Polarforschung 48 (1/2): 103-119, 1978

Vertebrale Paleontology and the Cenozoic Historyof the North Atlantic Region *

By R. M. West and M. R. Dawson ..

Abstract: Fossil vertebrates have been recovered from several lithofacies within the Paleogene EurekaSound Formation at ab out 80° nor th latitude on Ellesmere Island, Canada. Both terrestrial and aquaticvertebrates are present, representing the classes Chondrfdithyes Osteichthyes, Amphibia, Reptilia, Avesand Mammalia. Th e fossil vertebrates lend support to paleoclimatic interpretations of the Paleogene Arctieas warm, meist and seasonal. Tbe vertebrat es corne f rorn two distinct levels in the- upper part of the EurekaSound Formation. The fossiliferous rocks are probably Early to Middle Eocene in aqe, and the faunasappear to postdate faunal separation from Europe. However, geologie data suggest that actual physicalcontact between Europe and North America via either Spitsbergen or Iceland was not terminated untilat least mid-Tertiary.

Zusammenfassung: Fossile Wirbeltiere wurden aus mehreren Lithofazies-Bereichen innerhalb der paläcqe­nen Eureka Sound-Formation unter etwa 80° nördlicher Breite auf El lesmere Island, Kanada, geborgen.Vertreten sind sowohl aquatische als auch terrestrische Wirbeltiere aus den Klassen Chondrichthyes,Osteichthyes, Amphibia, Reptilia, Aves und Mammalia. Die fossilen Wirbeltiere stützen die Vorstellungeneines warmen, feuchten und jahreszeitlich verschiedenen Klimas in der paläogenen Arktis. .Dte Wirbel­tiere kommen aus zwei verschiedenen Lagen im oberen Teil der Eureka Sound-Formation. Die fossilfüh­renden Gesteine sind wahrscheinlich früh- bis mitteleozänen Alters, und die Faunen scheinen jünger alsdas Datum der Faunen-Trennung von Europa zu sein. Geo loqis che Daten sprechen jedoch dafür, daß derreale Kontakt zwischen Europ a und Amerika über Spitzbergen oder über Island nicht vor dem mittlerenTer n e r aufhörte.

INTRODUCTION

The vertebrate fossil records of western Europe and western North America show avery high degree of faunal resemblance in the early Eocene (53-49 mya) followed by a

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/ ,50 / / ,

/ ,/ -,

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// ,/ '

/ \/ ,,,

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-, ,Fig. I: Degree of mammalian ge·neric similarity between Europeand North America, late Paleoceneto late Eocene. Adapted trom LEH·MANN,1973.

TimeAbb. I: Prozentualer Anteil derauch in Nordamerika vorkorn­menden Gattungen europäischerSäugetier-Faunen vom oberenPaläozän bis oberen Eozän .

v ,Eocene

-------...,----J'~---------y_,_----.J

Pateocene

Thanetla~'TI f f aruan Sp arnacran CUISla%asatc~~~~tla~rldgerlanL

• Paper presented at the "Confer ence on Ge op hv si cs , Geology. Geomorphology and Geodesy of Spits­bergen. held by the German Soeiety 01 Polar Research in Hamburg, Oetober 2-3, 1978.

.. Dr , Robert M. West, Department of Geology, Milwaukee Publie Museum, Milwaukee, Wiseonsin 53233(USA).Dr. Mary R. Dawson, Seelion of Vertebrate Fossils, Carnegie Museum of Natural History, Pittsburgh,Pennsylvania 15213 (USA).

103

sudden decrease in similarity during the later part of that epoch (49-38 mya) (RUSSELL,1968: SAVAGE, 1971; McKENNA, 1975) (Fig. 1). Such an abrupt change suggests thatin the early Eocene North America and Europe were part of a single zoogeographierealm which was disrupted by middle Eocene time. The current plate tectonics model

Fig. 2: Distribution of ma jor Eocene fossil vertebrale regions (wcs tcrn United States, Paris-London Basin,end Ellesmere Is land indicated b y squares) and th e major n or th er n Atlantic Paleogcne floral regions(Sp its berqen, East Greenland and West Crccnland, indicated by the crrcles) .

Abh. 2: Verteilung der bedeutenderen eozänen Vorkommen fossiler Wirbeltiere (westliche Vereinigte Staa­ten, Per i s-Lcndonar Becken, Elle s me re Island, durch Quadrate bezeichnet) und der bedeutenderen nordat­lantischen paläogenen Pflanzen-Vorkommen (Spitzbergen, Ost-Grönland, West-Gränland, durch Kreise be­zeichnet) .

FJg. 3: Potential truns-No rth AtIantic te r re s tr lal di s per s a l rou te s . Th e nor the as te rn laute i s termed theDeGeer Route, and the southeastern route is called the Thulean Route.

Abb. 3: Mögliche Trans-Atlantische terrestrische Ausbreitungsbahnen. Die nördliche Bahn wird die deGeer-Route genannt, die südliche die Thule-Route.

