great transitions: the origins of tetrapods educator materials
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Short Film Great Transitions: The Origins of Tetrapods Educator Materials
PublishedNovember2014RevisedMarch2017
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IN-DEPTHFILMGUIDE
DESCRIPTIONIntheHHMIfilmGreatTransitions:TheOriginofTetrapods,wejoinUniversityofChicagoevolutionarybiologistNeilShubinasherelivestheexcitingdiscoveryofTiktaalikroseae,aspeciesthatlivedaround375millionyearsago(mya)andhadcharacteristicsofbothfishandfour-leggedanimals(ortetrapods).Thefilmtakesusonacompellingjourneythroughtheprocessofscience—includingtheaskingofimportantquestions,synthesizingknownfactsinnovelways,generatingandtestinghypotheses,andperseveringdespiterepeatedfailures.
KEYCONCEPTSA. Speciesdescendfromotherspecies.Evendistantlyrelatedspecies,likehumansandsponges,cantracetheir
sharedancestrybacktoacommonancestor.B. ThefossilrecordprovidesahistoryoflifeonEarth.Itincludesfossilswithfeaturesthatareintermediate,or
transitional,betweenthoseofmajorgroupsofanimals.C. Whenaseriesoftransitionalfossilsareviewedtogether,theyrevealthegradualsequenceofchange
connectingonemajorgrouptoanother.D. Evidencethatlandvertebratesdescendedfromfishincludestransitionalfossils,anatomicalsimilarities
amongembryosandadultanimals,andgeneticevidenceofcommonancestry.E. Thelimbsofmammals,amphibians,reptiles,andbirdslookdifferent,buttheyareallbuiltonasharedbasic
arrangementof“onebone,twobones,manybones,anddigits.”F. Tofindfossils,scientistsdevelophypothesesaboutthetypesofhabitatsinwhichearlieranimalslivedand
whentheylivedthere.Theythenpredictwhichtypesandagesofrockswouldhousefossilsofthoseanimals.
CURRICULUMANDTEXTBOOKCONNECTIONS
PRIORKNOWLEDGEItwouldbehelpfulforstudentstobefamiliarwiththeconceptsofnaturalselectionandadaptation,andtohavelearnedabouttectonicplatemovements.
Curriculum StandardsNGSS(April2013) MS-LS4-1,MS-LS4-2
HS-LS4-1,LS4.A,LS4.B,LS4.C,LS4-2,LS4-4,LS4-5,HS-ESS1-5,HS-ESS2.BAPBiology(2012–13) 1.A.1,1.A.2,1.A.4,1.B.1,1.C.1,1.C.3,1.D.2,4.B.3,4.B.4IBBiology(2016) 5.1 Textbook ChapterSectionsMillerandLevine,Biology(2010ed.) 16.2,16.3,16.4,17.3,19.1,19.2Reeceetal.,CampbellBiology(9thed.) 22.1,22.2,22.3,25.2,25.5,25.6
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PAUSEPOINTSThefilmmaybeviewedinitsentiretyorpausedatspecificpointstoreviewcontentwithstudents.Thetablebelowlistssuggestedpausepoints,indicatingthebeginningandendtimesinminutesinthefilm.
Begin End ContentDescription ReviewQuestions Standards1
0:00
5:00
• Darwinpredictedthattransitionalorganisms’fossilscouldbeintermediateformsbetweendifferentgroups.Manyfossilsoftransitionalorganismshavebeenfoundandhaveenabledscientiststoreconstructtheoriginsofmanygroups.
• Althoughtheydon’talwayslookorfunctionsimilarly,thelimbsofmammals,amphibians,reptiles,andbirdshaveacommonarchitecture,suggestingaconnectionbetweenverydifferentgroupsofanimals.
• Thehistoryofvertebratesiscapturedinrockthatcanbedated;birdsareyoungest,thenmammals,reptiles,andamphibians.At370millionyearsago,therearenofossilsoftetrapods.
• Fishandtetrapodsarebothvertebrates,andinearlydevelopmenttheylookverysimilar.DNAevidenceindicatesthatfisharetetrapods’closestrelatives.
• Whataretransitionalfossils?Whyaretheyimportant?
