Figure
5.10). To make them more efficient in this form of locomotion, spider monkeys evolved to not have thumbs so that their
hands work more like hooks that can easily let go of branches while swinging. Howler monkeys are another well-known
member of this group, earning their name due to their loud calls, which can be heard for miles away. To make these
loud vocalizations, howler monkeys have a specialized vocal system that includes a large larynx and hyoid bone. Howler
monkeys are the most folivorous of the platyrrhines and are known for spending a large portion of their day digesting
their food.
There are many other monkeys in the New World, including the gregarious capuchins (Figure 5.26) and squirrel
monkeys, the pair-living titi monkeys, and the nocturnal owl monkeys.There are also the seed-eating monkeys such as
saki monkeys and uakaris. In many areas across Central and South America, multiple different species of platyrrhine
will share the forests, and some species will even travel together in associations that you will learn about in Chapter
6. According to molecular evidence, the diversity of platyrrhines that we see today seems to have originated about 25
million years ago (Schneider and Sampaio 2015). Figure 5.29 summarizes the key traits of platyrrhines relative to the
other infraorders of Haplorrhini.
21 | Meet the Living Primates
Figure 5.27 (Clockwise from top-right) golden-headed lion
tamarin, pygmy marmoset, Goeldi’s monkey, bare-eared
marmoset, emperor tamarin, and common marmoset.
Figure 5.28 (Clockwise from top right) howler monkey, woolly
monkey, woolly spider monkey, and spider monkey.
Platyrrhini traits
Flat nose with rounded nostrils pointing to the side
Highly arboreal
Less sexually dimorphic on average
2:1:3:3 dental formula*
Polymorphic color vision*
Figure 5.29 Platyrrhini at a glance: Summary of the key traits we use to distinguish platyrrhines. Traits indicated with
an * are those with exceptions detailed in the text.
Infraorder Catarrhini of Asia and Africa
Infraorder Catarrhini includes Old World monkeys, apes, and humans. Non-human catarrhines are found all over
Africa and South and Southeast Asia, with some being found as far north as Japan. The most northerly and southerly
catarrhines are from the superfamily that includes the Old World monkeys. In contrast, apes are less tolerant of drier,
more seasonal environments and so have a relatively restricted geographic range.
Meet the Living Primates | 22
When compared to the other haplorrhine infraorders, catarrhines are distinguished by
several characteristics. Catarrhines have a distinctive nose shape, with teardrop-shaped
nostrils that are close together and point downward (Figure 5.30). Old World monkeys, apes,
and humans also have one fewer premolar than most other primates, giving us a dental
formula of 2:1:2:3 (Figure 5.31). On average, catarrhines are the largest and most sexually
dimorphic group of primates. Gorillas are the largest of all living primates, with males
weighing up to 220 kg. The most sexually dimorphic of all primates are mandrills. Mandrill
males not only have much more vibrant coloration than mandrill females but also have larger
canines and can weigh up to three times more (Setchell et al. 2001). The larger body size of
catarrhines is related to the more terrestrial lifestyle of many members of this infraorder. In
fact, the most terrestrial of living primates can be found in this group. Among all primate taxa,
Figure 5.30 A Wolf’s guenon
demonstrating a typical
catarrhine nose with
teardrop-shaped nostrils
close together and pointed
downward.
vision is the most developed in catarrhines. Catarrhines independently evolved the same
adaptation as howler monkeys in having each X chromosome with sufficient genes to
distinguish both reds and yellows, so all catarrhines are trichromatic. Trichromatic color
vision is particularly useful to catarrhines, which are all diurnal.
Figure 5.31 Catarrhines are distinguished in that they only have two premolars compared to the three premolars seen in
most other primate taxa, including the platyrrhines shown here for comparison. In these images you can also see one of
the derived traits of cercopithecoids, their bilophodont molars, which differ from the more primitive Y-5 molars that apes
and humans have.
Infraorder Catarrhini is divided into two superfamilies: Superfamily Cercopithecoidea, which includes Old World
monkeys, and Superfamily Hominoidea, which includes apes and humans. Molecular estimates place the split between
cercopithecoids and hominoids at about 32 million years ago (Pozzi et al. 2014), which fits well with the fossil record
showing evidence of the lineages by about 25 million years ago (see Chapter 8 on primate evolution).
