NEW INFORMATION ON THE CRANIUM OF BRACHYLOPHOSAURUS CANADENSIS(DINOSAURIA, HADROSAURIDAE), WITH A REVISION OF ITS PHYLOGENETIC POSITION

ALBERT PRIETO-MARQUEZ1

1Museum of the Rockies, Montana State University, Bozeman, Montana 59717, redshore@hotmail.com

ABSTRACT—The cranium of the hadrosaurid dinosaur Brachylophosaurus canadensis is redescribed on the basis ofabundant and complete material from the Lower Campanian Judith River Formation of Malta, northeastern Montana.The diagnosis of this taxon is emended, and the species Brachylophosaurus goodwini is now considered to be a juniorsynonym of Brachylophosaurus canadensis. Autapomorphies of Brachylophosaurus are: nasal greatly developed intopaddle-like solid crest extending caudodorsally, overhanging dorsal region of skull; nasal possessing anteroposteriorlyoriented groove terminating in elongated foramen located medial to prefrontal; prefrontal projecting posteriorly andresting dorsomedially over anterior process of postorbital and, more posteriorly, extending ventromedially under nasal;only anterior sharp tip of lacrimal contacting maxilla; jugal with ventrally projecting semicircular flange; extremelyelongated, rod-like anterodorsal process of maxilla projecting medial to narial cavity along most of anteroposterior lengthof external naris; anteroposteriorly short exoccipital-supraoccipital roof posterior and dorsal to foramen magnum.

Most autapomorphies of the junior synonym species Brachylophosaurus goodwini originated from misplacement of anasal fragment and individual variation of the jugal. The new osteological information supports Brachylophosauruscanadensis as the sister taxon to Maiasaura peeblesorum, and suggests that the two taxa form a robust and basal cladewithin the Hadrosaurinae. Two new characters are discussed as phylogenetically informative for hadrosaurids: themediolateral and anteroposterior predentary proportions and the length of the prequadratic process of the squamosal.

INTRODUCTION

The Late Cretaceous hadrosaurids were among the most de-rived and specialized herbivorous dinosaurs. Abundant remainsof these animals, including complete and partial skeletons, eggs,nests, babies, and even integumentary traces, have been col-lected for more than one hundred and fifty years in the Americas(Lull and Wright, 1942; Dodson, 1971; Bonaparte et al., 1984),Europe (Weishampel et al., 1993; Casanovas et al., 1999), Asia(Maryañska and Osmolska, 1982; Buffetaut and Tong-Buffetaut,1993), and the Antarctica (Case, 2000).

Brachylophosaurus canadensis was originally erected andbriefly described by Sternberg in 1953 on the basis of a completeskull and partial postcranial skeleton found in the Oldman (Ju-dith River) Formation of southern Alberta. Later, Horner (1988)named a second species, B. goodwini, on the basis of a partialskull and skeleton collected from the Judith River Formation ofcentral Montana, and emended Sternberg’s diagnosis of B.canadensis. In the mid-1990s, new skeletal remains of the had-rosaurid dinosaur B. canadensis were excavated from Campa-nian (Upper Cretaceous) strata in the lower Judith River For-mation of eastern Montana (Harmon, 1997). These remains in-clude an isolated, nearly complete articulated skeleton as well asa bone bed containing hundreds of disarticulated elements rep-resenting individuals from different ontogenetic stages. All thespecimens were found in medium-grained, tan sandstones thataccumulated in shallow meandering channels under low-flowconditions (LaRock, 2000). This preservational environment leftthe bones in a pristine state of preservation, and even preservedsoft-tissue impressions (Negro and Prieto-Marquez, 2001; Mur-phy et al., 2002).

The completeness of the new material allowed a revision ofthe taxonomy, phylogeny, and cranial osteology of B. canadensis.In particular, B. canadensis is rediagnosed and the cranium isredescribed, extracting information on intraspecific variationand reassessing its phylogenetic position using a recent characterlist for the Hadrosauridae (Horner et al., in press). The resultsadd further support to the hypothesis that B. canadensis is arelatively primitive hadrosaurine and the sister taxon of Ma-

iasaura peeblesorum (Weishampel and Horner, 1990; Horner,1992). In addition, a few new characters that are phylogeneticallyinformative for hadrosaurids are discussed and integrated intothis phylogenetic hypothesis. Finally, B. goodwini is considered ajunior synonym of B. canadensis.

Institutional Abbreviations—AMNH, American Museum ofNatural History (New York City, New York, USA); FMNH,Field Museum of Natural History (now housed at the Museum ofthe Rockies, Bozeman, Montana, USA); MOR, Museum of theRockies (Bozeman, Montana, USA); OTM, Old Trail Museum(Choteau, Montana, USA); UCMP, University of California,Museum of Paleontology (Berkeley, California, USA).

Anatomical Abbreviations—an, angular; ap, alar process ofbasisphenoid; ax, axis; bo, basioccipital; bs, basisphenoid; bspr,basipterygoid process; c.n., cranial nerve(s); d, dentary; f, frontal;hy, hyoid; j, jugal; l, lacrimal; ls, laterosphenoid; mx, maxilla; ns,nasal; op, opisthotic; op-ex, opisthotic-exoccipital; os, orbito-sphenoid; pa, parietal; pd, predentary; pf, prefrontal; pmx, pre-maxilla; po, postorbital; pr, prootic; prs, presphenoid; ps, para-sphenoid; ptg, pterygoid; q, quadrate; qj, quadratojugal; sa, sur-angular; spl, splenial; sq, squamosal.

SYSTEMATIC PALEONTOLOGY

DINOSAURIA Owen, 1842ORNITHISCHIA Seeley, 1888ORNITHOPODA Marsh, 1881

HADROSAURIDAE Cope, 1869BRACHYLOPHOSAURUS Sternberg, 1953

BRACHYLOPHOSAURUS CANADENSIS (Sternberg, 1953)

Brachylophosaurus goodwini Horner, 1988

Referred Specimens—MOR 794, a complete adult articulatedskeleton lacking only the distal part of the tail; MOR 1071, morethan 800 subadult and adult specimens from a monospecific bonebed, including disarticulated or partially articulated and/or asso-ciated coracoids, scapulae, sternals, ilia, pubes, ischia, cervical,dorsal, sacral and posterior vertebrae, ribs, humeri, radii, ulnae,carpals, metacarpals, phalanges, femora, tibiae, fibulae, tarsals,

Journal of Vertebrate Paleontology 25(1):144–156, March 2005© 2005 by the Society of Vertebrate Paleontology

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metatarsals, pedal phalanges, premaxillae, maxillae, a partial na-sal, prefrontals, postorbitals, jugals, quadratojugals, quadrates,dentaries, predentary, splenials, surangular, angulars, articulars,pterygoids, ectopterygoids, palatines, frontals, and two articu-lated skull roofs with preserved braincases, plus a disarticulatedpartial subadult skull; FMNH 862, a partial skull roof with asso-ciated jugals, dentaries, pterygoid, nasals, right surangular, an-gulars, and left quadrate; UCMP 130139, a partial nasal from theholotype of B. goodwini.

Locality—The quarry of MOR 794 (MOR locality JR-168)and the bone bed of MOR 1071 (MOR locality JR-224) corre-spond to two stratigraphically equivalent sites located in PhillipsCounty, 27 km north of Malta, northeastern Montana, and 87 kmfrom the Canadian border (LaRock, 2000). FMNH 862 wasfound in 1922 by the Elmer S. Riggs expedition, in the Red DeerRiver area, north of Medicine Hat, Alberta, Canada. The nasalUCMP 130139 is material found by Mark Goodwin in 1981 in theJudith River Formation, UCMP locality no. V83125, CanadianCreek, Hill County, Montana.

