CHAPTERONE

FINDINGYOURINNERFISH

Typicalsummersofmyadultlifearespentinsnowandsleet,crackingrocksoncliffswellnorthoftheArcticCircle.MostofthetimeIfreeze,getblisters,andfindabsolutelynothing.ButifIhaveanyluck,Ifindancientfishbones.Thatmaynotsoundlikeburiedtreasuretomostpeople,buttomeitismorevaluablethangold.Ancientfishbonescanbeapathtoknowledgeaboutwho

weareandhowwegotthatway.Welearnaboutourownbodiesinseeminglybizarreplaces,rangingfromthefossilsofwormsandfishrecoveredfromrocksfromaroundtheworldtotheDNAinvirtuallyeveryanimalaliveonearthtoday.Butthatdoesnotexplainmyconfidenceaboutwhyskeletalremainsfromthepast—andtheremainsoffish,noless—offercluesaboutthefundamentalstructureofourbodies.Howcanwevisualizeeventsthathappenedmillionsand,

inmanycases,billionsofyearsago?Unfortunately,therewerenoeyewitnesses;noneofuswasaround.Infact,nothingthattalksorhasamouthorevenaheadwas

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aroundformostofthistime.Evenworse,theanimalsthatexistedbackthenhavebeendeadandburiedforsolongtheirbodiesareonlyrarelypreserved.Ifyouconsiderthatover99percentofallspeciesthateverlivedarenowextinct,thatonlyaverysmallfractionarepreservedasfossils,andthatanevensmallerfractionstillareeverfound,thenanyattempttoseeourpastseemsdoomedfromthestart.

DIGGINGFOSSILS—SEEINGOURSELVES

IfirstsawoneofourinnerfishonasnowyJulyafternoonwhilestudying375-million-year-oldrocksonEllesmereIsland,atalatitudeabout80degreesnorth.MycolleaguesandIhadtraveleduptothisdesolatepartoftheworldtotrytodiscoveroneofthekeystagesintheshiftfromfishtoland-livinganimals.Stickingoutoftherockswasthesnoutofafish.Andnotjustanyfish:afishwithaflathead.Oncewesawtheflatheadweknewwewereontosomething.Ifmoreofthisskeletonwerefoundinsidethecliff,itwouldrevealtheearlystagesinthehistoryofourskull,ourneck,evenourlimbs.Whatdidaflatheadtellmeabouttheshiftfromseato

land?Morerelevanttomypersonalsafetyandcomfort,whywasIintheArcticandnotinHawaii?Theanswerstothesequestionslieinthestoryofhowwefindfossilsandhowweusethemtodecipherourownpast.

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Fossilsareoneofthemajorlinesofevidencethatweusetounderstandourselves.(Genesandembryosareothers,whichIwilldiscusslater.)Mostpeopledonotknowthatfindingfossilsissomethingwecanoftendowithsurprisingprecisionandpredictability.Weworkathometomaximizeourchancesofsuccessinthefield.Thenweletlucktakeover.Theparadoxicalrelationshipbetweenplanningand

chanceisbestdescribedbyDwightD.Eisenhower’sfamousremarkaboutwarfare:“Inpreparingforbattle,Ihavefoundthatplanningisessential,butplansareuseless.”Thiscapturesfieldpaleontologyinanutshell.Wemakeallkindsofplanstogetustopromisingfossilsites.Oncewe’rethere,theentirefieldplanmaybethrownoutthewindow.Factsonthegroundcanchangeourbest-laidplans.Yetwecandesignexpeditionstoanswerspecific

scientificquestions.Usingafewsimpleideas,whichI’lltalkaboutbelow,wecanpredictwhereimportantfossilsmightbefound.Ofcourse,wearenotsuccessful100percentofthetime,butwestrikeitrichoftenenoughtomakethingsinteresting.Ihavemadeacareeroutofdoingjustthat:findingearlymammalstoanswerquestionsofmammalorigins,theearliestfrogstoanswerquestionsoffrogorigins,andsomeoftheearliestlimbedanimalstounderstandtheoriginsofland-livinganimals.Inmanyways,fieldpaleontologistshaveasignificantly

easiertimefindingnewsitestodaythanweeverdidbefore.Weknowmoreaboutthegeologyoflocalareas,thanksto

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thegeologicalexplorationundertakenbylocalgovernmentsandoilandgascompanies.TheInternetgivesusrapidaccesstomaps,surveyinformation,andaerialphotos.Icanevenscanyourbackyardforpromisingfossilsitesrightfrommylaptop.Totopitoff,imagingandradiographicdevicescanseethroughsomekindsofrockandallowustovisualizethebonesinside.Despitetheseadvances,thehuntfortheimportant

fossilsismuchwhatitwasahundredyearsago.Paleontologistsstillneedtolookatrock—literallytocrawloverit—andthefossilswithinmustoftenberemovedbyhand.Somanydecisionsneedtobemadewhenprospectingforandremovingfossilbonethattheseprocessesaredifficulttoautomate.Besides,lookingatamonitorscreentofindfossilswouldneverbenearlyasmuchfunasactuallydiggingforthem.Whatmakesthistrickyisthatfossilsitesarerare.To

maximizeouroddsofsuccess,welookfortheconvergenceofthreethings.Welookforplacesthathaverocksoftherightage,rocksoftherighttypetopreservefossils,androcksthatareexposedatthesurface.Thereisanotherfactor:serendipity.ThatIwillshowbyexample.Ourexamplewillshowusoneofthegreattransitionsin

thehistoryoflife:theinvasionoflandbyfish.Forbillionsofyears,alllifelivedonlyinwater.Then,asofabout365millionyearsago,creaturesalsoinhabitedland.Lifeinthesetwoenvironmentsisradicallydifferent.Breathinginwaterrequiresverydifferentorgansthanbreathinginair.

