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Short Film
Great Transitions:
The Origins of Tetrapods
Educator Materials
IN-DEPTHFILMGUIDE
DESCRIPTION
IntheHHMIfilmGreatTransitions:TheOriginofTetrapods,wejoinUniversityofChicagoevolutionarybiologist
NeilShubinasherelivestheexcitingdiscoveryofTiktaalikroseae,aspeciesthatlivedaround375millionyears
ago(mya)andhadcharacteristicsofbothfishandfour-leggedanimals(ortetrapods).Thefilmtakesusona
compellingjourneythroughtheprocessofscience—includingtheaskingofimportantquestions,synthesizing
knownfactsinnovelways,generatingandtestinghypotheses,andperseveringdespiterepeatedfailures.
KEYCONCEPTS
A. 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
Curriculum
NGSS(April2013)
APBiology(2012–13)
IBBiology(2016)
Textbook
MillerandLevine,Biology(2010ed.)
Reeceetal.,CampbellBiology(9thed.)
Standards
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.B
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.4
5.1
ChapterSections
16.2,16.3,16.4,17.3,19.1,19.2
22.1,22.2,22.3,25.2,25.5,25.6
PRIORKNOWLEDGE
Itwouldbehelpfulforstudentstobefamiliarwiththeconceptsofnaturalselectionandadaptation,andtohave
learnedabouttectonicplatemovements.
www.BioInteractive.org
PublishedNovember2014
RevisedMarch2017
Page1of10
Short Film
Great Transitions:
The Origins of Tetrapods
Educator Materials
PAUSEPOINTS
Thefilmmaybeviewedinitsentiretyorpausedatspecificpointstoreviewcontentwithstudents.Thetable
belowlistssuggestedpausepoints,indicatingthebeginningandendtimesinminutesinthefilm.
1
2
3
Begin End
0:00 5:00
ContentDescription
• Darwinpredictedthattransitional
organisms’fossilscouldbeintermediate
formsbetweendifferentgroups.Many
fossilsoftransitionalorganismshave
beenfoundandhaveenabledscientists
toreconstructtheoriginsofmany
groups.
• Althoughtheydon’talwayslookor
functionsimilarly,thelimbsofmammals,
amphibians,reptiles,andbirdshavea
commonarchitecture,suggestinga
connectionbetweenverydifferent
groupsofanimals.
• Thehistoryofvertebratesiscapturedin
rockthatcanbedated;birdsare
youngest,thenmammals,reptiles,and
amphibians.At370millionyearsago,
therearenofossilsoftetrapods.
• Fishandtetrapodsarebothvertebrates,
andinearlydevelopmenttheylookvery
similar.DNAevidenceindicatesthatfish
aretetrapods’closestrelatives.
5:01 13:10 • Findingfossilscanbechallenging.Tofind
fossils,scientistsdevelophypotheses
aboutthetypesofhabitatsinwhich
earlieranimalslivedandwhentheylived
there.Theythenpredictwhichtypesand
agesofrockswouldhousefossilsof
thoseanimals.
• Fossilizationhappensonlyundercertain
conditions.
• Afteryearsofsearching,ateamof
paleontologistsdiscoveredTiktaalikata
remotefieldsiteinAlaskawithDevonian
agerocks.
13:11 17:11 • Tiktaalikhasamixoffishlikeand
tetrapod-likefeatures.Ithasscalesand
finswithfinrays,likeafish.Likea
tetrapod,ithasaflatheadwitheyeson
www.BioInteractive.org
ReviewQuestions
• Whatare
transitional
fossils?Whyare
theyimportant?
• Whatevidence
suggeststhat
four-legged
animalsevolved
fromfish?
Standards
NGSS(April2013)
MS-LS4.A,MSLS4.C,MS-ESS1.C,
HS-LS4.C,HSLS4.D
APBiology
(2012–13)
1.A.1,1.A.4,
1.B.1,1.C.1,
1.C.3,4.B.4
IBBiology(2016)
5.1
•
Whydidthe
paleontologists
decidetohunt
forthe
transitionalfossil
inAlaska?
NGSS(April2013)
MS-ESS1.C
APBiology
(2012–13)
1.A.4,1.B.1
IBBiology(2016)
5.1
WhyisTiktaalik
considereda
transitional
fossil?