• Whatevidencesuggeststhatfour-leggedanimalsevolvedfromfish?
NGSS(April2013)MS-LS4.A,MS-LS4.C,MS-ESS1.C,HS-LS4.C,HS-LS4.DAPBiology(2012–13)1.A.1,1.A.4,1.B.1,1.C.1,1.C.3,4.B.4IBBiology(2016)5.1
2
5:01
13:10
• Findingfossilscanbechallenging.Tofindfossils,scientistsdevelophypothesesaboutthetypesofhabitatsinwhichearlieranimalslivedandwhentheylivedthere.Theythenpredictwhichtypesandagesofrockswouldhousefossilsofthoseanimals.
• Fossilizationhappensonlyundercertainconditions.
• Afteryearsofsearching,ateamofpaleontologistsdiscoveredTiktaalikataremotefieldsiteinAlaskawithDevonianagerocks.
• WhydidthepaleontologistsdecidetohuntforthetransitionalfossilinAlaska?
NGSS(April2013)MS-ESS1.CAPBiology(2012–13)1.A.4,1.B.1IBBiology(2016)5.1
3
13:11
17:11
• Tiktaalikhasamixoffishlikeandtetrapod-likefeatures.Ithasscalesandfinswithfinrays,likeafish.Likeatetrapod,ithasaflatheadwitheyeson
• WhyisTiktaalikconsideredatransitionalfossil?
NGSS(April2013)MS-LS4.A,MS-LS4.C,MS-ESS1.C,HS-LS4.C,HS-
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top,interlockingribssuggestingithadlungs,aneck,ahipbone,andaforelimbwiththebeginningofabonepatternlikethatoftetrapods.
• Thegreattransitionfromfishtotetrapodhappenedgraduallyovermanymillionsofyears.
• Otherfossilshaveprovidedevidenceofothertransitions.
• Didthetransitionfromfishtotetrapodhappenquicklyorslowly?
LS4.DAPBiology(2012–13)1.A.1,1.A.2,1.A.4,1.B.1,1.C.1,1.C.3IBBiology(2016)5.1
BACKGROUNDTiktaalik(pronouncedtic-TAH-lick)means“shallowwaterfish”inthelanguageoftheNunavutpeoplewholiveintheCanadianArctic,whereTiktaalikwasfoundin2004.TheteamthatmadethediscoveryincludedNeilShubin;hisformergraduatestudent,TedDaeschler,whoisnowatTheAcademyofNaturalSciencesofDrexelUniversity;andShubin’sformergraduateadvisor,HarvardUniversityevolutionarybiologistFarishJenkins.ThediscoveryofTiktaalikisdescribedindetailintheaccompanyingarticle“It’saFishapod!”bySeanB.Carrollhttp://www.hhmi.org/biointeractive/article-fishapod.Tiktaalikisatetrapod—agroupthatincludesfour-leggedanimalslikedogsandhorses,aswellaswhalesandsnakes,whichevolvedfromfour-leggedancestorsbutnolongerhavefourlegs.
HowAreFossilsFound?
Oneofthemajorthemesofthefilmishowfossilsarefound.Thefirststepinlocatingfossilsoftherightageandtypeistomakepredictionsaboutwhereandwhentheorganismwouldhavelived.Beforeabout385millionyearsago(mya),notetrapodsareknownfromthefossilrecord.Thefirstfossilsoftetrapods,AcanthostegaandIchthyostega,weredatedto365mya.So,Shubinandhiscolleagueshypothesizedthatthefishintheprocessofbecomingmoretetrapod-likelivedbetween385and365mya.This20-million-year-spaniswithinageologicalepochcalledtheUpperDevonian.
Figure1.Rocksagedbetween385and365myawerepredictedtocontainfossilswithtransitionalfeaturesbetweenthoseoffishandtetrapods.
Inthefilm,weseeamapofDevonianrocks.ThemapcomesfromatextbookentitledEvolutionoftheEarthbyDottandBatten,whichcontainsmanygeologicalmaps.Likeallmaps,geologicalmapsaredesignedtoshowwherecertainthingsarelocated.Whereasthemapsweknowbestshowthedistributionofroads,rivers,orcountyboundaries,ageologicalmapshowsthedistributionofgeologicalfeatures,includingdifferentkindsofrocks(e.g.,sedimentary,igneous,andmetamorphic)andthedifferentagesofrocks.Thesemapsaretypicallygeneratedtoguideoilandmineralexpeditions.
