2Characteristics of Mammals Mammals are well adapted for terrestrial living and are able to retain water more efficiently than reptiles.The mammalian kidney has an exceptional ability to concentrate waste products in a small volume of urine.
3Characteristics of Mammals HairOf all animal species, only mammals have hair.A hair is a filament composed mainly of dead cells filled with the protein keratin.The primary function of hair is insulation.The dense coat of hair that covers most mammals holds heat in.The coloration and pattern of a mammal’s coat often enables the animal to blend in with its surrounds.Some animals show a seasonal change in the color of their coat.The color of a mammal’s coat may also be a signal, such as the black and white fur of a skunk to warn predators to stay away.
4Characteristics of Mammals In some animals, specialized hairs serve a sensory function.The whiskers of cats and dogs are stiff hairs that are very sensitive to touch.Mammals that are active at night or that live underground often rely on their whiskers or information about the environment.Other specialized hairs can be used as a defensive weapon such as the porcupines sharp, barbed quills.
5Mammalian Teeth Mammals usually have only two sets of teeth. The first set, commonly called baby teeth or milk teeth, is replaced by permanent teeth, which are not replaced if lost or damaged.Animals use their teeth in a variety of ways:To secure and chew food,For protection,As a threat signal,To perform tasks (such as cutting down trees).
6Mammalian Teeth Most mammals have four types of teeth: Incisors,Canines,Premolars,Molars.Each type of tooth performs a different function in eating.
7Mammalian Teeth Incisors, the front teeth, are for biting and cutting. Canines are used for stabbing and holding.Lining the jaw are the premolars and molars.As the mammal chews its upper and lower molars fit together, crushing and grinding the food.A mammal’s teeth are specialized for the food it eats, and it is usually possible to determine a mammal’s diet by examining its teeth.
8Body TemperatureMammals are endotherms, generating heat internally through the rapid metabolism of food.Because a mammal’s body temperature remains relatively constant regardless of the temperature of its surroundings, mammals can be active at any time of the day or night.They also can live in very cold climates.Endothermic metabolism permits mammals to sustain activities that require high levels of energy, such as running or flying long distances.To maintain a high metabolic rate, mammals must eat about 10 times as much food as an ectotherm (of similar size) and have efficient respiratory and circulatory systems for distributing oxygen.
9Respiratory SystemMammalian lungs have a large internal surface area that aids the exchange of oxygen and carbon dioxide.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, drawing air into the lungs.
10Respiratory SystemThe lungs of mammals contain small, grape-shaped chambers called alveoli.Alveoli provide a very large respiratory surface area.In more active mammals, the alveoli are smaller and more numerous, further increasing the surface area for diffusion.
11Heart and Circulatory System Like crocodiles and birds, mammals have a four-chambered heart with a septum that completely divides the ventricle.The division of the ventricle creates two pumping chambers, one for each loop of the mammal’s double-loop circulatory system.
12Heart and Circulatory System One chamber pumps oxygen-rich blood to the body, while the other pumps oxygen-poor blood to the lungs.Because the two do not mix, only oxygen-rich blood is delivered to the tissues.
13Parental CareMammals are unique among vertebrates in the way that they nourish their young after birth.Mammary glands located on the female’s chest or abdomen produce a nutrient-rich energy source called milk and give this class its name.Milk is rich in protein, carbohydrates (sugar lactose), and fat. It also contains water, which prevents dehydration, and minerals, such as calcium, that are critical to early growth.Young mammals are nourished on milk from birth until weaning, the time when their mother stops nursing them.Unlike other vertebrates, young mammals are dependent on their mother for a relatively long period, receiving milk and other food, protection, and shelter from her.
14Today’s Mammals Diversity Reproduction Mammals range in size from tiny shrews that weigh about 1.5 g (less than .1 oz) to gigantic blue whales that can weigh up to 136,000 kg (150 tons).ReproductionAll mammals reproduce by internal fertilization.The male releases sperm into the female’s reproductive tract where one or more eggs are fertilized.Present-day mammals are divided into three groups based on their pattern of development.MonotremesMarsupialsPlacental Mammals
15MonotremesThe most primitive of the mammals are represented by the order Monotremata.All modern monotremes live in Australia, New Guinea, and South America.This distribution may be the result of the movement of these landmasses by continental drift.The three living monotreme species include the duckbill platypus and two species of echidnas (spiny anteaters).