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Thesameistrueforexcretion,feeding,andmovingabout.Awholenewkindofbodyhadtoarise.Atfirstglance,thedividebetweenthetwoenvironmentsappearsalmostunbridgeable.Buteverythingchangeswhenwelookattheevidence;whatlooksimpossibleactuallyhappened.Inseekingrocksoftherightage,wehavearemarkable

factonourside.Thefossilsintherocksoftheworldarenotarrangedatrandom.Wheretheysit,andwhatliesinsidethem,ismostdefinitelyordered,andwecanusethisordertodesignourexpeditions.Billionsofyearsofchangehaveleftlayeruponlayerofdifferentkindsofrockintheearth.Theworkingassumption,whichiseasytotest,isthatrocksonthetopareyoungerthanrocksonthebottom;thisisusuallytrueinareasthathaveastraightforward,layer-cakearrangement(thinktheGrandCanyon).Butmovementsoftheearth’scrustcancausefaultsthatshiftthepositionofthelayers,puttingolderrocksontopofyoungerones.Fortunately,oncethepositionsofthesefaultsarerecognized,wecanoftenpiecetheoriginalsequenceoflayersbacktogether.Thefossilsinsidetheserocklayersalsofollowa

progression,withlowerlayerscontainingspeciesentirelydifferentfromthoseinthelayersabove.Ifwecouldquarryasinglecolumnofrockthatcontainedtheentirehistoryoflife,wewouldfindanextraordinaryrangeoffossils.Thelowestlayerswouldcontainlittlevisibleevidenceoflife.Layersabovethemwouldcontainimpressionsofadiversesetofjellyfish-likethings.Layersstillhigherwouldhave

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creatureswithskeletons,appendages,andvariousorgans,suchaseyes.Abovethosewouldbelayerswiththefirstanimalstohavebackbones.Andsoon.Thelayerswiththefirstpeoplewouldbefoundhigherstill.Ofcourse,asinglecolumncontainingtheentiretyofearthhistorydoesnotexist.Rather,therocksineachlocationonearthrepresentonlyasmallsliveroftime.Togetthewholepicture,weneedtoputthepiecestogetherbycomparingtherocksthemselvesandthefossilsinsidethem,muchasifworkingagiantjigsawpuzzle.Thatacolumnofrockshasaprogressionoffossilspecies

probablycomesasnosurprise.Lessobviousisthatwecanmakedetailedpredictionsaboutwhatthespeciesineachlayermightactuallylooklikebycomparingthemwithspeciesofanimalsthatarealivetoday;thisinformationhelpsustopredictthekindsoffossilswewillfindinancientrocklayers.Infact,thefossilsequencesintheworld’srockscanbepredictedbycomparingourselveswiththeanimalsatourlocalzoooraquarium.Howcanawalkthroughthezoohelpuspredictwherewe

shouldlookintherockstofindimportantfossils?Azoooffersagreatvarietyofcreaturesthatarealldistinctinmanyways.Butlet’snotfocusonwhatmakesthemdistinct;topulloffourprediction,weneedtofocusonwhatdifferentcreaturesshare.Wecanthenusethefeaturescommontoallspeciestoidentifygroupsofcreatureswithsimilartraits.AllthelivingthingscanbeorganizedandarrangedlikeasetofRussiannestingdolls,withsmaller

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groupsofanimalscomprisedinbiggergroupsofanimals.Whenwedothis,wediscoversomethingveryfundamentalaboutnature.Everyspeciesinthezooandtheaquariumhasaheadand

twoeyes.Callthesespecies“Everythings.”Asubsetofthecreatureswithaheadandtwoeyeshaslimbs.Callthelimbedspecies“Everythingswithlimbs.”Asubsetoftheseheadedandlimbedcreatureshasahugebrain,walksontwofeet,andspeaks.Thatsubsetisus,humans.Wecould,ofcourse,usethiswayofcategorizingthingstomakemanymoresubsets,buteventhisthreefolddivisionhaspredictivepower.Thefossilsinsidetherocksoftheworldgenerallyfollow

thisorder,andwecanputittouseindesigningnewexpeditions.Tousetheexampleabove,thefirstmemberofthegroup“Everythings,”acreaturewithaheadandtwoeyes,isfoundinthefossilrecordwellbeforethefirst“Everythingwithlimbs.”Moreprecisely,thefirstfish(acard-carryingmemberofthe“Everythings”)appearsbeforethefirstamphibian(an“Everythingwithlimbs”).Obviously,werefinethisbylookingatmorekindsofanimalsandmanymorecharacteristicsthatgroupsofthemshare,aswellasbyassessingtheactualageoftherocksthemselves.Inourlabs,wedoexactlythistypeofanalysiswith

thousandsuponthousandsofcharacteristicsandspecies.Welookateverybitofanatomywecan,andoftenatlargechunksofDNA.Thereissomuchdatathatweoftenneed

