SECTION 3 Vertebrate Animals 417 What is a chordate? Suppose you asked your classmates to list their pets. Dogs, cats, birds, snakes, and fish probably would appear on the list. Animals that are familiar to most people are animals with a back- bone. These animals belong to a larger group of animals called chordates (KOR dayts). Three characteristics of all chordates are a notochord, a nerve cord, and pharyngeal pouches at some time during their development. The notochord, shown in Figure 12, is a flexible rod that extends along the length of the developing organism. Pharyngeal pouches are slitlike openings between the body cavity and the outside of the body. They are present only during the early stages of the organism’s develop- ment. In most chordates, one end of the nerve cord develops into the organism’s brain. Vertebrates Scientists classify the 42,500 species of chordates into smaller groups. The animals within each group share simi- lar characteristics, which may indicate that they have a common ancestor. Vertebrates, which include humans, are the largest group of chordates. Vertebrates have an internal system of bones called an endoskeleton. Endo- means “within.” The vertebrae, skull, and other bones of the endoskeleton support and protect inter- nal organs. For example, vertebrae surround and protect the nerve cord. Many muscles attach to the skeleton and make movement possible. Vertebrate Animals ■ Classify vertebrate animals. ■ Identify the major systems that compose vertebrate animals. ■ Explain the differences between vertebrate animals. You and other vertebrate animals have an internal skeleton that supports and protects your internal organs. Figure 12 Lancelets are filter feeders that grow to 7 cm in length and live in the ocean. Its pharyngeal pouches develop into gill slits. Notochord Gill slits Nerve cord Movement of water Benchmarks—SC.F.1.3.1 (pp. 417–428): The student understands that living things are composed of major systems that function in reproduction, growth, maintenance, and regulation. Also covers: SC.F.1.3.4 (pp. 417–428), SC.F.2.3.1 (pp. 417–428), SC.F.2.3.3 (pp. 417–428), SC.G.1.3.2 (p. 428), SC.H.1.3.1 Annually Assessed (p. 432), SC.H.1.3.2 (p. 432), SC.H.1.3.3 (pp. 421, 432), SC.H.1.3.4 Annually Assessed (p. 429), SC.H.1.3.5 Annually Assessed (p. 430), SC.H.1.3.6 (pp. 421, 432), SC.H.3.3.2 (pp. 430–431) Review Vocabulary life cycle: the entire sequence of events in an organism’s growth and development New Vocabulary • chordate herbivore • ectotherm carnivore • endotherm omnivore • amniotic egg FCAT Vocabulary
Transcript
SECTION 3 Vertebrate Animals 417
What is a chordate? Suppose you asked your classmates to list their pets. Dogs,
cats, birds, snakes, and fish probably would appear on the list.Animals that are familiar to most people are animals with a back-bone. These animals belong to a larger group of animals calledchordates (KOR dayts). Three characteristics of all chordates area notochord, a nerve cord, and pharyngeal pouches at sometime during their development. The notochord, shown inFigure 12, is a flexible rod that extends along the length of thedeveloping organism. Pharyngeal pouches are slitlike openingsbetween the body cavity and the outside of the body. They arepresent only during the early stages of the organism’s develop-ment. In most chordates, one end of the nerve cord developsinto the organism’s brain.
Vertebrates Scientists classify the 42,500 species of chordatesinto smaller groups. The animals within each group share simi-lar characteristics, which may indicate that they have a commonancestor. Vertebrates, which include humans, are the largestgroup of chordates.
Vertebrates have an internal system of bones called anendoskeleton. Endo- means “within.” The vertebrae, skull, andother bones of the endoskeleton support and protect inter-nal organs. For example, vertebrae surround and protect thenerve cord. Many muscles attach to the skeleton and makemovement possible.
Vertebrate Animals
■ Classify vertebrate animals.■ Identify the major systems that
compose vertebrate animals.■ Explain the differences between
vertebrate animals.
You and other vertebrate animalshave an internal skeleton thatsupports and protects yourinternal organs.
Figure 12 Lancelets are filterfeeders that grow to 7 cm in lengthand live in the ocean. Its pharyngealpouches develop into gill slits.
