Bài giảng Biology - Chapter 34: Vertebrates

Chapter 34VertebratesOverview: Half a Billion Years of BackbonesBy the end of the Cambrian period, some 540 million years agoAn astonishing variety of animals inhabited Earth’s oceansOne of these types of animalsGave rise to vertebrates, one of the most successful groups of animalsThe animals called vertebratesGet their name from vertebrae, the series of bones that make up the backboneFigure 34.1There are approximately 52,000 species of vertebratesWhich include the largest organisms ever to live on the EarthConcept 34.1: Chordates have a notochord and a dorsal, hollow nerve cordVertebrates are a subphylum of the phylum ChordataChordates are bilaterian animalsThat belong to the clade of animals known as DeuterostomiaTwo groups of invertebrate deuterostomes, the urochordates and cephalochordatesAre more closely related to vertebrates than to invertebratesA hypothetical phylogeny of chordatesChordatesCraniatesVertebratesGnathostomesOsteichthyansLobe-finsTetrapodsAmniotesMilkAmniotic eggLegsLobed finsLungs or lung derivativesJaws, mineralized skeletonVertebral columnHeadBrainNotochordAncestral deuterostomeEchinodermata(sister group to chordates)Urochordata(tunicates)Cephalochordata(lancelets)Myxini(hagfishes)Cephalaspidomorphi(lampreys)Chondrichthyes(sharks, rays, chimaeras)Actinopterygii(ray-finned fishes)Actinistia(coelacanths)Dipnoi(lungfishes)Amphibia(frogs, salamanders)Reptilia(turtles, snakes,crocodiles, birds)Mammalia(mammals)Figure 34.2Derived Characters of ChordatesAll chordates share a set of derived charactersAlthough some species possess some of these traits only during embryonic developmentMusclesegmentsBrainMouthAnusDorsal,hollownerve cordNotochordMuscular,post-anal tailPharyngealslits or cleftsFigure 34.3NotochordThe notochordIs a longitudinal, flexible rod located between the digestive tube and the nerve cordProvides skeletal support throughout most of the length of a chordateIn most vertebrates, a more complex, jointed skeleton developsAnd the adult retains only remnants of the embryonic notochordDorsal, Hollow Nerve CordThe nerve cord of a chordate embryoDevelops from a plate of ectoderm that rolls into a tube dorsal to the notochordDevelops into the central nervous system: the brain and the spinal cordPharyngeal Slits or CleftsIn most chordates, grooves in the pharynx called pharyngeal cleftsDevelop into slits that open to the outside of the bodyThese pharyngeal slitsFunction as suspension-feeding structures in many invertebrate chordatesAre modified for gas exchange in aquatic vertebratesDevelop into parts of the ear, head, and neck in terrestrial vertebratesMuscular, Post-Anal TailChordates have a tail extending posterior to the anusAlthough in many species it is lost during embryonic developmentThe chordate tail contains skeletal elements and musclesAnd it provides much of the propelling force in many aquatic speciesTunicatesTunicates, subphylum UrochordataBelong to the deepest-branching lineage of chordatesAre marine suspension feeders commonly called sea squirtsFigure 34.4cTunicates most resemble chordates during their larval stageWhich may be as brief as a few minutesPharynx with slitsNotochordTailDorsal, hollownerve cordAtriumStomachIntestineExcurrent siphonIncurrentsiphonMusclesegments(c) A tunicate larva is a free-swimming butnonfeeding “tadpole” in which all fourchief characters of chordates are evident.As an adultA tunicate draws in water through an incurrent siphon, filtering food particles(a) An adult tunicate, or sea squirt, is a sessile animal (photo is approximately life-sized).(b) In the adult, prominent pharyngeal slits function in suspension feeding, but other chordate characters are not obvious.TunicPharynxwith numerousslitsAtriumExcurrentsiphonIncurrentsiphonto mouthStomachEsophagus IntestineAnusExcurrent siphonFigure 34.4a, bLanceletsLancelets, subphylum CephalochordataAre named for their bladelike shapeTentacleMouthPharyngeal slitsAtriumDigestive tractAtrioporeSegmentalmusclesAnusNotochordDorsal, hollownerve cordTail 2 cmFigure 34.5Lancelets are marine suspension feedersThat retain the characteristics of the chordate body plan as adultsEarly Chordate EvolutionThe current life history of tunicatesProbably does not reflect that of the ancestral