Canadian Journal of Earth Sciences

Cranial variation in Gryposaurus and biostratigraphy of hadrosaurines (Ornithischia: Hadrosauridae) from the Dinosaur Park Formation of Alberta, Canada

Journal: Canadian Journal of Earth Sciences

Manuscript ID cjes-2019-0073.R1

Manuscript Type: Article

Date Submitted by the 17-Aug-2019 Author:

Complete List of Authors: Lowi-Merri, Talia; Royal Ontario Museum, Department of Natural History; University of Toronto, Ecology & Evolutionary Biology Evans, David C.; Royal Ontario Museum, Department of Natural History; University Draftof Toronto, Ecology & Evolutionary Biology dinosaur, geometric morphometrics, biostratigraphy, allometry, Keyword: Hadrosauridae

Is the invited manuscript for consideration in a Special Not applicable (regular submission) Issue? :

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1 Cranial variation in Gryposaurus and biostratigraphy of hadrosaurines (Ornithischia:

2 Hadrosauridae) from the Dinosaur Park Formation of Alberta, Canada

3

4 Talia M. Lowi-Merria,b* and David C. Evansa,b

5

6 Affiliations

7 a. Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks St. Rm

8 3055, Toronto, ON M5S 3B2, Canada

9 b. Department of Natural History, Royal Ontario Museum, 100 Queens Park, Toronto, ON M5S

10 2C6, Canada 11 Draft 12 *Corresponding Author

13 Talia M. Lowi-Merri

14 E-mail Address: [email protected]

15 Mailing Address: Department of Natural History, Royal Ontario Museum, 100 Queens Park, Toronto,

16 ON M5S 2C6, Canada

17 Telephone number: +1 416-300-3757

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26 ABSTRACT

27 The Dinosaur Park Formation (Campanian) of Alberta documents one of the most diverse

28 assemblages of hadrosaurine dinosaurs. Historically, two species of the genus Gryposaurus have

29 been recognized in the Dinosaur Park Formation, G. notabilis and G. incurvimanus, which are

30 differentiated primarily on their nasal arch morphology. These two species have recently been

31 suggested to represent either variable morphs within G. notabilis (e.g., ontogeny) or two distinct

32 taxa within an evolving Gryposaurus lineage (e.g., anagenesis). These alternative hypotheses

33 have never been adequately tested via detailed morphological comparisons, morphometrics, or

34 biostratigraphy. A geometric morphometric analysis of hadrosaurine skulls from the Dinosaur

35 Park Formation was performed to assessDraft the influence of ontogeny on skull morphology. G.

36 incurvimanus skulls were found to be distinctly smaller, and morphologically divergent from

37 those of G. notabilis, with larger G. notabilis skulls having higher nasal arches set farther back

38 on the skull, a feature commonly seen in adult individuals of other hadrosaurids, such as

39 Brachylophosaurus and lambeosaurines. Stratigraphic data were used to map this morphology

40 through time, to evaluate the anagenesis hypothesis. The stratigraphic distributions of the two

41 species showed considerable overlap, indicating that the sampled individuals lived over a short

42 period of time (< 0.5 mya). Overall, our results suggest that the hypothesis that G. incurvimanus

43 and G. notabilis represent different ontogenetic stages within a single species cannot be rejected.

44 This study improves our understanding of the extent of potential individual variation within a

45 single Gryposaurus species, which can be useful in assessing the validity of other hadrosaurines.

46 KEYWORDS: dinosaur, Hadrosauridae, biostratigraphy, geometric morphometrics, allometry

47

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49 INTRODUCTION

50 Hadrosauridae are among the most common and diverse late Cretaceous ornithischian

51 dinosaurs in the Northern Hemisphere. In terms of relative abundance, the family dominates

52 many Campanian-Maastrichtian dinosaur faunas of western North America. Notably,

53 hadrosaurids are particularly abundant and diverse in the middle to upper Campanian Dinosaur

54 Park Formation (DPF) of southern Alberta, Canada (Dodson 1971; Brinkman 1990; Brinkman et

55 al. 1998; Ryan and Evans 2005). The hadrosaurid fauna of the DPF includes at least six species,

56 with multiple taxa assignable to the each of the two classically recognized subfamilies,

57 Hadrosaurinae and Lambeosaurinae (Ryan and Evans 2005; Mallon et al. 2012). Most recent

58 taxonomic assessments recognize the lambeosaurineDraft genera Corythosaurus Brown, 1914,

59 Lambeosaurus Parks, 1923, and the rare Parasaurolophus Parks, 1922 (Ryan and Evans 2005;

60 Mallon et al. 2012). Lambeosaurines are numerically more common than hadrosaurines in the

61 assemblage, and due to the large sample of skulls preserved at different growth stages, have been

62 the focus of considerable ontogenetic and taxonomic research (Dodson 1975; Ryan and Evans

63 2005; Evans and Reisz 2007; Evans 2007; Evans 2010).

64 The hadrosaurines from the DPF have been less intensively studied than the

65 lambeosaurines, likely due to the smaller available sample sizes and less complete ontogenetic

66 representation. The hadrosaurines from the DPF are typically assigned to two genera,

67 Prosaurolophus Brown, 1916 and Gryposaurus Lambe, 1914 (Ryan and Evans 2005). Only one

68 species of Prosaurolophus has been recognized from the DPF, P. maximus (McGarrity et al.

69 2013). However, the taxonomic history and diversity within Gryposaurus has been controversial

70 since Lambe (1914) first described the genus based on the type specimen (CMN 2278 from the

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71 DPF). The holotype was assigned the species name G. notabilis and was described based on a

72 few characteristic cranial features: a dorsally arched nasal crest anterior to the orbits, a

73 circumnarial depression near the anterior end of the lacrimal, broad posterior nasal processes,

74 and frontals that bifurcate at the midline of the skull (Horner 1992). Shortly after the initial

75 description of CMN 2278, a field crew from the Royal Ontario Museum collected a nearly

76 complete hadrosaurine skeleton (ROM 764) that was designated as the type specimen of

77 Kritosaurus incurvimanus Parks, 1920, based on several cranial characters, most notably, a more

78 anterior projection of nasal prominence, as well as generally smaller size (Parks 1920; Fig. 1).

79 The genus Gryposaurus was later recognized as a junior subjective synonym of Kritosaurus by

80 Lull and Wright (1942), which was followed by Ostrom (1961) and most subsequent authors

81 over the course of the next several decades.Draft Horner (1992) argued that Gryposaurus was distinct

82 from Kritosaurus at the generic level, and revised the genus to include three species: G.

83 notabilis, G. incurvimanus, and G. latidens Horner, 1992. Subsequent phylogenetic analyses and

84 systematic revisions of Hadrosauridae have supported this generic division (e.g., Gates and

85 Sampson 2007; Prieto-Márquez 2010a, 2012).

86 Despite an adequate sample, the systematics of Gryposaurus species from the DPF are still

87 unresolved. Although the holoype of G. incurvimanus, ROM 764, includes an articulated

88 skeleton and skull, the skull is incompletely preserved, and lacks the majority of its rostrum,

89 including the nasal crest, which is a diagnostic feature for the genus (Parks 1920; Prieto-Márquez

90 2010b). Hopson (1975) was the first to hint that G. incurvimanus might be better considered a

91 junior synonym of G. notabilis when he suggested the two were sexual dimorphs of a single

92 species. However, Horner (1992) recognized G. incurvimanus as a distinct species, as did Gates

93 and Sampson (2007). Most recently, Prieto-Márquez (2010b) argued that G. incurvimanus may

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94 in fact be a junior synonym of G. notabilis, and that their morphological differences can be

95 attributed to ontogenetic and intraspecific variation. This opinion was followed by Bertozzo et al.

96 (2017), but with no additional insights into the issues. Several morphological characters have

97 been used to distinguish G. notabilis and G. incurvimanus as two separate species, including the

98 shape of the orbit relative to the infratemporal fenestra (ITF), the height and anteroposterior

99 position of the nasal arch, and posterior breadth of the narial fenestra (Parks 1920; Horner 1992;

100 Gates and Sampson 2007). G. notabilis specimens have a strikingly taller nasal arch, which sits

101 much farther posteriorly on the skull, closer to the nasofrontal suture, than those of G.

102 incurvimanus. G. notabilis also possesses a tightly “U”-shaped posterior margin of the narial

103 fenestra, which is broader in G. incurvimanus. The only specimens unequivocally referred to G.

104 incurvimanus, ROM 764 and TMP 1980.022.0001,Draft are of smaller overall size than those of G.

105 notabilis and display similar nasal arch morphologies to one another (Ryan and Evans 2005). A

106 greater number of specimens have been definitively assigned to G. notabilis (CMN 2278, ROM

107 873, AMNH 5350), compared with the G. incurvimanus morphotype (ROM 764, TMP

108 1980.022.0001), whereas MSNM v345 has been ambiguously referred to as either G.

109 incurvimanus or G. notabilis by different researchers (e.g., Pinna 1979; Currie and Russell 2005;

110 Prieto-Márquez 2010b; Bertozzo et al. 2017).

111 TMP 1980.022.0001, has been assigned to G. incurvimanus, and is the only complete skull

112 for the species discovered to date (Currie and Russell 2005; Gates and Sampson 2007). Hopson

113 (1975) and Prieto-Márquez (2010b) have challenged this classification and consider the

114 specimen as representing G. notabilis, despite the fact that it has never been formally described.

115 Prieto-Márquez (2010b) argues that the morphological differences between G. incurvimanus and

116 G. notabilis specimens do not necessarily provide sufficient evidence to consider them distinct

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117 species, and that the postcranial features highlighted in the original G. incurvimanus description

118 were not actually diagnostic at the genus or species level. Furthermore, Prieto-Márquez (2010b)

119 hypothesizes that the shallow nasal arch in G. incurvimanus merely represents the subadult

120 condition for G. notabilis, which would suggest ontogenetic allometry, if this morphology were

121 to show a correlation with overall size.