Notochord
Gill slitsNerve cord
Movementof water
Benchmarks—SC.F.1.3.1 (pp. 417–428): The student understands that living things are composed of majorsystems that function in reproduction, growth, maintenance, and regulation.
Body Temperature Most vertebrate body temperatureschange as the surrounding temperature changes. These animalsare ectotherms (EK tuh thurmz), or cold-blooded animals. Fishand reptiles are ectotherms.
Humans and many other vertebrates are endotherms(EN duh thurmz), or warm-blooded animals. Their body tem-perature doesn’t change with the surrounding temperature.Your body temperature is usually about 37°C, but it can vary byabout 1°C, depending on the time of day. Changes of more thana degree or two usually indicate an infection or overexposure toextreme environmental temperatures.
Are humans endotherms or ectotherms?
FishThe groups of vertebrates are shown in Figure 13. The
largest group of vertebrates—fish—lives in water. There arethree classes of fish: jawless, jawed cartilaginous, and bony. Fishare ectotherms that can be found in warm desert pools and thesubfreezing Arctic Ocean. Some species are adapted to swim inshallow freshwater streams and others in salty ocean depths.
Fish have fleshy filaments called gills, shown in Figure 14,where carbon dioxide and oxygen are exchanged. Water, con-taining oxygen, flows over the gills. When blood is pumped intothe gills, the oxygen in the water moves into the blood. At thesame time, carbon dioxide moves out of the blood in the gillsand into the water.
Most fish have pairs of fanlike fins. The top and the bottomfins stabilize the fish. Those on the sides steer and move the fish.The tail fin propels the fish through the water. Most fish havescales. Scales are thin structures made of a bony material thatoverlap like shingles on a house to cover the skin.
Animal Kingdom
Chordates
Tunicates Lancelets Vertebrates
Jawlessfish
Jawedcartilaginous
fishBony fish Amphibians Reptiles Birds Mammals
Invertebrates
Figure 13 This diagram illustrateshow vertebrates are classified.Infer what characteristics may havebeen used to classify vertebrates.
Gills
Gillfilament
Figure 14 Gas exchange occursin the gill filaments.
SECTION 3 Vertebrate Animals 419
Amphibians A spy might lead a double life, but what about an animal?
Amphibians (am FIH bee unz) are animals that spend part oftheir lives in water and part on land. In fact, the term amphibiancomes from the Greek word amphibios, which means “doublelife.” Frogs, toads, newts, and salamanders, such as the red-spottedsalamander pictured in Figure 15, are examples of amphibians.
Amphibian Characteristics Amphibians are vertebrateswith a strong endoskeleton made of bones. The bones help sup-port their body while on land. Adult frogs and toads have stronghind legs that are used for swimming and jumping.
Adult amphibians use lungs instead of gills to exchange oxy-gen and carbon dioxide. This is an important adaptation forsurvival on land. However, because amphibians have three-chambered hearts, the blood carrying oxygen mixes with theblood carrying carbon dioxide. This mixing makes less oxygenavailable to the amphibian. Adult amphibians also exchangeoxygen and carbon dioxide through their skin, which increasestheir oxygen supply. Amphibians can live on land, but they muststay moist so this gas exchange can occur.
Amphibian hearing and vision also are adapted to life onland. The tympanum (TIHM puh nuhm), or eardrum, vibratesin response to sound waves and is used for hearing. Large eyesassist some amphibians in capturing their prey.
What amphibian senses are adapted for life on land?
Land environments offer a great variety of insects as food foradult amphibians. A long, sticky tongue extends quickly to cap-ture an insect and bring it into the waiting mouth.
Figure 15 Amphibians havemany adaptations that allow forlife both on land and in the water.This red-spotted salamanderspends most of its life on land.Explain why they must return tothe water.
Topic: AmphibiansVisit fl7.msscience.com for Weblinks to information about theenvironment and amphibians.
Activity List as many possiblecauses of amphibian declines as you can find. Explain why it is important to humans to deter-mine what could be causing thesedeclines.
Amphibian Metamorphosis Young animals such as kittensand calves are almost miniature versions of their parents, butyoung amphibians do not look like their parents. Most amphib-ians go through a series of body changes called metamorphosis,as illustrated in Figure 16. Eggs are laid most often in water andhatch into larvae. Most adult amphibians live mainly on land.
