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Vertebrate 25 Diversity

Big Idea are a diverse group of land-based and aquatic that share certain characteristics.

25.1 Origins 7A, 8B, 8C

25.2 Diversity 8B, 10A

25.3 a Closer Look at Bony Fish 7B, 7E Data Analysis Constructing Scatterplots 2G

25.4 7A, 7D, 7E, 8B, 8C

25.5 Vertebrates on Land 7A, 7B

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ONLINE Labs ■■ Video Lab Live Observation ■■ Fish ■■ QuickLab Frog Development ■■ of a Bony Fish ■■ Vanishing —an Indicator ■■ Homologies in Vertebrate ■■ Examining Development (t) ©Gregory Dimijian/Photo Inc. G. Researchers,

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Q Why is this frog see-through? The Fleischmann’s glass frog is one of several members of the Centrolenidae. Glass lack pigment on their undersides, making their transparent. The skin on the top portion of their has a pigment that reflects the same wavelength of light as plants, helping them to blend in with the green leaves on which they live.

R E a d IN G T ool bo x This reading tool can help you learn the material in the following pages.

USING LANGUAGE Your Turn Comparisons Comparing is a way of looking for In the following sentences, identify the things that are similarities among different things. Contrasting is a way of being compared or contrasted. looking for the differences. Comparison words include 1. Like oranges, bananas have a thick peel. However, the like, similar to, and also. Contrast words include unlike, seeds of bananas can be eaten easily. however, and although. 2. Like fish, frogs lay in water. Unlike fish, frogs do not have scales.

Chapter 25: Vertebrate Diversity 727 DO NOT EDIT--Changes must be made through “File info” CorrectionKey=A

25.1 Vertebrate Origins

7a, 8b, 8c Key Concept All vertebrates share common characteristics. MAIN IDEAS VOCABULARY The Chordata contains all vertebrates and some . All vertebrates share common features. evidence sheds light on the origins of vertebrates. endoskeleton Connect to Your World 7A analyze and evaluate Just like the glass frog, you too are a vertebrate. So are , tigers, , and how evidence of common ancestry among groups is provided by the squirrels. While the vertebrates you most often see are those that live on land like us, fossil record, , and the group first evolved in the . The first vertebrates were fish, and even today homologies, including anatomical, molecular, and developmental; the vast majority of vertebrates are still fish. 8B categorize organisms using a hierarchical classification system based on similarities and differences shared among groups; 8C compare characteristics of taxonomic groups, 7A, 8B including archaea, bacteria, protists, MAIN IDEA fungi, plants, and animals The phylum Chordata contains all vertebrates and some invertebrates. Biology IDEO V CLI The phylum Chordata is made up of three groups. One group includes all P vertebrates. Vertebrates are large, active animals that have a well-developed HMDScience.com encased in a hard . The other two groups are the and go online , which are both invertebrates. Tunicates, or the urochordates, include Chordate Characteristics both free-swimming and sessile animals such as squirts. Lancelets, or the (sehf-uh-luh-KAWR-dayts), are small -like animals that are commonly found in shallow, tropical . Although lancelets can swim, they spend most of their buried in sand, filtering water for food particles. Despite their enormous differences in body plans and ways of , all share the four features illustrated in Figure 1.1 at some stage of their development. • Notochord A notochord is a flexible skeletal support FIGURE 1.1 A sea squirt shows rod embedded in the ’s back. all four features of a chordate • Hollow nerve cord A hollow nerve cord runs along the as a . animal’s back. The nerve cord forms from a section of the that rolls up during development. • Pharyngeal slits ­­ Pharyngeal (fuh-RIHN-jee-uhl) slits are hollow nerve cord notochord slits through the body wall in the , the part of the gut immediately beyond the . Water can enter the mouth and leave the animal through these slits without passing through the entire digestive system. • Tail A tail extends beyond the anal opening. The tail, as well as the rest of the animal, contains segments pharyngeal slits of muscle tissue used for movement.

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(t) ©Robert Yin/Corbis; (b) ©Untitled/Alamy All vertebrates features. sharecommon How are they different? Contrast and Compare

Some are of parts these shown on ape the in fibers that are embedded in a matrix, or combination, of harder materials.and are both dense connective tissues. Each tissue is made of subjected to large forces get thicker. response to forces on avertebrate’s body. For example, shed as animal the be grows. It change can also shape in changes size, unlike , which must slowly change sizeand shape. It can grow as avertebrate This characteristic means avertebrate endoskeleton can can actively break down skeletal material and rebuild it. muscles and protects internal organs. It contains cells that eton. An One characteristic that allows vertebrates to grow to large sizes is the Vertebrateendoskel- an Indonesian than smaller afingernail, is larger than most invertebrates. Vertebrates tend large, to be active animals. Even smallest the living vertebrate, shown in four chordate characteristics. However, an adult squirt, sea . For example, form have squirts of sea larval the all is adjacent vertebrae are remnants of notochord. the during later development. disks between The fluid-filled chord that is for most the replaced part by vertebrae the for filter feeding. Similarly, vertebrate embryos have anoto- slits. pharyngeal the Adult slits pharyngeal the use squirts sea Connected • Vertebrae • Braincase • MAI tics inadulthood,tics but are they present and larvae intheir Ver The e Most chordate groups some lose or of character- all these ment. body’s tissues soft and provide points for muscle attach- vertebraethe backbone let the as animal the bend moves. can resist forces produced by large muscles. Joints between It replaces also notochord the with harder material that by joints. This internal backbone protects spinal the cord. N ID tebrate endoskeletons divided into can be distinctparts. ndoskeleton forms aframework that supports endoskeleton E Figure 1.2, Figure A

