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Journal of Vertebrate Paleontology

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First dinosaur (Ornithopoda) from EarlyCretaceous (Albian) of Oregon, U.S.A.

Gregory J. Retallack, Jessica M. Theodor, Edward B. Davis, Samantha S. B.Hopkins & Paul Z. Barrett

To cite this article: Gregory J. Retallack, Jessica M. Theodor, Edward B. Davis, Samantha S. B.Hopkins & Paul Z. Barrett (2018): First dinosaur (Ornithopoda) from Early Cretaceous (Albian) ofOregon, U.S.A., Journal of Vertebrate Paleontology, DOI: 10.1080/02724634.2018.1486847

To link to this article: https://doi.org/10.1080/02724634.2018.1486847

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SHORT COMMUNICATION

FIRST DINOSAUR (ORNITHOPODA) FROM EARLY CRETACEOUS (ALBIAN) OFOREGON, U.S.A.

GREGORY J. RETALLACK,*,1 JESSICA M. THEODOR,2 EDWARD B. DAVIS,1 SAMANTHA S. B. HOPKINS,1 andPAUL Z. BARRETT1

1Department of Earth Sciences, University of Oregon, 1275 E. 13th Avenue, Eugene, Oregon 97403, U.S.A, gregr@uoregon.edu;2Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N 1N4, Canada

SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

Citation for this article: Retallack, G. J., J. M. Theodor, E. B. Davis, S. S. B. Hopkins, and P. Z. Barrett. 2018. First dino-saur (Ornithopoda) from Early Cretaceous (Albian) of Oregon, U.S.A. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2018.1486847.

A fossil toe bone discovered in 2015 by GJR is the first diag-nostic nonavian dinosaur fossil from Oregon, a state whoseMesozoic rocks are mostly marine (Orr and Orr, 2012). This dis-covery is novel evidence of Cretaceous terrestrial environmentsand faunas in Oregon. The pedal phalanx was recovered from themid–Cretaceous (Albian–Cenomanian) Hudspeth Shale and ishere identified informally as the ‘Mitchell ornithopod.’ This newornithopod fills a geographic gap between the Early Cretaceous(Aptian) ‘Ono ornithopod’ of northern California (Hilton et al.,1997) and the Late Cretaceous (Campanian) ‘Sucia Islandtheropod’ of Washington (Peecook and Sidor, 2015), as one ofthe few nonavian dinosaur specimens known from marine rocksof the Pacific Northwest. Other Pacific coastal nonavian dinosaursfrom southeast Alaska to Baja California reviewed by Peecockand Sidor (2015) include a possible Oregon hadrosaur sacrumfrom the Late Cretaceous (Maastrichtian) Cape SebastianSandstone (Orr and Orr, 2012), but our examination of thisunprepared specimen cannot yet determine whether it was a dino-saur, marine turtle, or plesiosaur.Institutional Abbreviations—BM, British Museum, now

Natural History Museum, London, U.K.; IRB, Institut Royaldes Sciences Naturelles de Belgique, Brussels, Belgium; JRF,Judith River Foundation, Malta, Montana, U.S.A.; MOR,Museum of the Rockies, Bozeman, Montana, U.S.A.; UMM,University of Manchester Museum, Manchester, U.K.; UO,Condon Collection, University of Oregon Museum of NaturalHistory, Eugene, Oregon, U.S.A.

METHODS

A single bone regarded as a dinosaur phalanx (UOF118600)was collected from near Mitchell, Oregon (locality UO13418),along with an ichthyosaur centrum and marine invertebrates(UOF11895–F118606) and cataloged into the CondonCollection of the Museum of Natural and Cultural History ofthe University of Oregon (paleo.uoregon.edu). Examination ofspecimens from the Museum of the North (Fairbanks, Alaska),Royal Tyrrell Museum (Drumheller, Alberta), Currie Museum

(Wembley, Alberta), Museum of the Rockies (Bozeman,Montana), and Utah State Museum (Salt Lake City, Utah)were used to guide literature search for taxonomic placementof the Mitchell phalanx. A photogrammetric three-dimensional(3D) image of the bone as a PDF using Agisoft PhotoScan isavailable as Supplementary Data 1.

SYSTEMATIC PALEONTOLOGY

DINOSAURIA Owen, 1842ORNITHISCHIA Seeley, 1887ORNITHOPODA Marsh, 1881

gen et sp. indet.

