CHAPTER 28. Mammals 28-1

Transcription

1 CHAPTER 28 Mammals 28-1

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3 Features and Diversity Features and Diversity Characteristics Hair Protection, concealment, waterproofing and buoyancy, signaling, sensory function, and thermal insulation Most are placental Specialized teeth and jaws for processing diverse foods in most Nervous system more advanced than in other animal groups 28-3

4 Features and Diversity Mammary glands nourish the newborn Convoluted turbinate bones in the nasal cavity Provide a high surface area for warming and moistening inspired air and for reducing moisture loss during exhalation 28-4

5 Diversity Features and Diversity Approximately 4800 living species Among the most highly differentiated groups in animal kingdom Domesticated for use as food, clothing, pets, beasts of burden, and in research Exotic mammal introductions have usually disrupted the ecology In 2006, 510 species were listed as critically endangered or endangered 28-5

6 History Origin and Evolution of Mammals Evolution of mammals from earliest amniote ancestors is well documented Over last 150 million years, small, ectothermic, hairless ancestors evolved into today s endothermic, furry mammals Skull structures, especially teeth, provide abundant evidence of evolutionary descent Amniotes classified as synapsids, anapsids, or diapsids 28-6

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10 Origin and Evolution of Mammals Mammals evolved from synapsids that have a pair of temporal openings in the skull Synapsids were first amniotes to radiate widely into terrestrial habitats Anapsids have solid skulls and include turtles and their ancestors Diapsids have two pairs of openings in the skull roof and include dinosaurs, lizards, etc

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12 Therapsid Lineage Earliest synapsids radiated into diverse herbivorous and carnivorous pelycosaurs One of the early carnivorous synapsids gave rise to the therapsids Therapsids were the only synapsid group to survive beyond the Paleozoic Therapsids were first to have an efficient erect gait with upright limbs beneath body Most of the variety of herbivores and carnivores disappeared in the Permian extinction The cynodonts were the only therapsid Origin and Evolution of Mammals subgroup that survived

13 Origin and Evolution of Mammals Cynodonts Evolved a high metabolic rate that supported a more active life Enhanced jaw musculature and skeletal changes for greater agility A secondary bony palate permits breathing while holding prey or chewing food Important later to mammal evolution by allowing young to breathe while suckling Heterodont teeth Improved food processing for variety of foods 28-13

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15 Origin and Evolution of Mammals Turbinate bones the nasal cavity aided in the retention of heat Number of ribs reduced Increased flexibility of vertebral column Loss of lumbar ribs correlated with the evolution of a diaphragm Small carnivorous group, trithelodontids, resembles mammals 28-15

16 Early Mammals of the Triassic Period Earliest mammals of late Triassic were small and mouse- or shrew-sized Diphyodonts Teeth replaced only once as deciduous and permanent teeth Believed to have been endothermic although cooler than modern placental mammals Hair was essential for insulation and indicates that sebaceous and sweat glands were present No fossil evidence, but mammary glands must have evolved before end of the Triassic Origin and Evolution of Mammals

17 Origin and Evolution of Mammals Young early mammals would have hatched from eggs and relied on maternal milk All non-mammalian synapsid groups became extinct when the dinosaurs became abundant 28-17

18 Origin and Evolution of Mammals Cenozoic Radiation of Mammals Mammals survived first as shrew-like nocturnal animals Radiation occurred in the Eocene Epoch Attributed to the many habitats vacated by extinction of many amniote groups at the end of the Cretaceous Agile, endothermic, intelligent, adaptable, and gave birth to young they protected Transformation of three middle ear bones Malleus, incus, and stapes 28-18

19 Stapes Origin and Evolution of Mammals Homologous to the columella or hyomandibula of other vertebrates Already functioned in hearing in early synapsids Malleus and incus Originated from articular and quadrate bones that previously served as jaw joint but became reduced in size to better transmit sound vibrations New jaw joint formed between the dentary and squamosal bones Defining characteristic for fossil mammals 28-19

