CHAPTERONE
FINDINGYOURINNERFISH
Typicalsummersofmyadultlifearespentinsnowand
sleet,crackingrocksoncliffswellnorthoftheArcticCircle.
MostofthetimeIfreeze,getblisters,andfindabsolutely
nothing.ButifIhaveanyluck,Ifindancientfishbones.That
maynotsoundlikeburiedtreasuretomostpeople,butto
meitismorevaluablethangold.
Ancientfishbonescanbeapathtoknowledgeaboutwho
weareandhowwegotthatway.Welearnaboutourown
bodiesinseeminglybizarreplaces,rangingfromthefossils
ofwormsandfishrecoveredfromrocksfromaroundthe
worldtotheDNAinvirtuallyeveryanimalaliveonearth
today.Butthatdoesnotexplainmyconfidenceaboutwhy
skeletalremainsfromthepast—andtheremainsoffish,no
less—offercluesaboutthefundamentalstructureofour
bodies.
Howcanwevisualizeeventsthathappenedmillionsand,
inmanycases,billionsofyearsago?Unfortunately,there
werenoeyewitnesses;noneofuswasaround.Infact,
nothingthattalksorhasamouthorevenaheadwas
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aroundformostofthistime.Evenworse,theanimalsthat
existedbackthenhavebeendeadandburiedforsolong
theirbodiesareonlyrarelypreserved.Ifyouconsiderthat
over99percentofallspeciesthateverlivedarenow
extinct,thatonlyaverysmallfractionarepreservedas
fossils,andthatanevensmallerfractionstillareeverfound,
thenanyattempttoseeourpastseemsdoomedfromthe
start.
DIGGINGFOSSILS—SEEINGOURSELVES
IfirstsawoneofourinnerfishonasnowyJulyafternoon
whilestudying375-million-year-oldrocksonEllesmere
Island,atalatitudeabout80degreesnorth.Mycolleagues
andIhadtraveleduptothisdesolatepartoftheworldto
trytodiscoveroneofthekeystagesintheshiftfromfishto
land-livinganimals.Stickingoutoftherockswasthesnout
ofafish.Andnotjustanyfish:afishwithaflathead.Once
wesawtheflatheadweknewwewereontosomething.If
moreofthisskeletonwerefoundinsidethecliff,itwould
revealtheearlystagesinthehistoryofourskull,ourneck,
evenourlimbs.
Whatdidaflatheadtellmeabouttheshiftfromseato
land?Morerelevanttomypersonalsafetyandcomfort,why
wasIintheArcticandnotinHawaii?Theanswerstothese
questionslieinthestoryofhowwefindfossilsandhowwe
usethemtodecipherourownpast.
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Fossilsareoneofthemajorlinesofevidencethatweuse
tounderstandourselves.(Genesandembryosareothers,
whichIwilldiscusslater.)Mostpeopledonotknowthat
findingfossilsissomethingwecanoftendowithsurprising
precisionandpredictability.Weworkathometomaximize
ourchancesofsuccessinthefield.Thenweletlucktake
over.
Theparadoxicalrelationshipbetweenplanningand
chanceisbestdescribedbyDwightD.Eisenhower’sfamous
remarkaboutwarfare:“Inpreparingforbattle,Ihavefound
thatplanningisessential,butplansareuseless.”This
capturesfieldpaleontologyinanutshell.Wemakeallkinds
ofplanstogetustopromisingfossilsites.Oncewe’rethere,
theentirefieldplanmaybethrownoutthewindow.Facts
onthegroundcanchangeourbest-laidplans.
Yetwecandesignexpeditionstoanswerspecific
scientificquestions.Usingafewsimpleideas,whichI’lltalk
aboutbelow,wecanpredictwhereimportantfossilsmight
befound.Ofcourse,wearenotsuccessful100percentof
thetime,butwestrikeitrichoftenenoughtomakethings
interesting.Ihavemadeacareeroutofdoingjustthat:
findingearlymammalstoanswerquestionsofmammal
origins,theearliestfrogstoanswerquestionsoffrog
origins,andsomeoftheearliestlimbedanimalsto
understandtheoriginsofland-livinganimals.
Inmanyways,fieldpaleontologistshaveasignificantly
easiertimefindingnewsitestodaythanweeverdidbefore.
Weknowmoreaboutthegeologyoflocalareas,thanksto
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thegeologicalexplorationundertakenbylocal
governmentsandoilandgascompanies.TheInternetgives
usrapidaccesstomaps,surveyinformation,andaerial
photos.Icanevenscanyourbackyardforpromisingfossil
sitesrightfrommylaptop.Totopitoff,imagingand
radiographicdevicescanseethroughsomekindsofrock
andallowustovisualizethebonesinside.
Despitetheseadvances,thehuntfortheimportant
fossilsismuchwhatitwasahundredyearsago.
Paleontologistsstillneedtolookatrock—literallytocrawl
overit—andthefossilswithinmustoftenberemovedby
hand.Somanydecisionsneedtobemadewhen
prospectingforandremovingfossilbonethatthese
processesaredifficulttoautomate.Besides,lookingata
monitorscreentofindfossilswouldneverbenearlyas
muchfunasactuallydiggingforthem.
