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Chapter 33: Mammals Section 1: Mammals Mammals Includes many diverse species that vary greatly in appearance Range in size from a _______________________ to a ____________________________ Mammals can be found flying in the air, running along the ground, and swimming in the sea Although they differ in size and habitats, all members of the ______________________________________ share certain characteristics What Is a Mammal? Mammals are endothermic animals, which means they are able to generate substantial heat ____________________________ Most species are experts at maintaining a constant body temperature Mammals use various combinations of _______________, ________________, and ___________________________________ to conserve body heat Many mammals also have __________________________________ that help cool the body Sweat produced by sweat glands evaporates from the _______________, lowering body temperature whenever necessary With the exception of a few species, all mammals are ___________________________ This means that young mammals develop within the mother for a time and then are __________________________ Female mammals have __________________________________, which produce milk to nourish the young for some time after they are born Mammary glands, which give mammals their name, are probably the most important characteristic that scientists use to include an animal in class Mammalia Mammals have several kinds of _____________________ Combined with their jaws, the teeth of mammals bite, chew, and grind food efficiently Mammals have well-developed breathing muscles, including a ______________________ Mammals have a ________________________________________ Evolution of Mammals The first mammals were __________________________ By the end of the Cretaceous Period, the mammals had split into three groups o ____________________________ Only ________________ species survive today Duckbill platypus o ____________________________ Has a _______________ in which its young lives for a time Kangaroo o ______________________________________________ Mammals you are most familiar with Mice, cats, whales, elephants, etc. Because the fossil record is incomplete, it is hard to say precisely where and when each of these three groups appeared Form and Function in Mammals Mammals have _____________________ and _________________________________ that have evolved many shapes to serve many functions in different environments Feeding Carnivorous mammals, such as cats and dogs, have strong, sharp teeth called _________________________ and __________________________ that are used for biting and ripping flesh from their prey Carnivores use an __________________________________ chopping movement of their jaws to chew their food The behavioral and physical characteristics of many mammals allow them to capture prey Herbivorous mammals, from cows to giraffes, eat plants that are tough and require ____________________________________________ in order to be digested Herbivorous animals have evolved strong ________________ and flat edged incisors that grasp and tear this tough vegetation They chew by moving their jaws from __________________________________, using flattened molars to grind the plant food into a pulp Despite this efficient chewing, the _____________________________ that most plant tissues contain is impossible for mammals to digest on their own The vertebrate digestive system has never evolved the ability to produce enzymes that digest cellulose To help in the digestion of plant material, many grazing mammals have a chamber in their digestive tract called the ____________________, in which newly swallowed plant food is stored and processed for a time The rumen contains thriving colonies of __________________________ that produce enzymes needed to break down cellulose After a certain amount of time, the mammal __________________________________ the plant food from the rumen into its mouth There the partially digested food is again chewed and mixed with saliva _______________________________________ The 2nd time the food is swallowed, it moves through the rest of the digestive tract, where digestion is completed and nutrients are absorbed Some herbivores, such as rabbits, lack a rumen but have a large dead-end sac, or _____________________, forming part of their intestines Many of the same kinds of microorganisms that digest cellulose are found in the cecum The ancestors of modern humans had a cecum, but over time it has shrunk to the small, sometimes troublesome pouch we call the _________________________ Respiration All mammals use _________________ powered by two sets of muscles ___________________________________ pull air in and push air out by moving the ribs up and down to increase and decrease the size of the chest cavity When the large muscles known as the ___________________________ contracts, it pulls the bottom of the chest cavity downward, further increasing the cavity size and causing air to rush into the lungs Many mammals are able to use exhaled air to vibrate their vocal cords and produce a variety of sounds, such as a ____________________, a _______________, or even a _________________ Internal Transport The mammalian circulatory system is an arrangement of ___________________________ ____________________ The main pump, ______________________________, sends deoxygenated blood to the lungs After it leaves the lungs, the now oxygenated blood returns to the heart and is pumped throughout the rest of the body via blood vessels The two separate circuits – one to and from the lungs, the other to and from the rest of the body – efficiently transports gases and nutrients to every cell of a mammal’s body Excretion Mammals have the most highly developed ________________________ of all vertebrates Mammalian kidneys extract nitrogenous wastes from the blood in the form of ________________ Urea, water, and other wastes form _______________________ From the kidneys, urine flows to a urinary bladder, where it is stored until it is eliminated The kidneys can also retain salts, sugars, and other compounds the body cannot afford to lose Response Mammals have the most highly developed ________________________ of any animals The brain consists of three parts: cerebrum, cerebellum, and medulla o ______________________________: thinking, learning, understanding o ______________________________: movement o ______________________________: breathing, heart rate Mammals depend on highly developed senses to provide themselves with information about their environment ___________________ vary a great deal from one mammal species to another With the exception of apes, monkeys, and humans, mammals do not see ___________________ well All mammalian ears are built on the same basic plan, they also vary a great deal in their abilities The senses of smell and taste are often more highly developed in other mammals than in humans More than any other animal group, mammals depend on _________________________ ___________________________ for protection Movement From the four limbs they inherited from their ancestors, mammals have evolved different structures for movement Running mammals can achieve great speeds on level ground Climbing mammals have hands and feet with ____________________________________ that can grasp vines and branches Flying mammals have arms modified to support flaps of skin that form _____________________ Aquatic mammals have arms modified into _______________________________, which they use to control their speed and direction in the water Reproduction The three groups of mammals differ greatly in their methods of reproduction Egg-laying mammals, the ______________________________, are the most primitive mammals and reproduce much like reptiles o Oviparous o Lays eggs that are incubated _________________________ the mothers body o Once the young hatch, however, they nurse on __________________ provided by the mother Marsupials are _____________________________ and bear their young alive The fertilized egg grows into an embryo inside the mother’s reproductive tract The embryo is supplied with nourishment by a __________________________ on the egg Because this yolk is not large enough to nourish the embryo through its entire developmental period, the embryo must leave its mothers womb _________________________________ At such an early age of development, the embryo is unable to survive alone Instinctively, it crawls across its ________________________________ mother’s fur into a pouch called the It spends the next several months there, growing sufficiently large and independent so that it can leave the pouch The early stages of placental embryos are much like those of marsupials But in placental mammals, the embryo’s chorion, amnion, and allantois develop differently Tissues from these membranes join with tissues from the mother’s uterus to form an organ called the ___________________________ Nutrients, oxygen, carbon dioxide, and wastes are exchanged between embryo and mother through the placenta The time the embryo spends inside the uterus is called the _________________________ ___________________ The gestation period of mammals ranges from a few weeks in mice and rats to as long as two years in elephants The gestation period in humans is ___________________________________ After birth, most placental mammals provide their young with a period of care The duration of parental care varies among different species During the time infant and mother live together, the infant learns a great deal about its surroundings from its mother Many biologists believe that this long learning period is one of the most important benefits of the prolonged childhood of many mammals