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powerfulcomputerstoshowusthegroupswithingroups.Thisapproachisthefoundationofbiology,becauseitenablesustomakehypothesesabouthowcreaturesarerelatedtooneanother.Besideshelpingusrefinethegroupingsoflife,hundreds

ofyearsoffossilcollectionhaveproducedavastlibrary,orcatalogue,oftheagesoftheearthandthelifeonit.Wecannowidentifygeneraltimeperiodswhenmajorchangesoccurred.Interestedintheoriginofmammals?GotorocksfromtheperiodcalledtheEarlyMesozoic;geochemistrytellsusthattheserocksarelikelyabout210millionyearsold.Interestedintheoriginofprimates?Gohigherintherockcolumn,totheCretaceousperiod,whererocksareabout80millionyearsold.Theorderoffossilsintheworld’srocksispowerful

evidenceofourconnectionstotherestoflife.If,diggingin600-million-year-oldrocks,wefoundtheearliestjellyfishlyingnexttotheskeletonofawoodchuck,thenwewouldhavetorewriteourtexts.Thatwoodchuckwouldhaveappearedearlierinthefossilrecordthanthefirstmammal,reptile,orevenfish—beforeeventhefirstworm.Moreover,ourancientwoodchuckwouldtellusthatmuchofwhatwethinkweknowaboutthehistoryoftheearthandlifeonitiswrong.Despitemorethan150yearsofpeoplelookingforfossils—oneverycontinentofearthandinvirtuallyeveryrocklayerthatisaccessible—thisobservationhasneverbeenmade.

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Whatwediscoveronourwalkthroughthezoomirrorshowfossilsarelaidoutintherocksoftheworld.

Let’snowreturntoourproblemofhowtofindrelatives

ofthefirstfishtowalkonland.Inourgroupingscheme,thesecreaturesaresomewherebetweenthe“Everythings”andthe“Everythingswithlimbs.”Mapthistowhatweknowoftherocks,andthereisstronggeologicalevidencethattheperiodfrom380millionto365millionyearsagois

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thecriticaltime.Theyoungerrocksinthatrange,thoseabout360millionyearsold,includediversekindsoffossilizedanimalsthatwewouldallrecognizeasamphibiansorreptiles.MycolleagueJennyClackatCambridgeUniversityandothershaveuncoveredamphibiansfromrocksinGreenlandthatareabout365millionyearsold.Withtheirnecks,theirears,andtheirfourlegs,theydonotlooklikefish.Butinrocksthatareabout385millionyearsold,wefindwholefishthatlooklike,well,fish.Theyhavefins,conicalheads,andscales;andtheyhavenonecks.Giventhis,itisprobablynogreatsurprisethatweshouldfocusonrocksabout375millionyearsoldtofindevidenceofthetransitionbetweenfishandland-livinganimals.Wehavesettledonatimeperiodtoresearch,andsohave

identifiedthelayersofthegeologicalcolumnwewishtoinvestigate.Nowthechallengeistofindrocksthatwereformedunderconditionscapableofpreservingfossils.Rocksformindifferentkindsofenvironmentsandtheseinitialsettingsleavedistinctsignaturesontherocklayers.Volcanicrocksaremostlyout.Nofishthatweknowofcanliveinlava.Andevenifsuchafishexisted,itsfossilizedboneswouldnotsurvivethesuperheatedconditionsinwhichbasalts,rhyolites,granites,andotherigneousrocksareformed.Wecanalsoignoremetamorphicrocks,suchasschistandmarble,fortheyhaveundergoneeithersuperheatingorextremepressuresincetheirinitialformation.Whateverfossilsmighthavebeenpreservedin

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themhavelongsincedisappeared.Idealtopreservefossilsaresedimentaryrocks:limestones,sandstones,silt-stones,andshales.Comparedwithvolcanicandmetamorphicrocks,theseareformedbymoregentleprocesses,includingtheactionofrivers,lakes,andseas.Notonlyareanimalslikelytoliveinsuchenvironments,butthesedimentaryprocessesmaketheserocksmorelikelyplacestopreservefossils.Forexample,inanoceanorlake,particlesconstantlysettleoutofthewaterandaredepositedonthebottom.Overtime,astheseparticlesaccumulate,theyarecompressedbynew,overridinglayers.Thegradualcompression,coupledwithchemicalprocesseshappeninginsidetherocksoverlongperiodsoftime,meansthatanyskeletonscontainedintherocksstandadecentchanceoffossilizing.Similarprocesseshappeninandalongstreams.Thegeneralruleisthatthegentlertheflowofthestreamorriver,thebetterpreservedthefossils.Everyrocksittingonthegroundhasastorytotell:the

storyofwhattheworldlookedlikeasthatparticularrockformed.Insidetherockisevidenceofpastclimatesandsurroundingsoftenvastlydifferentfromthoseoftoday.Sometimes,thedisconnectbetweenpresentandpastcouldnotbesharper.TaketheextremeexampleofMountEverest,nearwhosetop,atanaltitudeofoverfivemiles,lierocksfromanancientseafloor.GototheNorthFacealmostwithinsightofthefamousHillaryStep,andyoucanfindfossilizedseashells.Similarly,whereweworkintheArctic,temperaturescanreachminus40degreesFahrenheitinthe