23 | Meet the Living Primates
Superfamily Cercopithecoidea of Africa and Asia
Compared to hominoids, Old World monkeys have a more primitive quadrupedal body plan (discussed later in Figure
5.39), but they do have a couple of derived traits shared by all members of this group. Cercopithecoidea have
bilophodont molars (“bi” meaning two, “loph” referring to ridge, and “dont” meaning tooth). Referring back to Figure
5.31, you will see how the molars of cercopithecoids have four cusps arranged in a square pattern and have two ridges
connecting them. It is thought that this molar enabled Old World monkeys to eat a wide range of foods, thus allowing
them to live in habitats that apes cannot. The other key derived trait that all cercopithecoids share is having ischial
callosities (Figure 5.32). The ischium is the part of your pelvis that you are sitting on right now (see Appendix A:
Osteology). In Old World monkeys, this part of the pelvis has a flattened surface that, in living animals, will have callused
skin over it. These function as seat pads for cercopithecoids, who often sit above branches when feeding and resting.
Figure 5.32 The second derived trait of cercopithecoids are
their ischial callosities, shown here on a crested black
macaque.
Figure 5.33 Geographic distribution of the Old World
monkeys. Catarrhines have the widest geographic
distribution due to the success of cercopithecoid monkeys
who are found all across Africa and Asia.
The cercopithecoid monkeys are the most geographically widespread group of non-human
primates (Figure 5.33). Since their divergence from hominoids, this monkey group has
increased in numbers and diversity. In part, their success over hominoids is due to the
faster reproductive rates of cercopithecoids relative to hominoids. On average, Old World
monkeys will reproduce every one to two years, whereas hominoids will reproduce once
every four to nine years, depending on the taxon.
Cercopithecoidea is split into two groups, the leaf
monkeys and the cheek-pouch monkeys. Both
groups coexist in Asia and Africa; however, the
majority of leaf monkey species live in Asia with only
Figure 5.34 Silver leaf monkey
infants are born with orange
fur, dramatically contrasting
the adult coat color of their
mothers. After a few months,
the infants gradually change
color to that of their parents.
a few taxa in Africa. In contrast, only one genus of
cheek-pouch monkey lives in Asia, and all the rest of
them in Africa. As you can probably guess based on
their names, the two groups differ in terms of
diet.Leaf monkeys are primarily folivores, with some
species eating a significant amount of seeds. Cheek-
pouch monkeys tend to be more frugivorous or omnivorous, with one taxon,
geladas, eating primarily grasses. The two groups also differ in some other
Figure 5.35 Proboscis monkeys are one of
several “odd-nosed” leaf monkeys. Male
proboscis monkeys, like the one shown
here, have large, pendulous noses.
Female proboscis monkey noses are
much smaller; in this species nose size is
a sexually dimorphic trait.
Meet the Living Primates | 24
interesting ways. Leaf monkeys tend to produce infants with natal coats—infants whose fur is a completely different
color from their parents (Figure 5.34).Leaf monkeys are also known for having odd noses (Figure 5.35), and so they are
sometimes called “odd-nosed monkeys.” Cheek-pouch monkeys are able to pack food into their cheek pouches (Figure
5.36), thus allowing them to move to a location safe from predators or aggressive individuals of their own species where
they can eat in peace.
Figure 5.36 This bonnet macaque has filled its cheek
pouches with food. This adaptation is useful in
transporting food to a safer location to eat.
SPECIAL TOPIC: PRIMATES IN CULTURE AND RELIGION
In the introduction to this chapter, I mentioned the innate
affinity that humans have toward non-human primates even
when we do not fully understand our exact relationship to
them. In fact, recognition of similarities between humans and
other primates is very ancient, dating back far earlier than
Linnaeus.For many of us, we only ever get to see primates in
zoos and animal parks, but in many areas of the world, humans
have coexisted with these animals for thousands of years. In
areas where humans and primates have a long, shared history,
non-human primates often play key roles in creation myths and
cultural symbolism.
Figure 5.37 Because of important monkey-like
figures in the Hindu religion, macaques are
protected in India and often live near temples
where they are fed by local peoples.