122 Interestingly, all Gryposaurus specimens collected from the DPF to date have occurred

123 within the lowest 20 metres of the formation, which spans approximately 0.5 myr (Evans 2007;

124 Mallon et al. 2012). Currie and Russell (2005) regarded G. incurvimanus as a valid species

125 derived from G. notabilis presumably via anagenesis, noting that all G. incurvimanus specimens

126 occur later in the geological record than G. notabilis with little chronological overlap. However,

127 the biostratigraphic analysis by Currie andDraft Russell (2005) used altitudes and are not corrected to

128 account for geological structural variation. Furthermore, a number of the specimens are

129 misidentified, and therefore their results are questionable, pending more detailed biostratigraphic

130 analysis.

131 Given these uncertainties, we herein describe several new or otherwise poorly described

132 specimens of Gryposaurus from the Dinosaur Park Formation, conduct detailed morphometric

133 analyses to test whether shape variation could reflect ontogenetic change, and assess the

134 biostratigraphy of the more nearly complete Gryposaurus specimens in order to test whether G.

135 incurvimanus is a junior synonym or evolutionary chronospecies of G. notabilis.

136

137 Institutional Abbreviations – ACM, Amherst College Museum, Amherst,

138 Massachusetts, USA; AMNH, American Museum of Natural History, New York, New York,

139 USA; CMN, Canadian Museum of Nature, Ottawa, Ontario, Canada; FMNH, Field Museum of

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140 Natural History, Chicago, Illinois, USA; MSNM, Museo Civico di Storia Naturale di Milano,

141 Milano, Italy; ROM, Royal Ontario Museum, Toronto, Ontario, Canada; TMM, Texas

142 Memorial Museum, Austin, Texas, USA; TMP, Royal Tyrrell Museum of Palaeontology,

143 Drumheller, Alberta, Canada; UMNH, Utah Museum of Natural History, Salt Lake City, Utah,

144 USA; USNM, United States National Museum (Smithsonian Institution), Washington D.C.,

145 USA.

146

147 MATERIALS AND METHODS

148 Our review of hadrosaurid cranial material from the Dinosaur Park Formation of Alberta

149 reveals that there are nine (TMP 1980.022.0001, TMP 1991.081.01, ROM 764, ROM 873,

150 MSNM v345, CMN 2278, AMNH 5350,Draft ROM 1939, ROM 8784) partial to complete skulls that

151 can confidently be assigned to species of Gryposaurus based on the morphology of the nasal

152 (Table 1). We have also identified several specimens in the literature that have been referred to

153 Gryposaurus but lack sufficient characters to confidently identify them to a specific morphotype,

154 or even to genus (e.g., ACM 578, ROM 667; Currie and Russell 2005). Several of these

155 specimens have either not been previously illustrated or described in the literature, or have

156 received only passing reference. Here, we briefly describe and identify these problematic

157 specimens, and conduct morphometric and biostratigraphic analyses to assess the nature of

158 variation in Gryposaurus based on the most robust dataset available to date. Gryposaurus

159 specimens are referred to by their species name as provided by the papers that first described

160 them (Lambe 1914; Parks 1920; Pinna 1979), or Currie and Russell (2005) if they are

161 undescribed.

162

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163 Anatomical Description

164 The cranial anatomy of Gryposaurus has been described in detail in several publications

165 (Parks 1920; Pinna 1979; Gates and Sampson 2007; Prieto-Márquez 2010b; Prieto-Márquez

166 2012; Bertozzo et al. 2017). Since the anatomy of Gryposaurus from Alberta is well known, we

167 provide brief notes on salient aspects of the cranial anatomy of previously undescribed or poorly

168 described specimens referred to Gryposaurus from the Dinosaur Park Formation. We briefly

169 document the morphology of TMP 1980.022.0001, which has been referred to G. incurvimanus

170 (Horner 1992; Gates and Sampson 2007) and has been discussed in multiple papers (Horner

171 1992; Gates and Sampson 2007; Prieto-Márquez 2010b) but remains poorly described. We also

172 document TMP 1991.081.0001, an undescribed specimen that has a low nasal arch. In addition,

173 we document the morphology of severalDraft specimens previously referred to as Gryposaurus (ROM

174 667, ACM 578) that do not show any of the diagnostic morphologies for the genus as outlined by

175 Prieto-Márquez (2010b).

176 TMP 1980.022.0001 includes a skeleton and the most nearly complete skull that has been

177 assigned to G. incurvimanus (Horner 1992; Gates and Sampson 2007). It was collected in 1980

178 from Dinosaur Provincial Park (DPP) on the south side of the Red Deer River, 10.3 metres above

179 the contact with the Oldman Formation (Currie and Russell 2005), by crews from the Provincial

180 Museum of Alberta (now Royal Alberta Museum). TMP 1991.081.0001 is another nearly

181 complete Gryposaurus skull that was collected in the Sandy Point area of Alberta, 75 km east of

182 DPP, and although it was collected from the Dinosaur Park Formation, its precise stratigraphic

183 position is unknown. ACM 578 is from Dinosaur Provincial Park Quarry 76 (Currie and Russell,

184 2005), and has been identified as Gryposaurus despite significant plaster reconstructions. Lastly,

185 ROM 667, from an unknown location in DPP, consists of a braincase and a few skull roof

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186 elements. The specimen FMNH ? (Quarry 77) referred to as G. incurvimanus in Currie and

187 Russell (2005) cannot be relocated and is not considered further in this study.

188

189 Morphometric Analysis

190 The goal of this study was to analyze the cranial variation of hadrosaurines from the

191 Dinosaur Park Formation of Alberta to test conflicting hypotheses of species identity. The

192 difference in size among the specimens is generally small, but is central to understanding

193 whether this morphological variation is inter- or intraspecific. Primarily, our aim was to answer

194 whether this variation in cranial morphology is explained by ontogenetic allometry, or by

195 interspecific variation. Geometric morphometrics and biostratigraphy were employed to answer

196 two main questions: (1) whether the morphologicalDraft variation in hadrosaurines correlates with

197 skull size; (2) whether the morphological variation correlates with stratigraphic position. If

198 relative skull morphology is significantly correlated with skull size, we predict that G. notabilis

199 and G. incurivmanus represent variable morphs in an ontogenetic series, displayed by allometric

200 growth. However, if they differ significantly in both morphology and biostratigraphy, we may

201 predict that anagenetic evolution has occurred, with one species having given rise to a second

202 species.

203 Of the nine skulls that can be referred to one of the cranial morphs of Gryposaurus (G.

204 notabilis or G. incurvimanus), six are sufficiently complete and undistorted for geometric

205 morphometric analysis. Because the sample size is low, Prosaurolophus was included as a

206 control group to Gryposaurus for the following reasons: (1) a sizeable sample of both genera has

207 been obtained from the DPF; (2) it is a relatively closely related taxon to Gryposaurus; and (3)

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208 Prosaurolophus contains only one species (P. maximus), despite a wide range of morphological

209 variation (McGarrity et al. 2013).

210 A series of geometric morphometric analyses are performed to capture and compare

211 overall morphology of significant portions of the skulls. Fragmentary Gryposaurus material,

212 such as AMNH 5350, had to be excluded from the analysis as significant missing information

213 made the ensuing statistical analysis untenable. For all morphometric analyses, type 1 and type 2

214 landmarks and semi-landmarks were identified and placed in R (v. 3.2.1; Bookstein 1991; R

215 Core Team, 2018) and aligned with generalized Procrustes superimposition in the package

216 ‘geomorph’ (Adams and Otarola-Castillo, 2013). A generalized Procrustes superimposition

217 provided shape data, which were then subjected to principal component analysis (PCA) to

218 capture the underlying variance of data Draftand produce principal component (PC) axes of the

219 greatest variation. Eigenvectors were then calculated to determine the landmarks that contributed

220 most to the variation.

221 In the first analysis (Analysis 1), 11 type 1 or type 2 landmarks were identified and

222 placed on photographs of 13 hadrosaurine skulls from the DPF (Fig. 2A). Due to taphonomic

223 distortion and poor preservation in a number of important specimens, this analysis only includes

224 landmarks that were present on all 13 skulls for maximum inclusivity, and thus omits all

225 elements of the rostrum. Six Gryposaurus skulls (CMN 2278, MSNM v345, ROM 764, ROM

226 873, TMP 1980.022.0001, TMP 1991.081.0001; Fig. 3-5) and seven Prosaurolophus skulls

227 (AMNH 5386, CMN 2870, ROM 787, ROM 1928, TMM 41262, TMP 1984.001.0001, USNM

228 12712) were included.

229 The second geometric morphometric analysis (Analysis 2) used sliding semi-landmarks

230 as well as type 1 or type 2 landmarks and incorporated the rostrum (Fig. 2B). For this reason, the

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231 holotype of G. incurvimanus (ROM 764), which lacks a rostrum, had to be omitted from this

232 analysis, leaving a total of five Gryposaurus specimens, instead of the previous six, and a total of

233 12 hadrosaurine individuals in the analysis. The 12 additional specimens listed above were

234 included- using 20 type 1 or 2 landmarks and 26 sliding semi-landmarks, for a total of 46

235 landmarks. Semi-landmarks are used to capture shape along a curve and slide along lines tangent

236 to the curve on which they are placed (Gunz and Mitteroecker 2013). Therefore, the placement

237 of these semi-landmark points is less rigid than the strict homology necessary for type 1 or type 2

238 landmarks. In this analysis, semi-landmarks are placed along curves present on significant

239 elements of the skull, including the posterodorsal margin of the narial fenestra, the dorsal margin

240 of the nasal arch, the ventral edge of the ITF, and the ventral edge of the jugal (Fig. 2B).

241 The third analysis (Analysis 3) focusedDraft on jugal morphology only, using six type 1 or

242 type 2 landmarks and 14 semi-landmarks, for a total of 20 landmarks (Fig. 2C). This analysis

243 included all previously mentioned specimens, as well as ACM 578, for a total of 14 specimens.

