Vertebrate fossils (Dinosauria) from the BonnetPlume Formation, Yukon Territory, Canada

David C. Evans, Matthew J. Vavrek, Dennis R. Braman, Nicolás E. Campione,T. Alexander Dececchi, and Grant D. Zazula

Abstract: Dinosaurs and other terrestrial vertebrates are poorly documented in the Mesozoic of the Canadian polar region.Here, we provide a complete review of the Upper Cretaceous (Maastrichtian) vertebrate fauna of the Bonnet Plume Forma-tion in the northeastern Yukon Territory, Canada, which includes the description of the first newly collected dinosaur bonesfrom this unit in almost half a century. Previously reported fragmentary dinosaur remains collected in the early 1960’s per-tain to an indeterminate hadrosaurid. New material includes a poorly preserved forelimb bone and a pedal phalanx. Thesenew remains pertain to at least one species of non-hadrosaurid ornithischian dinosaur, and the humerus is tentatively referredto a small-bodied basal ornithopod. The new vertebrate fossils from the Bonnet Plume Formation provide further evidenceof vertebrates from this unit. However, directed field surveys in 2008 and 2009 suggest that vertebrate fossils are not abun-dant. A review of the known localities of terrestrial Mesozoic vertebrates from the Canadian Arctic indicate that it had a rel-atively diverse community of terrestrial vertebrates, including dinosaurs, during the Late Cretaceous, but emphasizes ourlimited knowledge of the Mesozoic Arctic and considerable potential for future exploration and discovery.

Résumé : Peu de dinosaures et d’autres vertébrés terrestres sont documentés dans le Mésozoïque des régions polaires cana-diennes. La faune vertébrée du Crétacé supérieur (Maastrichtien) de la Formation de Bonnet Plume, dans le nord-est du Yu-kon (Canada), fait l’objet d’un examen exhaustif, et les premiers nouveaux ossements de dinosaures prélevés de cette unitéaprès près d’un demi-siècle sont également décrits. Des restes fragmentaires de dinosaures recueillis au début des années1960 et déjà signalés se rapportent à un hadrosauridé indéterminé. Le nouveau matériel comprend un os de membre anté-rieur mal préservé et une phalange pédieuse. Ces nouveaux restes se rapportent à au moins une espèce de dinosaures orni-thischien non hadrosauridé, et l’humérus est provisoirement affecté à un ornithopode basal à petit corps. Les nouveauxfossiles de vertébrés de la Formation de Bonnet Plume constituent de nouvelles preuves de la présence de vertébrés danscette unité. Des travaux de terrain dirigés menés en 2008 et 2009 portent toutefois à croire que les fossiles de vertébrés n’ysont pas abondants. Un examen des localités connues de vertébrés terrestres mésozoïques de l’Arctique canadien indiqueque cette région présentait une assez grande diversité de vertébrés terrestres, dont des dinosaures, au Crétacé tardif, maissouligne le peu de connaissances disponibles sur l’Arctique au Mésozoïque et l’important potentiel que présente cette régionsur le plan de l’exploration et de découvertes futures.

[Traduit par la Rédaction]

Introduction

Late Cretaceous and Early Paleogene high latitude terres-trial vertebrate faunas are poorly known, despite significantamounts of Late Cretaceous outcrop in the Canadian Arctic(Embry 1991; Nichols and Sweet 1993). This lack of data isdue in large part to the difficulties of sampling in the North.Fragmentary remains of Late Cretaceous dinosaurs have beenrecovered in the eastern Canadian Arctic (Nunez-Betelu et al.2005; Larsson et al. 2007), and a significantly more complete

assemblage is known from the North Slope of Alaska(Brouwers et al. 1987; Parrish et al. 1987; Gangloff 1998;Fiorillo 2006; Fiorillo et al. 2010a). The high palaeolatitudeof these localities implies extreme seasonal variation in sun-light and vegetation (Spicer and Parrish 1990). The implica-tions of these conditions on dinosaur palaeobiology,distributions, and extinction are poorly understood and con-troversial (Brouwers et al. 1987; Paul 1988; Rich et al.2002; Buffetaut 2004; Godefroit et al. 2009). Furthermore,

Received 27 May 2011. Accepted 19 August 2011. Published at www.nrcresearchpress.com/cjes on 25 January 2012.

Paper handled by Associate Editor Hans-Dieter Sues.

D.C. Evans and M.J. Vavrek. Department of Natural History, Royal Ontario Museum, 100 Queen’s Park, Toronto, ON M5S 2C6,Canada.D.R. Braman. Royal Tyrrell Museum of Palaeontology, Box 7500, Drumheller, AB T0J 0Y0, Canada.N.E. Campione. Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks St., Toronto, ON M5S 3B2,Canada.T.A. Dececchi. Department of Biology, Redpath Museum, McGill University, 859 Sherbrooke St. West, Montreal, QC H3A 2K6, Canada.G.D. Zazula. Yukon Palaeontology Program, Department of Tourism & Culture, Government of Yukon, P.O. Box 2703, Whitehorse, YKY1A 2C6, Canada.

Corresponding author: David C. Evans (e-mail: d.evans@utoronto.ca).