NGSS(April2013)
MS-LS4.A,MSLS4.C,MS-ESS1.C,
HS-LS4.C,HS-
•
PublishedNovember2014
RevisedMarch2017
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Short Film
Great Transitions:
The Origins of Tetrapods
•
•
Educator Materials
top,interlockingribssuggestingithad
•
lungs,aneck,ahipbone,andaforelimb
withthebeginningofabonepatternlike
thatoftetrapods.
Thegreattransitionfromfishtotetrapod
happenedgraduallyovermanymillions
ofyears.
Otherfossilshaveprovidedevidenceof
othertransitions.
Didthetransition
fromfishto
tetrapodhappen
quicklyorslowly?
LS4.D
APBiology
(2012–13)
1.A.1,1.A.2,
1.A.4,1.B.1,
1.C.1,1.C.3
IBBiology(2016)
5.1
BACKGROUND
Tiktaalik(pronouncedtic-TAH-lick)means“shallowwaterfish”inthelanguageoftheNunavutpeoplewholive
intheCanadianArctic,whereTiktaalikwasfoundin2004.TheteamthatmadethediscoveryincludedNeil
Shubin;hisformergraduatestudent,TedDaeschler,whoisnowatTheAcademyofNaturalSciencesofDrexel
University;andShubin’sformergraduateadvisor,HarvardUniversityevolutionarybiologistFarishJenkins.The
discoveryofTiktaalikisdescribedindetailintheaccompanyingarticle“It’saFishapod!”bySeanB.Carroll
http://www.hhmi.org/biointeractive/article-fishapod.Tiktaalikisatetrapod—agroupthatincludesfour-legged
animalslikedogsandhorses,aswellaswhalesandsnakes,whichevolvedfromfour-leggedancestorsbutno
longerhavefourlegs.
HowAreFossilsFound?
Oneofthemajorthemesofthefilmishowfossilsarefound.Thefirststepinlocatingfossilsoftherightageand
typeistomakepredictionsaboutwhereandwhentheorganismwouldhavelived.Beforeabout385million
yearsago(mya),notetrapodsareknownfromthefossilrecord.Thefirstfossilsoftetrapods,Acanthostegaand
Ichthyostega,weredatedto365mya.So,Shubinandhiscolleagueshypothesizedthatthefishintheprocessof
becomingmoretetrapod-likelivedbetween385and365mya.This20-million-year-spaniswithinageological
epochcalledtheUpperDevonian.
Figure1.Rocksagedbetween385and365myawerepredictedto
containfossilswithtransitionalfeaturesbetweenthoseoffishand
tetrapods.
Inthefilm,weseeamapofDevonianrocks.ThemapcomesfromatextbookentitledEvolutionoftheEarthby
DottandBatten,whichcontainsmanygeologicalmaps.Likeallmaps,geologicalmapsaredesignedtoshow
wherecertainthingsarelocated.Whereasthemapsweknowbestshowthedistributionofroads,rivers,or
countyboundaries,ageologicalmapshowsthedistributionofgeologicalfeatures,includingdifferentkindsof
rocks(e.g.,sedimentary,igneous,andmetamorphic)andthedifferentagesofrocks.Thesemapsaretypically
generatedtoguideoilandmineralexpeditions.
www.BioInteractive.org
PublishedNovember2014
RevisedMarch2017
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Short Film
Great Transitions:
The Origins of Tetrapods
Educator Materials
ThemapinthefilmshowsthreeDevoniandepositsinNorthAmerica.Twoofthosedepositshadalreadybeen
searchedforfossils.ThethirdDevoniandeposithadbeenexploredbyCanadiangeologicalsurveyorsandafew
oilcompanygeologistsbutnofossilhunters.Thisthirdformationcontainedsedimentaryrocklayers—thetype
ofrockswherefossilsaremostcommonlyfound.Aftersomeadditionalresearch,ShubinandDaeschler
discoveredthattherockshadformedinwhatwereshallow,meanderingstreamsinDevoniantimes.
Evenafteridentifyingrocksoftherightageandtype,scientistscannotbesurethattheywillfindfossilsinthose
rocks.AlmostallorganismsthathavelivedonEarthleftnotraceoftheirexistence.Mostareeatenordecaybefore
theyarefossilized,andsofttissuesdonotfossilizewell.Andevenifanorganismisburiedinsedimentsand
becomesfossilized,therocklayerwiththatfossilhastobecomeexposedonEarth’ssurfaceforsomeonetofindit.