104

of the history of the North Atlantic region (PITMAN & TALWANI, 1972; TALWANI &

ELDHOLM, 1977) permits some explanation of this, It suggests that open ocean wasbeing formed in the area between Greenland and Europe by about 58 mya, producing apartial barrier between western European arid North American terrestrial faunas. Onthe other hand, several restricted areas were probably emergent until relatively late in ,the Tertiary and could have served as conduits for direct faunal exchanges betweenwestern Europe and North America.

Until recently, the only significant vertebrate paleontological data available on thismatter were derived from the intermontane basins of western North America and theParis-London Basin area of western Europe (Hg. 2). Our interest in documenting thehistory of a possible North Atlantic Paleogene terrestrial vertebrate fauna lerl us towork in the vast intervening area. Our hope was to obtain vertebrate fossil evidencewhich could contribute to our understanding of the termination of terrestrial biologicalcontinuity between Europe and North America.

It is convenient to regard potential Paleogene North Atlantic terrestrial exchange areasas a Y with its base to the west (Fig. 3). The southeast branch of the Y extends from

Fig. 4: The Canadian Arctic IsIands.

Abb. 4: Die kanadischen arktischen Inseln.

Greenland to the British Isles via the lceland-Greenland Ridge and the Iceland-FaeroesRidge; this is referred to as the Thulean route. The northeast branch of the Y extendsfrom Greenland to Scandinavia by way of Spitsbergen and the Barents Shelf; this iscalled the DeGeer route (McKENNA, 1971). The common western end of the Y extendsfrom Greenland to North America via the northeastern Canadian Arctic. Regardless ofwhich of the eastern possibilities is used, communication from Europe to North Americawent by way of northeastern Canada. This was the region in which we started oursearch for geographically intermediate Paleogene faunas.

105

Late Cretaeeous and Paleogene clastiedeposition in northern Canada is represented bythe Eureka Sound Formation. This unit, which overlaps the lirnits of the Sverdrup Basin(BALKWILL, 19'8). extends from Ellesmere Island on the :northeast to Banks Island onthe southwest (Fig. 4). Lithologieally similar rocks appear in Peary Land, northern Green­land (DAW.ES, 1976) and along the Saganavirktok River, northern Alaska (DETTERMANet al., 1975). The formation, which is eomposed of shales, mudstones, sandstones, loealeonglomerates and prominent eoal seams and eoaly deposits, reaches its maximumknown thickness, about 3340 meters, south of the eastern end of Bay Fiord, eentralEllesrnere Island (.A. D. MIALL, pers. cornm., July 1977). It is loeally divisible into adark shale and sandstone lower unit with modest coals, a light shale and sandstonemiddle unit, and a variegated shale and sarrdstone upper unit with prominent eoal beds(Fig. 5). The middLe unit in the Bay Fiord region is largely marine (WEST et al., 1975).and seattered evidenee of marine Eureka Sound has been no ted elsewhere (TOZER,1972; TRETTIN et al., 1972; MIA'LL, 1976). The lower and upper units represent moremarginal to nonmarine paleoenvironments.

Erostonal Top

<;c.c.

=>

-------------------Shale;Coal

Unit

320m

Sand/CoolUnit

840m

Loca! Con

IVariable

Sand/ShaleUni!

1000-1400m

DarkShale/Sand

Unit

780m

Kanguk Formation

Upper Tetrapod level

Lower Tetrapod Level

gk>merate

Marine Vertebrates

F1g. 5: Diagrammatic stratigraphy of theEureka Sound Formation, Central EllesmereIsland (based on fieId work by A. MIALL,1977).

Abb. 5: Stratigraphische Tabelle der Eure­ka Sound-Formation im zentralen Ellesrne­re Island (nach Gelände-Arbeiten von A.MIALL, 1977).

Our field work in the Eureka Sound Formation began in 1973. In 1975 the firs] tetrapodswere found (DAWSON et. al., 1976). and in 1976 and 1977 the record was greatlyaugmented (WEST & DAWSON, 1977; WiEST et al., 1977). The fossil vertebrates from

106

the Eureka Sound Formation now are adequately known for approximate age assignmentarid some paleogeographic and paleoclimatologic interpretations.

FOSSILS OF THE EUREKA SOUND FORMATION

The Eureka Sound Formation is wellexposed on Banks, Ellef Ringnes, Amund Ringnes,Lougheed, Axel Heiberg, Devon and Ellesmere Islands, the most extensive exposuresare on Ellesmere and Axel Heiberq Islands (Hg. 6). While plant arid invertebrate fossilshave been found in most Eureka Sound Formation exposure areas, fossil vertebratesare thus far known only from a sm all area on west-central Ellesmere Island (Fig. 7).Plant fossils fFig. 8) are one of the most characteristic features of the Eureka SoundFormation. Fossil wood, silicified, carbonized, and replaced by siderite, occurs in manyplaces. Remains of trees up to 1.5 meters in diameter, and complete with annual rings,

Fig. S: Exposure of Eureka Sound Forma­tion on Ellesmere and Axel Heiberg Is­lands.