20 Structural and Functional Adaptations of Mammals Integument and Its Derivatives Mammal s skin generally thicker than in other vertebrates Composed of an epidermis and dermis Dermis thicker than the epidermis In regions subject to abrasion, outer layers of epidermis become thicker and cornified with keratin 28-20

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22 Structural and Functional Adaptations of Mammals Hair Characteristic of mammals Reduced on humans and exists as a few bristles on whales Hair follicle is an epidermal structure, but lies in dermis of skin A hair grows continuously by rapid proliferation of cells in the follicle Cells in hair shaft are shifted upward away from their source of nourishment, accumulate keratin, and die Keratin is same protein as is found in nails, claws, hooves and feather 28-22

23 Structural and Functional Adaptations of Mammals Dense and soft underhair Serves as insulation by trapping a layer of air Coarse and longer guard hairs Protect against wear and provide coloration Hair consists of three layers Medulla is in the center of the hair Cortex with pigment granules lies outside medulla Cuticle is outermost layer and composed of imbricated scales 28-23

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25 Structural and Functional Adaptations of Mammals Different mammals have unique hair structure Brittle hairs of deer are deficient in cortex Hollow, air-filled hairs of the wolverine are deficient in medulla Hairs of rabbits and others are scaled to interlock when pressed together Curly hair of sheep grows from curved follicles 28-25

26 Structural and Functional Adaptations of Mammals Hair stops growing at a certain length Remains in follicle until new growth pushes it out In most mammals, there are periodic molts of the entire coat Foxes and seals shed once every summer Most mammals molt twice, in the spring and in the fall, with the winter coat much heavier Some have white winter coats for camouflage and brown summer coats Arctic mammals are not genetically albino where eye and skin pigments are also missing White winter fur is result of leukemism; animals have dark eyes, dark-colored ear tips, noses, etc

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28 Structural and Functional Adaptations of Mammals Patterns including spots, stripes, salt-andpepper, etc. are disruptive and conceal the animal Vibrissae or whiskers are sensory hairs Provide a tactile sense for nocturnal mammals Porcupine, hedgehog, and echidna quills are barbed and break off easily 28-28

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30 Structural and Functional Adaptations of Mammals Horns and Antlers True Horns Found in ruminants such as sheep and cattle Hollow sheaths of keratinized epidermis Surround a core of bone rising from skull Normally not shed and are usually not branched, but may be curved Grow continuously and occur in both sexes May be longer in males 28-30

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32 Structural and Functional Adaptations of Mammals Antlers Formed in the deer family Composed of solid bone when mature Develop beneath an annual spring covering of highly vascular soft skin or velvet Except for caribou, only males produce antlers When growth is complete just before breeding season Blood vessels constrict in velvet Velvet removed by rubbing antlers against trees 28-32

33 Structural and Functional Adaptations of Mammals Antlers are shed after breeding season and a new bud appears for the next growth Each year, the new pair of antlers is larger than the previous set Growing antlers may require a moose or elk to accumulate over 50 pounds of calcium salts Rhinoceros Horn Hairlike keratinized filaments arise from dermal papillae and are cemented together Not attached to the skull 28-33

34 Glands Mammals have the greatest variety of integumentary gland All derived from epidermis Sweat glands are tubular, highly coiled glands found in mammals Eccrine Sweat Glands Secrete a watery fluid that draws heat away from the skin surface Found in hairless regions such as footpads in most mammals and scattered all over body in horses and primates Ecrine sweat glands are reduced or absent in rodents, rabbits and whales Structural and Functional Adaptations of Mammals

35 Structural and Functional Adaptations of Mammals Apocrine Sweat Glands Larger than eccrine glands with longer, convoluted ducts Glands may be present in dermis or hypodermis Apocrine glands open into hair follicles In humans, they develop near puberty and are restricted in distribution Secretion is milky and dries to form a film on the skin Do not function in temperature regulation and are correlated with reproductive function 28-35

36 Structural and Functional Adaptations of Mammals Scent Glands Present in nearly all mammals Vary in location and function Allow for communicate with members of the same species Mark territory, warning and defense signals Scent glands of skunks, minks, and weasels open into the anus and are very odoriferous Many mammals release strong scents during the mating season to attract opposite sex 28-36