244 ACM 578 was tentatively referred to ?Gryposaurus by Sternberg (1950) and G. incurvimanus by

245 Currie and Russell (2005), however it remains undescribed and without robust identification.

246 Evans (2007) suggested that the fully preserved jugal of ACM 578 resembles that of

247 Prosaurolophus much more closely than Gryposaurus. Furthermore, the diagnostic nasal and

248 skull roof elements were not preserved, and therefore reconstructed, revealing a scarcity of

249 information to justify referral of this specimen to Gryposaurus. The purpose of this jugal

250 analysis was to include this controversial specimen in our study and allow us to place it within a

251 hadrosaurine morphospace, so that we could make informed predictions on its taxonomic

252 identity.

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253 PC 1 and 2 axes were plotted against quadrate length in Analyses 1 and 2 using an

254 Ordinary Least Squares (OLS) regression, which assumes an absence of error on one axis, which

255 in this case is quadrate length, along the x-axis. The quadrate length acts as a proxy for skull size

256 for a number of reasons: 1) the rostrum is missing in ROM 764, precluding us from using skull

257 length; 2) the quadrate is present in almost all included hadrosaurine cranial specimens, and 3) it

258 increases in length isometrically with skull size without sustaining too much distortion from its

259 original state (Evans and Reisz 2007; McGarrity et al. 2013). As neither quadrate is preserved in

260 TMP 1991.081.0001, quadrate length was approximated by measuring the distance between the

261 ventral curve of the squamosal and the surangular. Separate regression lines were produced for

262 Prosaurolophus and for Gryposaurus. In Analysis 3, centroid size is used instead of quadrate

263 length, since the quadrate is not completelyDraft preserved in ACM 578 and would present skewed

264 results. Given the uncertain taxonomic identity of ACM 578, this specimen is also included in

265 both Prosaurolophus and Gryposaurus regression analyses for Analysis 3. The null hypothesis

266 of isometry for all morphometric analyses was tested using a two-tailed t-test, which tests

267 whether the slopes of regression lines were significantly different from 0, since the distances

268 between landmarks are unchanged under isometric growth.

269 Standard hadrosaur skull measurements (Table 2) were taken from known Gryposaurus

270 skulls using ImageJ v. 1.49 (Schneider et al. 2012), and a series of bivariate plots were produced

271 to observe their relationships with overall skull size. All linear measurements were log-

272 transformed prior to analysis. Quadrate length was used to represent skull size. Reduced Major

273 Axis (RMA) regressions were then conducted using the ‘smatr’ package in R (Warton et al.

274 2012). This type of regression was chosen for bivariate plots because it assumes that error is

275 present in both x- and y-axes, which is applicable here when both variables are linear

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276 measurements. The null hypothesis of isometry for all linear measurement analyses was tested

277 using a two-tailed t-test, which tests whether the slopes of regression lines were significantly

278 different from 1, since morphology changes are proportional to size under isometric growth.

279

280 Biostratigraphy

281 Hadrosaurine material with accessible stratigraphic data were plotted in a biostratigraphic

282 context to visualize their chronostratigraphic range and test for the possibility of anagenesis

283 within Gryposaurus, as well as the biostratgraphic range of the genus in relation to other

284 hadrosaurine taxa known from DPP. This analysis differs from previous studies in that the

285 stratigraphic position of most Gryposaurus quarries (six of the eight definitively identified

286 specimens) were directly field-measuredDraft for this project by DCE; previous studies used estimates

287 as described above (Mallon et al. 2012) or used raw altitude (Currie and Russell 2005).

288 The detailed stratigraphic position of each specimen is given relative to the basal contact

289 with the Oldman Formation, a chronstratigraphic datum across the area of DPP. The stratigraphic

290 position of each quarry was determined by either direct measurement in the field using a Jacob’s

291 Staff (DCE), and/or estimated using a structural contour map of the Oldman-Dinosaur Park

292 formational contact of Eberth and Getty (2005) subtracted from the altitude (m asl) provided by

293 Currie and Russell (2005), as in Mallon et al (2012).

294

295 RESULTS

296

297 Notes on the anatomy of previously undescribed Gryposaurus skulls

298 TMP 1980.022.0001

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299 The premaxilla flares laterally into a premaxillary “lip”. Its ventral margin, which

300 opposes the predentary, is transversely flattened ventrally, unlike in G. notabilis in which the

301 rostrum is rounded at its anteroventral end. The nasal contacts the premaxilla anteromedially and

302 ventrally to define the bony narial fenestra. The nasal forms the posterodorsal region of the narial

303 fenestra, which has a broadly “U”-shaped margin in TMP 1980.022.0001 (Fig. 3). Most other

304 Gryposaurus specimens have a more restricted, narrower posterior narial margin (e.g., AMNH

305 5350, CMN 2278, ROM 873, TMP 1991.081.0001; Fig. 4, 5). TMP 1980.022.0001 is notable for

306 having the most weakly developed nasal arch of any large-sized Gryposaurus specimen.

307 Interestingly, it is most similar to a juvenile specimen, CMN 8784 (Waldman 1969), which also

308 appears to lack a nasal arch. The apex of the long, low nasal arch occurs dorsal to the posterior

309 end of the bony naris, whereas larger specimensDraft have the crest apex situated more posteriorly,

310 near the nasal contact with the frontal. The nasal is relatively anteroposteriorly longer than in G.

311 notabilis, contributing to the elongated appearance of the skull. The prefrontal contributes to the

312 most lateral portion of the dorsal skull roof between the dorsal nasal depression and the

313 articulation with the frontal. Each frontal possesses a smooth concavity located centrally on the

314 dorsal surface of the bone. The frontal extends laterally, and is incorporated into the dorsal

315 margin of the orbital rim, which is typical for Gryposaurus (Prieto-Márquez 2010b). The

316 postorbital process of the jugal ascends posterodorsally, contributes to the lower ~25% of the

317 postorbital bar in lateral view, and contacts the ventral process of the postorbital bone.

318

319 TMP 1991.081.0001

320 This specimen (Fig. 4) is anatomically similar to TMP 1980.022.0001. The posterior

321 margin of the narial fenestra is a slightly narrower “U”- shape than in TMP 1980.022.0001 (Fig.

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322 3), similar to CMN 2278 (Fig. 5C). The nasal arch is shallow like in TMP 1980.022.0001, but it

323 has more distinctive nasal arch. It exhibits a much flatter, squarer dorsal margin that most closely

324 resembles the nasal arch of AMNH 5350 (Fig. 5D; Prieto-Márquez 2010b). This flat, square

325 nasal arch poses some difficulty for determining the position of the “apex” of the crest, as it is

326 not clearly rounded with single apex at its center, like in other specimens. For our analysis (See

327 ‘Morphometric Analysis’), we chose to mark the center of the square margin as the apex of the

328 crest. The dorsal arch is also notably rugose, a feature also present in AMNH 5350, but that is

329 not well developed in any other Gryposaurus skull we have examined. Furthermore, the position

330 and height of the nasal arch is intermediate between G. incurvimanus and G. notabilis. The

331 frontal bone contributes to the dorsal part of the orbital rim, as in TMP 1980.022.0001, and

332 contacts the parietal posteriorly in a W-shapedDraft suture. The quadrates on TMP 1991.081.0001 are

333 not preserved, however their articulation points on the squamosal and surangular are clearly

334 defined.

335

336 ACM 578

337 Although ACM 578 (Fig. 6A-6D) is reconstructed with the facial profile of Gryposaurus,

338 its taxonomic identity is problematic. The skull roof and nasal, arguably the most diagnostic

339 features of hadrosaurine skulls, are reconstructed with plaster in this specimen, while the maxilla

340 and lower jaw, and jugal are preserved. The jugal constricts more narrowly below both the orbit

341 and the ITF in Gryposaurus than in Prosaurolophus, and ACM 578 appears intermediate in these

342 regards. The postorbital process of the jugal ascends posterodorsally and contributes to the lower

343 ~25% of the postorbital bar in lateral view. The jugal bears a relatively poorly defined ventral

344 process, referred to as the free ventral flange that is offset defined by the constriction of the

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345 posterior blade below the ITF. It is deep and relatively triangular in Gryposaurus specimens (e.g.

346 TMP 1980.022.0001, CMN 2278; Fig. 3-5), and descends as far downward as the maxillary

347 tooth row in lateral view. With some individual variation, the free ventral flange is typically

348 much more rounded and shallower in Prosaurolophus than in Gryposaurus. Based on these

349 criteria, the jugal of ACM 578 resembles that of Prosaurolophus far more than Gryposaurus,

350 however it is unclear if this feature has been reconstructed correctly, as the free ventral flange

351 and the posterior blade appears to be heavily plastered. The section below the orbit, however,

352 appears to be bone, and this portion is wider than in most Gryposaurus skulls, appearing more

353 similar to Prosaurolophus.

354 Taxonomic assessment: the lack of diagnostic characters makes it difficult to conclusively

355 identify this specimen. The features availableDraft resemble Prosaurolophus more closely than they

356 do Gryposaurus. We therefore identify this specimen as c.f. Prosaurolophus maximus, the only

357 recognized species of Prosaurolophus (McGarrity et al. 2013).

358

359 ROM 667

360 This specimen consists of an incomplete braincase that is damaged on the orbital margins

361 and in the region of the naso-frontal suture (Fig. 6E, 6F). It has been previously referred to as G.

362 notabilis (Currie and Russell 2005), despite consisting of only a poorly preserved braincase. The

363 primary diagnostic features, including nasal bone morphology, nasofrontal contact, and orbital

364 margin, are absent or severely damaged, making interpretation difficult.

365 Taxonomic assessment: this specimen lacks diagnostic features of Gryposaurus and is not

366 confidently identifiable, and therefore is best regarded as ‘Hadrosaurinae indet’.