Abb. S: Ausstrich der Eureka Sound-For­mation auf den Inseln Ellesmere und AxelHeiberg.

are found at several localities. Coal seams and coaly mudstones, often containingidentifiable spores and pollen, are also widespread. T'his pollen qives an age rangewithin the formation from Maastrichtian for pollen from Amund and Ellef RingnesIslands (FORTIER et al., 1963; HOPKINS, 1973; FELIX & BURBRIiDGE, 1973), to Eocene,for pollen from the Lake Hazen region, northern Ellesmere Island (CHRISTIE & ROUSE,1976). The macrofloras, both leaves and seeds, of the Eureka Sound Formation (listedin FORTIER et al., 1963, and noterl by numerous earlier authors) have not been asthoroughly studied as those of the Paleogene of Spitsbergen (SCHWElTZER, 1974) and

107

Greenland (Koch, 1963), which also give a range in age of Late Cretaceous to Eocene.The Eureka Sound macrofloras have a number of forms in common with the floras ofSpitsbergen and Greenland, suggesting a similar age and paleoecology. These variousfloras all indicate a temperate climate at their localities during the late Cretaceous andPaleogene.

Icecap

Flg. 1: Strathcone and Bay Fiord area of central Ellesmere Island. Stars indicate major sites of vertebratefossils.

Abb. 7: Die Gebiete von Strethcona und Bay Fjord im zentralen Ellesmere Island. Sterne geben bedeu­tendere FundsteIlen fossiler Wirbeltiere an.

Prior to our work the main occurrences of invertebrate fossils in the Eureka SoundFormation were a microfossil assemblage from Banks Island (THORSTEINSSON &

TOZER, 1962) and pelecypod fragments from the Viks Fiord area, Devon Island(FORTIER et al., 1963), and from the Lake Hazen area, northeastern Ellesmere Island(PETRYK, 1968). In the course of our investigations, marine Foraminifera, scaphopodsand pelecypods (WEST et al., 1975) have been found in the middle unit on EllesmereIsland, and freshwater gastropods and pelecypods have been recovered from the lowerunit on Devon, Axel Heiberg and Ellesmere Islands and the upper unit on EllesmereIsland. These materials are suitable for oxygen-isotope paleotemperature determinations,but the relationships and age of the specimens are still undetermined.

The only Paleogene vertebrate from within the modern Arctic Circle reported previousto our work is a freshwater amiid fish from J1~:H~ogene continental rocks at Heerodden,Spitsbergen (LEHMAN, 1951). Our work has no w produced abundant vertebrate remainsfrom a sm all area (Fig. 7) in the Eureka Sound Formation, in the vicinity of StrathconaFiord and Bay Fiord, central Ellesmere Island. ne ar the eastern margin of the SverdrupBasin. All the kno wn vertebrate localities are in the same synclinal valley, the structureof which has preserved the upper beds of the Eureka Sound Formation from .removulby erosion. Several fiords and covered areas disrupt continuity of the exposures and

108

the local structure is complex and not yet fully understood. However, the generalgeologieal picture is clear, and it is certain that the vertebrate localities are c1usteredin the upper part of the formation. Fossil plants and invertebrates occur with thevertebrates, permitting relatively complete environmental reconstructions.

Our collecting was done primarily by surface prospecting. Dry and underwaterscreening of several of the rnost productive areas produced remains of some smalleranimals not found by surface prospecting. Vertebrate fossils are now known to occurin three lithofacies (Fig. 5). Siltstones and fine-grained sandstones of the middle unit ofthe Eureka Sound Formation have produced oto liths of several genera of marine teleostfish (WEST et al., 1975) and shark teeth of the wide-ranging genus Odonlaspis (J. H.HUTCHISON, pers. comm., 1977). Gray to brown siltstones and fissile shales low inthe upper uni t yielded the first Eureka Sound tetrapods (DAWSON et al., 1976); thefauna from this lithofacies consists mostly of aquatic turtles and alligatorines, althoughmammals and fishes are also present. The most productive vertebrate localities nowknown are in fine to medium-grained arkosic sands tones cut into Iight-colored siltstonesand interbedded with thick coal seams. These localities have produced fishes, salaman­ders, a snake, lizards, alligatorines, turtles, birds and mammals. Both of these tetrapod­producing facies are in the upper part of the formation, as indicated in Fig. 5.

Flg. 8: Fossilized wood exposed by natural erosion, upper Eureka Sound Formation, neer Bay Fiord,ElJesrnere Island.

Abb. 8: Herausgewitlertes fossiles Holz, obere Eureka Sound-Formalion, bei Bay Fjord, Ellesmere Isl and,

Detailed systematic and anatomie studies of the various fossils from the Eureka SoundFormation are still in progress, so comparison with other Paleogene faunas is notcomplete. However, determinations of the tetrapods to the level of family or genus(Table 1) lead to some well-grounded interpretations of the geographie affinities, age,and environments of the assemblages.

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OsteichthyesHolostei

LepisosteidaeAmiidae

AmphibiaUrodela

ScapherpetonlidaeBatrachosauroididae

RepliliaChelonia

TrionychidaeTestudinidae

CarettochelyidaeCryptodira indel.