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Chondrichthyes animals include lampreys, of atype fish. relationships among classes of seven the vertebrates. Reptilia animals include , frogs (including toads), and . water and on land, reproduce although they inwater or on moist land. These Amphibia of atype bony fish, Ray-finned are fish, most the diverse group of vertebrates. made of cartilage. animals These include , rays, and chimeras. The shown in Vertebrate Classes lost these cells,lost or these tunicates are closest the indeed relatives to vertebrates. have such cells. This could evidence indicate that either lancelets secondarily that tunicates have cells that resemble crest, neural the but lancelets do not into of parts system, nervous the , bone, and Scientists teeth. have found vertebrate embryos have strips crest, neural the of cellswhich called develops indicates that tunicates may closest the relatives be actually of vertebrates. All anatomical comparisons and molecular evidence. However, recent research vertebrates than tunicates were. on this fossil based They evidence, along with In past, the scientists thought that lancelets were more closely related to Closest Relatives Vertebrates of provide of evidence earliest the chordates. invertebratethe remains found site. at quarry fossils the Other with of traces contents and muscles. Fossils of , worms, and are among explosion and include exoskeletons, preserved limbs, and insome gut cases, late 1960s.Fossils found within Burgess the Shale date from the fossil site, discovered early inthe 1900s,was not explored fully until the found Burgess inthe Shale located Canadian inthe Mountains. Rocky This Much of what we know about early vertebrates comes from fossil evidence MAI sively on land. produce that eggs do not have to develop inwater. Reptiles include , lizards, , alligators, and turtles. N Aves ID , along with other features.

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FIGURE 1.5 Vertebrate Phylogenetic Tree

Each vertebrate class has unique characteristics that separate one class from another.

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s from the cold and allow for flight. frog

Hair Hair helps mammals to maintain constant body by providing insulation from the cold.

Amnion An amniotic encloses an during development, letting animals reproduce on land.

Four Limbs Four limbs let animals move from the water to life on land.

Jaws help vertebrates to become successful predators.

Vertebrae Vertebrates have a segmented backbone.

CRITICAL What characteristic is common among reptiles, birds, and mammals? 7a, 8b VIEWING

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25.2 Fish Diversity

8b, 10a Key Concept the dominant aquatic vertebrates are fish. MAIN IDEAS VOCABULARY Fish are vertebrates with and paired fins. Jaws evolved from gill supports. countercurrent flow Only two groups of jawed fish still exist. Connect to Your World In to move in a swimming pool, you need to push your body through a thick, 8B categorize organisms heavy blanket of water. Swimming for a long time is tiring. Long-distance swimming using a hierarchical classification system based on similarities and requires endurance and a lot of energy. Fish spend their entire lives moving through differences shared among groups and 10A describe the interactions water, but to an aquatic environment make their movements through that occur among systems that water much more energy‑efficient than yours. perform the functions of regulation, nutrient absorption, reproduction, and defense from injury or illness in animals MAIN IDEA 10a Fish are vertebrates with gills and paired fins. You get the you need by in the air that surrounds you. Because fish live underwater, the way that they get oxygen is completely different from the way you breathe. Fish use specialized organs called gills to take in the oxygen dissolved in water. Gills are large sheets of thin frilly tissue filled with capillaries that take in dissolved oxygen from the water and release . As shown in Figure 2.1, gills have a very large surface area, which increases the amount of gases they can exchange with the water. Muscles in the body wall expand and contract, creating a current of water that brings a steady supply of oxygen to the blood. Just like you, fish have body systems that provide their cells with oxygen and nutrients and also remove waste products. Fish circulatory systems pump blood in a single circulatory loop through a with two main chambers. An atrium collects blood returning from the body and moves it into the ventricle. The ventricle pumps blood through the gills, where carbon dioxide is released and oxygen is picked up by the blood. The blood then carries the oxygen directly to the tissues and picks up more carbon dioxide. The blood Biology returns to the heart, and the process begins again. HMDScience.com go online How Fish Breathe

FIGURE 2.1 Fish use the large sur- face area of their gills to exchange carbon dioxide and oxygen with the water in which they live.

