Redescription of Lophorhothon Atopus (Ornithopoda: Dinosauria) from the Late Cretaceous of Alabama Based on New Material

Canadian Journal of Earth Sciences

Redescription of Lophorhothon atopus (Ornithopoda: Dinosauria) from the Late Cretaceous of Alabama based on new material

Journal: Canadian Journal of Earth Sciences

Manuscript ID cjes-2020-0173.R1

Manuscript Type: Article

Date Submitted by the 10-Dec-2020 Author:

Complete List of Authors: Gates, Terry; North Carolina State University, Biological Sciences; North Carolina Museum of Natural Sciences, Paleontology Lamb, James; The Black Belt Museum, University of West Alabama, PaleontologyDraft Keyword: Dinosaur, Anatomy, Hadrosaur, Campanian, Santonian, Biogeography

Is the invited manuscript for consideration in a Special Tribute to Dale Russell Issue? :

1 A redescription of Lophorhothon atopus (Ornithopoda: Dinosauria) from the Late

2 Cretaceous of Alabama based on new material

4 Terry A. Gates*, Department of Biological Sciences, North Carolina State University,

5 100 Brooks Hall, Raleigh, NC, 27695, USA, [email protected]

6 James P. Lamb, Department of Paleontology, Black Belt Museum, University of

7 Western Alabama, Station 45, Livingston, AL, 35470, USA, [email protected]

8 * Corresponding author

9 10 Draft

11 Abstract

12 Diagnostic dinosaur fossils of the southeastern United States are rare

13 discoveries, and even more precious are those fossils that preserve a large portion of a

14 skeleton. Sixty years ago, the dinosaur Lophorhothon atopus was described from Upper

15 Cretaceous sediments of Alabama. It then represented the oldest, most complete,

16 dinosaur in the southeast United States. Based on a reexamination of the holotype

17 material and a new specimen collected from the same beds, we provide a new

18 diagnosis of this taxon. In particular, the solid nasal crest has several autapomorphies

19 including caudally projecting frontal processes that are oval in cross-section, meaning

20 that they did not coalesce at the midline. Other autapomorphies are found on the

21 prefrontal and squamosal. CombiningDraft the two Lophorhothon specimens provides nearly

22 the entire skeleton for phylogenetic analysis, which we find as a hadrosauromorph just

23 outside of Hadrosauridae. The original diagnosis of this taxon included the frontonasal

24 fontanelle as a distinguishing character, but comparing the many examples of

25 frontonasal openings across hadrosauromorph taxa shows that in at least a few

26 species, such as Lophorhothon, the structures should be considered a frontonasal

27 fenestra instead of a fontanelle. Additionally, the notion that dinosaurs from the East

28 Coast of the United States represent primitive relicts is an idea that originated before

29 many of the European and Asian hadrosauromorphs known today had been discovered.

30 With new dating and phylogenetic information, it appears that Appalachian dinosaurs

31 are on par evolutionarily with most of the global community and the term ‘relict fauna’

32 should be abandoned.

33 Keywords: Dinosaur, Anatomy, Hadrosaur, Campanian, Santonian, Biogeography

34 Introduction

35 Dale Russell was driven to understand the world in which dinosaurs lived and the

36 way that the Mesozoic world influenced their evolution. In fact, he told one of us (TAG)

37 that he moved to North Carolina as a faculty member at North Carolina State University

38 in 1997 to be closer to the environment in which Cretaceous dinosaurs lived. With that,

39 Dale took a great interest in the dinosaurs of the American Southeast, a region that has

40 been given the name Appalachia, because during the height of Late Cretaceous global

41 sea level the Western Interior Seaway flooded North America and created three island

42 continents, of which eastern North America was one.

43 The southeast United States has long provided valuable specimens to the study

44 of dinosaur paleontology, such as theDraft first dinosaurs skeletons described from North

45 America (e.g., Leidy 1858, Schwimmer et al. 1993, Prieto-Márquez et al. 2006b,

46 Brownstein 2021). Indeed, Kaye and Russell (1973) described the oldest ‘hadrosaur’

47 remains known from North America, a partial skeleton from Santonian deposits in

48 Mississippi. Since this publication, new discoveries and the advent of phylogenetics in

49 paleontology has shown that hadrosaurid dinosaurs are but one clade within an ever

50 expanding tree of ornithopod dinosaurs; and that many taxa of hadrosauroids have

51 synapomorphies that grade across the hadrosaurid taxonomic boundary. One of those

52 new discoveries is Eotrachodon, a hadrosaurid that dates to the Santonian of Alabama

53 that shows Kaye and Russell (1973) were possibly correct in their taxonomic

54 assignment.

55 Of all the states that encompass the Appalachia paleo-region, Alabama has the

56 most prestigious record of dinosaur species that are still considered valid. The first of

57 these dinosaurs, and the first ornithopod with exquisite cranial material from the East

58 Coast of North America, was described by Langston (1960) and called Lophorhothon

59 atopus. Lophorhothon remained the most diagnostic ornithopod in Appalachia until the

60 discovery of Eotrachodon by one of us (JL) and the subsequent description of the

61 specimen by Prieto-Marquez et al. (2016a, 2016b). In light of 40 years of ornithopod

62 discoveries across North America since the original publication, it is time to provide

63 more context and an updated description of Lophorhothon, including a new specimen

64 that adds important information about this species’ anatomy. Dale Russell's dream of

65 understanding the dinosaurs of the East coast is one that is shared by many

66 paleontologists today. In order to realize this dream it is more important than ever that

67 we obtain the most accurate informationDraft on anatomy and evolutionary relationships.

69 Systematic Paleontology

71 DINOSAURIA (Owen 1842)

72 ORNITHISCHIA (Seeley 1887)

73 ORNITHOPODA (Marsh 1881)

74 IGUANODONTIA (Dollo 1888)

75 HADROSAUROIDEA (Sereno 1986)

76 HADROSAUROMORPHA (Norman 2015)

77 Lophorhothon atopus (Langston 1960) lsid:zoobank.org:pub:2FF0FC92-8CB7-4E53-

78 A8C6-BF4A542C76AC

79 Type specimen - FMNH P27383. Partial skull consisting of partial right maxilla,

80 partial right pterygoid, partial left jugal, partial right and left nasals, partial right lacrimal,

81 complete left lacrimal, partial right prefrontal, mostly complete left prefrontal, complete

82 right and left frontals, complete right and left postorbitals, mostly complete right

83 squamosal, partial left squamosal, partial right quadrate, partial left quadrate, complete

84 right and left orbitosphenoids, mostly complete right laterosphenoid, partial left

85 laterosphenoid, complete basioccipital, partial right exoccipital, complete left occipital,

86 possible predentary fragment. Incomplete postcrania consisting of the axis, a single

87 cervical vertebra, two(?) dorsal vertebrae, four(?) sacral vertebrae, 35(?) caudal

88 vertebrae, 28(?) neural arches and neural spines, fragmentary ribs, eight(?) sacral ribs,

89 10 chevrons, mostly complete left femur,Draft mostly complete right and left tibiae, mostly

90 complete right and left fibulae, mostly complete right astragalus, partial left astragalus,

91 complete right and left calcaneum, complete right and left metatarsals II, III, and IV, 12

92 pedal phalanges, and five pedal unguals.

93 Locality - From Langston (1960) “Site 9 (Zangerl, 1948, p.10 and pl 3.), southeast

94 of Marion Junction, and 10 miles west of Selma, Dallas County, Alabama, on the Moore

95 Brothers’ farm.” Field checked by J.L. = N 32.41888° W 87.18471° (Fig. 1).

96 Horizon - Unnamed lower member of the Mooreville Chalk Fm. Approximately 10

97 m below the Santonian/Campanian boundary (Fig. 1).

98 Original Diagnosis - “Crested hadrosaurines with elevated cranium and short

99 snout, broad orbits and wide temporal fenestrae; pyramidal crest on nasals resembling

100 crest of Prosaurolophus but situated well forward of the orbits. Immature individuals with

101 large fontanelle. Teeth with heavily crenulated enamel surfaces and denticulate coronal

102 margins,” (Langston 1960, p. 321).

103 Revised Diagnosis - Ornithopod dinosaur with the following autapomorphies:

104 nasal with rostromedial facing shallow concavities separated by a median ridge, an

105 elongated, ovular posterior process that tapers dorsoventrally distally (when combined

106 with its opposite nasal, the posterior processes diverge instead of coalescing);

107 prefrontal with elongated lacrimal buttress well-offset from thin rostromedial lacrimal

108 body, and incised narrow lacrimal fossa (for accepting a complimentary process from

109 the lacrimal); squamosal with a rostral process that possesses a ventrally-directed fold

110 of bone that overlaps the corresponding postorbital caudal process.

111 Additionally, Lophorhothon possessesDraft the following unique combination of

112 characters: premaxilla with a ‘double-layer’ morphology at oral rim and conical denticles

113 along the oral margin; frontonasal fenestra; jugal with a rostroventrally oriented

114 vermiform extension of rostral process; prefrontal orbital margin with a sharp lateral

115 edge.

116 Referred specimen - AUMP 2995 partial skull and postcranial skeleton consisting

117 of fragmentary left premaxilla, fragmentary left maxilla, partial left jugal, partial right

118 nasal, partial right squamosal, partial right quadrate, complete orbitosphenoid, complete

119 basioccipital, fragmentary dentary, partial left surangular, and a complete left articular.

120 Postcranial skeleton includes five cervical vertebrae, six dorsal vertebrae, seven

121 sacrals, 30 caudal vertebrae, 21 unassociated neural arches and neural spines, four

122 chevrons, fragmentary ribs, four sacral ribs, mostly complete right scapula, complete left

123 sternal, complete right and left coracoids, complete right and left humeri, partial right

124 ulna, mostly complete left ulna, complete left radius, a single carpal (ulnare?), complete

125 right and left metacarpal II, complete right? Metacarpal III, complete right and left

126 metacarpal IV, complete right metacarpal V, complete right phalanges (II-1, III-1, IV-1,

127 III-2, V-2), complete left phalanges (II-2, III-2, II-ungual), mostly complete left ilium,

128 fragments of right ilium, partial left pubis, partial right and left ischia, fragmentary right

129 femur, mostly complete left femur, mostly complete right tibia, complete left tibia, mostly

130 complete right fibula, complete left fibula, fragmentary right astragalus, complete left

131 metatarsal III, mostly complete left metatarsal IV, complete right phalanges (II-1, II-2),

132 complete left phalanges (II-2, IV-2), and two terminal pedal unguals.

133 Locality - Erosional badlands in sec. 28, T19N, R4E, near Cedarville, Hale Co.,

134 AL, old Alex Crawford Farm (Jim Dobie,Draft per comm. 1996). Excavated by J. Dobie of

135 Auburn University in 1966 and 1972. The precise locality is obscured as the area is now

136 covered with extensive catfish farms, but using Dobie’s verbal descriptions and old

137 aerial photo quads, we place the specimen at N 32.60015° W 87.68163° (Fig. 1).

138 Horizon - Unnamed lower member of the Mooreville Chalk Fm. Approximately 10

139 m above the Santonian/Campanian boundary (Fig. 1).

140 Remarks - Puckett (1994) noted that the Santonian/Campanian boundary (83.6

141 Ma) in Dallas County, Alabama, occurs 105’ (32m) above the contact of the Tombigbee

142 Greensand Member of the Eutaw Formation and the lower unnamed member of the

143 Mooreville Chalk (top of the Dicarinella asymetrica zone). He also noted that the

144 Mooreville Chalk in Dallas County at the Alabama Power Selma Site Test Well, site 3,

145 hole 3, was completely recovered and measured 406’ (123.7m) (Liu 2007). Liu (2007)

146 further calculated the duration of the Mooreville Chalk as spanning calcareous

147 nannofossil zones CC17 to CC19a, a duration of 4 million years (Shipboard Scientific

148 Party, 1998) to 4.51 million years (Hardenbolt ,et al. 1998). Thus, a sedimentation rate

149 for the Mooreville Chalk Formation of between .0261 - .0294 mm/year can be estimated,

150 at least for deposits in central Alabama (Liu 2007). However, based upon

151 disagreements in sedimentation rate between different studies across Alabama and

152 Mississippi, here we use an intermediate depositional rate of 0.027 mm/year to account

153 for all known data in estimating the ages of FMNH P27383 and AUMP 2295.