SquamataAnguidae?VaranidaeOphidia indet,

CrocodiliaAlligatoridae

AvesNeognathae

Diatrymatidaecl. Pres byornithidae

MammaliaMultituberculata

Ectypodidae

ProleutheriaLepliclidaePantoleslidae

Dermopt.eraPlagiomenidae

PrimatesParomomyidae

RodentiaIschyromyidae

TaeniodontaStylinodonlidae

PantodontaCoryphodonlidae

CreodontaHyaenodonlidae

CarnivoraMiacidae

PerissodactylaHyrachyidaeJlrontotheriidae

Equidae

Occurrence

Rare, LepisosteusAbundant, Amia

Rare, ?ScapherpetonRare, Piceoerpeton

Abundant, TrionyxAbundant, cf , HadrianusAbundant, Emydinae, 1 genusRare, Anoetetra, 1 species1 genus .

Rare, Glyptosauridae, 1 genu.Rare, 1 genusRare, 1 genus

Abundant, Allognathosuchu.

Rare, cf . DiatrvmaRare, 1 genus

Rare, Neoplagiaulax

Rare, 1 speciesRare, Panlolestes, 1 species

Abundant, 5 ± species

Common, 2 species

Rare, 3 ± genera

Rare, 1 species

Abundant, Coryphodon,1 species

Rare, FrolimnocyonRare, 1 species

Rare, ViverravusRare, Miacinae

Abundant, Hyrachyus, 1 sp;ciesRare, cf , Murt reocercsModerate, LambdolheriumRare, Hv t acottierium, 1 spectes

Geographie Distributionin Paleogene

North America, Europe, AsiaNorth America, Europe, Asia

North AmericaNorth America

N orth America, Europe, AsiaN orth America, Europe, AsiaNorth America, Europe, AsiaNorth America, Europe, Asia

North America, AsiaNorth America, Europe

North America, Europe

North America, EuropeNorth America, South America

North America, Europe

North America, EuropeNorth America, Europe, Asta

North America ')

North America, Europe, Asia

North America, Europe, Asia

North America, Asia

North America, Europe, Asia

North America, EuropeNorth America, Europe, Asia

North America, EuropeNorth America, Europe

North America, Europe, AsiaNorth America, AsiaNorth AmerfcaN or th America, Europe

Temporal Distribution01 Most Closely AlliedTaxon in Paleogene

EoceneEocene

PaleogeneEarly Eocene

EoceneEarly to Middle EoceneLate PaleoceneMiddle Eocene

EoceneEocene

Early to Middle Eocene

Early to Middle EoceneMiddle Eocene

Late Paleocene

Early EoceneMiddle Eocene

Early Early Eocene

Early Eocene

Early to Middle Eocene

Eocene

Early Eocene

Early to Middle EoceneEarly to Middle Eocene

EoceneEocene

Late Early to Middle EoceneMiddle 10 Late EoceneLate Early EoceneEarly Eocene

') Dermopterans have been reported fr orn the Eocene 01 Europe (RUSSELL et al., 1973), but ROSE (1973) and ROSE 8SIMONS (1977) consider this an equivocal or din a l assignmenl.

Tab. 1: Fossil Vertebrates, Eureka Sound Formation: Abundance, Distribution, Age.

Tab. 1: Fossile Wirbeltiere, Eureka Sound-Formation: Häufigkeiten, Verteilung, Alter.

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The fossil tetrapods from the upper part of the Eureka Sound Formation represent twodiserete faunal levels, eaeh ineorporating 300 to 400 meters of sediment (Fig. 5). Thelower of these assernblaqes is by far the most diverse (Table 2) and much the largernumerieally. The most striking feature of this assemblage is the abundanee and diver­sity of the dermopterans (flying lemurs) (Hg. 9), whieh are the most eommon smallmammals known from the Eureka Sound Formation. In eontrast, dermopterans are rarein more southerly Paleoeene and Eoeene loealities in North Ameriea (.ROSE, 1973; ROSE&' SIMONS, 1977) and laek the taxonomie diversity shown by the Eureka Sound For­mation dermopterans. Preliminary studies suggest the presenee of perhaps as many asfive speeies of Aretie dermopterans.

The other most eommon mammals from the lower faunal zone of the Eureka Sound For­mation are the tapiroid Hyrachyus and the pantodont Coryphodon (iFig. 10), both ofwhich are represented in many more southerly early Eoeene loealities in North Americaand western Europe. Pantodonts are also present in the Eoeene of eastern Asia, andHyrachyus has been reported from the Chinese Eoeene.

Distribution inUpper Eureka Sound Fm.

L U

AvesPresbyornithidae XDiatrymatidae X

AmphibiaUrodela

Cryptobranchidae X

MammaliaMuItituberculata

Ectypodidae X

Distribution inUpper Eureka Sound Fm.