water flow

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Countercurrent Flow Arteries in the gills carry blood to the exchange surfaces. The arteries are arranged so that blood flows in the opposite direction of the current of water CONNECT TO entering the gills. Countercurrent flow is the opposite movement of water VISUAL VOCAB Diffusion against the flow of blood in the fish’s Recall from Cell Structure Countercurrent flow maximizes and Function that diffusion gills. Because oxygen dissolved in the the amount of oxygen the fish can is the movement of dissolved water is at a greater concentration pull from the water. molecules in a fluid from a region than the oxygen in the fish’s blood, of higher concentration to a water flow region of lower concentration. countercurrent flow maximizes the amount of oxygen the fish can pull oxygen from the water by diffusion. In exchange counter­current flow, blood is always blood flow passing by water that contains more oxygen than it does. Both well-aerated water entering the gills and depleted water leaving the gills pass by blood with an even lower oxygen load. Oxygen diffuses into the blood along the entire length of the gill. Swimming and Maneuvering R E ADI N G TO OLB ox Most fish swim by contracting large segmented muscles on either side of their from the head to the tail. These muscle segments power the TAKING NOTES contractions that produce a series of S-shaped waves that move down the fish’s Draw a simple picture of a fish in your notes and label body and push it through the water. These waves also tend to nudge the fish the five kinds of fins found from side to side. Such horizontal movements waste energy, so fish counteract on most fish. them with their fins. As you can see in Figure 2.2, fins are surfaces that project from a fish’s body. Most fish have dorsal fins on their backs and anal fins on their bellies. Most fish also have two sets of lateral paired fins. One set, the pectoral fins, are found just behind the head. The other set, the pelvic fins, are often found near FIGURE 2.2 This clown anemone the middle of the belly. The caudal is another name for the tail fin. Fin fish shows the main types of fins tissue is supported by part of the endoskeleton, and its associated muscles let commonly found in fish. fish actively move their fins as they swim. Fins keep fish stable. Their movements redirect water around the fish as it swims, producing forces that keep it from rolling, pitching up and down, and moving from side to side. The dorsal and anal fins keep the fish from rolling over. The caudal fin moves the fish in a forward direction. caudal fin The pectoral and pelvic paired fins help the fish to maneuver, stop, and hover in the water. Infer What is the connection between countercurrent flow and a fish’s movement in the water? 10a pectoral fin anal fin ©David Fleetham/Bluegreen

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MAIN IDEA Figure 2.3 Jaws evolved from gill supports. Evidence from animal development studies sup- ports the idea that jaws evolved from gill arches. The jaws of fish evolved from gill arches, also known as pharyngeal arches. Located on both sides of the pharynx, gill cranium arches are structures made of bone or cartilage that function as a support for a fish’s gills. As shown in Figure 2.3, jaws developed from gill arches near the mouth, which fused to the cranium. The upper section of the third gill arch attached to the cranium, forming the upper jaw. Because the gill arches are jointed, the bottom part of the gill arch could bend to mouth gill arches open and close the mouth, forming the lower jaw. Agnatha Jawless fish such as lampreys evolved from In most fish, the fourth set of gill arches are also fused to filter-feeding ancestors. In jawless fish, the filters the cranium. In these animals, the upper part of the gill arch were modified to function as gills. reinforces the jaws. The gill arch’s lower part supports the tissue inside the floor of the mouth. Most jawed vertebrates cranium have teeth on their upper and lower jaws. Teeth are used to capture and process food. They evolved from the armored scales that covered early jawless fish. As a result of , jaws gave vertebrates a huge advantage as predators and quickly pushed them to the top of the . But the original function of jaws may not have been to help fish capture food. Evidence suggests that the mouth earliest jaws prevented backflow as a fish pumped water over its Placoderms Jaws developed from what was the third gill arch in Agnatha. gills. Clamping the front pair of arches together prevented oxygen-rich water from escaping through the mouth, ensuring cranium that it all flowed over the gills. The fact that they also kept prey from escaping was a happy accident. Compare What advantages are provided to an animal that has jaws, compared with an animal that does not have jaws?

MAIN IDEA 8B Only two groups of jawed fish mouth

still exist. Modern fish In modern fish such as sharks, the fourth set of gill arches fused to the cranium. Jawed fish diversified very quickly after their first appearance about 440 million years ago. Four groups of fish appeared at this time. • Acanthodians Acanthodians were fish covered with spines. They became extinct about 250 million years ago. Biology VIDEO C • Placoderms Placoderms were heavily armored with huge bony plates. LIP They became extinct about 350 million years ago. HMDScience.com • Cartilaginous fish Cartilaginous fish are one of the two groups of fish that go online survive today. The cartilaginous fish include sharks, rays, and chimeras. Fish Adaptations • Bony fish Bony fish are the group that includes all other living fish and is the other group of fish still in existence.

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word meaning “fish.” -ichthyes comes from aGreek word meaning “cartilage,” and chondr- comes from aGreek In theword Chondrichthyes, VOCABULARY F F up to 48 km/h (30 mi/h). up to 48km/h(30 species may swim at speeds pursuing prey, some surrounding reefs. When is found inthetr into itsattacker. at thebase ofitstail to inject the ray use will avenomous barb beneath coral reefs. Ifthreatened, lives ocean onsandy bottoms IGURE IGURE Unit 8:Animals R E I D A 2.4 2.5 2.5

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The grey reef shark The blue-spott G opical waters TO B L O o ed ray x basking sharks, are filter feeders that eat . lions. and eatspecies sea seals The biggest sharks, sharks whale the and to “fly” through water. the Most rays, such as blue-spotted the ray shown in huge manta rays, are planktonic filter feeders. Most rays have poisonous Figure 2.5, Figure such as greyreef the shark shown in of300 species sharks and nearly of 400species rays and skates. Most sharks, other invertebrates. with fish platelikeof deep-sea on feed They grinding teeth. and thyes— and Elasmobranchs. major predators There ocean. are inevery two groups within Chondrich- the relatively skeletons, flexible have cartilaginous fish astrong bite, and are they stiffer than squishy the stuff found inhuman joints. Even have though they found skeletons intheir is unique. It contains calcium deposits that make it have fish These lost ability the to make bone. of In type cartilage the fact, characteristic means that cartilaginous their skeleton is not aprimitive trait. made of ancestors their cartilage, while had skeletons made of bone. This Members of class the Chondrichthyes, or have cartilaginous fish, skeletons Fish Cartilaginous Ray The E The H s and skates have flattened and large bodies that fins use pectoral they lasmobranchs include sharks, rays, and skates. There are more than olocephali include chimeras, or ratfish. Chimeras are group asmall crush invertebrates crush such as crustaceans for Others,such food. as the provides buoyancy that keeps from them sinking. areThey denser actually than water, but oil stored intheir fertilization, and many give species to birth live young. havethey many advanced features. have They internal attackers. but instead thorny use projections on backs their to fight off selves against predators. Skates do not have poisonous , venom to use defend , which they them- barbed intheir at lateral the system adistance line. called with a sensory ofsense prey’s their smell. sense can They also movements are swimmers powerful eyesight with good and an excellent