154 Davis et al. (1975) established that the Late Cretaceous rock units in central and

155 western Alabama dip to the south and southwest respectively, perpendicular to strike at

156 about 6.5m/km. Knowing the surface outcrop position of the Eutaw/Mooreville contact, it

157 is then possible to calculate the stratigraphicDraft position of FMNH 27383 and AUMP 2295

158 within the Mooreville Chalk, and use the deposition rate to calculate their age.

159 FMNH 27383 lies 3.55 km south of the Eutaw/Mooreville contact exposed along

160 the banks of the Cahaba River at 32.450392 N, 87.185556 W. This places the holotype

161 at about 22 meters above the Eutaw/Mooreville contact stratigraphically, and 10 meters

162 below the Santonian/Campanian boundary. If the Santonian/Campanian boundary is

163 placed at 83.6 Ma, and the Mooreville Chalk accumulated at the rate of .027 mm/year,

164 FMNH 27383 was deposited at about 83.97 Ma.

165 AUMP 2295 lies 6.87 km south of the Eutaw/Mooreville contact projected as a

166 line connecting exposures at Limestone Creek and Old Eerie Bluff, Hale County,

167 Alabama. This places AUMP 2295 42 m above the Eutaw/Mooreville contact, and 10 m

168 above the Santonian/Campanian Boundary. Thus AUMP 2295 was deposited at 83.23

169 Ma, making the temporal separation of FMNH 27383 and AUMP 2295 only about 0.74

170 million years (Fig. 1).

171

172 Description

173 Langston (1960) described the species Lophorhothon atopus based on a single,

174 presumably immature individual from the earliest Campanian-aged Mooreville Chalk.

175 Here we redescribe this species based on the holotype (FMNH P27383) and a second

176 specimen (AUMP 2295) attributed to this species collected from the same geologic unit

177 that contains overlapping skeletal material and additional, previously unknown

178 elements. AUMP 2295 has a tibia that is approximately 11% larger than the holotype.

179 Skeletal measurements are includedDraft in the Supplementary material.

180 Premaxilla - A single fragment of the left premaxilla from AUMP 2295 (Fig. 2)

181 shows two large and one small conical denticles along the oral margin just lateral to the

182 midline. Each denticle sequentially decreases in size and is smoothly conical as in the

183 lambeosaur Velafrons (Gates et al. 2007), but differing from the rugose or denticulate

184 pattern seen in Eotrachodon (Prieto-Márquez et al. 2016b), Gryposaurus

185 monumentensis (Gates and Sampson 2007), Tethyshadros (Dalla Vecchia 2009), and

186 Bactrosaurus (Prieto-Márquez 2011a). Most hadrosaurs have a smoother oral margin

187 that shows minimal evidence of denticles. The AUMP 2295 premaxilla displays a

188 prominent double layer morphology with a thickened section ventral to the oral margin

189 and separated from the dorsal region by a shallow sulcus. Eotrachodon lacks this

190 thickened area caudal to the oral margin, whereas Lophorhothon does not possess the

191 caudal set of denticles present on Eotrachodon (Prieto-Márquez et al. 2016b). Medially,

192 the AUMP 2295 premaxillary fragment possesses a shallow embayment along the

193 rostral suture for the right premaxilla. Such a feature is not present on other

194 iguanodontians to the best of our knowledge, yet this feature is so fragmentary we are

195 reluctant to use it in the diagnosis. Both dorsal and lateral premaxillary processes are

196 broken from AUMP 2295, although from the remaining surfaces it is clear that the dorsal

197 process was much more robust than the lateral, and that both processes seem not to

198 have had a strong caudodorsal angulation, but instead might have remained relatively

199 shallow throughout their length. Just lateral to the dorsal process is a deep

200 dorsoventrally oriented furrow that could be a foramen connecting the dorsal and ventral

201 surfaces of the premaxilla. Finally, a large embayment is present on the caudolateral

202 face of AUMP 2295. Broken edges surroundingDraft the perimeter of the embayment show

203 that it was surrounded even further by bone, including the premaxillary lateral process.

204 We interpret this feature as the rostral extension of the circumnarial fossa. If so, then

205 Lophorhothon possessed a premaxilla quite similar in overall appearance to

206 Bactrosaurus (Prieto-Márquez 2011a).

207 Maxilla - FMNH P27383 preserves a partial right maxilla (Fig. 2) that is heavily

208 eroded and AUMP 2295 preserves only the rostrodorsal process. Both specimens show

209 that the rostral region of the maxilla is slender with the rostrodorsal process being

210 straight, shallowly embayed along its length, and slightly inclined caudodorsally. This

211 morphology is much more similar to hadrosaurines such as Gryposaurus (Gates and

212 Sampson 2007), Prosaurolophus (McGarrity et al. 2013), and Naashoibitosaurus (Hunt

213 and Lucas 1993) than to more basal taxa such as Eotrachodon (Prieto-Márquez et al.

214 2016b), Choyrodon and Altirhinus (Gates et al. 2018), Jinzhousaurus (Barrett et al.

215 2009), and Proa (McDonald et al. 2012b), or even some hadrosaurines such as

216 Brachylophosaurus (Prieto-Márquez 2005). Following the dorsal surface of the maxilla,

217 the dorsal process is not preserved; however, there remains a slight bulge on the

218 mediodorsal ridge adjacent to the missing dorsal process that is likely the articulation

219 surface for the palatine (Fig. 2), which is found in the same region as on Eotrachodon

220 (Prieto-Márquez et al. 2016b). Following the ridge further caudally shows a slight rise

221 that is the pterygoid process. Remnants of the ectopterygoid shelf show that it slopes

222 caudoventrally. Angulation of the slope cannot be determined because the original

223 ventral margin of the tooth row has been eroded. Nonetheless, it appears that the dip is

224 less than that on many other taxa including Eotrachodon, as well as being much more

225 reduced in size (although this could Draftbe a consequence of erosion). Two small nutrient

226 foramina can be discerned rostral to the ectopterygoid shelf.

227 Maxillary teeth have a large primary ridge. Due to breakage it is not possible to

228 determine the number of functional teeth within the 24 tooth positions in FMNH P27383.

229 As preserved the maxilla has a rostrocaudal length of 205 mm, nearly the same length

230 as the left Eotrachodon maxilla. Jugal - FMNH P27383 and AUMP 2295 both contain

231 fragments of the anterior left jugal (Fig. 3 A–D); AUMP 2295 preserves only the rostral

232 process, whereas the Lophorhothon holotype possesses the entire anterior half of the

233 element. Both specimens have identical morphology of the rostral process, except that

234 AUMP 2295 is slightly larger than FMNH P27383. Generally, the rostral process is

235 dorsoventrally expanded as in more derived iguanodontians such as hadrosaurids

236 (Prieto-Márquez 2010), but differing distinctly from the more finger-like rostral process of

237 more primitive taxa such as Protohadros (Head 1998), Choyrodon and Altirhinus (Gates

238 et al. 2018), or the slightly more triangular rostral processes of Eolambia (McDonald et

239 al. 2012a) or Acristavus (Gates et al. 2011). Within Lophorhothon, the ventral margin of

240 the rostral process is slightly sinusoidal, terminating rostrally in a long tapering

241 vermiform process that is oriented rostroventrally, a feature that is shared with

242 Gobihadros (Tsogtbaatar et al. 2019). Along the dorsal margin, following caudally from

243 the rostral vermiform process, a thin, ovoidal lacrimal process rises dorsally subtly. This

244 feature has its long axis oriented rostrocaudally and a length to width ratio of 3 on

245 FMNH P27383 and 2.3 on AUMP 2295. Eotrachodon has a lacrimal process that

246 contrasts with the form seen on Lophorhothon in that it possesses sprawling dorsal

247 edges and more of a cup-like shape (Prieto-Márquez et al. 2016b) and a length to width

248 ratio of 1.1. The remainder of the expandedDraft rostral process forms a large articulation

249 facet for the maxilla. Two large fossae are present along the caudal-most margin of the

250 AUMP 2295 maxillary articulation. This same region is plastered over in FMNH P27383.

251 On the mid-body of the jugal, the postorbital process is oriented vertically as is typical

252 for more primitive iguanodontians and some hadrosaurids (Norman 2004, Gates and

253 Sampson 2007, Prieto-Márquez 2010, Prieto-Márquez and Norell 2010). Thicknesses

254 between the jugal neck (i.e., the area between the base of the orbit and jugal body) and

255 the base of the infratemporal fenestra and jugal body seem comparable despite

256 incomplete preservation of FMNH P27383.

257 Lacrimal - Like other iguandontians, Lophorhothon possesses a triangular,

258 wedge-shaped lacrimal (Fig. 3 E–G). A long shallow sulcus extends along the

259 anteroventral edge, presumably as a receptacle for the lateral process of the premaxilla,

260 which differs from Choyrodon in which the same surface is dominated by the contact

261 with the nasal (Gates et al. 2018). At the point where the premaxilla sulcus ends, the

262 lacrimal lateral surface is incised to show that the prefrontal sutured to the dorsal

263 surface. Along the ventral surface is a scarf joint for the maxilla and a columnar articular

264 facet with the jugal. The short length of the jugal process, being equal to the ventral

265 lacrimal margin, is most similar to taxa that do not possess an external antorbital

266 fenestra such as hadrosaurids (e.g., Prieto-Márquez 2005, 2010, Gates and Sampson

267 2007, Campione and Evans 2011, McGarrity et al. 2013, Gates and Scheetz 2015,

268 Prieto-Márquez et al. 2016b). Also, the location of the lacrimal articulation facet on the

269 jugal, being on the dorsal surface of the rostral process as opposed to the anterior end

270 of that process, in combination with the length of the jugal process of the lacrimal,

271 provides persuasive evidence that LophorhothonDraft did not possess an external antorbital

272 fenestra (see Norman 1980, Dalla Vecchia 2009, Gates et al. 2018 for comparison).

273 Posteriorly, a large groove extends dorsoventrally and feeds into the lacrimal foramen.

274 A prong extending from the dorsomedial margin of the posterior face hooks onto a

275 corresponding slot on the prefrontal for secure articulation. In medial view, the lacrimal

276 foramen can be seen extending rostroventrally in a broad, shallow groove, much more

277 extensive than seen on Eotrachodon (Prieto-Márquez et al. 2016b). Another distinction

278 with Eotrachodon is the presence of a slightly elevated plateau dorsal to the lacrimal

279 foramen fossa on Lophorhothon as opposed to the mostly unremarkable medial lacrimal

280 surface on the former taxon.

281 Nasal - Lophorhothon atopus was originally defined by Langston (1960) in large

282 part because of the unique morphology present on the caudodorsal surface of the

283 nasals (Fig. 4). FMNH P27383 partially preserves both nasals and AUMP 2295

284 preserves a partial right nasal, although all three examples of this element pertain to the

285 same region, the thickened portion caudal to the narial fenestra. It should be noted that

286 the caudal-most portions of the frontal processes are not present on any specimens, but

287 we estimate that only a small extent is missing.

288 As preserved, the rostral process of the nasal seems to rise from a straight

289 orientation similar to that seen on the hadrosaurids Prosaurolophus (Horner 1992,

290 McGarrity et al. 2013) or Edmontosaurus (Lambe 1920, Campione and Evans 2011).

291 This supposition derives from differences that can be seen in taxa that possess a nasal

292 bump as in Gryposaurus (Gates and Sampson 2007), Rhinorex (Gates and Scheetz

293 2015), Altirhinus (Norman 1998, Gates et al. 2018), Kritosaurus horneri (Lucas et al.