chordateGene expression in lanceletsHolds clues to the evolution of the vertebrate formBF1BF1OtxOtxHox3Hox3ForebrainMidbrainHindbrainNerve cord of lancelet embryoBrain of vertebrate embryo(shown straightened)Figure 34.6Concept 34.2: Craniates are chordates that have a headThe origin of a headOpened up a completely new way of feeding for chordates: active predationCraniates share some common characteristicsA skull, brain, eyes, and other sensory organsDerived Characters of CraniatesOne feature unique to craniatesIs the neural crest, a collection of cells that appears near the dorsal margins of the closing neural tube in an embryoNotochord(a) The neural crest consists of bilateral bands of cells near the margins of the embryonic folds that form the neural tube.(b) Neural crest cells migrate todistant sites in the embryo.Migrating neuralcrest cellsEctodermEctodermDorsal edgesof neural plateNeuralcrestNeuraltubeFigure 34.7a, bNeural crest cellsGive rise to a variety of structures, including some of the bones and cartilage of the skull(c) The cells give rise to some of the anatomical structuresunique to vertebrates, including some of the bones and cartilage of the skull.Figure 34.7cThe Origin of CraniatesCraniates evolved at least 530 million years agoDuring the Cambrian explosionThe most primitive of the fossilsAre those of the 3-cm-long HaikouellaFigure 34.8a(a) Haikouella. Discovered in 1999 in southern China, Haikouella had eyes and a brain but lacked a skull, a derived trait of craniates.In other Cambrian rocksPaleontologists have found fossils of even more advanced chordates, such as HaikouichthysFigure 34.8b(b) Haikouichthys. Haikouichthys had a skull and thus is considered a true craniate.5 mmHagfishesThe least derived craniate lineage that still survivesIs class Myxini, the hagfishesFigure 34.9Slime glandsHagfishes are jawless marine craniatesThat have a cartilaginous skull and axial rod of cartilage derived from the notochordThat lack vertebraeConcept 34.3: Vertebrates are craniates that have a backboneDuring the Cambrian periodA lineage of craniates evolved into vertebratesDerived Characters of VertebratesVertebrates haveVertebrae enclosing a spinal cordAn elaborate skullFin rays, in aquatic formsLampreysLampreys, class CephalaspidomorphiRepresent the oldest living lineage of vertebratesHave cartilaginous segments surrounding the notochord and arching partly over the nerve cordLampreys are jawless vertebratesInhabiting various marine and freshwater habitatsFigure 34.10Fossils of Early VertebratesConodonts were the first vertebratesWith mineralized skeletal elements in their mouth and pharynxDorsal viewof headDentalelementsFigure 34.11Armored, jawless vertebrates called ostracodermsHad defensive plates of bone on their skinPteraspisPharyngolepisFigure 34.12Origins of Bone and TeethMineralizationAppears to have originated with vertebrate mouthpartsThe vertebrate endoskeletonBecame fully mineralized much laterConcept 34.4: Gnathostomes are vertebrates that have jawsToday, jawless vertebratesAre far outnumbered by those with jawsDerived Characters of GnathostomesGnathostomes have jawsThat evolved from skeletal supports of the pharyngeal slitsMouthGill slitsCraniumSkeletal rodsFigure 34.13Other characters common to gnathostomes includeEnhanced sensory systems, including the lateral line systemAn extensively mineralized endoskeletonPaired appendagesFossil GnathostomesThe earliest gnathostomes in the fossil recordAre an extinct lineage of armored vertebrates called placodermsFigure 34.14a(a) Coccosteus, a placodermAnother group of jawed vertebrates called acanthodiansRadiated during the Devonian periodWere closely related to the ancestors of osteichthyansFigure 34.14b(b) Climatius, an acanthodianChondrichthyans (Sharks, Rays, and Their Relatives)Members of class ChondrichthyesHave a skeleton that is composed primarily of cartilageThe cartilaginous skeletonEvolved secondarily from an ancestral mineralized skeletonThe largest and most diverse subclass of ChondrichthyesIncludes the sharks and raysFigure 34.15a, bPectoral finsPelvic fins(a) Blacktip reef shark (Carcharhinus melanopterus). Fast swimmers with acute senses, sharks have paired pectoral and pelvic fins.