16Monotreme Characteristics Monotremes seem to resemble early mammals.The monotreme species have shoulders and forelimbs that are reptilian in appearance.Monotremes reproduce by laying leathery, shelled eggs.The female monotreme incubates her eggs with her body heat, and at hatching, the newborns are only partially developed.Like birds and reptiles, monotremes have a cloaca, a common passageway for the digestive, reproductive, and urinary systems.No other mammals have a cloaca.Adult monotremes do not have true teeth.
17Monotreme Characteristics Two features monotremes share with other mammals are hair and milk production.Unlike other mammals, monotremes do not have nipples and young monotremes do not nurse.The young lap up milk that oozes from glands located on their mother’s belly.The platypus inhabits lakes and streams.Its broad, flat tail and webbed front feet make it an excellent swimmer.The platypus uses its flat bill to probe for crustaceans, worms and snails.Echidnas are terrestrial and have very strong, sharp claws and an elongated, beaklike snout which they use for burrowing and digging out insects and other invertebrates.
18Marsupial Characteristics Order Marsupialia includes kangaroos, wombats, wallaroos, koalas, and the opossums.In marsupial mammals, the young are born only days or weeks after fertilization (tiny and incompletely developed, except for their front limbs).Without any parental help, the newborns crawl to their mother’s nipples (usually located in a pouch, the marsupium, on her abdomen).Each newborn attaches itself to a nipple and continues to grow and develop for several months.When the young marsupials are able to function on their own, they emerge from the pouch, although they continue to return there to nurse.
19Placental Mammal Characteristics The young of placental mammals develop within the female’s uterus, where they are nourished by nutrients from her blood.An organ called the placenta allows the diffusion of nutrients and oxygen from the mother’s blood, across placental membranes, and into the blood of the developing fetus.Waste materials from the fetus diffuse in the opposite direction and are eliminated by the mother’s excretory system.
20Placental Mammal Characteristics The period of time between fertilization and birth is called the gestation period.Most placental mammals have a longer gestation period than marsupial mammals and their young are more completely developed at birth.Some placental animals like a foal can stand and walk within a few hours of birth. Others like a rabbit are born blind, deaf, and helpless.
21Placental Mammal Characteristics Placental mammals vary greatly in size, shape, diet, and habits.They live in a variety of habitats, from hot, moist rainforests to the frigid tundra.Although mammals share many similarities, species have different characteristics.Some placental mammals are adapted for running, leaping, swimming, or flying.
22Placental Mammal Characteristics Some placental mammals have hooves, horns, or antlers.Hooves are specialized pads that cover the toes of many running mammals.Hooves are made of keratin, a protein that is a component of many mammalian structures.The horns of sheep, cattle, and antelope are composed of a core of bone surrounded by a sheath of keratin.This bony core is firmly attached to the skull, and the horn is never shed.The horn of rhinoceros is composed not of bone but of hair-like fibers of keratin that form a hard structure.
23Placental Mammal Characteristics Other placental mammals, such as deer and elk, grow and shed a set of antlers each year.Antlers grown only by the male, are composed of bone but are not covered by a keratin sheath.While they are growing, the antlers are covered by a thin layer of soft skin called velvet.When the antlers are fully grown, the velvet dries up and comes off.The male uses his antlers during breeding season to attract females and to combat other males.After the breeding season is over, the antlers are shed, and a new pair grows the next year.Because the male grows a larger pair of antlers each year, antler size gives an indication of a male deer’s age.
24Domestic AnimalsDomestic animals are animals that have been kept and bred by people for special purposes.Most domestic animals are placental mammals whose association with humans dates back at least 2,000 years.These animals include dogs, cats, cattle, horses, donkeys, mules, rabbits, sheep, goats, pigs, camels, llamas, and alpacas.Different breeds of domestic mammals have been developed through selective breeding.For example, some breeds of goats produce more milk than others. The milk is used to produce dairy products. Other goats, such as angora goats, are bred for their fine hair that is spun into yarn.Some domestic mammals are hybrids of two different species. Mules are the offspring of a female horse (mare) and a male donkey. Like most hybrids, mules are sterile. The mule’s strength, endurance, and surefootedness make it valuable as a pack animal and for chores such as plowing.
