Biology in the Present The OtherLiving PrimatesCLARK .docx

Biology in the Present: The Other
Living Primates
CLARK SPENCER LARSEN
E S S E N T I A L S O F
PHYSICAL ANTHROPOLOGY
SECOND EDITION
CHAPTER
6
*
Copyright ©2013 W.W. Norton, Inc.
Biology in the Present: The Other Living PrimatesQuestions
addressed in this chapter:Why study primates?What is a
primate?What are the different kinds of primates?
Let’s start with a short, but profound, observation. We are
primates. We share many of the same characteristics as other
primates, like a large brain, a strong parenting instinct, grasping
hands, and generalized teeth. It is important too to recognize
that our close resemblance to many primates is not a
coincidence. Instead, we are so similar to them because we are
related to them; we share a recent common ancestor with them.
In particular, we share a very recent ancestor with the African

apes, a more distance ancestor with the monkeys, and an even
more distant ancestor with the prosimians. Do not make the
mistake of thinking that we study primates as living time-
machines, to somehow go back in time and see how our
ancestors lived. Primates today have evolved too. But, they do
provide us with examples of how a closely related animal has
adapted to its environment, sometimes the same environment
occupied by early human ancestors. In this chapter, we will dive
into the field of primatology. Hopefully, you will be able to see
why we study primates in the first place. We will examine what
exactly a primate is, what features they share in common, and
how one would identify a fossil primate. Finally, we will look at
the different kinds of primates, from lemurs and baboons to
chimpanzees and humans.
*
What is a Primate?Arboreal mammalsDietary plasticityParental
investment
Humans are primates. But, what are primates? Primates are a
group of closely related mammals that live in the tropics. The
map above shows the distribution of non-human primates, found
along the equator in South America, Africa, and Asia. They are
arboreally adapted mammals—possessing many behaviors and
anatomies that help them live a life in the trees. Primates also
display remarkable dietary plasticity—eating a wide variety of
foods from grasses and leaves, compared to other animals.
Finally, among the mammals, primates engage in the highest
amount of parental investment, spending considerable time and
energy in the few offspring they have. Let’s look in more detail
at these characteristics, and the adaptations that help primates
survive.

*
What is a Primate?
This figure has a lot of information on it, so we’ll walk through
it in detail. In the middle is a diorama showing the diversity of
primates that can live in one forest in West Africa. The location
of the forest is shown here in the map in the bottom right corner
of the image. There are 13 different species of primate
represented here, including humans. Notice that most of them
live in the trees. Most live during the daytime, though others,
like the small prosimians, come out at night. Primates have a
generalized skeletal structure, giving them great flexibility
when moving through the trees. Certainly, some species have
evolved specializations, like the long arms of gibbons and the
long legs of humans. Primates have dexterous hands, giving
them grasping ability. This is enhanced by dermal ridges on
their hands and feet, which make their sense of touch more
sensitive. Primates also have forward-facing eyes, which gives
them overlapping visual fields, a greater sense of depth, and
thus enhanced vision. But, this comes at the expense of the
sense of smell, which is reduced in most primates, and results in
a shorter snout than what is found in other mammals.
Importantly, primates have such a generalized tooth structure
that they can eat a wide variety of foods. The teeth shown here
are the upper and lower teeth of the red colobus monkey. Notice
that the different shapes of the incisors, canines, premolars, and
molars give primates the ability to chew up many different
kinds of foods. Humans have the exact same number and kinds
of teeth as other Old World monkeys and apes.
*