Whatmakesthistrickyisthatfossilsitesarerare.To
maximizeouroddsofsuccess,welookfortheconvergence
ofthreethings.Welookforplacesthathaverocksofthe
rightage,rocksoftherighttypetopreservefossils,and
rocksthatareexposedatthesurface.Thereisanother
factor:serendipity.ThatIwillshowbyexample.
Ourexamplewillshowusoneofthegreattransitionsin
thehistoryoflife:theinvasionoflandbyfish.Forbillionsof
years,alllifelivedonlyinwater.Then,asofabout365
millionyearsago,creaturesalsoinhabitedland.Lifein
thesetwoenvironmentsisradicallydifferent.Breathingin
waterrequiresverydifferentorgansthanbreathinginair.
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Thesameistrueforexcretion,feeding,andmovingabout.A
wholenewkindofbodyhadtoarise.Atfirstglance,the
dividebetweenthetwoenvironmentsappearsalmost
unbridgeable.Buteverythingchangeswhenwelookatthe
evidence;whatlooksimpossibleactuallyhappened.
Inseekingrocksoftherightage,wehavearemarkable
factonourside.Thefossilsintherocksoftheworldarenot
arrangedatrandom.Wheretheysit,andwhatliesinside
them,ismostdefinitelyordered,andwecanusethisorder
todesignourexpeditions.Billionsofyearsofchangehave
leftlayeruponlayerofdifferentkindsofrockintheearth.
Theworkingassumption,whichiseasytotest,isthatrocks
onthetopareyoungerthanrocksonthebottom;thisis
usuallytrueinareasthathaveastraightforward,layer-cake
arrangement(thinktheGrandCanyon).Butmovementsof
theearth’scrustcancausefaultsthatshiftthepositionof
thelayers,puttingolderrocksontopofyoungerones.
Fortunately,oncethepositionsofthesefaultsare
recognized,wecanoftenpiecetheoriginalsequenceof
layersbacktogether.
Thefossilsinsidetheserocklayersalsofollowa
progression,withlowerlayerscontainingspeciesentirely
differentfromthoseinthelayersabove.Ifwecouldquarry
asinglecolumnofrockthatcontainedtheentirehistoryof
life,wewouldfindanextraordinaryrangeoffossils.The
lowestlayerswouldcontainlittlevisibleevidenceoflife.
Layersabovethemwouldcontainimpressionsofadiverse
setofjellyfish-likethings.Layersstillhigherwouldhave
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creatureswithskeletons,appendages,andvariousorgans,
suchaseyes.Abovethosewouldbelayerswiththefirst
animalstohavebackbones.Andsoon.Thelayerswiththe
firstpeoplewouldbefoundhigherstill.Ofcourse,asingle
columncontainingtheentiretyofearthhistorydoesnot
exist.Rather,therocksineachlocationonearthrepresent
onlyasmallsliveroftime.Togetthewholepicture,we
needtoputthepiecestogetherbycomparingtherocks
themselvesandthefossilsinsidethem,muchasifworking
agiantjigsawpuzzle.
Thatacolumnofrockshasaprogressionoffossilspecies
probablycomesasnosurprise.Lessobviousisthatwecan
makedetailedpredictionsaboutwhatthespeciesineach
layermightactuallylooklikebycomparingthemwith
speciesofanimalsthatarealivetoday;thisinformation
helpsustopredictthekindsoffossilswewillfindinancient
rocklayers.Infact,thefossilsequencesintheworld’srocks
canbepredictedbycomparingourselveswiththeanimals
atourlocalzoooraquarium.
Howcanawalkthroughthezoohelpuspredictwherewe
shouldlookintherockstofindimportantfossils?Azoo
offersagreatvarietyofcreaturesthatarealldistinctin
manyways.Butlet’snotfocusonwhatmakesthem
distinct;topulloffourprediction,weneedtofocusonwhat
differentcreaturesshare.Wecanthenusethefeatures
commontoallspeciestoidentifygroupsofcreatureswith
similartraits.Allthelivingthingscanbeorganizedand
arrangedlikeasetofRussiannestingdolls,withsmaller
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groupsofanimalscomprisedinbiggergroupsofanimals.
Whenwedothis,wediscoversomethingveryfundamental
aboutnature.
Everyspeciesinthezooandtheaquariumhasaheadand
twoeyes.Callthesespecies“Everythings.”Asubsetofthe
creatureswithaheadandtwoeyeshaslimbs.Callthe
limbedspecies“Everythingswithlimbs.”Asubsetofthese
headedandlimbedcreatureshasahugebrain,walkson
twofeet,andspeaks.Thatsubsetisus,humans.Wecould,
ofcourse,usethiswayofcategorizingthingstomakemany
moresubsets,buteventhisthreefolddivisionhas
predictivepower.
Thefossilsinsidetherocksoftheworldgenerallyfollow
thisorder,andwecanputittouseindesigningnew
expeditions.Tousetheexampleabove,thefirstmemberof
thegroup“Everythings,”acreaturewithaheadandtwo
eyes,isfoundinthefossilrecordwellbeforethefirst
“Everythingwithlimbs.”Moreprecisely,thefirstfish(a
card-carryingmemberofthe“Everythings”)appearsbefore
thefirstamphibian(an“Everythingwithlimbs”).
Obviously,werefinethisbylookingatmorekindsof
animalsandmanymorecharacteristicsthatgroupsofthem
share,aswellasbyassessingtheactualageoftherocks
themselves.
