ASIM'S WEBWORLD View: Main School Main AP Biology Chapter Guides RELATED LINKS Review Questions and Answers		AP BIOLOGY: Chapter Forty-Two Outline THE CHORDATES Characteristic Features of the Phylum Chordata fig 42.1 Three principal features Single, hollow dorsal nerve cord Flexible dorsal notochord Pharyngeal slits or pouches General features Segmented body plan, most visible in blocks of embryonic muscle fig 42.2 Internal skeleton against which muscles work A postanal tail that extends beyond the anus Non-Vertebrate Chordates Tunicates fig 42.3 Most specimens are sessile as adults, may be colonial Possess notochord and nerve cord only in adult stage Adults lack body cavity and visible segmentation Adults are filter feeders Create water currents with ciliary action Stream of water drawn into pharynx Food particles trapped in mucus produced by endostyle Adults secrete a cellulose tunic around themselves Colony of individuals may possess common sac and external opening Many possess symbiotic photosynthetic bacteria Tadpole-shaped larvae appear distinctly different from adults fig 42.4 Exhibit most primitive chordate characteristics Do not feed and have a poorly developed gut Some species do not change into sessile adult form Lancelets fig 42.5 Scaleless, fish-like marine organisms Notochord runs entire length of body and persists in adults Segmentation of muscles readily visible HAve more pharyngeal gill slits than fishes Skin only one cell layer thick, lacks pigmentation No obvious head, eyes, nose or ears Filter feeders, create water currents via cilia on anterior end of gut Possess an oral hood with tentacles that extend beyond the mouth True primitive condition, unlikely that they evolved from degenerate fishes Vertebrate Chordates Vertebrates are chordates with a backbone First vertebrates were marine, without jaws or paired fins fig 42.6 Became dominant creatures in the sea Amphibian ancestors first to invade the land Replaced by reptile more suited to live out of water Dinosaurs ruled the earth for 150 million years Mammals became dominant 65 million years ago Characteristics of the vertebrates A vertebral column replaces the notochord Possess a distinct skull (cranium) enclosing the brain Hollow dorsal nerve cord enclosed in a groove in vertebral column fig 42.7 Possess characteristic liver, kidneys, endocrine glands Have a heart and closed blood vessels Circulatory, excretory functions much different from other animals Seven principal classes of vertebrates fig 42.8 Three classes are aquatic fishes Class Agnatha: lampreys and hagfish Class Chondrichthyes: cartilaginous sharks, skates and rays Class Osteichthyes: bony fishes Four classes are terrestrial tetrapods Class Amphibia: salamanders, frogs and toads Class Reptilia: reptiles Class Aves: birds Class Mammalia: mammals FISHES History of the Fishes The first fishes Appeared over 505 million years ago Jawless, toothless filter feeders Breathed with gills, had tail but no fins Only existing vertebrates for 50 million years Developed fins by end of period Had massive bone shields protecting the head and neck Comprised five ostracoderm orders Internal skeleton was made of cartilage Survived by the Agnatha: parasitic lampreys and hagfish fig 42.6 Invention of jaws occurred 410 million years ago fig 42.9 Evolved from modified gill arches, the area between gill slits Gill arch formed by cartilage looking like a sideways V Modifications of arches resulted in modern jaws Teeth evolved from skin that lined the mouth Members of order Acanthodia, spiny sharks Internal skeletons of cartilage Skin scales contained small plates of bone Were predators, more efficient swimmers that ostracoderms Possess maximum of 7 paired fins, reinforced with spines All spiny sharks are extinct Evolution of heavily armored placoderms Dominant during Devonian, extinct by its end Front of body heavily armored, rear was completely naked Jaw improved with upper jaw fused to skull The rise of active swimmers Pioneer vertebrates replaced by sharks and bony fishes fig 41.10 Further improvement of the jaw Superior, streamlined design for swimming Mobile fins for propulsion, stabilization and directional movement Sharks become top predators Occurred more than 287 million years ago, in the Carboniferous Period Shark skeleton is made of cartilage that is calcified Large pectoral fins improved swimming enormously Aggressive predators that achieved large size fig 42.11 Among first vertebrates to develop teeth Teeth sit on top of jaw, not firmly anchored