Table of Contents

• Introduction
• Building on the Mammal Pattern (with mammal images)
• Table of Mammal Characteristics
• What Makes a Primate a Primate?
• Skeletal Features of Primates (with primate images)
• Primate Evolutionary Trends (with primate images)
• Primate Behavior (with primate images)

Introduction

Maybe you just watched a film about Madagascar and met some lemurs jumping and running through the forest. Maybe you visited the zoo and saw gorillas grooming each other and eating leaves. Maybe you passed an elementary school and saw kids swinging on the monkey bars. Or maybe you just looked at your thumb as you picked up a carrot to eat it and thought “wow, that’s pretty cool I can pick things up like that!” In all these scenarios, you are contemplating what it means to be a primate.

Building on the Mammal Pattern

One of the important things to know as we ask “what makes a primate a primate” is that the primate characteristics we see are all built on mammal characteristics. All primates are mammals. This means that based on what we know about mammals, we can assume some basic things about how primates are put together, how they function, and what they do. Four kinds of mammals are pictured below so when you look at the table below about mammal characteristics, you will be able to look for those traits in these pictures.

Click on an image to view larger version & data in a new window Ateles (Red Spider Monkey) shows thermoregulation by his hair for insulation and by sitting in the shade, showing he does not need the sun to maintain body temperature © 2001	Click on an image to view larger version & data in a new window Homo sapiens (Human) children, in the childhood stage unique to humans, are showing their first set of teeth (baby teeth) the first of two sets mammals have to promote nutritional efficiency © 1993 Ethan Michelson
Click on an image to view larger version & data in a new window Orycteropus afer (Aardvark) shows one way of moving - quadrupedally, or on four limbs. How do these other mammals move? © 2001	Click on an image to view larger version & data in a new window Diceros bicornis (Black rhinoceros) Notice the environment these rhinos occupy and think about the different environments that are illustrated in these pictures that can all be occupied by mammals © 2000 Greg and Marybeth Dimijian

Table of Mammal Characteristics

Trait	This means they can	They have
Thermoregulation	Maintain and change body temperature	Hair to insulate, sweat glands to cool off, and are “warm-blooded” so unlike reptiles, they don’t have to be in a sunny spot to stay warm
Nutritional Efficiency	Eat and digest a lot to keep themselves going	A hard palate that divides chewing and breathing apparatus so they can eat and breathe at the same time, two sets of teeth over the lifetime and several different kinds of teeth for different functions
Locomotion and Posture	Move in many different ways	A variety of options when traveling through the environment and seeking food
Multiple, Developed Life Stages	Spread growth and development over a longer period	Four main stages: In Utero Infancy Juvenile Adult Humans add Childhood between Infancy and Juvenile
Behavioral Flexibility	Change behavior to cope with changes in the environment	A better chance of using resources, surviving and reproducing due to larger brains

See Morbeck, Galloway and Zihlman's book The Evolving Female for more on what it means to be a mammal and how primates build on those mammal characteristics.

What Makes a Primate a Primate?

We look at 3 kinds of evidence:

• Skeletal Features
  • Related to teeth and snout
  • Related to eyes and ears
  • Related to arms and legs
  • Related to fingers and toes
• Primate Evolutionary Trends
• Primate Behavior

Note: The primate characterisitics below are drawn mainly from Falk's Primate Diversity, with additional information from Fleagle's Primate Adaptation and Evolution.

Skeletal Features Related to Teeth and Snout

• Shortened snout
  • Why? Primates rely less on their sense of smell and more on vision. Primates also have a reduced number of teeth as compared to other mammals.
• Several types of teeth: incisors, canines, premolars, molars
  • Why? With different types of teeth, they can eat a variety of foods and process food efficiently. They have incisors for biting, canines for shearing and premolars and molars for crunching food into digestable packages.

Click on an image to view larger version & data in a new window Cercopithecus aethiops (Vervet or Green Monkey). Notice his small snout © 1999 Greg and Marybeth Dimijian

Click on an image to view larger version & data in a new window Cercopithecus aethiops (Vervet or Green Monkey). Notice this monkey's tooth display, showing off canine teeth © 2000 Greg and Marybeth Dimijian

Skeletal Features Related to Eyes and Ears

• Forward facing eye orbits
  • Why? Primates have an increased emphasis on vision, so natural selection acted to position the eyes best for taking in the most visual stimuli.
• Stereoscopic vision
  • Why? Stereoscopic vision means that the fields of vision provided by each eye overlap, resulting in what's called depth perception. This is extremely useful for forest-dwelling primates, as it lets them judge how far away the next branch is as they are moving from tree to tree.
• Three bones of the middle ear housed in a skull outgrowth (the auditory or petrosal bulla)

Click on an image to view larger version & data in a new window Pan troglodytes schweinfurthii (Common chimpanzee) Notice his forward facing orbits. This is a portrait of a high-ranking male from Gombe National Park in Tanzania © 2005 David Bygott

Click on an image to view larger version & data in a new window Quercus macrocarpa (Bur Oak) Using your stereoscopic vision, you can see that some of the branches of the oak tree are closer than others. Without that depth perception, all the branches would look flat and equally far away from you. Image courtesy of the US Forest Service, St. Paul Field Office.