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Can. J. Earth Sci. 49: 396–411 (2012) doi:10.1139/E11-064 Published by NRC Research Press

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there are few records of Mesozoic terrestrial fossils reportedbetween these localities and central Alberta, where dinosaurfaunas are well documented (Weishampel et al. 2004; Arbourand Graves 2008; Currie et al. 2008; Fanti and Miyashita2009). These sampling issues at higher latitudes impact ourability to construct and test hypotheses about latitudinal var-iation in faunal composition and palaeobiogeography in rela-tion to palaeoclimatic gradients in the Mesozoic of NorthAmerica.In the late 1960’s, geologists collected fragmentary hadro-

saurid dinosaur bones from Upper Cretaceous sediments ofthe Bonnet Plume Formation, at a locality on the Peel River,northeastern Yukon (Rouse and Srivastava 1972; Russell1984). During the Late Cretaceous, the palaeolatitude of theBonnet Plume Basin was likely considerably farther norththan it is today, at approximately 77°–80°N (Scotese 2001,2002; Lawver et al. 2002). This places the locality wellwithin the Arctic Circle at the time the sediments and associ-ated faunal remains were deposited. In the Late Cretaceous,the Yukon Territory was also an important biogeographiccorridor linking Northeast Asia via Beringia with the remain-der of western North America (Russell 1993; Fiorillo 2008).The palynology of the formation has been relatively wellstudied through drill cores (Nichols and Sweet 1993) andoutcrop sampling. The formation is rich in coal, suggestingexcellent potential for plant macrofossils; however, little tar-geted palaeontological fieldwork has been conducted in thisregion to date.The excellent preservation of the dinosaur bones recovered

in the 1960’s and extent of outcrop suggests that the BonnetPlume Formation has considerable potential to produce Cre-taceous-aged vertebrate fossils with detailed palaeoenviron-mental context (e.g., palynology, plant macrofossils) and tocontribute critical data on Late Cretaceous terrestrial verte-brate distributions (Rouse and Srivastava 1972; Weishampelet al. 2004). To survey palaeontological resources of thisunit, the Royal Ontario Museum in collaboration with theYukon Palaeontology Program conducted a 2 year field proj-ect to the Bonnet Plume Basin, Yukon, in the summers of2008 and 2009, with the goal of recovering new Late Creta-ceous macrofossil material. Although fossil material wasfound to be rare in the areas surveyed, the project succeededin recovering new dinosaur remains from the Maastrichtianportion of the unit that increase the diversity of vertebratesknown from this formation. Here, we describe these newbones, and review the vertebrate remains from the BonnetPlume Formation in the context of the Mesozoic terrestrialvertebrate fossil record of Arctic Canada.

Institutional abbreviationsMOR, Museum of the Rockies, Bozeman, Montana, USA;

ROM, Royal Ontario Museum, Toronto, Ontario, Canada;TMP, Royal Tyrrell Museum of Palaeontology, Drumheller,Alberta, Canada; UA, University of Alberta, Edmonton, Al-berta, Canada; YG, Yukon Palaeontology Program, White-horse, Yukon Territory, Canada.

Geological settingThe Bonnet Plume Basin, primarily located between the

Bonnet Plume, Peel, and Wind rivers, is approximately

1800 km2 in areal extent (Norris and Hopkins 1977, fig. 1).The known outcrop area is located entirely within the NationalTopographic System (NTS) map 106E (Wind River), and ap-proximate coordinates of the field area are 66°N 135°W. TheBonnet Plume Basin was first surveyed by Count V.E. deSainville in 1893 (in Camsell 1906), and shortly thereafterby Camsell (1906). Both of these surveys noted the pres-ence of burning lignites within the basin, and these appearto be the same burning lignites our party observed. Stelck(1944) made the first concerted effort to describe and mapthe geology of the basin; however, he described the entiresuccession as Tertiary (Paleogene) in age. A GeologicalSurvey of Canada project by the name of Operation Porcu-pine was the first to recognize the lower beds as Cretaceous(Mountjoy 1967), and further palynological refinements ofthe stratigraphy were made by Rouse and Srivastava(1972), Norris and Hopkins (1977), and Nichols and Sweet(1993). Mountjoy (1967) estimated the thickness of the for-mation at greater than 1500 m thick; however, later surveyshave estimated a thickness at much less, possibly on the or-der of only a few hundred metres (Norris and Hopkins1977).The Bonnet Plume Formation is dominated by cross-

bedded sandstones, organic-rich mudstones, and conglomer-ates, with notable deposits of coal. Based on the palynofloralbiostratigraphy, Rouse and Srivastava (1972) subdivided theBonnet Plume Formation into three informal zones. Thestratigraphically lowest unit (zone 1) consists of 140 m ofconglomeritic sediment that is hypothesized to be Albian inage and rests unconformably on several Paleozoic formations(Norris and Hopkins 1977). Zone 2 spans the Campanian andMaastrichtian stages and therefore correlates with a series offossiliferous formations from Alberta (Belly River and Ed-monton Groups), the western United States (e.g., Two Medi-cine, Hell Creek, Lance, and Judith River formations), aswell as the North Slope of Alaska. Zone 3 is Paleogene inage. Nichols and Sweet (1993) further subdivided the forma-tion into 10 assemblage zones based on a detailed examina-tion of fossil pollen from drill cores, and hypothesized arelatively continuous sequence of deposition throughout theformation. Although zone 3 is Early Paleogene in age andzone 2 spans the Late Maastrichtian, there is no definitiveevidence for the presence of the Cretaceous–Paleogene boun-dary (Nichols and Sweet 1993). The first dinosaur fossilsfrom the formation were reported by Rouse and Srivastava(1972) and subsequently briefly described by Russell (1984)(Fig. 1, site 1; Fig. 2A).