294 2006, Prieto-Márquez 2014), etc., specifically,Draft a steeper angulation of the anterior nasal

295 process and a rounded dorsal margin posterior to the narial fenestra. A series of

296 structures converge on the dorsal surface of the nasals to produce the unique

297 ornamentation demarcating Lophorhothon. The midline rises caudodorsally at

298 approximately a 15° angle (relative to the ventral margin of the rostral process) in a

299 subtly concave line to form a pronounced protuberance. Descent on the posterior side

300 of the protuberance is at approximately a 50° angle, giving the structure, in lateral view,

301 a ramp-like appearance. Extending lateral from the apex of the midline protuberance on

302 the holotype, is a well-defined ridge that slopes lateroventrally while simultaneously

303 arcing anterolaterally (Fig. 4). This feature seems to be the posterior margin of the

304 circumnarial fossa. The result of this morphology is a smooth arcuate concave basin

305 facing anteriorly. Another rounded ridge runs laterally across the basin in FMNH

306 P27383. This second ridge is not present on AUMP 2295, nor is the obvious arcuate

307 basin. As seen in Figure 4, there is clearly an embayment on the lateral surface of the

308 protuberance, but the shape is substantially different from the holotype. Even the

309 posterior morphology of the nasals differs. Posterior to the arced ridge on FMNH

310 P27383, the nasal slopes posteroventrally slightly convexly, whereas AUMP 2295

311 possesses another embayment. The difference between the specimens could derive

312 from taxonomic distinctness (which we consider unlikely), individual variation, sexual

313 variation, or inaccurate preparation. Superficially, the nasal ornamentation is most

314 similar to Prosaurolophus (Langston 1960).

315 Caudal to the ornamented region, the nasals possess a process that directs

316 caudolaterally toward its articulation with the frontals. The frontal process inserts into a

317 small excavation medial to the prefrontalDraft articulation. Residing between the frontal

318 processes of the paired nasals is an opening created by the aforementioned elements

319 not coalescing. Openings between the nasals and frontals have been noted in other

320 iguanodontian taxa such as Altirhinus (Norman 1998), Bactrosaurus (Godefroit et al.

321 1998), Choyrodon (Gates et al. 2018), Eotrachodon (Prieto-Márquez et al. 2016b),

322 Levnesovia (Sues and Averianov 2009), Gobihadros (Tsogtbaatar et al. 2019), and in

323 juvenile lambeosaurine hadrosaurids (Evans et al. 2005).

324 Prefrontal - FMNH P27383 preserves a partial left prefrontal (Fig. 5) and right

325 postorbital that demonstrate Lophorhothon had an orbital margin that was more arcuate

326 than the same margin seen in Eotrachodon, as well as sharp and unadorned, which

327 differs from the rugose and textured margin seen on the latter taxon (Prieto-Márquez et

328 al. 2016b), as well as Jeyawati (McDonald et al. 2010). The rostrolateral portion of the

329 Lophorhothon prefrontal is dominated by a prominent process that articulates with the

330 posterodorsal region of the lacrimal. Immediately caudomedial to the process is a

331 smooth tapering indentation that harbored a long process from the lacrimal that is not

332 preserved on the latter element. Articulation between the prefrontal and lacrimal

333 continues in a scarf joint until approximately the midline of the prefrontal, at which point

334 it is likely that the premaxillary lateral process overlapped at least a small portion of both

335 the lacrimal and prefrontal. Proceeding caudally along the smooth orbital margin, the

336 prefrontal terminates in an extensive articulation with the frontal demonstrated by a a

337 shallow incision, broad on the frontal. Lesnesovia has a similar prefrontal-frontal make

338 up (Sues and Averianov 2009), except lacking the rostral platform of Lophorhothon. The

339 entire medial portion of this element is composed of a thin sheet of bone whose medial-

340 most edges overlap the nasal throughoutDraft most of the rostrocaudal length. When taken

341 in total, it seems that the prefrontal of Lophorhothon has a unique shape suggesting that

342 the entire skull was relatively flat compared to other ornithopod taxa, for example, its

343 geographic partner Eotrachodon.

344 Frontal - The frontals of Lophorhothon atopus (Fig. 6) differ from many species in

345 that an opening is present along the midline formed by a caudally recessed contact

346 between the conjoining frontal. Short, narrow outgrowths of bone from each frontal

347 protrude into the opening. Along the rostrolateral margin of the frontal are shallow

348 articular facets for the caudal process of the nasal. Large prefrontal articulation facets

349 dominate the rostrolateral corners of the frontals, just rostral to the considerable frontal

350 contribution to the orbit, which is common among may non-hadrosaurid iguanodontians

351 (e.g., Bactrosaurus (Godefroit et al. 1998), Eotrachodon (Prieto-Márquez et al. 2016b),

352 Iguanodon (Norman 1980), Proa (McDonald et al. 2012b), etc.). This general

353 configuration of the frontonasal region is nearly identical to that seen on Eotrachodon,

354 including the presence of a nasofrontal space (Prieto-Márquez et al. 2016b). Exact

355 shape of the contact with the postorbitals is unclear because exuberant preparation of

356 the specimen destroyed the external morphology, leaving only the underlying structure

357 that is a smooth arch across the postorbital. Medial to the postorbitals a dome is

358 present, as in juvenile hadrosaurids (Evans et al. 2005, Gates et al. 2007). Parietals

359 articulate with the caudal region of the frontals with a “U”-shaped suture. A simple

360 concave suture with the parietal is observed in some species such as Lophorhothon

361 and Eotrachodon (Prieto-Márquez et al. 2016b), but is more complicated in other taxa

362 such as hadrosaurids and Choyrodon (Gates et al. 2018) in that the parietal projects a

363 tab into the midline of the caudal frontalDraft midline. The ventral side of the frontals shows a

364 ridge that extends rostrolaterally from the contact with the laterospehoid to the ventral

365 tip of the prefrontal articulation facet. Medial to this ridge the frontals gradually thin

366 dorsally and rostrally. Articulations with the laterosphenoid are still observable on FMNH

367 P27383 lateral to the endocranial excavations.

368 Postorbital - Lateral to the frontals, the postorbitals of FMNH P27383 are typical

369 of iguanodontians. Tripartite, the rostral region articulates with the frontal contribution to

370 the orbit, and continues a connection with the frontal throughout the entire medial

371 surface, articulate with the parietal caudomedially. The orbital rim has small rugosities,

372 not as many or as large as the iguanodontian Jayewati (McDonald et al. 2010) or the

373 hadrosaurid Acristavus (Gates et al. 2011). The jugal process descends rostroventrally

374 at a small angle. This, combined with the wide arching of the prefrontal orbital rim

375 shows that the dorsal region of the orbit is relatively larger than in Eotrachodon (Prieto-

376 Márquez et al. 2016b), a trait that may have changed with ontogeny. Proceeding

377 horizontally from the main body of the postorbital, the caudal (or squamosal) ramus is

378 short and bifid, i.e., the ramus has two distinct articulation surfaces that are only visible

379 as impressions on the corresponding rostral ramus of the squamosal. The dorsal of the

380 two tongues contacts the dorsal side of the corresponding squamosal rostral process in

381 a lap joint, whereas the ventral process slides into an overhanging groove on the ventral

382 half of the squamosal rostral process. This configuration is unique among ornithopods

383 to the best of our knowledge. Horizontal postorbital and squamosal processes are

384 present variably among iguanodontians including taxa such as Eotrachodon (Prieto-

385 Márquez et al. 2016b), Eolambia (McDonald et al. 2012a), Protohadros (Head 1998),

386 Iguanodon (Norman 1980), AltirhinusDraft (Norman 1998, Gates et al. 2018), Tethyshadros

387 (Dalla Vecchia 2009), and Acristavus (Gates et al. 2011), among others. Farke and

388 Herrero (2014) showed that as individuals of the saurolophine hadrosaurid Gryposaurus

389 attain larger size through ontogeny that the inflection of the postorbital caudal ramus

390 increases. As such, the immature nature of FMNH P27383 may preface angled

391 postorbital and squamosal processes at skeletal maturity.

392 Squamosal - Composing the caudal corners of the skull, FMNH P27383

393 possesses both left and right squamosals and AUMP 2295 preserves a partial right (Fig.

394 7). The rostral (or postorbital) process of the Lophorhothon squamosal is relatively

395 short. It is divided into two regions where each accepts one of two corresponding

396 processes from the postorbital. The dorsal region is lightly incised whereas the ventral

397 one is roofed by a long fold of bone that creates a tight groove not seen in other

398 ornithopods. Ventral to the rostral process, the precotyloid process extends

399 rostroventrally to a distance greater than the deep quadrate cotylus. Along the midline,

400 a rugose suture denotes the articulation with another bone, likely the parietal given the

401 orientation of the suture.

402 Quadrate - A mostly complete left quadrate and a small section of dorsal right

403 quadrate is present with FMNH P27383 (Fig. 8). A similar sized dorsal section of

404 quadrate was recovered from AMUP 2295. As preserved, the shaft of the FMNH

405 P27383 left quadrate is straight with a slight caudal deflection toward the top. The

406 posture of the quadrate resembles most closely that of hadrosaurids, but also has close

407 similarities to Eotrachodon (Prieto-Márquez et al. 2016b). Other, more basal taxa, have

408 quadrates that sharply curve caudodorsally. When viewed dorsally, the quadrate has a

409 gracile tripartite appearance. LophorhothonDraft apparently does not possess the large

410 caudal buttress found on many saurolophines. Additionally, the overall quadrate head is

411 narrower in all dimensions compared to most other iguanodontians. FMNH P27383 is

412 missing the pterygoid wing and lateral wing, which makes it difficult to comment on the

413 position and shape of the quadratojugal notch; although, the notch appears to be

414 located in the lower 30% of the quadrate body. The mandibular condyle is a single large

415 knob with a much smaller condyle medially. Of special note is the overall appearance of

416 the holotype quadrate just dorsal to the mandibular condyle. This specimen shows a

417 well-defined notch just dorsal to the mandibular condyle with an all around narrow

418 structure ventral to the lateral wing. Even though this makeup is unique among

419 ornithopods, these features are not present on AUMP 2295, and therefore, we consider

420 them to be taphonomic modifications.

421 Pterygoid - Most of the right pterygoid from FMNH P27383 is present, however it

422 is fragmentary and does not differ from that of other iguanodontians in the preserved

423 portion.

424 Parietal - Only the rostral portion of the parietal is preserved in FMNH P27383

425 (Fig. 6). This element contacts the frontals rostromedially with a defined “U”-shaped

426 suture and the postorbital rostrolaterally, preventing the frontals from contributing to the

427 supratemporal fenestra. The suture between the frontals and the parietal represents the

428 most dramatic change between this taxon and more derived iguanodontians. More

429 primitive taxa such as Iguanodon have a straight suture between the parietal and frontal

430 (Norman 1980), Eotrachodon (Prieto-Márquez et al. 2016b) among others has a style

431 akin to Lophorhothon, and hadrosauridsDraft attain the derived form of a parietal tab inserted

432 between the caudal frontals (e.g., Horner 1992).

433 Orbitosphenoid - Both isolated orbitosphenoids (Fig. 6) are present in FMNH

434 P27383 and a single orbitosphenoid is present in AUMP 2295. These elements are

435 small, disc-like, and possess a shallow indentation as in other hadrosauroids. The

436 rostral edges of each bone taper to a smooth edge with about one-fifth the distance of

437 the circumference, whereas the remaining edges are tongue and grooved for

438 articulation with surrounding elements.

439 Laterosphenoid - As preserved, the right laterosphenoid of FMNH P27383 (Fig.

440 6) contacts the frontal dorsally, and the postorbital laterally via a rod-like process ending

441 in a ball joint, and parietal caudally. Although not in articulation, but present in the

442 specimen, the orbitosphenoids would have contacted the laterosphenoid rostrally. The

443 overall structure of this bone does not differ from other hadrosauroids as can be

444 discerned.

445 Prootic - A small section of the prootic is preserved on FMNH P27383 articulated

446 to the exoccipital complex (Fig. 9). The opening for cranial nerve V is seen at the rostral

447 margin of the element as the prootic makes up over two-thirds of the encapsulation. A

448 smaller opening for cranial nerve VII is seen just caudal to that for cn V.

449 Exoccipital - Fused left and right exoccipital-opisthotics are present in FMNH

450 P27383 (Fig. 9). The caudal articular surface for the supraoccipital rests at a 45° angle

451 to the base of the exoccipital. Within the basal structure are articulations for the

452 basioccipital and fenestrae for cranial nerves X, XI, and XII, which are all clearly visible.

453 The paroccipital processes arch caudolaterallyDraft and, despite being broken, seem to have

454 terminated at or just below the level of the foramen magnum ventral margin.