Hamadryas baboons feature significantly in Ancient Egyptian
iconography. Ancient Egyptian deities and beliefs transformed
over time, as did the role of hamadryas baboons.Early on,
baboons were thought to represent dead ancestors, and one
monkey deity, called Babi or Baba, was thought to feed off of dead souls. Later, baboons became the totem
animal for Thoth, the deity of science, writing, wisdom, and measurement, who also wrote the book of the
dead. Sunbathing hamadryas baboons led ancient Egyptians to associate them with Ra, the sun god, who
25 | Meet the Living Primates
was the son of Thoth. During mummification, human organs were removed and put into canopic jars, one of
which was topped with the head of the baboon-headed god, Hapi. Hamadryas baboons were also often kept
as pets, as depicted in hieroglyphics, and occasionally mummified as well.
On Madagascar, indris and aye-ayes play roles in the creation myths and omens of local people.There are
many myths regarding the origins of indris and their relationship to humans, including one where two
brothers living in the forest separated, with one brother leaving the forest and becoming a human while the
other stayed in the forest to become the indri. Indris are considered sacred and are therefore protected,
due to their similarities to humans in having long legs, no tail, and upright posture. Unfortunately, the ayeaye is not treated with the same reverence. Aye-ayes, due to their unusual appearance, are thought to be
omens of death.They are usually killed when encountered because it is believed that someone will die if an
aye-aye points at them.
In India, monkeys play a key role in the Hindu religion. Hanuman, who resembles a monkey, is a key figure in
the Ramayana. Hanuman is thought to be a guardian deity, and so local monkeys like Hanuman langurs and
macaques are protected in India (Figure 5.37). In Thailand, where Hinduism is also practiced, the Hindu
reverence for monkeys extends to “monkey feasts,” where large quantities of food are spread out in
gratitude to the monkeys for bringing good fortune.
The people of Japan have coexisted with Japanese macaques for thousands of years, and so monkeys play
key roles in both of the major Japanese religions. In the Shinto religion, macaques are thought of as
messengers between the spirit world and humans and monkey symbols are thought to be good luck. The
other major religion in Japan is Buddhism, and monkeys play a role in symbolism of this religion as well.The
“Three Wise Monkeys” who see no evil, speak no evil, and hear no evil derive from Buddhist iconography of
monkeys.
In the New World, monkeys feature often in Mayan and Aztec stories. In the Mayan creation story, the Popol
Vuh, the “hero brothers” are actually a howler monkey and a spider monkey, who represent ancestors of
humans in the story. In the Aztec religion, spider monkeys are associated with the god of arts, pleasure, and
playfulness.A spider monkey is also represented in a Peruvian Nazca geoglyph, a large design made on the
ground by moving rocks.
In many of these regions today, the relationships between humans and non-human primates are
complicated. The bushmeat and pet trades make these animals valuable at the expense of many animals’
lives, and in some areas, non-human primates have become pests who raid crop fields and consume
valuable foods. All of this has led to the development of a new subarea of anthropology called
Ethnoprimatology, which involves studying the political, economic, symbolic, and practical relationships
between humans and non-human primates.This field highlights the particular challenges for humans of
having to coexist with animals with whom we share so much in common. It also provides insight into some
of the challenges facing primate conservation efforts (see Appendix A: Primate Conservation).
Meet the Living Primates | 26
Superfamily Hominoidea of Africa and Asia
The Superfamily Hominoidea of Africa and Asia (Figure 5.38)
includes the largest of the living primates, apes and humans, but
our superfamily differs from other primates in some other key
ways as well. When compared to cercopithecoids, hominoids
have more primitive teeth.Whereas Old World monkeys have
bilophodont molars, hominoids have Y-5 molars, which feature
five cusps separated by a “Y”-shaped groove pattern (Figure
5.31). The Y-5 molar was present in the common ancestors of
hominoids and cercopithecoids, thus telling us it is the more
primitive molar pattern of the two. Where hominoids differ the
most from other primates, however, is in our body plans. This is
due to the unusual form of locomotion that hominoids are
adapted for, brachiation (Figure 5.39).
Figure 5.38 Geographic distribution of apes across Central
and West Africa, and Southeast Asia. Hominoids overlap
geographically with cercopithecoid monkeys but have a lower
tolerance for seasonal environments and so are found only in
tropical forests across these regions.