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ThemapinthefilmshowsthreeDevoniandepositsinNorthAmerica.Twoofthosedepositshadalreadybeensearchedforfossils.ThethirdDevoniandeposithadbeenexploredbyCanadiangeologicalsurveyorsandafewoilcompanygeologistsbutnofossilhunters.Thisthirdformationcontainedsedimentaryrocklayers—thetypeofrockswherefossilsaremostcommonlyfound.Aftersomeadditionalresearch,ShubinandDaeschlerdiscoveredthattherockshadformedinwhatwereshallow,meanderingstreamsinDevoniantimes.
Evenafteridentifyingrocksoftherightageandtype,scientistscannotbesurethattheywillfindfossilsinthoserocks.AlmostallorganismsthathavelivedonEarthleftnotraceoftheirexistence.Mostareeatenordecaybeforetheyarefossilized,andsofttissuesdonotfossilizewell.Andevenifanorganismisburiedinsedimentsandbecomesfossilized,therocklayerwiththatfossilhastobecomeexposedonEarth’ssurfaceforsomeonetofindit.
Sohowcanpaleontologistsexpecttofindfossilsatall,letalonefossilsofspeciesthatexistedataparticularpointintime?Onecriticalfactmakesthispossible.Asinglespeciescanexistformillionsofyearsandconsistofhundredsofmillionsorevenbillionsofindividuals.Theprobabilityoffindingthefossilremainsofanyoneindividualistiny,butnotimpossible.
FindingTiktaalik
In2004,Shubinandcolleaguesfoundthefossilofanewspeciesthatshedlightonakeytransitionintheevolutionoftetrapods:thefin-to-limbtransition.ThecrewwasexcavatingonedayinanareawithlotsofDevonianfishfossils(a“wholeaquarium,”asShubinsaidinthefilm).Stickingoutofarockyedgeinthequarrywasthetipofthesnoutofaflat-headedfish.Whywastheflatheadsuchanimportantclue?
Manyfishhaveflatheads.Butwhatissignificantinthiscaseisthattheearliesttetrapodsthathadbeendiscovered(i.e.,AcanthostegaandIchthyostega)hadflatheads.Sofindingaflat-headedfishwasagoodindicatorthatthisfossilwaspartofthegradualevolutionarysequencefromfishtotetrapods.
Oncethefossilwascleaned,itshowedthatithadtwonostrilsandtwoeyesmountedontopofitsflathead.Mostfishhavenostrils,buttetrapod-likefishlikeTiktaalikhaveaspecializedkindofnostrilthatconnectstotheinsideofthemouth.Fishthatarenotcloselyrelatedtotetrapodshavenostrilsthatonlyconnectwiththeexterior.
AnotherimportantfeatureofthisfossilisthatTiktaalik’sheadwasnotconnecteddirectlytoitsshouldersliketheheadofafishwouldhavebeen(Figure2).Instead,itsheadsatinfrontoftheshoulders,attheendofaflexibleneck—meaningtheheadwasfreetomoveupanddownandsideways.
Figure2.Tiktaalikhasamixoffishandtetrapodfeatures.Oneoftheimportanttetrapodcharacteristicsisthepresenceofaneck,whichallowsTiktaaliktomorefreelymoveitshead.(Figuretakenfromtheinteractive“MeetTiktaalikroseae”availableontheUniversityofChicagowebsiteathttp://tiktaalik.uchicago.edu/meetTik2.html).
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Likeafish,thefossilofTiktaalikshowsevidenceofscales,gills,andfins.Butinsidethefins,Tiktaalikcontainslimbbonesthatarecharacteristicofanearlytetrapod.Onebone(thehumerus)extendsfromtheshoulderandconnectstotwoadditionalbones(theradiusandulna),whicharesharedbyalllobe-finnedfish(i.e.,coelacanths,lungfish,tetrapods,andalltheirextinctrelatives).WhatisspecialaboutthefinofTiktaalikisthatthosethreebonesthenconnecttomanysmallbonesthatformwhatDr.Shubindescribesas“aversionofawrist.”