(b) Southern stingray (Dasyatis americana). Most rays are flattened bottom-dwellers thatcrush molluscs and crustaceans for food. Some rays cruise in open water and scoop food into their gaping mouth.A second subclassIs composed of a few dozen species of ratfishesFigure 34.15c(c) Spotted ratfish (Hydrolagus colliei). Ratfishes, or chimaeras, typically live at depths greaterthan 80 m and feed on shrimps, molluscs, and sea urchins. Some species have a poisonous spine at the front of their dorsal fin.Most sharksHave a streamlined body and are swift swimmersHave acute sensesRay-Finned Fishes and Lobe-FinsThe vast majority of vertebratesBelong to a clade of gnathostomes called OsteichthyesNearly all living osteichthyansHave a bony endoskeletonAquatic osteichthyansAre the vertebrates we informally call fishesControl their buoyancy with an air sac known as a swim bladderFishes breathe by drawing water over four or five pairs of gills Located in chambers covered by a protective bony flap called the operculumNostrilBrainSpinal cordSwim bladderDorsal finAdipose fin(characteristic oftrout)Caudal finCut edge of operculumGillsHeartLiverKidneyStomachIntestineGonadAnusUrinary bladderLateral lineAnal finPelvic finFigure 34.16Ray-Finned FishesClass Actinopterygii, the ray-finned fishesIncludes nearly all the familiar aquatic osteichthyans(a) Yellowfin tuna (Thunnus albacares), a fast-swimming, schooling fish that is an important commercial fish worldwide(b) Clownfish (Amphiprion ocellaris), a mutualistic symbiont of sea anemones(c) Sea horse (Hippocampus ramulosus), unusual in the animal kingdom in that the male carries the young during their embryonic development(d) Fine-spotted moray eel (Gymnothorax dovii), a predator that ambushes prey from crevices in its coral reef habitatFigure 34.17a–dThe fins, supported mainly by long, flexible raysAre modified for maneuvering, defense, and other functionsLobe-FinsThe lobe-fins, class SarcopterygiiHave muscular and pectoral finsInclude coelacanths, lungfishes, and tetrapodsFigure 34.18Concept 34.5: Tetrapods are gnathostomes that have limbs and feetOne of the most significant events in vertebrate historyWas when the fins of some lobe-fins evolved into the limbs and feet of tetrapodsDerived Characters of TetrapodsTetrapods have some specific adaptationsFour limbs and feet with digitsEars for detecting airborne soundsThe Origin of TetrapodsIn one lineage of lobe-finsThe fins became progressively more limb-like while the rest of the body retained adaptations for aquatic lifeTetrapodlimbskeletonBonessupportinggillsFigure 34.19Extraordinary fossil discoveries over the past 20 yearsHave allowed paleontologists to reconstruct the origin of tetrapodsFigure 34.20AmniotesAmphibiansGreerpetonHynerpetonlchthyostegaAcanthostegaMetaxygnathusElginerpetonEusthenopteron PanderichthysLungfishes CoelacanthsRay-finned fishesPaleozoicSilurianDevonianCarboniferousPermianTo present420415400385370355340325310295280265Millions of years agoAmphibiansClass AmphibiaIs represented by about 4,800 species of organismsMost amphibiansHave moist skin that complements the lungs in gas exchangeOrder UrodelaIncludes salamanders, which have tailsFigure 34.21a(a) Order Urodela. Urodeles (salamanders) retain their tail as adults.Order AnuraIncludes frogs and toads, which lack tailsFigure 34.21b(b) Order Anura. Anurans, such as this poison arrow frog, lack a tail as adults.Order ApodaIncludes caecilians, which are legless and resemble wormsFigure 34.21c(c) Order Apoda. Apodans, or caecilians, are legless, mainly burrowing amphibians.Amphibian means “two lives”A reference to the metamorphosis of an aquatic larva into a terrestrial adultFigure 34.22a–c(a) The male grasps the female, stimulating her to release eggs. The eggs are laid and fertilized in water. They have a jelly coat but lack a shell and would desiccate in air.(b) The tadpole is an aquatic herbivore witha fishlike tail and internal gills.