Quadrupedalism
Brachiation
Arm length vs. leg length
About equal
Arms are longer
Shoulder position
More on the front
Out to the side
Deep front-to-back
Shallow front-to-back
Narrow side-to-side
Wide side-to-side
Length of lower back
Long
Short
Collar bone length
Short
Long
Ulnar olecranon process
Long
Short
Ulnar styloid process
Long
Short
Tail
Short to long
None
Ribcage shape
Figure 5.39 Quadrupedalism vs. brachiation: Summary of the key anatomical differences between a quadrupedal
primate and one adapted for brachiation. To view and compare these traits using photos of bones, check out the
interactive skeletal websites listed under the “Further Explorations” section at the end of this chapter.
To successfully swing below branches, many changes to the body needed to occur. The arms of a hominoid are much
longer than the legs in order to increase reach, and the lower back is shorter and less flexible to increase control
when swinging. The torso, shoulders, and arms of hominoids have evolved to increase range of motion and flexibility
27 | Meet the Living Primates
(Figure 5.9). The clavicle, or collar bone, is longer in order to stabilize the shoulder joint out to the side, thus enabling
us to rotate our arms 360 degrees.Our rib cages are wider side to side and shallower front to back than those of
cercopithecoids and we do not have tails, as tails are useful for balance when running on all fours but not useful when
swinging. Hominoids also have modified ulnae, one of the two bones in the forearm (see Appendix A: Osteology). At the
elbow end of the ulna, hominoids have a short olecranon process, which allows for improved extension in our arms. At
the wrist end of the ulna, hominoids have a short styloid process, which enables us to have very flexible wrists, a trait
critical for swinging.Both the olecranon process and styloid process are long in quadrupedal animals who carry much of
their weight on their forelimbs when traveling and who therefore need greater stability rather than flexibility in those
joints.
Apes and humans also differ from other primates in behavior and life history characteristics. Hominoids all seem to
show varying degrees of female dispersal at sexual maturity. Dispersal refers to leaving the area or group where an
individual was born.As you will learn about in Chapter 6, it is more common that males leave. Indeed, some apes
show males dispersing in addition to females, but the broader tendency for female dispersal in hominoids is a bit
unusual among primates. Our superfamily is also characterized by the most extended life histories of all primates. All
members of this group live a long time and take a long time to grow and start reproducing. Hominoids also reproduce
much less frequently compared to cercopithecoid monkeys. The slow pace of this life history is likely related to why
hominoids have decreased in diversity since they first evolved. In the past, hominoids were tremendously diverse in
both geography and adaptations. Today, there are only five types of hominoids left: gibbons and siamangs, orangutans,
gorillas, chimpanzees and bonobos, and humans.
Infraorder Catarrhini
Downward facing, tear-drop shaped nostrils, close together
Arboreal and more terrestrial taxa
On average, largest primates
On average, most sexually dimorphic taxonomic group
2:1:2:3 dental formula
All trichromatic
Superfamily Cercopithecoidea
Superfamily Hominoidea
Wide geographic distribution
Tropical forests of Africa and Asia
Bilophodont molars
Y-5 molars
Ischial callosities
Adaptations for brachiation
Reproduce every 1-2 years
Reproduce every 4-9 years
Meet the Living Primates | 28
Figure 5.40 Catarrhini at a glance: Summary of key traits of the Infraorder Catarrhini as well as the characteristics used
to distinguish between the two superfamilies within this group.
Family Hylobatidae of Southeast Asia
The number of genera in this group has been changing in recent
years, but the taxa included can broadly be discussed as gibbons
and siamangs. Both are found across Southeast Asian tropical
forests. These are the smallest of the hominoids and so are
sometimes referred to as the “lesser apes.” Gibbons weigh, on
average, about 13 pounds and tend to be more frugivorous,
whereas siamangs are about twice the size of gibbons and are
more folivorous.Unlike the larger-bodied apes (orangutans,
chimps, bonobos, and gorillas) who make nests to sleep in every
night, gibbons and siamangs will develop callused patches on their
Figure 5.41 Siamangs are the largest of the Hylobatidae
family. They are all black and, as you can see inflated in
this photo, have a throat sac that they use to give loud
calls.
ischium resembling ischial callosities. There are many different
gibbon species that vary in their coloration and markings.