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winter.Yetinsidesomeoftheregion’srocksareremnantsofanancienttropicaldelta,almostliketheAmazon:fossilizedplantsandfishthatcouldhavethrivedonlyinwarm,humidlocales.Thepresenceofwarm-adaptedspeciesatwhattodayareextremealtitudesandlatitudesatteststohowmuchourplanetcanchange:mountainsriseandfall,climateswarmandcool,andcontinentsmoveabout.Oncewecometogripswiththevastnessoftimeandtheextraordinarywaysourplanethaschanged,wewillbeinapositiontoputthisinformationtouseindesigningnewfossil-huntingexpeditions.Ifweareinterestedinunderstandingtheoriginoflimbed

animals,wecannowrestrictoursearchtorocksthatareroughly375millionto380millionyearsoldandthatwereformedinoceans,lakes,orstreams.Ruleoutvolcanicrocksandmetamorphicrocks,andoursearchimageforpromisingsitescomesintobetterfocus.Weareonlypartlyonthewaytodesigninganew

expedition,however.Itdoesusnogoodifourpromisingsedimentaryrocksoftherightageareburieddeepinsidetheearth,oriftheyarecoveredwithgrass,orshoppingmalls,orcities.We’dbediggingblindly.Asyoucanimagine,drillingawellholetofindafossiloffersalowprobabilityofsuccess,ratherlikethrowingdartsatadartboardhiddenbehindaclosetdoor.Thebestplacestolookarethosewherewecanwalkfor

milesovertherocktodiscoverareaswherebonesare“weatheringout.”Fossilbonesareoftenharderthanthe

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surroundingrockandsoerodeataslightlyslowerrateandpresentaraisedprofileontherocksurface.Consequently,weliketowalkoverbarebedrock,findasmatteringofbonesonthesurface,thendigin.Sohereisthetricktodesigninganewfossilexpedition:

findrocksthatareoftherightage,oftherighttype(sedimentary),andwellexposed,andweareinbusiness.Idealfossil-huntingsiteshavelittlesoilcoverandlittlevegetation,andhavebeensubjecttofewhumandisturbances.Isitanysurprisethatasignificantfractionofdiscoverieshappenindesertareas?IntheGobiDesert.IntheSahara.InUtah.InArcticdeserts,suchasGreenland.Thisallsoundsverylogical,butlet’snotforget

serendipity.Infact,itwasserendipitythatputourteamontothetrailofourinnerfish.Ourfirstimportantdiscoveriesdidn’thappeninadesert,butalongaroadsideincentralPennsylvaniawheretheexposurescouldhardlyhavebeenworse.Totopitoff,wewerelookingthereonlybecausewedidnothavemuchmoney.IttakesalotofmoneyandtimetogotoGreenlandorthe

SaharaDesert.Incontrast,alocalprojectdoesn’trequirebigresearchgrants,onlymoneyforgasandturnpiketolls.Thesearecriticalvariablesforayounggraduatestudentoranewlyhiredcollegeteacher.WhenIstartedmyfirstjobinPhiladelphia,thelurewasagroupofrockscollectivelyknownastheCatskillFormationofPennsylvania.Thisformationhasbeenextensivelystudiedforover150years.ItsagewaswellknownandspannedtheLateDevonian.In

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addition,itsrockswereperfecttopreserveearlylimbedanimalsandtheirclosestrelatives.Tounderstandthis,itisbesttohaveanimageofwhatPennsylvanialookedlikebackintheDevonian.Removetheimageofpresent-dayPhiladelphia,Pittsburgh,orHarrisburgfromyourmindandthinkoftheAmazonRiverdelta.Therewerehighlandsintheeasternpartofthestate.Aseriesofstreamsrunningeasttowestdrainedthesemountains,endinginalargeseawherePittsburghistoday.Itishardtoimaginebetterconditionstofindfossils,

exceptthatcentralPennsylvaniaiscoveredintowns,forests,andfields.Asfortheexposures,theyaremostlywherethePennsylvaniaDepartmentofTransportation(PennDOT)hasdecidedtoputbigroads.WhenPennDOTbuildsahighway,itblasts.Whenitblasts,itexposesrock.It’snotalwaysthebestexposure,butwetakewhatwecanget.Withcheapscience,yougetwhatyoupayfor.Andthenthereisalsoserendipityofadifferentorder:in

1993,TedDaeschlerarrivedtostudypaleontologyundermysupervision.Thispartnershipwastochangebothourlives.Ourdifferenttemperamentsareperfectlymatched:Ihaveantsinmypantsandamalwaysthinkingofthenextplacetolook;Tedispatientandknowswhentositonasitetomineitforitsriches.TedandIbeganasurveyoftheDevonianrocksofPennsylvaniainhopesoffindingnewevidenceontheoriginoflimbs.Webeganbydrivingtovirtuallyeverylargeroadcutintheeasternpartofthestate.Toourgreatsurprise,shortlyafterwebeganthesurvey,

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Tedfoundamarvelousshoulderbone.WenameditsownerHynerpeton,anamethattranslatesfromGreekas“littlecreepinganimalfromHyner.”Hyner,Pennsylvania,isthenearesttown.Hynerpetonhadaveryrobustshoulder,whichindicatesacreaturethatlikelyhadverypowerfulappendages.Unfortunately,wewereneverabletofindthewholeskeletonoftheanimal.Theexposuresweretoolimited.By?Youguessedit:vegetation,houses,andshoppingmalls.