in it Teeth lost readily, replaced by one from row behind Skin covered with tooth-like scales with a sandpaper texture Reproduction in sharks is advanced for a fish Internal fertilization Eggs generally develop in female's body, young born alive Extinction of many varieties at end of Permian Period (249 million years ago) Followed by burst of evolution during age of dinosaurs Flattened skates and rays evolved at this time Bony fishes dominate the sea Class Osteichthyes, bony fish, evolved at same time as sharks Developed heavy skeleton made completely of bone Process of ossification replaces cartilage with bone External plates and scales also ossified Comprise large group called teleosts fig 42.12 Unlike sharks, bony fish evolved in fresh water Had air sacs at back of throat for buoyancy Have highly mobile fins, this scales and symmetrical tails fig 42.13 Became divided into two groups Lobe-finned fish: ancestors of land mammals Ray-finned fish: ancestors of most modern fish Internal skeleton of bony rays supports and stiffens each fin Air sacs transformed into an air pouch for buoyancy The path to land Lobe-finned fishes comprise seven modern species fig 42.14 Paired fins consist of fleshy, muscular lobe supported by bone core Bony rays only at tip of fin Muscles move fins independently of one another Amphibians most certainly evolved from this group Characteristics of Fishes Gills Extract dissolved oxygen from water around them Swallowed water passes over filaments rich in blood vessels Water forced out slits in side of throat Blood moves opposite the flow of water Backbone Internal skeleton with backbone surrounding spinal cord Brain fully encased in protective skull Single-loop blood circulation Blood pumped from heart to gills Oxygenated blood from gills passes to rest of body Heart is series of four chambers that contract in sequence Nutritional deficiencies Unable to synthesize aromatic amino acids All vertebrates must consume these amino acids in their diet Important Adaptations of Bony Fishes Swim bladder Gas-filled sac that allows regulation of buoyant density Fish can remain suspended at any depth in the water fig 42.115 Sharks must move through the water or sink Cells of swim bladder can generate own carbon dioxide Lateral line system Series of sensory organs that project into a canal beneath skin surface fig 42.16 Cilia of organs deflected by movement of water as it passes over them Fish can assess movement through water Fish can detect motionless objects by water deflection off them Terrestrial vertebrate sound receptors may have evolved from these organs Gill cover Hard plate covering gills called the operculum fig 42.17 Flexion of covers pumps water over gills Volume of cavity increased when mouth open and gill cover closed Closing mouth decreases volume, forcing water over gills to outside Water moves over gills while fish is stationary AMPHIBIANS History of Amphibians Are able to live in two worlds, in water and on land Origin of amphibians Likely evolved from lobe-finned fishes DNA analysis shows closer relationship to lungfish than coelocanths Pattern of skull and bones show greater resemblance to rhipidistian fishes Innovations associated with invasion of land Legs to support body weight and for movement fig 42.18 Lungs needed because gills require buoyancy of water for support Redesigned heart to deliver more oxygen to walking muscles Water-bound reproduction to prevent eggs from drying out Needed to devise means to keep body from drying out Earliest amphibian fossil, Ichthyostega, found in Greenland fig 42.19 For 100 million years amphibian fossils found only in North America Spread throughout world when Pangaea formed Strongly built animal with four well supported legs Backbone more substantial than in fish Long, broad overlapping ribs encased lungs and heart Likely breathed by raising and lowering floor of mouth Rise and fall of amphibians Common during Carboniferous Period (360-287 million years ago) Shared wet tropical environment with early reptiles Moved into dry upland regions during Permian Period (286-249 million years ago) Developed bony plates and armor, some grew to pony size fig 42.20 Developed leathery skin to prevent water loss Didn't breathe through skin like most modern amphibians Ousted from niche by therapsid reptiles by end of Permian Only 15 families of amphibians by end of Triassic Only two families through the Jurassic Amphibians today Current amphibians all descended from 2 families Expansion during Tertiary Period (65-3 million years ago) into wet habitats Presently 37 families and over 4,200 species Characteristics of Living Amphibians Classified into three orders fig 42.21 Order Anura: frogs and toads Order Urodela: salamanders and newts Order Apoda: caecilians Key characteristics Legs (except burrowing caecilians) Cutaneous respiration Frogs, salamanders and caecilians supplement lung respiration Moist skin provides extensive surface area, but limits body size Lungs Internal surfaces are not as well developed as-in reptiles or mammals Breathe by moving floor of mouth Pulmonary veins Veins return blood from lungs to heart Aerated blood leaves heart at greater pressure than lungs Partially divided heart First chamber of heart in fish is missing in amphibians Second (atrium) and last (conus arteriosus) chambers separated by wall Prevents aerated blood from lungs from mixing with nonaerated blood from body Separation is imperfect since third chamber (ventricle) is not divided Other characteristics Zone of weakness between base and crown of teeth Caecilians have greatly reduced eyes and ears Frogs and salamanders have two bones in middle ear (reptiles have one) Possess sensory rod in retina called a "green rod" Orders of Living Amphibians Anura Include frogs and toads, amphibians without tails fig 42.22 Frogs have smooth, moist skin; long legs; live in or near water Toads have bumpy, dry skin; short legs; are adapted to dry environments Are carnivores, eat a wide variety of insects Return to water to reproduce Eggs lack water-tight membranes and dry out readily Eggs fertilized externally Eggs hatch into algae-eating, swimming larval tadpoles Larva metamorphose into adult forms after a period of growth Tail, gills and lateral line system disappear Legs grow from body Mouth broadens and develops jaws and teeth Sac-like bladder in throat becomes two lungs Pulmonary vein appears, heart develops internal wall Urodela Have elongated bodies, long tails and smooth moist skin fig 42.23 Most live in moist places, newts live entirely in water Reproduction Lay eggs in water or moist areas Fertilization is external in most species Just-hatched young look like adults, do not undergo profound metamorphosis Apoda Highly specialized group of burrowing amphibians Lack legs, have small eyes, are often blind Eat worms and soil invertebrates Male deposits sperm directly into female, young are born alive REPTILES Improved on Amphibian Innovations to Colonize the Land Legs support body better, enable reptiles to run Lungs and heart are more efficient Skin covered with scales to minimize water loss Eggs encased in water-tight covers The Rise and Fall of Dominant Reptile Groups Dominant large land vertebrates for 250 million years Four major forms took turns as dominant type fig 42.24 Pelycosaurs: becoming a better predator fig 42.25 Early reptiles that evolved water tight eggs Powerful jaws were anchored to holes in the skull Died out 250 million years ago Therapsids: speeding up metabolism fig 42.26 Ate more frequently than ancestors to produce body heat Far more active than other vertebrates of that time Called "mammal-like reptiles," reined for 20 million years Replaced by cold-blooded thecodont line 230 million years ago Gave rise to mammals before extinction 170 million years ago Thecodonts: wasting less energy fig 42.27 Were ectotherms like amphibians and early reptiles Endothermy no longer advantageous with warmer climate, needed less food First bipedal land vertebrates, walked on two feet Dominant for 15 million years Replaced by direct descendants, dinosaurs Dinosaurs: learning to run upright fig 42.28 Legs positioned directly underneath body Enabled running with speed and agility Hole in side of hip socket distinguishes them from thecodonts Dominated for 150 million years, abruptly went extinct 65 million years ago Today's reptiles Of 16 orders of reptiles, only four survive today fig 42.29 Turtles are most ancient reptile line Have solid skulls like first reptiles Have changed little since before time of dinosaurs Most reptiles belong to second line to evolve, lizards and snakes Evolved 250 million years ago in late Permian Became diverse only with disappearance of dinosaurs Rhynchocephalonts are the third linage fig 42.24 Appeared shortly before dinosaurs Common in Jurassic, declined in Cretaceous Unable to compete with lizards, only one species survives, the tuatara Crocodiles are fourth linage, appeared much later Descended from same line that produced dinosaurs Little change in the