What is a Primate? Skeletal StructureMobile jointsHands and
feetPrecision and power grips
Primates tend to have very mobile joints, which allow them to
navigate through the trees, at times in acrobatic ways. They
have mobile shoulders and elbows, and have quite dexterous
hands and feet. An important primate characteristic is the
opposable thumb, which means that the thumb can touch the tips
of the other finders. This anatomy allows primates to grasp
small objects, like thin branches, or insects. With our long,
robust thumbs, humans have the greatest opposability, and this
has allowed humans to possess both a power grip, like our
ability to grasp and wield a hammer, and a precision grip, which
allows us to pick up fine objects, like a pencil.
*
What is a Primate? Skeletal Structure
Most primates, like the chimpanzee shown here on the left, also
have a grasping big toe (hallux), which allows them to climb
trees easily. Humans, and many human ancestors, however, lost
this anatomy as bipedalism became the primary means of
locomotion. Shown on the right is a primate vertebral column,
which consists of five different kinds of vertebrae: cervical
(neck), thoracic (chest), lumbar (lower back), sacral, and
coccyx (tail). Apes in particular tend to have vertically oriented
spines, which is a pre-adaptation to human bipedality. Notice
the s-shaped curvature of the human spine, which positions the

head and hips in the same plane and balances the body in an
upright posture.
*
What is a Primate? Enhanced TouchEnhanced sense of
touchDermal ridgesNails instead of claws
As previously mentioned, primates also have an enhanced sense
of touch compared to other mammals. There are sensitive
dermal ridges on the tips of the fingers, which give us our
unique fingerprints. This sensitivity provides important
information about the texture of objects, which can be food or
the branches many of our primate relatives walk on. In addition
to this, primates are equipped mostly with fingernails, instead
of claws. Claws can be beneficial to some mammals, but are a
bit bulky and would get in the way of a fine precision grip.
Many primates require fine gripping of branches or the insects
they eat, and have evolved nails. Nails can be seen in this
orangutan hand, and, of course, are present on human hands as
well.
*
What is a Primate? Enhanced Vision
Compared to many other mammals, primates also have an
increased reliance on vision. Primates have forward-facing eyes,
as can be seen in this image of an orangutan. Forward-facing, or

convergent, eyes result in the fields of vision produced by each
eye overlapping, giving primates depth perception. This makes
certain primates excellent insect hunters. Additionally, this
depth perception is critical in an arboreal environment: Imagine
leaping from one branch to another without knowing the
distance between them! In many primates, the eye orbit is also
fully encased in bone, protecting this important sense organ.
Additionally, in many primates, color vision evolved, which
was an important adaptation for identifying ripe fruit or insects
in diurnal primates, active during the day. The drawings on the
right show a anthropoid primate (gibbon) at the top, a prosimian
(lemur) in the middle, and a non-primate (raccoon) at the
bottom. Notice that raccoons do not have bone surrounding their
eyes at all. Lemurs have a postorbital bar, which encases the
eye orbit. Anthropoid primates, like the gibbon, or humans,
have an eye orbit fully encased in bone. Of course, there are
always trade-offs in biology, and the enhanced sense of vision
in primates has come at the expense of our reliance on both
smell and hearing. While prosimians retain long snouts and a
rhinarium (the wet nose that most mammals, like dogs, have),
anthropoid primates have short snouts and a dry nose separated
from our mouths by an upper lip.
*
Primate Diets and Teeth
Many mammal species have evolved quite specialized teeth.
Primates, however, have retained the primitive mouth—with
four different kinds of teeth: incisors, canines, premolars, and
molars. This allows primates to eat a wide range of different
foods. Not only do primates have these different kinds of teeth,
but they appear in quite consistent patterns. All Old World

anthropoids, for instance, (monkeys and apes) have a 2/1/2/3
dental formula. That means that in each quadrant of their
mouth, they have 2 incisors, 1 canine, 2 premolars, and 3
molars. Check your own mouth: this is your dental formula.
New World monkeys and many prosimians have an extra
premolar (2/1/3/3 dental formula). Tarsiers are like this too, but
they have lost a bottom incisor for a dental formula of 1/1/3/3
in the lower dentition. This image on the right shows the teeth
from the side (left) and front (right) of five primates from top to
bottom: human, chimpanzee, gorilla, orangutan, and baboon.
Notice that although humans have differently shaped canines,
they have exactly the same number of each tooth type, and the
same 2/1/2/3 dental formula, as all of the other primates shown
here.
*
Primate Diets and Teeth
We will spend some more time on teeth. The reason for this
detailed look at teeth is twofold. First, teeth are very effective
at distinguishing different groups of animals, and this includes
the different primates. Second, teeth are some of the hardest
objects in the body, and they therefore preserve very well in the
fossil record. Much of what we know about fossil primates is
from their preserved teeth. An example of how teeth differ
between different primates is shown at the top. As we just saw,
Old World monkeys and apes have the exact same number of
teeth (they have the same dental formula: 2/1/2/3). That means
monkeys and apes both have three cheek teeth (molars) in each
quadrant of their mouth. So, if you find a fossil molar, how can
you tell if it is from a large monkey or a small ape? One way is
to look at the shape of the tooth. Monkeys have four high ridges