Referred Material—UOF118600, a pedal phalanx.Age and Occurrence—The locality, UO13418 Mitchell, is a

gentle shale slope below low cliffs of lowest Hudspeth Formationon public lands administered by the Bureau of Land Managementnear Mitchell, Oregon, at roughly 44.6�N, 120.2�W. The locality isin the Hudspeth Shale at a stratigraphic level of 374.9 m in thenearby measured section (Fig. 1) of Wilkinson and Oles (1968).The biostratigraphic age is late early Albian, in the Brewericerashulenense zone (Jones et al., 1965). Associated fossils include theammonites Brewericeras hulenense (UOF118598, UOF118606),Leconteites lecontei (UOF118597), Cleoniceras jonesi(UOF118596A–B), Anisoceras merriami (UOF118599), snailAmberleya dilleri (UOF118601), bivalves Lithophaga carolinensis(UOF118602), Entolium utukokense (UOF118603), Aucellinadowlingi (UOF118604), an ichthyosaur centrum(UOF118595A–B), and conifer wood (UOF118605). Many ofthese ammonites are endemic North American species, butcosmopolitan ammonites also are found near the Mitchell locality,which is stratigraphically above the local first appearance ofMortoniceras inflatum and below the local first appearance ofMortoniceras fallax, or 102.5–103.0Ma (Lehmann, 2015). Precisecoordinates and further locality details are on file in the PrinevilleOffice of the Bureau of Land Management and the Museum ofNatural and Cultural History of the University of Oregon.*Corresponding author.

Journal of Vertebrate Paleontology e1486847 (5 pages)# by the Society of Vertebrate PaleontologyDOI: 10.1080/02724634.2018.1486847

Published online 15 Oct 2018

Description—The putative dinosaur phalanx (Fig. 2) is widermediolaterally (47.6mm) than proximodistally (30.3mm), witha moderately concave proximal end. The distal end has aweakly saddle-shaped, convex condyle curved anteriorly 13�from vertical. A mediolateral sulcus on the dorsal surface iscontinuous to the lateral surfaces, with a shallow basal ridgedividing it from a short plantar sulcus below. This shallow,rimmed, lateral basin is better preserved in other dinosaur pha-langes (Fig. 2G) than the worn and broken Mitchell specimens(Fig. 2C, F) and is in the position where deep collateral pitsare seen on many other dinosaur phalanges (Fig. 2 L, O). Abasal rim to the lateral basins also distinguishes the Mitchellphalanx from dinosaur phalanges with a girdling mediolateralsulcus (Fig. 2M–O).The maximum distal width is 47.6mm, and the maximum

proximal width is at least 46.6mm. Exact measurement is com-promised by postmortem erosion of the cortex, especiallywhere the museum number has been placed (Fig. 2).Taxonomic and Anatomical Position—The lateral rimmed

basin of the dorsal sulcus is distinct from a completely girdling sul-cus or waist in other large dinosaur phalanges that are shorter thanwide in sauropods (Bonnan, 2005:figs. 16.8–16.9; D’Emic et al.,2011:figs. 1–2), stegosaurs (Maidment et al., 2015:figs. 76–77),nodosaurs (Carpenter et al., 1995:fig. 16), ankylosaurs (Carpenter,1984:fig. 5; Currie et al., 2011:figs. 9–10), and ceratopsians (Brown,1914:fig. 19; Chinnery and Horner, 2007:fig. 4P). A ceratopsianphalanx with girdling sulcus is illustrated here in Figure 2M–O.The shallow end to the dorsal sulcus is distinct from collateral pitsand a narrow waist, found in phalanges of theropods (White et al.,2016:fig. 2), pachycephalosaurs (Perle et al., 1982:pl.44, figs. 4–7;Sues and Galton, 1987:text-fig. 14), and small ornithopods such asHypsilophodon (Hulke, 1882:pl. 79, fig. 4; Galton, 1971:fig. 1A)and Tenontosaurus (Tennant, 2013:fig. 31). An ornithopod

phalanx with collateral pits is illustrated here in Figure 2J–L.Generally, similar short phalanges with lateral rimmed basins likethe Mitchell bone are found in Iguanodon (Norman, 1980:figs.71–72), Corythosaurus (Brown, 1916:fig. 14), Edmontosaurus(Zheng et al., 2011:figs. 1–3, 5–6), Hypacrosaurus (Brown,1913:fig. 7), Brachylophosaurus (Fig. 2G–I; Prieto-Marquez,2007:fig. 6.7), and Saurolophus (Marya�nska and Osm�olska,1984:pl. 23, figs. 11a–b). The Mitchell ornithopod (Fig. 2A–F) isregarded as a third pedal phalanx of the central digit (III) of theright pes of an iguanodont or hadrosaur dinosaur, by comparisonwith these other ornithopods (Fig. 2I; Brown, 1913, 1916; Norman,1980; Maryanska and Osm�olska, 1984; Zheng et al., 2011).Ornithopods are common herbivores in Early Cretaceous rocks ofUtah and Wyoming, but at 102.5–103Ma (late Albian); our phal-anx falls within a gap in the North American dinosaur recordbetween the Aptian–Albian Tenontosaurus and the CenomanianEolambia (McDonald et al., 2012).

SIZE ESTIMATE OF WHOLE ANIMAL

The Mitchell ornithopod phalanx is robust, flattened, andwide, thus being a load-bearing subunguligrade toe bone froman animal of substantial size (Moreno et al., 2007). Althoughmass cannot be precisely reconstructed without more completematerial, comparison with six Cretaceous ornithopods knownfrom complete skeletons (Hulke, 1882: BM39460; Norman,1980: IRB1534, 1536, 1561; Seebacher, 2001: BM5764,IRB1535; Tennant, 2013: UMM12275; Tweet et al., 2008:JRF115) gives a general idea. The Mitchell ornithopod waslarger than Tenontosaurus tilleti and smaller than Iguanodonbernissartensis, but the Ono ornithopod was a much smalleranimal, closer in size to Hypsilophodon foxi (Hilton et al.,

FIGURE 1. Stratigraphic location of the Mitchell ornithopod within a reconstructed geological section of the Hudspeth Formation (fromWilkinson and Oles, 1968), showing local ammonite zones (Jones et al., 1965) and first appearances of important ammonites, which are availablein the Condon Collection of the Museum of Natural and Cultural History, University of Oregon (paleo.uoregon.edu).