Horizon—MOR 794 and MOR 1071 correspond to the lowerJudith River Formation. FMNH 862 was unearthed from strataof the Two Medicine Formation. Both formations are Campa-nian in age.

Emended Diagnosis for the Genus and Species—Brachylo-phosaurus canadensis is rediagnosed on the basis of the followingautapomorphies: nasals greatly developed into paddle-like solidcrest extending caudodorsally, overhanging dorsal region ofskull; nasals possessing anteroposteriorly oriented groove termi-nating in elongated foramen, located medial to prefrontal; pre-frontal projected posteriorly, resting dorsomedially over anteriorprocess of postorbital and, more posteriorly, extending ventro-medially, underlying nasal; only anterior sharp tip of lacrimalcontacting maxilla; jugal with ventrally projected semicircularflange deeper overall than that of M. peeblesorum but morelightly built than in remaining hadrosaurines; extremely elon-gated, rod-like anterodorsal process of maxilla projecting medialto narial cavity along most of anteroposterior length of externalnaris; anteroposteriorly short exoccipital-supraoccipital roof pos-terior and dorsal to foramen magnum.

CRANIAL OSTEOLOGY

Mandibular Complex

Predentary—Brachylophosaurus canadensis has a subrectan-gular skull, with a relatively deep premaxilla that makes contactventrally with a wide predentary. As in M. peeblesorum (Horner,1983:fig. 4A), the predentary of B. canadensis is twice as widemediolaterally as anteroposteriorly (Fig. 1A, B), whereas inother taxa, such as Prosaurolophus blackfeetensis and Hypacro-saurus stebingeri, the lateral process is as long as the transversalbar. A large keel-shaped symphyseal process divides the pos-terodorsal region of the predentary into two symmetrical halves(Fig. 1A). Along the anterodorsal triturating surface, there aresix small conical nodes at each side of the symphyseal process(Fig. 1A, arrow). A central pair of smaller nodes is located on theparasagittal plane of the bone (Fig. 1A). The anterodorsal edgewith its series of processes is dorsally elevated relative to a trans-verse row of nutrient foramina symmetrically arranged acrossthe parasagittal plane. The anterior face of the anterodorsal bor-der of the predentary is slightly convex dorsoventrally and formsthe dorsal half of the anterior side of the bone. The ventralregion of the anterior surface of the bone shows a bifurcated,posteroventrally projecting process at the center (Fig. 1B), thatunderlies the dentary symphysis. This process is also bilobate inM. peeblesorum and the genus Gryposaurus, but in other had-rosaurids such as H. stebingeri this process is a single triangularunit. Posterior to the bilobate process are a pair of deep oval

excavations. The lateral branches show a strongly depressed lat-eral portion adjacent to a convex medial surface. Ventromedi-ally, they possess flat surfaces bounded by a ridge that forms themedial border of these branches.

Dentary—The diastema accounts for one third of the length ofthe dentary (Fig. 1C) and its ventral deflection is well developed.The dental battery shows a maximum of 33 tooth positions andbetween 2 and 5 teeth arranged vertically on each tooth position,depending on its location along the tooth row. The crown has asingle keel, faces medially forming an angle of 35° with the longaxis of the root, and is longitudinally bisected by a median carina.In occlusal view, as many as three teeth are exposed. The occlu-sal surface runs obliquely and, as in M. peeblesorum (OTMF138), Kritosaurus notabilis (AMNH 5465) and Edmontosauruscf. E. annectens (MOR 003) the occlusal surface is concave. In P.blackfeetensis and H. stebingeri the occlusal surface is flat, andthe section of each tooth position is obliquely directed, not me-diolaterally straight as in B. canadensis.

FIGURE 1. Dorsal (A) and ventral (B) views of Brachylophosauruscanadensis predentary (MOR 1071–7-28–98–299). C, Medial view of B.canadensis right dentary.

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Surangular—The surangular (Fig. 2A) has a long anterolateralprocess that ascends dorsally from the anterior region of thebone. Most of the medial border of the surangular is divided bya low, longitudinal ridge that separates the dorsal splenial groovefrom the articular one. The splenial groove is much wider thanthe articular groove. From the quadrate joint, the surangularelongates posteriorly into an obliquely compressed and posteri-orly projected process that tapers caudally into a sharp edge.

Articular—The articular (Fig. 2B) is relatively small andsaddle shaped. The medial side bears two surfaces separated bya diagonal and posteroventrally directed low ridge. The remain-

ing posterodorsal surface of the medial side of the articular isslightly concave and faces nearly dorsally. The dorsolateral bor-der of the articular thickens along the anterior half of the ele-ment into a narrow concavity that receives a small medioventralprocess of the quadrate.

Splenial—The splenial (Fig. 2C) is dorsally convex in lateralprofile. The medial side is dorsoventrally convex, whereas thelateral side is concave. Anteriorly, the bone is deeper and bifur-cates to form a deeper ventral expansion and a shallow expan-sion dorsally. The triangular groove for the splenial process ofthe dentary is limited ventrally by a sharp edge in P. blackfeeten-

FIGURE 2. Brachylophosaurus canadensis mandibular elements. A, Dorsal view of a left surangular (MOR 1071). B, mediodorsal view of a rightarticular (MOR 1071–8-13–98–554A). C, lateral view of a right splenial (MOR 1071–8-6–98–483). D, lateral view of a right angular (MOR 1071).

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sis that is not seen in B. canadensis. Posteroventrally, the splenialis mediolaterally compressed. In P. blackfeetensis, the splenial isdeeper, especially along the central and the posterior regions.The splenial of B. canadensis is more elongated and slender thanthat in P. blackfeetensis.

Angular—The angular is rod-like and, posteriorly, it is medio-laterally compressed (Fig. 2D). The angular is relatively smoothlaterally, whereas the medial side shows an array of longitudinalgrooves and ridges, especially along the posterior segment, whichis mediolaterally compressed. Anteriorly, the angular becomesgradually thicker and nearly cylindrical. The angular of B.canadensis is more slender compared with that of P. blackfeeten-sis, which is mediolaterally thicker, less variable in thickness, andless irregular in morphology.

Hyoid Apparatus—A pair of hyoid bones lies parallel to theposterior region of the dentary, angular, surangular, and retro-articular process, forming a V-shaped structure along the ven-tromedial posterior half of the mandible (Fig. 3A). Each hyoidconsists of a compressed, rod-like shaft curved posterodorsally.Anteriorly the shaft gradually becomes more mediolaterallycompressed and dorsoventrally expanded, showing a triangularoutline (Fig. 3B). Each hyoid in B. canadensis is relatively longerand shows a more expanded rostral end than in M. peeblesorum.

Facial Complex

Premaxilla—In B. canadensis, the anterior border of the pre-maxilla is ventrally deflected, triangular, and rounded (Fig. 4A).

This condition is also found in M. peeblesorum (OTM F138) anddiffers from the reflected anterior rim of P. blackfeetensis (MOR454–7-8–2-9) and Gryposaurus sp (MOR 553S-7–18–91–107).The anterior portion of the premaxilla is “pocket-like” dorsallyand expanded laterally. Posteriorly, the element diverges intothe long posterodorsal and the short posteroventral processes.The anterior edge of the narial cavity is mostly formed by thespace enclosed by these processes. The posteroventral process ismediolaterally thin, and its laterodorsal surface is strongly con-cave longitudinally, containing the circumnarial depression. An-terior to the deflection of the premaxilla, the posteroventral pro-cess bulges to form a ventral convexity. The anterior edge of thepremaxilla is denticulate. Two large foramina are located antero-medially. One foramen is located near the anterior border of theanterior depression. Dorsomedial to this foramen is another, lo-cated near of the base of the posterodorsal process. This foramenexits ventrally and perforates the premaxilla. It corresponds tothe ventral premaxillary foramen of P. blackfeetensis (Horner,1992).