367

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368 Morphometric analysis

369 All measurements taken for these analyses are recorded in Table 2; Tables 3 and 4 report

370 regression statistics for each plot. We assigned specimens to morphotype following the literature,

371 however TMP 1991.081.0001 has not been referenced prior to this study, and shows a mix of

372 characters making it difficult to definitively assign to either G. incurvimanus or G. notabilis

373 morphs (for example, an intermediate position and height of the nasal arch). It is therefore

374 referred to as Gryposaurus sp.

375 In geometric morphometric analysis 1 (Fig. 2A), PC 1 (71.6%) and PC 2 (11.6%)

376 contribute to 83.2% of the total variation (Fig. 7A). Specimens assigned to G. incurvimanus are

377 separated from G. notabilis specimens along the PC 1 axis in morphospace, while the

378 Prosaurolophus specimens are scattered,Draft isolated from Gryposaurus, without any visible

379 clustering. The PC 1 axis is influenced most prominently by the landmark placed at the inflection

380 point of the nasal arch, representing the position of the crest relative to the rest of the skull. The

381 PC 2 axis is primarily driven by the muscle scar posterodorsal to the infratemporal fenestra, and

382 shows little separation within or between genera. The first PC axis was plotted against quadrate

383 length in an OLS regression to test for an allometric relationship between relative skull

384 morphology and skull size. There is a significant correlation between PC 1 (nasal arch position)

385 and quadrate length (skull size) in Gryposaurus (Fig. 7C; Table 3; R-squared = 0.78, p < 0.05),

386 with a slope of 0.62. Prosaurolophus specimens in this comparison exhibit a similar trend, with a

387 slope of 0.44, although in this case the test for linearity is not deemed statistically significant (R-

388 squared = 0.24, p = 0.26). The correlation between PC 2 (ITF muscle scar) and skull size is not

389 significant in both Gryposaurus (R-squared = 0.08, p= 0.58) and Prosaurolophus (R-squared =

390 0.04, p= 0.68).

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391 In geometric morphometric Analysis 2 (which does not include the holotype of G.

392 incurvimanus), where semi-landmarks capture nasal arch shape (Fig. 2B), PC 1 (74.8%) and PC

393 2 (6.1%) contribute to 80.9% of the total variation (Fig. 8A). Gryposaurus is completely

394 separated from Prosaurolophus on the PC 1 axis. The G. incurvimanus specimen and the

395 indeterminate TMP 1991.081.0001 plot farther on the positive end of the PC 2 axis relative to all

396 of the G. notabilis specimens (Fig. 8A). There does not seem to be any obvious morphospace

397 clustering among Prosaurolophus specimens. PC 1 is influenced by the landmark at the contact

398 between the premaxilla and the nasal within the dorsal part of the naris. PC 2 is driven by

399 landmarks associated with the posterior margin of the infratemporal fenestra and its adjacent

400 muscle scar. PC 3 and PC 4 exhibit no discernable trends between taxa or within Gryposaurus.

401 Regressions of PC 1 and PC 2 scores forDraft this analysis against skull size are not significant (Table

402 3). An OLS regression shows non-significant relationship between PC 1 (rostrum) and skull size

403 in Gryposaurus (Fig. 8C; R-squared = 0.73, p= 0.07), with a slope of 0.43. This correlation is

404 also not significant in Prosaurolophus (R-squared = 0.09, p= 0.51) with a slope of 0.21. The

405 relationship between PC 2 (ITF muscle scar) and skull size is not significant in either

406 Gryposaurus (R-squared = 0.71, p= 0.08) or Prosaurolophus (R-squared= 0.11, p= 0.48).

407 In Analysis 3, which encompasses only the jugal and includes the problematic specimen

408 ACM 578, PC 1 (45.5%) and PC 2 (20.9%) contribute to 66.4% of the total variation (File S11).

409 Gryposaurus and Prosaurolophus are partially separated only on PC 1, where they overlap in the

410 region of the origin (0). ACM 578 falls in this zone of overlap. The PC 1 axis is driven by the

411 landmark defined by the contact of the jugal and lacrimal along the margin of the orbit, and

412 semi-landmarks associated with the anteroventral margin of the jugal. PC 2 is driven by

1 Supplementary data are available with the article through the journal website

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413 landmarks that capture the posterior end of the ventral curve. The relationship between both PC

414 axes against skull size (centroid) across both genera was not significant (File S1, Table 3).

415 The bivariate regressions for Gryposaurus (Fig. 9) show that variables associated with

416 nasal crest morphology – notably the distance from the naris to crest apex plotted against

417 quadrate length – had a significant positive relationship (Fig. 9C; Table 4; slope = 2.18, R-

418 squared = 0.94, p < 0.05), while frontal to base of crest (Fig. 9A; slope = -0.54, R-squared =

419 0.16, p = 0.44) and frontal to crest apex (Fig. 9B; slope =-0.41, R-squared = 0.22, p = 0.43) did

420 not (Table 4). Jugal length (Fig. 9D; slope = 0.88, R-squared = 0.87, p < 0.05), jugal height

421 below the orbit (Fig. 9E; slope = 1.10, R-squared = 0.90, p < 0.05), and jugal height below the

422 ITF (Fig. 9F; slope = 1.32, R-squared = 0.69, p = 0.04) had significant positive relationships with

423 quadrate length. These three jugal measurementDraft plots show positive slopes with 95% confidence

424 intervals that cross the number one, and therefore these relationships are deemed isometric

425 (Table 4). P-values from the two-tailed t-test are provided in Table 4.

426

427 Biostratigraphy

428 Sixteen hadrosaurine specimens with skulls could be plotted in a detailed biostratigraphic

429 context, including eight specimens of Gryposaurus, and seven specimens of Prosaurolophus

430 (Fig. 10) from the Dinosaur Park Formation. The holoype of Brachylophosaurus canadensis

431 (CMN 8893; Cuthbertson and Holmes 2010), also included in this analysis, is the only taxon that

432 occurs in the Oldman Formation at DPP. The DPF is approximately 75 metres thick at this

433 locality (Eberth 2005). All Gryposaurus specimens occur in the lowest 20 meters of the

434 formation. Specimens historically assigned to G. incurvimanus show stratigraphic overlap with

435 those assigned to G. notabilis, and all specimens of the genus likely span a temporal range of less

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436 than 0.5 Mya (see Eberth 2005). Prosaurolophus specimens occur in the DPF between ~32 and

437 55 metres above the contact with the Oldman Formation, higher than all definitive occurrences

438 of Gryposaurus. ACM 578 falls within the known Prosaurolophus range, at 37.5 metres above

439 the Oldman Formation (Evans 2007), which is consistent our identification of this specimen

440 based on the jugal morphology.

441

442 DISCUSSION

443 Historically, Gryposaurus incurvimanus has been recognized as a distinct hadrosaurid

444 taxon characterized by a low nasal arch that does not rise above the plane of the skull roof and

445 broad, U-shaped posterior nasal fenestra (Horner 1992; Gates and Sampson 2007). However, in

446 the most recent taxonomic revision of theDraft genus from the Belly River Group of Alberta, Prieto-

447 Márquez (2010b) demonstrated that many of the characters previously used to distinguish

448 Gryposaurus species are intraspecifically variable, and hypothesized that characters that did

449 distinguish G. incurvimanus from the larger G. notabilis (most notably features of the nasal

450 crest) were indicative of subadulthood, and that nasal crest height underwent changes in location

451 and prominence during ontogeny. They further argued that G. incurvimanus should be

452 considered a subjective junior synonym of G. notabilis. However, Prieto-Márquez (2010b) did

453 not consider the biostratigraphy of specimens nor the possibility of anagensis as suggested by

454 Currie and Russell (2005), and executed only a preliminary morphometric analysis consisting of

455 a single bivariate plot of four specimens. Mallon et al. (2012) followed the taxonomy of Prieto-

456 Márquez (2010b) in their analysis of DPF megaherbivore faunal turnover, but did not assess the

457 potential for stratigraphic separation of the two species of Gryposaurus. Despite small sample

458 sizes, the stratigraphic dataset and the series of morphometric analyses conducted here represent

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459 the first comprehensive test of these hypotheses, and are based on the majority of articulated

460 skulls of the genus Gryposaurus from the Dinosaur Park Formation.

461 Our more robust morphometric assessment of nasal arch and skull ontogeny in

462 Gryposaurus, using the majority of available specimens, confirms that, independent of size, the

463 specimens that have been historically referred to G. incurvimanus (ROM 764; TMP

464 1980.022.0001) are more similar to each other than to those tentatively referred to G. notabilis,

465 but that morphological variation in crest morphology is correlated with skull size, consistent with

466 ontogenetic growth. Larger skulls have taller crests that are set farther posteriorly, closer to the

467 nasofrontal suture, than in smaller skulls. Analysis 1 demonstrated that the position of the crest is

468 the most variable morphological feature across Gryposaurus skulls in this analysis, and that the

469 crest becomes more posteriorly positionedDraft towards the orbits as skull size increases. This is

470 consistent with ontogenetic change within the growth series of a single taxon (e.g., Dodson 1975,

471 Evans 2010). Analysis 2 captures more shape variation using both type 1 and type 2 landmarks

472 and semi-landmarks to describe the entire skull, including semi-landmarks along the nasal arch

473 and the jugal (Fig. 2B). The size-independent morphospace (Fig. 8A) shows that the referred

474 specimen of G. incurvimanus, TMP 1980.022.0001, and the morphologically intermediate TMP

475 1991.081.0001, are separated from G. notabilis along both PC 1 and PC 2 axes. When PC scores

476 of this analysis are compared with skull size to test if these morphological differences are size-

477 related, there are no significant correlations, however PC 1 vs Quadrate Length is only very

478 weakly non-significant, with a high R-squared value of 0.728 (Table 3). The intermediate

479 morphology of TMP 1991.081.0001 is consistent with its intermediate size between specimens

480 of G. incurvimanus and G. notabilis (Fig. 8C, 8D). This suggests that the morphology of the

481 narial region is ontogenetically variable, as an ontogenetic trend is clearly visible in the PC 1

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482 growth plot (Fig. 8C); its marginal statistical significance (p = 0.066) is likely an artifact of the

483 necessary sample size reduction and increased number of variables (i.e. landmarks).