37 Structural and Functional Adaptations of Mammals Sebaceous Glands Most associated with hair follicles May open directly onto the skin surface Glandular cells produce an oily secretion, sebum Lubricates skin and hairs Most mammals have sebaceous glands over the entire body 28-37

38 Structural and Functional Adaptations of Mammals Mammary Glands Modified apocrine glands Rudimentary in males and occur on all females Epidermis thickens to form a milk line along each side of abdomen Mammae located along milk line Human females develop mammary glands at puberty Other mammals have swollen mammae periodically when pregnant or nursing Mammary glands increase in size at maturity 28-38

39 Structural and Functional Adaptations of Mammals In most mammals milk is secreted from mammary glands via nipples or teats Exception: Monotremes lack nipples and simply secrete milk into a depression on the mother s belly where it is lapped up by young 28-39

40 Structural and Functional Adaptations of Mammals Food and Feeding Mammals exploit a wide variety of food sources Some are specialists and others are generalists Teeth Structure of teeth reveal the habits of a mammal Reptiles have homodont dentition or uniform tooth patterns Differentiation of teeth for cutting, seizing, gnawing, etc., resulted in heterodont dentition 28-40

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42 Structural and Functional Adaptations of Mammals Incisors: Sharp edges for snipping or biting Canines: Specialized for piercing Premolars: Compressed crowns with one or two cusps for shearing and slicing Molars: Larger bodies and variable cusp arrangements for crushing and grinding Primitive mammal tooth formula 3 incisors, 1 canine, 4 premolars and 3 molars Mammals do not continually replace teeth Have one deciduous set and a permanent set Generally, incisors, canines, and premolars are deciduous Molars are a single permanent set

43 Structural and Functional Adaptations of Mammals Feeding Specializations Insectivores Shrews, moles, anteaters, and most bats Due to limited ingestion of fibrous vegetable matter, digestive tract is short Feed primarily on insects 28-43

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45 Structural and Functional Adaptations of Mammals Herbivores Browsers and grazers include horses, deer, antelope, cattle, sheep, and goats Gnawers include rodents, rabbits, and hares Herbivores have reduced or absent canines, but molars are broad and high-crowned Rodents have chisel-shaped incisors that grow throughout life Cellulose is a chain of glucose molecules, but the chemical bonds are difficult to break Herbivores use anaerobic fermentation chambers so microorganisms can metabolize cellulose A side pocket or cecum may also serve as a fermentation chamber and absorptive area

46 Structural and Functional Adaptations of Mammals Rodents eat fecal pellets in order to provide additional fermentation Ruminants have a large, four-chambered stomach Food is regurgitated, re-chewed, and passed to the rumen, reticulum, omasum, and abomasum Herbivores generally have long digestive tracts for the prolonged time needed to digest fiber 28-46

47 Structural and Functional Adaptations of Mammals Carnivores Most feed on herbivores Requires specialization for killing prey High protein diet is easily digestible and, therefore, the digestive tract is shorter Do not have to continuously graze Capturing prey also requires more intelligence, stealth, and cunning In turn, this has driven herbivores to develop keen senses and escape behaviors Some herbivores use size (i.e., rhinos, elephants) or defensive group behaviors Humans have exterminated many carnivores from some areas Production of crops and elimination of carnivores has benefited small rodent pests

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49 Structural and Functional Adaptations of Mammals Omnivores Feed on both plant and animal tissues Include pigs, raccoons, rats, bears, and most primates including humans Many carnivores will switch to fruits, berries, etc. when other food sources are scarce Food supplies in temperate regions vary by season Migration and hibernation are solutions Some mammals store food during times of plenty, a common behavior of rodents 28-49

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51 Structural and Functional Adaptations of Mammals Body Weight and Food Consumption The smaller the animal, the greater is its metabolic rate Requires more food per unit size Amount of food varies in proportion to the body surface area rather than the body weight Surface area is proportional to about 0.7 power of body weight Amount of food a mammal or bird eats is also about 0.7 power of body weight A 3 gram mouse will consume per gram of body weight five times more food than does a 10 kilogram dog and about 30 times more food than does a 50,000 kilogram elephant 28-51