Inourlabs,wedoexactlythistypeofanalysiswith
thousandsuponthousandsofcharacteristicsandspecies.
Welookateverybitofanatomywecan,andoftenatlarge
chunksofDNA.Thereissomuchdatathatweoftenneed
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powerfulcomputerstoshowusthegroupswithingroups.
Thisapproachisthefoundationofbiology,becauseit
enablesustomakehypothesesabouthowcreaturesare
relatedtooneanother.
Besideshelpingusrefinethegroupingsoflife,hundreds
ofyearsoffossilcollectionhaveproducedavastlibrary,or
catalogue,oftheagesoftheearthandthelifeonit.Wecan
nowidentifygeneraltimeperiodswhenmajorchanges
occurred.Interestedintheoriginofmammals?Gotorocks
fromtheperiodcalledtheEarlyMesozoic;geochemistry
tellsusthattheserocksarelikelyabout210millionyears
old.Interestedintheoriginofprimates?Gohigherinthe
rockcolumn,totheCretaceousperiod,whererocksare
about80millionyearsold.
Theorderoffossilsintheworld’srocksispowerful
evidenceofourconnectionstotherestoflife.If,diggingin
600-million-year-oldrocks,wefoundtheearliestjellyfish
lyingnexttotheskeletonofawoodchuck,thenwewould
havetorewriteourtexts.Thatwoodchuckwouldhave
appearedearlierinthefossilrecordthanthefirstmammal,
reptile,orevenfish—beforeeventhefirstworm.Moreover,
ourancientwoodchuckwouldtellusthatmuchofwhatwe
thinkweknowaboutthehistoryoftheearthandlifeonitis
wrong.Despitemorethan150yearsofpeoplelookingfor
fossils—oneverycontinentofearthandinvirtuallyevery
rocklayerthatisaccessible—thisobservationhasnever
beenmade.
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Whatwediscoveronourwalkthroughthezoomirrors
howfossilsarelaidoutintherocksoftheworld.
Let’snowreturntoourproblemofhowtofindrelatives
ofthefirstfishtowalkonland.Inourgroupingscheme,
thesecreaturesaresomewherebetweenthe“Everythings”
andthe“Everythingswithlimbs.”Mapthistowhatwe
knowoftherocks,andthereisstronggeologicalevidence
thattheperiodfrom380millionto365millionyearsagois
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thecriticaltime.Theyoungerrocksinthatrange,those
about360millionyearsold,includediversekindsof
fossilizedanimalsthatwewouldallrecognizeas
amphibiansorreptiles.MycolleagueJennyClackat
CambridgeUniversityandothershaveuncovered
amphibiansfromrocksinGreenlandthatareabout365
millionyearsold.Withtheirnecks,theirears,andtheirfour
legs,theydonotlooklikefish.Butinrocksthatareabout
385millionyearsold,wefindwholefishthatlooklike,well,
fish.Theyhavefins,conicalheads,andscales;andtheyhave
nonecks.Giventhis,itisprobablynogreatsurprisethatwe
shouldfocusonrocksabout375millionyearsoldtofind
evidenceofthetransitionbetweenfishandland-living
animals.
Wehavesettledonatimeperiodtoresearch,andsohave
identifiedthelayersofthegeologicalcolumnwewishto
investigate.Nowthechallengeistofindrocksthatwere
formedunderconditionscapableofpreservingfossils.
Rocksformindifferentkindsofenvironmentsandthese
initialsettingsleavedistinctsignaturesontherocklayers.
Volcanicrocksaremostlyout.Nofishthatweknowofcan
liveinlava.Andevenifsuchafishexisted,itsfossilized
boneswouldnotsurvivethesuperheatedconditionsin
whichbasalts,rhyolites,granites,andotherigneousrocks
areformed.Wecanalsoignoremetamorphicrocks,suchas
schistandmarble,fortheyhaveundergoneeither
superheatingorextremepressuresincetheirinitial
formation.Whateverfossilsmighthavebeenpreservedin
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themhavelongsincedisappeared.Idealtopreservefossils
aresedimentaryrocks:limestones,sandstones,silt-stones,
andshales.Comparedwithvolcanicandmetamorphic
rocks,theseareformedbymoregentleprocesses,including
theactionofrivers,lakes,andseas.Notonlyareanimals
likelytoliveinsuchenvironments,butthesedimentary
processesmaketheserocksmorelikelyplacestopreserve
fossils.Forexample,inanoceanorlake,particles
constantlysettleoutofthewaterandaredepositedonthe
bottom.Overtime,astheseparticlesaccumulate,theyare
compressedbynew,overridinglayers.Thegradual
compression,coupledwithchemicalprocesseshappening
insidetherocksoverlongperiodsoftime,meansthatany
skeletonscontainedintherocksstandadecentchanceof
fossilizing.Similarprocesseshappeninandalongstreams.
Thegeneralruleisthatthegentlertheflowofthestreamor
river,thebetterpreservedthefossils.
Everyrocksittingonthegroundhasastorytotell:the
storyofwhattheworldlookedlikeasthatparticularrock
formed.Insidetherockisevidenceofpastclimatesand
surroundingsoftenvastlydifferentfromthoseoftoday.