Skeletal Features Related to Arms and Legs

• Clavicles (collarbones)
  • Why? Primates have very extensive shoulder motion because the clavicle provides the only bony link between the upper limb and the trunk.
• Two separate bones in the forearm and lower leg
  • Why? Having two bones allows for better limb motion and more precise movements.

Click on an image to view larger version & data in a new window Pan troglodytes schweinfurthii (Common chimpanzee) This photo shows a female chimpanzee with an infant begging for meat from the males who have captured a small monkey. Note that her arm is raised, showing the range of shoulder motion common to primates © 2005 David Bygott

Click on an image to view larger version & data in a new window Nycticebus pygmaeus (Pygmy loris) This loris is descending a branch, taking advantage of the limb motion afforded by two bones in the primate forearm and lower leg.

Skeletal Features Related to Fingers and Toes

• Nails instead of claws
  • Why? Nails allow primates to manipulate objects more easily.
• Increased thumb mobility
  • Why? Again, related to manipulating objects. As you move across the primate order from lemurs and lorises to great apes, including humans, the thumb becomes more and more mobile
• Grasping feet
  • Why? Primates have more big toe mobility for grasping and climbing. The only exception is humans (Homo sapiens). We have lost the grasping ability in our feet because our feet are designed to serve as a platform for walking

Click on an image to view larger version & data in a new window Papio anubis (Olive baboon) Notice how this baboon is manipulating his meal with his mobile thumbs © 2005 David Bygott

Click on an image to view larger version & data in a new window Lemur catta (Ring-tailed lemur) Look at the grasping hands and feet on this mother lemur.  Her baby also has good grasping ability, as it hangs on to mom's back as she travels © 2000 Greg and Marybeth Dimijian

Primate Evolutionary Trends

• Trend toward more vertical posture
  • Why? Primates tend to move with a more vertical posture, even if they are rarely upright.
• Trend toward different use of forelimbs and hindlimbs
  • Why? Primates use their limbs for more than just locomotion (moving around)
• Trend toward longer lives with longer periods of infancy, childhood and adulthood
  • Why? Longer lives and longer life stages are good for increased growth, especially brain growth. Primates have larger brains for their body size than a lot of other mammals, and are born with brains that still need to develop quite a bit outside of the mother’s body. Primates also spend a lot of time learning skills and strategies for food gathering and survival from their mothers and others in their social groups.
• Trend toward enlarged brains with increased areas for vision and reduced areas for olfaction

Click on an image to view larger version & data in a new window Indri indri (Indri) Though this indri moves by clinging to tree trunks and using powerful hindlimbs to leap from tree to tree, it maintains the more vertical posture seen in many primates © 2000	Click on an image to view larger version & data in a new window Pan troglodytes schweinfurthii (Common chimpanzee) The chimpanzee in the foreground of the photo is using its hindlimbs to stand upright and its forelimbs to insert a stick into a termite nest (in the very front of the photo) to capture the termites to eat © 2005 David Bygott
Click on an image to view larger version & data in a new window Pan troglodytes schweinfurthii (Common chimpanzee) This mother cradles her day-old infant © 2005 David Bygott	Click on an image to view larger version & data in a new window Homo sapiens (Human) Notice how large the braincase of this skull is as compared to the face, reflecting the enlarged brain of primates © 2005 Kathryn Orzech

Primate Behavior

So what do primates DO that makes them primates? They spend time:

• Using their limbs to climb in trees by grasping with hands and feet
• Using their hands to bring food to their mouth for feeding
• Being a part of social group life, building and reinforcing bonds between individuals and learning from their mothers and others

Click on an image to view larger version & data in a new window Eulemur mongoz (Mongoose lemur) Notice how this lemur is climbing by grasping.	Click on an image to view larger version & data in a new window Saimiri sciureus (Squirrel monkey) Look at how this monkey is bringing food to its mouth with its hands © 2001
Click on an image to view larger version & data in a new window Papio anubis (Olive baboon) This picture shows an infant baboon nursing and being groomed by another member of its troop © 2005 David Bygott	Click on an image to view larger version & data in a new window Pongo pygmaeus (Orangutan) Orangutans rely solely on their mothers to teach them how to survive in the world.  It is typical for an orangutan to stay with its mother until it is 7 years old © 2001

References

1) Falk, Dean. 2000. Primate Diversity. W.W. Norton & Company, Inc. New York, NY.

2) Fleagle, John G. 1999. Primate Adaptation and Evolution. 2nd Ed. Academic Press. San Diego, CA.

3) Morbeck, Mary Ellen, Alison Galloway and Adrienne L. Zihlman, Eds. 1997. The Evolving Female: A Life History Perspective. Princeton University Press. Princeton, NJ.

Learning Information

• ToL Learner Level:
  • Intermediate; Advanced
• Target Grade/Age Level:
  • All Grade/Age levels.