Car Whi tilaginous are fish incredibly efficient hunters. They le the cartilaginous fish as cartilaginousle fish agroup the may ancient, be Figure 2.4, 2.4, Figure hunt other although fish, some

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©Roberto Rinaldi/Bluegreen Contrast 25.2 2. 3. 1. Re the mouththe toward through gills the low-pressure the area by operculum. the just outside Water gills. the flows from high-pressure the area in movefish water over by gills their creating alow-pressure area pr bo of on time periods land. other One fish. group of bony can fish even spend short trenches.oceans, and deep-sea Some have become parasites of includingon Earth, tropical freshwater streams, Antarctic ofspecies bony living aquatic fish innearly environment every Greek word meaning “bone”). There are more than 20,000 arefish Osteichthyes the called prefix (the oste- comes from a otherAll living have fish skeletons made of bone. bony These Bony Fish have fish All a detect the electric currents electric the generateddetect by heartbeat the of ahiding animal. sensitive. In experiments other are inwhich all senses blocked, ashark can still electroreceptivethe cells are clustered on snout, the and are they extremely electroreceptive receive In signals. they cells because cartilaginous fish, electric by muscular contractions organs inother animals. sensory These are called swim. they feel movements the water inthe currents created by more distant animals as movement. The lateral line gives of asense fish “distant touch,” letting them sides of made fish the up of cells that are sensitive to changes small inwater shown in

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F lobe-fin ray-fin VOCABULARY and ambushingprey. a torpedo-shaped bodyis of diversity inandamongspecies adaptation andto thedevelopment relationship ofnatural selection to 7E analyze andevaluate the groups inthefossil record; stasis, andsequential of any data ofsuddenappearance, scientific explanations concerning data; 7Banalyze andevaluate inferences, andpredict trends from dapted for quick swimming IGURE Unit 8:Animals 2Ganalyze, evaluate, make 3.1 25.3

A barracuda’s 2G, 7B, 7E A Closer Lookat BonyFish Ray-finned fish have fish fins. Ray-finned their in afan ofbones trout orbass. ofthese All fishesare examples ofbonyfish. carnival orate for atunafishsandwich lunch.Ormaybe you fishat alocal lake for Most ofthefishyou are familiar withare bonyfish.Perhaps you won agoldfish at a Connect to Your World Ke lobe-finned fish.

y bodies of bonybodies for are swimming fish and specific specialized feeding strategies. water.the But others can quite look different. As aresult of natural the selection, have streamlined that torpedo-shaped bodies make it easier to through swim up nearly of half vertebrate all Most species. familiar such species, as , The ray-finned are fish most the diverse group of living vertebrates, making Diversity Body of have thickened ray-fins that around letshuffle them slowly on land. to stand straws. on afewSome soda ray-finned such fish, as , water. would They buckle under fish’s the weight. It would like trying be verability means also that are they and thin to weak too provide support out of shape, more makingfish the maneuverable water. inthe But fins’ the maneu- light, collapsable, and to easy move. can fish quickly Ray-finned change afin’s fish’sthe This wall. arrangement body of bones and muscles makes fin the of skinand connective tissue. The muscles that move bones the are found in shaped array of a bones called ray-finned suchAll fish, as and tuna, have supported fins by afan- MAI MAI C

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lan seen byseen predators lurking above surface. the invertebrates from avoiding while surface the being point up. plan This body allows to them slurp up havesome killifish, flattened and that or beds, algae inlarge schools of own their species. able. are They usually found on coral reefs, indense cannot fish, fly quickly swim but are maneuver very Fish t Fish t accelerate quickly and prey. their surprise shown in Lon ed rounded finssupported by asingle bone. s g, torpedo-shapedg, such fish, as barracuda the hat are flattened from side to side, such as butter hat on feed of surface the water, the such as ray-fin. Figure 3.1, Ray-fins areRay-fins layer inathin embedded are ambush predators that can

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©2006 Kare Telnes/Image Quest Marine E maintains buoy T F xplain IGURE he uniquefeatures oftheanatomy ofabonyfishincludeswim bladder that swim bladder. Most ray-finned have fish into modified abuoyancy a called Afloat Staying like a loudspeaker.like a bladderbones. swim the even use to Afew fish make sounds by vibrating it up sound waves and transmitting to them inner the through of aseries ancy. Some species’ bladders swim are adapted for as an use amplifier, picking you more buoyant. Reabsorbing oxygen into bloodstream the reduces buoy- bloodstreamthe increases buoyancy same the way inflating alife vest makes air from bladder swim the to maintain neutral buoyancy. Adding oxygen from toward surface. the But changes fish ifthe depth, it must either add or remove neutrally buoyant not does fish have to to swim keep from sinking or floating or lower water. inthe The bladder swim save fish lets the a because energy breathe air and out survive of water for hours several at atime. lives instagnant streams inWest have fish These but Africa. gills, can also • • gills