AlongtheroadsinPennsylvania,wewerelookingatanancientriverdelta,muchliketheAmazontoday.ThestateofPennsylvania(bottom)withtheDevoniantopographymappedaboveit.

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AfterthediscoveryofHynerpetonandotherfossilsfromtheserocks,TedandIwerechampingatthebitforbetter-exposedrock.Ifourentirescientificenterprisewasgoingtobebasedonrecoveringbitsandpieces,thenwecouldaddressonlyverylimitedquestions.Sowetooka“textbook”approach,lookingforwell-exposedrocksoftherightageandtherighttypeindesertregions,meaningthatwewouldn’thavemadethebiggestdiscoveryofourcareersifnotforanintroductorygeologytextbook.OriginallywewerelookingatAlaskaandtheYukonas

potentialvenuesforanewexpedition,largelybecauseofrelevantdiscoveriesmadebyotherteams.Weendedupgettingintoabitofanargument/debateaboutsomegeologicalesoterica,andintheheatofthemoment,oneofuspulledtheluckygeologytextbookfromadesk.Whilerifflingthroughthepagestofindoutwhichoneofuswasright,wefoundadiagram.Thediagramtookourbreathaway;itshowedeverythingwewerelookingfor.Theargumentstopped,andplanningforanewfield

expeditionbegan.Onthebasisofpreviousdiscoveriesmadeinslightly

youngerrocks,webelievedthatancientfreshwaterstreamswerethebestenvironmentinwhichtobeginourhunt.ThisdiagramshowedthreeareaswithDevonianfreshwaterrocks,eachwithariverdeltasystem.First,thereistheeastcoastofGreenland.ThisishometoJennyClack’sfossil,averyearlycreaturewithlimbsandoneoftheearliestknowntetrapods.ThenthereiseasternNorthAmerica,

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wherewehadalreadyworked,hometoHynerpeton.Andthereisathirdarea,largeandrunningeast–westacrosstheCanadianArctic.Therearenotrees,dirt,orcitiesintheArctic.Thechancesweregoodthatrocksoftherightageandtypewouldbeextremelywellexposed.TheCanadianArcticexposureswerewellknown,

particularlytotheCanadiangeologistsandpaleobotanistswhohadalreadymappedthem.Infact,AshtonEmbry,theleaderoftheteamsthatdidmuchofthiswork,haddescribedthegeologyoftheDevonianCanadianrocksasidenticalinmanywaystothegeologyofPennsylvania’s.TedandIwerereadytopackourbagstheminutewereadthisphrase.ThelessonswehadlearnedonthehighwaysofPennsylvaniacouldhelpusintheHighArcticofCanada.Remarkably,theArcticrocksareevenolderthanthe

fossilbedsofGreenlandandPennsylvania.Sotheareaperfectlyfitallthreeofourcriteria:age,type,andexposure.Evenbetter,itwasunknowntovertebratepaleontologists,andthereforeun-prospectedforfossils.

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Themapthatstarteditall.ThismapofNorthAmericacaptureswhatwelookforinanutshell.ThedifferentkindsofshadingreflectwhereDevonianagerocks,whethermarineorfreshwater,areexposed.Threeareasthatwereonceriverdeltasarelabeled.Modifiedfromfigure13.1,R.H.DottandR.L.Batten,EvolutionoftheEarth(NewYork:McGraw-Hill,1988).ReproducedwiththepermissionofTheMcGraw-HillCompanies.

Ournewchallengesweretotallydifferentfromthosewe

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facedinPennsylvania.AlongthehighwaysinPennsylvania,weriskedbeinghitbythetrucksthatwhizzedbyaswelookedforfossils.IntheArcticweriskedbeingeatenbypolarbears,runningoutoffood,orbeingmaroonedbybadweather.Nolongercouldwepacksandwichesinthecaranddrivetothefossilbeds.Wenowhadtospendatleasteightdaysplanningforeverysingledayspentinthefield,becausetherockswereaccessibleonlybyairandthenearestsupplybasewas250milesaway.Wecouldflyinonlyenoughfoodandsuppliesforourcrew,plusaslendersafetymargin.And,mostimportant,theplane’sstrictweightlimitsmeantthatwecouldtakeoutonlyasmallfractionofthefossilsthatwefound.CouplethoselimitationswiththeshortwindowoftimeduringwhichwecanactuallyworkintheArcticeveryyear,andyoucanseethatthefrustrationswefacedwerecompletelynewanddaunting.Entermygraduateadviser,Dr.FarishA.Jenkins,Jr.,from