on their teeth—two in the front and two in the back—producing
what is called a bilophodont pattern. But, apes do not. Apes
have five low cusps that form a pattern that looks like the letter
Y. This is called a Y-5 pattern and helps us identify ape teeth.
Similarly, while most monkeys and apes have flat, vertically
oriented incisors, many prosimians have combined their lower
incisors and canines into a scraper-like structure called a tooth
comb, shown here at the bottom. This helps these little primates
extract sap from tree bark.
*
Primate TeethCanine/premolar honing
complexDiastemaSectorial premolar
One final anatomy of the primate dentition we’ll look at is the
canine. We’ve already mentioned that the canine tooth is much
larger in the male compared to the female in primates that
engage in intense male-male competition for access to mating
opportunities. Small canines, or canines that are not sexually
dimorphic, tend to be found more in primates that form long-
term pair bonds. These large upper canines, shown for instance
on this yawning male baboon, serve to warn competitors and
even predators. But, how do these primates keep the canines
sharp as they get older? Through something called the
canine/premolar honing complex. When a primate with a large
upper canine closes its mouth, the upper canine slides into a
space between the lower canine and premolar called a diastema.
This is shown on the lower jaw to the left. Notice, the human
jaw on the right does not have a diastema (or a large upper
canine for that matter). When the canine slides into the
diastema, the back side of the canine rubs against the front side
of the sharp, or sectorial, premolar, keeping that upper canine

nice and sharp. Humans, in contrast, wear the very tip of the
canine when they close their mouths, something called apical
wearing. This dulls the tooth over time, which would not be
beneficial if we used our canines to ward off competitors.
*
What is a Primate? Parental InvestmentPrimates usually have
one offspring at a time.Primates can go several years between
births.Primate mothers care for their offspring for a long period
of time.
Compared to many other mammals, primate mothers are very
dedicated. They give birth to few offspring, and spread out their
births so they can invest time and energy in each of their babies.
For instance, orangutans will have a baby and then nurse and
care for it for up to seven years before having another child.
Chimpanzee mothers, like the one shown here, will go an
average of four years between offspring. These behaviors are
beneficial because of the important role that social learning has
in improving a primate’s chance of survival. Shown here as well
is the growth and development of six different primates: lemurs,
macaques, gibbons, orangutans, chimpanzees, and humans.
Notice that apes tend to have an elongated life history: They
have longer infancy periods, longer childhoods, and longer
overall lives than monkeys or prosimians. Humans are the most
extreme, having a very long childhood and long lifespan.
Related to this stretched-out juvenile period is the opportunity
to learn, and this requires a high level of intelligence.
*

What is a Primate? Brains
Elevated primate intelligence can be seen in the organ of
intelligence—the brain. Compared to other mammals, primates
have large brains. The graph on the right compares the sizes of
the brain (on the y-axis) in mammals of different body mass
(plotted on the x-axis). The average mammal is represented by
the straight line. Notice that primates in general fall above the
line, meaning they have larger brains than expected for a
mammal of their size. Humans in particular have much larger
brains than expected, and we can trace this increase in brain
size (called encephalization) through the human fossil record.
On the left are cartoon drawings of three different primates: a
prosimian, monkey, and ape (a chimpanzee). Notice that the
brain of the chimpanzee is more folded and complex than the
brain of the prosimian. Also notice that the olfactory bulb,
which processes smell, is reduced in monkeys and apes,
compared to prosimians. We have already discussed how the
reliance on the sense of smell is reduced in anthropoid primates,
and even the brain reflects this. Notice, however, that the
occipital lobe is increased in monkeys and apes: This is where
visual signals are processed, and the enlarged size reflects a
greater reliance on the sense of sight in monkeys and apes.
*
What are the Kinds of Primates?
Humans are one of over 200 different species of primates. But,
we are not equally related to all of them. As we discussed in
chapter 2, primates, like all other animals, can be clustered into