25Modern Placental Mammals There are 19 orders of placental mammals, which include more than 90% of all mammal species.Terrestrial placental mammals inhabit all continents except Antarctica, and aquatic placental mammals inhabit all oceans.
26Order RodentiaOver 40% of all placental mammals are gnawing mammals called rodents.Rodents are distinguished from most other mammals by their teeth, which are specialized for gnawing.All rodents have two pairs of large, curling incisor teeth that grow continuously.As the rodent gnaws, the back side of the incisors wears away faster than the front, creating a sharp chisel edge on the teeth.The success of this group of herbivores can be attributed to their intelligence, small size, and rapid rate of reproduction.Most rodents are small, but a few are larger, like the beaver.
27Order ChiropteraThis order is composed of bats, the only mammals capable of true flight.A bat’s front limbs are modified into wings.The thumb, which is not attached to the wing, has a curved claw that can be used for clinging or grasping.Bats generally live in groups and are active only at night.During the day, bats hang upside down in caves or some other protected place.Most bats are carnivorous, using echolocation to find insects, which they catch while in flight.Other bats eat fruit or nectar from night-blooming flowers.
28Order InsectivoraInsectivores are the mammals most similar to the ancestors of the placental mammals.As their name implies, these small mammals eat mainly insects, but their diet may also include fruit, small birds, and snakes, as well as other insectivores.Insectivores have an enormous appetite, and some such as the shrew must eat more than two times their body weight daily to fuel their extremely high metabolic rate.
29Order CarnivoraSome of the best-known animals are the flesh-eating hunters called carnivores.Scientists generally divide this order into two subgroups, the cat family and the dog family.Carnivores are strong and extremely intelligent, and they have keen senses of smell, vision, and hearing, which have enabled them to become successful hunters.Their long canine teeth are specialized for capturing prey and tearing flesh.Some members of this order are no longer carnivorous.Raccoons and bears are omnivores.Pandas are herbivores.
31Order PinnipediaThis order of marine carnivores includes seals and sea lions that feed at sea but return to land to mate, rear their young, and rest.All four limbs are modified as flippers for swimming, and their bodies are streamlined for rapid movement through the water.An insulating layer of blubber protects them from the cold ocean waters.Most species live in large colonies called rookeries which are headed by a large male.
32Order 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.Most nonhuman primates, like the monkey, are tree dwellers, and many of their characteristic features are adaptations for living in trees.Flexible, grasping hands and feet aid tree-dwelling primates in climbing.Monkeys and prosimians have a tail that is used for balance.The excellent depth perception of the primates is critical for those that live in the trees.Primates are extremely curious and their ability to learn is exceptional.
33Order ArtiodactylaMammals belonging to this order and the Perissodactyla Order are classified as ungulates, mammals with hoofs.Ungulates walk, not on their entire foot as most vertebrates do, but with their weight supported by their hoof-covered toes.Most ungulates are herbivores that live together in herds.The young are well developed at birth and can move along with the herd within a day or two.An ungulate’s main means of defense are the security of the herd and the ability to run very fast when danger approaches.
34Order ArtiodactylaArtiodactyls have an even number of toes within their hooves.Many of these mammals have a stomach chamber called a rumen. Microbes in the rumen break down the cellulose in the plant material artiodactyls eat.Mammals with a rumen regurgitate partly digested food, called cud, rechew it, and swallow it again for further digestion.This order includes pigs, hippopotamuses, camels, deer, antelope, cattle, goats, giraffes, and sheep.
35Order PerissodactylaUngulates with an odd number of toes within their hooves are classified as perissodactyls.This order includes horses, zebras, tapirs, and rhinoceroses.Perissodactyls do not chew their cud.Instead of a rumen, they have a cecum, a pouch branching from their large intestine.The cecum contains microbes that digest the cellulose in their diet.Perissodactyls are far less numerous than artiodactyls.