last 200 million years Comprise archosaurs along with thecodonts and dinosaurs Are more closely like birds than other reptiles Both groups care for their young, have four-chambered heart Share other anatomical features Crocodiles and birds more closely related to dinosaurs and each other than they are related to lizards and snakes Key Characteristics of Reptiles Amniotic egg Water-tight eggs contain food source (yolk) and four membranes fig 42.30 Membranes are: yolk sac, amnion, allantois and chorion Each plays role in making egg an independent life-support system Just beneath the shell, the chorion allows oxygen to enter, but retains water Inner amnion encased developing embryo within fluid-filled cavity Yolk sac sends food from yolk to embryo through amnion via blood vessels Allantois surrounds cavity into which waste products are excreted Dry skin Layer of scales or amour cover bodies to prevent water loss fig 42.31 Scales develop as surface cells fill with keratin Same protein forms human fingernails and bird feathers Thoracic breathing Expand and contract rib cage to suck air in and force it out Capacity limited only be volume of lungs Other Important Characteristics Internal fertilization External fertilization not possible since sperm cannot penetrate egg membranes Male places sperm inside female, fertilize egg before membranes form Circulatory system provides more oxygen to body fig 42.32 Septum in heart extended from atrium partway into ventricle Tends to decrease mixing of oxygen-poor and oxygen-rich blood in ventricle Septum totally divides ventricle in crocodiles and birds (and likely dinosaurs) Endothermy versus ectothermy Endothermy = cold-blooded = poikilothermy: body temperature fluctuates with ambient temperature Ectothermy = warm-blooded = homeothermy: constant body temperature maintained Reptiles regulate body temperature by behavior, bask in sun, hide in shade Thecodont ancestors of crocodiles were ectothermic, as are crocodiles Kinds of Living Reptiles Classified into 16 orders, 12 of which are extinct fig 42.33 Reptiles occur worldwide, except in coldest regions Humans have recently had negative impact on number and distribution of reptiles Chelonia: turtles and tortoises fig 42.34 Turtles live in water, tortoises live on land Only reptiles whose bodies are encased in a protective shell Lack teeth, but have sharp beak Composition of shell Made of hard plates in some, tough leathery skin in others Composed of two basic parts Carapace covers dorsal surface Plastron covers ventral portion Vertebrae and ribs of most species are fused to inside of carapace Support for muscle attachment comes from shell Tortoise shells are dome-shaped, turtle shells are streamlined, disk-shaped Freshwater turtles have webbed toes, marine turtles have flippers Marine turtles migrate long distances to lay eggs on land Placed by many biologists into own subclass Testudines Rhynchocephalia: tuatara Single species makes up entire order, found only on islands off New Zealand Has conspicuous spiny crest running down back Has inconspicuous parietal or third eye on top of head Concealed under scales, has lens, retina and is connected to brain May function as a thermostat, protect it from overheating Squamata: lizards and snakes fig 42.35 Suborders Suaria: snakes and Serpentes: lizards Have paired male reproductive organs and lower jaw not joined directly to skull Movable hinge with five joints allows flexibility in jaw movements Lizards lack lower arch of bone below lower opening of skull Snakes versus lizards Lizards have limbs, snakes do not Snakes lack movable eyelids and external ears Lizards are more ancient group Rely on agility and speed to catch prey and avoid predators Many lizards can loose tail to escape predator and regenerate new one Crocodilia: crocodiles and alligators fig 42.36 Primitive-looking reptiles also includes caimans and gavials Practically unchanged since they evolved from thecodonts 200 million years ago Live in or near water in tropical or subtropical regions Are aggressive carnivores, bodies adapted for hunting by stealth Eyes and nostrils on top of head, lie submerged in water Enormous mouths with sharp teeth and strong neck Can feed underwater, valve prevents water from entering air passage Only reptiles that care for their young BIRDS One of Four Groups to Conquer the Air Success derived from development of the feather Developed from reptilian scale Lightweight, readily replaced if damaged Most successful of all terrestrial vertebrates The History