Maxilla—The anteroventral and anterodorsal processes areseparated by a crescentic notch (Fig. 4C). The anteroventral pro-cess is relatively short and tapers anteroventrally in a very pro-nounced slope. The anterodorsal process is very long and ex-tends along the anteroposterior length of the narial cavity (Fig.

FIGURE 3. A, detail of the ventral view of the cranium of Brachylo-phosaurus canadensis, showing the articulated hyoid apparatus (MOR794). B, lateral view of a right hyoid of B. canadensis (MOR1071–7-16–98–248K).

FIGURE 4. A, lateral view of the left premaxilla of a subadult Brachy-lophosaurus canadensis (MOR 1071–7-7–98–84). B, medial view of B.canadensis left quadratojugal (MOR 1071–7-15–98–218A). C, lateralview of a B. canadensis right maxilla (MOR 1071–7-6–98–79). D, lateralview of B. canadensis right jugal (MOR 1071–7-16–98–248G).

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1A). The jugalar process has a rather symmetrical triangularoutline. The ectopterygoid shelf has a slight posteroventral slope,in contrast to the more horizontal shelf present in other taxa suchas Edmontosaurus sp. (AMNH 5879) and Kritosaurus notabilis(AMNH 5472). Anterior and mediodorsal to the short postero-medial pterygoid process, the ridge that receives the ventralgroove of the palatine is very narrow. Between 40 and 43 verticaltooth families are present, with 2 teeth on the occlusal plane andat least 3 teeth per family. A single median carina bisects thecrown longitudinally without reaching its apical end. Small pa-pillae are present along the edges of the crown.

Jugal—The lateral outline of the rostral process is triangularand symmetrical, and it tapers anteriorly into a sharp andpointed end that arches anteroventrally (Fig. 4D). The maxilla-lacrimal joint prevents the jugal from contact with the nasal. Thepalatine joint on the medial side of the anterior process of thejugal is ellipsoidal and oblique. Heaton (1971) noted that thelacrimal flange of the maxilla participates in the articulation withthe anterolateral process of the palatine. In B. canadensis it isunlikely because of the distance separating the posterior edge ofthe lacrimal flange and the jugal-palatine articulation. At themiddle of its length, the dorsal edge of the jugal shows a long andslender postorbital process. Posteroventrally, the jugal expandsinto an oval boss. The quadratojugal process is dorsoventrallyexpanded and flared.

Quadratojugal—The quadratojugal (Fig. 4B) is dorsoven-trally deeper and mediolaterally thicker near its posterior bor-der. The element is anteriorly projected into a triangular edge.Two depressions are present on the medial side of the element,flush with the posterior edge. One is located posterodorsally andis relatively narrow. The other depression is deeper and locatedposteroventrally.

Lacrimal—The lacrimal (Fig. 5A, B) resembles that of M.peeblesorum (Horner, 1983) in its wedge-shaped, triangular lat-eral outline bordered by a horizontal ventral border. On its me-dial side the lacrimal shows a triangular posterodorsal processthat indents into the prefrontal. The posterior border of thelacrimal bears a dorsally projected process that borders the pos-teroventral edge of the prefrontal and inserts into a deep cleft onthe posterior side of this element. Whereas in B. canadensis thatprocess arches dorsomedially, in P. blackfeetensis it projectsstraight dorsally. Another dorsally projecting but shorter pos-teromedial process forms the medial wall of the lacrimal fora-men. The dorsal surface of this process receives the posteroven-tral process of the prefrontal. The medial lacrimal canal beginsanteriorly as a wide depression and exits through the dorsal thirdof the posterior border of the bone.

Prefrontal—Anterodorsal to the frontal articulation, the me-diodorsal border of the prefrontal is medioventrally tilted andjoins the lateral border of the nasal. The lateral edge of theprefrontal extends farther posteriorly over the orbit and overliesthe frontal extending parallel to the nasals. Along that posteriorsegment the prefrontal tapers as seen in dorsal view and extendsmedioventrally underneath the nasal crest (arrow on Fig. 5D).The dorsal side of the prefrontal contains a deep groove, parallelto the lateral border of the nasal, and ending anteriorly in a largeforamen, posterior to the supraorbital one. The supraorbital fo-ramen is located on the anterodorsal surface of the prefrontal, infront of the anterodorsal corner of the orbit. In that area somespecimens exhibit more than one foramen. The medial side ofthe anteroventral lamina of the prefrontal is separated from theventral surface of the anterodorsal roof of the orbit by a sharpridge; a triangular groove receives the posterodorsal process ofthe lacrimal (Fig. 5B). The anterior edge of the prefrontal over-laps a small portion of the posterodorsal end of the posteroven-tral process of the premaxilla. The anterodorsal rim of the orbitis crenulated and dorsally elevated relative to the dorsal surfaceof the skull.

Postorbital—The anterior, triangular, and rostrally directedprocess of the postorbital has an indented border as in the pre-frontal (Fig. 5C). Most of that anteromedial border joins thefrontal through a thick, crenulated suture. That border furtherprojects caudomedially, forming a process that meets the an-terodorsal and lateral crenulated border of the parietal, locateddorsal and adjacent to the laterosphenoid. The jugal processprojects anteroventrally and is slightly offset lateroventrally fromthe parasagittal plane to meet the jugal. Near the anterodorsalrim of the orbit the supraorbital foramen penetrates the postor-bital dorsoventrally.

Squamosal—The squamosal (Fig. 5E) is excluded from con-tacting its counterpart by the parasagittal crest of the parietal.The parietal process projects medially from the posterior cornerof the element. This process curves posteriorly and then anteri-orly, joining the supraoccipital ventrally. The postorbital processis dorsoventrally compressed and thins mediolaterally while ex-tending anteriorly. Its dorsal surface bears a deep groove thatreceives the squamosal process of the postorbital. The spike-likepre-quadratic process is relatively short in B. canadensis,whereas it is longer and more robust in other taxa, such as P.blackfeetensis, E. cf. E. annectens (MOR 003), and H. stebingeri.The postquadratic process projects lateroventrally and posteri-orly from the posterolateral corner of the squamosal. Mediallyand adjacent to the posterior concavity on the postquadraticprocess for the exoccipital is a shallow depression.

FIGURE 5. Left lacrimal and prefrontal of a subadult Brachylopho-saurus canadensis (MOR1071–8-5–99–447G) in (A) lateral and (B) me-dial views. C, left postorbital of a subadult B. canadensis (MOR 1071–7-13–99–87-G) in ventromedial view. D, ventral view of FMNH 862, apartial B. canadensis skull roof, showing the prefrontal underlying thenasal crest; the arrow points to the posterior edge of the prefrontal. E,right squamosal of a subadult B. canadensis (MOR 1071–7-13–99–87-H)in anterolateral view. F, fragment of right nasal of B. canadensis (UCMP130139) in laterodorsal view.