455 Eotrachodon shares the same ventral depth of the paroccipital processes (Prieto-

456 Márquez et al. 2016b), unlike taxa that have much lower protruding processes such as

457 Jintasaurus (You and Li 2009) and Lesnesovia (Sues and Averianov 2009).

458 Basioccipital - Making up the caudoventral region of the braincase and the floor

459 of the foramen magnum, the basioccipital has the typical shape for iguanodontians with

460 a dome-like rostral articulation facet with the basisphenoid and box-like caudal region.

461 On its dorsal surface is a central groove that makes up the ventral portion of the

462 endocavity. Lateral to the central groove are paired articulation facets for the prootics

463 and exoccipitals. The most obvious difference between the Lophorhothon basioccipital

464 and that of other taxa is the relative size of the basitubera, the bulbous structures on the

465 rostral end of the element that fasten to the basisphenoid. In the case of Lophorhothon,

466 the basitubera are small, similar to those found in the brachylophsaurin hadrosaurids

467 Acristavus (Gates et al. 2011) and Brachylophosaurus (Prieto-Márquez 2005). Other

468 taxa, such as Eolambia (McDonald et al. 2012a) and Lesnesovia (Sues and Averianov

469 2009), have more prominent, less-rounded basitubera.

470 Surangular - AUMP 2295 preserves a partial left surangular (Fig. 10). The major

471 rostrodorsal and caudal processes are broken away, but the remaining section shows a

472 flat medial shelf for the angular, and a raised process just lateral to this shelf. Lateral to

473 the median ridge is an expanded flat area that held the large mandibular condyle of the

474 quadrate.

475 Articular - Both AUMP 2295 and FMNH P27383 possess a complete articular

476 (Fig. 10). The right articular of FMNHDraft P27383 shows a broad rostral shelf for reception

477 of the smaller mandibular condyle of the quadrate, but no other structure caudally. The

478 AUMP 2995 left articular shows the same rostral shelf as the latter specimen, but also

479 preserves a shallow trough that is separated from the rostral shelf by a caudolaterally

480 projecting ridge with prominences on either terminal end. n lateral view, both articulars

481 are saddle-shaped as described for other iguanodontians (e.g., Prieto-Márquez 2005).

482 Dentition - Isolated teeth are known from FMNH P27383 and AUMP 2295.

483 Additionally, in situ dentition is preserved within the FMNH P27383 maxilla. As

484 described by Langston (1960), maxillary teeth are narrow, diamond-shaped and

485 ornamented with a single median carina. The maxillary teeth from AUMP 2295 (Fig. 10)

486 show the same morphology. It is unclear based on the preservation of FMNH P27383

487 how many functional teeth existed within the maxilla, but Langston (1960) reported

488 approximately 25 tooth positions in this element. This number should be taken as an

489 approximation because of the poor preservation of the maxilla. Dentary teeth have a

490 secondary carina, and in some cases tertiary ridges (Langston 1960).

491 Scapula - Overall, the scapula preserved with AUMP 2295 (Fig. 11) has a

492 dorsoventrally expanded head, constricted neck, and expanded blade. The glenoid has

493 a lateral expansion then contracts toward the articulation with the coracoid. Dorsolateral

494 to the glenoid, eroded bone prevents the exact morphology of the scapula head to be

495 ascertained. Caudal to the head, the scapular neck constricts to less than half of the

496 width of the head. Further, the scapular blade extends caudally while curving along both

497 dorsal and ventral borders as is typical in more derived iguanodontians such as

498 hadrosaurids (Prieto-Márquez 2010), but not in more basal taxa such as Eolambia

499 (McDonald et al. 2012a), GobihadrosDraft (Tsogtbaatar et al. 2019), or Bactrosaurus

500 (Godefroit et al. 1998, Prieto-Márquez 2011a). At its termination, the scapular blade is

501 expanded beyond the width of the scapular neck.

502 Coracoid - Both right and left coracoids are present in AUMP 2295 (Fig. 11). A

503 rugose ridge is present along the rim of the glenoid fossa. The outer margin of the

504 coracoid forms a broad semicircular arc, unlike Gobihadros that has a squared dorsal

505 and medial edge (Tsogtbaatar et al. 2019), or Bactrosaurus (Prieto-Márquez 2011a)

506 with straight dorsal and medial margins and an oblique angle. The prior coracoid

507 morphology is also present in an unnamed ornithopod from the Wahweap Formation

508 described by Gates et al. (2014). The ventral hook extends to produce a well-

509 demarcated notch laterally, unlike the shorter ventral processes of Eolambia (McDonald

510 et al. 2012a). A large dorsolateral foramen pierces the body of the coracoid posterior to

511 the glenoid.

512 Sternal - Overall, the left sternal from AUMP 2295 (Fig. 11) is axe-shaped with a

513 broad rostromedial expansion and a caudolateral extension. The caudomedial corner

514 forms a pointed triangular intersection whereas the caudolateral border (i.e., the

515 junction between the lateral shaft and the medial expansion) is perpendicular. The base

516 of the shaft is mildly mediolaterally expanded. In sum, the morphology of the AUMP

517 2295 specimen is nearly identical to Equijubus (McDonald et al. 2014).

518 Humerus - Of the two humeri preserved in AUMP 2295, the right is better

519 preserved than the left (Fig. 11). The humeral head has the articular facet just medial to

520 the central head. A broad ridge runs caudally from the articular facet down the shaft,

521 terminating at the same level as the deltopectoral crest, and demarcates the rim of an

522 elongate depression medial to the ridge.Draft Just lateral to the humeral midline, and on the

523 caudal side of the element, there is a shallow arcuate depression on both the right and

524 left humeri. This latter feature arises on the lateral rim of the humeral head and

525 descends ventrally without much expansion and gradually curves to reconnect with the

526 shaft. The gentle curvature is seen on more primitive ornithopods whereas derived

527 species tend to have a more squared deltopectoral crest. This morphology is possibly a

528 consequence of specimen immaturity, given that previous studies have shown the

529 deltopectoral crest to lengthen and become more square through growth (Dilkes 2001).

530 Following the measurements of Prieto-Márquez (2010) and Prieto-Márquez (2011b),

531 Lophorhothon has a ratio of deltopectoral crest to humeral length of 0.46, which is

532 slightly smaller than the ratio seen in iguanodontians phylogenetically less derived than

533 Saurolophidae (Prieto-Márquez 2011b). The shaft bends medially a small amount

534 before expanding into terminal condyles.

535 Ulna - Plastic deformation has flattened the right ulna of AUMP 2295, leaving

536 only the left as an accurate representation of that element (Fig. 11). The olecranon

537 process rises as a large bulge above the level of the olecranon fossa, which is a shallow

538 embayment on the rostral side of the ulna surrounded on its medial and lateral sides by

539 protuberances that form a shelf for accepting the humeral condyle. Distally, the shaft is

540 fairly straight and terminates in a nondescript rounded buttress.

541 Radius - The radius (Fig. 11) of AUMP 2295 possesses a typical rounded

542 proximal end with a slightly indented dorsal surface for reception of the other humeral

543 condyle. The shaft is not rounded as in the ulna, but instead subtly flattened throughout

544 its length becoming progressively more exaggerated at the distal end. This element

545 articulates with the carpals via a ventralDraft rounded prominence that is more hemispherical

546 than the ventral articular surface of the ulna.

547 Metacarpal II - Right and left complementary metacarpal II elements are present

548 with AUMP 2295 (Fig. 11). In dorsal view the articular surface has four distinct sides,

549 two less defined that lie on the medial aspect of the manus, one that articulates with

550 metacarpal III, and the final side that faces posteromedially on the hand. The

551 articulation surface for metacarpal III has an elongated shallow trough that rises trivially

552 at its termination approximately 20% the length of the bone. The remainder of the shaft

553 is rounded, expanding at the ventral end with a rounded articular facet.

554 Metacarpal III - Only the right metacarpal III is preserved with AUMP 2295 (Fig.

555 11). In dorsal view, the articular head is triangular. It connects with metacarpal II via the

556 rounded medial apex of this triangle and with metacarpal IV through a long flattened

557 region on the lateral side of the triangle. The aforementioned flattened region begins at

558 the dorsal head and continues over half way down the shaft. At this point, metacarpal III

559 begins to expand mediolaterally and forms an ovoid articulation for its corresponding

560 phalanx.

561 Metacarpal IV - Of the two specimens associated with AUMP 2295, the left

562 metacarpal IV preserves its morphology without deformation (Fig. 11). Proximally, the

563 head of metacarpal IV is trapezoidal, the rostral and caudal margins being parallel with

564 the rostral one shorter between the two. The shaft is rounded except for the

565 caudomedial side which is flattened throughout the entire length. This element contacts

566 the phalanx with a rounded end that is narrower than the proximal end.

567 Metacarpal V - This short and stout element, presumably from the right side, has

568 an expanded proximal region with a Draftmuted depression on its dorsal surface. The

569 rounded shaft gives way to a ball-shaped ventral articulation (Fig. 11).

570 Ilium - The type specimen of Lophorhothon did not preserve an ilium, but this

571 element was recovered with AUMP 2295 (Fig. 12). Anteriorly, the preacetabular process

572 proceeds rostroventrally, maintaining a nearly consistent width throughout the

573 extension. There is not a large lateral folding of the dorsal margin of the preacetabular

574 process as seen in Gryposaurus monumentensis (Gates et al. 2013), but instead is thin

575 and smooth throughout. Moving to the iliac plate, there is not an exaggerated raised

576 hillock over the rostral region as seen in Hadrosaurus (Leidy 1858, Prieto-Márquez et al.

577 2006b) or Brachylophosaurus (Prieto-Márquez 2007). Across the dorsal margin of the

578 ilium, the depression occurring at the origin of the postacetabular process is subtle to

579 non-existent. Such shallow depressions are seen in taxa outside Hadrosauridae

580 (Godefroit et al. 1998, Prieto-Márquez 2011b, McDonald et al. 2012a, Gates et al.

581 2018), although exceptions to this generalization occur such as Huehuecanauhtlus

582 (Ramírez-Velasco et al. 2012). A large supraacetabular crest folds over the lateral side

583 of the iliac plate on AUMP 2295, terminating at the level of the ischial process. The

584 acetabular margin is damaged, leaving little information to report on its morphology.

585 Pubic and ischial processes are also typical of iguanodontians.

586 Pubis - The presence of a pubis in the AUMP 2295 (Fig. 12) specimen provides

587 valuable information not available in the holotype. Expansion of the dorsal and ventral

588 margins of the rostral process is a feature seen in many iguanodontian taxa from

589 Tethyshadros (Dalla Vecchia 2009), Eolambia (McDonald et al. 2012a), to

590 Edmontosaurus regalis (Campione 2015). The fragmentary nature of the AUMP 2295

591 pubic rostral process leaves in questionDraft the overall shape. Despite the uncertainty in

592 this trait it is evident that any expansion of the rostral process occurs at a more distal

593 position than in Gobihadros (Tsogtbaatar et al. 2019). Otherwise, the caudal process

594 and pubis iliac process do not differ remarkably from other taxa.

595 Ischium - On the head of the ischium, only the pubic process is preserved on

596 either AUMP 2295 or FMNH P27383 (Fig. 12). No other information can be gleaned

597 from this element except that the shaft is straight and slender. Hadrosaurid ischia tend

598 to be stouter, and even curving in some cases (Brett-Surman and Wagner 2006). It is

599 unclear if a boot is present on the distal end of the shaft, but given the straight nature

600 throughout the preserved portion we believe it is unlikely that the structure was present.

601 Femur - A complete left femur is present on AUMP 2295 (Fig. 13)

602 showing that the femoral head is separated from the greater trochanter by a well-

603 defined crevasse. The lesser trochanter is separated from the greater trochanter by

604 being set down the lateral side of the femur, yet still retaining a distinct paddle-shaped

605 process. Overall, the shaft of the femur is straight, with the fourth trochanter located

606 midshaft. As seen on Figure 13, the fourth trochanter of Lophorhothon is obliquely

607 triangular in lateral view, possessing a concave distal edge. At the distal end of the

608 shaft, the femoral condyles appear pendulum-shaped in lateral view and can be seen in

609 anterior view to be separated by a shallow crevasse as opposed to a deep one or even

610 possessing a circular opening towards their medioproximal connection.