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53 Structural and Functional Adaptations of Mammals Small mammals must spend much more time hunting and eating food than do large mammals A small shrew weighing 2 grams must eat more than its body weight each day and will starve if deprived of food for a few hours In contrast, a mountain lion may kill an average of one deer a week 28-53

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55 Structural and Functional Adaptations of Mammals Migration Few terrestrial mammals make regular seasonal migrations Most remain in a home range More migratory animals in North America than any other continent Caribou migrates twice each year, spanning kilometers ( miles) Gray whales migrate 18,000 kilometers (11,250 miles) between Alaska and Baja, Mexico annually 28-55

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57 Structural and Functional Adaptations of Mammals The fur seal breeds on the Pribilof Islands and then journeys to wintering grounds off the southern California coast Although bats can fly and could migrate similar to birds, most bats hibernate in winter 28-57

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59 Structural and Functional Adaptations of Mammals Flight and Echolocation Mammals have not exploited the skies extensively Bats can fly and some mammals glide from trees Bats are nocturnal or crepuscular (active at twilight) Echolocation, along with flight, allows bats to navigate and eat insects in total darkness Bats inhabit totally dark deep caves, a habitat ignored by other mammals and birds 28-59

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61 Structural and Functional Adaptations of Mammals Bats use frequencies from 30,000 to 100,000 Hz (cycles per second), well beyond our hearing range Ten to 200 pulses of signals are sent to locate prey Echo is received before next pulse is sent Some moths have evolved ultrasonic sensors to detect and avoid approaching bats External ears of bats are large to focus in on sound location Bat navigation may allow bats to build mental image of surroundings similar to visual images 28-61

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63 Structural and Functional Adaptations of Mammals All bats are nocturnal Fruit-eating bats use sight and olfaction to locate food Some flowers evolved to utilize bats as pollinators Produce fragrant white flowers that open at night Tropical vampire bat has razor-sharp incisors and anticoagulant saliva 28-63

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65 Structural and Functional Adaptations of Mammals Reproduction Reproductive Cycles Estrous Cycle Most mammals have mating seasons timed to coincide with most favorable time to give birth and rear young Female usually restrict mating to a fertile period during the estrus cycle Commonly called heat or estrus 28-65

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67 Structural and Functional Adaptations of Mammals Stages of the Estrus Cycle Proestrus: Period of preparation when new follicles grow Estrus: When mating occurs Timed to be simultaneous with ovulation Metestrus: Period of repair that occurs if female does not become pregnant Diestrus: Uterus becomes small and anemic until the cycle repeats Some animals lengthen gestation period by delayed implantation Blastocyst remains dormant Implantation in the uterine wall is postponed to align birth with a favorable season

68 Structural and Functional Adaptations of Mammals Animals with only one breeding season a year are monestrous Recurrent breeding is polyestrous Menstrual Cycle Old World monkeys and humans have a cycle terminated by menstruation Menstruation involves shedding of the endometrium or lining of the uterus Female is receptive to male year round 28-68

69 Structural and Functional Adaptations of Mammals Reproductive Patterns Egg-Laying monotremes Monotremes, such as the duck-billed platypus, lay eggs with one breeding season per year Eggs are fertilized in oviduct before albumin and a thin, leathery shell are added Eggs are layed in a burrow nest and incubated for 12 days No gestation period and egg provides all nutrients After hatching, young nourished by milk lapped off mother s fur near mammary glands 28-69

70 Structural and Functional Adaptations of Mammals Pouched Marsupials Pouched, viviparous mammals Although only eutherians are placental mammals, marsupials do have a primitive choriovitelline placenta Embryo is first encapsulated by shell membranes and floats free in uterus for several days After hatching from shell membranes, embryo erodes a shallow depression in the uterine wall and absorbs nutrient secretions by a vascularized yolk sac Gestation is brief and marsupials give birth to tiny young that are still embryos 28-70