Palaeontological survey resultsNew palaeontological surveys were undertaken during the

summers of 2008 and 2009, with field crews of four andthree palaeontologists in each season, respectively. Duringthe first year of the project, an attempt was made to relocatethe original hadrosaurid site mentioned by Rouse and Srivas-tava (1972) and survey the most extensive outcrop of the for-mation along the Peel River. The 2008 field crew was able tovisit the exposure from which the original hadrosaur fossilswere recovered (65°53′51.6″N, 135°04′39.2″W, 197 m abovesea level; Fig. 1, site 1; Fig. 2A) using the location descrip-tion and published map for section 8 of Rouse and Srivastava

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(1972). Due to generally poor weather conditions and logisti-cal difficulties, outcrop was examined only from 7 to 11 Au-gust 2008. No vertebrate fossils were recovered or observed.However, a Paleogene plant fossil locality was discovered,which contained a number of deciduous species, includingMetasequoia, Paleocarpinus, and Ettingshausenia (Vavrek etal., in press). A geological section was taken through the pre-sumed area where the hadrosaur fossils were collected (Rouse

and Srivastava 1972), and palynological and bentonitic sam-ples were taken to date these beds.From 23 to 28 June 2009, the basin was revisited, and

camp was set up further to the west on the Peel River. Anextensive series of outcrop was surveyed on foot, and it wasduring this time that the new vertebrate fossils were recov-ered. A geological section was taken through the bone layer(Figs. 3, 4), and a series of palynological samples were

Fig. 1. Map of region with prospected areas and fossil localities noted. Previously described hadrosaurid fossils were collected at locality 1,while the new, non-hadrosaurid archosaur fossils were recovered from locality 2. Camp a was occupied in the 2008 field season, and camp bwas occupied in the 2009 season. Image of the polar region was modified from Rich et al. (2002).

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taken. A helicopter was also used to visit a number of other-wise inaccessible sections of outcrop on the east bank of theWind River (Fig. 1). All of the sections accessed by helicop-ter were barren of any fossil vertebrate or macroplant mate-rial.Several bentonite and ash samples were collected for ra-

diometric age dating. Unfortunately, the recovered bentonitescould not be radiometrically dated (D.A. Eberth, personal

communication, 2008), but the new sediment samples wererich in fossil pollen (see below). Palynological processingand identification was done by D.R.B. at Global GeolabsLtd., Medicine Hat, Alberta, using standard procedures.Slides utilized in this study are stored in the permanent col-lections of the Royal Tyrrell Museum of Palaeontology,Drumheller, Alberta, and the Yukon Paleontology Program,Whitehorse, Yukon Territory, Canada.

Fig. 2. Photos of the exposed Bonnet Plume Formation strata along the Peel River. (A) Outcrop visited in 2008, where the original hadrosaurmaterial was collected (site 1 in Fig. 1; Rouse and Srivastava 1972). (B) Easternmost portion of outcrop prospected in 2009, in the sameexposure that the new fossil material was found in. The site that the fossils came from is just out of frame to the right. (C) The area the newfossils were recovered from (site 2 in Fig. 1). The fossils were found in a creek valley, marked by the star.

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In 2008, six palynological samples were taken from theeastern portion of the outcrop, at approximately the samesite where the first dinosaur bones were recovered (Fig. 1,site 1; Fig. 2A). The six samples strongly suggest an age oflate Maastrichtian for the measured section. The presence ofAquilapollenites reductus, Porosipollis porosus, Wodehouseiaelegans, and W. spinata support this age assignment. To thesouth in Alberta and Saskatchwan, Porosipollis porosus andWodehouseia elegans have been recovered from a narrow in-terval near the base of the upper Maastrichtian. Nichols andSweet (1993) would associate these samples with assemblagezone 9.In the 2009 season, a further six palynological samples

were taken from a more western portion of the formation,from the same site as the newly collected dinosaur fossils(Fig. 1, site 2; Figs. 2C 3, 4). The six samples suggest anage of early Maastrichtian for these samples. The presenceof Mancicorpus gibbus, Scollardia trapaformis, and Tripro-jectus magnus would suggest a slightly older age for the as-semblages than was noted in the samples collected in 2008and tends to suggest a closer comparison with assemblagezone 8 of Nichols and Sweet (1993). Mancicorpus gibbusand Scollardia trapaformis have been recorded from a rela-tively narrow interval at the top of the lower Maastrichtian

in Alberta and Saskatchewan. For a detailed checklist of thespecies recorded from all 12 sample sites, please see TableA1.The geologic sections of the vertebrate localities are sum-

marized below, along with the detailed systematic descriptionof the vertebrate fossils recovered from the formation to date.The fossils are stored at the University of Alberta Laboratoryfor Vertebrate Paleontology, Edmonton (UA), and YukonGovernment Paleontology Program, Whitehorse (YG), collec-tions.

Systematic palaeontologyDinosauria Owen, 1842Ornithischia Seeley, 1887Ornithopoda Marsh, 1881Hadrosauridae Cope, 1869

Hadrosauridae indet.