611 Tibia - AUMP 2295 contains two nearly complete tibiae (Fig. 13). The proximal

612 condyles are flanked laterally by the cnemial crest, a structure that expands slightly to

613 cup the fibula. As in other iguanodontians, the tibial shaft constricts in the middle then

614 expands again towards the articulationDraft facet for the astragalus and calcaneum.

615 Fibula - A complete well-preserved right fibula from AUMP 2295 shows that the

616 form of this element in Lophorhothon (Fig. 13) does not differ from that of other

617 iguanodontians in having a mediolaterally compressed and rostrocaudally expanded

618 head that tapers to a kinked distal end. Campione (2015) illustrates an Edmontosaurus

619 regalis fibula that has a more similar width of the fibular head to the distal end compared

620 to AUMP 2295.

621 Metatarsal II - This medial-most metatarsal has a rostrocaudally compressed

622 body with wider proximal and distal ends than midshaft width. The laterodistal region of

623 the shaft expands abruptly laterally, providing an irregular profile along the lateral side

624 of the shaft (Fig. 13).

625 Metatarsal III - The middle metatarsal (Fig. 13) is approximately 25% longer than

626 either the second or fourth metatarsal. Overall, this element has a cylindrical shaft,

627 although the proximolateral region is inclined at the articular surface for the fourth

628 metatarsal.

629 Metatarsal IV - In rostral view, the fourth metatarsal (Fig. 13) has a distinctly bent

630 shape. On the proximomedial side, there is a large flat region that sidles next to a

631 matching region on the third metatarsal, which in articulation would produce a widely

632 splayed foot. The shaft maintains a more or less constant width throughout its distal

633 progression.

634

635 Phylogenetic Analysis

636 Our phylogenetic analysis of Lophorhothon atopus (Fig. 14) was performed using

637 the Eotrachodon matrix of Prieto-MárquezDraft et al. (2016a) in PAUP 4.01a168 (X86),

638 retaining all character ordering from the original publication, as well as a second

639 iteration where all of the characters were considered unordered. Codings for

640 Lophorhothon were altered according to the new information available in this study. A

641 character matrix, NEXUS files of all most-parsimonious-trees, and a NEXUS of the

642 consensus trees are provided in the supplementary material. Iguanodon was used as

643 the outgroup, using random sequence addition with 10 replicates and holding 10 trees

644 at each step. Branch swapping was performed by TBR, swapping only the best trees

645 and a reconnection limit of 8.

646 A total of 18 most parsimonious trees resulted from the analysis as outlined by

647 Prieto-Márquez et al. (2016a), consisting of a tree score of 989. The strict consensus

648 aligned Lophorhothon as sister taxon with Jintasaurus, one node below Hadrosauridae.

649 This series of trees had remarkable stability over the most parsimonious set, resulting in

650 every resolved branch of the 50% Majority Rule Tree being at 100 percent

651 concordance.

652 In contrast to the previous analysis, removing assumptions about character

653 ordering resulted in 4,374 trees retained with a score of 937. In this case, Eotrachodon

654 formed a polytomy with Hadrosaurus, and Lophorhothon was placed in a large polytomy

655 with many other hadrosauroids when trees were coalesced in a strict consensus. Within

656 the 50% Majority Rule tree, Lophorhothon stands at one node below Hadrosauridae

657 isolated, whereas Jintasaurus is much further down the tree between Equijubus and

658 Probactrosaurus.

659

660 Discussion Draft

661 Phylogenetic Significance

662 Originally, Langston (1960) placed Lophorhothon as a hadrosaurine hadrosaurid

663 ornithopod on the basis of the solid crest made exclusively from the nasals. Subsequent

664 analyses, such as Prieto-Márquez and Salinas (2010) and Prieto-Márquez et al.

665 (2016a), found that Lophorhothon was actually placed outside of Hadrosauridae. The

666 analyses presented in this study concur with those of the latter phylogenetic hypotheses

667 (not unexpected given that we used the phylogenetic matrix from Prieto-Márquez et al.

668 (2016a)); however, we found that the new information added to the matrix from the

669 elements present in AUMP 2295 as well as recordings from the original matrix brought

670 Lophorhothon closer to the Hadrosauridae node. Since it is known that juvenile

671 hadrosaurs plot lower on phylogenetic trees than their adult counterparts (e.g., Evans et

672 al. 2005, Gates et al. 2007, Takasaki et al. 2018), perhaps future discoveries of adult

673 Lophorhothon remains will elucidate its position as a basal hadrosaurid.

674

675 Fontanels in hadrosauromorphs

676 As described above, an opening between the nasals and frontals occurs in many

677 hadrosauroids and has been lumped into a single category of anatomical feature called

678 a fontanel. Closer examination of these openings across species demonstrates that only

679 a subset of these species possess a fontanel sensu stricto. By definition, a fontanel is

680 an opening between two bones (typically from the skull) that have not completely grown

681 together at an early stage of development, but will coalesce during ontogeny (Oxford,

682 2015; Britannica, 2017). Using this definitionDraft as a standard, the taxa Choyrodon and

683 Eotrachodon possess a hole between the medial contacts of the frontals and nasals, but

684 the margins of both the frontals and nasals seem to be smooth, lacking characteristics

685 that would indicate continued growth across a fontanel such as crenulations and small

686 irregular projections towards the center of the open space. The holotypes of Gobihadros

687 (Tsogtbaatar et al. 2019) and Lophorhothon atopus do indeed show these features of

688 continued growth on the frontal, but not on the nasals. The nasal caudal processes on

689 Lophorhothon show no evidence for continued medial growth in any form, much less,

690 evidence that they would eventually coalesce together at the midline or even an

691 articular surface for major rostral expansion of the frontals to conceal the space

692 currently open. Lophorhothon is unique among these other taxa with a frontonasal

693 opening in that its caudal nasal processes are nearly columnar in form as opposed to

694 thin, flat, and broad. The latter morphology could at least lead to hypotheses that these

695 flat broad nasal processes could coalesce through ontogeny.

696 As such, we posit that the frontonasal opening of at least Lophorhothon, if not all

697 iguanodontian taxa without clear evidence of continued frontal and nasal growth

698 towards the center of the opening, should be classified as a nasofrontal fenestra that

699 would remain open throughout life, instead of the classically termed fontanel.

700 Differentiating between the two terms, fenestra and fontanel, is important because they

701 distinguish openings present after maturation as opposed to holes present on a

702 specimen prior to maturation but absent after maturation. Evans (2010) described the

703 utility of using the closure of fontanels for assessing species identification and

704 developmental stage in LambeosauriniDraft hadrosaurids. Fenestrae would not provide the

705 same utility since they do not close over ontogeny. Semantically, proper identification of

706 the openings would facilitate communication about the final morphology in addition to

707 staying in more conventional anatomical usage.

708

709 A reconsideration of Appalachian relict faunas

710 Phylogenetic analyses of Appalachian dinosaur taxa have continuously proposed

711 that the species present in this region of North America were of a more primitive

712 evolutionary state compared to faunas in the western portion of the continent (i.e.,

713 Laramidia) (Schwimmer 1997, Carr et al. 2005, Prieto-Márquez et al. 2016a, Brownstein

714 2018, 2021). This phenomenon has provided the foundation for inflicting the term ‘relict’

715 as a descriptor of the eastern dinosaur fauna (Schwimmer 1997, Brownstein 2018,

716 2021).

717 Grandcolas et al. (2014) define relict species as those that are the last

718 representatives of a once larger, more wide-spread, clade. The relict nature of

719 Appalachian dinosaur faunas is based on comparisons to penecontemporaneous

720 faunas from Laramidia without a consideration of dinosaurs found elsewhere in the

721 world. Penecontemporaneous Asian hadrosauromorphs are on a similar, if not more,

722 primitive portion of the phylogenetic tree as Appalachian hadrosauromorphs until the

723 migration of hadrosaurids from North America into Asia during the late Campanian

724 (Godefroit et al. 2012b, 2012a). Penecontemporaneous European faunas are sparser,

725 but evidence from Romania (Weishampel et al. 1993), Italy (Dalla Vecchia 2009), and

726 Spain (Prieto-Márquez et al. 2006a, 2019, Prieto-Márquez and Wagner 2009, Conti et

727 al. 2020) show that these taxa eitherDraft fall outside of Hadrosauridae or as basal taxa

728 within their respective hadrosaurid clades (e.g., the basal lambeosaurine

729 Pararhabdodon).

730 Bringing this information to bear on the relict nature of Appalachian faunas

731 provides the perspective that Late Cretaceous dinosaurs from eastern North America

732 are not phylogenetically any different from those taxa across Laurasia generally. It

733 seems, on the other hand, that hadrosaurids from western North America are aberrant,

734 more derived than would be expected. This phenomenon can arise from a decrease in

735 evolutionary rates of all iguanodontian taxa globally except those living in Laramidia

736 (which seems unlikely), or from an increase in evolutionary rates for Laramidian

737 dinosaurs. Indeed, Gates et al. (2012) posited higher rates of speciation for

738 hadrosaurids during the late Campanian due to unique physiographic conditions in

739 western North America and Burgener et al. (in press) have shown that climate gradients

740 dramatically altered forest structures in this region. As such, it seems that Laramidia

741 provided a unique set of circumstances that perpetuated higher rates of evolution

742 compared to other regions of the globe.

743 With this perspective, we believe that the dinosaurian faunas of Appalachia

744 should no longer be thought of as relicts of a primitive Cretaceous fauna, but instead as

745 an evolutionary fauna that held the line. In fact, with this approach, understanding

746 Appalachian dinosaurs becomes even more important because these dinosaurs could

747 represent the baseline evolutionary trajectory of Late Cretaceous dinosaurs in North

748 America with which to properly measure changes in Laramidian dinosaur faunas.

749

750 Conclusions Draft

751 Here we describe the skeletal anatomy of the hadrosauromorph ornithopod

752 Lophorhothon atopus using the holotype material as well as a new specimen collected

753 from the same Upper Cretaceous beds in Alabama. This dinosaur is diagnosed on the

754 basis of several autapomorphies including unique morphology of the nasal and

755 prefrontal in addition to a combination of traits present on other ornithopods. Overall, the

756 skull of Lophorhothon seems to have been dorsoventrally short, more like the shape

757 seen in Prosaurolophus (in agreement with Langston (1960)), differentiating it from the

758 more rounded skull of Eotrachodon. Incorporation of the new anatomical information

759 into a phylogenetic analysis places Lophorhothon one node outside of Hadrosauridae,

760 in a more derived position than previously hypothesized (Prieto-Márquez et al. 2016a).

761 In fact, all Late Cretaceous dinosaurs from eastern North America are more primitive

762 than their counterparts in western North America; yet, the prior classification of these

763 dinosaurs as relicts is misused, because Laramidian dinosaurs appear to have

764 experienced elevated rates of evolution. Discovery of more Appalachian dinosaurs is

765 becoming critically important to not only understand what animals lived in the eastern

766 portion of North America, but also to provide a calibration for studying the evolution of

767 dinosaurian faunas around the world.

768

769 Acknowledgments

770 We would like to thank heartily William Simpson (Field Museum of Natural

771 History) for assistance with loaning the holotype specimen and additional specimen

772 pictures during the 2020 COVID-19 pandemic. Thanks also goes to Jim Dobie and Ray

773 Wilhite of Auburn University for accessDraft to AUMP 2295, and to Natalie Mooney of the

774 University of West Alabama for some of the photos used in this paper. Jordan Mallon,

775 Kathy Stewart, and Phil Currie kindly organized and edited this special volume. We

776 thank Liz Freedman-Fowler, Jordan Mallon, and an anonymous reviewer for

777 suggestions that improved the paper greatly. Finally, we would like to thank Dale

778 Russell for his boundless energy, independent thinking, his always positive outlook on

779 life in general, and his infectious passion for the world of the dinosaurs. It was

780 impossible not to feel excited about paleontology in his presence.