Sohowcanpaleontologistsexpecttofindfossilsatall,letalonefossilsofspeciesthatexistedataparticular
pointintime?Onecriticalfactmakesthispossible.Asinglespeciescanexistformillionsofyearsandconsistof
hundredsofmillionsorevenbillionsofindividuals.Theprobabilityoffindingthefossilremainsofanyone
individualistiny,butnotimpossible.
FindingTiktaalik
In2004,Shubinandcolleaguesfoundthefossilofanewspeciesthatshedlightonakeytransitioninthe
evolutionoftetrapods:thefin-to-limbtransition.Thecrewwasexcavatingonedayinanareawithlotsof
Devonianfishfossils(a“wholeaquarium,”asShubinsaidinthefilm).Stickingoutofarockyedgeinthequarry
wasthetipofthesnoutofaflat-headedfish.Whywastheflatheadsuchanimportantclue?
Manyfishhaveflatheads.Butwhatissignificantinthiscaseisthattheearliesttetrapodsthathadbeen
discovered(i.e.,AcanthostegaandIchthyostega)hadflatheads.Sofindingaflat-headedfishwasagood
indicatorthatthisfossilwaspartofthegradualevolutionarysequencefromfishtotetrapods.
Oncethefossilwascleaned,itshowedthatithadtwonostrils
andtwoeyesmountedontopofitsflathead.Mostfishhave
nostrils,buttetrapod-likefishlikeTiktaalikhaveaspecialized
kindofnostrilthatconnectstotheinsideofthemouth.Fishthat
arenotcloselyrelatedtotetrapodshavenostrilsthatonly
connectwiththeexterior.
AnotherimportantfeatureofthisfossilisthatTiktaalik’shead
wasnotconnecteddirectlytoitsshouldersliketheheadofa
fishwouldhavebeen(Figure2).Instead,itsheadsatinfrontof
theshoulders,attheendofaflexibleneck—meaningthehead
wasfreetomoveupanddownandsideways.
Figure2.Tiktaalikhasamixoffishandtetrapodfeatures.One
oftheimportanttetrapodcharacteristicsisthepresenceofa
neck,whichallowsTiktaaliktomorefreelymoveitshead.
(Figuretakenfromtheinteractive“MeetTiktaalikroseae”
availableontheUniversityofChicagowebsiteat
http://tiktaalik.uchicago.edu/meetTik2.html).
www.BioInteractive.org
PublishedNovember2014
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Short Film
Great Transitions:
The Origins of Tetrapods
Educator Materials
Likeafish,thefossilofTiktaalikshowsevidenceofscales,gills,andfins.Butinsidethefins,Tiktaalikcontainslimb
bonesthatarecharacteristicofanearlytetrapod.Onebone(thehumerus)extendsfromtheshoulderand
connectstotwoadditionalbones(theradiusandulna),whicharesharedbyalllobe-finnedfish(i.e.,coelacanths,
lungfish,tetrapods,andalltheirextinctrelatives).WhatisspecialaboutthefinofTiktaalikisthatthosethree
bonesthenconnecttomanysmallbonesthatformwhatDr.Shubindescribesas“aversionofawrist.”
ThefossilofTiktaalikalsorevealedinterconnecting(orimbricate)ribsthatsurroundedthelungs.Lungfishhave
lungs,buttheydonothaveimbricateribs.Thelungsoflungfishandtetrapodsarehomologous,whichmeans
theyevolvedfromacommonancestorthathadlungs.TheimbricateribsofTiktaalikandlatertetrapodswould
haveprovidedextrabodyrigidityinconditionsinwhichthesurroundingwatercouldnotsupporttheweightof
theanimal(i.e.,inshallowwaterorsubaerialconditions).Onehypothesisisthattheribsprovidedanadvantage
inthoseenvironmentsbykeepingtheweightoftheanimalfromputtingpressureonthelungsandpreventing
themfromfillingwithair.
SowhyisTiktaalikreferredtoasatransitionalcreature?Itsmixofcharacteristicsoffishandoftetrapods
suggestthatitrepresentsoneofthemomentsinthetransitionbetweenfishandtetrapods.
