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The First Pachycephalosaurine (Dinosauria) from the Paleo-Arctic of Alaska and Its Paleogeographic Implications Author(s): Roland A. Gangloff, Anthony R. Fiorillo and David W. Norton Reviewed work(s): Source: Journal of , Vol. 79, No. 5 (Sep., 2005), pp. 997-1001 Published by: Paleontological Society Stable URL: http://www.jstor.org/stable/4095071 . Accessed: 13/06/2012 19:50

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J. Paleont., 79(5), 2005, pp. 997-1001 Copyright C 2005, The Paleontological Society 0022-3360/05/0079-997$03.00

THE FIRST PACHYCEPHALOSAURINE (DINOSAURIA) FROM THE PALEO-ARCTIC OF ALASKA AND ITS PALEOGEOGRAPHICIMPLICATIONS

ROLAND A. GANGLOFF,' ANTHONY R. FIORILLO,2 AND DAVID W. NORTON3 'Universityof Alaska Museum,907 YukonDrive, Fairbanks99775-6960, ,2Dallas Museum of NaturalHistory, P.O. Box 150349, Dallas, Texas 75315, ,and 3ArcticRim Research,1749 Red Fox Drive, Fairbanks,Alaska 99709,

INTRODUCTION 1982; Williamson and Carr, 2002). The presence of a pachyce- of this and data THE LAST 15 years of field work along the beaches and bluffs phalosaurine age geographic position represents of the Colville River, on Alaska's Arctic Coastal Plain, have consistent with the hypothesis that a major faunal exchange took between Eurasia and produced a diverse record of high-latitude . Seven fam- place during Campanian time. ilies and eight genera are documented with several other families and less remains genera possibly being represented by diagnostic INSTITUTIONAL ABBREVIATIONS and only a few scattered elements (Table 1; Nelms, 1989; Gan- American Museum of Natural New gloff, 1994, 1998; Fiorillo et al., 1999; Fiorillo and Gangloff, AMNH, , York, Museum of Natural 2000, 2001). Virtually all of the common major groups of the- New York; CM, Carnegie History, Pittsburgh, Institute of ropods and ornithopods typical of the Late of northern Pennsylvania; PAL, Paleobiology, Warsaw, Poland; of Alaska Earth Science North America are present. Most of the skeletal remains are found UAM, University Museum, Collections, in rocks assigned to the Prince Creek Formation of the Colville Fairbanks. et al., 1963, 1975; The diver- Group (Detterman Phillips, 1990). SYSTEMATIC PALEONTOLOGY sity of the record in Alaska has been significantly in- creased with the discovery of abundant tracks and trackways Order ORNITHISCHIASeeley, 1888 along the North Slope and Arctic Coastal Plain over the last six Suborder PACHYCEPHALOSAURIAMaryanska and Osmolska, years. The majority of the ichnofossil record is contained in var- 1974 ious terrestrial coal-bearing rocks assigned to the Early Creta- Family PACHYCEPHALOSAURIDAESternberg, 1945 ceous Nanushuk Group (Ahlbrandt et al., 1979). The dinosaur Subfamily PACHYCEPHALOSAURINAESereno, 2000 biozone spans the upper part of the Nanushuk group and all of Figure 2.1-2.5 the Colville Group, ranging from the mid to Late Cretaceous (Al- Description.-The specimen is a nearly complete left squa- bian to Maastrichtian; Mull, 1985). The already diverse and abun- mosal that ranges in height from 5.63 to 6.82 cm and width from dant record of dinosaur skeletal was increased by the dis- 4.29 to 6.49 cm. The thickness of this specimen ranges from 1.50 covery in 1999 of the first evidence of pachycephalosaurs from cm at the thinnest part of the nuccal shelf to 4.05 cm at the this region (Fig. 1). This taxon is now represented by a nearly thickest part of the dome. A total of 12 nodes or tubercles are complete left squamosal and the contiguous, posterior, basal part present on the external or dorsal surface. A shallow and narrow of the dome. The highly thickened bone with characteristic pris- groove defines the base of the nodes along the contact with the matic internal structure accompanied by the distinctive ornamen- dome above as well as the contact with the upper margin of the tation diagnostic of this group allows for an unequivocal identi- nuchal crest or ridge (Fig. 2.1, 2.2). Nine nodes are fully devel- fication to the subfamily level. The specimen (UAM # oped and three appear to be incipient. The largest node borders AK-493-V-001, Fig. 2.2) is most of the left squamosal and in- the descending part of the parietal bone and possesses the stron- cludes a portion of a thickened dome. The specimen is bounded gest apex. The largest node is followed by two diverging rows of on three sides by parted sutures interpreted as representing the smaller nodes. These two rows of nodes diverge at an angle of contacts with the quadrate, exoccipital, and the narrow descending 300. The smallest fully developed node is rectangular in shape, portion of the parietal bone (see Fig. 2.2, 2.4). The remaining measuring 5.0 X 15.0 mm. The largest is polygonal and nearly margin exhibits a broken surface that reflects the polygonal pris- equidimensional, measuring 18.0 X 20.0 mm. A single, distal, matic internal structure of a part of the parietal-frontal dome. The and fully developed node is located nearly halfway between the sutures are well preserved and show little or no evidence of fluvial two rows of diverging nodes at the distal end of the nodal rows abrasion or weathering due to subaerial exposure prior to burial. where it is in contact with one of the incipient nodes (Fig. 2.2). The strength and basic pattern of the ornamental nodes or tu- The upper or dorsal margins of the upper row of nodes border bercles, although not identical to, most closely resemble those the thickened bone of the dome. This part of the dome appears exhibited by Pachycephalosaurus Brown and Schlaikjer, 1943. to be an extension of the squamosal because there is no suture This determination establishes, for the first time at paleolatitudes dorsal to the row of nodes. The dome's surface slopes at an angle between 700 and 800 N (Witte et al., 1987), the presence of one of 35'. The broken dorsal margin of the dome exhibits the typical of the more highly evolved lineages of this distinctive and exclu- prismatic structure of domed taxa such as Pachycephalosaurus, sively Cretaceous taxon. This discovery significantly extends the Stegoceras Lambe, 1902, and Prenocephale Maryanska and Os- paleolatitudinal range of the Pachycephalosaurinae, whose pre- molska, 1974. viously highest paleolatitudinal position was approximately 53'- The lower or ventral margin of the nodal rows is bordered 550 N in the lower part of the Horseshoe Canyon Formation (late ventrally by a distinct, narrow (1.62-2.02 cm), and rounded su- Campanian) of Alberta, Canada (Smith et al., 1981; Ziegler et al., praoccipital ridge (=nuchal crest). This ridge is equivalent to the 997 998 JOURNAL OF PALEONTOLOGY,V. 79, NO. 5, 2005