Harvard.FarishhadledexpeditionstoGreenlandforyearsandhadtheexperiencenecessarytopullthisventureoff.Theteamwasset.Threeacademicgenerations:Ted,myformerstudent;Farish,mygraduateadviser;andIweregoingtomarchuptotheArctictotrytodiscoverevidenceoftheshiftfromfishtoland-livinganimal.ThereisnofieldmanualforArcticpaleontology.We

receivedgearrecommendationsfromfriendsandcolleagues,andwereadbooks—onlytorealizethatnothingcouldprepareusfortheexperienceitself.Atnotimeisthis

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moresharplyfeltthanwhenthehelicopterdropsoneoffforthefirsttimeinsomegodforsakenpartoftheArctictotallyalone.Thefirstthoughtisofpolarbears.Ican’ttellyouhowmanytimesI’vescannedthelandscapelookingforwhitespecksthatmove.Thisanxietycanmakeyouseethings.InourfirstweekintheArctic,oneofthecrewsawamovingwhitespeck.Itlookedlikeapolarbearaboutaquartermileaway.WescrambledlikeKeystoneKopsforourguns,flares,andwhistlesuntilwediscoveredthatourbearwasawhiteArcticharetwohundredfeetaway.Withnotreesorhousesbywhichtojudgedistance,youloseperspectiveintheArctic.TheArcticisabig,emptyplace.Therockswewere

interestedinareexposedoveranareaabout1,500kilometerswide.Thecreatureswewerelookingforwereaboutfourfeetlong.Somehow,weneededtohomeinonasmallpatchofrockthathadpreservedourfossils.Reviewersofgrantproposalscanbeaferociouslot;theylightonthiskindofdifficultyallthetime.AreviewerforoneofFarish’searlyArcticgrantproposalsputitbest.Asthisrefereewroteinhisreviewoftheproposal(notcordially,Imightadd),theoddsoffindingnewfossilsintheArcticwere“worsethanfindingtheproverbialneedleinthehaystack.”IttookusfourexpeditionstoEllesmereIslandoversix

yearstofindourneedle.Somuchforserendipity.Wefoundwhatwewerelookingforbytrying,failing,and

learningfromourfailures.Ourfirstsites,inthe1999field

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season,werewayoutinthewesternpartoftheArctic,onMelvilleIsland.Wedidnotknowit,butwehadbeendroppedoffontheedgeofanancientocean.Therockswereloadedwithfossils,andwefoundmanydifferentkindsoffish.Theproblemwasthattheyallseemedtobedeep-watercreatures,notthekindwewouldexpecttofindintheshallowstreamsorlakesthatgaverisetoland-livinganimals.UsingAshtonEmbry’sgeologicalanalysis,in2000wedecidedtomovetheexpeditioneasttoEllesmereIsland,becausetheretherockswouldcontainancientstreambeds.Itdidnottakelongforustobeginfindingpiecesoffishbonesaboutthesizeofaquarterpreservedasfossils.

Ourcamp(top)lookstinyinthevastnessofthelandscape.Mysummerhome(bottom)isasmalltent,

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usuallysurroundedbypilesofrockstoprotectitfromfifty-mile-per-hourwinds.Photographsbytheauthor.

Therealbreakthroughcametowardtheendofthefield

seasonin2000.Itwasjustbeforedinner,aboutaweekbeforeourscheduledpickuptoreturnhome.Thecrewhadcomebacktocamp,andwewereinvolvedinourearly-eveningactivities:organizingtheday’scollections,preparingfieldnotes,andbeginningtoassembledinner.JasonDowns,thenacollegeundergraduateeagertolearnpaleontology,hadn’treturnedtocampontime.Thisisacauseforworry,aswetypicallygooutinteams;orifweseparate,wegiveeachotheradefinitescheduleofwhenwewillmakecontactagain.Withpolarbearsintheareaandfiercestormsthatcanrollinunexpectedly,wedonottakeanychances.Iremembersittinginthemaintentwiththecrew,theworryaboutJasonbuildingwitheachpassingmoment.Aswebegantoconcoctasearchplan,Iheardthezipperonthetentopen.AtfirstallIsawwasJason’shead.Hehadawild-eyedexpressiononhisfaceandwasoutofbreath.AsJasonenteredthetent,weknewwewerenotdealingwithapolarbearemergency;hisshotgunwasstillshouldered.Thecauseofhisdelaybecameclearashisstillshakinghandpulledouthandfulafterhandfuloffossilbonesthathadbeenstuffedintoeverypocket:hiscoat,pants,innershirt,anddaypack.Iimaginehewouldhavestuffedhissocksandshoesifhecouldhavewalkedhomethatway.Alloftheselittlefossilboneswereonthesurfaceofasmallsite,nobiggerthanaparkingspotforacompact