Sometimes,thedisconnectbetweenpresentandpastcould
notbesharper.TaketheextremeexampleofMount
Everest,nearwhosetop,atanaltitudeofoverfivemiles,lie
rocksfromanancientseafloor.GototheNorthFacealmost
withinsightofthefamousHillaryStep,andyoucanfind
fossilizedseashells.Similarly,whereweworkintheArctic,
temperaturescanreachminus40degreesFahrenheitinthe
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winter.Yetinsidesomeoftheregion’srocksareremnants
ofanancienttropicaldelta,almostliketheAmazon:
fossilizedplantsandfishthatcouldhavethrivedonlyin
warm,humidlocales.Thepresenceofwarm-adapted
speciesatwhattodayareextremealtitudesandlatitudes
atteststohowmuchourplanetcanchange:mountainsrise
andfall,climateswarmandcool,andcontinentsmove
about.Oncewecometogripswiththevastnessoftimeand
theextraordinarywaysourplanethaschanged,wewillbe
inapositiontoputthisinformationtouseindesigningnew
fossil-huntingexpeditions.
Ifweareinterestedinunderstandingtheoriginoflimbed
animals,wecannowrestrictoursearchtorocksthatare
roughly375millionto380millionyearsoldandthatwere
formedinoceans,lakes,orstreams.Ruleoutvolcanicrocks
andmetamorphicrocks,andoursearchimagefor
promisingsitescomesintobetterfocus.
Weareonlypartlyonthewaytodesigninganew
expedition,however.Itdoesusnogoodifourpromising
sedimentaryrocksoftherightageareburieddeepinside
theearth,oriftheyarecoveredwithgrass,orshopping
malls,orcities.We’dbediggingblindly.Asyoucanimagine,
drillingawellholetofindafossiloffersalowprobabilityof
success,ratherlikethrowingdartsatadartboardhidden
behindaclosetdoor.
Thebestplacestolookarethosewherewecanwalkfor
milesovertherocktodiscoverareaswherebonesare
“weatheringout.”Fossilbonesareoftenharderthanthe
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surroundingrockandsoerodeataslightlyslowerrateand
presentaraisedprofileontherocksurface.Consequently,
weliketowalkoverbarebedrock,findasmatteringof
bonesonthesurface,thendigin.
Sohereisthetricktodesigninganewfossilexpedition:
findrocksthatareoftherightage,oftherighttype
(sedimentary),andwellexposed,andweareinbusiness.
Idealfossil-huntingsiteshavelittlesoilcoverandlittle
vegetation,andhavebeensubjecttofewhuman
disturbances.Isitanysurprisethatasignificantfractionof
discoverieshappenindesertareas?IntheGobiDesert.In
theSahara.InUtah.InArcticdeserts,suchasGreenland.
Thisallsoundsverylogical,butlet’snotforget
serendipity.Infact,itwasserendipitythatputourteam
ontothetrailofourinnerfish.Ourfirstimportant
discoveriesdidn’thappeninadesert,butalongaroadside
incentralPennsylvaniawheretheexposurescouldhardly
havebeenworse.Totopitoff,wewerelookingthereonly
becausewedidnothavemuchmoney.
IttakesalotofmoneyandtimetogotoGreenlandorthe
SaharaDesert.Incontrast,alocalprojectdoesn’trequire
bigresearchgrants,onlymoneyforgasandturnpiketolls.
Thesearecriticalvariablesforayounggraduatestudentor
anewlyhiredcollegeteacher.WhenIstartedmyfirstjobin
Philadelphia,thelurewasagroupofrockscollectively
knownastheCatskillFormationofPennsylvania.This
formationhasbeenextensivelystudiedforover150years.
ItsagewaswellknownandspannedtheLateDevonian.In
19
addition,itsrockswereperfecttopreserveearlylimbed
animalsandtheirclosestrelatives.Tounderstandthis,itis
besttohaveanimageofwhatPennsylvanialookedlike
backintheDevonian.Removetheimageofpresent-day
Philadelphia,Pittsburgh,orHarrisburgfromyourmindand
thinkoftheAmazonRiverdelta.Therewerehighlandsin
theeasternpartofthestate.Aseriesofstreamsrunning
easttowestdrainedthesemountains,endinginalargesea
wherePittsburghistoday.
Itishardtoimaginebetterconditionstofindfossils,
exceptthatcentralPennsylvaniaiscoveredintowns,
forests,andfields.Asfortheexposures,theyaremostly
wherethePennsylvaniaDepartmentofTransportation
(PennDOT)hasdecidedtoputbigroads.WhenPennDOT
buildsahighway,itblasts.Whenitblasts,itexposesrock.
It’snotalwaysthebestexposure,butwetakewhatwecan
get.Withcheapscience,yougetwhatyoupayfor.
Andthenthereisalsoserendipityofadifferentorder:in
1993,TedDaeschlerarrivedtostudypaleontologyunder
mysupervision.Thispartnershipwastochangebothour
lives.Ourdifferenttemperamentsareperfectlymatched:I
haveantsinmypantsandamalwaysthinkingofthenext
placetolook;Tedispatientandknowswhentositonasite
tomineitforitsriches.TedandIbeganasurveyofthe
DevonianrocksofPennsylvaniainhopesoffindingnew
evidenceontheoriginoflimbs.Webeganbydrivingto
virtuallyeverylargeroadcutintheeasternpartofthestate.