Retallack et al.—Cretaceous ornithopod from Oregon (e1486847-2)

1997). Closest in size to the Mitchell ornithopod is a phalanx(MOR1071B-7-99460.0) 47.3mm wide on distal plantar edgeand 20.6mm long on left plantar edge (Fig. 2G–I) of the LateCretaceous hadrosaur Brachylophosaurus canadensis (Prieto-Marquez, 2007), best known from the ca. 5.1 m long subadultmummy ‘Leonardo’ (Murphy et al., 2007; Tweet et al., 2008).Body mass of a similarly proportioned ornithopod, Iguanodonmantelli, 5.1 m long, has been estimated at 678 kg bySeebacher (2001).

PALEOECOLOGY

Sparse plant material found in the Hudspeth Shale offersinsight into the terrestrial environment in which the Mitchellornithopod lived. Fossil conifer wood was found with the fossiland is common in the Hudspeth Formation (Wilkinson andOles, 1968). Other fossil plants from the Hudspeth Formationin UO collections include conifer shoots of Sequoia condita(F118840) and Elatocladus montanensis (F118838, F118841,F120581), fern fragments of Nathorstia sp. cf. N. firma(F120569), horsetails Equisetites sp. cf. E. burchardtii (F120635,F120661), and indeterminate cycad or cycadeoid scales(F120030A–B). No fossil angiosperms have yet been found,and this flora predates the late Albian advent of convincingangiosperm fossils in California (Retallack and Dilcher, 1986).Paleomagnetic studies of the Hudspeth Shale reveal a paleo-latitude of 39.2� ± 4.8�N (Housen and Dorsey, 2005), more likemodern Mendocino, California (39.3�N), than Mitchell,Oregon (45.6�N). Vegetation in which the Mitchell ornithopodlived may have been comparable to the modern coast redwood(Sequoia sempervirens) forests of northern California (Barbouret al., 2007).

TAPHONOMY

The Mitchell ornithopod was found with a diverse assem-blage of marine molluscs and ichthyosaur centrum in a darkgray shale with siderite nodules. The Hudspeth Shale alsohas yielded a variety of echinoids, starfish, crabs, shrimp, fishbones, shark teeth, a plesiosaur, and the pterosaur,‘Bennettazhia’ oregonensis (Welton, 1972; Vega et al., 2010;Averianov, 2012; Orr and Orr, 2012). The nodular darkshales of outer marine continental shelf environments areinterbedded with conglomerates of alluvial plains, fan deltas,shingle beaches, and submarine canyons of a rocky coast(Dorsey and Lenegan, 2007). As the only dinosaur bonefound in the Mitchell area in 150 years of prospecting there(Orr and Orr, 2012), the Mitchell ornithopod is a rare speci-men of a terrestrial animal, likely preserved by floating outto sea and disarticulated with decay. Similarly, the Ono orni-thopod from marine shales of California is a single lowerlimb with many toes missing (Hilton et al., 1997). Only a sin-gle set of sauropod remains is known from the Early JurassicPosidonienschiefer of Holzmaden, southern Germany, whichhas been quarried for tiles and fossils since the 12th century(Wild, 1978; Etter and Tang, 2002). Dinosaurs in marinerocks are very rare, but the Mitchell ornithopod offers aglimpse into terrestrial environments poorly represented inOregon’s Mesozoic record.

ACKNOWLEDGMENTS

We thank E. W. Woodard and J. Zancanella of the Bureauof Land Management Prineville Office for permissions andhelp in the field. J. B. Scannella demonstrated phalanges inthe Museum of the Rockies. Useful advice also came from P.

FIGURE 2. Pedal phalanx of Mitchell ornithopod, in standard views (A–F); comparable phalanx of Brachylophosaurus canadensis (G–H, arrow in I;MOR1070-7-31-99-281E); and distinct phalanges with collateral pits and girdling sulci of Tenontosaurus tilletti (J–L; MOR787) and Einiosaurus procurvi-cornis (M–O; MOR956-32-33), respectively. In all images, plantar surface is down, dorsal is up, proximal is left, and distal is right. Scale bars equal 10mm(A–H, J–O) and 50mm (I). (A 3D digital image of the Mitchell ornithopod is also available as Supplementary Data 1.)

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J. Currie, J. I. Kirtland, P. M. Sander, P. C. Sereno, P. E.Olsen, D. M. Henderson, and T. C. Hunt.

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Submitted October 19, 2017; revisions received April 17, 2018;accepted April 24, 2018.Handling editor: Michael D’Emic.

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