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car,aboutamileawayfromcamp.Dinnercouldwait.Withtwenty-fourhoursofdaylightintheArcticsummer,

wedidnothavetoworryaboutthesettingsun,sowegrabbedchocolatebarsandsetoffforJason’ssite.Itwasonthesideofahillbetweentwobeautifulrivervalleysand,asJasonhaddiscovered,wascoveredinacarpetoffossilfishbones.Wespentafewhourspickingupthefragments,takingphotos,andmakingplans.Thissitehadallthemakingsofpreciselywhatwewerelookingfor.Wereturnedthenextdaywithanewgoal:tofindtheexactlayerofrockthatcontainedthebones.ThetrickwastoidentifythesourceofJason’smessof

bonefragments—ouronlyhopeoffindingintactskeletons.TheproblemwastheArcticenvironment.Eachwinter,thetemperaturesinkstominus40degreesFahrenheit.Inthesummer,whenthesunneversets,thetemperaturerisestonearly50degrees.Theresultingfreeze-thawcyclecrumblesthesurfacerocksandfossils.Eachwintertheycoolandshrink;eachsummertheyheatandexpand.Astheyshrinkandswellwitheachseasonoverthousandsofyearsatthesurface,thebonesfallapart.Confrontedbyajumbledmassofbonespreadacrossthehill,wecouldnotidentifyanyobviousrocklayerastheirsource.Wespentseveraldaysfollowingthefragmenttrails,diggingtestpits,practicallyusingourgeologicalhammersasdiviningrodstoseewhereintheclifftheboneswereemerging.Afterfourdays,weexposedthelayerandeventuallyfoundskeletonuponskeletonoffossilfish,oftenlyingoneontopofanother.We

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spentpartsoftwosummersexposingthesefish.

Thisiswherewework:southernEllesmereIsland,inNunavutTerritory,Canada,1,000milesfromtheNorthPole.

Failureagain:allthefishwewerefindingwerewell-

knownspeciesthathadbeencollectedinsitesofasimilarageinEasternEurope.Totopitoff,thesefishweren’tverycloselyrelatedtoland-livinganimals.In2004,wedecidedtogiveitonemoretry.Thiswasado-or-diesituation.TheArcticexpeditionswereprohibitivelyexpensiveand,short

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ofaremarkablediscovery,wewouldhavetocallitquits.Everythingchangedoveraperiodoffourdaysinearly

July2004.Iwasflippingrockatthebottomofthequarry,crackingicemoreoftenthanrock.IcrackedtheiceandsawsomethingthatIwillneverforget:apatchofscalesunlikeanythingelsewehadyetseeninthequarry.Thispatchledtoanotherblobcoveredbyice.Itlookedlikeasetofjaws.Theywere,however,unlikethejawsofanyfishIhadeverseen.Theylookedasiftheymighthaveconnectedtoaflathead.Onedaylater,mycolleagueSteveGatesywasflipping

rocksatthetopofthequarry.Steveremovedafist-sizerocktorevealthesnoutofananimallookingrightoutathim.Likemyice-coveredfishatthebottomofthepit,ithadaflathead.Itwasnewandimportant.Butunlikemyfish,Steve’shadrealpotential.Wewerelookingatthefrontend,andwithlucktherestoftheskeletonmightbesafelysittinginthecliff.Stevespenttherestofthesummerremovingrockfromitbitbybitsothatwecouldbringtheentireskeletonbacktothelabandcleanitup.Steve’smasterfulworkwiththisspecimenledtotherecoveryofoneofthefinestfossilsdiscoveredtodateatthewater–landtransition.Thespecimenswebroughtbacktothelabathomewere

littlemorethanboulderswithfossilsinside.Overthecourseoftwomonths,therockwasremovedpiecebypiece,oftenmanuallywithdentaltoolsorsmallpicksbythepreparatorsinthelab.Everydayanewpieceofthefossil

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creature’sanatomywasrevealed.Almosteverytimealargesectionwasexposed,welearnedsomethingnewabouttheoriginofland-livinganimals.Whatwesawgraduallyemergefromtheserocksduring

thefallof2004wasabeautifulintermediatebetweenfishandland-livinganimals.Fishandland-livinganimalsdifferinmanyrespects.Fishhaveconicalheads,whereastheearliestland-livinganimalshavealmostcrocodile-likeheads—flat,withtheeyesontop.Fishdonothavenecks:theirshouldersareattachedtotheirheadsbyaseriesofbonyplates.Earlyland-livinganimals,likealltheirdescendants,dohavenecks,meaningtheirheadscanbendindependentlyoftheirshoulders.Thereareotherbigdifferences.Fishhavescalesallover

theirbodies;land-livinganimalsdonot.Also,importantly,fishhavefins,whereasland-livinganimalshavelimbswithfingers,toes,wrists,andankles.Wecancontinuethesecomparisonsandmakeaverylonglistofthewaysthatfishdifferfromland-livinganimals.

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Theprocessoffindingfossilsbeginswithamassinarockthatisgraduallyremovedovertime.HereIshowafossilasittravelsfromthefieldtothelabandiscarefullypreparedasaspecimen:theskeletonofthenewanimal.Photographinupperleftbyauthor;otherphotographscourtesyofTedDaeschler,AcademyofNaturalSciencesofPhiladelphia.