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Nasal—The nasal (Figs. 5C, F, 6A-C) extends from the an-terodorsal area of the external naris to the posterodorsal regionof the skull. Posterodorsally, the nasal forms a paddle-like crestthat covers either entirely or partially (depending on the speci-men) the supratemporal fenestra (see intraspecific variation forfurther details). The parasagittal plane of the skull is formed bythe articulation of the nasals. The nasal forms a sheet over therostrum of B. canadensis that is convex laterally throughout thelaterodorsal middle region and the anterodorsal portion of theskull. Anteriorly, the nasal consists of a central subtriangularbody from which three processes emerge. Two of these projectanteroventrally and articulate with the two processes of the pre-maxilla to collectively enclose the external naris. The third ex-tends posterodorsally over the skull forming the flat crest andcontacts the prefrontal and the frontal. The nasal crest overhangsthe parietal posterior to the articulation with the frontal. Thehook-like anterodorsal process of the nasal is very long andarches anteroventrally to form nearly the entire dorsal rim of theexternal naris. The anterodorsal process of the nasal overlapslaterally the posterodorsal process of the premaxilla, except forits anteriormost region, over which the nasal tapers anteroven-trally into a hooked end. The anteroventral process is very shortand reduced to a triangular wedge that forms the posteroventralborder of the external naris. Its ventral portion is medially re-cessed to join the posteroventral process of the premaxilla. Thecentral body of the nasal articulates with the prefrontal postero-ventrally. Along this articulation, the lateral convex wall of thenasal changes in orientation and forms the crest. At the anteriorportion of the crest the nasal forms a sharp lateral edge over theprefrontal and postorbital. The nasal overlaps dorsally with themediodorsal border of the prefrontal and fits into an excavationon the ventral side of the roof of the nasal. Medially, the centralbody of the nasal overlaps a portion of the anterodorsal region ofthe concave medial face of the lacrimal. The nasal also abuts thedorsal border of the lacrimal flange of the maxilla. The articu-lation with the frontal occurs ventrally, where the nasals overliethe posterodorsal surface of the skull. In a subadult individual(MOR 1071–8-5–99–447), the nasofrontal joint extends antero-posteriorly over two-thirds the length of the frontals. Mediolat-erally, this articulation is also limited to the two medial thirds ofthe frontal. The posterior end of the nasofrontal articulation isM-shaped in outline across both frontals and is bounded by asharp rim of bone. Posterior to the frontal joint, in all specimens,the nasal crest is supported ventrally by the expanded postero-medial portion of the prefrontal. The crest is solid and tongue-like, and contains the parasagittal plane of the skull. The jointbetween the two nasals forms a low ridge along the crest. Aforamen is located medial to the prefrontal (Fig. 6B, C). On theventral surface of the nasal, an anteroposteriorly directed narrowgroove emerges anteriorly from the foramen (arrows on Fig. 6C).On the dorsal surface another groove of similar proportions de-parts posteriorly from the foramen. Anteromedial to the nasalforamina, the ventral surface of the nasal contains a shallowbulge around the nasal joint.

Quadrate—The anteromedial pterygoid process is very ex-panded, trapezoidal, and curves slightly medially (Fig. 7A, B). Itsmedial surface is strongly concave where the posterodorsal andposteroventral quadrate processes of the pterygoid articulate. Asmall buttress hangs a short distance posteroventrally and later-ally from the posterior border of the quadrate head to meet theanterior side of the posteroventral process of the squamosal.

Palatal Complex

Pterygoid—Anteriorly, a vaulted, folded palatine ramus pro-jects anterodorsally (Fig. 7A, B). A shorter process projects ven-trally to contact the posterior end of the maxilla and theectopterygoid laterally. The dorsal quadrate wing is a triangular

lamina that projects caudodorsally and laterally. The ventralquadrate ramus is caudoventrally and laterally projected. On themedial side, a strongly buttressed process projects caudomediallyfrom the center of the element. The palatine ramus links withthis buttress, which is also linked to the ventral quadrate andectopterygoid processes by two thin flanges. Longitudinally thepalatine ramus is about one third longer than the dorsal quadratewing. As in M. peeblesorum (Trexler, 1995), the lateral border ofthe palatine ramus possesses a dorsal expansion in the form of asmall flange near its anterodorsal sharp end.

Palatine—The ventral elongated maxillary segment splits ros-trally into the anterolateral and anterodorsomedial processes(Fig. 7C). At its anterior extreme, a sharp ridge divides the ven-tral side of the palatine into a deep, lateral cleft and a shallow,medial, and rugose surface. A mediolaterally compressed pyra-midal, rugose, and sharp elevation of the dorsomedial ridge ofthe maxilla fits into a corresponding concavity on the ventralgroove of the palatine. The anterolateral jugal process of thepalatine is compressed and dorsoventrally expanded distally.The anterodorsomedial process of the palatine is a fan-shapedflange of bone that contacts the palatine ramus of the pterygoid.Horner (1992) indicates that in P. blackfeetensis the palatinemeets the lacrimal, but this joint is not observed in B. canadensis.

Ectopterygoid—The ectopterygoid (Fig. 7D) is an L-shapedsheet of bone, elongated anteroposteriorly and compressed dor-soventrally. In B. canadensis, the ectopterygoid is proportionate-ly longer than that in M. peeblesorum but shorter than that in E.annectens. In B. canadensis the rostral long segment thins moregradually than does that in M. peeblesorum. The ectopterygoid isgradually expanded mediolaterally near its posterior border. Theposterodorsal corner of the ectopterygoid is dorsoventrallythickened and shows a posteromedially facing process (the tri-angular, ventrally projecting process of Trexler, 1995). In M.peeblesorum, this triangular process is more elongated, and itsposterodorsal edge is not blended into the medial side of thebone. In contrast, in B. canadensis the process has only a ventralapex and an anteroventral sharp edge, being less defined and lesstriangular.

Neurocranial Complex

Frontal—The nasofrontal joint (Fig. 8A, white arrow) consistsof a wide M-shaped area that extends along two thirds of thedorsal surface of the frontal. The frontals contribute to the roofof the posterior half of the skull, including the medial side of theorbital cavity and the olfactory and cerebral cavities. The inter-frontal articulation is posterodorsally elevated at the parietalcontact. Anteriorly the frontal is dorsoventrally thinner. As in M.peeblesorum, but unlike that of P. blackfeetensis and other had-rosaurines, the frontal forms a small portion of the dorsal rim ofthe orbit, between the prefrontal and the postorbital (Sternberg,1953). Anterior to its contribution to the orbit, the dorsal surfaceof the frontal is ventrally recessed and slightly curved ventrally,showing a deep fossa that is penetrated by the posteromedialtriangular process of the prefrontal. Ventrally, a notch boundedby an anterolateral hook-like projection of the frontal receivesthe posteromedial end of the posteromedial ridge of the prefron-tal. Ventrally, the anteromedial half of the cerebral cavity isbounded by the interfrontal articulation, whereas its posteriorhalf is limited by the parietal joint. A short ridge separates thepresphenoid from the orbitosphenoid articulation and anteriorlyseparates the olfactory from the orbital depression. A low ridgeseparates the orbital from the olfactory depression.

Parietal—The parasagittal crest is relatively high and extendsalong the anteroposterior length of the element (Fig. 8A). Thecrest is taller and thicker at the squamosal articulation. The an-terolateral postorbital process is curved. The central anteriorprocess shows a crenulated border and forms a triangular wedge

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FIGURE 6. A, Brachylophosaurus canadensis skull, MOR 794, in left lateral view. B, ventral view of the skull roof MOR 1071–7-7–98–86; therectangle indicates the area shown in C. C, ventral view of the nasal of MOR 1071–7-7–98–86, showing the location of the groove and foramina(arrows).

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that fits between the posteromedial corners of both frontals andseparates the interfrontal suture. On the ventral surface asmooth convexity lies between the cerebral cavity and its poste-rior canal, where the parietal is wider. The prootic contacts theventral lateral border of the supraoccipital, posterior to the lat-erosphenoid, but does not join the parietal.

Presphenoid—The presphenoid (Fig. 8B, C) consists of a con-vex wall of bone that is briefly projected anteroventrally. Thebone abuts rostrodorsally the ventral surface of the olfactorydepression of the frontal. Unlike in P. blackfeetensis (Horner,1992), the presphenoid does not join the parasphenoid.