closely related nested hierarchies. This is shown in this diagram
here, a family tree known as a phylogeny. By understanding the
phylogeny of living primates today, researchers can determine
which anatomies unite particular groups. This is important
because if researchers find a fossil with a particular anatomy,
they can determine which primate group it most likely is related
to, and also infer when certain features evolved. We’ll get into
some of these features, like upright walking and non-honing
canine teeth, in just a moment. For now, let’s look at the family
tree. The order primates can be split into two suborders,
prosimians and anthropoids. Prosimians are often called lesser
primates because they retain more primitive features than the
more derived anthropoids. But, do not make the mistake of
thinking that living prosimians represent what the earliest
primates looked like. Prosimians have evolved too, and some
features of their teeth are highly specialized and derived.
Interestingly, there are many features that unite one group of
prosimians (tarsiers) with the anthropoids. DNA evidence
supports this grouping as well. Therefore, some researchers will
subdivide primates into a group that includes the anthropoids
AND tarsiers, called haplorhines, while grouping all prosimians
like lemurs and lorises (but not the tarsiers) as stepsirrhines.
Your text uses the prosimian/anthropoid classification.
Anthropoids consist of the monkeys and the apes. But not all
monkeys are equally related. The New World monkeys in South
America, the platyrrhines, are less closely related than the Old
World monkeys (cercopithecoids) and apes (hominoids). These
latter two have the collective grouping of catarrhine. Within the
hominoids are the hylobatids, or gibbons, the pongids (great
apes—gorilla, chimpanzee, bonobo, and orangutan), and
hominids (humans). Let’s look at how the hominoids are
grouped together and named.
*

Classifying Primates
Based on anatomical similarities and differences, researchers
have historically grouped humans separately from the other
apes. Gibbons had their own grouping—the hylobatids—or
lesser apes. All of the great apes were thought to be closely
related to one another in the pongid family, and humans had
their own family—hominid. This all changed with the use of
DNA to determine which animals are most closely related to
humans. It turns out, the great apes are NOT all equally related
to one another. In fact, chimpanzees and bonobos are more
closely related to humans than they are to the other apes. This
new genetic classification groups humans and members of the
genus Pan (chimpanzees and bonobos) together in the subfamily
hominine. All of the great apes, including humans, are in the
hominid family and together with gibbons comprise the
hominoid superfamily. So, what do we call just the humans and
extinct human ancestors? In the first scenario, we called them
hominids. But, in the second genetic classification scheme,
hominids includes all of the great apes. So, the word we use for
just the human ancestors is “hominin.” So, which classification
scheme is better? Most researchers have adopted the genetic
classification scheme since it portrays the actual relationships
between these organisms. But, the first classification scheme
allows us to examine the adaptive shift humans took relative to
the other great apes, and thus we’ll use the anatomical
classification in these lectures. But, let’s get back to those other
primates, starting first with the prosimians.
*
Prosimians: The Lesser PrimatesProsimiansLemursLorises and

GalagosTarsiers
The least related primates to humans are the prosimians. These
are the lemurs, lorises, galagos, and a small primate found in
Asia called a tarsier. The tarsier is shown in this slide. They
have very large eyes to gather what little light there is at night
(they are nocturnal), and the long bones in their feet provide
excellent leverage for leaping through the trees. Prosimian
primates tend to have smaller brains for their body size than
anthropoids have. They rely heavily on their sense of smell for
finding food and therefore tend to have longer snouts than
monkeys and apes. The fossil record indicates that the very first
primates are similar in many ways to modern prosimians.
Prosimians are found today in Asia, Africa, and on the island of
Madagascar. In fact, the island of Madagascar was once home to
one of the largest primates: a gorilla-sized lemur called
Megaladapis. The image on the bottom of the slide shows how
big these lemurs used to be. Identified in the image on the right
are skulls of a mouse-lemur and an indri, the smallest and
largest lemurs on Madagascar today. The other skulls are from
extinct lemurs, many of which went extinct when humans
arrived in Madagascar over 1,000 years ago.
*
Prosimians vs. Anthropoids
Anthropoids and prosimians diverged from one another 40
million years ago. This divergence was, in part, because each
primate lineage evolved slightly different adaptations that
allowed them to survive. Many of these adaptations persist
today in the living anthropoids. For instance, anthropoids tend