Butournewcreaturebrokedownthedistinction

betweenthesetwodifferentkindsofanimal.Likeafish,ithasscalesonitsbackandfinswithfinwebbing.But,likeearlyland-livinganimals,ithasaflatheadandaneck.And,whenwelookinsidethefin,weseebonesthatcorrespondtotheupperarm,theforearm,evenpartsofthewrist.Thejointsarethere,too:thisisafishwithshoulder,elbow,andwristjoints.Allinsideafinwithwebbing.Virtuallyallofthefeaturesthatthiscreatureshareswith

land-livingcreatureslookveryprimitive.Forexample,the

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shapeandvariousridgesonthefish’supper“arm”bone,thehumerus,lookpartfishandpartamphibian.Thesameistrueoftheshapeoftheskullandtheshoulder.Ittookussixyearstofindit,butthisfossilconfirmeda

predictionofpaleontology:notonlywasthenewfishanintermediatebetweentwodifferentkindsofanimal,butwehadfounditalsointherighttimeperiodinearth’shistoryandintherightancientenvironment.Theanswercamefrom375-million-year-oldrocks,formedinancientstreams.

Thisfiguresaysitall.Tiktaalikisintermediatebetweenfishandprimitiveland-livinganimal.

Asthediscoverersofthecreature,Ted,Farish,andIhad

theprivilegeofgivingitaformalscientificname.Wewantedthenametoreflectthefish’sprovenanceintheNunavutTerritoryoftheArcticandthedebtweowedtothe

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Inuitpeopleforpermissiontoworkthere.WeengagedtheNunavutCouncilofElders,formallyknownastheInuitQaujimajatuqangitKatimajiit,tocomeupwithanameintheInuktitutlanguage.MyobviousconcernwasthatacommitteenamedInuitQaujimajatuqangitKatimajiitmightnotproposeascientificnamewecouldpronounce.Isentthemapictureofthefossil,andtheelderscameupwithtwosuggestions,SiksagiaqandTiktaalik.WewentwithTiktaalikforitsrelativeeaseofpronunciationforthenon-Inuktitut-speakingtongueandbecauseofitsmeaninginInuktitut:“largefreshwaterfish.”Tiktaalikwastheleadstoryinanumberofnewspapers

thedayafterthefindwasannouncedinApril2006,includingabove-the-foldheadlinesinsuchplacesasTheNewYorkTimes.Thisattentionusheredinaweekunlikeanyotherinmynormallyquietlife.Thoughformethegreatestmomentofthewholemediablitzwasnotseeingthepoliticalcartoonsorreadingtheeditorialcoverageandtheheateddiscussionsontheblogs.Ittookplaceatmyson’spreschool.Inthemidstofthepresshubbub,myson’spreschool

teacheraskedmetobringinthefossilanddescribeit.IdutifullybroughtacastofTiktaalikintoNathaniel’sclass,bracingmyselfforthechaosthatwouldensue.Thetwentyfour-andfive-year-oldsweresurprisinglywellbehavedasIdescribedhowwehadworkedintheArctictofindthefossilandshowedthemtheanimal’ssharpteeth.ThenIaskedwhattheythoughtitwas.Handsshotup.Thefirstchildsaid

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itwasacrocodileoranalligator.Whenqueriedwhy,hesaidthatlikeacrocodileorlizardithasaflatheadwitheyesontop.Bigteeth,too.Otherchildrenstartedtovoicetheirdissent.Choosingtheraisedhandofoneofthesekids,Iheard:No,no,itisn’tacrocodile,itisafish,becauseithasscalesandfins.Yetanotherchildshouted,“Maybeitisboth.”Tiktaalik’smessageissostraightforwardevenpreschoolerscanseeit.Forourpurposes,thereisanevenmoreprofoundtakeon

Tiktaalik.Thisfishdoesn’tjusttellusaboutfish;italsocontainsapieceofus.ThesearchforthisconnectioniswhatledmetotheArcticinthefirstplace.HowcanIbesosurethatthisfossilsayssomething

aboutmyownbody?ConsidertheneckofTiktaalik.AllfishpriortoTiktaalikhaveasetofbonesthatattachtheskulltotheshoulder,sothateverytimetheanimalbentitsbody,italsobentitshead.Tiktaalikisdifferent.Theheadiscompletelyfreeoftheshoulder.Thiswholearrangementissharedwithamphibians,reptiles,birds,andmammals,includingus.TheentireshiftcanbetracedtothelossofafewsmallbonesinafishlikeTiktaalik.

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Tracingarmbonesfromfishtohumans.Icandoasimilaranalysisforthewrists,ribs,ears,and

otherpartsofourskeleton—allthesefeaturescanbetracedbacktoafishlikethis.ThisfossilisjustasmuchapartofourhistoryastheAfricanhominids,suchasAustralopithecusafarensis,thefamous“Lucy.”SeeingLucy,wecanunderstandourhistoryashighlyadvancedprimates.SeeingTiktaalikisseeingourhistoryasfish.Sowhathavewelearned?Ourworldissohighlyordered

thatwecanuseawalkthroughazootopredictthekindsoffossilsthatlieinthedifferentlayersofrocksaroundtheworld.Thosepredictionscanbringaboutfossildiscoveriesthattellusaboutancienteventsinthehistoryoflife.Therecordofthoseeventsremainsinsideus,aspartofour

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anatomicalorganization.WhatIhaven’tmentionedisthatwecanalsotraceour

historyinsideourgenes,throughDNA.Thisrecordofourpastdoesn’tlieintherocksoftheworld;itliesineverycellinsideus.We’llusebothfossilsandgenestotellourstory,thestoryofthemakingofourbodies.

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