of Birds First bird, Archaeopteryx, from the late Jurassic fig 42.37 Shares features with small therapod dinosaurs Skull has teeth Very few bones are fused to each other Bones are solid (bird's bones are hollow) Has long reptilian tail and no breastbone to anchor flight muscles Originally classified as coelurosaur Compsognathus Distinctly avian due to presence of feathers on wings Some paleontologists classify it as a feathered dinosaur, not a true bird Birds best classified in own class due to feathers, hollow bones and super-efficient lungs Recent discovery of birds from Cretaceous that have features of modern birds Fossil record incomplete, feathers rarely fossilize, hollow bones are delicate Relationships of modern birds inferred from DNA studies Flightless types like ostrich, extinct elephant bird and Moa are most ancient Ducks, geese, other waterfowl evolved next in early Cretaceous Followed by woodpeckers, parrots, swifts, owls Songbirds evolved in mid-Cretaceous Shorebirds, birds of prey, flamingos, penguins evolved in late Cretaceous Key Characteristics of Birds Are clearly related to reptiles Lack teeth, have vestigial tail unlike reptiles Like reptiles lay amniotic eggs, have scales on feet and lower legs Feathers Modified reptilian scales Provide lift for flight and conserve heat Structure combines maximum flexibility with minimum weight fig 42.38 Develop from pits in skin called follicles Shaft emerges, pairs of vanes develop on opposite sides Vanes have branches called barbs Barbs have projections called barbules, equipped with microscopic hooks Hooks link barbs to one another Can be replaced, like scales Flight skeleton Bird bones are thin and hollow Many bones are fused to provide rigidity Only vertebrate to have fused collarbone (wishbone) or keeled breastbone Internal physiological changes necessary to cope with high energy demands of flight Efficient respiration Need greater contact surface to absorb enormous quantities of oxygen fig 42.39 Inhaled air goes past lungs to air sacs near and in bones of back Air then goes to lungs and is exhaled Air passes through lungs in only one direction, opposite the flow of blood Provides a counter-current flow to extract oxygen more efficiently Efficient circulation Oxygen captured by lungs must be transported to flight muscles quickly Wall dividing ventricle is complete, two circulations do not mix Flight muscles get fully oxygenated blood Most birds have a rapid heart beat Hummingbird = 600 times per minute, chickadee = 1000 bpm Ostrich = 70 beats per minute, same as human Endothermy Birds maintain higher body temperatures than most mammals Metabolism in flight muscles proceeds at faster rate Feathers provide insulation to conserve heat Kinds of Birds Can deduce habits and food by examining beak and feet Carnivorous birds have curved talons and sharp beak Duck beaks are flat to shovel through mud Finch beaks are short and thick to crush seeds MAMMALS Least Diverse of Five Classes of Vertebrates fig 42.41 Almost all large land vertebrates are mammals, tend to dominate communities Typical mammal is not large, 3200 of 4100 species are rodents, bats, shrews, moles History of the Mammals Arose from therapsids in mid-Triassic, 220 million years ago First mammals were small insectivores Large eye sockets indicate they may have been active at night Mammal jaw reduced to massive bone with a single joint Removed potentially weak junctions Two bones moved to middle ear to make three bone chain that improved hearing Were a minor group as long as dinosaurs flourished with only five orders Extinction of dinosaurs allowed for rapid diversification of mammals into 19 orders Key Mammalian Characteristics Hair Even naked whales and dolphins have bristles on snouts Allowed for regulation of body temperature, invasion of colder climates New structure, not derived from reptilian scales or feathers Each hair extends like stiff thread from bulb-like hair follicle Composed of dead cells filled with fibrous keratin protein Insulates against heat loss Provides camouflage Whiskers function as sensory structures May serve as defensive weapons as in porcupines and hedgehogs Milk-producing glands All females possess mammary glands that produce milk Milk is rich in fat, sugar, protein with 95% water Other Key Characteristics of Mammals Endothermy Allows activity at any time of day or night Supports colonization of severe environments, deserts to ice fields Hair provides insulation to support endothermy Higher metabolic rate required as