484 Bivariate plots and RMA regression analysis provides further insight into the ontogenetic

485 pattern observed in Gryposaurus skull morphology. Distance measurements of the frontal to the

486 base of the nasal crest (Fig. 9A) and from the frontal to the crest apex (Fig. 9B) produce

487 significant negative allometric relationships representing the ontogenetic nasal retraction

488 observed in Analysis 1; the feature decreases in absolute terms, as skull size increases. The

489 positive allometric trend between distance of naris to nasal crest apex and quadrate length with a

490 very high coefficient of determination (Table 4) strongly supports the hypothesis that crest height

491 proportionally increases through ontogenetic growth. Other indices, such as those associated

492 with the jugal predictably show high R-squaredDraft values and increase in length proportional to

493 skull size. TMP 1991.081.0001 falls in the middle of most Gryposaurus regression lines (Fig.

494 9A-F) and thus represents an important intermediate cranial morph and possibly sub-adult

495 condition of G. notabilis. This further supports the hypothesis that each specimen belonging to

496 G. incurvimanus and G. notabilis fall in an ontogenetic series within one species. The position of

497 the nasal crest is undoubtedly the most variable and diagnostic feature in Gryposaurus.

498 Combining our results from Analyses 1 and 2 with the bivariate plots provides strong

499 support for an ontogenetic growth trend across G. incurvimanus and G. notabilis overall skull

500 morphology independent of nasal arch height, which indicates that the anteroposterior position of

501 the arch is more relevant than the height of the arch itself. The magnitude of proposed

502 ontogenetic changes in Gryposaurus is consistent with that proposed for Prosaurolophus

503 (McGarrity et al. 2013), such as parallel trends including retraction of the crest and weak positive

504 allometry of crest height. Since nasal crest position is significantly correlated with skull size, we

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505 do not reject the hypothesis that ontogenetic development is driving change in crest morphology

506 and conclude that the nasal crest retracts posteriorly on the skull as the animal grows. This is

507 consistent with the hypothesis that ontogenetic allometry could explain the morphological

508 differences in the position of the nasal arch between G. incurvimanus and G. notabilis and, as

509 suggested by Prieto-Márquez (2010b), complies with the phenomenon of nasal retraction seen in

510 the cranial ontogeny of other hadrosaurs (Dodson 1975; Evans 2010; Bell 2011; Freedman

511 Fowler and Horner 2015). Although the allometric patterns in the hypothesized ontogenetic

512 series presented here do not necessarily reject Hopson’s (1975) hypothesis of sexual

513 dimorphism, the relatively small G. incurvimanus specimens cannot be differentiated from

514 immature individuals G. notabilis, and we therefore prefer an ontogenetic explanation in the

515 absence of histology and absolute age estimates,Draft which could be used to test this hypothesis in

516 the future.

517 Currie and Russell (2005) noted the possible biostratigraphic succession of G. notabilis to

518 G. incurvimanus within the Dinosaur Park Formation, and together with several other groups of

519 taxa, hypothesized that these may represent ‘transitional sequences of faunal elements’,

520 presumably a reference to anagenetic evolution within these lineages (e.g., Horner 1992).

521 However, they recognized G. incurvimanus as a distinct taxon, but noted the need for more

522 detailed anatomical and biostratigraphic work, as well as larger sample sizes to test for phyletic

523 evolution (Currie and Russell 2005). The detailed biostratigraphic analysis presented here

524 required reassessment of several problematic, previously undescribed specimens. Notably, the

525 undescribed ACM 578 was initially referred to as ?Gryposaurus by Sternberg (1950), however

526 the most taxonomically significant skull elements (i.e. premaxilla, nasal and frontal bones) have

527 been extensively reconstructed in plaster, and, if present at all, are unreliable for diagnosis. The

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528 jugal is reasonably complete and notably has a weakly developed free ventral flange compared to

529 the depth of the posterior blade, appearing more consistent with Prosaurolophus than

530 Gryposaurus. However, our supplementary morphometric analysis focusing only on the jugal

531 (Analysis 3, File S11) was equivocal. The morphology did not clearly separate these two genera

532 in the PCA morphospace, nor did any of the PC axes show a significant relationship with skull

533 size, and ACM 578 plots in between the data points that are positively assigned to either genus.

534 This suggests that the jugal has an overlapping range of morphological variation in these genera,

535 and/or that it may have included too many landmarks, producing noise in the analysis.

536 Regardless, the shape of the jugal does not allow ACM 578 to be confidently referred to either

537 Gryposaurus or Prosaurolophus. The highly diagnostic skull roof (see Prieto-Márquez 2010b) is

538 not preserved in ACM 578 (Fig. 6A-6D),Draft and given the overlapping variation in jugal

539 morphology in Gryposaurus and Prosaurolophus from the Dinosaur Park Formation, we

540 conservatively identify this specimen as an indeterminate hadrosaurine. Biostratigraphically,

541 ACM 578 occurs within the Prosaurolophus range, far later than any specimens that can be

542 definitively referred to Gryposaurus (Fig. 10).

543 The biostratigraphic analysis includes all of the relatively complete skulls of

544 Gryposaurus from the Dinosaur Park Formation for which quarry-level locality data are known,

545 as well as a large sample of Prosaurolophus maximus specimens, and the single

546 Brachylophosaurus canadensis specimen from Dinosaur Provincial Park for which the quarry

547 site is known (Fig. 10). The three hadrosaurine taxa show a non-random, segregated pattern of

548 stratigraphic distribution. The holotype of B. canadensis represents the only hadrosaurine so far

549 known from the Oldman Formation, representing the lowest stratigraphically located

550 hadrosaurine. Gryposaurus is thus far only known from the lower half of the Dinosaur Park

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551 Formation, and the sampled individuals lived during a short interval (< 0.5 mya) relative to the

552 time encompassed by the formation. Most importantly, the stratigraphic distributions of the two

553 nominal species of Gryposaurus overlap, with G. incurvimanus occurring within a

554 biostratigraphic interval that is otherwise defined by the range of G. notabilis (Fig. 10). This

555 distribution, which documents the co-occurrence of the two morphs for the first time, implores us

556 to reject the hypothesis that anagenetic evolution produced one morphotype from the other.

557 Ultimately, the correlation of crest morphology with size, as well as chronostratigraphic overlap

558 between the two morphotypes, is sufficient to confidently reject the anagenesis hypothesis.

559 Correlation of morphology with size indicates ontogenetic allometry, suggesting that G.

560 incurvimanus represents an immature, subadult ontogimorph of G. notabilis, and the

561 stratigraphic distributions of these fossilsDraft shows enough chronological overlap to reject the

562 anagenesis hypothesis.

563 Based on the results of the morphometric and biostratigraphic analyses in this study, we

564 concur with the hypothesis presented by Prieto-Márquez (2010b) that Gryposaurus incurvimanus

565 is a subjective junior synonym of G. notabilis, with the former having been based on a subadult

566 ontogimorph, rather than an individual representing a distinct species, anagenetic chronospecies,

567 or sexual dimorph of G. notabilis. The recognition that that holotype of “G. incurvimanus”

568 represents an immature individual of G. notabilis clarifies the composition and ecology of

569 dinosaur communities from the Dinosaur Park Formation (e.g., Mallon et al. 2012). Current data

570 provides little evidence of temporal overlap between hadrosaurine species inhabiting DPP over

571 the course of the depositional period of the DPF, which has implications for competition levels

572 among megaherbivorous dinosaurs (Mallon et al. 2013) as well as diversity dynamics studies.

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573 Reassignment of previously described hadrosaurine species as ontogimorphs of

574 previously described taxa has occurred in several other hadrosaurine taxa, but has taken longer to

575 address than in lambeosaurines, where allometric growth is more extreme (e.g. Dodson 1975;

576 Evans 2010). For example, Campione and Evans (2011) used a similar combined allometric and

577 biostratigraphic approach to demonstrate that Anatotitan copei is best interpreted as a large adult

578 Edmontosaurus annectens, which is also known only from the Hell Creek Formation and its

579 equivalents. That study also argued that specimens referred to Thespesius edmontoni and E.

580 saskatchewanensis represent subadult ontogimorphs of E. regalis and E. annectens respectively.

581 Further, Horner (1992) described a new species of Prosaurolophus, P. blackfeetensis,

582 from the upper Two Medicine Formation (upper Campanian) of Montana based on the size and

583 morphology of its nasal crest. Wagner (2001)Draft concluded that P. blackfeetensis was indistinct

584 from P. maximus based on comparative morphological description, and considered it as a junior

585 synonym of P. maximus, with which Prieto-Márquez (2010a) agreed based on the morphology of

586 the nasal crest. Subsequently, McGarrity et al. (2013) used a morphometric approach to argue

587 that P. blackfeetensis is as a junior synonym of P. maximus, stating that P. blackfeetensis

588 represents a sub-adult condition for P. maximus on the basis of its nasal crest morphology.

589 Although ‘G. incurvimanus’ is now more appropriately considered a junior synonym of

590 G. notabilis, Gryposaurus nonetheless remains a taxonomically diverse hadrosaurid, with at least

591 three species, and possibly a fourth, currently recognized: Gryposaurus notabilis, Gryposaurus

592 latidens and Gryposaurus monumentensis Gates and Sampson, 2007, that span the majority of

593 the Campanian. G. notabilis (including “G. incurivmanus”) occurs in the upper Campanian

594 (~76.6 and 76 Mya ;Evans et al. 2013; Bertozzo et al. 2017) in strata of the DPF in Alberta,

595 slightly younger than G. latidens, from the lower part of the Two Medicine Formation of

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596 Montana (~ 80 mya; Gates and Sampson 2007; Prieto-Márquez 2012). Gryposaurus specimens

597 from the Kaiparowits Formation (~76.1 – 74.0 mya) in Utah have been referred to G.

