Section 1: Characteristics of Mammals Preview Bellringer Key Ideas Key Characteristics of Mammals Endothermy Specialized Teeth Parental Care Movement and Response Summary

Bellringer Make a list of all the mammals that you can think of. What makes the animals on your list different from birds, reptiles, or other groups of animals?

Key Ideas What are the key characteristics of mammals? How are the respiratory and circulatory systems of mammals adapted for endothermy? What do specialized teeth reveal about mammals?

Key Ideas, continued How do mammals differ from other vertebrates in terms of parental care? What types of locomotion do mammals exhibit?

Key Characteristics of Mammals What makes a mammal a mammal? Mammals are endothermic, they have hair and specialized teeth, and females produce milk in mammary glands to nourish their young. Mammals are the only animals that have hair. Even whales and dolphins have a few small, sensitive hairs on their snouts.

Key Characteristics of Mammals, continued The primary function of hair is insulation. Hair can also help a mammal blend in with its surroundings. The hair of some mammals, such as arctic foxes, changes from white in winter to brown in summer.

Key Characteristics of Mammals, continued The black and white hair of a skunk warns predators to stay away. The thick mane of a male lion advertises how strong the lion is. In some mammals, specialized hairs such as whiskers serve a sensory function.

Visual Concept: Characteristics of Mammals Click the button below to watch the Visual Concept.

Endothermy Like birds, mammals are endotherms, animals that generate heat internally through metabolism of food. Unlike most amphibians and reptiles, mammals can live in very cold climates. Endothermy enables mammals to become very active.

Endothermy, continued Flying and running require a lot of energy and a high metabolism. A mammal needs to eat about 10 times as much food as an ectotherm of similar size does. Metabolizing food requires a lot of oxygen.

Endothermy, continued The respiratory and circulatory systems of mammals are adapted to endothermy. They acquire and distribute oxygen more efficiently than the respiratory and circulatory systems of ectotherms do. Respiratory System The lungs of mammals have a larger internal surface area than do those of reptiles or amphibians.

Endothermy, continued Mammals can exchange more oxygen and carbon dioxide in each breath then reptiles or amphibians can. Respiration in mammals is aided by the diaphragm, a sheet of muscle that separates the chest cavity from the abdominal cavity. When the diaphragm contracts, the chest cavity enlarges and air is drawn into the lungs.

Endothermy, continued Circulatory System Like birds, mammals have a four-chambered heart. A septum completely divides the ventricles.

Endothermy, continued The left ventricle pumps oxygen-rich blood to the body, while the right ventricle pumps oxygen-poor blood to the lungs. Only oxygen-rich blood is delivered to the tissues, a condition vital for meeting the oxygen needs of endotherms.

Specialized Teeth Unlike most other animals, mammals have specialized teeth that reflect the differences in their diets. A mammal also usually has only two sets of teeth during its life. Baby teeth are replaced by permanent teeth, which are not replaced if lost or damaged.

Specialized Teeth, continued Types of Teeth Most mammals have four types of teeth. Incisors, the front teeth, are used for biting and cutting. Canines, next to the incisors, are used for stabbing and holding. Premolars and molars, at the sides and back of the mouth, are used for crushing and grinding food.

Specialized Teeth, continued One can learn a lot about what mammals eat by looking at the teeth. A carnivore, such as a coyote, has long canine teeth that are suited for grasping prey. Carnivores also have sharp molars and premolars that can cut off pieces of flesh.

Specialized Teeth, continued An herbivore, such as a deer, has small, incisor-shaped canines. It uses its incisors and canines to nip off pieces of plant material. Its premolars and molars are flat and covered with ridges that form a surface on which plant material can be ground.

Visual Concept: Types of Teeth Click the button below to watch the Visual Concept.

Parental Care Unlike the young of other vertebrates, young mammals depend on their mother for a relatively long period of time. They receive milk and other food, protection, and shelter from her. Mammals nourish their young with milk produced in mammary glands, which are located on the female’s chest or abdomen.

Parental Care, continued All mammals reproduce by internal fertilization, but mammals differ in how and where their eggs develop. Mammals are classified into three groups based on their patterns of development. Monotremes Monotremes are oviparous, which means they reproduce by laying eggs.

Parental Care, continued The eggs hatch quickly, and the monotreme mother stays with and nurses the young for several months. The only living monotremes are the duckbill platypus and echidnas. Marsupials Marsupial embryos remain inside their mother for only a few days or weeks.

Parental Care, continued Then, the young marsupial crawls out of the mother, up the fur on her belly, and to her nipples, which are usually located inside a pouch. A young marsupial completes its development inside the mother’s pouch. Placental Mammals Placental mammals complete their development inside the mother.

Parental Care, continued A structure called the placenta attaches the fetus to the mother and allows the exchange of nutrients, oxygen, and wastes. The period of time between fertilization and birth is called the gestation period. Some placental mammals, such as horses, can move around or even run shortly after birth.

Visual Concept: Function of a Placenta Click the button below to watch the Visual Concept.

Movement and Response Mammals use various modes of locomotion, including running, hopping, climbing, burrowing, flying, and swimming. Adaptations in body structure help mammals to move in their particular environment.

Movement and Response, continued Mountain lions have powerful limbs for running and jumping. A bat’s front limbs are modified into wings for flight. The limbs of dolphins and whales are adapted for swimming.

Movement and Response, continued Mammals rely on their senses—vision, hearing, smell, taste, and touch—for survival. The importance of a given sense depends on a mammal’s lifestyle and habitat. Bats and dolphins both use sound to sense their environments, in a process called echolocation.

Visual Concept: Echolocation Click the button below to watch the Visual Concept.

Movement and Response, continued They make high-pitched clicks that spread through air or water. When the sound waves hit an object, such as a moth or a fish, the waves bounce back to the bat or dolphin. The bat or dolphin can use these sound echoes to find their prey or obstacles in the environment.

Summary Mammals are endothermic, they have hair and specialized teeth, and females produce milk in mammary glands to nourish their young. The respiratory and circulatory systems of mammals are adapted to endothermy. Mammals have specialized teeth that reflect the differences in their diets.

Summary, continued Young mammals depend on their mother for a relatively long period of time. They receive milk and other food, protection, and shelter from her. Mammals use various modes of locomotion, including running, hopping, climbing, burrowing, flying, and swimming.