Chapter 35

Mammals

Section 1: The Mammalian Body

Section 2: Today’s Mammals

Section 1

The Mammalian Body

Objectives:

•Describe three functions of hair.•Relate a mammal's teeth to its diet.•Summarize how mammals maintain a high body temperature.•Relate the characteristics of mammals to one mammal, the grizzly bear.•Describe parental care in mammals.

Section 1

The Mammalian Body

Key Characteristics of Mammals

•Hair Mammals are the only animals with hair. The primary function of hair is to insulate a mammal’s body, though it can also provide camouflage or a clear signal through coloration, serve a sensory function, or be a defensive weapon.

Section 1

The Mammalian Body

Mammalian Teeth

•Sets of Teeth Mammals usually have two sets of teeth in their lifetime. Teeth in the second set are not replaced, even if lost or damaged. •Types of Teeth The four types of mammalian teeth are highly specialized: incisors are for biting and cutting; canines are for stabbing and holding; and premolars and molars crush and grind the food.

Section 1

The Mammalian Body

Body Temperature

•Respiratory System The lungs of mammals contain clusters of alveoli that provide a very large internal surface area.•Heart and Circulatory System Mammals are endotherms, generating heat internally through the rapid metabolism of food. Endothermy is made possible by highly efficient respiratory and circulatory systems.

Section 1

The Mammalian Body

Parental Care

•Mammary Glands Mammals nurse their young with milk from the mammary glands of the female.

Section 2

Today’s Mammals

Objectives:

•Recognize how mammals are adapted to different environments.•Compare reproductive patterns in monotremes, marsupials, and placental mammals. •Relate the distribution of monotremes and marsupials to the breakup of Pangaea.

Section 2

Today’s Mammals

Mammalian Diversity

•Diversity In terms of anatomy and habitat, mammals are the most diverse of all vertebrate groups.

Section 2

Today’s Mammals

Reproduction

•Internal Fertilization All mammals reproduce by internal fertilization.•Monotremes Monotremes consist of three species that have a cloaca and lay eggs.•Marsupials Marsupials give birth to incompletely developed young that complete their development in the mother’s pouch.•Placental Mammals Placental mammals nourish their unborn young in the uterus through the placenta.

Section 2

Today’s Mammals

Modern Placental Mammals

•Order Rodentia Over 40 percent of all placental mammals are gnawing mammals called rodents.•Order Chiroptera Chiroptera is composed of bats, the only mammals capable of true flight.•Order Insectivora Insectivores are the mammals most similar to the ancestors of the placental mammals.•Order Carnivora Some of the best-known animals are the flesh-eating hunters called carnivores.

Section 2

Today’s Mammals

Modern Placental Mammals continued

•Order Pinnipedia This order of marine carnivores includes seals and sea lions that feed at sea but return to land to mate, rear their young, and rest. •Order Primates Humans belong to the order Primates. Other members of this order include the prosimians, which are active at night, and monkeys and apes, which are active during the day.•Order Artiodactyla Mammals belonging to this order and the following order, Perissodactyla, are classified as mammals with hoofs.

Section 2

Today’s Mammals

Modern Placental Mammals continued

•Order Perissodactyla Ungulates with an odd number of toes within their hooves are classified as perissodactyls.•Order Cetacea Cetaceans are divided into two groups: the predatory toothed whales, dolphins, and porpoises, and the filter-feeding baleen whales.•Order Lagomorpha This order is composed of rabbits and hares. •Order Sirenia These somewhat barrel-shaped marine animals include the dugongs and manatees.

Section 2

Today’s Mammals

Modern Placental Mammals continued

•Order Proboscidea The two living species of this order, the African elephant and the Indian elephant, are the largest land animals alive today.