(c) During metamorphosis, the gills and tail are resorbed, andwalking legs develop.Concept 34.6: Amniotes are tetrapods that have a terrestrially adapted eggAmniotes are a group of tetrapodsWhose living members are the reptiles, including birds, and the mammalsA phylogeny of amniotesFigure 34.23SynapsidsAncestralamnioteReptilesDiapsidsArchosaursSaurischiansLepidosaursDinosaursParareptilesTurtlesCrocodiliansPterosaursOrnithischiandinosaursSaurischiandinosaurs otherthan birdsBirdsPlesiosaursIchthyosaursTuataraSquamatesMammalsDerived Characters of AmniotesAmniotes are named for the major derived character of the clade, the amniotic eggWhich contains specialized membranes that protect the embryoThe extraembryonic membranesHave various functionsFigure 34.24ShellAlbumenYolk (nutrients)Amniotic cavitywith amniotic fluidEmbryoYolk sac. The yolk sac contains the yolk, a stockpile of nutrients. Blood vessels in the yolk sac membrane transport nutrients from the yolk into the embryo. Other nutrients are stored in the albumen (“egg white”).Allantois. The allantois is a disposalsac for certain metabolic wastes pro-duced by the embryo. The membraneof the allantois also functions withthe chorion as a respiratory organ.Amnion. The amnion protectsthe embryo in a fluid-filled cavity that cushions againstmechanical shock.Chorion. The chorion and the membrane of the allantois exchange gases between the embryo and the air. Oxygen and carbon dioxide diffuse freely across the shell.Extraembryonic membranesAmniotes also have other terrestrial adaptationsSuch as relatively impermeable skin and the ability to use the rib cage to ventilate the lungsEarly AmniotesEarly amniotesAppeared in the Carboniferous periodIncluded large herbivores and predatorsReptilesThe reptile clade includesThe tuatara, lizards, snakes, turtles, crocodilians, birds, and the extinct dinosaursReptilesHave scales that create a waterproof barrierLay shelled eggs on landFigure 34.25Most reptiles are ectothermicAbsorbing external heat as the main source of body heatBirds are endothermicCapable of keeping the body warm through metabolismThe Origin and Evolutionary Radiation of ReptilesThe oldest reptilian fossilsDate to about 300 million years agoThe first major group of reptiles to emergeWere the parareptiles, which were mostly large, stocky herbivoresAs parareptiles were dwindlingThe diapsids were diversifyingThe diapsids are composed of two main lineagesThe lepidosaurs and the archosaursThe dinosaursDiversified into a vast range of shapes and sizesIncluded the long-necked giants called the theropodsFigure 34.26Traditionally, dinosaurs were considered slow, sluggish creaturesBut fossil discoveries and research have led to the conclusion that dinosaurs were agile and fast movingPaleontologists have also discovered signs of parental care among dinosaursLepidosaursOne surviving lineage of lepidosaursIs represented by two species of lizard-like reptiles called tuataraFigure 34.27a(a) Tuatara (Sphenodon punctatus)Figure 34.27b(b) Australian thorny devil lizard (Moloch horridus)The other major living lineage of lepidosaursAre the squamates, the lizards and snakesLizardsAre the most numerous and diverse reptiles, apart from birdsSnakes are legless lepidosaursThat evolved from lizardsFigure 34.27c(c) Wagler’s pit viper (Tropidolaemus wagleri), a snakeTurtlesTurtlesAre the most distinctive group of reptiles alive todaySome turtles have adapted to desertsAnd others live entirely in ponds and riversAll turtles have a boxlike shellMade of upper and lower shields that are fused to the vertebrae, clavicles, and ribsFigure 34.27d(d) Eastern box turtle (Terrapene carolina carolina)Alligators and CrocodilesCrocodiliansBelong to an archosaur lineage that dates back to the late TriassicFigure 34.27e(e) American alligator (Alligator mississipiensis)BirdsBirds are archosaursBut almost every feature of their reptilian anatomy has undergone modification in their adaptation to flightDerived Characters of BirdsMany of the characters of birdsAre adaptations that facilitate flightA bird’s most obvious adaptations for flightAre its wings and feathersFigure 34.28a–c(a) wing(b) Bone structureFinger 1(c) Feather structureShaftBarbBarbuleHookVaneShaftForearmWristPalmFinger 3Finger 2The Origin of BirdsBirds probably descended from theropodsA group of small, carnivorous dinosaursBy 150 million years agoFeathered theropods had evolved into birdsArchaeopteryxRemains the oldest bird knownFigure 34.29Toothed beakAirfoil wing with contour feathersLong tail with many vertebraeWing clawLiving BirdsThe ratites, order StruthioniformesAre all flightlessFigure 34.30a(a) Emu. This ratite lives in Australia.The demands of flightHave rendered the general body form of many flying birds similar to one anotherFigure 34.30b–d(b) Mallards. Like many bird species, the mallard exhibits pronounced color differences between the sexes.