598 monumentensis and c.f. G. notabilis (Gates and Sampson 2007; Prieto-Márquez 2010a; Gates et

599 al. 2013). Additionally, the recently described ?Gryposaurus alsatei Lehman et al., 2016 was

600 discovered in the Javelina Formation in Texas, which occurs later, in the Maastrichtian, than the

601 others previously mentioned (Lehman et al. 2016).

602 Our study, which provides a morphometric baseline and model of variation within a

603 temporally constrained sample of a single Gryposaurus species, can be used to evaluate variation

604 within and between specimens referred to this genus from these other localities, which are

605 known from smaller sample sizes. Furthermore, this dataset can be used to test whether the more

606 southern Gryposaurus, including G. monumentensisDraft and G. alsatei, represent distinct taxa, or fall

607 within the range of cranial variation seen in G. notabilis.

608

609

610 ACKNOWLEDGEMENTS

611

612 We thank T. Cullen and D. Larson for assistance with the technical and theoretical

613 aspects of morphometric analyses. We are grateful to K. Chiba, A. Reynolds, D.J. Simon, D.C.

614 Woodruff, K. Seymour, and V. Arbour for discussions and comments on earlier versions of the

615 manuscript. Thanks to D. Dufault for assistance and expertise with photography and figures.

616 Thanks are extended to D. Eberth, P. Currie, M. Ryan, and J. Mallon for discussion on the fauna

617 of the Dinosaur Park Formation, and T. Gates and A. Prieto-Márquez for discussions on

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618 hadrosaur systematics. This research was funded by an NSERC Discovery Grant (RGPIN

619 355845) to DCE.

620

621 REFERENCES

622 Adams, D., and Otarola-Castillo, E. 2013. geomorph: an R package for the collection and 623 analysis of geometric morphometric shape data. Methods in Ecology and Evolution, 4: 393-399. 624 doi:10.1111/2041-210X.12035. 625 626 Bookstein, F.L. 1991. Morphometric tools for landmark data: geometry and biology. Cambridge 627 University Press, Cambridge. 628 629 Brinkman, D.B. 1990. Paleoecology of the Judith River Formation (Campanian) of Dinosaur 630 Provincial Park, Alberta, Canada: Evidence from vertebrate microfossil localities. 631 Palaeogeography, Palaeoclimatology, Palaeoecology, 78:37-54. doi:10.1016/0031- 632 0182(90)90203-J. 633 634 Brinkman, D.B., Ryan, M.J., and Eberth,Draft D.A. 1998. The Paleogeographic and Stratigraphic 635 Distribution of Ceratopsids (Ornithischia) in the Upper Judith River Group of Western Canada. 636 PALAIOS, 13:160-169. doi:10.2307/3515487 637 638 Brown, B. 1914. Corythosaurus casuarius, a New Crested Dinosaur from the Belly River 639 Cretaceous, with Provisional Classification of the Family Trachodontidae. Bulletin of the 640 American Museum of Natural History, 33: 559–565. 641 642 Brown, B. 1916. A new crested trachodont dinosaur Prosaurolophus maximus. Bulletin of the 643 American Museum of Natural History, 35: 701–708. 644 645 Bell, P.R. 2011. Cranial osteology and ontogeny of Saurolophus angustirostris from the Late 646 Cretaceous of Mongolia with comments on Saurolophus osborni from Canada. Acta 647 Palaeontologica Polonica, 56: 703–722. doi:10.4202/app.2010.0061. 648 649 Bertozzo, F., Dal Sasso, C., Fabbri, M., Manucci, F., and Maganuco, S. 2017. Redescription of a 650 remarkably large Gryposaurus notabilis (Dinosauria: Hadrosauridae) from Alberta, Canada. In 651 Memorie della Società Italiana di Scienze Naturali e del Museo Civico di Storia Naturale di 652 Milano Volume XLIII. Edited by M. Mura. Litografia Solari, Milan, Italy. pp 1-56. 653 654 Campione, N., and Evans, D.C. 2011. Cranial Growth and Variation in Edmontosaurs 655 (Dinosauria: Hadrosauridae): Implications for Latest Cretaceous Megaherbivore Diversity in 656 North America. PLoS ONE 6: e25186. doi:10.1371/journal.pone.0025186. 657 658 Currie, P. J., and Russell, D.A. 2005. The Geographic and Stratigraphic Distribution of 659 Articulated and Associated Dinosaur Remains. In Dinosaur Provincial Park: A Spectacular

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660 Ancient Ecosystem Revealed. Edited by P.J. Currie and E.B. Koppelhus. Indiana University 661 Press, Bloomington, Indiana. pp. 537-569. 662 663 Cuthbertson, R.S., and Holmes, R.B. 2010. The first complete description of the holotype of 664 Brachylophosaurus canadensis Sternberg, 1953 (Dinosauria: Hadrosauridae) with comments on 665 intraspecific variation. Zoological Journal of the Linnean Society, 159: 373–397. doi: 666 10.1111/j.1096-3642.2009.00612.x. 667 668 Dodson, P. 1971. Sedimentology and taphonomy of the Oldman Formation (Campanian), 669 Dinosaur Provincial Park, Alberta (Canada). Palaeogeography, Palaeoclimatology, 670 Palaeoecology, 10: 21-74. doi: 10.1016/0031-0182(71)90044-7. 671 672 Dodson, P. 1975. Taxonomic implications of relative growth in lambeosaurine hadrosaurs. 673 Systematic Biology, 24: 37–54. doi: 10.2307/2412696. 674 675 Eberth, D.A. 2005. The Geology. In Dinosaur Provincial Park: A Spectacular Ancient Ecosystem 676 Revealed. Edited by P.J. Currie and E.B. Koppelhus. Indiana University Press, Bloomington, 677 Indiana. pp. 54-82. 678 679 Eberth, D.A., and Getty, M.A. 2005. Ceratopsian bonebeds: occurrence, origins, and 680 significance. In Dinosaur Provincial Park:Draft A Spectacular Ancient Ecosystem Revealed. Edited by 681 P.J. Currie and E.B. Koppelhus. Indiana University Press, Bloomington, Indiana. pp. 501-536. 682 683 Evans, D. 2007. Ontogeny and evolution of lambeosaurine dinosaurs (Ornithischia: 684 Hadrosauridae). PhD Thesis, Department of Ecology and Evolutionary Biology, University of 685 Toronto, Toronto, ON. 686 687 Evans, D.C. 2010. Cranial anatomy and systematics of Hypacrosaurus altispinus, and a 688 comparative analysis of skull growth in lambeosaurine hadrosaurids (Dinosauria: Ornithischia). 689 Zoological Journal of the Linnean Society, 159: 398–434. doi: 10.1111/j.1096- 690 3642.2009.00611.x. 691 692 Evans, D.C., and Reisz, R.R. 2007. Anatomy and Relationships of Lambeosaurus 693 magnicristatus, a crested hadrosaurid dinosaur (Ornithischia) from the Dinosaur Park Formation, 694 Alberta. Journal of Vertebrate Paleontology, 27: 373-393. doi: 10.1671/0272-4634. 695 696 Evans, D. C., McGarrity, C.T., and Ryan, M.J. 2013. A Skull of Prosaurolophus maximus from 697 Southeastern Alberta and the Spatiotemporal Distribution of Faunal Zones in the Dinosaur Park 698 Formation. In Hadrosaurs. Edited by D. A. Eberth and D. C. Evans. Indiana University Press, 699 Bloomington, Indiana. pp. 200-207. 700 701 Freedman Fowler, E., and Horner, J. 2015. A New Brachylophosaurin Hadrosaur (Dinosauria: 702 Ornithischia) with an Intermediate Nasal Crest from the Campanian Judith River Formation of 703 Northcentral Montana. PLoS ONE 10: e0141304. doi:10.1371/journal.pone.0141304. 704

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705 Gates, T. A., and Sampson, S.D. 2007. A new species of Gryposaurus (Dinosauria: 706 Hadrosauridae) from the late Campanian Kaiparowits Formation, southern Utah, USA. 707 Zoological Journal of the Linnean Society, 151: 351-376. doi: 10.1111/j.1096- 708 3642.2007.00349.x. 709 710 Gates, T.A., and Scheetz, R. 2015. A new saurolophine hadrosaurid (Dinosauria: Ornithopoda) 711 from the Campanian of Utah, North America. Journal of Systematic Palaeontology, 13: 711-725. 712 doi: 10.1080/14772019.2014.950614. 713 714 715 Gates, T.A., Lund, E.K., Boyd, C.A., Getty, M.A., DeBlieux, D.D., Kirkland, J.I., Evans, D.C. 716 2013. Ornithopod dinosaurs from the Grand Staircase-Escalante National Monument Region, 717 Utah, and their role in paleobiogeographic and macroevolutionary studies. In At the top of the 718 Grand Staircase: The Late Cretaceous in Utah. Edited by A.L Titus and M.A. Loewen. Indiana 719 University Press, Bloomington, Indiana. pp. 463-481. 720 721 Gunz, P., and Mitteroecker, P. 2013. Semilandmarks: a method for quantifying curves and 722 surfaces. Hystrix, 24: 103–109. doi: 10.4404/hystrix-24.1-6292. 723 724 Hopson, J.A. 1975. The evolution of cranial display structures in hadrosaurian dinosaurs. 725 Paleobiology, 1: 21-43. doi:10.1017/S0094837300002165Draft 726 727 Horner, J. R. 1992. Cranial Morphology of Prosaurolophus (Ornithischia: Hadrosauridae): With 728 Descriptions of Two New Hadrosaurid Species and an Evaluation of Hadrosaurid Phylogenetic 729 Relationships. Museum of the Rockies, Occasional Paper 2: 1-119. 730 731 Lambe, L. 1914. On Gryposaurus notabilis, a new genus and species of trachodont dinosaur 732 from the Belly River Formation of Alberta, with a description of the skull of Chasmosaurus 733 belli. Ottawa Naturalist, 27: 145-155. 734 735 Lehman, T.M., Wick S. L. and Wagner J. R. 2016. Hadrosaurian dinosaurs from the 736 Maastrichtian Javelina Formation, Big Bend National Park, Texas. Journal of Paleontology, 90: 737 333- 356. doi:10.1017/jpa.2016.48 738 739 Lull R.S., and Wright, N.E. 1942. Hadrosaurian dinosaurs of North America. Geological Society 740 of America Special Papers 40: 1–242. 741 742 Mallon, J.C., Evans, D.C., Ryan, M.J., and Anderson, J.S. 2012. Megaherbivorous dinosaur 743 turnover in the Dinosaur Park Formation (upper Campanian) of Alberta, Canada. 744 Palaeogeography, Palaeoclimatology, Palaeoecology, 350: 124-138. 745 doi:10.1016/j.palaeo.2012.06.024 746 747 Mallon, J.C., Evans, D.C., Ryan, M.J., and Anderson, J.S. 2013. Feeding height stratification 748 among the herbivorous dinosaurs from the Dinosaur Park Formation (upper Campanian) of 749 Alberta, Canada. BMC Ecology, 13: 14. doi:10.1186/1472-6785-13-14 750