well More efficient circulation provided by four chambered heart More efficient breathing results from diaphragm breathing muscle Placenta fig 42.42 Most mammals are placental and viviparous (live birth) Blood stream of mother and fetus in close contact at placenta Food, water, oxygen pass from mother to child Wastes pass from child to mother, carried away Teeth Help mammals select and eat a wide variety of foods Whale teeth may form bony mesh to trap tiny crustaceans A few mammals are omnivores Adult mammal maintains same teeth through entire life Are highly specialized to match food eaten fig 42.43 Rodents are most common of all mammals, have incisors that grow throughout entire life Digestive systems for eating plants Most mammals are herbivores, cellulose is major source of food Mammals lack enzymes to release glucose units Rely on mutualistic partnership with bacteria that degrade cellulose Some mammals have four-chambered stomachs First chamber is largest, holds most cellulose-digesting bacteria Material is regurgitated and chewed again (cud-chewing) Swallowed again and digested by rest of stomach, passes to intestines Other mammals digest plant material in the large intestine Have relatively small stomachs, do not chew a cud Bacteria live in pouch called the caecum, off the large intestine Herbivores must eat a lot of material to gain sufficient nutrition Horns and hooves Keratin is structural material for claws, fingernails, hooves Hooves are keratin pads on toes of running mammals Protect toe, cushion from impact Horns are composed of a core of bone surrounded by keratin sheath Horns are not shed, bony core is attached to skull Outer layer is compacted hair-like layers Deer antlers are made only of bone Male deer grow and shed a set of antlers each year Covered by thin skin layer of velvet while growing Velvet dies and is scraped off when antlers are fully grown Antlers used to attract females, combat males in fall and winter Shed in spring after breeding season Flying mammals Amphibians are only group of land vertebrates that have never evolved flight Pteosaurs were flying reptiles for 130 million years Birds evolved 140 million years ago, flew with pterosaurs for 75 million years Bats evolved 50 million years ago, share skies with birds Bats are only mammals capable of powered flight fig 42.41d Wings are modified forelimbs WIng is leathery membrane of skin stretched over bones of four fingers Edges attach to side of body and to hind leg At rest hang upside down from legs Evolved sonar system to navigate in dark and find insects High frequency pulses emitted through mouth or nose Sound waves reflect off objects, captured by ears The Orders of Mammals Modern mammals comprise nineteen orders Seventeen are placental Two are non-placental Monotremes: egg-laying mammals fig 42.44 Includes duck-billed platypus and two species of echidna Retain a few reptilian characteristics Lay shelled eggs Structure of shoulder and pelvis similar to early reptiles Have a single opening through which feces, urine and reproductive products leave the body Most closely related to early mammals than any other mammal Possess fur and functioning mammary glands like other mammals Marsupials: pouched-mammals fig 42.45 Major difference in embryonic development of marsupials and other mammals In marsupials fertilized egg is surrounded by chorion and amnion, no shell forms as in monotremes Marsupial embryo nourished by abundant yolk within egg Short-lived placenta forms from chorion just before birth In as few as eight days after fertilization an embryonic marsupial is born Crawls into marsupial pouch, attaches to nipple, continues to develop Evolved shortly before placental mammals, 100 million years ago Nearly all of today's species live in Australia and New Guinea Only 20 species live elsewhere Marsupials in Australia and New Guinea have diversified to fill niches otherwise held by placental mammals Virginia opossum is the only marsupial in North America Placental mammals fig 42.41 Produce true placenta that nourishes embryos for entire development Placenta is first organ to form during course of development Held in womb of mother, contains abundant fetal and maternal blood vessels Fetal placenta formed from membranes of chorion and allantois Maternal placenta formed from wall of uterus Young undergo considerable development before being born Kinds of Mammals Most recent addition is a tree-dwelling kangaroo in Australia fig 42.46 Mammals exhibit a wide variety of body forms fig 42.47