MATERIAL: UA 19363 consists of parts of at least three differentbones: a complete caudal vertebra centrum, an almost com-plete fifth metacarpal, and a rib fragment, which are indistin-guishable from those of equivalently sized hadrosaurids(Russell 1984).LOCALITY AND HORIZON: This small collection was made at a singlesite, presumably low in the section at this locality (section 8in Rouse and Srivastava 1972) and Maastrichtian in age (Ap-pendix A). The outcrop in this area consists of Late Cretac-eous to Paleogene-aged sandstone, siltstone, mudstone, andconglomerate rocks and coal (65°53′51.6″N, 135°04′39.2″W,197 m above sea level; Fig. 1, site 1; Fig. 2A). The preciselayer that contained the original hadrosaur fossils describedby Russell (1984) could not be relocated, and no further verte-brate fossils were found in the outcrop surrounding this site.The lowermost portion of the section (below the massive

conglomerate layers) where the original material was presum-ably found was covered in approximately 15 m of slumpedsands. The remainder of the section, approximately 12 m inheight, consists of poorly consolidated, yellowish to rust-col-oured, fine- to coarse-grained sandstones and mudstones.Midway through the exposed portion of the section was adense low-grade coal bed, within which was a prominentgreen clay layer. The coal layer was 30 cm thick, and theclay layer inside it was 10 cm in thickness. The uppermostreaches of the section appeared to be composed of conglom-erates, but closer examination was not possible due to inac-cessible cliff-like outcrop. A massive burning coal layerseveral metres thick caps the section above the conglomeratesin this area, and is notable because it is probably the sameburning lignite layer originally described by de Sainville in1893 (see Camsell 1906) and noted at the top of section 8by Rouse and Srivastava (1972). The palynological samplestaken from this geological section suggest an early Maastri-chian age for the dinosaur bones, although the precise layerfrom which they were collected could not be relocated.DESCRIPTION: This material was first reported by Rouse and Sri-vastava (1972) and originally described by Russell (1984),who identified the bone fragments as pertaining to a smallhadrosaur (Fig. 5). As such, we only highlight new informa-tion here. UA 19363 consists of parts of at least three differ-

Fig. 3. Photograph of the section where the new fossils were foundin 2009 (site 2 in Fig. 1). The fossiliferous bed is marked with a star.

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ent bones. Russell (1984) identified two phalangiform frag-ments and noted their close resemblance to those of the “fifthdigit” of the manus in hadrosaurids. Subsequent work withthe specimens has found that these two fragments are in factpart of the same bone, and when joined, form an almostcomplete fifth metacarpal that is 41 mm in length, with a18 mm maximum diameter of the distal end (Russell 1984).The bone is identical to that of juvenile hadrosaurids of simi-

lar size, and is likely derived from an animal that is less than6 m in total length. As noted by Russell, a complete centrumof a distal caudal vertebra represents that of a hadrosaur. Asmall rib fragment that was not mentioned by Russell is alsopart of the collection (Fig. 5).The metacarpal and vertebra are virtually identical to those

of hadrosaurids (e.g., Parks 1920), and we agree with theiridentification as hadrosaurid by Russell (1984). The mor-

Fig. 4. Geologic section through the stratum where vertebrate fossils (YG 380.1 and YG 380.2) were collected. Stratigraphic positions of thepalynological samples from 2009 are noted with “PS” numbers on the left side of the column, and correspond with the subsamples for ac-cession number TMP2009.211. Cl, clay; Si, silt; Fss, fine sand; Mss, medium sand; Css, coarse sand; Cg, coarse gravel.

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phology of the rib fragment is consistent with that of hadro-saurids, but it cannot be ascribed to Hadrosauridae with cer-tainty.

?Ornithopoda

MATERIAL: YG 380.1, left humerus.LOCALITY AND HORIZON: YG 380.1 was found in situ within a discon-tinuous pebble lag within a larger cross-bedded sandstonebody (65°53′51.6″N, 135°04′39.2″W, 197 m above sea level)in 2009 (Fig. 1, site 2; Fig. 2C; Fig. 3; see below). The baseof the section where this specimen was recovered is largelycovered in slumped sediments, while the exposed portion ofthe section consists primarily of poorly consolidated yellow-ish silt to sandstones, with numerous pebble lags throughout(Fig. 4). The lags were highly localized, often no more than10 m in horizontal extent. The lags, in addition to containing

the two fossil bones, were primarily composed of ironstoneand clay clasts. Also within this portion of the section werelaterally discontinuous coal stringers. The upper portion ofthe section was primarily a light-grey silt to fine-grainedsandstone, with a large number of laterally localized swales.Further examination of the upper portion of the section wasnot possible.DESCRIPTION: YG 380.1 (Fig. 6) is the largest bone recoveredfrom the formation. Although it is incomplete and weathered,its morphology is consistent with identification as a left hu-merus of a small ornithischian dinosaur. As preserved, thespecimen measures 146 mm in length. The maximum breadthof the poorly preserved proximal end is 55 mm, and the dis-tal end is incomplete. The proximal end is expanded in boththe transverse and anteroposterior planes. In proximal view, aprominent thickening that is located medially to the center of

Fig. 5. Hadrosaurid dinosaur fossils from the Bonnet Plume Formation, Yukon Territory (UA 19363). Caudal centrum in (A) left lateral,(B) dorsal, (C) ventral, and (D) cranial views. Partial fifth metacarpal in (E) anterior, (F) lateral, (G) palmar, and (H) medial views. (I–K) Ribfragment. ha, articulation for haemal arch; na, portion of neural arch.