DISCUSSIONPOINTS
•
•
•
•
Studentsmayincorrectlyassumethatdiscoveringfossilsismostlyaboutluck.Askyourstudentsifanyof
themhavefoundfossils.Askthosestudentswhofoundfossilsiftheirfossilfindswereluckyoraproductof
deliberatesearching.Explainthatpaleontologistsdonotaccidentallystumbleuponthefossilstheydiscover,
butthatpaleontologyisaprocessofhypothesistesting.Throughcarefulplanning,readingscientificarticles,
andstudyinggeologyandgeologicaltime,paleontologistsformhypothesesaboutthetimeperiodsand
habitatsoccupiedbycertainorganisms.Theythendeveloppredictionsaboutwhatkindsofrockscertain
fossilsofthoseorganismsshouldbeburiedwithinandwhererocksofthosetypesandagesarefoundon
Earth.
Studentsmaywonderwhywedonotfindmorefossils—fossilsofeverytypeoforganismthateverlived.Ask
studentstoconsideramousethatisrunningneartheschoolatthisverymoment.Askthemtoconsiderthe
probabilitythatthatsinglemousewilldietoday,becomefossilized,andberediscoveredamillionyearsfrom
now.Theprobabilityisnearlyzero.Tobecomefossilized,themousemustnotbeeatenrightafteritdiesand
notdecomposewithinafewdays.Instead,themouse’sbodymustbequicklyandcompletelyburiedin
eithervolcanicashorsomekindofsediment.Itmustremainburieduntilthesedimentandthemouse
remainsturnintorock—aprocessthatmaytakethousandsorevenmillionsofyears.Enoughtimehas
passedinEarth’shistoryforsomeindividuals,fromthehundredsofthousandswithinanyonespecies,to
havebeenintherightconditionstobecomefossilized.
Aclassicquestionstudentsmayaskaboutevolutionis,“Ifweevolvedfromfish,whyaretherestillfish?”
Explaintostudentsthathumansandmodern-dayfishshareacommonancestorthatnolongerexists.The
aquatichabitatsinwhichfishthrivetodayhavebeenaroundforoverhalfabillionyears,andfisharewell
adaptedtoliveinthoseenvironments.Whensomefishpopulationsevolvedstronger,limblikestructuresin
fins,theywereabletoexploitnewtypesofhabitatsandreducecompetitionwithotherfishforresources.
Butfishcontinuetoexistbecausetherearestillenvironmentsinwhichfishcanthrive.
Askyourstudentswhatadvantageaneckmightprovide.Thelackofbonesconnectingtheheadtothebody
providesflexibilitytomovetheheadwithoutmovingtherestofthebody.Aflexibleneckcouldhavebeen
beneficialinmanypossiblescenarios.However,thisflexibilitymayhavealsocomeatacost—forexample,
thelossoftheprotectivegillcover.Wedon’tknowexactlyhowTiktaalikuseditsneck.
www.BioInteractive.org
PublishedNovember2014
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Great Transitions:
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•
•
•
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Studentsmayaskforexamplesofothertransitionsfromearliertolaterforms.Theevolutionofwhalesfrom
terrestrialmammalsandbirdsfromdinosaursarebothexcellentexampleswithrichfossilevidenceand
manytransitionalforms.Whalesevolvedfromterrestrialmammalsthatwalkedandranonfourlegs.Afun
factthatsupportsthisancestryisthataswimmingwhaleflexesitsbackboneupanddownlikearunning
cheetah,notsidetosidelikeaswimmingfish.Aswhaleancestorstransitionedfromaterrestrialtoamarine
life,manycharacteristicschanged.Forexample,legscanbealiabilityinanaquaticenvironmentratherthan
abenefit.Asaresult,whaleancestorsshowaprogressivedecreaseinthesizeoftheirhindlimbs.Allthat
remainsoftheselimbsinsomeoftoday’swhalespeciesisapairoftinybonesthatareburiedinsidethe
bodywallandarenotevenattachedtothepelvis.
Discusswithstudentswhytheterm“missinglink”isinaccurate.Thetermhasbeenpopularinthemediaand
hasbeenusedtoincorrectlyimplythatanunbrokenchainoforganismsisrequiredtodemonstratethatall
speciesarerelated.Theterms“transitionalform”and“transitionalfossil”moreaccuratelydescribespecies
thatillustratethesequenceofchangesthatoccurredduringtheevolutionofanewgroupoforganisms.