(c) Laysan albatrosses. Like most birds, Laysan albatrosses have specific mating behaviors, such as this courtship ritual.(d) Barn swallows. The barn swallow is a member of the order Passeriformes. Species in this order are called perching birds because the toes of their feet can lock around a branch or wire, enabling the bird to rest in place for long periods.Foot structure in bird feetShows considerable variationFigure 34.31Grasping bird (such as a woodpecker)Perching bird (such as a cardinal)Raptor(such as a bald eagle)Swimming bird(such as a duck)Concept 34.7: Mammals are amniotes that have hair and produce milkMammals, class MammaliaAre represented by more than 5,000 species Derived Characters of MammalsMammary glands, which produce milkAre a distinctively mammalian characterHair is another mammalian characteristicMammals generally have a larger brainThan other vertebrates of equivalent sizeEarly Evolution of MammalsMammals evolved from synapsids In the late Triassic periodThe jaw was remodeled during the evolution of mammals from nonmammalian synapsidsAnd two of the bones that formerly made of the jaw joint were incorporated into the mammalian middle earSoundSoundJaw jointJaw jointKeyDentaryAngularSquamosalArticularQuadrateDimetrodonMorganucodonDimetrodonMorganucodonEardrum Eardrum Middle earMiddle earStapesInner earInner earStapesIncus (evolvedfrom quadrate)Malleus (evolvedfrom articular)(b) During the evolutionary remodeling of the mammalian skull, the quadrate and articular bones became incorporated into the middle ear as two of the three bones that transmit sound from the eardrum to the inner ear. The steps in this evolutionary remodeling are evident in a succession of fossils.(a) The lower jaw of Dimetrodon is composed of several fused bones; two small bones, the quadrate and articular, form part of the jaw joint. In Morganucodon, the lower jaw is reduced to a single bone, the dentary, and the location of the jaw joint has shifted.Figure 34.32a, bLiving lineages of mammals originated in the JurassicBut did not undergo a significant adaptive radiation until after the CretaceousMonotremesMonotremesAre a small group of egg-laying mammals consisting of echidnas and the platypusFigure 34.33MarsupialsMarsupialsInclude opossums, kangaroos, and koalasA marsupial is born very early in its developmentAnd completes its embryonic development while nursing within a maternal pouch called a marsupiumFigure 34.34a(a) A young brushtail possum. The young of marsupials are born very early in their development. They finish their growth while nursing from a nipple (in their mother’s pouch in most species).In some species of marsupials, such as the bandicootThe marsupium opens to the rear of the mother’s body as opposed to the front, as in other marsupialsFigure 34.34b(b) Long-nosed bandicoot. Most bandicoots are diggers and burrowers that eat mainly insects but also some small vertebrates andplant material. Their rear-opening pouch helps protect the young from dirt as the mother digs. Other marsupials, such as kangaroos, have a pouch that opens to the front.In Australia, convergent evolutionHas resulted in a diversity of marsupials that resemble eutherians in other parts of the worldFigure 34.35Marsupial mammalsEutherian mammalsPlantigaleMarsupial moleSugar gliderWombatTasmanian devilKangarooDeer mouseMole WoodchuckFlying squirrelWolverinePatagonian cavyEutherians (Placental Mammals)Compared to marsupialsEutherians have a longer period of pregnancyYoung eutheriansComplete their embryonic development within a uterus, joined to the mother by the placentaPhylogenetic relationships of mammalsFigure 34.36 Ancestral mammalMonotremesMarsupialsEutheriansMonotremataMarsupialiaXenarthraProboscidea SireniaTubulidentata Hyracoidea Afrosoricida (golden moles and tenrecs)Macroscelidea (elephant shrews)RodentiaLagomorphaPrimatesDermoptera (flying lemurs)Scandentia (tree shrews)CarnivoraCetartiodactylaPerissodactylaChiropteraEulipotyphlaPholidota (pangolins)Possible phylogenetic tree of mammals. All 20 extant orders of mammals are listed at the top