32-1 Introduction to the Mammals

32-1 Introduction to the Mammals
Photo Credit: ©Zefa (RM)/M. Botzek/Masterfile Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall
Mammals Class Mammalia All mammals have two notable features: hair and mammary glands. In females, mammary glands produce milk to nourish the young. In addition to having hair and the ability to nourish their young with milk, all mammals breathe air have four-chambered hearts are endotherms Copyright Pearson Prentice Hall

Evolution of Mammals Evolution of Mammals Mammalian fossils are characterized by a lower jaw with a large, teeth-bearing bone connected directly to the skull by a joint complex teeth that are replaced once in a lifetime distinctive features of the limbs and the backbone. Mammals are descended from ancient reptiles. Ancestors of modern mammals diverged from ancient reptiles during the Carboniferous Period. For millions of years, various mammal-like reptiles lived alongside other reptile groups. Copyright Pearson Prentice Hall

Evolution of Mammals The first true mammals appeared during the late Triassic Period, about 220 million years ago. These mammals were very small, resembling the modern tree shrew. While dinosaurs were dominate during the Cretaceous Period, mammals were generally small and remained out of sight, and were most likely nocturnal, or active at night. Copyright Pearson Prentice Hall

Evolution of Mammals After the extinction of dinosaurs, mammals underwent an adaptive radiation. They increased in size and occupied many new niches. The Cenozoic Era is called the Age of Mammals. Three major groups of mammals had evolved by the beginning of the Cenozoic Era, and surviving members include monotremes, marsupials, and placental mammals. Copyright Pearson Prentice Hall

Form and Function in Mammals
Body Temperature Control Mammals are endotherms. A high rate of metabolism helps mammals generate body heat. Mammals have external body hair that helps them keep warm. Hair is part of the integumentary system: the outer coving of the body, the skin and all associated structures. Subcutaneous fat, which is a layer of fat located beneath the skin, also helps conserve body heat. Copyright Pearson Prentice Hall

Many mammals have sweat glands that help cool the body and are regulated by an internal negative feedback mechanism. If body temperature is too high, the mammal sweats. Evaporation of sweat then cools the body. Mammals that lack sweat glands pant to cool down. The ability of mammals to regulate their body heat from within is an example of homeostasis. Copyright Pearson Prentice Hall

Feeding Because of its high metabolic rate, a mammal must eat a lot of food to maintain homeostasis (as much as 10X the amount of a reptile of similar size). Mammals can be herbivores, carnivores, or omnivores. Certain whales are filter feeders. Early mammals ate insects. Copyright Pearson Prentice Hall

As mammals evolved, the form and function of their jaws and teeth became adapted to eat foods other than insects. The joint between the skull and lower jaw allowed mammals to evolve larger, more powerful jaw muscles and different ways of chewing. Carnivores’ jaws usually move up and down as they chew and herbivores’ jaws move side-to-side. Copyright Pearson Prentice Hall

Canines: Canines are pointed teeth. Carnivores use them for piercing, gripping, and tearing. In herbivores, they are reduced or absent. Canines The specialized jaws and teeth of mammals are adapted for different diets. Carnivorous mammals use sharp canines and incisors to grip and slice flesh from their prey. Their jaws usually move up and down as they chew. Herbivorous mammals use flat-edged incisors to grasp and tear vegetation, and flattened molars to grind the food. Their jaws generally move from side to side. Wolf Horse Copyright Pearson Prentice Hall

Incisors: Chisel-like incisors are used for cutting, gnawing, and grooming. The specialized jaws and teeth of mammals are adapted for different diets. Carnivorous mammals use sharp canines and incisors to grip and slice flesh from their prey. Their jaws usually move up and down as they chew. Herbivorous mammals use flat-edged incisors to grasp and tear vegetation, and flattened molars to grind the food. Their jaws generally move from side to side. Incisors Wolf Horse Copyright Pearson Prentice Hall

Molars crush and grind food. The ridged shape of the wolf’s molars and premolars allows them to interlock during chewing, like the blades of scissors. The broad, flattened molars and premolars of horses are adapted for grinding tough plants. The specialized jaws and teeth of mammals are adapted for different diets. Carnivorous mammals use sharp canines and incisors to grip and slice flesh from their prey. Their jaws usually move up and down as they chew. Herbivorous mammals use flat-edged incisors to grasp and tear vegetation, and flattened molars to grind the food. Their jaws generally move from side to side. Wolf Horse Molars and premolars Copyright Pearson Prentice Hall

A mammal’s digestive tract breaks down and absorbs the type of food that it eats. Carnivores have a short intestine because enzymes quickly digest meat. Herbivores have a longer intestine because tough, fibrous plant tissues take longer to digest. Copyright Pearson Prentice Hall

Many herbivores have specialized digestive organs to break down plant matter. Cows and their relatives have a stomach chamber called the rumen, in which swallowed plant food is stored and processed. It contains symbiotic bacteria that digest the cellulose of plant tissues. After some time, the grazer regurgitates the food into the mouth and the food is chewed and swallowed again. After several such cycles, it moves through the rest of the stomach to the intestines. Copyright Pearson Prentice Hall