IsTiktaalikourancestor?Tiktaalikisrepresentativeofananimalthatwasanancestortomoderntetrapods,
includinghumans.Butwecannotsaywhetheritwasadirectancestor.Acommonmisconceptionisthatall
fossils,includingtransitionalfossilslikeTiktaalik,aredirectancestorsofmodernspecies.Explainthatfossils,
likeTiktaalik,maybedirectancestors,buttheyaremuchmorelikelyrepresentativeofwhattheactual
ancestorslookedlikeandnottheancestorsthemselves.Infact,thedescendantsofTiktaalikmayhavegone
extinctlongago,butanotherspecies,relatedtoTiktaalik,andyettobediscovered,maybethecommon
ancestortoallmoderntetrapods.Wemayneverknow,butwecanbecertainthattheancestorlookedalot
likeTiktaalik.
StudentsmaybeconfusedaboutwhyfossilanimalslikeTiktaalikthatlivedinwarmhabitatsendupin
barrenlocationsliketheCanadianArcticIslands.RemindstudentsthatEarth’sbiologicalandgeological
historiesareconnected.Earth’scrustisdynamic.Platetectonicsmovelandmasses,andfossilsthatwere
onceattheequatorcanbemovedtodistantlocations.
RELATEDBIOINTERACTIVERESOURCES
It’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-studentsrecognize-transitional-fossil)
Thisshortvideodemonstratesthepowerofobservationandtheimportanceoffossilevidence.WhenNeil
ShubinshowsaTiktaalikfossiltosmallchildren,theyimmediatelynoticethepresenceofbothfishandtetrapod
characteristics.
ExploreYourInnerAnimals
(http://www.hhmi.org/biointeractive/explore-your-inner-animals)
Thisinteractiveexploresdifferentanatomicalfeaturesofthehumanbodyandwhattheyrevealaboutthe
evolutionaryhistorywesharewithotherorganisms,includingearlier,long-extinctspecies.
www.BioInteractive.org
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Great Transitions:
The Origins of Tetrapods
Educator Materials
USINGTHEQUIZ
Thequizisdesignedasasummativeassessmentthatprobesstudentunderstandingofthekeyconcepts
addressedinthefilm.However,someteachersusethequizbeforeandduringthefilmtoassessstudents’prior
knowledgeandtoguidestudentsastheywatchthefilm.Teachersareencouragedtochoosetheusethatbest
fitstheirlearningobjectivesandtheirstudents’needs.Moreover,becausethevocabularyandconceptsare
complex,teachersareencouragedtomodifythequiz(e.g.,onlyasksomeofthequestions,explaincomplicated
vocabularyforELLstudents)asneeded.Thelasttwoquestionsareintendedforstudentswithpriorknowledge
aboutmutations,genesexpression,anddevelopment.
QUIZQUESTIONSANDANSWERS
Thestudentversionofthisquizisavailableasaseparatefile.Keyconceptscoveredbyeachquestionarenotedhere.
1. (KeyConceptB)WhenCharlesDarwinconsideredsomeoftheuniquestructuresfoundinmodernanimals,
likethefeatheredwingsofbirds,hefamouslyproposedthatmodernanimalsmusthaveevolvedfrom
earlierformsthatlackedthosestructures.Healsopredicted.(Fillintheblankwith
oneofthestatementsbelow.)
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,and
scientificprocessesusedduringtheTiktaalikexpeditions.
a.
b.
c.
d.
Location
CanadianArctic
Iceland
Alaska
ArcticCircle
Maps/Photos
Geologicalmaps
Roadmaps
Aerialphotos
Animaltrackmaps
ScientificProcess
Hypothesestesting
Predicting
Questioning
Developingexplanations
www.BioInteractive.org
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4. (KeyConceptE)Whichstatementbelowisevidencethatalltetrapodssharedasinglecommonancestor?
a. Alltetrapodslivepartlyinwaterandpartlyonland. b. Alltetrapodsarewarm-blooded.
c. Alltetrapodlimbsconsistofrearrangedfishfinrays.
d. Alltetrapodlimbshaveacommonpatternofonebone,twobones,manybones,thendigits.
5. (KeyConceptC)Thetransitionfromfishtotetrapodsisbestdescribedas:
a. Likemostofthegreattransitionsinevolutionaryhistory,ithappenedinveryfewbigstepssothatthereare
veryfewintermediateforms.
b. Likemostofthegreattransitionsinevolutionaryhistory,ithappenedinmanysmallstepsleadingtomany
intermediateforms.
c. Likenoothertransitioninevolutionaryhistory,ithappenedinmanysteps,sotherearemanyintermediate
forms.
d. Likemostofthegreattransitionsinevolutionaryhistory,ithappenedinasinglestepwithnointermediate
forms.