TABLE1-Dinosaur subordersand families from The Prince Creek Formation, shelf of Williamson and Carr (2002). The ven- ColvilleRiver. parietosquamosal tral margin of the ridge/crest forms a relatively deep (1.0-1.20 cm) sulcus that shows pitting and scars reflective of strong muscle Theropoda attachments and functions as a nuchal crest. The lowermost (ven- Tyrannosauridae Troodontidae tral) margin possesses strong ridges and grooves and is interpreted Ornithomimidae as articulating with the exoccipital bone (Fig. 2.2). Dromaeosauridae The internal or ventral surface of the specimen is marked by a Ornithopoda rather deep (0.45-1.51 cm) and complex sulcus (Fig. 2.3). The Hadrosauridae distal end of the sulcus forms a flange with sutural surfaces that Hypsilophodontidae are interpreted as articulating with the ascending part of the quad- Ceratopsia rate bone (Fig. 2.1, 2.3). Portions of the distal or quadrate end of Ceratopsidae the sulcus are broken. The sulcus contains an oval (1.30 cm long) indentation that appears to be a primary feature rather than a puncture mark since it does not match any figured puncture marks sensu Fiorillo (1988, figs. 5, 6). The proximal end of the inden- tation has a broken margin (Fig. 2.3). Material examined.-UAM # AK-493-V-001: A nearly com- 156* 152' 148' plete left squamosal with an attached basal portion of the parietal Barrow ' dome from the Prince Creek Formation, Colville Group, North Beaufort Sea Slope Borough, Alaska. The specimen is housed in the Earth Sci- ence Collections, University of Alaska Museum. Cape Halkett e Occurrence.-This specimen was found as talus on a narrow beach at the base of bluffs on the west side of the Colville River. The bluffs are mainly comprised of poorly indurated sandstones, OceanPoint siltstones, and mudstones assignable to the Prince Creek Forma- Pachycephalosaur tion (s. Mull et al., 2003) and topped by Quaternary age sediments of the Gubik Formation. This locality is 4 river km south of a series of highly productive hadrosaur-dominatedbone beds (Gan- gloff, 1994, 1998) and 24.0 river km southeast of Point. The bone beds are interbedded with several rhyolitic tephra beds -v that have a series of K-Ar and Ar/Ar dates. Conventional 7s yielded approaches using glass shards produced dates ranging from 68 to co . 71 My with a weighted mean of 69 My (Conrad et al., 1990). The best results of a reanalysis using 40Ar/39Arsingle sanidine crystals (Obradovich, personal commun., 1993) would place the lowermost bone bed between 71 and 72 My. Therefore, the pa- chycephalosaur squamosal is assigned a late Campanian age based on the revised time scale of Obradovich (1993). Chandal SInvertebratefossils Discussion.-The squamosal from Alaska is clearly smaller (0.75X) than that found in Prenocephale prenes (Brown and o, ndalar? Schlaikjer, 1943) (PAL MgDI/104) or Pachycephalosaurus wyom- Bettles ingensis, Gilmore, 1931 (0.5 X; AMNH 1696). It is closest in size to Prenocephale edmontonensis (Brown and Schlaikjer, 1943) n. comb. and P. brevis (Lambe, 1918) n. comb. (Sullivan, 2000). * Dinosaur teeth and bones Williamson and Carr (2002) consider the former taxon to be a 'as nomen dubium and the latter to belong to Stegoceras. It is clear that the animal that belongs to this squamosal was a fully domed pachycephalosaur with a strong but unusual marginal nodal or- namentation pattern. The pattern is most similar to that found in FIGURE1-Symbols indicatecommon fossils foundat this site, including Pachycephalosaurus wyomingensis and in particular, specimen bones of hadrosaursand ceratopsians.Modified from Huffman Jr. CM 3180 (text-fig. 16b in Sues and Galton, 1987) in regard to (1985). the shape, number of rows, and distribution pattern of the nodes. This is quite different from the condition in Prenocephale prenes or P. edmontonensis in which the primary nodes form a single