ThefossilofTiktaalikalsorevealedinterconnecting(orimbricate)ribsthatsurroundedthelungs.Lungfishhavelungs,buttheydonothaveimbricateribs.Thelungsoflungfishandtetrapodsarehomologous,whichmeanstheyevolvedfromacommonancestorthathadlungs.TheimbricateribsofTiktaalikandlatertetrapodswouldhaveprovidedextrabodyrigidityinconditionsinwhichthesurroundingwatercouldnotsupporttheweightoftheanimal(i.e.,inshallowwaterorsubaerialconditions).Onehypothesisisthattheribsprovidedanadvantageinthoseenvironmentsbykeepingtheweightoftheanimalfromputtingpressureonthelungsandpreventingthemfromfillingwithair.
SowhyisTiktaalikreferredtoasatransitionalcreature?Itsmixofcharacteristicsoffishandoftetrapodssuggestthatitrepresentsoneofthemomentsinthetransitionbetweenfishandtetrapods.
DISCUSSIONPOINTS• Studentsmayincorrectlyassumethatdiscoveringfossilsismostlyaboutluck.Askyourstudentsifanyof
themhavefoundfossils.Askthosestudentswhofoundfossilsiftheirfossilfindswereluckyoraproductofdeliberatesearching.Explainthatpaleontologistsdonotaccidentallystumbleuponthefossilstheydiscover,butthatpaleontologyisaprocessofhypothesistesting.Throughcarefulplanning,readingscientificarticles,andstudyinggeologyandgeologicaltime,paleontologistsformhypothesesaboutthetimeperiodsandhabitatsoccupiedbycertainorganisms.TheythendeveloppredictionsaboutwhatkindsofrockscertainfossilsofthoseorganismsshouldbeburiedwithinandwhererocksofthosetypesandagesarefoundonEarth.
• Studentsmaywonderwhywedonotfindmorefossils—fossilsofeverytypeoforganismthateverlived.Askstudentstoconsideramousethatisrunningneartheschoolatthisverymoment.Askthemtoconsidertheprobabilitythatthatsinglemousewilldietoday,becomefossilized,andberediscoveredamillionyearsfromnow.Theprobabilityisnearlyzero.Tobecomefossilized,themousemustnotbeeatenrightafteritdiesandnotdecomposewithinafewdays.Instead,themouse’sbodymustbequicklyandcompletelyburiedineithervolcanicashorsomekindofsediment.Itmustremainburieduntilthesedimentandthemouseremainsturnintorock—aprocessthatmaytakethousandsorevenmillionsofyears.EnoughtimehaspassedinEarth’shistoryforsomeindividuals,fromthehundredsofthousandswithinanyonespecies,tohavebeenintherightconditionstobecomefossilized.
• Aclassicquestionstudentsmayaskaboutevolutionis,“Ifweevolvedfromfish,whyaretherestillfish?”Explaintostudentsthathumansandmodern-dayfishshareacommonancestorthatnolongerexists.Theaquatichabitatsinwhichfishthrivetodayhavebeenaroundforoverhalfabillionyears,andfisharewelladaptedtoliveinthoseenvironments.Whensomefishpopulationsevolvedstronger,limblikestructuresinfins,theywereabletoexploitnewtypesofhabitatsandreducecompetitionwithotherfishforresources.Butfishcontinuetoexistbecausetherearestillenvironmentsinwhichfishcanthrive.
• Askyourstudentswhatadvantageaneckmightprovide.Thelackofbonesconnectingtheheadtothebodyprovidesflexibilitytomovetheheadwithoutmovingtherestofthebody.Aflexibleneckcouldhavebeenbeneficialinmanypossiblescenarios.However,thisflexibilitymayhavealsocomeatacost—forexample,thelossoftheprotectivegillcover.Wedon’tknowexactlyhowTiktaalikuseditsneck.