36Order Cetacea Cetaceans are divided into two groups: The predatory toothed whales, dolphins, and porpoisesThe filter-feeding baleen whales.Whales, such as the orca, are probably descendants of land mammals that returned to the sea about 50 million years ago and have adapted to a fully aquatic life.Their streamlined bodies have front limbs modified into flippers, no hind limbs, and a broad, flat tail for swimming.A nostril called a blowhole is located on top of their head.Cetaceans are very intelligent animals that communicate with each other by making sounds that we hear as a series of clicks.
37Order Lagomorpha This order is composed of rabbits and hares. Like rodents, they have one pair of long, continually growing incisors, but they also have an additional pair of peg-like incisors that grow just behind the front pair.Rabbits and hares have long hind legs and are specialized for hopping.Rabbits build nests that the female lines with fur.The young are born furless and their eyes are closed.Hares do not construct nests.Their young are born with fur and their eyes are open.
38Order SireniaThese somewhat barrel-shaped marine animals include the dugongs and manatees.Like whales, they have front limbs modified as flippers and no hind limbs.A flattened tail is used for propulsion through the tropical oceans, estuaries, and rivers where sirenians live, grazing on aquatic plants.Despite their appearance and habitat, sirenians are closely related to elephants and are often called sea cows.
39Order ProboscideaThe two living species of this order are the African elephant and the Asian elephant.These species are the largest land animals alive today.Their long boneless trunk is really an elongated nose and upper lip and is used for a variety of tasks.An elephant’s upper incisor teeth are modified into long ivory tusks.Elephants live in herds made up of a dominant male, a number of females, and young of varying ages.
40Order EdentataOrder Edentata includes sloths, anteaters and armadillos.These mammals are toothless or with poorly developed teeth that lack enamel, in the ant-eaters they are absent entirely.The feet have well-developed claws, used for digging or hanging, and some edentates walk on the outsides of the feet.They are found only in the Western Hemisphere.
41Order MacroscelideaThe order Macroscelidea includes the elephant shrews.These are ground-dwelling insect eaters with long, flexible snouts, large eyes, and a long tail.They hop about somewhat like small kangaroos.The elephant shrews are active mainly in daytime, but in hot weather they may be nocturnal.The smaller species of elephant shrews feed on ants, termites, and slender shoots, roots, and berries, while some larger species prefer beetles.Elephant shrews live in thorn bush country, grassy plains, thickets, the under-growth of forests, and on rocky outcrops on continental Africa and on the island of Zanzibar.
42Order Scandentia The order Scandentia includes the tree shrews. Scandentia are omnivorous, small, squirrel-like mammals with long snouts, sharp teeth and a bushy tail.Tree shrews are territorial, omnivorous, and extremely active; they dart about constantly in the trees screaming and fighting with one another.They are found in Asia and live mainly on the ground, despite their name.
43Order PholidotaThe order Pholidota includes the pangolins also known as the scaly anteaters.Their body is covered with overlapping, triangular scales.Pangolins break open logs with their large, powerful claws and use their long, slender tongues to lap up insects.When threatened, the animal rolls into a ball and erects the scales, points upward, so that it resembles a large pinecone. It also secretes a foul-smelling liquid.Members of some species are tree dwellers and have prehensile, or grasping, tails; others are terrestrial.
44Order HyracoideaThe order Hyracoidea includes the hyraxes of Africa and SW Asia.These mammals have a rabbit-like body, short ears, four hoofed toes on their front feet and three hoofed toes on their back feet with moist padded soles that cling to steep surfaces by suction, making it an excellent climber.They feed on seeds, fruit, and leaves, and in large numbers can be serious agricultural pests.
45Order DermopteraThe order Dermoptera includes the flying lemurs native to the tropical lowland forests of S Asia, Malaya, and the Philippines.These mammals are squirrel-like that glide on a sheet of skin stretching between their forelegs and hind legs.Although its teeth resemble those of carnivores, the flying lemur's diet consists of fruit and leaves.It sleeps by day and forages at dusk.
46Order TubulidentataThe order Tubulidentata includes the aardvarks found in Africa and Europe.These mammals are nocturnal, with a pig-like body, big ears, and a long snout that is used to feed on ants and termites.The animal is able to bury its snout in earth and locate and swallow prey while continuing to breathe.The limbs are specialized for digging, which is used as a means of escape from danger as well as to obtain food.