to have larger brains and are more sexually dimorphic then
prosimians. That means that the males are larger and have larger
canines than the females. Anthropoids also have an eye orbit
that is fully encased in bone, and can see in color. But, their
enhanced vision has evolved at the expense of smell, which is
more dominant in the prosimians. Anthropoids also have a
generalized diet, and have fewer teeth than most prosimians.
Let’s look at the anthropoids in more detail.
*
Anthropoids: The Higher Primates
PlatyrrhinesNew World primatesBroad-nosed2/1/3/3 dental
formulaSome (ceboids) are suspensory and have prehensile
tails.
There are two infraorders of the anthropoids: platyrrhines and
catarrhines. We’ll start with platyrrhines. These are the New
World monkeys that live in South America. They are named
platyrrhine because their noses tend to be quite broad
(platyrrhine means broad-nosed), with round nostrils and a wide
septum between them. In contrast catarrhines (which means
hook-nosed) tend to have nostrils that are close together and
downwardly pointing as is illustrated here. Platyrrhines can be
identified in two distinct ways. First, they are the only primates
in South America. Second, they have a very distinctive dental
formula: 2/1/3/3. Catarrhines, as we’ll see, have one less
premolar in each quadrant (a dental formula of 2/1/2/3). There
is a group of platyrrhines called ceboids. These are the cebid
monkeys and the ateline monkeys. One type of ateline, called
the woolly spider monkey, is shown here. As you can see in this

image, these monkeys are more suspensory than most other
monkeys, using their arms to support their bodies in a manner
similar to how many apes move through the trees. They also
make use of a fifth appendage—their tails. These monkeys have
a grasping, or prehensile, tail. Though many have the
misconception that all monkeys can hang by their tails, it is
actually quite rare and possible in just a few species of
platyrrhine.
*
Catarrhines:
CercopithecoidsCercopithecoidsColobinesArborealLeaf-
eatingCercopithecinesMixed habitat—arboreal, terrestrialMore
fruit in dietProvide model for behavior of earliest hominids
Catarrhines are monkeys and apes that live in the Old World—
Africa and Asia. They first appear in the fossil record around 30
million years ago. Catarrhines diverged into the two groups—
monkeys and apes—about 25 million years ago. Old World
monkeys, or cercopithecoids, are quite numerous and
successful. They live in a wide range of habitats, have a diverse
diet, and live both on the ground and in trees. Most
cercopithecoids are quite sexually dimorphic. There are two
different subfamilies of cercopithecoid: colobines and
cercopithecines. Images a, b, and c are colobine monkeys—
black and white colobus, gray langur, and the Asian proboscis
monkey. The others are cercopithecines: mandrill, DeBrazza’s
monkey, and the olive baboon. Colobines tend to live in the

trees and eat mostly leaves. They have sharp molars to slice into
leaves and often have a multi-chambered stomach to help with
digestion of plant material. Cercopithecines have a more diverse
diet, consisting of more fruit, and thus have more rounded
molars and lack the multi-chambered stomach. Many
cercopithecine monkeys are well studied—these include
baboons, geladas, macaques, and vervet monkeys. Many of
these cercopithecines live in savanna environments in East
Africa and provide an interesting model for understanding the
evolution of our own lineage, which occupied a similar habitat.
By understanding how these monkeys adapt to their grassland
environment, researchers can gain some insight into how our
own ancestors did the same millions of years ago.
*
Catarrhines: Hominoids
Though cercopithecoids are a model for early human behavior,
we are not cercopithecoids. We are hominoids. Hominoids, or
apes, are large-bodied, large-brained, tailless primates with
broad faces, and a Y-5 pattern on the lower molars. Shown here
are, across the top, chimpanzees, bonobos, and orangutans, and
across the bottom, gorillas and gibbons. Keep in mind, however,
that humans belong in this grouping too. Chimpanzees,
bonobos, and gorillas live in Africa, while orangutans and the
lesser apes (gibbons and siamangs) live in the forests of
Southeast Asia.
*