FIGURE2-Left squamosalof pachycephalosaurine,UAM # AK-493-V-001.Specimen is orientedwith the basal portionof the dome up and the suturalcontact with the exoccipitalat the bottom(see 4, 5). All scale incrementsare in centimeters.1, Oblique-posteriorview showingornamentation consisting of four primarynodes and two incipientor incompletenodes above a narrow,rounded, supraoccipital ridge or shelf. Note the deep ventralmargin of this shelf and what appearto be muscle attachmentscars. Arrows point to suturalmargins; bg, basal groove of nodes;nc, nuchal crest. 2, Medial-posteriorview showingthe bifurcationof the nodes as well as the threeincipient nodes at the left-handmargin of the photo. Note the basal portionof the dome at the top of the photo and the largestof the primarynodes formingpart of the parietalmargin on the right side of the photo. Arrowspoint to suturalmargins; psb, parietosquamosalbar. 3, Ventralview showingthe prismaticstructure of the dome, uppermargin in photo, and the ventralsulcus with its long axis runningfrom the upperleft to the lower right.Note the indentationand flangein the lower right or quadrateend of the sulcus. The lower marginof the photo exhibitsthe well-preservedsutural surfaces (arrows) where the squamosalarticulates PALEONTOLOGICALNOTES 999

dome

- -- - I - -

dome

U -m -m -mm -

4 5 suture P nodes /f q f

P asor pb nodes n ; ----.-- no p•b

eopm ' suture PM\ bo bs ,' m ] / suture '