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• Studentsmayaskforexamplesofothertransitionsfromearliertolaterforms.Theevolutionofwhalesfromterrestrialmammalsandbirdsfromdinosaursarebothexcellentexampleswithrichfossilevidenceandmanytransitionalforms.Whalesevolvedfromterrestrialmammalsthatwalkedandranonfourlegs.Afunfactthatsupportsthisancestryisthataswimmingwhaleflexesitsbackboneupanddownlikearunningcheetah,notsidetosidelikeaswimmingfish.Aswhaleancestorstransitionedfromaterrestrialtoamarinelife,manycharacteristicschanged.Forexample,legscanbealiabilityinanaquaticenvironmentratherthanabenefit.Asaresult,whaleancestorsshowaprogressivedecreaseinthesizeoftheirhindlimbs.Allthatremainsoftheselimbsinsomeoftoday’swhalespeciesisapairoftinybonesthatareburiedinsidethebodywallandarenotevenattachedtothepelvis.
• Discusswithstudentswhytheterm“missinglink”isinaccurate.Thetermhasbeenpopularinthemediaandhasbeenusedtoincorrectlyimplythatanunbrokenchainoforganismsisrequiredtodemonstratethatallspeciesarerelated.Theterms“transitionalform”and“transitionalfossil”moreaccuratelydescribespeciesthatillustratethesequenceofchangesthatoccurredduringtheevolutionofanewgroupoforganisms.
• IsTiktaalikourancestor?Tiktaalikisrepresentativeofananimalthatwasanancestortomoderntetrapods,includinghumans.Butwecannotsaywhetheritwasadirectancestor.Acommonmisconceptionisthatallfossils,includingtransitionalfossilslikeTiktaalik,aredirectancestorsofmodernspecies.Explainthatfossils,likeTiktaalik,maybedirectancestors,buttheyaremuchmorelikelyrepresentativeofwhattheactualancestorslookedlikeandnottheancestorsthemselves.Infact,thedescendantsofTiktaalikmayhavegoneextinctlongago,butanotherspecies,relatedtoTiktaalik,andyettobediscovered,maybethecommonancestortoallmoderntetrapods.Wemayneverknow,butwecanbecertainthattheancestorlookedalotlikeTiktaalik.
• StudentsmaybeconfusedaboutwhyfossilanimalslikeTiktaalikthatlivedinwarmhabitatsendupinbarrenlocationsliketheCanadianArcticIslands.RemindstudentsthatEarth’sbiologicalandgeologicalhistoriesareconnected.Earth’scrustisdynamic.Platetectonicsmovelandmasses,andfossilsthatwereonceattheequatorcanbemovedtodistantlocations.
RELATEDBIOINTERACTIVERESOURCESIt’saFishapod(http://www.hhmi.org/biointeractive/article-fishapod)
ThisarticlebySeanB.CarrolltellsthestoryofthesearchforanddiscoveryofTiktaalik.
GreatTransitionsInteractive
(http://www.hhmi.org/biointeractive/great-transitions-interactive)
InthisClickandLearn,studentsexploreseveraltransitionalfossilsinthetransitionfromfishtotetrapods,includingTiktaalik.
YoungStudentsRecognizeaTransitionalTetrapod(http://www.hhmi.org/biointeractive/young-students-recognize-transitional-fossil)
Thisshortvideodemonstratesthepowerofobservationandtheimportanceoffossilevidence.WhenNeilShubinshowsaTiktaalikfossiltosmallchildren,theyimmediatelynoticethepresenceofbothfishandtetrapodcharacteristics.
ExploreYourInnerAnimals
(http://www.hhmi.org/biointeractive/explore-your-inner-animals)
Thisinteractiveexploresdifferentanatomicalfeaturesofthehumanbodyandwhattheyrevealabouttheevolutionaryhistorywesharewithotherorganisms,includingearlier,long-extinctspecies.
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USINGTHEQUIZThequizisdesignedasasummativeassessmentthatprobesstudentunderstandingofthekeyconceptsaddressedinthefilm.However,someteachersusethequizbeforeandduringthefilmtoassessstudents’priorknowledgeandtoguidestudentsastheywatchthefilm.Teachersareencouragedtochoosetheusethatbestfitstheirlearningobjectivesandtheirstudents’needs.Moreover,becausethevocabularyandconceptsarecomplex,teachersareencouragedtomodifythequiz(e.g.,onlyasksomeofthequestions,explaincomplicatedvocabularyforELLstudents)asneeded.Thelasttwoquestionsareintendedforstudentswithpriorknowledgeaboutmutations,genesexpression,anddevelopment.