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751 McGarrity, C., Campione, N., and Evans, D. 2013. Cranial anatomy and variation in 752 Prosaurolophus maximus (Dinosauria: Hadrosauridae). Zoological Journal of the Linnean 753 Society, 167: 531–568. doi: 10.1111/zoj.12009. 754 755 Ostrom, J.H. 1961. Cranial morphology of the hadrosaurian dinosaurs of North America. 756 Bulletin of the American Museum of Natural History 122: 33–186. 757 758 Parks, W.A. 1920. The osteology of the trachodont dinosaur Kritosaurus incurvimanus. 759 University of Toronto Studies, Geology Series 11: 1-75. 760 761 Parks, W.A. 1922. Parasaurolophus walkeri, a new genus and species of crested trachodont 762 dinosaur. University of Toronto Studies, Geological Series 13: 1–32. 763 764 Parks, W.A. 1923. Corythosaurus intermedius, a new species of trachodont dinosaur. University 765 of Toronto Studies, Geological Series 15: 1–57. 766 767 Pinna, G. 1979. Osteologia dello scheletro di Kritosaurus notabilis (Lambe, 1914) del Museo 768 Civico di Storia Naturale di Milano. Memorie della Societa Italiana di Scienze Naturali e del 769 Museo Civico di Storia Naturalle di Milano, 22: 33-56. 770 771 Prieto-Márquez, A. 2010a. Global phylogenyDraft of Hadrosauridae (Dinosauria: Ornithopoda) using 772 parsimony and Bayesian methods. Zoological Journal of the Linnean Society 159: 435-502. doi: 773 10.1111/j.1096-3642.2009.00617.x 774 775 Prieto-Márquez, A. 2010b. The braincase and skull roof of Gryposaurus notabilis (Dinosauria, 776 Hadrosauridae) with a taxonomic revision of the genus. Journal of Vertebrate Paleontology 30: 777 838-854. doi: 10.1080/02724631003762971. 778 779 Prieto-Márquez, A. 2012. The skull and appendicular skeleton of Gryposaurus latidens, a 780 saurolophine hadrosaurid (Dinosauria: Ornithopoda) from the early Campanian (Cretaceous) of 781 Montana, USA. Canadian Journal of Earth Sciences, 49: 510-532. doi: 10.1139/e11-069. 782 783 R Core Team. 2018. R: A Language and Environment for Statistical Computing. 784 785 Ryan, M. J., and Evans, D.C. 2005. Ornithischian Dinosaurs. In Dinosaur Provinical Park: A 786 Spectacular Ancient Ecosystem Revealed. Edited by P. J. Currie and E. B. Koppelhus. Indiana 787 University Press, Bloomington, Indiana. pp. 312-348. 788 789 Schneider, C.A., Rasband, W.S., and Eliceiri, K.W. 2012. NIH Image to ImageJ: 25 years of 790 image analysis. Nature methods, 9: 671–675. doi: 10.1038/nmeth.2089. 791 792 Sternberg, C.M. 1950. Steveville –West of the Fourth Meridian, Alberta. Geological Survey of 793 Canada Topographic Map 969A. 1/31,680 scale (1 inch to 1/2 mile). 794

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795 Wagner, J.R. 2001. The hadrosaurian dinosaurs (Ornithischia: Hadrosauria) of Big Bend 796 National Park, Brewster County, Texas, with implications for Late Cretaceous 797 Paleozoogeography. Unpublished M.Sc. Thesis, Texas Tech University, Lubbock, Texas, U.S. 798 799 Waldman, M. 1969. On an immature specimen of Kritosaurus notabilis (Lambe), (Ornithischia: 800 Hadrosauridae) from the Upper Cretaceous of Alberta, Canada. Canadian Journal of Earth 801 Sciences, 6: 569–576. doi: 10.1139/e69-057. 802 803 Warton, D. I., Duursma, R.A., Falster, D.S., and Taskinen, S. 2012. smatr 3 - an R package for 804 estimation and inference about allometric lines. Methods in Ecology and Evolution, 3:257-259. 805 doi: 10.1111/j.2041-210X.2011.00153.x. 806 807 808

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809 Table 1: Stratigraphic position of identifiable hadrosaurines from the Dinosaur Park Formation2.

Quarry Specimen # Genus Species Previous Elevation Elevation (m) Identifications (m asl) above Oldman Formation

Q103 CMN 8893 Brachylophosaurus canadensis canadensis 659.3 -7* (1.3 modeled)

Q034 ROM 873 Gryposaurus notabilis notabilis 648.1 0.1

Q035 CMN 2278 Gryposaurus notabilis notabilis 658.7 10.7

Q137 Milan v345 Gryposaurus notabilis notabilis (Pinna 1976) 665.1 3.1 incurvimanus (Currie and Russell 2005)

Q118 ROM 1939 Gryposaurus notabilis notabilis 673.1 9* (11.1 modeled)

Q149 TMP Gryposaurus incurvimanus incurvimanus 670.3 0.5* (10.3 modeled) 1980.022.0001

Q077 FMNH? ? ? incurvimanus (Currie 668.9 12.9 and Russell 2005)

Q097 TMP Gryposaurus ? Hadrosauridae, c.f. 664.5 8* (6.5 modeled) 1999.055.0115 Gryposaurus (Currie and Koppelhus, 2005) Q099 ROM 764 Gryposaurus Draftincurvimanus incurvimanus 677.0 16* (15 modeled) Q252 CMN 8784 Gryposaurus incurvimanus notabilis (Waldman 656 7.5* (0 modeled) 1969)

ROM 667 Gryposaurus ? notabilis ? ?

Q004a ROM 787 Prosaurolophus maximus 694.6 32.6

Q004b La Plata Prosaurolophus maximus 694.6 32.6

Q086 NMC 2277 Prosaurolophus maximus 693.7 33.7

Q046 USNM 12712 Prosaurolophus maximus 690 34

Q213 TMP Prosaurolophus maximus 696.1 36.1 1993.081.0001

Q208 TMP Prosaurolophus maximus 700.5 38.5 1980.016.0923

Q192 TMP Prosaurolophus maximus 700.5 42.5 1984.001.0001

U193 TMP Prosaurolophus maximus 702.3 44.3

Q116 TMM 41262 Prosaurolophus maximus 707.3 45.3

Q114 ROM 1928 Prosaurolophus maximus 714.6 54.6

Q076 ACM 578 Prosaurolophus? ?Gryposaurus 699.6 37.5* (43.6 (Sternberg 1950), modeled) incurvimanus (Currie and Russell, 2005)

2 An asterisk (*) indicates that the stratigraphic position was hand-measured in the field by DCE using a Jacob’s staff and a theodolite.

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810

811 Table 2: Measurements from Gryposaurus specimens used in morphometric analysis, in mm3

TMP ROM TMP ROM MSNM CMN 1980.022.0001 764 1991.081.0001 873 v345 2278 total skull length 675 -- 784 981 978 950 length of naris 190 -- 231 361 335 343 naris to nasal crest 50 -- 89 123 132 125 apex* height of quadrate* 305 345 391 473 440 480 lateral length of 152 145 214 245 191 235 postorbital length of jugal* 255 310 350 407 340 360 min. distance from 130 120 100 124 107 112 frontal to base of crest* frontals to crest 187 -- 187 180 195 160 apex* min. jugal height 38 52 56 63 60 66 below orbit* min. jugal height 36 50 65 57 56 72 below itf* 812 Draft 813

3 Measurements with an asterisk (*) were used in bivariate plots.

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814 Table 3: Regression statistics for all plots showing OLS regressions of PC axes against skull size for both 815 Gryposaurus and Prosaurolophus4.