5 cm with the parietaland exoccipitalbones and indicatesthat there was little transportationprior to burial.Separation along several suturessuggests that the individualdied priorto completefusion of skeletalcomponents. 4, Posteriorview of a hypotheticalreconstruction of a skull with the left squamosal-partialdome put in its probableorientation. Hypothetical skull is a compositebased primarilyon the featuresof Pachycephalosaurus wyomingensisGilmore, 1931 (AMNH 1696, Sues and Galton, 1987) and Prenocephaleprenes (PALMgDI/104, Sereno,2000). Abbreviationsare as follows: bo, basioccipital;bs, basisphenoid;eo, exoccipital;po, postorbital;psb, parietosquamosalbar; pt, pterygoid;q, quadrate;sq, squamosal. 5, Left-lateralview of the same hypotheticalskull reconstructionas in 4. Abbreviationsare the same as in 4 and asor, anteriorsupraorbital; f, frontal;j, jugal; 1, lacrimal;m, maxilla;n, nasal;pm, premaxilla;prf, prefrontal;psor, posterior supraorbital; qj, quadratojugal;nc, nuchalcrest. 1000 JOURNAL OF PALEONTOLOGY,V. 79, NO. 5, 2005 row. The divergence of the two rows as seen in the Alaskan spec- Denver Museum of Natural History for access to specimens in imen sets it apart from all known pachycephalosaurs. However, their care. near the contact between the quadrate and the squamosal, one REFERENCES large node and three incipient nodes form between the primary bifurcating rows and may represent clustering. Sullivan (2000) AHLBRANDT,T. S., A. C. HUFFMANJR., J. E. Fox, AND I. PASTERNACK. 1979. framework and Sereno (2000) cite the clustering of nodes as typical of Pa- Depositional and reservoir-qualitystudies of selected Nanushuk North Alaska, 14-32. In T S. chycephalosaurus. It should be noted that there appears to be Groupoutcrops, Slope, p. a bit of variation in the of the nodes within Ahlbrandt(ed.), Preliminarygeologic, petrologic, and paleontologic quite shape Pachy- resultsof the of the Nanushuk rocks,North Alaska. In P. AMNH the nodes are study Group Slope, cephalosaurus. wyomingensis 1696, United States GeologicalSurvey Circular,794. more and often lack the spherical polygonal bases and distinct BROWN, B., AND E. M. SCHLAIKJER. 1943. A study of the Troidont apices seen in the Alaskan specimen and P. wyomingensis CM dinosaurswith the descriptionof a new genus and four new species. 3180. Specimen AMNH 1696 may represent a more mature in- Bulletinof the AmericanMuseum of NaturalHistory, 82:115-150. dividual with more spherical nodes that exhibit a higher degree CONRAD,J. E., E. H. MCKEE,AND B. D. TURRIN.1990. Age of tephra of clustering. It is difficult to assess the importance of these dif- beds at the OceanPoint Dinosaur Locality, North Slope, Alaska,based ferences, given the high degree of variation in ornamentation that on K-Ar and 40Ar/39Aranalyses. United StatesGeological Survey Bul- letin, 1990-C:1-12. characterizes the pachycephalosaurs. Galton and Sues demonstrated that DETTERMAN, R. L., R. S. BICKEL, AND G. GRYC. 1963. of the (1983:469) Pachycephalo- ChandlerRiver of Naval PetroleumRe- saurus is in region, Alaska-exploration unique among pachycephalosaurs having a quadrate serve No. 4 andadjacent areas, northern Alaska, 1944-53-Pt. 3, aerial that is sutured to the squamosal. All other pachycephalosaurs have geology. United States Geological Survey ProfessionalPaper, 303E: a quadrate with a rounded dorsal end that fits into a socket on 233-324. the squamosal (Sues and Galton, 1987:26). The specimen from DETTERMAN,R. L., H. N. REISER,W. P BROSGE,AND J. T. BUTROJR. Alaska does appear to possess a flangelike ventral end that is 1975. Post-Carboniferousstratigraphy, northeastern Alaska. United States Professional interpreted (Fig. 2.1, 2.3) as articulating with the quadrate as in GeologicalSurvey Paper,886:1-46. FIORILLO,A. R. 1988. of HazardHomestead Pachycephalosaurus. If this interpretation is correct, then the Taphonomy Quarry(Ogal- lala Hitchcock Nebraska.Contributions to Geology, Alaskan specimen is most a member of this How- Group), County, probably genus. Universityof Wyoming,26:57-97. ever, the nature of the material and the distinctiveness fragmentary FIORILLO,A. R., AND R. A. GANGLOFF.2000. Theropod teeth from the of the ornamentation do not allow for an assignment to Pachy- Prince CreekFormation (Cretaceous) of northernAlaska, with specu- cephalosaurus at this time. Prudence dictates an assignment only lations on arcticdinosaur paleoecology. Journal of VertebratePaleon- to the subfamily level and therefore a designation as a pachyce- tology, 20:675-682. phalosaurine. An alternative conclusion would be that the speci- FIORILLO, A. R., AND R. A. GANGLOFF. 