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the proximal border presumably represents the humeral head.The bone is gently sigmoidal in anterior view, and gentlycurved in external view. The poorly developed deltopectoralcrest is marked by a rugose, depressed muscle scar adjacentto a small raised flange along the anterior surface. There isrelatively little flexture to the shaft at the level of the delto-pectoral crest, but this may be exaggerated by breakage andabrasion of the proximal region of YG 380.1. At its smallestpoint, the diaphysis is semicircular in cross section. Theminimum diaphyseal circumference (83 mm) occurs severalmillimetres from the incomplete distal end. The diaphysis be-gins to expand distally immediately proximal to the brokenend, presumably marking the expansion of the bone into thedistal condyles of the humerus. When complete, the humerusis estimated to have been approximately 25 cm in length. Thebroken distal end reveals a highly cancellous endosteal struc-ture without a particularly dense cortex, consistent with iden-

tification as an ornithischian, or at least a non-theropodarchosaur.The most distinctive characteristic of YG 380.1 is the

shape of the deltopectoral crest. The development of the del-topectoral crest as a short, small flange differs from the rela-tively strongly developed deltopectoral crests in ceratopsians(Dodson et al. 2004; Chinnery and Horner 2007), hadrosaur-ids (Horner and Currie 1994; Horner et al. 2004), and anky-losaurs (Vickaryous et al. 2004) that are common in theUpper Cretaceous deposits of Asia and North America. Theshape of the deltopectoral crest in YG 380.1 most closely re-sembles the condition in the “basal” ornithopod Oryctodro-meus (MOR 1636a) of the Black Leaf Formation, ofMontana (Varricchio et al. 2007). The deltopectoral crest isalso weakly developed in Parksosaurus warreni (ROM 804),but it is relatively large in other thescelosaurs, including The-scelosaurus and Orodromaeus (Norman et al. 2004). A low,

Fig. 6. Incomplete right humerus (YG 380.1) of an ornithischian dinosaur (?Ornithopoda) from the Bonnet Plume Formation in (A) medial,(B) lateral, (C) cranial, and (D) proximal views. dp, deltopectoral crest; hh, humeral head.

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weakly developed deltopectoral crest also occurs in Pachyce-phalosauria (Gilmore 1924; Perle et al. 1982). Although com-parative data for this group is scant, the humerus inStegoceras (Gilmore 1924) and Goyocephale (Perle et al.1982) have a straighter profile in anterior view and appearmuch more gracile than YG 380.1.

?OrnithischiaMATERIAL: YG 380.2, a pedal phalanx.LOCALITY AND HORIZON: This small bone was found less than 1 maway from YG 380.1, within the same pebble lag deposit(65°53′51.6″N, 135°04′39.2″W, 197 m above sea level), in2009 (Fig. 1, site 2; see above).DESCRIPTION: The pedal phalanx (YG 380.2; Fig. 7) is abraded atboth the proximal and distal ends such that the morphologyof the articular surfaces is indistinct. As preserved, the pha-

lanx measures 11.4 mm in length. In lateral view, the heightof phalanx is deepest proximally, and the bone becomes pro-gressively shallower towards the distal articular surface. Thedorsal margin is straight, while the ventral margin is onlyshallowly concave. The distal collateral ligament fossae, situ-ated at the approximate center of the distal articular arc, arerelatively shallow and do not form deep, well-demarcatedpits, as in theropods. In dorsal view, the phalanx is rectangu-lar in shape, with virtually no constriction at the midshaft(Fig. 7E). A very shallow, triangular midline depression oc-curs above the collateral ligament fossae on the dorsal surfaceof the bone. In proximal view, the general shape of the pre-served region indicates that the proximal articular surface istaller (6.9 mm) than wide (6.4 mm), as in many dinosaurs.The distal articular end has a subtrepzoidal in distal viewand is 5.4 mm wide as preserved. The distal condyles areabraded, but it is clear that the distal articular surface wasmediolaterally wider than high, and it is unlikely that it wasstrongly ginglymoid.As noted by Barrett et al. (2010), the identification of iso-

lated phalanges can be extremely difficult due to their stereo-typed morphology. The relatively elongate, symmetricalmorphology of YG 380.2 precludes its identification as asmall or juvenile iguanodontian ornithopod (Horner and Cur-rie 1994) or ceratopsian, which have specialized, shortenedpedal phalanges. The poorly defined distal articular end thatlacks well-defined, pit-like collateral ligament fossae is in-consistent with an assignment to Theropoda. Although YG380.2 is virtually identical to the distal phalanges of hypsilo-phodont-grade ornithopod dinosaurs of similar size, including“Laosaurus” minimus (ROM 46253), and Orodromeus, wecannot rule out the possibility it pertains to another small-bodied ornithischian group, particularly the poorly known pa-chycephalosaurs or heterodontosaurs, although the latterseems less likely due to the Maastrichtian age of the Yukonmaterial (e.g., Butler et al. 2010).

DiscussionThe new vertebrate fossils from the Bonnet Plume Forma-

tion provide further evidence of Late Cretaceous-aged archo-saurs from this unit and show that fossils are not restricted toa single isolated occurrence within the formation. However,directed field surveys failed to locate any articulated or asso-ciated skeletons, bonebeds, or significant microvertebratesites, and suggest that vertebrate fossils are not abundant inthe formation. The only previously described vertebrate fos-sils from the Bonnet Plume Formation are attributable to ha-drosaurids (Fig. 5; Russell 1984, 1990). Althoughpreservation makes the material difficult to precisely identify,the newly discovered bones clearly do not pertain to Hadro-sauridae, and provide evidence of a more diverse vertebrateassemblage than previously known in the formation. We ten-tatively identify YG 380.1 as pertaining to an indeterminatenon-iguanodontian ornithopod, and cannot preclude referralof YG 380.2 to basal Ornithopoda. However, due to theirpoor preservation and associated anatomical ambiguities, wecannot rule out the possibility that these bones pertain toother archosaur taxa. If the identification of YG 380.1 is cor-rect, it is the first record of a non-hadrosaurid ornithopodfrom the Canadian Arctic. Non-iguanodontian ornithopods

Fig. 7. Pedal phalanx (YG 380.2) of an ?ornithischian dinosaur fromthe Bonnet Plume Formation in (A) dorsal, (B) lateral, (C) ventral,(D) proximal, and (E) distal views.