The young larval forms of amphibians are dependent onwater. They have no legs and breathe through gills. Over time,they develop body structures needed for life on land, includinglegs and lungs. The rate at which this pattern occurs depends onthe species, the water temperature, and the amount of availablefood. If food is scarce and the water temperature is cool, thenmetamorphosis will take longer.
Figure 16 Most youngamphibians, like these tad-poles, look nothing like theirparents when they hatch.The larvae go through meta-morphosis in the water andeventually develop intoadult frogs that live on land.
Tadpoles hatch from eggs that are laidin or near water.
Tadpoles use their gills for gas exchange.
Legs begin to develop. Soon, the tailwill disappear.
An adult frog uses lungs and skin for gasexchange.
(tl tr bl)Runk/Schoenberger from Grant Heilman, (br)George H. Harrison from Grant Heilman
SECTION 3 Vertebrate Animals 421
ReptilesReptiles come in many shapes, sizes, and colors. Snakes, lizards,
turtles, and crocodilians are reptiles. Reptiles are ectothermic ver-tebrates with dry, scaly skin. Because reptiles do not depend onwater for reproduction, most are able to live their entire lives onland. They also have several other adaptations for life on land.
Types of Reptiles As shown in Figure 17, reptilian body plansvary. A turtle is covered with a hard shell. Turtles eat insects,worms, fish, and plants.
Alligators and crocodiles are predators that live in and nearwater. These large reptiles live in warmer climates such as thosefound in the southern United States.
Lizards and snakes make up the largest group of reptiles.Snakes and lizards have an organ in the roof of the mouth thatsenses molecules collected by the tongue. The constant in-and-out motion of the tongue allows a snake or lizard to smell itssurroundings. Lizards have movable eyelids and external ears,and most lizards have legs with clawed toes. Snakes don’t haveeyelids, ears, or legs. Instead of hearing sounds, they feel vibra-tions in the ground.
Figure 17 Reptiles havedifferent body plans.
Sea turtles, like this loggerheadturtle, are threatened around theworld because of pollution, loss ofnesting habitat, drowning in nets,and lighted beaches.
Colorado desert fringe-toedlizards are camouflaged, whichhelps them avoid their preda-tors. These lizards mostly eatinsects, but some includeplants in their diet.
A crocodilian, like this American alligator,builds its nest on land near a body of water.It protects its eggs while it waits for them to hatch.
Herpetologist Most peopleare familiar with herpetolo-gists, who are responsiblefor naming and classifyingreptiles and amphibians.They often work in muse-ums or universities. Theirwork usually involves fieldtrips and gathering infor-mation for publication.What methods do taxono-mists use to determinerelationships betweenorganisms? Write youranswer in your ScienceJournal.
LA.B.2.3.1
The rubber boa is one of only two species of boa constrictors in North America. Rubber boas have flexible jaws that enable them to eat prey that is larger than their head.
(t)Robert J. Erwin/Photo Researchers, (cl)Photo Researchers, (cr)Wendell D. Metzen/Bruce Coleman, Inc., (b)Dan Suzio/Photo Researchers
422 CHAPTER 14 Classifying Animals
Reptile Adaptations A thick, dry, waterproof skin is anadaptation that reptiles have for life on land. The skin is coveredwith scales that reduce water loss and help prevent injury.
What are two functions of a reptile’s skin?
All reptiles have lungs for exchanging oxygen and carbondioxide. Even sea snakes and sea turtles, which can stay sub-merged for long periods of time, must eventually come to thesurface to breathe. Reptiles also have a neck that allows them toscan the horizon.
Two adaptations enable reptiles to reproduce successfully onland—internal fertilization and laying shell-covered, amniotic(am nee AH tihk) eggs. During internal fertilization, sperm aredeposited directly into the female’s body. Water isn’t necessaryfor reptilian reproduction.
The embryo develops within the moist protective environ-ment of the amniotic egg, as shown in Figure 18. The yolk sup-plies food for the developing embryo, and the leathery shellprotects the embryo and yolk. When eggs hatch, young reptilesare fully developed. In some snake species, the female does notlay eggs. Instead, the eggs are kept within her body, where theyincubate and hatch. The young snakes leave her body soon afterthey hatch.