Respiration All mammals use lungs to breathe. The lungs are controlled by two sets of muscles. A diaphragm is a large, flat muscle at the bottom of a mammal’s chest cavity that helps in breathing. When an animal inhales, chest muscles lift the rib cage up and out, increasing the volume of the chest cavity. At the same time, the diaphragm pulls the chest cavity down to further increase the volume. The increase in volume pulls air into the lungs. Copyright Pearson Prentice Hall

When an animal exhales, chest muscles lower the rib cage. The diaphragm relaxes, and the volume of the chest cavity decreases. Air is then pushed out of the lungs. Lungs contain alveoli: small sacs, site of gas exchange. Copyright Pearson Prentice Hall

Circulation The mammalian circulatory system has two loops and a four-chambered heart. The right side of the heart receives oxygen-poor blood from the body and pumps it to the lungs. The left side receives oxygen-rich blood from the lungs and pumps it to the rest of the body. Copyright Pearson Prentice Hall

Excretion Kidneys extract nitrogenous wastes from the blood in the form of urea. Urea, other wastes, and water combine to form urine. From the kidneys, urine flows to a urinary bladder, where it is stored until it is eliminated. The kidneys of mammals help maintain homeostasis by filtering urea from the blood, as well as by excreting excess water or retaining needed water. Copyright Pearson Prentice Hall

Kidneys also retain salts, sugars, and other compounds the body cannot afford to lose. They control the amount of water in the body. This enables mammals to live in many habitats in which they could not otherwise survive. Copyright Pearson Prentice Hall

Response Mammals have well-developed brains with three main parts: cerebrum—controls thinking and learning cerebellum—controls muscular coordination medulla oblongata—regulates involuntary body functions Copyright Pearson Prentice Hall

Mammalian Brain Mammals have large brains in proportion to their body size. Most of the brain is taken up by an enlarged cerebrum, which contains a well-developed cerebral cortex. Copyright Pearson Prentice Hall

The cerebrum has a well-developed outer layer called the cerebral cortex, which is the center of thinking and other complex behaviors. Some behaviors, such as reading, are possible only with the human cerebral cortex. Mammals other than humans also exhibit complex behaviors. Mammals rely on highly developed senses to detect and respond to stimuli from their external environment. Many have well-developed senses of smell and hearing. Copyright Pearson Prentice Hall

All mammalian ears have the same basic parts, but they differ in their ability to detect sound. Dogs, bats, and dolphins detect sounds at higher frequencies than humans can - ultrasound. Elephants detect sounds at much lower frequencies - infrasound. The ability to distinguish colors varies among species. Color vision is most useful to animals that are active during the day, or diurnal. Copyright Pearson Prentice Hall

Chemical Controls Mammals have endocrine glands that regulate body activities by releasing hormones. Hormones are substances produced in one part of an organism that affect another part of the same organism. Hormones are carried by the blood to the organs that they affect. Copyright Pearson Prentice Hall

Fighting Disease The immune system helps protect animals from disease, and when they do get sick, it helps them recover. Barriers, such as the skin, prevent pathogens from entering the body. Specialized cells and chemicals recognize and destroy pathogens. Copyright Pearson Prentice Hall

Movement Mammals have backbones that flex vertically and side to side. This flexibility allows mammals to move with a bouncing, leaping stride. Shoulder and pelvic girdles are streamlined and flexible, permitting both front and hind limbs to move in many ways. Variations in limb bones and muscles permit a variety of movements including to run, walk, climb, burrow, hop, pounce, swing, fly, leap, and swim. Copyright Pearson Prentice Hall

The limbs and digits (fingers and toes) of many mammals are adapted to their particular way of life. Note the variety of lengths and shapes of the limb bones. Homologous bones are the same color in all the drawings. The limbs and digits (fingers and toes) of many mammals are adapted to their particular way of life. Note the variety of lengths and shapes of the limb bones that different mammals use for movement. Homologous bones are the same color in all the drawings. Seal Mole Bat Horse Monkey Copyright Pearson Prentice Hall

Reproduction Mammals reproduce by internal fertilization. The male deposits sperm inside the reproductive tract of the female, where fertilization occurs. All newborn mammals feed on their mother’s milk. Young mammals need care from one or both parents when they are born and for a long time afterward. Parental care ensures that young will survive and reproduce. The duration and intensity of parental care varies among different species. Copyright Pearson Prentice Hall

32-1 One characteristic commonly used to determine whether fossils are mammals is subcutaneous fat. mammary glands. a jaw joint that allows movement from side to side. hair or fur. Copyright Pearson Prentice Hall

32-1 How many chambers do mammalian hearts have? 2 3 4 6 Copyright Pearson Prentice Hall

32-1 Mammals are called endotherms because they produce milk to nourish their young. have well-developed sense organs. have powerful jaws and specialized teeth. generate their body heat internally. Copyright Pearson Prentice Hall

32-1 The first true mammals appeared in the fossil record soon after the extinction of the dinosaurs. about the same time as the first reptiles. during the Triassic when dinosaurs were the dominant land animals. long after the extinction of the dinosaurs. Copyright Pearson Prentice Hall

32-1 The duration of parental care in mammals varies among different species. is one to four weeks. is six months to a year. is intermediate compared to reptiles. Copyright Pearson Prentice Hall

32-1 Introduction to the Mammals

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