Siamangs, however, are all black with big throat sacs that are used
in their exuberant vocalizations (Figure 5.41). Both gibbons and
siamangs live in pairs with very little sexual dimorphism, although
males and females do differ in coloration in some species.
Pongo of Southeast Asia
The
Genus
Pongo
refers
to
orangutans. These large red apes
are found on the islands of Borneo
and Sumatra in Southeast Asia.
There are two well-known species
of orangutan, one on each island.
Recently, a third, very rare species
was
discovered
Sumatra
Figure 5.42a A female orangutan and her
infant.
in
(Nater
2017).Orangutans
Southern
et
are
al.
highly
frugivorous but will supplement
their diet with leaves and even
bark when fruit is less available. As mentioned earlier, orangutans are the
only diurnal, solitary taxon among primates and are extremely slow to
reproduce, producing only one offspring about every seven to nine years.
They are highly sexually dimorphic (Figure 5.42), with fully developed,
“flanged” males being approximately twice the size of females. These males
have large throat sacs; long, shaggy coats; and cheek flanges.The skulls of
male orangutans often feature a sagittal crest, which is believed to function
as both additional attachment area for chewing muscles but also in sexual
29 | Meet the Living Primates
Figure 5.42b A flanged adult male. Male
orangutans are about twice the size of females,
and in these photos you can also see the sexual
dimorphism in coat length, cheek flanges and
throat sac in the male.
competition (Balolia et al. 2017). An unusual feature of orangutan biology is male bimaturism. Male orangutans are
known to delay maturation until one of the more dominant, flanged males disappears. The males that delay maturation
are called “unflanged” males, and they can remain in this state for their entire life.Unflanged males resemble females in
their size and appearance and will sneak copulations with females while avoiding the bigger, flanged males. Flanged and
unflanged male orangutans represent alternative reproductive strategies, both of which successfully produce offspring
(Utami et al. 2002).
Gorilla of Africa
Figure 5.43a A female gorilla and her offspring.
There are several species of gorillas that can be found across Central
Africa.Gorilla males, like orangutan males, are about twice the size of female
gorillas (Figure 5.43). When on the ground, gorillas use a form of
quadrupedalism called knuckle-walking, where the fingers are curled under
and the weight is carried on the knuckles. Male gorillas have a large sagittal
crest and larger canines compared with females. Adult male gorillas are often
called “silverbacks” because when they reach about twelve to thirteen years
old, the hair on their backs turns silvery gray. Gorillas typically live in groups
of one male and several females. Gorillas are considered folivorous, although
they can be more frugivorous depending on fruit seasonality (Remis 1997).
Figure 5.43b A silverback male. Male gorillas
are about twice the size of females, but also
differ from females in having a large sagittal
crest, and silver back, which appears as they
mature.
Meet the Living Primates | 30
Pan of Africa
The Genus Pan includes two species: Pan troglodytes (the common chimpanzee) and
Pan paniscus (the bonobo). These species are separated by the Congo River, with
chimpanzees ranging across West and Central Africa and bonobos located in a
restricted area south of the Congo River. Chimpanzees and bonobos both have broad,
largely frugivorous diets and similar social groups.The two species differ
morphologically in that bonobos are slightly smaller, have their hair parted down the
middle of their foreheads, and are born with dark faces (Figure 5.44). In contrast,
chimpanzees do not have the distinctive parted hair and are born with light faces
which darken as they mature (Figure 5.45). Chimpanzees and bonobos live in a
Figure 5.44 Bonobo, Pan paniscus.
You can see the distinctive hair-part
on this bonobo.
grouping called a fission-fusion community, which you will learn more about in
Chapter 6. Both species are moderately sexually dimorphic, with males about 20%
larger than females. When on the ground, chimpanzees and bonobos knuckle-walk
like gorillas do.
Figure 5.45 A common chimpanzee, Pan troglodytes, female and her offspring. Note
the pink face of the youngest individual. Bonobos are born with dark-skinned
faces, but chimpanzees are born with pink faces that darken with age.