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are poorly known in the northern polar regions (Brown andDruckenmiller 2011), but appear to have been relatively com-mon in southern polar regions (Rich et al. 1988; Rich andRich 1989; Rich and Vickers-Rich 1999).

Review of Mesozoic terrestrial vertebratesfrom the Canadian ArcticCurrently, there are seven sites known from the Canadian

Arctic that have yielded Mesozoic terrestrial vertebrate re-mains or trace fossils (Table 1; Fig. 8). This report of dino-saurs from the Bonnet Plume Formation, Yukon, constitutesthe most detailed documentation of dinosaur skeletal remainsin the Canadian North to date. Unfortunately, only a handfulof bones are known, but they document at least two differenttypes of ornithischian dinosaurs in the northern Yukon duringthe Maastrichtian (see above). A second Yukon locality con-sists of a track site that was discovered in 1999 near RossRiver, in the southern part of the Territory (Gangloff et al.2004). This track site has produced six different ichnospeciesthat can be assigned to Ornithopoda, Ankylosauria, and Ther-opoda (Gangloff et al. 2004). Tracks occur at two differentstratigraphic horizons, and the footprints provide evidencethat a number of dinosaur genera inhabited the area for atleast some part of the year. However, the tracks occur in anisolated block within a graben that has been faulted down-wards into much older Precambrian and Proterozoic rocks.Based on their putative Early Cretaceous age, the footprintswere likely made well before the accretion of the Yukon–Tanana Terrane. Therefore, it is possible that the originalgeographic location of deposition was far to the southeastbefore being displaced to its current position (Gangloff etal. 2004).A single site in the Northwest Territories has yielded Meso-

zoic terrestrial vertebrate remains. The ventral half of a ceratop-sian quadrate was found by A.R. Sweet near the headwaters ofthe East Little Bear River, during a geological survey of thearea in 1983 (Russell 1984). The remains originated from theMaastrichtian portion of the Summit Creek Formation (Russell1984), southwest of the town of Norman Wells, in the westernpart of the Territory. This constitutes the only record of large-bodied ceratopsids in the Canadian Arctic, although at leastone pachyrhinosaur is known from equivalently aged depositsof the Prince Creek Formation, Alaska (Fiorillo and Gangloff2003; Fiorillo 2008; Fiorillo et al. 2010b).Of the Canadian territories, Nunavut has so far produced

the greatest quantity of Mesozoic terrestrial fossil materialand number of localities. The first discovery of Mesozoicvertebrate remains in the Canadian Arctic was made on Ca-meron Island during the search for the lost Franklin expedi-tion (Osborn 1855; Adams 1875; Russell 1990). It consistedof a single incomplete vertebra derived from the Triassic Hei-berg Formation that formed the basis of the taxon Arctosau-rus osborni (Adams 1875; Nesbitt et al. 2007). Since itsoriginal description, Arctosaurus has been assigned to a num-ber of different taxonomic groups, including Dinosauria,although it is presently considered an archosauriform of inde-terminate assignment (Nesbitt et al. 2007).The remainder of the Nunavut localities are Late Creta-

ceous in age. A diverse assemblage of nonmarine aquaticand semiaquatic vertebrates has been recovered from Expedi-T

able

1.Locations

ofprevious

discoveriesof

terrestrialvertebrate

remains

ortracefossils

from

theCanadianArctic.P

aleolatitudes

werecalculated

usingthePo

intTracker

program

from

Scotese(200

2).

Locality

Longitude

(°)

Latitu

de(°)

Palaeolatitude(°)

Form

ation

Age

Taxa

present

RossRiver,Y

ukon

Territo

ry–132.5

61.97

N/A

Albian–

Cenom

anian

Ornith

omimipus,A

mblydactylus,Gypsichnites,Tetrapodosaurus,Irenesauripus,

andColum

bosauripus

(six

species)

Peel

River,Y

ukon

Territo

ry–135.0775

65.8975

76.94734

BonnetPlum

eMaastrichtian

Hadrosaurinae,basalornithopod

(twospecies)

EastLittle

BearRiver,

NorthwestTe

rrito

ries

–125.8292

64.5556

74.13838

SummitCreek

Maastrichtian

Ceratopsidae(one

species)

Cam

eron

Island,Nunavut

–104.5

76.6

56.41801

Heiberg

LateTriassic

Arctosaurus

(one

species)

Eastern

AxelHeiberg,N

u-navut

–85.5408

79.3275

74.10477

Strand

Fiord–

Kanguk

Turonian–C

oniacian

Lepisosteid,A

miid

,Vidalam

iinae,Te

leostei,Osteoglossomorpha,

Borealochelys

axelheibergensis,A

urorachelysgaffn

eyi,Trionychid,C

hampsosaurus(ninespecies)

Western

AxelHeiberg,

Nunavut

–92.1817

79.3917

75.27741

Kanguk

LateCretaceous

Hadrosauridae

(one

species)

Bylot

Island,Nunavut

–78.35

72.88

70.68

Kanguk

LateCretaceous

Severalsharks,ratfish,actin

opterygians,Canadagaarctica,

turtle,h

adrosaur,

tyrannosaurid(9+

species)