L U

ProteutheriaLeptictidae XPantolestidae X

DermopteraPlagiomenidae X

PrimatesParomomyidae X

RodentiaIschyromyidae X X

TaeniodontaStylinodontidae X

PantodontaCoryphodontidae X

CredontaHyaenodontidae X

CarnivoraMiacidae X

PerissodactylaHyrachyidae XBrontotheriidae X XEquidae X

XXX

X

X

XX

X

X

X

X

SquamataAnguidae1VaranidaeOphidia indet.

CrocodiliaAJligatoridae

ReptiliaChelonia

TrionychidaeTestudinidaeCarettochelyidaeCryptodira indel.

Tab. 2: Distribution of fossil tetrapods in upper part of the Eureka Sound Formation.

Tab. 1: Verteilung der fossilen Wirbeltiere im oberen Teil der Eureka Sound-Formation.

The remainder of the fauna from the lower faunal zone includes among the lowertetrapods several speeimens of a giant salamander, abundant aquatie and terrestrialturtles, an anguid lizard, a snake, abundant alliga·tors of the genus Allognathosuchus(Fig. 10) and several birds, including the large flightless carnivore Diatryma and thewidespread aquatic Presbyornis. The mammals are a multitubereulate, a pantolestidproteutherian, two species of paromomyid primates, several genera of ischyromyidrodents, at least two genera of earnivorans, a single specimen referred to the primitiveequid Hyracotherium, and several teeth most similar to the late Early Eoeene NorthAmerican primitive brontothere Lambdotherium.

The upper level is less fossiliferous. Turtles are abundant, and include genera known

111

from the lower level as weIl as an anosteirine carettochelyid known from the MiddleEocene of the Holarctic. Crocodilians (AlIognalhosuchus) (Fiq. 9), and a varanid lizardconstitute the remainder of the lower tetrapod assemblage.

Mammals are rare in the upper level, but several are taxa not present in the lower level.They include a leptictid proteutherian, ischyromyid rodents, a taeniodont and anadvanced brontothere. Both taeniodonts and advanced brontotheres are known from theEocene of southern and eastern Asia as weH as from North America. The brontotheremore closely resembles the Middle Eocene North American genus Manleoceras than thesmaller Early Eocene Lambdotherium.

A conspicuous absence from both assemblages is Hyopsodus, a srnall condylarth thatis common in Eocene localities farther south. Other mammals well known in moresoutherly Eocene faunas but as yet absent from the Eureka Sound Formation includephenacodont condylarths, artiodactyls, many primates, and marsupials.

Fauna No. of Genera Probable Age

Eureka Sound Lower 13

{Late Wes etchten (N. Arn.] 53 53-49.5 mya

Sparnacian (Eur.) 55

Eureka Sound Upper 5

{Bridgerian (N. Am.) 71 19.5-47.5 mya

Lutetian (Eur.) 62

Ganda Kas (Pakistan) 15 53-47.5 mya

A

Tab. 3: Eoceue faunal sizes and radiometrie datings.

Tab. 3: Umfang eozäner Faunen und radi ometrisches Alter.

Fig. 9: Eureka Sound Formation vertebrate Ios s i ls. The solid bars represent lengths of 1 cm , A. cf.Plaglomene right mandib le , Pa-M:;, National Museum of Canada no. 30859. B. Allognalhosuchus rightmandible, National Museum of Canada uncatalogued.

Abb. 9: Fossile Wirbeltiere aus der Eureka Sound-Pcrme üon. St rtchlänqe = 1 cm. A. cf. Plagiomenc, rech­ter Unterkiefer mit P3 M3 • Kanadisches Nationalmuseum Nr. 30859. B. Allognalhosuchus, rechter Unterkie­fer, Kanadisches Nationalmuseum, nicht katalogisiert.

112

The low diversity of the Eureka Sound Formation tetrapods may reflect an actualimpoverishment, based on collections made during the three seasons' work. In total,about 18 mammalian genera are recognized in the Eureka Sound Formation faunas, 13Irorn the lower level and five from the upper leveL In contrast, the known Sparnacianfaunas of western Europe contain abouj 55 genera, the late Wasatchian of NorthAmerica about 53 genera, the Bridgerian of North America about 71 genera, and theLutetian of Europe about 62 genera (Table 3) (RUSSELL, 1968; WEST et al., in press).Comparison with Asian Paleogene faunas is very difficult, as South Asia is inadequatelyknown - the Ganda Kas Eocene of Pakistan contains about 15 genera (GINGERICH,1977; WEST, unpublished data) - and the Eocene of China and Mongolia is incompletelyrepoited, so a generic count was not attempted for this paper.

A

Fig. 10: Eureka Sound Formation vertebrale fossils. The solid bars represent lengths of 1 cm. A. Hyrachyusr i qh t rnax i ll a. National Museum 01 Canada no. 30804. B. Coryphodon right mand ib le, dP,,-dP4, NationalMuseum 01 Canada no. 30802.

Abb. 10: Fossile Wirbeltiere aus der Eureka Sound-Formation. Strichlänge = 1 cm. A. Hv t aciiiue, rechterUnlerkiefer, Kanadisches Nationalmuseum Nr. 30804. B. Coryphodon, rechter Unte rki ef e r, d Pa dP4r Kana­disches Nationalmuseum Nr. 30802.