Orbitosphenoid—The orbitosphenoid (Fig. 8B, C) is slightlyrounded anteriorly and extends posteriorly encasing the olfac-tory foramen. The posterior half of the orbitosphenoid wedgesposteroventrally under the anteroventral border of the lateros-phenoid. The dorsal trochlear foramen is located in the lateros-phenoid, posterior to the rounded termination of the orbitosphe-noid. Ventrally, the second foramen is more elongated and iscontained in the orbitosphenoid. The ventral surface of the or-bitosphenoid forms the dorsal roof of the optic foramen. Theposterior wedge-like extension of the orbitosphenoid contributesto the anterodorsal inner face of the oculomotor foramen.

Laterosphenoid—In the laterosphenoid (Fig. 8B, C), the or-bitosphenoid process is relatively small and forms a tongue-likeexpansion anteromedial to the ventral ridge of the postorbitalprocess. The prootic and the postorbital processes form a con-cave and posterolaterally facing surface, located adjacent and

posterior to the caudal limit of the orbital cavity anterior to thecrista prootica. The postorbital process is relatively short whencompared to other specimens, such as the lambeosaurinesAMNH 5248 and 5433. The prootic process is compressed me-diolaterally, deep dorsoventrally, and projects posteriorly. Thebasisphenoid process is subrectangular and forms the anteriorboundary of the trigeminal foramen, comprising the trigeminalgroove and extending ventrally. The posterior border of the ba-sisphenoid process joins the prootic. This joint forms the antero-ventral limit of the trigeminal foramen.

Prootic—The prootic (Fig. 8C) does not contact the parietaldue to the intervening supraoccipital. A large subtriangular pro-cess attaches to the opisthotic-exoccipital complex on its medialside. The prootic contributes to the trigeminal foramen dorsally,forms most of its ventral rim, and also its posterior boundary bymeans of a sharp edge. The anteroventral laterosphenoid processis subrectangular, mediolaterally expanded, and strongly con-cave laterally. The anterodorsal laterosphenoid process curvesdorsomedially and meets the intervening supraoccipital medio-dorsally. The facial foramen penetrates ventrally the centralbody of the prootic. The posterior central border of the prooticcontributes to the anterior half of the fenestra ovalis. A small,triangular process protrudes posteriorly from the inner portionof its lateral wall.

Opisthotic-Exoccipital—The paroccipital process (Fig. 8B, C)is anteroventrally and laterally directed, as in other hadrosau-rines, but unlike the lambeosaurines AMNH 5248 and 5433,where the process is posteroventrally and laterally directed. An-terior to the proximal end of the paroccipital process is the jointfor the prootic posterodorsal process. The wing-like supraoccipi-tal process is compressed dorsoventrally. At its anterior end, aridge connects this process with the medial surface of the basi-occipital process. Posteriorly, a smooth, triangular depressionsurrounds the dorsal portion of the foramen magnum. The ba-sioccipital process is subrectangular, compressed, and expandedanteroposteriorly. Anteriorly, the basioccipital process forms theposterior half of the fenestra ovalis.

Supraoccipital—The supraoccipital fuses with the exoccipitalsto form a dorsoventrally thin roof posterodorsal to the foramenmagnum. The element forms a greatly excavated and crescenticarea on the dorsal surface of this roof. In MOR 1071–7-13–99–87-I, a disarticulated braincase from a subadult individual, thesupraoccipital is subrectangular and wedges anteriorly betweenthe parietal above and the prootic below.

Basioccipital—The basioccipital (Fig. 8C) is anteroposteriorlylonger than mediolaterally wide. The basisphenoid-basioccipitaljoint is oblique and directed anteroventrally. Anterolaterally, thebasioccipital fuses with the prootic along a small portion of itsventrolateral border, between the basisphenoid-prootic and theopisthotic-prootic joints. Posteriorly, the basioccipital articulateswith the opisthotic ventral to the line of foramina for cranialnerves IX, X, XI, and XII. Posteroventrally, the basioccipitaljoins the exoccipitals to contribute ventrally to the occipital con-dyles.

Basisphenoid—In the basisphenoid (Fig. 8B, C) the postero-ventral constriction is relatively narrow mediolaterally. It boundsventrally the large ellipsoidal foramen that houses the internalcarotid artery through the carotid canal, a pathway of the facialnerve. In B. canadensis and M. peeblesorum, the alar processesare relatively large and well developed. The triangular surfacelocated between the pterygoid processes is flattened, in contrastto the depressed one present in other taxa such as Saurolophusosborni.

Parasphenoid—The parasphenoid (Fig. 8B) is fused to thebasisphenoid and probably consist only of the cultriform process.As in M. peeblesorum (Trexler, 1995), the anterior tip of thecultriform process is U-shaped and concave dorsally. Likewise, it

FIGURE 7. Brachylophosaurus canadensis right quadrate and pterygoid(MOR 1071) in (A) lateral and (B) posteromedial views. C, B. canaden-sis right palatine (MOR 1071–7-16–98–248S) in lateral view. D, left B.canadensis ectopterygoid (MOR 1071–8-13–98–559E) in medioventralview.

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FIGURE 8. A, dorsal view of the frontal of a subadult Brachylophosaurus canadensis skull (MOR 1071–8-5–99–447). The black arrows point to thefrontal depressions; the white arrow is placed on the surface of the nasofrontal joint and points to its posterior boundary. B, anterior and C, lateralviews of the braincase of B. canadensis (MOR 1071–7-7–98–86).

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is slightly arched longitudinally and posteriorly expanded dor-sally.

Intraspecific Morphological Variation

Specimens MOR 794, MOR 1071, and FMNH 862 show indi-vidual and ontogenetic morphological variation. Subadult speci-mens are approximately 50–60% of the size of the largest speci-mens (considered adult size). MOR 794 is an articulated skullmeasuring 830 mm in maximum length and 390 mm in maximumdorsoventral length. MOR 794, FMNH 862, and the two articu-lated skull roofs, MOR 1071–7-7–98–86 and MOR 1071–7-16–98–248, present the same size. Although only MOR 794 pre-serves the rostral half of the cranium, all four specimens measureapproximately 250 mm in mediolateral width across the pos-terodorsal edge of the orbits.

The following observations are based on the partial articulatedsubadult skull MOR 1071–8-5–99–447. The preorbital region ofthe subadult skull is shorter anteroposteriorly. The subadultskull shows relatively larger openings and proportionately largerforamina in the braincase. The subadult orbital cavity and theelements surrounding it are proportionately large. In subadults,the postorbital and prefrontal are near the size of those of theadult specimens. The brain cavity and the mediolateral breath ofthe laterosphenoids is narrow, but neurocranial foramina areproportionately large. The prefrontal is not extended caudallyand medially in subadults, a difference probably associated witha lesser development of the nasal crest.

Individual variation led to the recognition of a relatively ro-bust morphotype and a slender one. Each morphotype has thesame size range (as noted above) and there is a proportion of50% for each morphotype of the total sample of articulated cra-nia. The presence of intraspecific robust and slender morpho-types has been recognized in other dinosaur taxa, such as thero-pods (Carpenter, 1990; Raath, 1990) and ceratopsians (Lehman,1990). The robust morphotype is exemplified by MOR 794 (com-plete skeleton), MOR 1071–7-16–98–248-Q (jugal), and FMNH862 (partial skull roof). In this morphotype, the nasal crest ex-tends to the dorsal border of the squamosal, covering the supra-temporal fenestra and slightly widening posteriorly (Fig. 9B). Inextending farther caudally and medially underlying the nasal, theprefontal forms a sharp lateral border along the dorsolateraledge of the skull that ends caudal to the orbit. Other morpholo-gies found only in MOR 794 and FMNH 862 are: a relativelymore massive and deeper dentary; a deeper jugal with distinctivedeeper anterior processes, wider boss, and less dorsoventrallynarrowed segment between the anterior and postorbital andquadratojugal processes; and a relatively greater ornamentationof the postorbital. The slender morphotype is exemplified by thetwo skull roofs, MOR 1071–7-16–98–248 and MOR 1071–7-7–98–86, and cranial material from the bone bed associated withthese specimens. In this morphotype, the nasal crest does notreach the squamosal and is mediolaterally narrower. The crestcovers little more than half the width of the supratemporal fe-nestra, and posteriorly it narrows mediolaterally (Fig. 9A). Theprefrontal does not extend posterior to the orbit.

