0840-0840 C32CO BDOL-829900 8/4/04 11:01 PM Page 840 Mammals What You’ll Learn ■ You will identify the charac- teristics of mammals. ■ You will compare and contrast three groups of living mam- mals and examine their rela- tionships to their ancient ancestors. Why It’s Important Mammals play a major role in most ecosystems on Earth because they are one of the most successful groups of ani- mals. Humans are mammals, so studying mammal characteristics provides information about humans as well. Understanding the Photo Giraffes are the tallest mam- mals. Newborn giraffes average 1.8 meters and can grow to be about 5.5 meters as adults. They have long legs and can run quickly—about 60 km/h. Their long legs, as well as their long necks, help them reach leaves in tall acacia trees. Visit ca.bdol.glencoe.com to • study the entire chapter online • access Web Links for more information and activities on mammals • review content with the Interactive Tutor and self- check quizzes 840 Shin Yoshino/Minden Pictures 0841-0847 C32S1 BDOL-829900 8/4/04 10:39 PM Page 841 Mammal Characteristics 32.1 SECTION PREVIEW Objectives Mammals Make the following Foldable to help you identify Distinguish mammalian main characteristics of mammals. characteristics. Explain how the charac- STEP 1 STEP 2 teristics of mammals Fold a vertical Cut along every enable them to adapt to sheet of notebook paper fourth line of only the top layer most habitats on Earth. from side to side. to form tabs. Review Vocabulary metabolism: all of the chemical reactions that occur within an organism (p. 147) STEP 3 Label each tab. New Vocabulary gland mammary gland diaphragm Find Main Ideas As you read Chapter 32, list the main characteristics of mammals on the tabs. As you learn about the main characteristics, write a benefit of the adaptation under the tab for each. Physical What is a mammal? Science Mammals, like birds, are endotherms. The ability to maintain a fairly Connection constant body temperature enables mammals to live in almost every pos- Movement of sible environment on Earth. Mammals have important characteristics not heat through hair Compared to found in other animals. They have hair and produce milk to nurse their solids or liquids, young. Mammals also have diaphragms, four-chambered hearts, special- gases are poor ized teeth, modified limbs, and highly developed brains. conductors of heat. A layer of hair or fur on a Mammals have hair mammal’s skin contains many air Have you ever heard someone complain about a pet that is shedding pockets trapped its hair? There’s no doubt that such a pet is a mammal because hair is between the hair present on all mammals at some point in their lives. Like feathers, shafts. Because air is a poor heat mammalian hair, made out of the protein keratin, is also thought to conductor, heat have evolved from scales. The arrangement of hair provides insulation moves slowly through an air and waterproofing and thereby conserves body heat. If you have ever pocket. As a result, worn a wool sweater made from the hair of a sheep, you know how the rate at which warm wool can be on a cold day. As shown in Figure 32.1 on the next heat is lost by the mammal is page, hair also serves other functions. reduced. Although hair helps retain body heat, mammals also have internal feed- back mechanisms that signal the body to cool off when it gets too warm. Mammals cool off by panting and through the action of sweat glands. 32.1 MAMMAL CHARACTERISTICS 841 0841-0847 C32S1 BDOL-829900 8/4/04 10:40 PM Page 842 Figure 32.1 B The black stripes of a tiger’s fur Hair helps maintain a constant body aid in camouflaging this beautiful temperature. It also serves a variety cat as it hunts for prey. of other purposes. A The sharp, barb-tipped quills of a porcupine are a type of modified hair. C The white patch of hair on the rump of the fleeing deer signals danger to other members of the herd. Panting releases water from the nose You have already learned how sweat and mouth, which results in a loss of glands help keep a mammal cool. body heat. Sweat glands help regulate Mammals also feed their young body temperature by secreting mois- from mammary (MA muh ree) glands, ture onto the surface of the skin. As the possibly modified sweat glands, which om McHugh/Photo Researchers moisture evaporates, it transfers heat produce and secrete milk, a liquid that , (br)T from the body to the surrounding air. is rich in fats, sugars, proteins, miner- als, and vitamins. Mammals nurse their DRK Photo Figure 32.2 Mammals nurse their young young until they are able to digest and lain/ Large