781

782 References

783 Barrett, P.M., Butler, R.J., Xiao-Lin, W., and Xing, X. 2009. Cranial anatomy of the

784 iguanodontoid ornithopod Jinzhousaurus yangi from the Lower Cretaceous Yixian

785 Formation of China. Acta Palaeontologica Polonica, 54: 35–48.

786 Brett-Surman, M.K., and Wagner, J.R. 2006. Discussion of character analysis of the

787 appendicular anatomy in Campanian and Maastrichtian North American hadrosaurids-

788 variation and ontogeny. In Horns and beaks: Ceratopsian and ornithopod dinosaurs.

789 Edited by K. Carpenter. Indiana University Press, Bloomington, IN. pp. 135–169.

790 Britannica Encyclopedia. 2017. Fontanel. www.britannica.com/science/fontanel. Accessed

791 November 13, 2020.

792 Brownstein, C.D. 2018. The biogeography and ecology of the Cretaceous non–avian dinosaurs

793 of Appalachia. Palaeo. Elect, 21: 1–56.

794 Brownstein, C.D. 2021. Osteology and phylogeny of small-bodied hadrosauromorphs from an

795 end-Cretaceous marine assemblage. Zoological Journal of the Linnean Society, 191:

796 180–200.

797 Burgener, L., Hyland, E., Griffith, E., Mitášová, H., Zanno, L.E., and Gates, T.A. in press. An

798 extreme climate gradient-inducedDraft ecological regionalization in the Upper Cretaceous

799 Western Interior Basin of North America. Geological Society of America Bulletin.

800 Campione, N.E. 2015. Postcranial anatomy of Edmontosaurus regalis (Hadrosauridae) from the

801 Horseshoe Canyon Formation, Alberta, Canada. In Hadrosaurs. Edited by D.C. Evans

802 and D.A. Eberth. Indiana University Press, Bloomington, IN. pp. 208–244.

803 Campione, N.E., and Evans, D.C. 2011. Cranial growth and variation in edmontosaurs

804 (Dinosauria: Hadrosauridae): implications for latest Cretaceous megaherbivore diversity

805 in North America. PLoS One, 6: e25186.

806 Carr, T.D., Williamson, T.E., and Schwimmer, D.R. 2005. A new genus and species of

807 tyrannosauroid from the Late Cretaceous (Middle Campanian) Demopolis Formation of

808 Alabama. Journal of vertebrate Paleontology, 25: 119–143.

809 Conti, S., Vila, B., Sellés, A.G., Galobart, À., Benton, M.J., and Prieto-Márquez, A. 2020. The

810 oldest lambeosaurine dinosaur from Europe: Insights into the arrival of Tsintaosaurini.

811 Cretaceous Research, 107: 104286.

812 Dalla Vecchia, F.M. 2009. Tethyshadros insularis, a new hadrosauroid dinosaur (Ornithischia)

813 from the Upper Cretaceous of Italy. Journal of Vertebrate Paleontology, 29: 1100–1116.

814 Davis, M.E., Sanford, T. H., Jr, and Jefferson, P.O. 1975. Water Availability and

815 Geology of Hale County, Alabama. Geological Survey of Alabama, Map 136, 51

816 p.

817 Dilkes, D.W. 2001. An ontogenetic perspective on locomotion in the Late Cretaceous dinosaur

818 Maiasaura peeblesorum (Ornithischia: Hadrosauridae). Canadian Journal of Earth

819 Sciences, 38: 1205–1227.

820 Dollo, L. 1888. Iguanodontidae et Camptonotidae. Comptes rendus de l’Académie des

821 Sciences, 106: 775–777.

822 Evans, D.C., Forster, C.A., and Reisz, R.R. 2005. The type specimen of Tetragonosaurus 823 erectofrons (Ornithischia: Hadrosauridae)Draft and the identification of juvenile 824 lambeosaurines. In Dinosaur Provincial Park, a spectacular ancient ecosystem revealed.

825 Edited by P.J. Currie and E.B. Koppelhus. Indiana University Press, Bloomington, IN. pp.

826 349–366.

827 Farke, A.A., and Herrero, L. 2014. Variation in the skull roof of the hadrosaur Gryposaurus

828 illustrated by a new specimen from the Kaiparowits Formation (late Campanian) of

829 southern Utah. In Hadrosaurs. Edited by D.A. Eberth and D.C. Evans. Indiana University

830 Press, Indianapolis. pp. 191–199.

831 Gates, T.A., Horner, J.R., Hanna, R.R., and Nelson, C.R. 2011. New unadorned hadrosaurine

832 hadrosaurid (Dinosauria, Ornithopoda) from the Campanian of North America. Journal of

833 Vertebrate Paleontology, 31: 798–811.

834 Gates, T.A., Jinnah, Z., Levitt, C., and Getty, M.A. 2014. New hadrosaurid specimens from the

835 lower-middle Campanian Wahweap Formation of Utah. In Hadrosaurs. Edited by D.C.

836 Evans and D.A. Eberth. Indiana University Press, Bloomington, IN. pp. 156–173.

837 Gates, T.A., Lund, E.K., Boyd, C.A., Deblieux, D.D., Titus, A.L., Evans, D.C., Getty, M.A.,

838 kirkland, J.I., and Eaton, J.G. 2013. Ornithopod dinosaurs from the Grand Staircase-

839 Escalante National Monument region, Utah, and their role in paleobiogeographic and

840 macroevolutionary studies. In At the top of the Grand Staircase: The Late Cretaceous of

841 southern Utah. Edited by A.L. Titus and M.A. Loewen. Indiana University Press,

842 Bloomington, IN. pp. 463–481.

843 Gates, T.A., Prieto-Márquez, A., and Zanno, L.E. 2012. Mountain building triggered Late

844 Cretaceous North American megaherbivore dinosaur radiation. PloS one, 7: e42135.

845 Gates, T.A., and Sampson, S.D. 2007. A new species of Gryposaurus (Dinosauria:

846 Hadrosauridae) from the Late Campanian Kaiparowits Formation. Zoological Journal of

847 the Linnean Society, 151: 351–376.

848 Gates, T.A., Sampson, S.D., Delgado-Jesus, C.R., Zanno, L.E., Eberth, D.A., Hernandez-

849 Rivera, R., Martinez, M.C.A., andDraft Kirkland, J.I. 2007. Velafrons coahuilensis, a new

850 lambeosaurine hadrosaurid (Dinosauria: Ornithopoda) from the late Campanian Cerro

851 del Pueblo Formation, Coahuila, Mexico. Journal of Vertebrate Paleontology, 27: 917–

852 930.

853 Gates, T.A., and Scheetz, R. 2015. A new saurolophine hadrosaurid (Dinosauria: Ornithopoda)

854 from the Campanian of Utah, North America. Journal of Systematic Palaeontology, 13:

855 711–725.

856 Gates, T.A., Tsogtbaatar, K., Zanno, L.E., Chinzorig, T., and Watabe, M. 2018. A new

857 iguanodontian (Dinosauria: Ornithopoda) from the Early Cretaceous of Mongolia. PeerJ,

858 6: e5300.

859 Godefroit, P., Bolotsky, Y.L., and Bolotsky, I.Y. 2012a. Osteology and relationships of Olorotitan

860 arharensis, a hollow-crested hadrosaurid dinosaur from the latest Cretaceous of Far

861 Eastern Russia. Acta Palaeontologica Polonica, 57: 527–560.

862 doi:10.4202/app.2011.0051.

863 Godefroit, P., Bolotsky, Y.L., and Lauters, P. 2012b. A new saurolophine dinosaur from the

864 latest Cretaceous of Far Eastern Russia. PloS One, 7: e36849.

865 doi:10.1371/journal.pone.0036849.

866 Godefroit, P., Dong, Z., Bultynck, P., Li, H., and Feng, L. 1998. Sino-Belgian Cooperation

867 Program: “Cretaceous dinosaurs and mammals from Inner Mongolia” 1. New

868 Bactrosaurus (Dinosauria: Hadrosauroidea) material from Iren Dabasu (Inner Mongolia,

869 P.R. China). Bulletin de l’Institut Royal des Sciences Naturelles de Belgique, 68

870 (suppl.): 3–70.

871 Grandcolas, P., Nattier, R., and Trewick, S. 2014. Relict species: a relict concept? Trends in

872 ecology & evolution, 29: 655–663.

873 Hardenbolt, J., Thierry, J., Farley, M.B., Jacquin, T., de Graciansky, P.-C., Vail, P.R.

874 1998. Mesozoic and Cenozoic sequence stratigraphic framework of European

875 Basins. In: de Graciansky, P.-C,Draft Hardenbol, J., Jacquin, T., Vail, P.R. (Eds),

876 Mesozoic and Cenozoic Sequence Stratigraphy of Europeans Basins. SEPM

877 Special Publication 60: 3-13.

878 Head, J.J. 1998. A new species of basal hadrosaurid (Dinosauria, Ornithischia) from the

879 Cenomanian of Texas. Journal of Vertebrate Paleontology, 18: 718–734.

880 Horner, J.R. 1992. Cranial morphology of Prosaurolophus (Ornithischia: Hadrosauridae) with

881 descriptions of two new hadrosaurid species and an evaluation of hadrosaurid

882 phylogenetic relationships. Museum of the Rockies Occasional Paper, 2: 1–119.

883 Hunt, A.P., and Lucas, S.G. 1993. Cretaceous vertebrates of New Mexico. In Vertebrate

884 Paleontology in New Mexico. Edited by S.G. Lucas and J. Zidek. New Mexico Museum

885 of Natural History and Science, Albuquerque. pp. 77–91.

886 Kaye, J.M., and Russell, D.A. 1973. The oldest record of hadrosaurian dinosaurs in North

887 America. Journal of Paleontology,: 91–93.

888 Lambe, L.M. 1920. The hadrosaur Edmontosaurus from the Upper Cretaceous of Alberta.

889 Canada Department of Mines Memoir, 120: 1–79.

890 Langston, W., Jr. 1960. The vertebrate fauna of the Selma Formation of Alabama Part VI. The

891 dinosaurs. Fieldiana: Geology Memoirs, 3: 319–360.

892 Leidy, J. 1858. Hadrosaurus foulkii, a new saurian from the Cretaceous of New Jersey, related

893 to Iguanodon. Proceedings of the Academy of Natural Sciences of Philadelphia, 10:

894 213–218.

895 Liu, K. 2007. Sequence Stratigraphy and Orbital Cyclostratigraphy of the Mooreville

896 Chalk (Santonian-Campanian), northeastern Gulf of Mexico area, USA.

897 Cretaceous Research, 28: 405-418.

898 Lucas, S.G., Spielmann, J.A., Sullivan, R.M., Hunt, A.P., and Gates, T.A. 2006. Anasazisaurus, 899 a hadrosaurian dinosaur from theDraft Upper Cretaceous of New Mexico. New Mexico 900 Museum of Natural History and Science Bulletin, 35: 293–297.

901 Marsh, O.C. 1881. Principal characters of American Jurassic dinosaurs. Part IV. American

902 Journal of Science, series 3, 21: 167–170.

903 McDonald, A.T., Bird, J., Kirkland, J.I., and Dodson, P. 2012a. Osteology of the basal

904 hadrosauroid Eolambia caroljonesa (Dinosauria: Ornithopoda) from the Cedar Mountain

905 Formation of Utah. PloS one, 7: e45712.

906 McDonald, A.T., Espilez, E., Mampel, L., Kirkland, J.I., and Alcala, L. 2012b. An unusual new

907 basal iguanodont (Dinosauria: Ornithopoda) from the Lower Cretaceous of Teruel,

908 Spain. Zootaxa, 3595: 61–76.

909

910 McDonald, A.T., Maidment, S.C., Barrett, P.M., You, H.L., and Dodson, P. 2014. Osteology of

911 the basal hadrosauroid Equijubus normani (Dinosauria, Ornithopoda) from the Early

912 Cretaceous of China. In Hadrosaurs. Proceedings of the International Hadrosaur

913 Symposium. Indiana University Press, Bloomington and Indianapolis, Indiana. pp. 3–44.

914 McDonald, A.T., Wolfe, D.G., and Kirkland, J.I. 2010. A new basal hadrosauroid (Dinosauria:

915 Ornithopoda) from the Turonian of New Mexico. Journal of Vertebrate Paleontology, 30:

916 799–812.