PHYLOGENETIC ANALYSIS

A phylogenetic analysis is intended to reassess the position ofB. canadensis within hadrosaurids but is not intended to revisethe clade as a whole. I used 43 characters from a recent characterlist for the Hadrosauridae (Horner et al., in press) and 4 newcharacters not previously included in any hadrosaurid phyloge-ntic analysis (see discussion below and Appendix 1). Because myanalysis focused on the relationships within the Hadrosaurinae,only one of the ten selected taxa was chosen to represent theLambeosaurinae (H. stebingeri, because their remains were

available to the author for examination). Iguanodon bernissar-tensis was chosen as outgroup taxon to the Hadrosauridae sensuHead (1998). Only hadrosaurines with complete skeletal repre-sentation were included, and only those personally examined atthe Museum of the Rockies, including P. blackfeetensis, M.peeblesorum, species of Edmontosaurus, and Gryposaurus sp.The character list and data matrix are given in Appendices 1 and2. The 47 characters were equally weighted and analyzed withACCTRAN transformation. Two most-parsimonious trees of 79steps resulted from both exhaustive and branch-and-boundsearches in PAUP (Swofford, 2000), with a consistency index of0.76 and a retention index of 0.72 (Fig. 10). The strict-consensus,50% majority-rule, and bootstrap trees show the same topologyas the two trees provided by the branch-and-bound search, ex-cept that Telmatosaurus transsylvanicus is the most basal taxonafter I. bernissartensis in one cladogram, and Protohadros byrdiis the most basal taxon in the other (Fig. 10). These results addfurther support to the hypothesis that B. canadensis is the sistertaxon to Maiasaura and that the two taxa form a basal cladewithin the Hadrosaurinae (Weishampel and Horner, 1990; Hor-ner, 1992). The B. canadensis-M. peeblesorum clade is one of themost robust in the hadrosaurid phylogeny and is supported bythe following synapomorphies: predentary with anterior medio-lateral breath twice anteroposterior length of lateral processes;premaxilla with ventrally deflected anterior corner; symmetrical,pointed, and triangular anterior process of jugal; short squamosalprequadratic process only slightly longer than anteroposteriorwidth of quadrate cotylus; large development of alar process ofbasisphenoid; and presence of plantar keel on pedal unguals. Thenext most inclusive clade that includes B. canadensis (a di-chotomy composed of the B. canadensis-M. peeblesorum, andthe G. sp -P. blackfeetensis-S. osborni clades) is based on thepresence of a solid nasal or nasofrontal crest over the snout orbraincase and the inclusion of the nasal bone in this crest. In thepresent analysis, the genus Gryposaurus is not included in theBrachylophosaurus-Maiasaura clade, in contrast to previous

FIGURE 9. A, dorsal view of MOR 1071–7-7–98–86, one of the twoarticulated Brachylophosaurus canadensis skull roofs collected from theMalta bonebed. B, B. canadensis skull, MOR 794, in dorsal view.

PRIETO-MARQUEZ—CRANIUM OF BRACHYLOPHOSAURUS 153

studies (the Kritosaurini of Brett-Surman, 1989; Weishampel andHorner, 1990). Instead, it is considered here the sister taxon tothe Prosaurolophus-Saurolophus clade. This new position is po-tentially unstable because it is based on a single character: thepresence of a narrow reflected rim along the whole border of thepremaxilla, as observed in RTPM 80–22–1.

DISCUSSION AND CONCLUSION

In 1988, Horner emended Sternberg’s diagnosis of the genusBrachylophosaurus. He characterized the taxon as having a solid,low, sheet-like nasal crest that is directed posteriorly, a nasaldepression that does not extend to the crest, a lightly constructedjugal with a ventrally projecting boss, and a cranioposteriorlyshort supraoccipital-exoccipital roof posterior to the foramenmagnum (Horner, 1988, emended diagnosis). This diagnosis hasbeen extended here to accommodate additional autapomor-phies, such as the presence of a foramen on the nasal, medial tothe prefrontal, and the presence of a prefrontal that extendsposteromedially, underlying the nasal crest. In the same paperthe species B. goodwini was described, named, and diagnosed onthe basis of fragmentary cranial elements from the Judith RiverFormation of Montana. The diagnosis of B. goodwini consistedof a deep and rounded dorsal depression or pit at or near thejunction of the frontal and postorbital, dorsally concave upperprocess of the nasal, contact of the posterolateral surface of thenasal with the orbital rim, and quadratojugal process of the jugalparallel with postorbital process (Horner, 1988). The depressionon the dorsal surface of the frontal near the postorbital joint hasalso been found other specimens, such as for example MOR1071–7-13–99–87-I (Fig. 8A, black arrows) and MOR 1071–6-30–98–4. These depressions are elongated rather than rounded, butindividual and/or ontogenetic variation might well account forthat difference. This trait has not been considered here an auta-pomorphy of B. canadensis because it is also present in otherhadrosaurids, such as in a lambeosaurine braincase (AMNH5248). The nasal characters result from the reconstruction ofUCMP 130139 (Fig. 5F), a nasal fragment in a very poor condi-tion of preservation. UCMP 130139 was interpreted as having a

concave relief, in contrast to the arched relief of the holotype andthe other specimens of B. canadensis. However, the UCMP nasalwas incorrectly oriented, as evidenced by comparisons with thewell-preserved specimens MOR 794 and MOR 1071. What wasdescribed as the dorsal edge of UCMP 130139 is actually theventral border. Therefore, UCMP 130139 corresponds to therostral preorbital facial sheet of the nasal, drawing the convexdorsal outline seen in all B. canadensis skulls. The parallelismbetween the quadratojugal and postorbital processes of the jugalis a case of individual variation. MOR 794 shows jugals withpostorbital processes only slightly divergent. The bone-bedspecimens show variation in the divergence between the postor-bital and quadratojugal processes, coupled with a remarkablevariation in the size and shape of the quadratojugal process.Therefore, B. goodwini is considered invalid and a junior syn-onym of B. canadensis.

Two of the new characters that are proposed in the presentstudy are the length of the pre-quadratic process of the squamo-sal and the relative proportions of the anteroposterior and me-diolateral dimensions of the predentary. I hypothesize that thebasal condition of the hadrosaurid squamosal, exemplified by M.peeblesorum and B. canadensis, is characterized by a pre-quadratic process that is only slightly longer than the width of thequadrate cotylus. In the remaining hadrosaurids, the pre-quadratic process is much longer than the quadrate cotylus, as inP. blackfeetensis and E. annectens. The ratio of the mediolateralbreath of the predentary to the length of the lateral bars sets M.peeblesorum and B. canadensis apart from the remaining hadro-saurids. The predentary of these two hadrosaurids is twice asbroad mediolaterally as it is long anteroposteriorly, a conditionhere considered derived, at least among the examined taxa.Primitively, the predentary is as wide as it is long, as in I. ber-nissartensis and P. byrdi. The predentary becomes wider thanlonger in hadrosaurines such as P. blackfeetensis and the genusGryposaurus, and also in lambeosaurines, such as H. stebingeri.This trend is further expressed in M. peeblesorum and B.canadensis.