HominoidsY-5Sagittal crest
As has already been discussed, apes have a Y-5 pattern to their
lower molars, quite distinct from the bilophodont pattern seen
on Old World monkey teeth. In addition, the large male apes
have huge chewing muscles that are attached to the top of the
skull via a large ridge of bone called a sagittal crest. This
feature appears in some human ancestors too, so it is useful to
understand it now. If you put your hands on the sides of your
jaw and clench your teeth, you’ll feel the masseter muscle, an
important chewing muscle. Likewise, if you put your hands on
the sides of your skull and bite down, you’ll feel the temporalis
muscle contract and bulge. Imagine if the muscle was not only
on the side of your head, but was large enough to continue to
the very top of your skull. That is the situation in large male
apes, and in some human ancestors. Therefore, by finding a
skull with a sagittal crest, researchers can infer that these
creatures had large chewing muscles and were eating leaves and
plant stems, like modern gorillas eat.
*
HominoidsSuspensoryOrthogradeBrachiationKnuckle-walking
Though there are clearly differences in the skull between apes
and other primates, many of the differences actually reside in
the postcranial skeleton, or the bones below the neck. These
bones are important in locomotion. The non-human apes all

have very long arms and long curved fingers to help them
navigate through the trees, as is shown in the drawing of the
gibbon skeleton on the right. These anatomies allow apes to
engage in suspensory, arm-hanging, postures in which the body
is positioned in an upright, or orthograde, manner. Gibbons are
very suspensory, and these animals can fling themselves from
tree limb to tree limb in a form of locomotion known as
brachiation. The larger apes, like chimpanzees and gorillas, will
often come to the ground and move from food patch to food
patch along the ground (terrestrially). They tuck those long
arms and fingers under their bodies in a quadrupedal form of
locomotion called knuckle-walking. This is shown in the image
on the left, a gorilla bearing most of its weight on its knuckles.
*
Hominoids
What is important to recognize is that the human body plan
generally resembles that of the African great apes. However,
there are some differences, and these differences allow us to
walk on two legs more often and more efficiently than any of
the great apes do. For instance, as can be seen in the drawing on
the left, the position of the hole in the base of the skull for the
spinal cord, the foramen magnum, is toward the back of the
skull in quadrupedal monkeys and apes, but at the bottom of the
skull in humans. Keep in mind why this is important. If we find
a skull, we can tell how it may have moved around its world by
seeing whether the foramen magnum is under the skull or
toward the back. The hip joint is also quite different between
humans and apes, and this results in small anatomical
differences in both the pelvis and the femur. Muscles that
extend the leg in apes are repositioned in humans so that they

help balance the body when we stand on one leg. In fact, the
next time you are walking around, put your hands on your hips
and you will feel these muscles contracting to keep the body
from falling over when you walk (they contract on the same side
as the leg you are standing on). These muscles are crucial for
balancing our bodies during two-legged walking, and they are
able to do so because the pelvis and the femur are shaped a bit
differently in humans compared to apes. If we find a fossil
femur and it is shaped more like a human, we can infer that
these muscles served the same role, and that the creature walked
on two legs, like we do. Notice too in these drawings that
humans have slightly different proportions of our limb bones;
we have longer legs and shorter arms, while other apes have
longer arms and shorter legs. We’ll discuss these differences,
and how we can detect the evolution of these features using
fossils, in later chapters.
*
Biology in the Present: The Other
Living Primates
*
Clark • Spencer • Larsen
Essentials of Physical Anthropology
Second Edition
CHAPTER
This concludes the Lecture PowerPoint presentation for:
6
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