Toourgreatsurprise,shortlyafterwebeganthesurvey,
20
Tedfoundamarvelousshoulderbone.Wenameditsowner
Hynerpeton,anamethattranslatesfromGreekas“little
creepinganimalfromHyner.”Hyner,Pennsylvania,isthe
nearesttown.Hynerpetonhadaveryrobustshoulder,which
indicatesacreaturethatlikelyhadverypowerful
appendages.Unfortunately,wewereneverabletofindthe
wholeskeletonoftheanimal.Theexposuresweretoo
limited.By?Youguessedit:vegetation,houses,and
shoppingmalls.
AlongtheroadsinPennsylvania,wewerelookingatan
ancientriverdelta,muchliketheAmazontoday.The
stateofPennsylvania(bottom)withtheDevonian
topographymappedaboveit.
21
AfterthediscoveryofHynerpetonandotherfossilsfrom
theserocks,TedandIwerechampingatthebitforbetterexposedrock.Ifourentirescientificenterprisewasgoing
tobebasedonrecoveringbitsandpieces,thenwecould
addressonlyverylimitedquestions.Sowetooka
“textbook”approach,lookingforwell-exposedrocksofthe
rightageandtherighttypeindesertregions,meaningthat
wewouldn’thavemadethebiggestdiscoveryofourcareers
ifnotforanintroductorygeologytextbook.
OriginallywewerelookingatAlaskaandtheYukonas
potentialvenuesforanewexpedition,largelybecauseof
relevantdiscoveriesmadebyotherteams.Weendedup
gettingintoabitofanargument/debateaboutsome
geologicalesoterica,andintheheatofthemoment,oneof
uspulledtheluckygeologytextbookfromadesk.While
rifflingthroughthepagestofindoutwhichoneofuswas
right,wefoundadiagram.Thediagramtookourbreath
away;itshowedeverythingwewerelookingfor.
Theargumentstopped,andplanningforanewfield
expeditionbegan.
Onthebasisofpreviousdiscoveriesmadeinslightly
youngerrocks,webelievedthatancientfreshwaterstreams
werethebestenvironmentinwhichtobeginourhunt.This
diagramshowedthreeareaswithDevonianfreshwater
rocks,eachwithariverdeltasystem.First,thereistheeast
coastofGreenland.ThisishometoJennyClack’sfossil,a
veryearlycreaturewithlimbsandoneoftheearliest
knowntetrapods.ThenthereiseasternNorthAmerica,
22
wherewehadalreadyworked,hometoHynerpeton.And
thereisathirdarea,largeandrunningeast–westacrossthe
CanadianArctic.Therearenotrees,dirt,orcitiesinthe
Arctic.Thechancesweregoodthatrocksoftherightage
andtypewouldbeextremelywellexposed.
TheCanadianArcticexposureswerewellknown,
particularlytotheCanadiangeologistsandpaleobotanists
whohadalreadymappedthem.Infact,AshtonEmbry,the
leaderoftheteamsthatdidmuchofthiswork,had
describedthegeologyoftheDevonianCanadianrocksas
identicalinmanywaystothegeologyofPennsylvania’s.
TedandIwerereadytopackourbagstheminuteweread
thisphrase.Thelessonswehadlearnedonthehighwaysof
PennsylvaniacouldhelpusintheHighArcticofCanada.
Remarkably,theArcticrocksareevenolderthanthe
fossilbedsofGreenlandandPennsylvania.Sothearea
perfectlyfitallthreeofourcriteria:age,type,andexposure.
Evenbetter,itwasunknowntovertebratepaleontologists,
andthereforeun-prospectedforfossils.
23
Themapthatstarteditall.ThismapofNorthAmerica
captureswhatwelookforinanutshell.Thedifferent
kindsofshadingreflectwhereDevonianagerocks,
whethermarineorfreshwater,areexposed.Three
areasthatwereonceriverdeltasarelabeled.Modified
fromfigure13.1,R.H.DottandR.L.Batten,Evolutionof
theEarth(NewYork:McGraw-Hill,1988).Reproduced
withthepermissionofTheMcGraw-HillCompanies.
Ournewchallengesweretotallydifferentfromthosewe
24
facedinPennsylvania.AlongthehighwaysinPennsylvania,
weriskedbeinghitbythetrucksthatwhizzedbyaswe
lookedforfossils.IntheArcticweriskedbeingeatenby
polarbears,runningoutoffood,orbeingmaroonedbybad
weather.Nolongercouldwepacksandwichesinthecarand
drivetothefossilbeds.Wenowhadtospendatleasteight
daysplanningforeverysingledayspentinthefield,
becausetherockswereaccessibleonlybyairandthe
nearestsupplybasewas250milesaway.Wecouldflyin
onlyenoughfoodandsuppliesforourcrew,plusaslender
safetymargin.And,mostimportant,theplane’sstrict
weightlimitsmeantthatwecouldtakeoutonlyasmall
fractionofthefossilsthatwefound.Couplethose
limitationswiththeshortwindowoftimeduringwhichwe
canactuallyworkintheArcticeveryyear,andyoucansee
thatthefrustrationswefacedwerecompletelynewand
daunting.
Entermygraduateadviser,Dr.FarishA.Jenkins,Jr.,from
Harvard.FarishhadledexpeditionstoGreenlandforyears
andhadtheexperiencenecessarytopullthisventureoff.
