雅思精讲阅读班精讲班第8讲讲义

雅思精讲阅读班精讲班第8讲讲义Questions25-28说明：录音开始的2分钟内容已经在上一讲中讲过。。。Questions25-28Whatisadinosaur?A.AlthoughthenamedinosaurisderivedfromtheGreekfor“terriblelizard”,dinosaurswerenot,infact,lizardsatall.Likelizards,dinosaursareincludedintheclassReptilia,orreptiles,oneofthefivemainclassesofVertebrata,animalswithbackbones.However,atthenextlevelofclassification,withinreptiles,significantdifferencesintheskeletalanatomyoflizardsanddinosaurshaveledscientiststoplacethesegroupsofanimalsintotwodifferentsuperorders:Lepidosauria,orlepidosaurs,andArchosauria,orarchosaurs.B.Classifiedaslepidosaursarelizardsandsnakesandtheirprehistoricancestors.Includedamongthearchosaurs,or“rulingreptiles”,areprehistoricandmoderncrocodiles,andthenowextinctthecondonts,pterosaursanddinosaurs.Paleontologistsbelievethatbothdinosaursandcrocodilesevolved,inthelateryearsoftheTriassicPeriod(c.248-208millionyearsago),fromcreaturescalledpseudosuchianthecodonts.Lizards,snakesanddifferenttypesofthecondontarebelievedtohaveevolvedearlierintheTriassicPeriodfromreptilesknownaseosuchians.C.Themostimportantskeletaldifferencesbetweendinosaursandotherarchosaursareinthebonesoftheskull,pelvisandlimbs.Dinosaurskullsarefoundinagreatrangeofshapesandsizes,reflectingthedifferenteatinghabitsandlifestylesofalargeandvariedgroupofanimalsthatdominatedlifeonEarthforanextraordinary165millionyears.However,unliketheskullsofanyotherknownanimals,theskullsofdinosaurshadtwolongbonesknownasvomers.Thesebonesextendedoneithersideofthehead,fromthefrontofthesnouttotheleveloftheholesintheskullknownastheantorbitalfenestra,situatedinfrontofthedinosaur’sorbitsoreyesockets.D.Alldinosaurs,whetherlargeorsmall,quadrupedalorbipedal,fleet-footedorslow-moving,sharedacommonbodyplan.Identificationofthisplanmakesitpossibletodifferentiatedinosaursfromanyothertypesofanimal,evenotherarchosaurs.Mostsignificantly,indinosaurs,thepelvisandfemurhadevolvedsothatthehindlimbswereheldverticallybeneaththebody,ratherthansprawlingouttothesideslikethelimbsofalizard.Thefemurofadinosaurhadasharplyin-turnedneckandaball-shapedhead,whichslottedintoafullyopenacetabulumorhipsocket.Asupra-acetabularcresthelpedpreventdislocationofthefemur.Thepositionofthekneejoint,alignedbelowtheacetabulum,madeitpossibleforthewholehindlimbtoswingbackwardsandforwards.Thisuniquecombinationoffeaturesgavedinosaurswhatisknowasa“fullyimprovedgait”.Evolutionofthishighlyefficientmethodofwalkingalsodevelopedinmammals,butamongreptilesitoccurredonlyindinosaurs.E.Forthepurposeoffurtherclassification,dinosaursaredividedintotwoorders:Saurischia,orsaurischiandinosaurs,andOrnithischia,orornithischiandinosaurs.Thisdivisionismadeonthebasisoftheirpelvicanatomy.Alldinosaurshadapelvicgirdlewitheachsidecomprisedofthreebones:thepubis,lliumandischium.However,theorientationofthesebonesfollowsoneoftwopatterns.Insaurischiandinosaurs,alsoknownaslizard-hippeddinosaurs,thepubispointsforwards,asisusualinmosttypesofreptile.Bycontrast,inornithischian,orbird-hipped,dinosaurs,thepubispointsbackwardstowardstherearoftheanimal,whichisalsotrueofbirds.（26F.Ofthetwoordersofdinosaurs,theSaurischiawasthelargerandthefirsttoevolve.Itisdividedintotwosuborders:Therapoda,ortherapods,andSauropodomorpha,orsauropodomorphs.Thetherapods,or“beastfeet”,werebipedal,predatorycarnivores.TheyrangedinsizefromthemightyTyrannosaurusrex,12mlong,5.6mtallandweighingasestimated6.4tonnes,tothesmallestknowndinosaur,Compsognathus,amere1.4mlongandestimated3kginweightwhenfullygrown.Thesauropodomorphs,or“lizardfeetforms”,includedbothbipedalandquandrupedaldinosaurs.Somesauropodomorphswerecarnivorousoromnivorousbutlaterspeciesweretypicallyherbivorous.Theyincludedsomeofthelargestandbest-knownofalldinosaurs,suchasDiplodocus,ahugequadrupedwithanelephant-likebody,along,thintailandneckthatgaveitatotallengthof27m,andatinyhead.G.Ornithischiadinosaurswerebipedalorquadrupedalherbivores.Theyarenowusuallydividedintothreesuborders:Ornithipoda,ThyreophoraandMarginocephalia.Theornithopods,or“birdfeet”,bothlargeandsmall,couldwalkorrunontheirlonghindlegs,balancingtheirbodybyholdingtheirtailsstifflyoffthegroundbehindthem.Anexampleislguanodon,upto9mlong,5mtallandweighing4.5tonnes.Thethyreophorans,or“shieldbearers”,alsoknownasarmoureddinosaurs,werequadrupedswithrowsofprotectivebonyspikes,studs,orplatesalongtheirbacksandtails.TheyincludedStegosaurus,9mlongandweighing2tonnes.H.Themarginocephalians,or“marginedheads”,werebipedalorquadrupedalornithischianswithadeepbonyfrillornarrowshelfatthebackoftheskull.AnexampleisTriceratopsarhinoceros-likedinosaur,9mlong,weighing5.4tonnesandbearingaprominentneckfrillandthreelargehorns.Questions25-28hooseonephrase(A-H)fromtheListoffeaturestomatchwiththeDinosaurslistedbelow.Writetheappropriateletters(A-H)inBoxes25-28onyouranswersheet.Theinformationinthecompletedsentencesshouldbeanaccuratesummaryofthepointsmadebythewriter.NB.Therearemorephrases(A-H)thansentences,soyouwillnotneedtousethemall.Youmayuseeachphraseonceonly.Dinosaurs25.Dinosaursdifferedfromlizards,because…26.Saurischianandornithischiandinosaurs…27.Unlike