917 McGarrity, C.T., Campione, N.E., and Evans, D.C. 2013. Cranial anatomy and variation in

918 Prosaurolophus maximus (Dinosauria: Hadrosauridae). Zoological Journal of the

919 Linnean Society, 167: 531–568.

920 Norman, D.B. 1980. On the ornithischian dinosaur Iguanodon bernissartensis from the Lower

921 Cretaceous of Bernissart (Belgium). Mémoire de l’Institut Royal des Sciences Naturelles

922 de Belgique, 178: 1–104.

923 Norman, D.B. 1998. On Asian ornithopods (Dinosaura: Ornithischia). 3. A new species of

924 iguanodontid dinosaur. Zoological Journal of the Linnean Society, 122: 291–348.

925 Norman, D.B. 2004. Basal Iguanodonita.Draft In The Dinosauria. Edited by D.B. Weishampel, P.

926 Dodson, and H. Osmolska. University of California Press, Berkeley. pp. 413–437.

927 Norman, D.B. 2015. On the history, osteology, and systematic position of the Wealden (Hastings

928 group) dinosaur Hypselospinus fittoni (Iguanodontia: Styracosterna). Zoological Journal of

929 the Linnean Society, 173: 1–98.

930 Owen, R. 1842. Report on British fossil reptiles. Report of the British Association of Advanced

931 Sciences, 9: 60–204.

932 Oxford Concise Medical Dictionary. 2015. Martin, E. (ed.). Oxford University Press.

933 Prieto-Márquez, A. 2005. New information on the cranium of Brachylophosaurus canadensis

934 (Dinosauria, Hadrosauridae), with revision of its phylogenetic position. Journal of

935 Vertebrate Paleontology, 25: 144–156.

936 Prieto-Márquez, A. 2007. Postcranial osteology of the hadrosaurid dinosaur Brachylophosaurus

937 canadensis from the Late Cretaceous of Montana. In Horns and Beaks. Edited by K.

938 Carpenter. Indiana University Press, Bloomington, IN. pp. 91–116.

939 Prieto-Márquez, A. 2010. Global phylogeny of Hadrosauridae (Dinosauria: Ornithopoda) using

940 parsimony and Bayesian methods. Zoological Journal of the Linnean Society, 159: 435–

941 502.

942 Prieto-Márquez, A. 2011a. Cranial and appendicular ontogeny of Bactrosaurus johnsoni, a

943 hadrosauroid dinosaur from the Late Cretaceous of northern China. Palaeontology, 54:

944 773–792.

945 Prieto-Márquez, A. 2011b. Revised diagnoses of Hadrosaurus foulkii Leidy, 1858 (the type

946 genus and species of Hadrosauridae Cope, 1869) and Claosaurus agilis Marsh, 1872

947 (Dinosauria: Ornithopoda) from the Late Cretaceous of North America. Zootaxa, 2765:

948 61–68.

949 Prieto-Márquez, A. 2014. Skeletal morphology of Kritosaurus navajovius (Dinosauria:

950 Hadrosauridae) from the Late CretaceousDraft of the North American south-west, with an

951 evaluation of the phylogenetic systematics and biogeography of Kritosaurini. Journal of

952 Systematic Palaeontology, 12: 133–175. Taylor & Francis.

953 Prieto-Márquez, A., Erickson, G.M., and Ebersole, J.A. 2016a. A primitive hadrosaurid from

954 southeastern North America and the origin and early evolution of ‘duck-billed’dinosaurs.

955 Journal of Vertebrate Paleontology, 36: e1054495.

956 Prieto-Márquez, A., Erickson, G.M., and Ebersole, J.A. 2016b. Anatomy and osteohistology of

957 the basal hadrosaurid dinosaur Eotrachodon from the uppermost Santonian

958 (Cretaceous) of southern Appalachia. PeerJ, 4: e1872.

959 Prieto-Márquez, A., Fondevilla, V., Sellés, A.G., Wagner, J.R., and Galobart, À. 2019.

960 Adynomosaurus arcanus, a new lambeosaurine dinosaur from the Late Cretaceous

961 Ibero-Armorican Island of the European Archipelago. Cretaceous Research, 96: 19–37.

962 Prieto-Márquez, A., Gaete, R., Rivas, G., Galobart, Á., and Boada, M. 2006a. Hadrosauroid

963 dinosaurs from the Late Cretaceous of Spain: Pararhabdodon isonensis revisited and

964 Koutalisaurus kohlerorum, gen. et sp. nov. Journal of Vertebrate Paleontology, 26: 929–

965 943.

966 Prieto-Márquez, A., and Norell, M.A. 2010. Anatomy and relationships of Gilmoreosaurus

967 mongoliensis (Dinosauria: Hadrosauroidea) from the Late Cretaceous of Central Asia.

968 American Museum Novitates, 2010: 1–49.

969 Prieto-Márquez, A., and Salinas, G.C. 2010. A re-evaluation of Secernosaurus koerneri and

970 Kritosaurus australis (Dinosauria, Hadrosauridae) from the Late Cretaceous of

971 Argentina. Journal of Vertebrate Paleontology, 30: 813–837.

972 Prieto-Márquez, A., and Wagner, J.R. 2009. Pararhabdodon isonensis and Tsintaosaurus

973 spinorhinus: a new clade of lambeosaurine hadrosaurids from Eurasia. Cretaceous

974 Research, 30: 1238–1246.

975 Prieto-Márquez, A., Weishampel, D.B., and Horner, J.R. 2006b. The dinosaur Hadrosaurus

976 foulkii, from the Campanian of theDraft East Coast of North America, with a reevaluation of

977 the genus. Acta Palaeontologica Polonica, 51: 77–98.

978 Puckett, T. M. 1994. Planktonic Foraminiferal and Ostracode Biostratigraphy of Upper

979 Santonian through Lower Maastrichtian Strata in Central Alabama. Geological

980 Survey of Alabama, Reprint Series 104.

981 Ramírez-Velasco, A.A., Benammi, M., Prieto-Márquez, A., Ortega, J.A., and Hernández-Rivera,

982 R. 2012. Huehuecanauhtlus tiquichensis, a new hadrosauroid dinosaur (Ornithischia:

983 Ornithopoda) from the Santonian (Late Cretaceous) of Michoacán, Mexico. Canadian

984 Journal of Earth Sciences, 49: 379–395.

985 Schwimmer, D.R. 1997. Late Cretaceous dinosaurs in eastern USA: a taphonomic and

986 biogeographic model of occurrences. In Dinofest International. Edited by D.L. Wolberg,

987 E. Stump, and G.D. Rosenberg. Academy of Natural Sciences, Philadelphia. pp. 203–

988 211.

989 Schwimmer, D.R., Williams, G.D., Dobie, J.L., and Siesser, W.G. 1993. Late Cretaceous

990 dinosaurs from the Blufftown Formation in western Georgia and eastern Alabama.

991 Journal of Paleontology, 67: 288–296.

992 Seeley, H. 1887. On the classification of the fossil animals commonly called Dinosauria.

993 Proceedings of the Royal Society of London, 43: 165–171.

994 Sereno, P.C. 1986. Phylogeny of the bird-hipped dinosaurs (Order Ornithischia). National

995 Geographic Research, 2: 234–256.

996 Shipboard Scientific Party. 1998. Explanatory notes. In: Norris, R.D., Kroon, D., Klaus,

997 A., et al (Eds), Proceedings of the Ocean Drilling Program, Initial Reports, 171B:

998 11-44.

999 Sues, H.-D., and Averianov, A. 2009. A new basal hadrosauroid dinosaur from the Late 1000 Cretaceous of Uzbekistan and theDraft early radiation of duck-billed dinosaurs. Proceedings 1001 of the Royal Society B: Biological Sciences, 276: 2549–2555.

1002 Takasaki, R., Chiba, K., Kobayashi, Y., Currie, P.J., and Fiorillo, A.R. 2018. Reanalysis of the

1003 phylogenetic status of Nipponosaurus sachalinensis (Ornithopoda: Dinosauria) from the

1004 Late Cretaceous of Southern Sakhalin. Historical Biology, 30: 694–711.

1005 Tsogtbaatar, K., Weishampel, D.B., Evans, D.C., and Watabe, M. 2019. A new hadrosauroid

1006 (Dinosauria: Ornithopoda) from the Late Cretaceous Baynshire Formation of the Gobi

1007 Desert (Mongolia). PloS one, 14: e0208480.

1008 Weishampel, D.B., Norman, D.B., and Grigorescu, D. 1993. Telmatosaurus transsylvanicus

1009 from the Late Cretaceous of Romania: the most basal hadrosaurid dinosaur.

1010 Palaeontology, 36: 361–385.

1011 You, H.-L., and Li, D.-Q. 2009. A new basal hadrosauriform dinosaur (Ornithischia:

1012 Iguanodontia) from the Early Cretaceous of northwestern China. Canadian Journal of

1013 Earth Sciences, 46: 949–957.

1014

1015

1016

1017

Draft

1018 Figure captions

1019 Figure 1. Relevant ornithopod specimens from the Mooreville Chalk placed in

1020 geographic and stratigraphic context within the state of Alabama. Map modified from

1021 Prieto-Márquez et al., 2016b.

1022

1023 Figure 2. Lophorhothon atopus premaxillary and maxillary elements. A) AUMP 2295 left

1024 premaxilla fragment in dorsal view; B) AUMP 2295 left premaxilla in rostroventral view;

1025 C) AUMP 2295 left premaxilla in medial view; D) FMNH P27383 right maxilla in lateral

1026 view; E) FMNH P27383 right maxilla in medial view. Abbreviations: dnt, oral denticle;

1027 me, median embayment; opp, oral pachyostic plate; palp, palatine process; pas,

1028 premaxillary articular surface. ScaleDraft bar in A, B, and C equals 5 cm. Scale bar in D and

1029 E equals 10 cm.

1030

1031 Figure 3. Lophorhothon atopus jugal and lacrimal. A) FMNH P27383 left jugal in lateral

1032 view; B) FMNH P27383 left jugal in medial view; C) AUMP 2295 left jugal in lateral view;

1033 D) AUMP left jugal in medial view; E) FMNH P27383 right lacrimal in lateral view; F)

1034 FMNH P27383 right lacrimal in posterior view; G) FMNH P27383 right lacrimal in medial

1035 view. Abbreviations: jp, jugal process; lf, lacrimal foramen; lff, lacrimal foramen fossa; lp,

1036 lacrimal process; pop, postorbital process; rp, rostral promenade. Scale bar equals 5

1037 cm.

1038

1039 Figure 4. Lophorhothon atopus nasals. A) FMNH P27383 right nasal in dorsal view; B)

1040 FMNH P27383 left nasal in dorsal view; C) AUMP 2295 right nasal in dorsal view; D)

1041 FMNH P27383 right nasal in lateral view; E) FMNH P27383 left nasal in lateral view; F)

1042 AUMP 2295 right nasal in lateral view; G) FMNH P27383 right nasal in medial view; H)

1043 FMNH P27383 left nasal in medial view; I) AUMP 2295 right nasal in medial view.

1044 Abbreviations: ap, anterior process; mdr, median ridge; na, nasal amphitheater; pp,

1045 posterior process. Scale bars equals 5 cm.

1046

1047 Figure 5. Lophorhothon atopus FMNH P27383 prefrontal in A) lateral view; and B)

1048 ventromedial view. Abbreviations: lb, lacrimal buttress; ns, nasal suture; or, orbital rim; .

1049 Scale bar equals 5 cm.

1050

1051 Figure 6. Lophorhothon atopus FMNHDraft P27383 articulated skull roof in A) dorsal view; B)

1052 ventral view; and C) right lateral view. Abbreviations: F, Frontal; fnf, frontonasal

1053 fenestra; jp, jugal process; Ls, Laterosphenoid; na, nasal articulation; Os,

1054 Orbitosphenoid; Pa, Parietal; pfa, prefrontal articulation; Po, Postorbital; sp, squamosal

1055 process. Scale bar equals 5 cm.