Theteamwasset.Threeacademicgenerations:Ted,my
formerstudent;Farish,mygraduateadviser;andIwere
goingtomarchuptotheArctictotrytodiscoverevidence
oftheshiftfromfishtoland-livinganimal.
ThereisnofieldmanualforArcticpaleontology.We
receivedgearrecommendationsfromfriendsand
colleagues,andwereadbooks—onlytorealizethatnothing
couldprepareusfortheexperienceitself.Atnotimeisthis
25
moresharplyfeltthanwhenthehelicopterdropsoneofffor
thefirsttimeinsomegodforsakenpartoftheArctictotally
alone.Thefirstthoughtisofpolarbears.Ican’ttellyouhow
manytimesI’vescannedthelandscapelookingforwhite
specksthatmove.Thisanxietycanmakeyouseethings.In
ourfirstweekintheArctic,oneofthecrewsawamoving
whitespeck.Itlookedlikeapolarbearaboutaquartermile
away.WescrambledlikeKeystoneKopsforourguns,flares,
andwhistlesuntilwediscoveredthatourbearwasawhite
Arcticharetwohundredfeetaway.Withnotreesorhouses
bywhichtojudgedistance,youloseperspectiveinthe
Arctic.
TheArcticisabig,emptyplace.Therockswewere
interestedinareexposedoveranareaabout1,500
kilometerswide.Thecreatureswewerelookingforwere
aboutfourfeetlong.Somehow,weneededtohomeinona
smallpatchofrockthathadpreservedourfossils.
Reviewersofgrantproposalscanbeaferociouslot;they
lightonthiskindofdifficultyallthetime.Areviewerforone
ofFarish’searlyArcticgrantproposalsputitbest.Asthis
refereewroteinhisreviewoftheproposal(notcordially,I
mightadd),theoddsoffindingnewfossilsintheArctic
were“worsethanfindingtheproverbialneedleinthe
haystack.”
IttookusfourexpeditionstoEllesmereIslandoversix
yearstofindourneedle.Somuchforserendipity.
Wefoundwhatwewerelookingforbytrying,failing,and
learningfromourfailures.Ourfirstsites,inthe1999field
26
season,werewayoutinthewesternpartoftheArctic,on
MelvilleIsland.Wedidnotknowit,butwehadbeen
droppedoffontheedgeofanancientocean.Therockswere
loadedwithfossils,andwefoundmanydifferentkindsof
fish.Theproblemwasthattheyallseemedtobedeepwatercreatures,notthekindwewouldexpecttofindinthe
shallowstreamsorlakesthatgaverisetoland-living
animals.UsingAshtonEmbry’sgeologicalanalysis,in2000
wedecidedtomovetheexpeditioneasttoEllesmereIsland,
becausetheretherockswouldcontainancientstreambeds.
Itdidnottakelongforustobeginfindingpiecesoffish
bonesaboutthesizeofaquarterpreservedasfossils.
Ourcamp(top)lookstinyinthevastnessofthe
landscape.Mysummerhome(bottom)isasmalltent,
27
usuallysurroundedbypilesofrockstoprotectitfrom
fifty-mile-per-hourwinds.Photographsbytheauthor.
Therealbreakthroughcametowardtheendofthefield
seasonin2000.Itwasjustbeforedinner,aboutaweek
beforeourscheduledpickuptoreturnhome.Thecrewhad
comebacktocamp,andwewereinvolvedinourearlyeveningactivities:organizingtheday’scollections,
preparingfieldnotes,andbeginningtoassembledinner.
JasonDowns,thenacollegeundergraduateeagertolearn
paleontology,hadn’treturnedtocampontime.Thisisa
causeforworry,aswetypicallygooutinteams;orifwe
separate,wegiveeachotheradefinitescheduleofwhenwe
willmakecontactagain.Withpolarbearsintheareaand
fiercestormsthatcanrollinunexpectedly,wedonottake
anychances.Iremembersittinginthemaintentwiththe
crew,theworryaboutJasonbuildingwitheachpassing
moment.Aswebegantoconcoctasearchplan,Iheardthe
zipperonthetentopen.AtfirstallIsawwasJason’shead.
Hehadawild-eyedexpressiononhisfaceandwasoutof
breath.AsJasonenteredthetent,weknewwewerenot
dealingwithapolarbearemergency;hisshotgunwasstill
shouldered.Thecauseofhisdelaybecameclearashisstill
shakinghandpulledouthandfulafterhandfuloffossil
bonesthathadbeenstuffedintoeverypocket:hiscoat,
pants,innershirt,anddaypack.Iimaginehewouldhave
stuffedhissocksandshoesifhecouldhavewalkedhome
thatway.Alloftheselittlefossilboneswereonthesurface
ofasmallsite,nobiggerthanaparkingspotforacompact
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car,aboutamileawayfromcamp.Dinnercouldwait.
Withtwenty-fourhoursofdaylightintheArcticsummer,
wedidnothavetoworryaboutthesettingsun,sowe
grabbedchocolatebarsandsetoffforJason’ssite.Itwason
thesideofahillbetweentwobeautifulrivervalleysand,as
Jasonhaddiscovered,wascoveredinacarpetoffossilfish
bones.Wespentafewhourspickingupthefragments,
takingphotos,andmakingplans.Thissitehadallthe
makingsofpreciselywhatwewerelookingfor.Wereturned
thenextdaywithanewgoal:tofindtheexactlayerofrock
thatcontainedthebones.