AKNOWLEDGMENTS

I am grateful to my mentor at Montana State University, JohnR. Horner, for opening for me the door to dinosaur research. Iam very grateful to Mr. Terry and Mrs. Mary Kohler for fundingthis project. Thanks also go to graduate students Jill Holiday andJeff LaRock, and to Professors James G. Schmitt, David J. Var-ricchio, David B. Weishampel, Carlos Bonet, and especiallyGregory Erickson and Anne Thistle, whose reviews greatly im-proved this manuscript. Thanks go to Catherine A. Forster,David B. Weishampel, and John R. Horner for allowing me theuse of their character list for the Hadrosauridae.

LITERATURE CITED

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Brett-Surman, M. K. 1989. A revision of the Hadrosauridae (Reptilia:Ornithischia) and their evolution during the Campanian and Maas-trichtian. Unpublished Ph.D. dissertation, George Washington Uni-versity, Washington D.C., 272 pp.

Buffetaut, E., and H. Tong-Buffetaut. 1993. Tsintaosaurus spinorhinusYoung and Tanius sinensis Wiman: a preliminary comparative studyof two hadrosaurs (Dinosauria) from the Upper Cretaceous ofChina. Comptes Rendus de l’Academie de Sciences II 317:1255–1261.

Carpenter, K. 1990. Variation in Tyrannosaurus rex; pp. 141–145 in K.Carpenter and P. J. Currie (eds.), Dinosaur Systematics: Ap-proaches and Perspectives. Cambridge University Press, New York.

FIGURE 10. Strict consensus cladogram showing the evolutionary po-sition of Brachylophosaurus canadensis within the Hadrosaurinae; num-bers represent only unambiguous synapomorphies, and numbers in pa-rentheses represent character states, corresponding to those listed inAppendix 1.

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Casanovas, M. L., X. Pereda Suberbiola, J. V. Santafe, and D. B.Weishampel. 1999. First lambeosaurine hadrosaurid from Europe:palaeogeographical implications. Geological Magazine 136:205–211.

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Harmon, R. 1997. The excavation and recovery of an articulated adultBrachylophosaurus skeleton. Journal of Vertebrate Paleontology17(3, supplement):51A.

Head, J. J. 1998. A new species of basal hadrosaurid (Dinosauria, Orni-thischia) from the Cenomanian of Texas. Journal of Vertebrate Pa-leontology 18:718–738.

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Horner, J. R. 1983. Cranial osteology and morphology of the type speci-men of Maiasaura peeblesorum (Ornithischia: Hadrosauridae), withdiscussion of its phylogenetic position. Journal of Vertebrate Pale-ontology 3:29–38.

Horner, J. R. 1988. A new hadrosaur (Reptilia, Ornithischia) from theUpper Cretaceous Judith River Formation of Montana. Journal ofVertebrate Paleontology 8:314–321.

Horner, J. R. 1992. Cranial Morphology of Prosaurolophus (Ornithis-chia: Hadrosauridae) with Descriptions of Two New HadrosauridSpecies and an Evaluation of Hadrosaurid Phylogenetic Relation-ships. Museum of the Rockies, Bozeman, Montana, 119 pp.

Horner, J. R., D. B. Weishampel, and C. A. Forster. In press. Hadro-sauridae; in D. B. Weishampel, P. Dodson, and H. Osmólska (eds.),The Dinosauria, 2nd edition. University of California Press, Berke-ley.

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Lehman, T. M. 1990. The ceratopsian subfamily Chasmosaurinae: sexualdimorphism and systematics; pp. 211–229 in K. Carpenter and P. J.Currie (eds.), Dinosaur Systematics: Approaches and Perspectives.Cambridge University Press, New York.

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Raath, M. A. 1990. Morphological variation in small theropods and itsmeaning in systematics: evidence from Syntarsus rhodesiensis; pp.91–105 in K. Carpenter and P. J. Currie (eds.), Dinosaur Systemat-ics: Approaches and Perspectives. Cambridge University Press, NewYork.

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Trexler, D. 1995. Detailed description of newly discovered remains ofMaiasaura peeblesorum (Reptilia: Ornithischia) and revised diagno-sis of the genus. Unpublished MS thesis, University of Calgary, Al-berta, 217 pp.

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Submitted 20 January 2004; accepted 31 March 2004.

APPENDIX 1

Characters and character states used for reassessing the phylogeneticposition of B. canadensis. Characters were taken from a character list inHorner et al. (in press), except 12, 38, 39, and 47. Characters 5, 9, 15, 29,and 34 have been modified from the list in Horner et al. (in press).

Skull

1. Number of tooth positions in dentary and maxillary tooth rows: 30 orless (0); 34–40 (1); 42–45 (2); 47 or more (3).

2. Number of replacement teeth per tooth position: 1–2 (0); 3 or more(1).

3. Number of functional teeth per tooth position: one (0); at least two,and often three, teeth in vertical series contributing to occlusal sur-face (1).

4. Maxillary tooth crown length-to-width ratio: broad relative to length,ratio less than 2.4:1 (0); lanceolate, ratio at least 2.5:1 (1).

5. Dentary tooth crown length-to-width ratio at center of tooth row: 3:1or less (0); 3.2–3.8:1 (1); �4:1 (2). Originally, this character wasstated as: relatively broad, ratio of 2.9:1 or less (0); elongate, ratio of3.2–3.8:1 (1) (Horner et al., in press). However, the last ratio hasbeen modified here to accommodate the observed range in H. ste-bingeri.

6. Dentary teeth, ornamentation on lingual surface: numerous subsid-iary ridges present (0); one or two subsidiary ridges present (1); allbut primary carina absent (2).

7. Maxillary teeth, ornamentation on labial surface: numerous subsid-iary ridges present (0); one or two subsidiary ridges present (1); allbut primary carina absent (2).

8. Teeth, position of apex: offset (0); central, tooth straight and nearlysymmetrical (1).

9. Dentary, length of diastema between first dentary tooth and preden-tary: short, no more than width of 3–4 teeth (0); moderate, equal to1/4 or 1/3 of tooth row (1); long, more than 1/3 of tooth row but lessthan 1/2 (2); extremely long, more than 1/2 tooth row length (3). Thischaracter was originally stated by Horner et al. (in press) as: short, nomore than width of 4 or 5 teeth (0); long, equal to approximately 1/5to 1/4 length of tooth row (1); extremely long, equal to approximatelyone third of tooth row (2). It has been modified here to better ac-commodate the range of ratios observed in the examined specimensof P. blackfeetensis, E. annectens, B. canadensis, M. peeblesorum, andGryposaurus sp.

10. Dentary tooth row, posterior extent of dentary tooth row relative toapex of coronoid process: even with or anterior to (0); posterior (1).

11. Dentary, anterior portion: moderately downturned, dorsal margin ofpredentary resting above ventral margin of dentary body (0); strik-ingly downturned, dorsal margin of anterior dentary extending belowventral margin of dentary body, premaxillary bill margin extendingwell below level of maxillary toothrow (1).

12. Predentary relative proportions: anterior mediolateral width ilessthan or equal to anteroposterior length of lateral processes (0); an-terior mediolateral width greater than anteroposterior length of lat-eral processes (1); anterior mediolateral width twice anteroposteriorlength of lateral processes (2).

13. Angular size: large, deep, broadly exposed in lateral view (0); small,dorsoventrally narrow, exposed only in medial view (1).