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©Reg Morrison/Auscape/Minden Pictures Identify 25.3 3. 2. 1. Re from ancient , and have they changed indifferent ways over time. direct ancestorsthe of terrestrial vertebrates. groups Both are descended body. However, characteristic this not does mean that lungfish modern are only animals with separate circuits blood for lungs the and rest the of the supports For idea. this example, lungfish and terrestrial vertebrates are the relatives of terrestrial vertebrates. Anatomical also evidence mitochondrial DNA suggest that lungfish are closest the living terrestrial vertebrates are controversial. Recent studies of pond. their refills as water the up. dries breathe Then they air until next the rain up.ponds dry make They burrows mud, inthe which hardens cannot tolerate. Lungs even keep some alive species their when can livethey instagnant, oxygen-poor water that other fish breathe with eitheror gills lungs. This characteristic means that and swamps inAustralia, can South They America,and Africa. Lungfish, such as one the shown in Lungfish off coast the ofAnother South Africa. was discovered near Indonesia in1997. at same the as time . the In 1938,amodern was caught fossilthe record. Before 1938,scientists assumed that had gone they extinct (410to 65million yearsperiods ago), and completely then disappear from and shallow marine deposits from Devonian the until late the live waterBoth indeep Indian inthe Ocean. withare fat and filled provide buoyancy. There are of two species coelacanth. andfins with atail threebreathe They lobes. Their bladders swim with gills. (SEE-luh-kanths) are distinctive-looking with fish thick, fleshy Coelacanths

from ray-finned fish? brate evolution? How are l How are related to thefin’s function? ray-fin? How isthearrangement How are thebonesarranged ina vi The r Coe e

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enet CO means “.” Greek word akantha,which means “hollow,” andthe Greek word koilos, which from thecombination ofthe The namecoelacanth comes VOCABULARY feature. appearance ofthisnovel responsible for thesudden how in modernspecies.Explain the fossil record andpersist anal fins appear suddenly in Second sets ofdorsal and single dor Early coelacanth fossils have Chapter 25:Vertebrate Diversity NNE R HMDScience.com Self-check Online 3.4 E Hox ics ADI C

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Something Smells FISHY

Web BIOLOGY Fish and Oxygen Needs Fisheries on the Brink What Type of Fish Is It? Determine the relationship Worldwide, many marine fisheries have Can you tell a ray-finned between fish distribution been fished to their sustainable limits fish from a cartilaginous and oxygen availability in or overfished, while more people are fish? Use physical character- Lake Malawi in Africa. depending on fish for food. Explore istics to categorize a set of the problems facing the marine fisher- jawed fish. ies and what we can do to save them. ©Jeffrey L. ©Jeffrey Rotman/Corbis L.

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25.4 Amphibians

7A, 7D, 7E, 8B, Key Concept Amphibians evolved from lobe-finned fish. 8C MAIN IDEAS VOCABULARY Amphibians were the first animals with four limbs. Amphibians return to the water to reproduce. amphibian Modern amphibians can be divided into three groups.

Connect to Your World 7A analyze and evaluate What would it really be like to be a “fish out of water”? On shore, the air does not how evidence of common ancestry among groups is provided by the support your body. Gravity pulls on you and makes it hard to move. Your lateral line fossil record, biogeography, and does not work. You are deaf because your body absorbs sound waves before they homologies, including anatomical, molecular, and developmental; reach your ear. The air is too thin to let you suck food into your mouth, and it is so 7D analyze and evaluate how the dry that you start losing water through your skin. These are just a few of the condi- elements of natural selection, including inherited variation, the tions animals faced when they first moved onto land. potential of a population to produce more offspring than can survive, and a finite supply of 7a environmental resources, result in MAIN IDEA differential reproductive success; 7E analyze and evaluate the Amphibians were the first animals with relationship of natural selection to adaptation and to the development four limbs. of diversity in and among species; 8B categorize organisms using a One of the oldest known fossils of a four-limbed vertebrate was found in hierarchical classification system based on similarities and differences 360-million-year-old rocks from Greenland. We know that Acanthostega had shared among groups; 8C compare lungs and eight-toed legs. But it also had gills and a lateral line system, neither characteristics of taxonomic groups, including archaea, bacteria, protists, of which work in air. These features suggest that the earliest animals with four fungi, plants, and animals limbs were aquatic and used their limbs to paddle underwater. All of the vertebrates that live on land, as well as their descendants that have returned to aquatic environments, are . A tetrapod is a verte- brate that has four limbs. Each evolved from a lobe-fin. Tetrapod legs contain bones arranged in the same branching pattern as lobe-fins, except that the fan of bones at the end of the fin is replaced by a set of jointed fingers, , or . Animals such as snakes, which do not have four limbs, are still considered to be tetrapods because they evolved from limbed ancestors. Limbs and lungs were features that made these animals successful in an oxygen-poor, debris-filled underwater environment. But, over time, these adaptations let tetrapods climb out of the water to search for food or escape predators. These animals gave rise to the first amphibians. Amphibians are animals that can live both on land and in water. In the word amphibian, the Biology IDEO root amphi comes from a Greek word meaning “on both sides,” while the V CLIP suffix -bian comes from a Greek word meaning “life.” HMDScience.com A number of adaptations help amphibians to live on land. Large shoulder go online and bones help support more weight, while interlocking projections on Tetrapod Evolution the vertebrae help keep the backbone from twisting and sagging. A mobile, muscular allows amphibians to capture and manipulate food. Develop- ment of a helps some amphibians to hear out of the water.