of the tree. Boldfaced orders are explored on the facing page.This diverse clade includes terrestrial and marine mammals as well as bats,the only flying mammals. A growingbody of evidence, including Eocene fossils of whales with feet,supports putting whales inthe same order (Cetartiodactyla) as pigs, cows, and hippos.This is the largest eutherian clade. It includes the rodents, which make up the largest mammalian order by far, with about 1,770 species. Humansbelong to the order Primates.All members of this clade, which underwent an adaptive radiation in South America, belong to the order Xenarthra. One species, the nine-banded armadillo, is found in the southern United States.This clade of eutherians evolved in Africa when the continent was isolated from other landmasses. It includesEarth’s largest living land animal (the African elephant), as well as species that weighless than 10 g.The major eutherian ordersFigure 34.36 ORDERSAND EXAMPLESMAIN CHARACTERISTICSMonotremata Platypuses, echidnasProboscidea ElephantsSireniaManatees,dugongsCetartiodactylaArtiodactylsSheep, pigs cattle, deer,giraffes Lagomorpha Rabbits, hares, picasCarnivora Dogs, wolves,bears, cats, weasels, otters,seals, walrusesXenarthra Sloths, anteaters,armadillosCetaceansWhales,dolphins,porpoisesEchidnaAfrican elephantManateeTamanduaJackrabbitCoyoteBighorn sheepPacific white-sided porpoiseLay eggs; nonipples; young suck milk fromfur of motherLong, musculartrunk; thick, loose skin; upper incisors elongated as tusksAquatic; finlikeforelimbs and no hind limbs; herbivorousReduced teeth orno teeth; herbivorous(sloths) or carnivorous (anteaters, armadillos)Chisel-like incisors; hind legs longer than forelegs and adapted for running and jumpingSharp, pointed canineteeth and molars for shearing; carnivorousHooves with an even number of toes on each foot; herbivorousAquatic; streamlinedbody; paddle-like forelimbs and no hind limbs; thicklayer of insulating blubber; carnivorousDiet consists mainly of insects and other small invertebratesAdapted for flight; broad skinfold that extends from elongated fingers to body and legs; carnivorous or herbivorousHooves with an odd number of toeson each foot; herbivorousOpposable thumbs; forward-facing eyes; well-developed cerebral cortex; omnivorousChisel-like, continuously growing incisors worn down by gnawing;herbivorousShort legs; stumpy tail; herbivorous; complex, multichamberedstomachTeeth consisting of many thin tubes cemented together; eats ants and termitesEmbryo completes development in pouch on motherORDERSAND EXAMPLESMAIN CHARACTERISTICSMarsupialiaKangaroos,opossums,koalasTubulidentataAardvarkHyracoideaHyraxesChiropteraBatsPrimatesLemurs,monkeys,apes,humans PerissodactylaHorses,zebras, tapirs,rhinocerosesRodentiaSquirrels,beavers, rats, porcupines,mice   Eulipotyphla“Core insecti-vores”: some moles, some shrewsStar-nosed moleFrog-eating batIndian rhinocerosGolden lion tamarinRed squirrelRock hyraxAardvarkKoalaPrimatesThe mammalian order Primates includeLemurs, tarsiers, monkeys, and apesHumans are members of the ape groupDerived Characters of PrimatesMost primatesHave hands and feet adapted for graspingPrimates also have A large brain and short jawsForward-looking eyes close together on the face, providing depth perceptionWell-developed parental care and complex social behaviorA fully opposable thumbLiving PrimatesThere are three main groups of living primatesThe lemurs of Madagascar and the lorises and pottos of tropical Africa and southern AsiaFigure 34.37The tarsiers of Southeast AsiaThe anthropoids, which include monkeys and hominids worldwideThe oldest known anthropoid fossils, about 45 million years oldIndicate that tarsiers are more closely related to anthropoidsFigure 34.38605040302010Millions of years ago Ancestral primateLemurs, lorises, and pottosTarsiersNew World monkeysOld World monkeysGibbonsOrangutansGorillasChim-panzeesHumansAnthropoids0The fossil record indicates that monkeysFirst appeared in the New World (South America) during the OligoceneThe first monkeysEvolved in the Old World (Africa and Asia)New World and Old World monkeysUnderwent separate adaptive radiations during their many millions of years of separationFigure 34.39a, b(a) New World monkeys, such as spider monkeys (shown here), squirrel monkeys, and capuchins, have a prehensile tail and nostrils that open to the sides.