QUIZQUESTIONSANDANSWERSThestudentversionofthisquizisavailableasaseparatefile.Keyconceptscoveredbyeachquestionarenotedhere.
1. (KeyConceptB)WhenCharlesDarwinconsideredsomeoftheuniquestructuresfoundinmodernanimals,likethefeatheredwingsofbirds,hefamouslyproposedthatmodernanimalsmusthaveevolvedfromearlierformsthatlackedthosestructures.Healsopredicted.(Fillintheblankwithoneofthestatementsbelow.)
a. thatitwouldbeimpossibletofindfossilevidenceforthisideabecausethefossilrecordissoincomplete.
b. thatgeneticevidencewouldshowthatallorganismsshareacommonancestor.
c. thatfossilswouldbefoundwithstructuresthatareintermediatebetweenearlyandmodernforms.
d. thatfossilevidencewouldinsteadshowthatallmodernanimalshavealwaysexistedintheirpresentform.
2. (KeyConceptsBandC)WhichofthefollowingfeaturesdescribeTiktaalik?
i. Neck
ii. Lungs
iii. Roundhead
iv. Fins
a. iiandivonly
b. i,ii,andiv
c. i,iii,andiv
d. i,ii,iii,andv
3. (KeyConceptF).Examinethetablebelowandselecttherowthatbestdescribesthesetting,resources,andscientificprocessesusedduringtheTiktaalikexpeditions.
Location Maps/Photos ScientificProcessa. CanadianArctic Geologicalmaps Hypothesestestingb. Iceland Roadmaps Predictingc. Alaska Aerialphotos Questioningd. ArcticCircle Animaltrackmaps Developingexplanations
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4. (KeyConceptE)Whichstatementbelowisevidencethatalltetrapodssharedasinglecommonancestor?
a. Alltetrapodslivepartlyinwaterandpartlyonland.
b. Alltetrapodsarewarm-blooded.
c. Alltetrapodlimbsconsistofrearrangedfishfinrays.
d. Alltetrapodlimbshaveacommonpatternofonebone,twobones,manybones,thendigits.
5. (KeyConceptC)Thetransitionfromfishtotetrapodsisbestdescribedas:
a. Likemostofthegreattransitionsinevolutionaryhistory,ithappenedinveryfewbigstepssothatthereareveryfewintermediateforms.
b. Likemostofthegreattransitionsinevolutionaryhistory,ithappenedinmanysmallstepsleadingtomanyintermediateforms.
c. Likenoothertransitioninevolutionaryhistory,ithappenedinmanysteps,sotherearemanyintermediateforms.
d. Likemostofthegreattransitionsinevolutionaryhistory,ithappenedinasinglestepwithnointermediateforms.
6. (KeyConceptsAandD)Whichevidencesupportsthefactthattetrapodsandfisharecloselyrelated?
i. Theembryosofmodernfishandtetrapodlooksimilar.
ii. Bothmodernfishandtetrapodscanswim.
iii. Bothmodernfishandtetrapodsarevertebrates.
iv. TheDNAofmodernfishandtetrapodssuggeststhattheyhaveacommonancestor.
v. Modernfishhavelimbbonesthatsupporttheirbodies.
a. i,ii,andvonly
b. i,iii,andivonly
c. iiiandvonly
d. itovareallsupportingevidence
7. (KeyConceptsB)TrueorFalse.“Transitionalorganismsarenotactualspecies.”Justifyyouranswerinoneortwosentences.
False.Transitionalformsarespeciesintheirownright.Theyarecalledtransitionalformsbecausetheypossesstraits,likefins,thatarefoundinearlierfossilanimals,butalsopossesstraits,likelimbbones,thatarefoundinlaterfossilanimals.
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8. (KeyConceptsF)Studythegraphicbelowofrocklayerswithfossilsinthem.ExplainhowNeilShubinandhisteampredictedthattheywouldfindafossilanimallikeTiktaalikinrocksaround375millionyearsold.