BirdsOstriches have strong legs for running, and pelicans have
specialized bills for scooping fish. Penguins can’t fly but areexcellent swimmers, and house wrens and hummingbirds areable to perch on branches. These birds are different, but they,and all birds, have common characteristics. Birds are endother-mic vertebrates that have two wings, two legs, and a bill or beak.Birders, or bird-watchers, can tell where a bird lives and what iteats by looking at the type of wings, feet, and beak or bill it has.Birds are covered mostly with feathers—a feature unique tobirds. They lay hard-shelled eggs and sit on these eggs to keepthem warm until they hatch. Besides fish, birds are the mostnumerous vertebrates on Earth. Figure 19 illustrates some of themore than 8,600 species of birds and their adaptations.
Birds play important roles in nature. Many are sources offood for humans and many other animals. Some birds, like the owl, help control rodent populations. Some, like barn swal-lows, control the number of insects. Many birds are useful forplant reproduction. Some, like hummingbirds, are pollinatorsfor many flowers. Others eat fruits and release seeds in theirdroppings.
Figure 18 Young reptileshatch from amniotic eggs.Describe the advantages of this.
SECTION 3 Vertebrate Animals 423
Adaptations for Flight The bodies of most birds are designedfor flight. They are streamlined and have light yet strong skele-tons. The inside of a bird’s bone is almost hollow. Internal criss-crossing structures strengthen the bones without making them asheavy as mammal bones are. Because flying requires a rigid body,a bird’s tail vertebrae are joined together to provide the neededrigidity, strength, and stability. Birds use their tail to help themsteer through the air. While a bird can still fly without a tail, theirflight is usually shorter and not as smooth.
What advantage do birds’ bones give them for flight?
Flight requires a lot of energy and oxygen. Birds eat insects,nectar, fish, meats, or other high-energy foods. They also havea large, efficient heart and a specialized respiratory system. Abird’s lungs connect to air sacs that provide a constant supplyof oxygen to the blood and make the bird more lightweight.
Slow-motion video shows that birds beat their wings up anddown as well as forward and back. A combination of wingshape, surface area, air speed, and angle of the wing to the mov-ing air, along with wing movements, provide an upward pushthat is needed for flight. Inventors of the first flying machines,such as gliders, used the body plan of birds as a model for flight.
Emus can’t fly but they have stronglegs and feet that are adapted forrunning.
Figure 19 Birds have many dif-ferent adaptations for survival.
Birds of prey, like this osprey,have sharp, strong talons thatenable them to grab their prey.
An albatross glides in the air.
Horned puffins can fly and their sleekbodies and small, pointed wings alsoenable them to “fly” underwater.
Topic: Wing DesignsVisit fl7.msscience.com for Weblinks to information about wingdesigns of different aircraft.
Activity Draw as many wingdesigns as you can find and explainhow they are different.
Functions of Feathers Birds are the only animals withfeathers. They have two main types of feathers—contour feath-ers and down feathers. Strong, lightweight contour feathers giveadult birds their stream-lined shape and coloring. A close lookat the contour feather in Figure 20 shows the parallel strands,called barbs, that branch off the main shaft. Outer contourfeathers help a bird move through the air or water. It is theselong feathers on the wings and tail that help the bird steer andkeep it from spinning out of control. Feather colors and patternscan help identify species. They also are useful in attracting matesand protecting birds from predators because they can be a formof camouflage. Birds have down feathers that trap and keepwarm air next to their bodies. These fluffy feathers, as shown inFigure 21, provide an insulating layer under the contour feath-ers of adult birds and cover the bodies of some young birds.
What are two ways feathers protect birds?
Birds preen to clean and reorganize their feathers. Duringpreening, many birds also spread oil over their bodies and feath-
ers. This oil comes from agland found on the bird’sback at the base of its tail.The oil helps keep the skinsoft, and feathers and scalesfrom becoming brittle. It is not this oil that water-proofs feathers, as oncethought, but the arrange-ment of the feathers’ micro-scopic structures.