(b) Old World monkeys lack a prehensile tail, and their nostrils open downward. This group includes macaques (shown here), mandrills, baboons, and rhesus monkeys.The other group of anthropoids, the hominoidsConsists of primates informally called apesFigure 34.40a–e(a) Gibbons, such as this Muller's gibbon, are found only in southeastern Asia. Their very long arms and fingers are adaptations for brachiation.(b) Orangutans are shy, solitary apes that live in the rain forests of Sumatra and Borneo. They spend most of their time in trees; note the foot adapted for grasping and the opposable thumb.(c) Gorillas are the largest apes: some males are almost 2 m tall and weigh about 200 kg. Found only in Africa, these herbivores usually live in groups of up to about 20 individuals.(d) Chimpanzees live in tropical Africa. They feed and sleep in trees but also spend a great deal of time on the ground. Chimpanzees are intelligent, communicative, and social.(e) Bonobos are closely related to chimpanzees but are smaller. They survive today only in the African nation of Congo.HominoidsDiverged from Old World monkeys about 20–25 million years agoConcept 34.8: Humans are bipedal hominoids with a large brainHomo sapiens is about 160,000 years oldWhich is very young considering that life has existed on Earth for at least 3.5 billion yearsDerived Characters of HominidsA number of characters distinguish humans from other hominoidsUpright posture and bipedal locomotionLarger brainsLanguage capabilitiesSymbolic thoughtThe manufacture and use of complex toolsShortened jawThe Earliest HumansThe study of human originsIs known as paleoanthropologyPaleoanthropologists have discovered fossils of approximately 20 species of extinct hominoids That are more closely related to humans than to chimpanzeesThese species are known as hominidsFigure 34.41HomosapiensHomoneanderthalensisHomoergaster?HomoerectusHomohabilisHomorudolfensisParanthropusrobustusParanthropusboiseiAustralopithecusgarhiAustralopithecusafricanusAustralopithecusafarensisKenyanthropusplatyopsAustralopithecusanamensisArdipithecusramidusOrrorin tugenensisSahelanthropustchadensis7.06.56.05.55.04.54.03.53.02.52.01.51.00.50Millions of years agoHominids originated in Africa Approximately 6–7 million years agoEarly hominidsHad a small brain, but probably walked upright, exhibiting mosaic evolutionTwo common misconceptions of early hominids includeThinking of them as chimpanzeesImagining human evolution as a ladder leading directly to Homo sapiensAustralopithsAustralopiths are a paraphyletic assemblage of hominidsThat lived between 4 and 2 million years agoSome species walked fully erectAnd had human-like hands and teethFigure 34.42a–c(a) Lucy, a 3.24-million-year-old skeleton, represents the hominid species Australopithecus afarensis.(b) The Laetoli footprints, more than 3.5 million years old, confirm that upright posture evolved quite early in hominid history.(c) An artist’s reconstruction of what A. afarensis may have looked like. BipedalismHominids began to walk long distances on two legsAbout 1.9 million years agoTool UseThe oldest evidence of tool use—cut marks on animal bonesIs 2.5 million years oldEarly HomoThe earliest fossils that paleoanthropologists place in our genus HomoAre those of the species Homo habilis, ranging in age from about 2.4 to 1.6 million yearsStone tools have been found with H. habilisGiving this species its name, which means “handy man”Homo ergasterWas the first fully bipedal, large-brained hominidExisted between 1.9 and 1.6 million yearsFigure 34.43Homo erectusOriginated in Africa approximately 1.8 million years agoWas the first hominid to leave AfricaNeanderthalsNeanderthals, Homo neanderthalensisLived in Europe and the Near East from 200,000 to 30,000 years agoWere large, thick-browed hominidsBecame extinct a few thousand years after the arrival of Homo sapiens in EuropeHomo sapiensHomo sapiensAppeared in Africa at least 160,000 years agoFigure 34.44The oldest fossils of Homo sapiens outside AfricaDate back about 50,000 years agoThe rapid expansion of our speciesMay have been preceded by changes to the brain that made symbolic thought and other cognitive innovations possibleFigure 34.45