Studentsshouldexplainthatfromthefossilrecord,Shubinandhisteamknewthatbefore385myathefossilrecorddoesnotcontaintetrapods.Around365myathefossilrecordshowsthefirstevidenceoforganismswithtetrapodlimbcharacteristics,includingdigits.Shubinandhisteamhypothesizedthattheevolutionofafunctionaltetrapodlimbwasagradualprocess,andfossilsshowingintermediatestepsinthatprocessshouldbelocatedinrocksofagesinbetween385millionand365millionyears.
9. (KeyConceptE)Thediagramsbelowillustratethebonesintheforelimbsoffourdifferentorganisms.Althoughtheselimbsalllookdifferent,theysharesomecommonpatterns.Thesecommonpatternssuggestthat
a. Theseorganismsaremembersofthesamespecies.
b. Theorganismsexistedataboutthesamepointintime.
c. Theseorganismsshareacommonancestor.
d. Theseorganismshaveexactlythesamegenes.
10. (KeyConceptsF)ExplainwhyNeilShubinandhiscolleagueshadtotraveltoanareaabovetheArcticCircletofindthefossilofananimalthatoncelivedinawarmswamplikehabitat.
WhenTiktaaliklivedandbecamefossilized,thecontinentitwasonwaslocatedclosertoEarth’sequatorwherewarm,freshwaterhabitatswereabundant.Overtime,piecesofEarth’scrust,andallthefossilsintherocksontopofthecrust,movedtodifferentlocationsduetocontinentaldrift.Studentsmayalsomention
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thatShubinandcolleaguesknewthattheArcticcontainsrocksfromtheDevonianperiodthatwereexploredatthesurface.
11. (KeyConceptsBandF)Inthefilm,NeilShubinisshownhikinguparockyhillsidewhilerecallingforusoneoftheexcitingmomentsduringthehuntforaTiktaalik-likefossilanimal.Neilsays,“Beneathourfeetwerefossilfishbones,fragmentsoffossilfishbones,manythousandsofpieces.Itwasn’tjustonefish;itwasawholeaquarium,itwasdifferentspecies.”Whatdidthisdiscoverymeanforthefossil-huntingteam?
ThefossilizedfishboneswereevidencethattheteamhaddiscoveredalayerofrockthathadformedinthekindofhabitatwhereananimallikeTiktaalikcouldalsohavelived.Therocklayercontainedmanyfishspecies,soitmightalsocontainananimalthatexistedduringthetransitionfromwatertoland.
KEYREFERENCESDaeschler,E.B.,Shubin,N.H.,andJenkinsJr.,F.A.(2006).ADevoniantetrapod-likefishandtheevolutionofthetetrapodbodyplan.Nature440:757-763.Daeschler,Ted.http://clade.ansp.org/vert_zoology/people/daeschler/.Downs,J.P.,Daeschler,E.B.,JenkinsJr.,F.A.,andShubin,N.H.(2008).ThecranialendoskeletonofTiktaalikroseae.Nature455:925-929.Shubin,Neil.http://pondside.uchicago.edu/oba/faculty/shubin_n.html.Shubin,N.H.,Daeschler,E.B.,andJenkins,F.A.(2006).ThepectoralfinofTiktaalikroseaeandtheoriginofthetetrapodlimb.Nature440:764-771.Tiktaalikroseaehttp://tiktaalik.uchicago.edu/.
AUTHORSWrittenbyPaulStrode,PhD,FairviewHighSchool,Boulder,andLauraBonetta,PhD,HHMIReviewedbyJustinLemberg,PhD,TheUniversityofChicagoFieldtestedbyKimberlySaltsburg,WestminsterHighSchool,Westminster,MD;ZachMurray,PoncaCityHighSchool,PoncaCity,OK;JackSaffer,CentralIslipHighSchool,CentralIslip,NY;MinuBasu,DoughertyValleyHighSchool,SanRamon,CA;JudithPinto,BergenCountyAcademies,Hackensack,NJ;SteveMeyer,LakotaWestHighSchool,WestChester,OH;ClarissaFurlong,FranklinHeightsHighSchool,Columbus,OH;CharlotteSmith,LakesideHighSchool,Evans,GA;VandanaGudi,RobertMorganEducationalCenter,Miami,FL;BarryGreenwald,HardingHighSchool,St.Paul,MN