Ch. 32

Introduction to the Mammals

Mammals are characterized by hair and mammary glands. In addition to having hair and the ability to nourish their young with milk, all mammals breathe, air have four-chambered hearts, and are endotherms that generate their body heat internally.

Evolution of Mammals

  • Mammals not only are defined by fur and glands but also by a lower jaw and large teeth.

  • Mammals descended from reptiles during the Carboniferous Period.

    • The first true mammals appeared during the late Triassic Period, about 220 million years ago.

  • During the Cretaceous Period mammals were small and remained out of sight.

    • Most likely nocturnal.

  • After the dinosaurs became extinct mammals began to grow.

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Form and Function in Mammals

Body Temperature Control

  • Mammals are endotherms; meaning they generate heat quickly.

  • They have external body hair to keep them warm.

    • Subcutaneous fat: a layer of fat located beneath the skin, also helps conserve body heat.

  • The ability of mammals to regulate their body heat from within is an example of homeostasis.


  • Mammals eat almost ten times as much as a reptile of the same size because of homeostasis.

  • There are three different kinds of diets in animals, they are: carnivores, herbivores, and omnivores.

    • Carnivores eat only meat.

    • Herbivores eat only plants.

    • Omnivores eat both plants and meat.

  • As mammals evolved, the form and function of their jaws and teeth became adapted to eat foods other than insects.

    • Carnivores have different jaws than herbivores.

  • The intestines in animals are also different depending on what kind of food they have to break down.

    • Rumen: a stomach chamber that cows and relatives have that allow plant food to be stored and processed.


  • All mammals use lungs to breathe.

    • These muscles are put into two sets.

    • Diaphragm: a powerful muscle that pulls the bottom of the chest cavity downward, which further increases it’s volume.


  • Mammalian circulatory system is the heart that is divided into four chambers.

    • Right side receives oxygen poor blood and moves it to the lungs.

    • Left side receives oxygen rich blood and pumps it throughout the whole body.


  • Kidneys extract waste known as urea. Urea combined with water is known as urine.

    • The kidneys of mammals help maintain homeostasis by filtering urea from the blood, as well as by excreting excess water or retaining needed water.


  • Most highly developed brains of any animals.

  • Three main part

    • Cerebrum

    • Cerebellum

    • Medulla Oblongata

  • Outer layer of the brain is known as the cerebral cortex.

  • Different mammals have different stronger senses.

    • For example dogs are known for being able to identify people by their smell.

Chemical Controls

  • Chemicals called hormones affect other organs and tissues.

Fighting Disease

  • The immune systems of animals help them recover when they become sick.

    • This system contains barriers such as skin that prevent harmful pathogens from entering the body.


  • A variety of adaptations have been made in animals to help with movement throughout their bodies.

  • Variations allow different species to run, walk, climb, burrow, hop, pounce, swing, fly, leap, and swim.


  • Internal fertilization is the process by which mammals reproduce.

  • Newborns feed on mother’s milk in all mammals.

    • Some young mammals have a period where the live with the mother and learn the ways to survive from her.

  • Other mammals live in groups.

Diversity of Mammals

The class mammalia contains about 4500 species. The three groups of living mammals are the monotremes, the marsupials, and the placentals.

Monotremes and Marsupials

Monotremes lay eggs. Marsupials bear live young, but at a very early stage of development.

  • Monotremes: egg laing mammals. Their digestive system, reproductive, and urinary systems are similar to reptiles. Only three species of Monotremes exist today, (platypus, anteaters, and echidnas.)
  • Marsupials: Kangaroos, koals, and wombats are examples of marsupials. The development of these mammals take place in the mother's pouch.

Placental Mammals

  • Mice, cats, dogs, whales, elephants, humans, and sea lions all fall in this category. This groups is called placantal, because of the placenta. This is formed when the embryo's tissues join with tissues from within the mother's body.
  • In placental mammals wastes are exchanged in the placenta.
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Biogeography of Mammals

  • During the Paleozoic Era, the continents were one large landmass, and mammals could migrate freely across it. Living mammals reflect the diversity of the events from the late Cenozoic Era.

What is a Primate?

In general, primates have binocular vision, a developed cerebrum, long fingers and toes, and arms that rotate around their shoulder joints.

  • Fingers, toes, and shoulders: normally have five fingers and toes that are very flexible. Their arms are well adjusted to climbing.
  • Well-Developed Cerebrum: display very complex behaviors. For example, they have very elaborate social behaviors.
  • Binocular Vision: the ability to merge visual images from both eyes, thereby providing depth perception and three-dimensional view of the world.
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Evolution of Primates

Primates that evolved from the two earlier branches look very little like monkeys, and the other group of primates known as anthropoids include monkeys, apes, and humans.

  • Prosimians: small, nocturnal primates with large eyes that are adapted to seeing in the dark.
  • Anthropoids: humanlike primates. Two major branches, the New World Monkeys and the Old World Monkeys.

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Hominid Evolution

  • The hominid family displayed several distinct evolutionary trends. They evolved and became able to walk upright. Many factors changed how they were able to walk.
  • bipedal: the ability to use two feet to walk. Changed how they used their hands as tools.
  • opposable thumb: enabled grasping objects and using tools.
  • Brains began to grow in hominids.
  • Early hominids are looked at like the oldest relatives of your family that date back to centuries ago.
  • Australopithecus: lived about 4 million to a million years ago. Spent at least some time in trees. Lucy is the most famous australopithecus and was only about 1 meter tall.
  • Paranthropus: huge, grinding back teeth.
  • Recent hominid discoveries: brains were rather small and facial features resembled those of humans.
  • Sahelanthropus: a fossil whose brain was about the size of a modern chimp's.
  • A large number of species was produced and the relationships between these groups are hard to determine.

The Road to Modern Humans

  • The genus homo: about 2.5 million years ago a new hominid appeared that resembled humans. Homo habilis was the first of several species to arise in Africa. Later a larger species appeared, with a bigger brain and downward-facing nostrils.
  • We originated in Africa. Many researches believe that H. Erectus is the first genus that left Africa. Paleontologists are unsure of when homo sapiens arose.

Modern Homo Sapiens

Two main groups:

Homo neanderthalensis: not only made stone tools, but also lived in organized social groups.

Homo sapiens: people whose skeletons looked like those of humans today. joined neanderthals and lived in what is now Israel, Lebanon, Syria, and Turkey. They lived in similar ways to us.