Homo
The last member of the Hominoidea to discuss is our own taxon, Genus Homo. Humans differ from apes in many aspects
of our morphology, behavior, and life history, all of which you will be learning about in later chapters. One of the
objectives of this chapter, however, and of biological anthropology in general, is to understand our place in nature.This
means looking for the aspects of human biology that lead us to place humans within the taxonomic diversity we have
just discussed. To accomplish this, we not only consider how humans are different from other species but also examine
the traits that unite us with the other primates, our similarities—that is our focus here.
There are clear similarities between humans and the other apes in our morphology and life history. Like other
hominoids, humans lack a tail and possess upper-body adaptations for brachiation. While our lower body has been
modified for a bipedal gait, we are still able to swing from branches or “monkey bars,” or throw a fastball, all thanks to our
31 | Meet the Living Primates
mobile shoulder joint.Humans, like other hominoids, also have a Y-5 cusp pattern on our molars. As discussed earlier,
all hominoids have an extended life history, taking a long time to grow and develop, and have a long life span. Humans,
too, exhibit these same characteristics. Lastly, while humans show a great deal of variation across cultures, many human
societies show patterns of female dispersal in which males stay in the group into which they were born while females
leave (Burton et al. 1996).
Among the hominoids, humans show particular affinities with other members of the African Clade, Pan and Gorilla.
Humans share over 96% of our DNA with gorillas (Scally et al. 2012), and over 98% with Pan (Ebersberger et al. 2002).
Even without this strong genetic evidence, the African Clade of hominoids share many morphological similarities. These
shared traits include eye sockets that are slightly farther apart and are more square or rounded compared to the closely
placed, ovoid eyes of orangutans.Also, the cheekbones of the African clade sweep backward compared to the more
flattened orangutan cheekbones. Today, Pan and Gorilla knuckle-walk when on the ground, and it has been suggested
that the last common ancestor of chimpanzees, bonobos, gorillas, and humans shared this trait (Richmond et al. 2001).
Our closest living relatives today are chimpanzees and bonobos. Because of our close relationship, humans share
many additional traits in common with Pan. Humans, chimpanzees, and bonobos all live in similar social groups that
are characterized by territoriality and male cooperation, among other things. Chimpanzee males are well-known to
cooperate in hunting, a common trait across human societies as well. As you will learn more about in the next chapter,
chimpanzee populations have also been observed to make and use tools for different purposes, not unlike what humans
do.
LEARNING FROM PRIMATES
While primates are fascinating animals in their own right, we study non-human primates in anthropology with the
ultimate goal of understanding more about our own biology and evolutionary history.The close relationship between
humans and non-human primates makes them excellent for studying humans via homology, looking at traits that
are shared between two taxa because they inherited the trait from a common ancestor. Consider, for example, the
characteristics discussed in the previous section that are shared by humans and Pan. Since both taxa exhibit these traits,
they are likely homologous, meaning these shared traits were probably present in the last common ancestor of humans
and Pan approximately 6-8 million years ago .
Non-human primates also make excellent comparators for learning about humans via analogy (sometimes called
convergent evolution, parallel evolution, or homoplasy). Many non-human primates live in environments or social
groups similar to those in which our ancestors lived and therefore exhibit similar behavioral and morphological traits as
what we see in humans.For example, baboons and humans share the trait of having long legs. In humans, this is because
about 1.7 million years ago, our ancestors moved into open savanna habitats, like those baboons live in today, and longer
legs enabled them to move over long distances more efficiently. Baboons independently evolved longer arms and legs
for the same reason—to be able to cover more ground, more efficiently, in an open habitat. This means that having long
legs is an analogous trait in baboons and humans—that is, this adaptation evolved independently in the two species but
for the same purpose.
Conclusion
The Order Primates is a diverse and fascinating group of animals united in sharing a suite of characteristics—visual
specialization, grasping hands and feet, large brains, and extended life histories—that differentiates us from other groups
Meet the Living Primates | 32
of mammals. In this chapter, we surveyed the major taxonomic groups of primates, discussing where humans fit among
our close relatives as well as discovering that primates are interesting animals in their own right. We discussed a
range of key traits used to distinguish between the many taxa of living primates, including dietary, locomotor, and
behavioral characteristics. Because of our long, shared evolutionary history with these animals, non-human primates
provide a crucial resource for understanding our current biology.In the next chapter, you will discover the fascinating
and complex social behaviors of non-human primates which provide further insight into our evolutionary biology.