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72 Structural and Functional Adaptations of Mammals Early birth is followed by a prolonged interval of lactation and parental care in mother s pouch In red kangaroos Pregnancy is followed by a 33-day gestation and then birth Mother immediately becomes pregnant again Presence of a suckling young arrests development of the new embryo at the 100-cell stage Period of arrest is called embryonic diapause Possible to stairstep three young with one external, one suckling, and one embryonic With wide variation, marsupials have young born at extremely early stages of development 28-72

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75 Structural and Functional Adaptations of Mammals Placental Mammals Eutherians are viviparous placental mammals Embryo nourished in uterus through a placenta Gestation is longer than in marsupials and is much longer for large mammals Gestation and body size are loosely correlated due to variation in maturity at birth Humans have slower developmental period than any other mammal 28-75

76 Structural and Functional Adaptations of Mammals Patterns Number of young produced per year depends on mortality rate Small rodents that are prey for carnivores usually produce more than one litter each season Meadow mice can produce up to 17 litters of four to nine young each year An elephant produces on average four calves during her 50-year life Although placentals have the advantage of higher reproductive rates Marsupial mode of reproduction may be advantageous in highly unpredictable climates 28-76

77 Structural and Functional Adaptations of Mammals Territory and Home Range An animal may use a burrow or den as the center of its territory If it has no set address, the territory is marked, usually with scent glands A grizzly bear may have a territory of several square kilometers that it defends against other grizzlies When an intruder knows it is in another s territory, it usually flees upon an encounter A beaver represents a mammal that forms a strong monogamous bond that last a lifetime 28-77

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79 Structural and Functional Adaptations of Mammals The male beaver, assisted by the female, expends substantial energy building dams and lodges A prairie dog is unusual in relinquishing its home to the young and moving to the edge of the town A home range of a mammal extends much further beyond the defended territory 28-79

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81 Structural and Functional Adaptations of Mammals Mammalian Populations A population of animals includes all members of a species that can potentially interbreed in a region All mammals live in ecological communities with other animal and plant species Density-independent factors Affect animals regardless of their density Fires, severe weather, etc. Density-dependent factors Related to crowding of populations Infectious diseases The snowshoe hare cycles in population size, apparently due to density-related psychogenic causes 28-81

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84 Humans and Mammals Domesticated Animals Dogs were probably the first domesticated animals, being an adaptable offspring of social wolves The domestic cat is probably derived from an African race of wildcat Nomadic people probably subdued horses, camels, oxen, and llamas Some totally domesticated animals no longer exist as wild species (e.g., dromedary camel, llama) Many have been selectively bred to yield characteristics desirable for human purposes 28-84

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87 Humans and Mammals Mammals, Crop Damage, and Human Disease Rodents and rabbits are major pests of growing crops and stored foods Human monocultures and the elimination of predators have made this a more severe problem Many rodents carry diseases Norway rats and prairie dogs carry bubonic plague and typhus Tularemia is transmitted to humans by wood ticks and carried by rabbits and other rodents 28-87

88 Humans and Mammals Rocky Mountain spotted fever is carried to humans by ticks from ground squirrels and dogs Ticks from white-tailed deer transmit Lyme disease Trichina worms and tapeworms are acquired by humans who eat meat of infected mammals 28-88

89 History Human Evolution Darwin devoted the book The Descent of Man and Selection in Relation to Sex to human evolution At that time there was essentially no fossil evidence linking apes and humans Darwin s evidence was based on anatomical comparisons Two skeletons of Neanderthals were collected in the 1880s 28-89

90 Human Evolution In 1891, Eugene DuBois discovered Java man, Homo erectus Major finds in Africa, between 1967and 1977, provided many intermediates Modern biochemical studies have also shown humans and chimpanzees to be genetically similar 28-90

91 Human Evolution Evolutionary Radiation of the Primates Primates have grasping fingers, flat fingernails, and forward-pointing eyes Ancestral primates split into two major lineages One gave rise to lemurs and lorises (traditionally called prosimians) The other gave rise to tarsiers, monkeys and apes (traditionally called simians or anthropods) Both were probably arboreal Required a large cerebral cortex (for precise timing, judgement of distance, etc.), grasping limbs, and tool use 28-91