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to atetrapod’s. neckandribsfunctional similar shoulders, along witha digits, proto-wrists, elbows, and beginnings oflimbs, including However, italso hasthe fins andscales like afish. tetrapods. roseae has species between fishand fossil remains ofatransitional In 2006,scientists uncovered the H pouch moist F IGURE Unit 8:Animals is CO t

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further intofurther ear the cavity to middleand the inner ear. tympanicthe membrane, or eardrum, which transfers sound the waves top arch. of part second the gill Sound waves moving through air the vibrate me of water through it skinwhen their is available and store it season. for dry the during brief the rainy can species absorb Desert-living large season. amounts live where burrowA few species they indeserts, underground, emerging only This for need moisture is why you rarely an find amphibian inarid habitats. and amphibians out move riskifthey drying far too from asource of water. An amphibian’s and skinis thin wet. Water constantly evaporates from it, outfrom air. inthe drying to live on land. But did not they evolve ways to keep themselves or eggs their to organs the blood and returns oxygen-poor to heart. the blood and lungs. pumped Blood through systemic the circuit brings oxygen-rich double circuit. pumped Blood through pulmonary the circuit goes to skin the separated bypartially is two the pumped atria. Blood through on heart the a up of two atria and one ventricle. Oxygenated and deoxygenated are blood heart, amphibians have a three-chambered heart. An amphibian heart is made and pressure of air inits mouth. Unlike which have fish, atwo-chambered structure. An amphibian its uses lungs to breathe by changing amount the ofor use the gills lungs. lungs The balloonlike of an amphibian are simple in MAI Some amphibians can hear sound due to development the of atympanic Ove Depe mbrane attached . the to The abone stapes called evolved from the N

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aquatic of frogs. larvae have and gills abroad-finned tail, and by swim limbless their they wiggling like fish. bodies

They typicallyThey eat algae, but some may eat inverte- small brates or even other tadpoles. 7D Some frogs lives their start as tadpoles. wet, including Amphibians many use strategies to keep eggs their out and dry die withoutwill a source of moisture. Their do not eggs have ashell, and embryos the Amphibians asource need of water to reproduce. StrategiesReproduction • • • •

bro wrap lay lay as shown in ing on eggs moist ground ing directly inwater eggs oding eggs in pockets on inpockets eggs oding female’s the back, ping inleaves eggs Figure 4.1 Figure T adpoles are

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kidney intestine FIGURE 4.2 Amphibian Metamorphosis

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Amphibian Metamorphosis To grow into terrestrial adults, tadpoles must undergo metamorphosis. Recall R E ADI N G TO OLB ox that metamorphosis is the change in form and habits of an animal. Similar to the metamorphosis of a butterfly, the metamorphosis of a tadpole into an TAKING NOTES Draw a simple diagram of adult frog affects nearly every organ in the tadpole’s body. It produces enor- amphibian metamorphosis in mous changes in the animal’s body form, , and behavior. The stages your notes. At each step, label of amphibian metamorphosis, in which a tadpole transforms into its adult the changes that occur as the form, are shown in Figure 4.2. amphibian changes from an egg to its adult form. During metamorphosis, the tadpole undergoes many changes. The gills are reabsorbed and lungs develop, shifting the frog from a water-breathing to an air-breathing mode of life. The is reorganized to send blood to the lungs. The tail fin (if not the entire tail) is reabsorbed. The body grows limbs and completely reorganizes its skeleton, muscles, and parts of the . The digestive system is rebuilt to handle a carnivorous diet. In the adult amphibian, occurs in the animal’s stomach, and wastes are expelled through the cloaca. The cloaca is also a part of the . Many amphibians do not undergo metamorphosis. Adult females lay eggs on the ground or keep them in their bodies, and the young develop directly into their terrestrial forms. Infer Describe the stages of amphibian metamorphosis.

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There are more thanof 300species salamanders. As shown in Salamanders feeding habits and requirements of habitats the live. inwhich they (suh-SIHL-yuhnz). plans The body of amphibians these are adapted to the The three groups of amphibians modern are salamanders, frogs, and caecilians

at its prey and pulling it back into its mouth. mouths asdo. fish On land, asalamander hunts by its flinging sticky tongue and frogs. and Salamander some larvae aquatic adults suck into food their worms,as , and snails. Large eat species vertebrates smaller such as fish throughgases lining the of skinand their mouth. Members of largest the family of salamanders do not have lungs and exchange mature, growing into aquatic adults that like look giant tadpoles with legs. such retain as axolotl the some (AK-suh-laht-uhl), juvenile features as they a number of adaptations to way their specific of life. Some salamander species, probablypods walked.But appearances deceiving. can Salamanders be have a side-to-side movement biologists is similar to think way the ancient tetra- salamanders have along body, four limbs, walking and with atail. walk They d various MAI wings, andputthemintheproper sequence. C