14. Coronoid process configuration: apex only slightly expanded anteri-orly, surangular large and forming much of posterior margin of coro-noid process (0); dentary forming nearly all of greatly anteroposte-

PRIETO-MARQUEZ—CRANIUM OF BRACHYLOPHOSAURUS 155

riorly expanded apex, surangular reduced to thin sliver along poste-rior margin and not reaching distal end of coronoid process (1).

15. Premaxilla reflected rim: absent (0); deflected at anterolateral cornerand posteriorly reflected (1); reflected along entire rim and narrow(2); reflected along entire rim, but thickend at anteroventral corner(3). This character was originally stated by Horner et al. (in press) as:premaxilla, undercut (“reflected”) rim around oral margin absent(0); present (1). The presence of a reflected rim has been split intotwo states to accommodate the variation seen in the way the pre-maxilla is reflected in hadrosaurids.

16. Premaxillary foramen ventral to anterior margin of external naresthat opens onto palate: absent (0); present (1).

17. Premaxilla, auxiliary narial fossa: absent (0); present (1).18. Premaxillary posterior processes (PM1, PM2) and nasal passages:

posterodorsal premaxillary process short, processes not meeting pos-terior to external nares, nasal passges opening ventrally beneath na-sals (0); both processes posteriorly elongate, joining behind externalnares to exclude nasals, nasal passage enclosed ventrally by folded,divided premaxillae (1).

19. External nares/basal skull length ratio: 20% or less (0); 30% or more(1).

20. External nares, composition of posteriormost apex: formed entirelyby nasal (0); formed equally by nasal (dorsally) and premaxilla (ven-trally) (1).

21. Circumnarial fossa, posterior margin: absent (0); light depressionincised into nasal and premaxilla (1); well demarcated, deeply in-cised, and usually invaginated (2).

22. Nasals and anterodorsal premaxilla in adults: flat, restricted to areaanterior to braincase, cavum nasi small (0); premaxilla extended pos-teriorly and nasals retracted posteriorly to lie over braincase inadults resulting in convoluted, complex narial passage and hollowcrest, cavum nasi enlarged (1).

23. Hollow nasal crest: absent (0); present (1).24. Solid nasal or nasofrontal crest over snout or braincase, not housing

portion of nasal passage: absent (0); present (1).25. Solid nasal crest, association with posterior margin of circumnarial

fossa: absent, circumnarial fossa not excavating side of crest (0);present, circumnarial fossa not excavating lateral side of crest (1);present and excavated laterally by circumnarial fossa (2).

26. Solid crest composition: absent (0); nasals only (1); frontals and na-sals (2).

27. Maxilla, anterodorsal process: with separate anterior process extend-ing medial to posteroventral process of premaxilla to form part ofmedial floor of external naris (0); forming sloping shelf contactingposteroventral process of premaxilla (1).

28. Maxillary foramen: opening on anterolateral maxilla (0); opening ondorsal maxilla along maxilla-premaxilla suture (1).

29. Lacrimal-maxilla contact: present (0); extremely reduced, only ante-rior sharp tip of lacrimal contacting maxilla (1); lost or covered asresult of jugal-premaxilla contact (2). This character was originallystated by Horner et al. (in press) as: maxilla-lacrimal contact present(0); lost or covered due to jugal-premaxilla contact (1). An additionalstate has been added to include the condition observed in B.canadensis.

30. Maxilla, apex location: posterior to center (0); at or anterior to center(1).

31. Maxilla, shape of apex in lateral exposure: tall and sharply peaked(0); low and gently rounded (1).

32. Jugal, anterior shape: with distinct, anteriorly-pointed process fittingbetween maxilla and lacrimal (0); truncated, rounded anterior mar-gin (1).

33. Jugal, anteriorly pointed process: absent (0); present, restricted todorsal portion of jugal, anterior jugal appearing symmetrical (1);present, centered on anterior jugal, anterior jugal appearing sym-metrically triangular in shape (2).

34. Jugal, flange size: slightly developed, dorsoventral depth of jugalfrom ventral border of infratemporal fenestra to ventral edge offlange approximately equal to minimum dorsoventral depth of an-terior segment of jugal between anterior and postorbital process (0);dorsoventral depth of jugal from ventral border of infratemporalfenestra to ventral edge of flange less than twice minimum dorso-ventral depth of anterior segment of jugal between anterior andpostorbital process (1); strongly projected ventrally into semicircularboss, dorsoventral depth of jugal from ventral border of infratem-poral fenestra to ventral edge of flange twice or nearly twice mini-mum dorsoventral depth of anterior segment of jugal between ante-rior and postorbital process (2). Horner et al. (in press) originallystated this character as: depth of jugal at constriction below lowertemporal fenestra/free ventral flange on jugal: small, .70-.90 (0);prominent, well set off from body of jugal, .55-.66 (1). It has beenmodified here to better accommodate the variation observed in P.blackfeetensis, E. annectens, B. canadensis, M. peeblesorum, and Gry-posaurus sp.

35. Frontal at orbit margin: forming part of margin (0); excluded byprefrontal-postorbital joint (1).

36. Squamosals on skull roof, separation: widely separated (0); squamo-sals separated by narrow band of parietal (1); squamosals havingbroad contact with each other (2).

37. Squamosal, shape of posteroventral surface: nearly horizontal (0);“folded” down to form near-vertical face in posterior view (1).

38. Squamosal prequadratic process: short, only slightly longer than an-teroposterior width of quadrate cotylus or dorsal head of quadrate (0);strikingly longer than anteroposterior width of quadrate cotylus (1).

39. Basisphenoid, relative size of alar process: process relatively small(0); process relatively large and very expanded (1).

Postcranium

40. Cervical vertebrae, number: 11 or fewer (0); 12 to 15 (1).41. Dorsal (posterior) and sacral neural spines: relatively short, less than

3 times centrum height (0); elongate, more than 3 times centrumheight (1).

42. Deltopectoral crest: short, much less than half length of humerus,narrowing distally (0); extending at least to midshaft or farther, dis-tally broad (1).

43. Ischium, shape of distal end: small, knob-like (0); large and pendantfoot (1).

44. Pubis, distal width of prepubic blade: dorsoventrally expanded to nomore than twice shaft width (0); greatly expanded to more than twiceshaft width (1).

45. Pubis, length of prepubic shaft: long, dorsoventral expansion re-stricted to distal process (0); neck short, dorsoventral expansion be-ginning almost at base of process (1).

46. Pes, distal phalanges of pedal digits II through IV: axially shortenedto disc-like elements with width at least 3 times length (0); greatlyshortened, width at least 4 times length (1).

47. Pes, plantar keel on unguals: absent (0); present (1).

APPENDIX 2. Character matrix. For a list of characters, see Appendix 1.

Characters

1–5 6–10 11–15 16–20 21–25 26–30 31–35 36–40 41–45 46–47

I. bernissartensis 00000 00000 00000 00000 00000 00000 001?0 000?0 00000 00P. byrdi 1???? ???00 10100 000?? ?00?? 00??0 00000 ????? ????? ??B. canadensis 21110 21121 02111 11010 10011 10011 00220 11011 01010 11E. annectens 31110 21131 0?113 11011 10000 00021 00110 111?1 01010 10Gryposaurus sp. 21110 21111 01112 11010 10010 10001 00120 111?1 01010 10H. stebingeri 21111 11101 11110 001?? 01100 01121 11011 21101 11111 10M. peeblesorum 21110 21111 02111 11000 10011 200?1 00220 11011 01010 11P. blackfeetensis 21110 21121 01112 11011 10012 10001 00111 11101 01010 10S. osborni 31110 21111 0?112 01001 10012 10001 00111 211?1 01000 1?T. transsylvanicus 01011 11001 0?000 ?0000 00000 000?1 00200 00??? 0???? ??

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