The larger assemblage, from the lower productive level, is in detail unlike any otherknown from North Amcrica or Eurasia. With the exception of Neoplagiaulax andPatnolestes, all the families and genera are known from the early Eocene (Sparnacian!Cuisian) of western Europe (Table 1). Neoplagiaulax is from the Late Paleocene ofEurope and North America, while Patüolestes is from the middle Eocene of NorthAmerica. A lower level of similarity can be demonstrated with eastern and southern

113

Asia. This lower assemblage suggests a late early Eoeene age, based on eorrelations ofthe North Ameriean Wasatehian Land Mammal Age with the European Sparnacian andCuisian. On the .North Ameriean radiometrie seale this fauna would be dated in therange of 53-49.5 mya (WEST et al., in press).

The small assemblage from the upper beds is not so definitive, as most taxa are knownfrom both Early and Middle Eoeene rocks in North Ameriea. Again, there are no non­North Ameriean endemies in the assemblage. The presenee of an anosteirine turtle fromlow in the upper faunal level, along with a relatiively advaneed brontothere, is evideneefor a signifieantly later age for this level than for the lower faunal level.

Although the assemblage is smalI, aMiddie Eoeene age seems probable, utilizingeorrelation of the North Ameriean Bridgerian with the early part of the EuropeanLutetian. If this is the ease, this assemblage would be dated in the range of 49.5-47.5mya (WEST et al., in press).

DISCUSSION

Climate

The recently reeovered fossils from the Eureka Sound Formation add to the evideneealready available from diverse geologieal and paleontological investigations whichin die at es that areas now within or very close to the Aretie Circle possessed a temperateto warm temperate climate during the Paleogene.

The thiek Eureka Sound Formation eoal beds were reported by numerous early Arcticexplorers, who also made modest eolleetions of fossil wood and leaves. More reeently,during Operation Frank!in, the Geologieal Survey of Canada sampled the Eureka SoundFormation paleobotanieally fFORTIER et al., 1963). and palynologieal studies have beeneondueted in association with petroleum and rninerals exploration. Pollen sampies havebeen eolleeted at several of our vertebrate Iocalities, but these are still being proeessed.Floral !ists from the Eureka Sound Formation eompare well with those from the moreintensively-studied Paleogene of Spitsbergen (MANUM, 1962; SCHWEITZER, 1974), andGreenland (KOOH, 1964). KOCH (1964: 99, 114) regarded the West Greenland Paleogenefloras as indieative of temperate to warm temperate humid climates. SCHWEITZER(1974: 3) indieated a close similarity of, the Spitsbergen eonifers to the modern warmtemperate flora of southern Asia. He also pointed out, by analogy, the probable sen­sitivity of several of the Spitsbergen Paleogene genera to frost, as well as the require­ment of modern Metasequoia, an abundant Aretie Paleogene taxen, for seasonal rainfall.Thus, the paleobotanieal data for the Spitzbergen Paleogene indieate a well-watered,warm temperate area with a January isotherm above 0° C and well-marked seasona!ity.The ineompletely studied Eureka Sound Formation floras also suggest temperate climatieeonditions for the Paleogene Canadian Aretie (McGR:EGOR in CHRISTIE, 1964: 55).

Warm Paleogene eonditions in the Canadian Aretie oeeans are suggested by oxygenisotope paleotemperatures ealculated on seaphopod remains eolleeted from ealeareoussandstones below the lower vertebrate level of the Eureka Sound Formation. An averageisotherm of 15° C (MeKENNA, pers. cornrn., September, 1978) for the Paleogene oeeanwater eonforms weil with the eonclusions drawn by CLARK (1974) on early Cenozoiephytoplankton eollected in a eore taken from iee island T 3 north of Ellesmere Island.This is eonsiderably lower than the Eoeene paleotemperatures (20°-30° Cl reportedfrom the North Sea by BUCHARDT (1978). Both !ines of evidenee strongly suggest awarm, ice-free Aretie oeean through the Paleogene.

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Sorne of the fossil vertebrates of the Eureka Sound Formation are further confirmationof the warm Paleogene Arctic. The presence of amphibians, abundant large testudinidtortoises, and alligators testifies to an equable temperate climate (HIBBARD, 1960;BERG, 1964; AUFFENBERG, 1974).

The fossiliferous upper units of the Eureka Sound Formation, including fine-grainedsandstones and mudstones iriterbedded with thick coals, were deposited as part of adeltaic shoreline sequence on the western sideof the central Ellesmere Island craton(A. D. MIALL, pers. comm., July, 1977). The common occurrence of aquatic turtles andalligators supports this interpretation. This coastal lowland fauna seems to have livedin a depositional environment more similar to that represented in the western Europeanand South Asian Eocene than to the intermontane basin habitats from which most of theNorth American Early and Middle Eocene tetrapod assemblages have come. ThePaleogene rocks of Spitsbergen lithologically are markedly similar to the productivebeds of the Eureka Sound Formation (W. B. HARLAND, pers. comm., Oct. 1978).