ThetrickwastoidentifythesourceofJason’smessof
bonefragments—ouronlyhopeoffindingintactskeletons.
TheproblemwastheArcticenvironment.Eachwinter,the
temperaturesinkstominus40degreesFahrenheit.Inthe
summer,whenthesunneversets,thetemperaturerisesto
nearly50degrees.Theresultingfreeze-thawcyclecrumbles
thesurfacerocksandfossils.Eachwintertheycooland
shrink;eachsummertheyheatandexpand.Astheyshrink
andswellwitheachseasonoverthousandsofyearsatthe
surface,thebonesfallapart.Confrontedbyajumbledmass
ofbonespreadacrossthehill,wecouldnotidentifyany
obviousrocklayerastheirsource.Wespentseveraldays
followingthefragmenttrails,diggingtestpits,practically
usingourgeologicalhammersasdiviningrodstoseewhere
intheclifftheboneswereemerging.Afterfourdays,we
exposedthelayerandeventuallyfoundskeletonupon
skeletonoffossilfish,oftenlyingoneontopofanother.We
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spentpartsoftwosummersexposingthesefish.
Thisiswherewework:southernEllesmereIsland,in
NunavutTerritory,Canada,1,000milesfromtheNorth
Pole.
Failureagain:allthefishwewerefindingwerewellknownspeciesthathadbeencollectedinsitesofasimilar
ageinEasternEurope.Totopitoff,thesefishweren’tvery
closelyrelatedtoland-livinganimals.In2004,wedecided
togiveitonemoretry.Thiswasado-or-diesituation.The
Arcticexpeditionswereprohibitivelyexpensiveand,short
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ofaremarkablediscovery,wewouldhavetocallitquits.
Everythingchangedoveraperiodoffourdaysinearly
July2004.Iwasflippingrockatthebottomofthequarry,
crackingicemoreoftenthanrock.Icrackedtheiceandsaw
somethingthatIwillneverforget:apatchofscalesunlike
anythingelsewehadyetseeninthequarry.Thispatchled
toanotherblobcoveredbyice.Itlookedlikeasetofjaws.
Theywere,however,unlikethejawsofanyfishIhadever
seen.Theylookedasiftheymighthaveconnectedtoaflat
head.
Onedaylater,mycolleagueSteveGatesywasflipping
rocksatthetopofthequarry.Steveremovedafist-size
rocktorevealthesnoutofananimallookingrightoutat
him.Likemyice-coveredfishatthebottomofthepit,ithad
aflathead.Itwasnewandimportant.Butunlikemyfish,
Steve’shadrealpotential.Wewerelookingatthefrontend,
andwithlucktherestoftheskeletonmightbesafelysitting
inthecliff.Stevespenttherestofthesummerremoving
rockfromitbitbybitsothatwecouldbringtheentire
skeletonbacktothelabandcleanitup.Steve’smasterful
workwiththisspecimenledtotherecoveryofoneofthe
finestfossilsdiscoveredtodateatthewater–land
transition.
Thespecimenswebroughtbacktothelabathomewere
littlemorethanboulderswithfossilsinside.Overthe
courseoftwomonths,therockwasremovedpiecebypiece,
oftenmanuallywithdentaltoolsorsmallpicksbythe
preparatorsinthelab.Everydayanewpieceofthefossil
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creature’sanatomywasrevealed.Almosteverytimealarge
sectionwasexposed,welearnedsomethingnewaboutthe
originofland-livinganimals.
Whatwesawgraduallyemergefromtheserocksduring
thefallof2004wasabeautifulintermediatebetweenfish
andland-livinganimals.Fishandland-livinganimalsdiffer
inmanyrespects.Fishhaveconicalheads,whereasthe
earliestland-livinganimalshavealmostcrocodile-like
heads—flat,withtheeyesontop.Fishdonothavenecks:
theirshouldersareattachedtotheirheadsbyaseriesof
bonyplates.Earlyland-livinganimals,likealltheir
descendants,dohavenecks,meaningtheirheadscanbend
independentlyoftheirshoulders.
Thereareotherbigdifferences.Fishhavescalesallover
theirbodies;land-livinganimalsdonot.Also,importantly,
fishhavefins,whereasland-livinganimalshavelimbswith
fingers,toes,wrists,andankles.Wecancontinuethese
comparisonsandmakeaverylonglistofthewaysthatfish
differfromland-livinganimals.
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Theprocessoffindingfossilsbeginswithamassina
rockthatisgraduallyremovedovertime.HereIshowa
fossilasittravelsfromthefieldtothelabandis
carefullypreparedasaspecimen:theskeletonofthe
newanimal.Photographinupperleftbyauthor;other
photographscourtesyofTedDaeschler,Academyof
NaturalSciencesofPhiladelphia.
Butournewcreaturebrokedownthedistinction
betweenthesetwodifferentkindsofanimal.Likeafish,it
hasscalesonitsbackandfinswithfinwebbing.But,like
earlyland-livinganimals,ithasaflatheadandaneck.And,
whenwelookinsidethefin,weseebonesthatcorrespond
totheupperarm,theforearm,evenpartsofthewrist.The
jointsarethere,too:thisisafishwithshoulder,elbow,and
wristjoints.Allinsideafinwithwebbing.