1056

1057 Figure 7. Lophorhothon atopus squamosal. A) FMNH P27383 right squamosal in

1058 anterodorsal view; B) FMNH P27383 left squamosal in anterodorsal view; C) FMNH

1059 P27383 right squamosal in dorsal view; D) FMNH P27383 left squamosal in dorsal view;

1060 E) FMNH P27383 left squamosal in ventral view; F) FMNH P27383 right squamosal in

1061 ventral view; G) FMNH P27383 left squamosal in lateroventral view; H) FMNH P27383

1062 right squamosal in lateroventral view; I) FMNH P27383 right squamosal in rostroventral

1063 view to show the autapomorphic fold on the postorbital process; J) AUMP 2295 right

1064 squamosal in dorsal view. Abbreviations: mr, median ramus; pcp, precotyloid process;

1065 pp, postorbital process; qc, quadrate cotylus. Scale bars equal 5 cm, except in I and J,

1066 which equal 2.5 cm.

1067

1068 Figure 8. Lophorhothon atopus quadrate. A) FMNH P27383 in medial view; B) FMNH

1069 P27383 in lateral view; C) AUMP 2295 in posterior view; D) AUMP 2295 in ventral view.

1070 Abbreviations: mc, mandibular condyle.

1071

1072 Figure 9. Lophorhothon atopus FMNH P27383 braincase elements. A) Exoccipitals-

1073 opisthotics in caudal view; B) exoccipitals-opisthotics in left lateral view; C) basioccipital

1074 in dorsal view; D) basioccipital in ventralDraft view. Abbreviations: Ba, Basioccipital; bt,

1075 basitubera; cno, cranial nerve opening; Ex, Exoccipitals; fm, foramen magnum; pop,

1076 paroccpital process; Pr, Prootic. Scale bar equals 10 cm.

1077

1078 Figure 10. Lophorhothon atopus mandibular elements. A) AUMP 2295 left surrangular

1079 in dorsal view; B) AUMP 2295 left surrangular in medial view; C) AUMP 2295 left

1080 articular in medial view; D) AUMP 2295 maxillary tooth in lingual view; E) AUMP 2295

1081 dentary tooth in labial view; F) FMNH P27383 left maxilla in ventral view with

1082 magnification of two regions of the tooth row to show replacement teeth. Note that the

1083 contrast in F has been raised to make identification of replacement teeth more obvious.

1084 Scale bar in A, B, and C equals 5 cm. Scale bar in F equals 10 cm.

1085

1086 Figure 11. Pectoral and forelimb elements from Lophorhothon atopus AUMP 2295. A)

1087 Right coracoid in rostral view; B) left coracoid in rostral view; C) left sternal in rostral

1088 view; D) left scapula in lateral view; E) left humerus in rostral view; F) left ulna in rostral

1089 view; G) metacarpals. Abbreviations: dpc, deltopectoral crest; gl, genoid; hh, humeral

1090 head; MC, metacarpal; op, olecranon process; svp, sternal ventral process. Scale bars

1091 in A, B, and C equal 5 cm. Scale bars in D, E, F, and G equal 10 cm.

1092

1093 Figure 12. Pelvic elements from Lophorhothon atopus. A) AUMP 2295 left ilium in

1094 medial view; B) AUMP 2295 left ilium in lateral view; C) close-up of AUMP 2295 left

1095 ilium supraacetabular crest; D) AUMP 2295 right pubis in lateral view; E) AUMP 2295

1096 right and left ischia in lateral view; andDraft F) FMNH P27383 left ischium in lateral view.

1097 Abbreviations: atm, acetabulum; ipp, ischium pubic process; isp, iliac process; pilp,

1098 pubis iliac process; poip, post iliac process; prip, preiliac process; prp, pubis rostral

1099 process; pucp, pubis caudal process; pup, pubic process; sac, supraacetabular crest.

1100 Scale bars equal 10 cm.

1101

1102 Figure 13. Hindlimb elements of Lophorhothon atopus. A) AUMP 2295 left femur in

1103 caudal view; B) AUMP 2295 fourth trochanter; C) AUMP 2295 left femur in rostral view;

1104 D) AUMP 2295 right tibia in rostral view; E) AUMP 2295 left tibia in caudolateral view; F)

1105 FMNH P27383 left tibia in rostral view; G) FMNH P27383 fibula left in lateral view; H)

1106 AUMP 2295 right fibula in lateral view; I) FMNH P27383 left metatarsals in dorsal view;

1107 J) FMNH P27383 left metatarsals and phalanges in rostral view. Abbreviations: cc,

1108 cnemial crest; fh, femoral head; gt, greater trochanter; lt, lesser trochanter; MT,

1109 metatarsal. Scale bars equal 10 cm.

1110

1111 Figure 14. Strict consensus phylogenetic tree constructed from 18 most parsimonious

1112 trees obtained from the matrix provided in Prieto-Marquez et al. (2016a). Tree scores:

1113 Length - 989; CI - 0.40; RC - 0.31; RI - 0.78. The country or North American paleoregion

1114 in which each species is known adjoins the species name.

Draft

Figure 1. Ornithopod species from the Mooreville Chalk placed in geographic and stratigraphic context within the state of Alabama. Map modified from Prieto-Márquez et al., 2016b under CCBY.

Draft

Draft Figure 2. Lophorhothon atopus premaxillary and maxillary elements. A) AUMP 2295 left premaxilla fragment in dorsal view; B) AUMP 2295 left premaxilla in rostroventral view; C) AUMP 2295 left premaxilla in medial view; D) FMNH P27383 right maxilla in lateral view; E) FMNH P27383 right maxilla in medial view. Abbreviations: dnt, oral denticle; me, median embayment; opp, oral pachyostic plate; palp, palatine process; pas, premaxillary articular surface. Scale bar in A, B, and C equals 5 cm. Scale bar in D and E equals 10 cm.

Draft

Figure 3. Lophorhothon atopus jugal and lacrimal. A) FMNH P27383 left jugal in lateral view; B) FMNH P27383 left jugal in medial view; C) AUMP 2295 left jugal in lateral view; D) AUMP left jugal in medial view; E) FMNH P27383 right lacrimal in lateral view; F) FMNH P27383 right lacrimal in posterior view; G) FMNH P27383 right lacrimal in medial view. Abbreviations: jp, jugal process; lf, lacrimal foramen; lff, lacrimal foramen fossa; lp, lacrimal process; pop, postorbital process; rp, rostral promenade. Scale bar equals 5 cm.

Draft

Figure 4. Lophorhothon atopus nasals. A) FMNH P27383 right nasal in dorsal view; B) FMNH P27383 left nasal in dorsal view; C) AUMP 2295 right nasal in dorsal view; D) FMNH P27383 right nasal in lateral view; E) FMNH P27383 left nasal in lateral view; F) AUMP 2295 right nasal in lateral view; G) FMNH P27383 right nasal in medial view; H) FMNH P27383 left nasal in medial view; I) AUMP 2295 right nasal in medial view. Abbreviations: ap, anterior process; mdr, median ridge; na, nasal amphitheater; pp, posterior process. Scale bars equals 5 cm.

Draft

Figure 5. Lophorhothon atopus FMNH P27383 prefrontal in A) lateral view; and B) ventromedial view. Abbreviations: lb, lacrimal buttress; ns, nasal suture; or, orbital rim; . Scale bar equals 5 cm.

Draft

Figure 6. Lophorhothon atopus FMNH P27383 articulated skull roof in A) dorsal view; B) ventral view; and C) right lateral view. Abbreviations: F, Frontal; fnf, frontonasal fenestra; jp, jugal process; Ls, Laterosphenoid; na, nasal articulation; Os, Orbitosphenoid; Pa, Parietal; pfa, prefrontal articulation; Po, Postorbital; sp, squamosal process. Scale bar equals 5 cm.

Draft

Figure 7. Lophorhothon atopus squamosal. A) FMNH P27383 rightleft squamosal in anterodorsal view; B) FMNH P27383 leftright squamosal in anterodorsal view; C) FMNH P27383AUMP right squamosal in dorsal view; D) FMNH P27383 left squamosal in dorsallateroventral view; E) FMNH P27383 leftright squamosal in lateroventral view; F) FMNH P27383AUMP 2295 right squamosal in lateroventral view; G) FMNH P27383 left squamosal in lateroventralrostral view; H) FMNH P27383 right squamosal in lateroventralrostral view; I) FMNH P27383AUMP 2295 right squamosal in rostroventralal view to show the autapomorphic fold on the postorbital process; J) AUMP 2295FMNH P27383 rightleft squamosal in laterodorsal view; K) FMNH P27383 right squamosal in laterodorsal view; L) AUMP 2295 right squamosal in laterodorsal view. Abbreviations: mr, median ramus; pcp, precotyloid process; pp, postorbital process; qc, quadrate cotylus. Scale bars equals 5 10 cm, except in I and J, which equal 2.5 cm..

Draft

Figure 8. Lophorhothon atopus quadrate. A) FMNH P27383 in medial view; B) FMNH P27383 in lateral view; C) AUMP 2295 in posterior view; D) AUMP 2295 in ventral view. Abbreviations: mc, mandibular condyle. Scale bar equals 10 cm.

Figure 9. Lophorhothon atopus FMNH P27383 braincase elements. A) Exoccipitals-opisthotics in caudal view; B) exoccipitals-opisthotics in left lateral view; C) basioccipital in dorsal view; D) basioccipital in ventral view. Abbreviations: Ba, Basioccipital; bt, basitubera;Draft cno, cranial nerve opening; Ex, Exoccipitals; fm, foramen magnum; pop, paroccpital process; Pr, Prootic. Scale bar equals 10 cm.

Draft

Figure 10. Lophorhothon atopus mandibular elements. A) AUMP 2295 left surangular in dorsal view; B) AUMP 2295 left surangular in medial view; C) AUMP 2295 left articular in medial view; D) AUMP 2295 maxillary tooth in lingual view; E) AUMP 2295 dentary tooth in labial view; F) FMNH P27383 left maxilla in ventral view with magnification of two regions of the tooth row to show replacement teeth. Note that the contrast in F has been raised to make identification of replacement teeth more obvious. Scale bar in A, B, and C equals 5 cm. Scale bar in F equals 10 cm.

Draft

Figure 11. Pectoral and forelimb elements from Lophorhothon atopus AUMP 2295. A) Right coracoid in rostral view; B) left coracoid in rostral view; C) left sternal in rostral view; D) left scapula in lateral view; E) left humerus in rostral view; F) left ulna in rostral view; G) metacarpals. Abbreviations: dpc, deltopectoral crest; gl, genoid; hh, humeral head; MC, metacarpal; op, olecranon process; svp, sternal ventral process. Scale bars in A, B, and C equal 5 cm. Scale bars in D, E, F, and G equal 10 cm.

Draft

Figure 12. Pelvic elements from Lophorhothon atopus. A) AUMP 2295 left ilium in medial view; B) AUMP 2295 left ilium in lateral view; C) close-up of AUMP 2295 left ilium supraacetabular crest; D) AUMP 2295 right pubis in lateral view; E) AUMP 2295 right and left ischia in lateral view; and F) FMNH P27383 left ischium in lateral view. Abbreviations: atm, acetabulum; ipp, ischium pubic process; isp, iliac process; pilp, pubis iliac process; poip, post iliac process; prip, preiliac process; prp, pubis rostral process; pucp, pubis caudal process; pup, pubic process; sac, supraacetabular crest. Scale bars equal 10 cm.

Draft

Figure 13. Hindlimb elements of Lophorhothon atopus. A) AUMP 2295 left femur in caudal view; B) AUMP 2295 fourth trochanter; C) AUMP 2295 left femur in rostral view; D) AUMP 2295 right tibia in rostral view; E) AUMP 2295 left tibia in caudolateral view; F) FMNH P27383 left tibia in rostral view; G) FMNH P27383 fibula left in lateral view; H) AUMP 2295 right fibula in lateral view; I) FMNH P27383 left metatarsals in dorsal view; J) FMNH P27383 left metatarsals and phalanges in rostral view. Abbreviations: cc, cnemial crest; fh, femoral head; gt, greater trochanter; lt, lesser trochanter; MT, metatarsal. Scale bars equal 10 cm.

Draft

Figure 14. Strict consensus phylogenetic tree constructed from 18 most parsimonious trees obtained from the matrix provided in Prieto-Márquez et al. (2016a). Tree scores: Length - 989; CI - 0.40; RC - 0.31; RI - 0.78. The country or North American paleoregion in which each species is known adjoins the species name.