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.”Justifyyouranswerinoneor
twosentences.
False.Transitionalformsarespeciesintheirownright.Theyarecalledtransitionalformsbecausethey
possesstraits,likefins,thatarefoundinearlierfossilanimals,butalsopossesstraits,likelimbbones,thatare
foundinlaterfossilanimals.
www.BioInteractive.org
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8. (KeyConceptsF)Studythegraphicbelowofrocklayerswithfossilsinthem.ExplainhowNeilShubinandhis
teampredictedthattheywouldfindafossilanimallikeTiktaalikinrocksaround375millionyearsold.
Studentsshouldexplainthatfromthefossilrecord,Shubinandhisteamknewthatbefore385myathefossil
recorddoesnotcontaintetrapods.Around365myathefossilrecordshowsthefirstevidenceoforganisms
withtetrapodlimbcharacteristics,includingdigits.Shubinandhisteamhypothesizedthattheevolutionofa
functionaltetrapodlimbwasagradualprocess,andfossilsshowingintermediatestepsinthatprocessshould
belocatedinrocksofagesinbetween385millionand365millionyears.
9. (KeyConceptE)Thediagramsbelowillustratethebonesintheforelimbsoffourdifferentorganisms.
Althoughtheselimbsalllookdifferent,theysharesomecommonpatterns.Thesecommonpatternssuggest
that
a. Theseorganismsaremembersofthesamespecies.
b. Theorganismsexistedataboutthesamepointintime.
c. Theseorganismsshareacommonancestor.
d. Theseorganismshaveexactlythesamegenes.
10. (KeyConceptsF)ExplainwhyNeilShubinandhiscolleagueshadtotraveltoanareaabovetheArcticCircle
tofindthefossilofananimalthatoncelivedinawarmswamplikehabitat.
WhenTiktaaliklivedandbecamefossilized,thecontinentitwasonwaslocatedclosertoEarth’sequator
wherewarm,freshwaterhabitatswereabundant.Overtime,piecesofEarth’scrust,andallthefossilsinthe
rocksontopofthecrust,movedtodifferentlocationsduetocontinentaldrift.Studentsmayalsomention
www.BioInteractive.org
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Educator Materials
thatShubinandcolleaguesknewthattheArcticcontainsrocksfromtheDevonianperiodthatwereexplored
atthesurface.
11. (KeyConceptsBandF)Inthefilm,NeilShubinisshownhikinguparockyhillsidewhilerecallingforusoneof
theexcitingmomentsduringthehuntforaTiktaalik-likefossilanimal.Neilsays,“Beneathourfeetwere
fossilfishbones,fragmentsoffossilfishbones,manythousandsofpieces.Itwasn’tjustonefish;itwasa
wholeaquarium,itwasdifferentspecies.”Whatdidthisdiscoverymeanforthefossil-huntingteam?
Thefossilizedfishboneswereevidencethattheteamhaddiscoveredalayerofrockthathadformedinthe
kindofhabitatwhereananimallikeTiktaalikcouldalsohavelived.Therocklayercontainedmanyfish
species,soitmightalsocontainananimalthatexistedduringthetransitionfromwatertoland.
KEYREFERENCES
Daeschler,E.B.,Shubin,N.H.,andJenkinsJr.,F.A.(2006).ADevoniantetrapod-likefishandtheevolutionofthe
tetrapodbodyplan.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).ThecranialendoskeletonofTiktaalik
roseae.Nature455:925-929.
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AUTHORS
WrittenbyPaulStrode,PhD,FairviewHighSchool,Boulder,andLauraBonetta,PhD,HHMI
ReviewedbyJustinLemberg,PhD,TheUniversityofChicago
FieldtestedbyKimberlySaltsburg,WestminsterHighSchool,Westminster,MD;ZachMurray,PoncaCityHighSchool,
PoncaCity,OK;JackSaffer,CentralIslipHighSchool,CentralIslip,NY;MinuBasu,DoughertyValleyHighSchool,San
Ramon,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
www.BioInteractive.org
PublishedNovember2014
RevisedMarch2017
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