Virtuallyallofthefeaturesthatthiscreatureshareswith
land-livingcreatureslookveryprimitive.Forexample,the
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shapeandvariousridgesonthefish’supper“arm”bone,
thehumerus,lookpartfishandpartamphibian.Thesame
istrueoftheshapeoftheskullandtheshoulder.
Ittookussixyearstofindit,butthisfossilconfirmeda
predictionofpaleontology:notonlywasthenewfishan
intermediatebetweentwodifferentkindsofanimal,butwe
hadfounditalsointherighttimeperiodinearth’shistory
andintherightancientenvironment.Theanswercamefrom
375-million-year-oldrocks,formedinancientstreams.
Thisfiguresaysitall.Tiktaalikisintermediate
betweenfishandprimitiveland-livinganimal.
Asthediscoverersofthecreature,Ted,Farish,andIhad
theprivilegeofgivingitaformalscientificname.We
wantedthenametoreflectthefish’sprovenanceinthe
NunavutTerritoryoftheArcticandthedebtweowedtothe
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Inuitpeopleforpermissiontoworkthere.Weengagedthe
NunavutCouncilofElders,formallyknownastheInuit
QaujimajatuqangitKatimajiit,tocomeupwithanamein
theInuktitutlanguage.Myobviousconcernwasthata
committeenamedInuitQaujimajatuqangitKatimajiitmight
notproposeascientificnamewecouldpronounce.Isent
themapictureofthefossil,andtheelderscameupwith
twosuggestions,SiksagiaqandTiktaalik.Wewentwith
TiktaalikforitsrelativeeaseofpronunciationforthenonInuktitut-speakingtongueandbecauseofitsmeaningin
Inuktitut:“largefreshwaterfish.”
Tiktaalikwastheleadstoryinanumberofnewspapers
thedayafterthefindwasannouncedinApril2006,
includingabove-the-foldheadlinesinsuchplacesasThe
NewYorkTimes.Thisattentionusheredinaweekunlike
anyotherinmynormallyquietlife.Thoughformethe
greatestmomentofthewholemediablitzwasnotseeing
thepoliticalcartoonsorreadingtheeditorialcoverageand
theheateddiscussionsontheblogs.Ittookplaceatmy
son’spreschool.
Inthemidstofthepresshubbub,myson’spreschool
teacheraskedmetobringinthefossilanddescribeit.I
dutifullybroughtacastofTiktaalikintoNathaniel’sclass,
bracingmyselfforthechaosthatwouldensue.Thetwenty
four-andfive-year-oldsweresurprisinglywellbehavedasI
describedhowwehadworkedintheArctictofindthefossil
andshowedthemtheanimal’ssharpteeth.ThenIasked
whattheythoughtitwas.Handsshotup.Thefirstchildsaid
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itwasacrocodileoranalligator.Whenqueriedwhy,hesaid
thatlikeacrocodileorlizardithasaflatheadwitheyeson
top.Bigteeth,too.Otherchildrenstartedtovoicetheir
dissent.Choosingtheraisedhandofoneofthesekids,I
heard:No,no,itisn’tacrocodile,itisafish,becauseithas
scalesandfins.Yetanotherchildshouted,“Maybeitis
both.”Tiktaalik’smessageissostraightforwardeven
preschoolerscanseeit.
Forourpurposes,thereisanevenmoreprofoundtakeon
Tiktaalik.Thisfishdoesn’tjusttellusaboutfish;italso
containsapieceofus.Thesearchforthisconnectionis
whatledmetotheArcticinthefirstplace.
HowcanIbesosurethatthisfossilsayssomething
aboutmyownbody?ConsidertheneckofTiktaalik.Allfish
priortoTiktaalikhaveasetofbonesthatattachtheskullto
theshoulder,sothateverytimetheanimalbentitsbody,it
alsobentitshead.Tiktaalikisdifferent.Theheadis
completelyfreeoftheshoulder.Thiswholearrangementis
sharedwithamphibians,reptiles,birds,andmammals,
includingus.Theentireshiftcanbetracedtothelossofa
fewsmallbonesinafishlikeTiktaalik.
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Tracingarmbonesfromfishtohumans.
Icandoasimilaranalysisforthewrists,ribs,ears,and
otherpartsofourskeleton—allthesefeaturescanbetraced
backtoafishlikethis.Thisfossilisjustasmuchapartof
ourhistoryastheAfricanhominids,suchas
Australopithecusafarensis,thefamous“Lucy.”SeeingLucy,
wecanunderstandourhistoryashighlyadvanced
primates.SeeingTiktaalikisseeingourhistoryasfish.
Sowhathavewelearned?Ourworldissohighlyordered
thatwecanuseawalkthroughazootopredictthekindsof
fossilsthatlieinthedifferentlayersofrocksaroundthe
world.Thosepredictionscanbringaboutfossildiscoveries
thattellusaboutancienteventsinthehistoryoflife.The
recordofthoseeventsremainsinsideus,aspartofour
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anatomicalorganization.
WhatIhaven’tmentionedisthatwecanalsotraceour
historyinsideourgenes,throughDNA.Thisrecordofour
pastdoesn’tlieintherocksoftheworld;itliesineverycell
insideus.We’llusebothfossilsandgenestotellourstory,
thestoryofthemakingofourbodies.
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