Figure 20 Microscopic barbs,located along contour feathers,keep the feathers smooth by hold-ing the individual parts of thefeather together.
Color-enhanced SEMMagnification: 844!
Figure 21Some species ofbirds, like chickensand these pheas-ants, are covered withfeathers when they hatch. Explain how this might be an advantage.
Mammals How many different kinds of mammals can you name?
Moles, dogs, bats, dolphins, horses, and people are all mammals.More than 4,000 mammals exist on Earth today. Mammals arefound on every continent, from cold arctic regions to hotdeserts. They live in water and in many different climates onland. They burrow through the ground and fly through the air.Each species of mammal has certain adaptations that enable itto live and reproduce successfully in its environment. Mammalsare important parts of food webs. Some mammals, like bats,pollinate flowers. Others disperse seeds. Mammals are impor-tant in maintaining the balance in the environment.
Mammals are endothermic vertebrates. They have mam-mary glands in their skin. In females, mammary glands pro-duce milk that nourishes the young. A mammal’s skin usuallyis covered with hair that insulates its body from cold and heat. Italso protects the animal from wind and water. Some mammals,such as bears, are covered with thick fur. Others, like humans,have only patches of thick hair while the rest of their body issparsely covered with hair. Still others, like the dolphins shownin Figure 22, have little hair. Wool, spines, quills, and certainhorns are modified hair. What function do you think quills andspines serve?
Mammary Glands Mammals put a great deal of time andenergy into the care of their young, even before birth. Whenfemale mammals are pregnant, the mammary glands increase insize. After birth, milk is produced and released from theseglands. For the first weeks or months of a young mammal’s life,the milk provides all of the nutrition the young mammal needs.
Figure 22 The type of hair mammals have varies from speciesto species.Explain the advantages and disad-vantages of having hair.
Porcupines have fur next to theirskin but sharp quills on the outside.Quills are modified hairs.
Dolphins do not have much hair ontheir bodies. A layer of fat under theskin acts as insulation.
Inferring How BlubberInsulatesProcedure1. Complete a safety
worksheet.2. Fill a self-sealing plastic
bag about one-third fullwith solid vegetable shortening.
3. Turn another self-sealingplastic bag inside out. Placeit inside the first bag so youare able to zip one bag tothe other. This is a blubbermitten.
4. Put your hand in theblubber mitten. Place yourmittened hand in ice waterfor 5 s. Remove the blubbermitten when finished.
5. Put your other bare hand inthe same bowl of ice waterfor 5 s.
Analysis1. Which hand seemed colder? 2. Infer the advantage a layer
Different Teeth Mammals have teeth that are specialized for the type of food they eat. Plant-eating animals are calledherbivores. Animals that eat meat are called carnivores, andanimals that eat plants and animals are called omnivores. Asshown in Figure 23, you usually can tell from the kind of teetha mammal has whether it eats plants, other animals, or both.The four types of teeth are incisors, canines, premolars, andmolars.
How are herbivores, carnivores, and omnivoresdifferent?
Body Systems Mammals live active lives. They run, swim,climb, hop, and fly. Their body systems must interact and beable to support all of these activities.
Mammals have well-developed lungs made of millions ofmicroscopic sacs called alveoli, which enable the exchange ofcarbon dioxide and oxygen during breathing. They also have acomplex nervous system and are able to learn and remembermore than many other animals. The brain of a mammal is usu-ally larger than the brain of other animals of the same size.
All mammals have internal fertilization. After an egg is fer-tilized, the developing mammal is called an embryo. Most mam-mal embryos develop inside a female organ called the uterus.Mammals can be divided into three groups based on how theirembryos develop. The three groups of mammals are mono-tremes, marsupials, and placentals.
Figure 23 A mammal’s teethare adapted to its diet.
Herbivores, like this beaver, haveincisors that cut vegetation and large,flat molars that grind it.
Humans are omnivores. They have incisors that cutvegetables, premolars that aresharp enough to chew meat,and molars that grind food.
Mountain lions are carnivores.They have sharp canines that areused to rip and tear flesh.