mammals usually Chamber Mammals have several types of absorb nutrients from solid foods. have few young. Infer glands, which are a group of cells that Figure 32.2 shows that the number of l)M.C Why do mammals that secrete fluids. They include glands that young each mother has and the length , (b are prey for many predators tend to produce saliva, sweat, oil, digestive of time she nurses her young vary have larger litters? enzymes, hormones, milk, and scent. among species. asemann/DRK Photo Kr A An Indian rhinoceros usually has one calf at a time. Calves begin to graze at two months of age. , (tr)Stephen J ynn/Photo Researchers , (tc)Renee L B Mice have four to nine Dennis/Photo Researchers offspring in each litter, and up . to 17 litters a year. The young nurse for just a few weeks. (tl)Nigel J 842 0841-0847 C32S1 BDOL-829900 8/4/04 10:40 PM Page 843 Respiration and circulation in mammals Mammals need a high level of energy to maintain their endother- mic metabolism. This energy level Compare and Contrast is sustained when large amounts of Anatomy of a Tooth Most mammals have nutrients and oxygen enter the body teeth. Teeth are adapted to a mammal’s diet. and reach the cells. The mammals’ diaphragm helps Procedure ! Examine a prepared longitudinal expand the chest cavity to aid the flow Longitudinal section view slide of a human tooth section of a of oxygen into their lungs. A under low-power magnification. canine tooth diaphragm (DI uh fram) is the sheet of CAUTION: Use caution when working muscle located beneath the lungs that with a microscope and slides. separates the chest cavity from the @ Locate the different areas—enamel, dentine, and pulp cav- abdominal cavity, where other organs ity—that form the tooth. Move the slide to see all areas. are located. Once in the lungs, oxygen # Diagram the tooth as it appears under low power. diffuses into the blood. As the chest cavity returns to its resting position, Analysis air is released. 1. Explain Most of the tooth you studied is composed of the root Mammals, like birds, have four- under the gums. How is the part chambered hearts in which oxygen- above the gum adapted to the ated blood is kept entirely separate diet of humans? from deoxygenated blood. This en- 2. Interpret Scientific sures that a good supply of nutrients Illustrations Examine the and oxygen are delivered to cells which diagrams of mammal skulls and supports their endothermic metabo- predict what kinds of food these mammals might eat based on lism. Circulation also removes waste the shape of their teeth. products from cells and helps regulate body temperature. Blood helps keep a constant cellular environment, which maintains homeostasis. The pointed incisors of moles Most mammals have grasp and hold small prey. The chisel- Physical specialized teeth Science like incisors of beavers are modified Connection Teeth are a distinguishing feature for gnawing. A lion’s canines punc- Teeth as simple of most mammals. Although fishes ture and tear the flesh of its prey. machines Teeth and reptiles have teeth, their teeth are Premolars and molars are used for and chisels are relatively uniform and are used pri- slicing or shearing, crushing, and shaped like wedges. A wedge is a simple marily for tearing, grasping, and grinding. You can get a closer look at machine that holding prey. mammalian teeth in the MiniLab on increases an applied force and changes Mammals with teeth have different this page. By examining the teeth of a its direction. As a kinds that are adapted to the type of mammal, a scientist can determine result, a downward food the animal eats. Think of the dif- what kind of food it eats. force applied to a tooth is changed to ferent tools you might use to build a Many hoofed mammals have an a larger sideways piece of furniture, such as a chisel for adaptation called cud chewing that force. scraping or a saw for cutting. Like a enables the cellulose in plant cell cabinetmaker’s tools, teeth are shaped walls to be broken down into nutri- to match the types of jobs they do. ents they can absorb and use. 32.1 MAMMAL CHARACTERISTICS 843 SIU/Photo Researchers 0841-0847 C32S1 BDOL-829900 8/4/04 10:41 PM Page 844 Have you ever seen cows slowly chewing while lying in a pasture? When plant material is swallowed, it Analyze Information moves into the first two of four pouches in the stomach where cellu- Which animal has the longest digestive system? A mam- mal may be an herbivore, carnivore, or omnivore. Is there a rela- lose in the cell walls is broken down tionship between length of a mammal’s digestive tract and its by bacteria.