Paleogeography

The Eureka Sound Formation tetrapods contribute new data to the problem of paleo­geographie relationships between Eurasia and North America. Since the vertebratefauna from the Early Eocene part of the Eureka Sound Formation has affinities withboth North American and western European Early Eocene assemblages, the concept ofa North Atlantic faunal continuity is reinforced. It appears that during the Early Eocenethis northern faun al exchange area acted as a filter since, 1) both North America andwestern Europe retained a number of endemie Eocene taxa, and 2) the Eureka SoundFormation fauna is compositionally unique. Also, some groups that are very prominentin the North American Early Eocene (e. g., condylarths) are rare European elements.

The Eureka Sound Formation fossil assemblages also contribute to biochronologie datingof the latest possible time of terrestrial faunal continuity between North America andwestern Europe across the North Atlantic. The absence of any European endemies andtheextension of North American Early Eocene faun al elements northward suggest thatthis assemblage postdates the faunal disjunction. If this is correct, the severing of theNorth Atlantic faunal connection was effective by SOor 51 million years ago.

This faun al date does not correspond weil to the current models of the history of theNorth Atlantic. Based on the presence of anomalies 23 and presumably 24, NorthAtlantic seafloor in the Greenland-Norwegian Sea region initially came into beingsometime prior to 58 million years ago, although there were several areas of longerlasting physical contact between the two continents (e.g., the Spitsbergen-north Green­land, DeGeer, area arid the proto-Iceland, Thule, area). TALWANI & ELDHOLM's (1977)reconstruction of the opening of the Norwegian-Greenland Sea indicates that it wasnot until about 38 million years aqo that Spitsbergen became physically separated fromGreenland; thus, a land route from North America at least as far east as Spitsbergenwas likely until the end of the Eocene or the beginning of the Oligocene. Both submarinetopography (HARLAND, 1969) and regional distributions of terrigenous sediments (ELD­HOLM & WINDLSCH, 1974) indicate that the Barents Shelf was emergent through much,if not all, of the Tertiary; this would then extend the northern land route onto thenorthern European mainland. However, the early Tertiary North Sea-Baltic basin(ZIEGLER, 1975) may have been a barrier to direct communication with more southerlyparts of western Europe.

In a similar fashion physical data from the erest and flanks of the Iceland-Faeroe Ridgeshow that subaerial weathering of basalts was occurring there until at least mid-

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Tertiary times (NILSEN, 1978; NILSEN & KERR, 1978). DSDP site 336 revealed an earlyTertiary lateritic paleosoil on the northeastern flank of the Iceland-Faeroe Ridge, some400 meters below the top of the ridge. This latente indicates warm, humid conditionsduring the early Tertiary, a substantiation of biologically-based conclusions mentionedabove. It also, however, suggests that the Iceland-Faeroe Ridge did not subside belowsea level until perhaps as recently as 20-24 million years ago (NILSEN & KERR, 1978:176). Thus, the southern exchange route may weil have been available weil after EarlyEocene,

Earlier discussions of the relationships between biological and geological disruptions ofthe North Atlantic continuity (McKENNA, 1972, 19'f5; DAWSON et al., 1976; WESTet al., 1977) have presumed that termination of elose biological similarity was essentiallysynchronous with physical geological separation. This now does not seem to be the case.The available vertebrate fossil reco rd does confirm a elose connection until approxi­mately earlyEocene, but does not pertain to any po st-middle Eocene contact. A sat­isfactory explanation of the abrupt decrease in North American-European faunal sim­ilarity prior to the middle Eocene, while one or two terrestrial connecti.ons remainedviable, is not yet available. However, it can be speculated that the relatively lowdiversity of the Eureka Sound faunas is a product of a strong elimatic filtering effect.Therefore it may tell us more about paleoelimate than ab out Eocene paleogeography.Two avenues of research may remedy the situation. First, arecent paper by BUCHARDT(1978) documents an abrupt paleotemperature drop in the North Sea in early Oligocenetime (37-35 million years aga). An average Oligocene paleotemperature of 5° C orless may have been enough to reduce terrestrial vertebrate occupation of the Arcticarid thereby impose an effective elimatologic barrier between the two landrnasses inspite of the availability of emergent exchange routes. Secondly, during the 1978 fieldseason, the Geological Survey of Canada recovered identifiable mammalian remainsIrorn presumed Miocene lacustrine rocks in Haughton Astrobleme on Devon Island at75° 22'N (FRISCH & THORSTEINSSON, 1978). Preliminary identification of the betterspecimens shows them to be pikas (Lagomorpha: Ochotonidae) which have a NeogeneHolarctic distribution and thus are not paleogeographically useful at this time. None­theless, the presence of these specimens indicates the ultimate availability of an ArcticNeogene mammal record which may assist in interpreting North Atlantic relationshipsover the past 35 million years.