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(t) ©Stephen Dalton/Photo Researchers, Inc.; (c) ©Michael & Patricia Fogden/Minden Pictures Contrast 25.4 2. 1. Re for alife burrowing through soil. the make like look them giant earthworms, and are they specialized (4 in.) to 1.5meters have Caecilians (5ft). that banded bodies are ranging 160species, inlength from about 10centimeters are legless, burrowing amphibians that live tropics. inthe There skeleton to stiffenits and body drive its headforward like abattering ram. would. Instead, like an earthworm, ahydrostatic uses acaecilian havethey cannot no legs, they digthrough way the soil the amole through searching soil the for earthworms and Because grubs. Caecilians (suh-SIHL-yuhnz),Caecilians such as one the shown in Caecilians and eat will any can animal catch. they Although mostdriest deserts. tadpoles eat algae, adult frogs are predators that they are . poisonousthese frogs and toads have bright coloration that warns predators frogs make that protect animals the from predators. Many of species jumpers. Glands bumpy inthe skinof toads and smooth the skinof tropical skin than do other frogs, as well as relatively shorter legs that make poor them absorb shock the of landing. and power. Their hind legs have bones that fused ,in their legs, and feet increase speed their arebodies adapted for jumping. Elongated bones eardrums, andexposed bulging . Their longbodies, muscular hind limbs, webbed feet, frogs are physically distinctive, with tailless amphibians, with more thanAdult 3000species. Frogs make up largest the group of living F

rogs living indeser How have amphibians adapted to first What evidence suggests that the vi Lik Fro Toa e wi tetrapods were

e other amphibians, caecilians are predators. burrow They gs live in every environmentgs live inevery except on at Earth poles and the inthe ds are one actually family of frogs. have They rougher and bumpier How are caecilians different from other amphibians? amphibians? other from different caecilians How are 7 7 F A d n ormative Assessment g t environments?

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25.5 Vertebrates on Land

7A, 7B Key Concept Reptiles, birds, and mammals are adapted for life on land. VOCABULARY MAIN IDEAS can retain moisture. Amniotes do not need to return to water to reproduce. amniotic egg placenta Connect to Your World Around 350 million years ago, one group of ancient amphibians evolved traits that let 7A analyze and evaluate how evidence of common ancestry them walk away from the water forever. Over time, they diversified into the types of among groups is provided by the vertebrates you are most familiar with, including reptiles, birds, and mammals—the fossil record, biogeography, and homologies, including anatomical, class that includes you. molecular, and developmental and 7B analyze and evaluate scientific explanations concerning any data of sudden appearance, stasis, and MAIN IDEA 7A, 7B sequential nature of groups in the fossil record Amniotes can retain moisture. An amniote is a vertebrate that has a thin, tough, membranous sac that encloses the embryo or fetus. Amniotes first appeared as small, lizardlike creatures in the late period. Since that time, amniotes have evolved into thousands of different forms and have invaded nearly every on Earth. They have become predators in the tropics, the most arid deserts, the Arctic, and in any number of freshwater and marine environ- ments. They have become burrowers, sprinters, sit-and-wait predators, and slow trackers. Some species never leave the trees. Some specialize in eating plants and have evolved symbiotic relationships with bacteria that can break down cellulose. Some have also developed powered flight.

CONNECT TO When you look at the phylogenetic tree of amniotes, it is clear that many of the species we see today are survivors of larger radiations that have gone extinct. Mammals are survivors of a huge line of animals that went extinct Recall from the chapter The Evolution of Populations that a about 245 million years ago. Birds are survivors of the radiation and mass extinction is an intense extinction. period of extinction that occurs All amniotes share a set of characteristics that prevent water loss. Skin cells on a global scale. In the - extinction, 95% of all are waterproofed with keratin. Keratin is a that binds to lipids inside species and over 50% of all the cell, forming a hydrophobic—or water repellent—layer that keeps the families disappeared. water inside the animal from reaching the skin. The presence of this hydro- phobic layer means that amniotes lose less water to evaporation than amphib- ians do. Waterproofing also means that amniotes cannot exchange gases across their skin. They rely on their lungs for . Kidneys and large intestines are bigger in amniotes than in amphibians. These organs contain tissues that reabsorb water. The increased surface area of these tissues enables amniotes to absorb more water internally, so they lose less to excretion than do amphibians. Connect What makes your skin cells waterproof? Why is this important?

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©Zigmund Leszczynski/Animals Animals/Earth Scenes. All rights reserved. to water to reproduce. to need not do Amniotes return Summarize 25.5 2. 1. Re

found in a typical amniotic egg. The Their eggs have no shells, but their embryos make the same series of membranes evolved ability the to give to birth living, well-developed young. hatch. Retaining protects eggs from them predators. Some amniotes have do not lay Instead, them. oviduct intheir keep eggs their they until they may 5to lose 30%of its weight body as it makes an egg. represents alarge investment of energy. For example, a build shell the around egg Each egg. fertilized the and white to embryo the until feed it hatches, then laying amniotes, mother the must make enough yolk anyLike is expensive. swimming egg the pool, In egg- a private that pool mother the builds for her embryo. partially envelops the fetus. develops in female mammals during pregnancy. It lines the uterine wall and there. The evolutionthe of amniotic the that egg letstay them could move into environments drier on land. But it was With adaptations that limit water loss, amniote adults to the embryo and also removes metabolic wastes from the embryo. not have to return to a wet environment to reproduce. out asdrying it develops. After it evolved, amniotes did waterproof container that keeps embryo the from