Review Questions
• Why does the field of anthropology, a field dedicated to the study of humans, include the study of
non-human animals? What important things can we learn from non-human primates in
anthropology?
• One of the important goals of an introductory biological anthropology course is to teach you about
your place in nature. What is the full taxonomic classification of humans, and what are some of the
traits we have of each of these categories?
• When you have seen primates in person, did you observe any facial expressions, behaviors, or physical
traits that seemed familiar to you? If so, which ones and why?
• Why is it important to try to place taxa into a clade classification rather than groupings based on
grade?Can you think of an example?
• Draw out a tree showing the major taxonomic group of primates described here, making sure to leave
room in between each level. Underneath each taxon, list some of the key features of this group so that
you can compare traits between groups.
Key Terms
Activity pattern: Refers to the time of day an animal is typically active.
African clade: A grouping that includes gorillas, chimpanzees, bonobos, humans, and their extinct relatives.
Analogy: When two or more taxa exhibit similar traits that have evolved independently, the similar traits evolve due to
similar selective pressures. (Also sometimes called convergent evolution, parallel evolution, or homoplasy.)
Arboreal: A descriptor for an organism that spends most of its time in trees.
Asian clade: A grouping that includes orangutans and their extinct relatives.
Bilophodont: Molar pattern of cercopithecoid monkeys in which there are usually four cusps that are arranged in a
square pattern and connected by two ridges.
Bipedalism: Walking on two legs.
Brachiation: A form of locomotion in which the organism swings below branches using the forelimbs.
33 | Meet the Living Primates
Bunodont: Low, rounded cusps on the cheek teeth.
Canines: In most primates, these are the longest of the teeth, often conical in shape and used as a weapon against
predators or others of their species.
Cathemeral: Active throughout the 24-hour period.
Clade: A grouping based on ancestral relationships; a branch of the evolutionary tree.
Cusps: The bumps on the chewing surface of the premolars and molars, which can be quite sharp in some species.
Dental formula: The number of each type of tooth in one quadrant of the mouth, written as number of incisors:
canines: premolars: molars.
Derived trait: A trait that has been recently modified, most helpful when assigning taxonomic classification.
Diastema: A space between the teeth, usually for large canines to fit when the mouth is closed.
Dichromatic: Being able to see only blues and greens.
Diurnal: Active during the day.
Dry nose: The nose and upper lip are separated and the upper lip can move independently; sometimes referred to as a
“hairy” or “mobile” upper lip.
Ethnoprimatology: A subarea of anthropology that studies the complexities of human-primate relationships in the
modern environment.
Evolutionary trade-off: When an organism, which is limited in the time and energy it can put into aspects of its biology
and behavior, is shaped by natural selection to invest in one adaptation at the expense of another.
Faunivorous: Having a diet consisting of animal matter: insects, eggs, lizards, etc.
Frugivore: Having a diet consisting primarily of fruit.
Folivore: Having a diet consisting primarily of leaves.
Fovea: A depressed area in the retina at the back of the eye containing a concentration of cells that allow us to focus on
objects very close to our face.
Generalized trait: A trait that is useful for a wide range of tasks.
Grade: A grouping based on overall similarity in lifestyle, appearance, and behavior.
Grooming claw: A claw present on the second pedal digit in strepsirrhines.
Gummivore: Having a diet consisting primarily of gums and saps.
Heterodont: Having different types of teeth.
Homodont: Having only one type of tooth.
Homology: When two or more taxa share characteristics because they inherited them from a common ancestor.
Hone: When primates sharpen their canines by wearing them on adjacent teeth.
Meet the Living Primates | 34
Incisors: The spatula-shaped teeth at the front of the mouth.
Insectivore: Having a diet consisting primarily of insects.
Ischial callosities: A flattened area of the ischium on the pelvis over which calluses form; functioning as seat pads for
sitting and resting atop branches.
Knuckle-walking: A form of quadrupedal movement used by Gorilla and Pan when on the ground, where the front
limbs are supported on the knuckles of the hands.