SECTION 3 Vertebrate Animals 427
Mammal Types Monotremes make up the smallestgroup of mammals. They lay eggs with tough, leatheryshells instead of having live births. The female incubatesthe eggs for about ten days. Monotremes lack nipples. Theyoung nurse by licking the milk from the fur surroundingthe mammary glands. Duck-billed platypuses are an exam-ple of monotremes.
Marsupials—such as kangaroos, koalas, Tasmaniandevils, and wallabies—live in Australia, Tasmania, and NewGuinea. The opossum is the only marsupial that lives in NorthAmerica. Most marsupials carry their young in a pouch. Theirembryos develop for only a few weeks within the uterus. Whenthe young are born, they are without hair, blind, and not fullyformed, like the opossums in Figure 24. Using their sense ofsmell, the young crawl toward a nipple and attach themselves toit. Here they feed and complete their development.
Figure 24 Marsupials, such asopossums, are born before they are completely developed.Newborn marsupials make thejourney to a nipple that is usuallyin the mother’s pouch where theywill finish developing.
Working with Percentages
1. On a typical day during those four months, how much time do elephant seals stay at thesurface from 11:00 P.M. until 6:00 A.M.?
2. On a typical day during those four months, how much time do elephant seals spendunderwater from 9:00 A.M. until 6:00 P.M.?
HOW MUCH TIME? It is estimated that during the four months elephant seals spend at sea,90 percent of their time is spent underwater. On a typical day, how much of the timebetween the hours of 10:00 A.M. and 3:00 P.M. does the elephant seal stay at the surface?
SolutionThis is what you know:
This is what you need toknow:
This is the procedure youneed to use:
Check your answer:
● Total time: From 10:00 A.M. to 3:00 P.M. is 5 h.1 h " 60 min, so 5 ! 60 " 300 min
● % of time on surface " 100% # 90% " 10% " 0.10
How much time is spent on the surface?
● Use this equation:surface time " (total time)(% of time on surface)
● Substitute the known values:surface time " (300 min)(0.10) " 30 min
Divide your answer by the total time. Is the answer equalto 10 percent?
Placentals The largest number ofmammals belongs to a group calledplacentals. Placentals are named for theplacenta, which is a saclike organ thatdevelops from tissues of the embryoand uterus. In the placenta, food, oxy-gen, and wastes are exchanged betweenthe mother’s blood and the embryo’sblood, but their bloods do not mix. Anumbilical cord, as seen in Figure 25,connects the embryo to the placenta.Food and oxygen from the mother’sblood are carried to the developingyoung by the blood vessels in the
umbilical cord. These blood vessels also carry wastes from thedeveloping young to the mother’s blood.
The time of development from fertilization to birth is called the gestation period. Mice and rats have a gestationperiod of about 21 days. Human gestation lasts about 280 days.The gestation period for elephants is about 616 days, or almosttwo years.
Figure 25 Placental embryosrely on the umbilical cord to bringnutrients and to remove wastes.Your navel is where your umbilicalcord was connected to you.
Self Check1. Compare and contrast ectothermic and endothermic
animals.
2. Explain why amphibians must live in wet or moist environments.
3. Infer how an amniotic egg is an important adaptationfor reptiles.
4. Describe how a bird’s body systems all work togetherto enable it to fly.
5. Think Critically Placentals are the most abundantmammal in the world. Why are they more successfulthan marsupials and monotremes?
SummaryWhat is a Chordate?
• All chordates have a notochord, a nerve cord,and pharyngeal pouches at some time duringtheir development.
Fish, Amphibians, and Reptiles
• All are ectotherms. Most fish have gills, fins,and scales.
• Amphibians spend part of their lives in waterand part on land.
• Reptiles have dry, scaly skin, and the embryosdevelop in an amniotic egg.
Birds and Mammals
• Both are endotherms. Birds are feathered ver-tebrates. They have wings and lay eggs.
• Mammals feed their young milk and have furor hair. They are either monotremes, marsupi-als, or placentals.
6. Use a Spreadsheet During every 10 seconds of flight,a crow beats its wings 20 times, a robin 23 times, achickadee 270 times, and a hummingbird 700 times.Use a spreadsheet to find out how many times thewings of each bird beat during a 5-minute flight.