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tion Fiord on western Axel Heiberg Island (Tarduno et al.1998). The assemblage occurs in a shale sequence at the tran-sition from the Strand Fiord lavas to the overlying KangukFormation (Tarduno et al. 1998). Magnetostratigraphy andammonite biozonation suggest an early Late Cretaceous(Turonian–Conacian) age for the assemblage. The site hasyielded several species of fish (Friedman et al. 2003), at leastthree species of turtle (Brinkman and Tarduno 2005; Vander-mark et al. 2009), and abundant remains of a champsosaur(Tarduno et al. 1998; Vandermark et al. 2007). To date, nodinosaur fossils have been reported from this locality.A single hadrosaur caudal centrum was recovered from the

eastern side of Axel Heiberg Island, also from the KangukFormation, during a regional survey of the stratigraphy andpalynology of the formation in this area (Nunez-Betelu et al.2005). A palynological sample from near the dinosaur bear-ing bed was dated as middle Campanian in age (Nunez-Betelu et al. 2005). The site is currently the most northerlyknown occurrence of a dinosaur, although depending on thetiming of the rotation of the North American craton local-ities in Alaska may have been deposited at a higher latitude(Table 1; Nunez-Betelu et al. 2005).

Finally, several collections of fossils have been made fromsouthern Bylot Island, also occurring stratigraphically withinthe Kanguk Formation (Russell 1990; Grady 1993; Larssonet al. 2007). This is the most thoroughly sampled Mesozoicvertebrate assemble to include dinosaur remains, but the sub-stantial material collected to date have yet to be described indetail. Preliminary reports note that remains of large thero-pods and both juvenile and adult hadrosaurs have been recov-ered, as well as a diverse fauna of other vertebrates (Russell1990; Larsson et al. 2007). The other remains consist of anichthyofaunal assemblage of four sharks, a ratfish, several ac-tinopterygians, and a possible coelacanth; mosasaurs and ple-siosaurs; a turtle shell fragment; and an hesperornithiformbird (Hou 1999; Larsson et al. 2007).Records of dinosaurs and other Mesozoic terrestrial verte-

brates to date from Arctic Canada remain frustratingly rare,and typically consist of isolated elements. Therefore, ArcticCanada’s contribution to understanding the diversity of thisregion, latitudinal variation in faunal composition and diver-sity, and their relationship to climatic variation during theMesozoic, is extremely limited. The high palaeolatitude ofthe Late Cretaceous localities implies extreme seasonal varia-

Fig. 8. Map of terrestrial vertebrate localities in the Canadian Arctic. Numbers correspond to localities as follows: 1, Peel River (this study);2, Ross River; 3, East Little Bear River; 4, Cameron Island; 5, Western Axel Heiberg; 6, Eastern Axel Heiberg; 7, Bylot Island.

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tion in sunlight and vegetation (Spicer and Parrish 1990). De-spite the high polar location of the arctic localities, climacticconditions were much warmer in the later Mesozoic (Barron1983; Hallam 1985; Tarduno et al. 1998). Evidence for theserelatively high temperatures is well established, with theoret-ical (Barron and Washington 1982), isotopic (Huber et al.2002; Amiot et al. 2004), zoologic (Friedman et al. 2003),and botanical evidence (Wolfe and Upchurch 1987; Sluijs etal. 2006; Spicer and Herman 2010). Although climactic con-ditions had been deteriorating through the Late Cretaceous,mean annual temperatures in Arctic regions during the Maas-trichtian were up to 15 °C warmer than today (Spicer andParrish 1990; Amiot et al. 2004; Spicer and Herman 2010).At sea level, conditions were likely ice-free during this pe-riod, although in the nearby mountains permanent ice packsmay have been able to form. Climate equability may havebeen greater during this time due to the increased sea leveland large regions of flooded inland areas, with nearby watersproviding a moderating effect and preventing typical conti-nental climate systems from forming (Wolfe and Upchurch1987), and may in part explain the existence of diverse non-marine reptilian faunas in the Arctic, but the widespread dis-tribution of dinosaurs throughout the Arctic continues topresent intriguing palaeobiological questions (Brouwers et al.1987; Paul 1988, Tarduno et al. 1998; Rich et al. 2002; Buf-fetaut 2004; Godefroit et al. 2009).

Conclusions

The new vertebrate fossils from the Bonnet Plume Forma-tion provide further evidence of vertebrates from this unit.Although specifically indeterminate, the new material per-tains to at least one species of non-hadrosaurid ornithischiandinosaur, and the humerus is tentatively referred to a small-bodied basal ornithopod. Although the Bonnet Plume Forma-tion may never be as rich as other mainland Arctic units inadjacent Alaska, with continued work it will provide new in-formation on Arctic terrestrial vertebrate faunas during theLate Cretaceous. A review of the known localities of terres-trial Mesozoic vertebrates from the Canadian Arctic indicatethat this region had a relatively diverse community of terres-trial vertebrates, including dinosaurs, during the Late Creta-ceous, but emphasizes our limited knowledge of the Arcticduring this time and highlights considerable potential for fu-ture exploration and discovery.

AcknowledgementsFunding for this work was provided by the Polar Conti-

nental Shelf Project to D.C.E. and G.D.Z, Natural Sciencesand Engineering Research Council of Canada (NSERC)Discovery Grant (RGPIN 355845–08) to D.C.E., YukonTerritorial Government funding to G.D.Z and M.J.V,Northern Scientific Training Program grants to M.J.V. andT.A.D., and a Natural Sciences and Engineering ResearchCouncil Canada Graduate Scholarship (doctoral) to M.J.V.Ian Morrison prepared YG 380.1 and YG 380.2, and theillustrations of these fossils were executed by Amy Janzen.We thank the Tetlit Gwich’in Council and Gwich’in Socialand Cultural Institute for their support and interest in thisresearch.