There are also suggestions, based on both lower and middle Eocene Eureka Soundfaunal levels, of relationships with Eocene faunas of. southern and eastern Asia.Taeniodonts and brontotheres areknown from both North America and southern andeastern Asia during the Eocene, but are unknown from western Europe until theOligocene. Of the lower faunal level taxa, fossil dermopterans are present only in theNorth American Eocene. The only living representatives are from southeastern Asia.Apart from their occurrence in the Eureka Sound Formation, the fossil recorrl ofdermopterans is very poor (ROSE & SIMONS, 1977), but their presence in the NorthAmerican Eocene and the Recent of southeastern Asia implies some connection betweenthese two areas.

This dual affinity, with western Europe on the one hand and with southern and easternAsia on the other, imposes the northern part of North America as an exchange areabetween the two ends of the Eurasian land mass. It obviously served a strong filteringfunction, as these two regions share very few taxa. However, continued work in latePaleocene-early Eocene rocks of Mongolia is revealing more taxa of North Americaaffinities (DASHZEVEG & McKENNA, 1977), so KURTEN's (1966) model of multiplefaunal exchange routes is seen to have increased validity.

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The temperate Aretie Paleogene climate indieated by so many disparate lines ofevidenee raises the question of the Paleogene latitude of these areas. Reeent studies(JURDY & VAN DER V,OO, 1975) indieate little apparent polar wander sinee at leastthe Paleoeene. Calculations of Paleogene pole position (SHIVE et al., 1977; BUTLER &

TAYLOR, 1978) indieate its placement within a few degrees of the present pole position.Therefore the Eureka Sound Formation was deposited at essentially its present latitude,and under a polar light-dark regime. Obviously the same held true for the' Spitsbergenand Greenland floras, and for eonditions on the various proposed North Ameriean­European Paleogene exchange routes as weIl.

CONCLUSIONS

The North Atlantie region was oeeupied, during early and middle Eoeene time, byrelatively diverse terrestrial vertebrates. These animals lived under temperate climaticeonditions, and apparently were not subject to extreme temperatures.

Paleogene vertebrates are found in two stratigraphie zones within the Eureka SoundFormation. The older of these, whieh is also the larger fauna, is probably early Eoeenein age. Its fauna shares numerous elements with western North Ameriean Wasatehianassemblages, and several with Sparnacian faunas of western Europe. In eontrast, theupper Eureka Sound Formation assemblage has greater affinities with eastern andsouthern Asia than with western Europe.

These differenees suggest termination of biologie eontinuity across the expanding NorthAtlantic by about 51 or 50 million years ago, thus permitting increased endemism inboth western Europe and North America. Simultaneously, a less efficient exchangebegan between North Ameriea and Asia, utilizing the Beringia area.

Geological data from the North Atlantie region indiea,te that the Norwegian Seabegan to open no less than 58 million years ago. Various lines of evidence show thatland areas were present at both thenorthern (iDeGeer) and southern (Thulean) endsof this opening sea until at least the middle Tertiary.

If both geologie and paleontologic data are correctly interpreted, the termination oftIans-North Atlantie biologie exchange oecurred weil before it was geologieally neees­sary. Much additional information on Neogene climate and vertebrates of the NorthAtlantie region must be gathered before these eonflieting models ean be resolved.

The re cent diseovery, by the Geological Survey of Canada, on Devon Island, of apocket of presumably Miocene marnmals, gives hope for extending the North Atlantiereqions paleontologie reeord and possibly answering this question.

ACKNOWLEDGEMENTS

Our study of the Eureka Sound Formation has been facilitated by logisties supportalloeated by the Polar Continental Shelf Projeet, Department of Energy, Mines andResourees, Canada. We are grateful to Dr. George D. Hobson, MI'. Frank Hunt and MI'.Fred Alt for their assistanee. Financial support has eome from the National. GeographieSociety, the O'Naill Fund of Carnegie Museum of Natural History. the Aretie Instituteof North America, the Royal Ontario Museum and the Milwaukee Publie Museum. TheInstitute of Sedimentary and Petroleum Geology, Geologieal Survey of Canada, has beenmost helpful; Dr. A. D. Miall paid us a field visit in 1977, and Dr. R. Thorsteinsson sentus the Devon Island vertebrates in September, 1978. MI'. Greg Whelan of the NationalMuseum of Canada worked with us for part of the 1977 season. Dr. J. H. Hutchison has

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been with us for the 1973, 1976 and 1977 seasons and has done the preliminary workon the lower vertebrates. Dr. M. C. McKenna, American Museum of Natural History.New York, worked in the field in 1976 and has assisted with specimen identifications.Dr.P. Raemakers spent the 1973 season in the field as a student at the University ofToronto. Dr. 1. Krishtalka, Carnegie Museum of Natural History, Dr. R. Estes, SanDiego State University, and Dr. W. Langston, Jr., University of Texas, have helpedwith specimen identifications. We are grateful to the Norsk Polarinstitutt and theDeutsche Gesellschaft für Polarforschung, and especially Dr. S. W. Duda, UniversitätHamburg, for the opportunity to present this paper at the 1978 Conference on Geo­physics, Geology, Geomorphology and Geodesy of Spitsbergen.

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