Sample Slope 95% CI p- R2 size (N) value Analysis quadrate vs. 6 0.62 0.16 to 1.08 0.78 0.02* 1 Gryposaurus PC1 quadrate vs. 6 0.27 -0.96 to 1.50 0.08 0.58 PC2 quadrate vs. 7 0.44 -0.45 to 1.32 0.24 0.26 Prosaurolophus PC1 quadrate vs. 7 0.11 -0.56 to 0.79 0.04 0.68 PC2 Analysis quadrate vs. 5 0.43 -0.05 to 0.90 0.73 0.07 2 Gryposaurus PC1 quadrate vs. 5 -0.53 -1.16 to 0.10 0.71 0.08 PC2 quadrate vs. 7 0.21 0.27 to 1.77 0.09 0.51 Prosaurolophus PC1 quadrate vs. 7 0.11 -0.26 to 0.48 0.10 0.48 PC2 Analysis centroid vs. PC 7 0.16 -0.49 to 0.81 0.08 0.55 3 Gryposaurus 1

centroid vs. PC 7 0.02 -0.69 to 0.73 0.01 0.95 2 Draft centroid vs. 8 0.20 -0.61 to 1.00 0.06 0.57 Prosaurolophus PC 1 centroid vs. 8 -0.08 -0.62 to 0.02 0.75 PC 2 0.47 816 817

4 Alpha: p=0.05. An asterisk (*) indicates a slope that is significantly different from 0 (two-tailed t-test p < 0.05).

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818 Table 4: Regression statistics for all bivariate plots showing two-measurement regressions for Gryposaurus5.

Sample Slope 95% CI R- p-value Trend p-value size (N) squared from t- distr. quadrate vs. frontal to 6 -0.54 -1.55 to -0.19 0.16 0.44 Neg. 1.99 base of crest quadrate vs. frontal to 5 -0.41 -1.43 to -0.11 0.22 0.43 Neg. 1.99 crest apex quadrate vs. naris to 5 2.18 1.42 to 3.32 0.94 0.006* Pos. 0.14 Bivariate crest apex plots quadrate vs. jugal 6 0.88 0.50 to 1.50 0.87 0.01* Iso. 1.29 length quadrate vs. jugal 6 1.10 0.71 to 1.69 0.90 0.004* Iso 0.77 height below orbit quadrate vs. jugal 6 1.32 0.65 to 2.70 0.69 0.04* Iso. 0.67 height below ITF 819 820 821 822 823 824 825 Draft 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849

5 Alpha: p=0.05. Significant p-values indicated with an asterisk (*).

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850 851 Figure captions: 852 853 Fig. 1: Photograph (A) and illustration (B) of G. incurvimanus holotype ROM 764 in left lateral view. d, 854 dentary; f, frontal; j, jugal; la, lacrimal; mx, maxilla; na, nasal; pf, prefrontal; po, postorbital; qj, 855 quadratojugal; qu, quadrate; sq, squamosal; su, surangular. Scale bar: 10 cm. 856 857 Fig. 2: Landmark and sliding semi-landmark placement for (A) Analysis 1, (B) Analysis 2, and (C) 858 Analysis 3. Landmarks are indicated by circles, and semi-landmarks by squares. Line drawing based on 859 ROM 873. Scale bar: 10 cm. 860 861 Fig. 3: Photograph (A) and illustration (B) of TMP 1980.022.0001 skull in left lateral view, referred to 862 Gryposaurus incurvimanus. Photograph (C) and illustration (D) of TMP 1980.022.0001 in dorsal view. 863 ar, articular; d, dentary; f, frontal; j, jugal; la, lacrimal; mx, maxilla; na, nasal; pd, predentary; pf, 864 prefrontal;p, premaxilla; po, postorbital; pt, parietal; qj, quadratojugal; qu, quadrate; sq, squamosal; stf, 865 supratemporal fenestra; su, surangular. Scale bar: 10 cm. 866 867 Fig. 4: Photographs of Gryposaurus sp. specimen TMP 1991.081.0001, skull in left lateral (A) and 868 dorsal view (B). Scale bar: 10 cm. 869 870 Fig. 5: Photographs of G. notabilis skulls including: (A) ROM 873, (B) MSNM v345 (from Bertozzo et 871 al. 2017), (C) CMN 2278 (holotype), and (D) AMNH 5350 (from Prieto-Márquez 2010b), all in left 872 lateral view. Scale bar: 10 cm. Draft 873 874 Fig. 6: Tentatively referred Gryposaurus specimens, including ACM 578 in left lateral view, photograph 875 (A) and illustration (B), in dorsal view, photograph (C) and illustration (D). Shaded portions of 876 illustrations represent parts of the skull that a reconstructed with plaster. ROM 667, hadrosaurine 877 braincase in right lateral view (E), and in dorsal view (F). Scale bar: 10 cm. 878 879 Fig. 7: Plots from Analysis 1: (A) Morphospace showing principal component (PC) axes 1 and 2 (71.6% 880 and 11.6% of the total variation, respectively), including both Gryposaurus and Prosaurolophus. Warp 881 grids show the direction in which landmarks are shifting along the axes. (B) Morphospace showing PC 882 axes 3 and 4 (4.9% and 4.1% of the total variation, respectively). (C) Regression plot testing for 883 allometric growth along PC 1 axis. (D) Regression plot testing for allometric growth along PC 2 axis. 884 Legends provided in figures. Test statistics provided in Table 3. 885 886 Fig. 8: Plots from Analysis 2: (A) Morphospace showing PC axes 1 and 2 (74.8% and 6.1% of the total 887 variation, respectively) including both Gryposaurus and Prosaurolophus. Warp grids show the direction 888 in which landmarks are shifting along the axes. (B) Morphospace showing PC axes 3 and 4 (4.9% and 889 4.0% of the total variation, respectively). (C) Regression plot testing for allometric growth along PC 1 890 axis (D) Regression plot testing for allometric growth along PC 2 axis. Legends provided in figures. Test 891 statistics provided in Table 3. 892 893 Fig. 9: Bivariate regression plots testing for allometry in various skull measurements for Gryposaurus. 894 All data is log-transformed. Legends provided in figures. Test statistics provided in Table 4. 895 896 Figure 10: Temporal range of hadrosaurines from Dinosaur Provincial Park; Gryposaurus and 897 Prosaurolophus specimens from the Dinosaur Park Formation with known stratigraphic data are included. 898 The hexagon indicates Brachylophosaurus. Closed circles indicate specimens previously identified as G. 899 notabilis, open circles indicate those previously identified as ‘G. incurvimanus’, and striped circles

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900 indicate Gryposaurus sp. Closed squares indicate Prosaurolophus maximus, and the striped square 901 indicates ambiguous specimen ACM 578. Skull illustrations are scaled against each other to show size 902 variation. Stratigraphic dates sourced from Freedman Fowler and Horner (2015). Scale bar: 10 cm. 903

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Photograph (A) and illustration (B) of G. incurvimanus holotype ROM 764 in left lateral view. d, dentary; f, frontal; j, jugal; la, lacrimal; mx, maxilla; na, nasal; pf, prefrontal; po, postorbital; qj, quadratojugal; qu, quadrate; sq, squamosal; su, surangular. Scale bar: 10 cm.

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Landmark and sliding semi-landmark placement for (A) Analysis 1, (B) Analysis 2, and (C) Analysis 3. Landmarks are indicated by circles, and semi-landmarks by squares. Line drawing based on ROM 873. Scale bar: 10 cm.

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Photograph (A) and illustration (B) of TMP 1980.022.0001 skull in left lateral view, referred to Gryposaurus incurvimanus. Photograph (C) and illustration (D) of TMP 1980.022.0001 in dorsal view. ar, articular; d, dentary; f, frontal; j, jugal; la, lacrimal; mx, maxilla; na, nasal; pd, predentary; pf, prefrontal;p, premaxilla; po, postorbital; pt, parietal; qj, quadratojugal; qu, quadrate; sq, squamosal; stf, supratemporal fenestra; su, surangular. Scale bar: 10 cm.

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Photographs of Gryposaurus sp. specimen TMP 1991.081.0001, skull in left lateral (A) and dorsal view (B). Scale bar: 10 cm.

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Photographs of G. notabilis skulls including: (A) ROM 873, (B) MSNM v345 (from Bertozzo et al. 2017), (C) CMN 2278 (holotype), and (D) AMNH 5350 (from Prieto-Márquez 2010b), all in left lateral view. Scale bar: 10 cm.

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Tentatively referred Gryposaurus specimens, including ACM 578 in left lateral view, photograph (A) and illustration (B), in dorsal view, photograph (C) and illustration (D). Shaded portions of illustrations represent parts of the skull that a reconstructed with plaster. ROM 667, hadrosaurine braincase in right lateral view (E), and in dorsal view (F). Scale bar: 10 cm.

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Plots from Analysis 1: (A) Morphospace showing principal component (PC) axes 1 and 2 (71.6% and 11.6% of the total variation, respectively), including both Gryposaurus and Prosaurolophus. Warp grids show the direction in which landmarks are shifting along the axes. (B) Morphospace showing PC axes 3 and 4 (4.9% and 4.1% of the total variation, respectively). (C) Regression plot testing for allometric growth along PC 1 axis. (D) Regression plot testing for allometric growth along PC 2 axis. Legends provided in figures. Test statistics provided in Table 3.

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Plots from Analysis 2: (A) Morphospace showing PC axes 1 and 2 (74.8% and 6.1% of the total variation, respectively) including both Gryposaurus and Prosaurolophus. Warp grids show the direction in which landmarks are shifting along the axes. (B) Morphospace showing PC axes 3 and 4 (4.9% and 4.0% of the total variation, respectively). (C) Regression plot testing for allometric growth along PC 1 axis (D) Regression plot testing for allometric growth along PC 2 axis. Legends provided in figures. Test statistics provided in Table 3.

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Bivariate regression plots testing for allometry in various skull measurements for Gryposaurus. All data is log-transformed. Legends provided in figures. Test statistics provided in Table 4.

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Temporal range of hadrosaurines from Dinosaur Provincial Park; Gryposaurus and Prosaurolophus specimens from the Dinosaur Park Formation with known stratigraphic data are included. The hexagon indicates Brachylophosaurus. Closed circles indicate specimens previously identified as G. notabilis, open circles indicate those previously identified as ‘G. incurvimanus’, and striped circles indicate Gryposaurus sp. Closed squares indicate Prosaurolophus maximus, and the striped square indicates ambiguous specimen ACM 578. Skull illustrations are scaled against each other to show size variation. Stratigraphic dates sourced from Freedman Fowler and Horner (2015). Scale bar: 10 cm.

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