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Appendix AThe appendix begins on the following page.

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Table A1. Palynological summary.

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0001 0002 0003 0004 0005 0006 0001 0002 0003 0004 0005 0006 0007Alisporites bilateralis Rouse, 1959 × × ×Alisporites grandis (Cookson) Dettmann, 1963 × ×Aquilapollenites aptus Srivastava, 1969 ×Aquilapollenites attenuatus Funkhouser, 1961 × ×Aquilapollenites notabile (Mtchedlishvili) Farabee, 1980 × ×Aquilapollenites quadrilobus Rouse emend. Srivastava & Rouse, 1970 × × × × × × × × × ×Aquilapollenites rectus Tschudy, 1969 ×Aquilapollenites reductus Norton, 1965Aquilapollenites senonicus (Mtchedlishvili) Tschudy & Leopold, 1971 × × ×Aquilapollenites turbidus Tschudy & Leopold, 1971 × ×Aquilapollenites sp. × × ×Azonia sp. ×Baculatisporites comaumensis (Cookson) Potonié, 1956 × × × ×Baculatisporites sp. × × × × ×Camarozonosporites ambigens (Fradkina) Playford, 1971 × ×Camarozonosporites sp. ×Cibotiumspora sp. ×Cranwellia rumseyensis Srivastava, 1967 × × × × × × × × ×cf. Cranwellia sp. × × ×Cyathidites australis Couper, 1953 ×Cyathidites australis rimalis Balme, 1957 ×Cyathidites minor Couper, 1953 × × ×Distaltriangulisporites perplexus (Singh) Singh, 1971 ×Erdtmanipollis procumbentiformis (Samoilovich) Krutzsch, 1966 × × × ×Foraminisporis undulatus Leffingwell, 1971 × × × ×Gleicheniidites delicatus (Bolkhovitina) Krutzsch, 1959 ×Gleicheniidites senonicus Ross ex Delcourt & Sprumont, 1955 × × × ×Heliosporites kemensis (Chlonova) Srivastava, 1972 × × × × × × ×Inaperturotetradites scabratus Tschudy, 1973 ×Interulobites sp. × ×Kurtzipites trispissatus Anderson, 1960 ×Laevigatosporites haardti (Potonié & Venitz) Thomson & Pflug, 1953 × × × × × × × × × × × ×Liacidites sp. ×Liburnisporis adnacus Srivastava, 1972 × ×Liliacidites variegatus Couper, 1953 ×Mancicorpus gibbus Srivastava, 1968 ×Mancicorpus rostratus Srivastava, 1968 × ×Osmundacidites wellmanii Couper, 1953 × × × × × × ×Pesavis parva Kalgutkar & Sweet, 1988 ×Pityosporites constrictus (Pierce) Krutzsch, 1971 × × × × ×Podocarpidites sp. × × ×Polycingulatisporites reduncus (Bolkhovitina) Playford & Dettmann,1965

× × × × × ×

Porosipollis porosus (Mtchedlishvili) Krutzsch, 1969 ×Pulcheripollenites krempii Srivastava, 1969 × × × × ×Reticuloidosporites pseudomurii Elsik, 1968 × ×

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Table A1 (concluded).

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0001 0002 0003 0004 0005 0006 0001 0002 0003 0004 0005 0006 0007

Retitriletes austroclavatidites (Cookson) Krutzsch, 1963 ×Retitriletes globosus Pierce, 1961 × ×Retitriletes mediocris (Bolkhovitina) Krutzsch, 1963 × × × × × × × ×Schizosporis parvus Cookson & Dettmann, 1959 ×Scollardia trapaformis Srivastava, 1966 ×Sequoiapollenites paleocenicus Stanley, 1965 × ×Siberiapollis sp. × × × × ×Sigmopollis carbonis (Newman) Srivastava, 1984 × × × × ×Stereigranisporis regius (Drozhastichich) Ravn & Witzke, 1995 ×Stereisporites antiquasporites (Wilson & Webster) Dettmann, 1963 × × × × × ×Stereisporites antiquus Krutzsch, 1963 × ×Stereisporites rodaensis Krutzsch, 1966 × × ×Striatellipollis striatellus (Mtchedlishvili) Krutzsch, 1969 ×Taxodiaceaepollenites hiatus (Potonié) Kremp, 1949 × × × × × × × × × × × ×Taxodiaceaepollenites vacuipites (Wodehouse) Wingate, 1980 × ×Todisporites sp. ×Trifossapollenites ellipticus Rouse, 1957 ×Triprojectus magnus (Mtchedlishvili) Stanley, 1970 × × × × × × ×Triprojectus unicus (Chlonova) Mtchedlishvili, 1961 × × × × × × × ×Verrucosisporites sp. × × × × ×Vitreisporites pallidus (Reissinger) Nilsson, 1958 × × × ×Wodehouseia elegans (Samoilovich) Wiggins, 1976 ×Wodehouseia gracile (Samoilovich) Pokrovaskaya, 1966 × ×Wodehouseia spinata Stanley, 1961 × × × ×Wodehouseia sp. ×

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This article has been cited by:

1. VavrekMatthew J., EvansDavid C., BramanDennis R., CampioneNicolás E., ZazulaGrant D., JinJisuo. 2012. A Paleogeneflora from the upper Bonnet Plume Formation of northeast Yukon Territory, Canada. Canadian Journal of Earth Sciences49:3, 547-558. [Abstract] [Full Text] [PDF] [PDF Plus]

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