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CHAPTER 25 G N I D A E R V

caption. Here’s anexample for theterm operculum. to illustrate Below theirmeaning. each picture, write a For each term below, use simple shapes,linesorarrows the definitionofterm. below, explain how themeaning oftheroot relates to Using theGreek orLatin word originsoftheterms the two terms ineach ofthefollowing pairs. Describe onesimilarity andonedifference between Compare andContrast R 25.2 25.1 vo Chapter 10. 12. 13. 11. 8. 6. 4. 2. 5. 9. 3. isualize 7. 1. eviewing

amniotic egg, pl amniotic egg, shark amemberofthegroup Chondrichthyes? comes from aGreek word meaning “cartilage.” Why isa In theterm chondrichthy tetrapod, amphibi In theterm t ray-fin, l Greek words meaning “back” and“gut orstring.” The word lung gill, meaning “blind.” (Hint:Consider where acaecilian lives.) endoskel lat The term c invert counter operire, whichmeans “to cover.” The word that c An operculum isaprotective plate

eral line operculum lateral line count gill endoskeleton not chordate overs ofabonyfish. thegills ebrate, vertebrate ochord V Review ocabulary current flow X O B L O O T obe-fin ercurrent flow eton, exoskeleton notochord comes from acombination ofthe operculum comes from theLatin word aecilian comes from theLatin word caecus, c V abu etrapod, theprefixtetra- means “four.” ocabulary acenta lary an O and Greek ri es, theword chondr- part g ins L 25.4 25.3 ati n Word Word n

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reproduce. Explain why amniotes do not needto return to water to reproduction, butboth are able to reproduce onland. Mammals andbirds ha why each for isimportant life onland. where anamniote can live? How doesthepres List two adap What are thethr relative to terrestrial vertebrates? What fe arches?gill What evidenc Name thesev these animals share at some pointintheirdevelopment? survive? How doesthestructure oftheirfinshelpthemto very diff Sea squirtsanddogs are both chordates, butthey are environment? Why doesamphibian repr ra What oftheswim isthefunction bladder ina and methodsoffindingfood, y Barracuda andflatfish have very different bodyshapes ofafish function How doescountercurrent flow contribute to the ofanendo parts vertebratesAll have anendoskeleton. What are the main y-finned fish? HMDScience.com Interact 7A ature ofalobe-fin fishmakes ittheclosest erent kindsofanimals. What four features do

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Use the image below to answer the next three questions. I Critical 28. 30. 34. 29. 32. 33. 27. 31. nterpreting Unit 8:Animals

kidneys that frogs have? a couple ofdays withoutwater betterthanthetypeof Connect beneficial for frogs? yet they have webbed feet. How are webbed feet I in thewater. how submarinesuse these systems to rise anddescend knowledge ofhow aswim bladder works to explain system that works muchlike aswim bladder. Use your A animal, what asalimb? mightfunction bodypart A A other at each station. happens andwhyasthewater andblood pass each atin agill whichgas exchange takes place. Describe what countercurrent flow. Imagine that there are five stations lungless breathe? your reasoning. group offishdoesthemudskipperbelong? Explain characteristics ofthemudskipper’s fin shape,to which A A wat Classify an endoskeleton. of thenotochord andtheinternal backbone of nfer pply pply nal nalyze nalyze er andisresting onarock. Based onthephysical yze

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per minute of time. measured as the number of seconds the male called male toad’s body and calling effort, is a scatterplot that shows the relationship between a were recorded for a population of Fowler’s toads. Below The calling activity, body size, and body temperature Use the data below to answer the next three questions. A Making Connections

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©Jane Burton/Nature Picture Library Biology End-of-Course Exam Practice

Record your answers on a separate piece of paper. 2G, 7A MULTIPLE CHOICE 4 f ish reptiles humans 2B, 2D 1 A scientist discovers a new type of organism in the deep ocean. Because this organism was found in the water, the scientist suspects it may be related to fish. This idea most closely resembles a scientific — According to the above, which of the A theory following statements is true? B hypothesis A Fish are more closely related to humans than C suggestion reptiles. D experiment B Reptiles are more closely related to marsupials 2G, 7B than fish. 2 Fossils found in New Zealand suggest that as C Marsupials and fish do not share a common many as 2,000 frog species lived there in the past. ancestor. Today, there are fewer than 300 frog species. D Marsupials and humans share a common What conclusion can be drawn from this ancestor. information? THINK THROUGH THE QUESTION A The climate conditions in New Zealand have changed over time. Recall that are based on common ­ancestry, and that they are read from left to right. B The species alive today are more specialized to a particular niche than the species of the past. C Biological diversity of frogs in New Zealand 10A has decreased. 5 Countercurrent flow in a fish’s gills allows blood D There are fewer frog species today because a to efficiently release carbon dioxide into the water mass extinction occurred. and absorb oxygen from the water. Which of the following best describes why this process is 2G, 7A referred to as “countercurrent flow”? 3 A Oxygen and carbon dioxide flow in opposite A B C directions. B Fish need to swim backwards in order for gas D exchange to take place. ancestor C The movement of the water flows in the opposite direction as the blood. After studying fossils of prehistoric fish in one D Fish need to swim against the current in order region, scientists developed this family tree to for gas exchange to take place. describe how the various species they found are 11B related. Which of the following is true with 6 About 245 million years ago, at the boundary of regard to the diagram above? the Permian and Triassic periods, 95 percent of all A The Ancestor species has gone extinct. species died out. This event is referred to as a(n) — B Species A and Species C are not related. A episode of C Species D evolved before Species A, B, and C. B population explosion D Species C evolved before Species A and B. C mass extinction D intense adaptation

Chapter 25: Vertebrate Diversity 753