托福TPO44阅读题目及答案

阅读⼀1-5BDACC6-10DAADB11-13CAA14AEFFromFishtoTerrestrialVertebratesOneofthemostsignificantevolutionaryeventsthatoccurredonEarthwasthetransitionofwater-dwellingfishtoterrestrialtetrapods(four-limbedorganismswithbackbones).Fishprobablyoriginatedintheoceans,andourfirstrecordsofthemareinmarinerocks.However,bytheDevonianPeriod(408millionto362millionyearsago),theyhadradiatedintoalmostallavailableaquatichabitats,includingfreshwatersettings.Oneofthegroupswhosefossilsareespeciallycommoninrocksdepositedinfreshwateristhelobe-finnedfish.ThefreshwaterDevonianlobe-finnedfishrhipidistiancrossopterygianisofparticularinteresttobiologistsstudyingtetrapodevolution.Thesefishlivedinriverchannelsandlakesonlargedeltas.Thedeltarocksinwhichthesefossilsarefoundarecommonlyredduetooxidizedironminerals,indicatingthatthedeltasformedinaclimatethathadalternatewetanddryperiods.Iftherewereperiodsofdrought,anyadaptationsallowingthefishtosurvivethedryconditionswouldhavebeenadvantageous.Intheserhipidistians,severalsuchadaptationsexisted.Itisknownthattheyhadlungsaswellasgillsforbreathing.Crosssectionscutthroughsomeofthefossilsrevealthatthemudfilingtheinteriorofthecarcassdifferedinconsistencyandtexturedependingonitslocationinsidethefish.Thesedifferencessuggestasaclikecavitybelowthefrontendofthegutthatcanonlybeinterpretedasalung.Gillswereundoubtedlythemainsourceofoxygenforthesefish,butthelungsservedasanauxiliarybreathingdeviceforgulpingairwhenthewaterbecameoxygendepleted,suchasduringextendedperiodsofdrought.So,thesefishhadalreadyevolvedoneoftheprimerequisitesforlivingonland,theabilitytouseairasasourceofoxygen.Asecondadaptationofthesefishwasinthestructureofthelobefins.Thefinswerethick,fleshy,andquitesturdy,withamedianaxisofbonedownthecenter.Theycouldhavebeenusedasfeeblelocomotordevicesonland,perhapsgoodenoughtoallowafishtoflopitswayfromonepoolofwaterthatwasalmostdrytoanadjacentpondthathadenoughwaterandoxygenforsurvival.Thesefinseventuallychangedintoshort,stubbylegs.ThebonesofthefinsofaDevonianrhipidistianexactlymatchinnumberandpositionthelimbbonesoftheearliestknowntetrapods,theamphibians.Itshouldbeemphasizedthattheevolutionoflungsandlimbswasinnosenseananticipationoffuturelifeonland.Theseadaptationsdevelopedbecausetheyhelpedfishtosurviveintheirexistingaquaticenvironment.Whatecologicalpressuresmighthavecausedfishestograduallyabandontheirwateryhabitatandbecomeincreasinglyland-dwellingcreatures?ChangesinclimateduringtheDevonianmayhavehadsomethingtodowiththisiffreshwaterareasbecameprogressivelymorerestricted.Anotherimpetusmayhavebeennewsourcesoffood.Theedgesofpondsandstreamssurelyhadscattereddeadfishandotherwater-dwellingcreatures.Inaddition,plantshademergedintoterrestrialhabitatsinareasnearstreamsandponds,andcrabsandotherarthropodswerealsomembersofthisearliestterrestrialcommunity.Thus,bytheDevonianthelandhabitatmarginaltofreshwaterwasprobablyarichsourceofproteinthatcouldbeexploitedbyananimalthatcouldeasilyclimboutofwater.Evidencefromteethsuggeststhattheseearliesttetrapodsdidnotutilizelandplantsasfood;theywerepresumablycarnivorousandhadnotdevelopedtheabilitytofeedonplants.Howdidthefirsttetrapodsmakethetransitiontoaterrestrialhabitat?Likeearlylandplantssuchasrhyniophytes,theymadeonlyapartialtransition,theywerestillquitetiedtowater.However,manyproblemsthatfacedearlylandplantswerenotapplicabletothefirsttetrapods.Theancestorsoftheseanimalsalreadyhadacirculationsystem,andtheyweremobile,sothattheycouldmovetowatertodrink.Furthermore,theyalreadyhadlungs,whichrhipidistianspresumablyusedforauxiliarybreathing.Theprincipalchangesfortheearliesttetrapodswereintheskeletalsystem-changesinthebonesofthefins,thevertebralcolumn,pelvicgirdle,andpectoralgirdle.Paragraph1OneofthemostsignificantevolutionaryeventsthatoccurredonEarthwasthetransitionofwater-dwellingfishtoterrestrialtetrapods(four-limbedorganismswithbackbones)Fishprobablyoriginatedintheoceans,andourfirstrecordsofthemareinmarinerocks.However,bytheDevonianPeriod(408millionto362millionyearsago),theyhadradiatedintoalmostallavailableaquatichabitats,includingfreshwatersettingsOneofthegroupswhosefossilsareespeciallycommoninrocksdepositedinfreshwateristhelobe-finnedfish.1.Paragraph1supportswhichofthefollowingstatementsaboutfishevolution?A.Lobe-finnedfishwereamongtheearliesttypesoffishtoappear.B.Fishbeganlivinginfreshwaterhabitatsonlyafteroriginatingelsewhere.C.Lobe-finnedfishradiatedintoalmostallavailableaquatichabitats.D.DuringtheDevonian,lobe-finnedfishweremorecommoninmarinethaninfreshwaterhabitats.Paragraph2ThefreshwaterDevonianlobe-finnedfishrhipidistiancrossopterygianIsofparticularinteresttobiologistsstudyingtetrapodevolution.Thesefishlivedinriverchannelsandlakesonlargedeltas.Thedeltarocksinwhichthesefossilsarefoundarecommonlyredduetooxidizedironminerals,indicatingthatthedeltasformedinaclimatethathadalternatewetanddryperiods.Iftherewereperiodsofdrought,anyadaptationsallowingthefishtosurvivethedryconditionswouldhavebeenadvantageous.Intheserhipidistians,severalsuchadaptationsexisted.Itisknownthattheyhadlungsaswellasgill