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93 Human Evolution Highly developed sense organs aided vision and coordination Earliest simian fossils are from Africa about 40 million years ago Many became diurnal rather than nocturnal Vision became the dominant sense enhanced by color vision Three major simian groups Ceboids: New World monkeys of Central and South America including howler monkeys, spider monkeys, and tamarins Cercopithecoids: Old World monkeys including the baboon, mandrill, and colobus Hominids: Humans, orangutans, and gorillas 28-93

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95 Human Evolution Old World monkeys and apes form the sister group of New World monkeys Old World monkeys Lack a grasping tail, have close-set nostrils, opposable thumbs, and derived teeth Humans, orangutans, gorillas, and chimpanzees are now recognized as belong to a single family, Hominidae, and are referred to as hominids Apes first appear in 25-million-year-old fossils 28-95

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97 Early Humans Human Evolution In the late Pliocene, grasslands replaced forests in eastern Africa The Savannah Hypothesis Proposes that standing upright provided a better view of predators, freed hands for using tools, aided in defense and care of young, and improved food gathering Upright posture required extensive redesigning of the skeleton and muscle attachments Four million year old "Near human" fossils discovered 28-97

98 Human Evolution Australopithecus afarensis Short, bipedal hominid Brain size similar to that of a chimpanzee Numerous fossils of A. afarensis have been discovered, including Lucy by Johanson in 1974 Ardipithecus ramidus Dates to 4.4 million years ago Both ape and humanlike traits Australopithecus anamensis Intermediate between Ardipithecus and A. afarensis 28-98

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101 Human Evolution Hominid lines branched for two million years Bipedal australopithecine lineage produced Australopithecus africanus, a side branch of Paranthropus robustus A. garhi may be the missing link between Australopithecus and Homo In 2001, a remarkably complete skull of a hominid dated at nearly 7 million years ago was discovered in Chad Named Sahelanthropus tchadensis Most ancient hominid yet discovered In last two decades Explosion of australopithecine fossil finds, with eight putative species requiring interpretation

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103 Human Evolution Emergence of Homo The first species of Homo and the definition of the genus are both controversial Three species shared the African landscape with australopithecines Homo habilis Fully erect hominid Used stone and bone tools Appeared about 2 million years ago Survived about 500,000 years

104 Human Evolution One brain cast shows a bulge representing Broca s motor speech area, suggesting that Homo habilis was capable of at least rudimentary speech Homo erectus Dated to about 1.5 million years ago Taller than Homo habilis Larger cranial capacity Had a complex culture and spread throughout the tropical and temperate Old World Disappeared about 300,000 years ago

105 Human Evolution Homo sapiens: Modern Hominids Neanderthals Among the many early subcultures of Homo sapiens, the Neanderthals emerged about 150,000 years ago and occupied most of Europe and the Middle East Proficient hunters and tool-users Robust, heavily muscled bodies allowed them to survive the cold climates of the Ice Age About 30,000 years ago, they were replaced and perhaps exterminated by modern humans Modern humans were tall people with a culture different from the Neanderthals

106 Human Evolution Unique Human Position Mutation, isolation, genetic drift, and natural selection affect human populations Only humans, however, have a non-genetic cultural evolution that provides constant feedback between our past and future experience Symbolic languages, conceptual thought, knowledge of history and an ability to manipulate our environment emerge from this cultural endowment

107 Human Evolution Recent molecular genetic studies indicate that human populations have formed a single evolutionary lineage for the past 1.7 million years The earliest human remains originally classified as Homo sapiens from 500,000 to 300,000 years ago, now are identified by anthropologists as Homo heidelbergensis Fossil and mtdna evidence indicates that characteristics of Homo sapiens, as presently defined, arose in Africa about 200,000 years ago

108 Human Evolution All mtdna can be traced to a single female, Eve who lived in Africa approximately 170,000 years age Neanderthals and remaining Homo erectus disappeared approximately 10,000 years after the first appearance of Homo sapiens in Europe and Eastern Asia