Life history: Refers to an organism’s pace of growth, reproduction, lifespan, etc.
Locomotion: How an organism moves around.
Male bimaturism: Refers to the alternative reproductive strategies in orangutans in which males can delay maturation,
sometimes indefinitely, until a fully mature, “flanged” male disappears.
Molars: The largest teeth at the back of the mouth; used for chewing; in primates, these teeth usually have between
three and five cusps.
Monochromatic: Being able to see only in shades of light to dark, no color.
Monomorphic: When males and females of a species do not exhibit significant sexual dimorphism.
Natal coat: Refers to the contrasting fur color of baby leaf monkeys compared to adults.
Nocturnal: Active at night.
Olecranon process: Bony projection at the elbow end of the ulna.
Opposable thumb or opposable big toe: Having thumbs and toes that go in a different direction from the rest of the
fingers, allows for grasping with hands and feet.
Pentadactyly: Having five digits or fingers and toes.
Polymorphic color vision: A system in which individuals of a species vary in their abilities to see color. In primates, it
refers to males being dichromatic and females being either trichromatic or dichromatic.
Postorbital bar: A bony ring that surrounds the eye socket, open at the back.
Postorbital closure/plate: A bony plate that provides protection to the side and back of the eye.
Prehensile tail: A tail that is able to hold the full body weight of an organism, which often has a tactile pad on the
underside of the tip for improved grip.
Premolars: Smaller than the molars, used for chewing. In primates, these teeth usually have one or two cusps.
Primitive trait: A trait that has been inherited from a distant ancestor.
Quadrupedalism: Moving around on all fours.
Rhinariums: Wet noses; produced when the nose is connected to the upper lip.
Sagittal crest: A bony ridge along the top/middle of the skull, used for attachment of chewing muscles.
Scent marking: The behavior of rubbing scent glands or urine onto objects as a way of communicating with others.
35 | Meet the Living Primates
Semi-brachiation: A form of locomotion in which an organism swings below branches using a combination of
forelimbs and prehensile tail.
Sexually dimorphic: When a species exhibits sex differences in morphology, behavior, hormones, and/or coloration.
Shearing crests: Sharpened ridges that connect cusps on a bilophodont molar.
Specialized trait: A trait that has been modified for a specific purpose.
Styloid process of ulna: A bony projection of the ulna at the end near the wrist.
Tactile pads: Sensitive skin at the fingertips for sense of touch. Animals with a prehensile tail have a tactile pad on the
underside of the tail as well.
Tapetum lucidum: Reflecting layer at the back of the eye that magnifies light.
Terrestrial: Spending most of the time on the ground.
Tetrachromatic: Having the ability to see reds, yellows, blues, greens, and ultraviolet.
Tooth comb or dental comb: A trait of the front, lower teeth of strepsirrhines in which, typically, the four incisors and
canines are long and thin and protrude outward.
Trichromatic color vision: Being able to distinguish yellows and reds in addition to blues and greens.
Vertical clinging and leaping: A locomotor pattern in which animals are oriented upright while clinging to vertical
branches, push off with hind legs, and land oriented upright on another vertical branch.
Y-5 molar: Molar cusp pattern in which five molar cusps are separated by a “Y”-shaped groove pattern.
About the Author
Stephanie Etting
Sacramento City College
Meet the Living Primates | 36
Dr. Stephanie Etting became hooked on biological anthropology as a freshman at UC
Davis when she took the “Introduction to Biological Anthropology” course. She obtained
her Ph.D. in anthropology in 2011 from UC Davis, where she studied anti-predator
behavior toward snakes in rhesus macaques, squirrel monkeys, and black-and-white
ruffed lemurs. While in graduate school, Dr. Etting discovered her love of teaching and,
since finishing her dissertation, has taught at UC Berkeley; Sonoma State University; UC
Davis; California State University, Sacramento; and Sacramento City College.In addition
to her interests in primate behavior, Dr. Etting is also very interested in primate evolution
and functional anatomy.
Stephanie Etting
For Further Exploration
Animal Diversity Web: https://animaldiversity.org/accounts/Primates/specimens/ This website is hosted by the
Zoology Department at the University of Michigan. It has photograp...
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