2001. The caribou migration men from Alaska represents a new genus and species that is model for Arctic hadrosaurs(Ornithischia: Dinosauria): A reassess- ment. Historical 15:323-334. closest phylogenetically to Pachycephalosaurus within the Pren- Biology, FIORILLO, A. R., R. A. GANGLOFF, AND D. NORTON.1999. The first ocephale-Pachycephalosaurus clade of Sues and Galton, 1987 or occurrenceof a pachycephalosaur(Dinosauria) from the Late Creta- Stygimoloch-Pachycephalosaurus clade of Sereno, 2000 and Wil- ceous of northernAlaska. 1999 Arctic Science Conference,American and liamson Carr, 2002. Associationfor the Advancementof Science, Arctic Division, p. 288. In his discussion of the biogeography of dinosaur assemblages, GALTON, P. M., ANDH.-D. SUES.1983. New dataon pachycephalosaurid Russell (1993) argues that North America was a poorly defined dinosaurs(Reptilia: Ornithischia) from North America. Canadian Jour- zoogeographic province. Further, he suggests that the major nal of EarthSciences, 20:462-472. groups of dinosaurs in North America during the Late Cretaceous GANGLOFF,R. A. 1994. The recordof Cretaceousdinosaurs in Alaska: had their origins in central Asia. This route An overview,p. 399-404. In D. K. Thurstonand K. Fujita(eds.), 1992 presumed dispersal InternationalConference on Arctic MineralMan- would have been a land connection between these conti- Proceedings Margins. bridge Service, OuterContinental Shelf nents Alaska. several workers agement Study. through present-day Though (Wil- GANGLOFF,R. A. 1998. Arctic dinosaurswith emphasis on the Creta- liamson and Carr, 2002; Sullivan, 2003) have argued for the dis- ceous recordof Alaska and the Eurasian-NorthAmerican connection, persal of the Pachycephalosauridae to North America prior to the p. 211-220. In S. G. Lucas,J. I. Kirkland,and J. W.Estep (eds.),Lower Campanian, the discovery of a pachycephalosaurine in the paleo- and MiddleCretaceous Terrestrial Ecosystems. New Mexico Museum Arctic of Alaska is consistent with the general biogeographic of NaturalHistory and Science Bulletin, 14:211-220. model because it establishes that pachycephalosaurids did exist at GILMORE,C. W. 1931. A new species of troadontdinosaur from the Lance Formationof of the United States high latitudes and, therefore, that high latitudes did not Wyoming.Proceedings Na- necessarily tional Museum,79:1-6. exclude this route as a potential route of dispersal. HUFFMANJR., A. C. 1985. Introductionto the geology of the Nanushuk Groupand relatedrocks, North Slope, Alaska,p. 2. In A. C. Huffman ACKNOWLEDGMENTS Jr. (ed.), Geology of the NanushukGroup and RelatedRocks, North Alaska.United States 1614. The National Science Foundation grant OPP 0424594 and the Slope, GeologicalSurvey Bulletin, Foundation financial for research on the LAMBE,L. M. 1902. New generaand species fromthe Belly Riverseries provided support (Mid-Cretaceous).Contributions to CanadianPaleontology, Geological North We Slope. gratefully acknowledge the Dallas Museum of Survey of Canada,3:25-81. Natural History, the University of Alaska Museum, American LAMBE, L. M. 1918. The Cretaceousgenus Stegoceras,typifying a new Airlines, Arco Alaska, Inc. (now Phillips Alaska, Inc.), Alyeska family referredprovisionally to the Stegosauria.Transactions of the Pipeline Service Company, Inc., the Arctic Management Unit of Royal Society of Canada,12:23-36. the Bureau of Land Management, and the village of Nuiqsut, for MARYArSKA, T., AND H. OSM6LSKA.1974. Pachycephalosauria, a new additional support in the field. The authors thank P. Currie for suborderof ornithischiandinosaurs. Palaeontologia Polonica, 30:45- 102. information regarding the occurrence of pachycephalosaurs in southern Alberta. We also thank M. Goodwin, T. Williamson, P. MULL,C. G. 1985. Cretaceoustectonics, depositionalcycles, and the NanushukGroup, Brooks Range and Arctic Slope, Alaska,p. 7-36. In Galton, and R. Sullivan for their thoughts on pachycephalosaurs A. C. HuffmanJr. (ed.), Geology of the NanushukGroup and Related and helpful reviews of the manuscript. Lastly, we thank the re- Rocks, NorthSlope, Alaska.United States Geological Survey Bulletin, spective staffs at the University of California Museum of Pale- 1614:7-36. ontology, the Royal Tyrrell Museum of Palaeontology, and the MULL, C. G., D. W. HOUSEKNECHT, AND K. J. . 2003. Revised PALEONTOLOGICALNOTES 1001

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