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Canadian Journal of Earth Sciences

Theropod Structure and the Tyrannosaurid Niche Assimilation Hypothesis: Implications for Predatory Macroecology and in later Late Asiamerica

Journal: Canadian Journal of Earth Sciences

Manuscript ID cjes-2020-0174.R1

Manuscript : Article

Date Submitted by the 04-Jan-2021 Author:

Complete List of Authors: Holtz, Thomas; University of Maryland at College Park, Department of Geology; NationalDraft Museum of Natural History, Department of Geology Keyword: Dinosaur, Ontogeny, Theropod, Paleocology, ,

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

© The Author(s) or their Institution(s) Page 1 of 91 Canadian Journal of Earth Sciences

1 Theropod Guild Structure and the Tyrannosaurid Niche Assimilation Hypothesis:

2 Implications for Predatory Dinosaur Macroecology and Ontogeny in later

3 Asiamerica

4

5

6 Thomas R. Holtz, Jr.

7

8 Department of Geology, University of Maryland, College Park, MD 20742 USA

9 Department of Paleobiology, National Museum of Natural History, Washington, DC 20013 USA

10 Email address: [email protected]

11 ORCID: 0000-0002-2906-4900 Draft

12

13 Thomas R. Holtz, Jr.

14 Department of Geology

15 8000 Regents Drive

16 University of Maryland

17 College Park, MD 20742

18 USA

19 Phone: 1-301-405-4084

20 Fax: 1-301-314-9661

21 Email address: [email protected]

22

23

1 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 2 of 91

24 ABSTRACT

25 Well-sampled dinosaur communities from the through the early Late Cretaceous show

26 greater taxonomic diversity among larger (>50kg) theropod taxa than communities of the

27 Campano-, particularly to those of eastern/central and . The large

28 guilds in Asiamerican assemblages are monopolized by tyrannosaurids, with adult

29 medium-sized (50-500 kg) predators rare or absent. In contrast, various of theropods are

30 found to occupy these body sizes in earlier , including early tyrannosauroids. Assemblages

31 with “missing middle sized” predators are not found to have correspondingly sparser diversity of

32 potential prey recorded in these same faunas. The “missing middle sized” niches in the

33 theropod guilds of Late Cretaceous Laramidia and Asia may have been assimilated by juvenile

34 and subadults of tyrannosaurid species, Draftfunctionally distinct from their adult ecomorphologies. It

35 is speculated that if tyrannosaurids assimilated the niches previously occupied by mid-sized

36 theropod predators that we would expect the evolution of distinct transitions in morphology and

37 possibly the delay of the achievement of somatic maturity in species of this .

38

39 Keywords: , ontogeny, theropod, paleoecology, Mesozoic, Tyrannosauridae

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2 © The Author(s) or their Institution(s) Page 3 of 91 Canadian Journal of Earth Sciences

47

48 INTRODUCTION

49 Dale Russell’s (1970) review of the Tyrannosauridae of the Late Cretaceous Western Canada

50 represents one of the most significant contributions to the study of the tyrant dinosaur in the mid-

51 20th Century. As well as introducing the species torosus and summarizing what

52 was then the most extensive collections of North American tyrannosaurids, Russell also

53 speculated on the anatomy and proportions of a hypothetical hatchling albertosaurine (Fig. 1),

54 extrapolated from observed allometric changes in subadult and adult specimens. This

55 hypothetical reconstruction emphasized that the early ontogenetic stages of an which

56 undergoes very large increases in size might have strikingly different functional morphology and

57 ecological roles than the adult of the sameDraft species.

58

59 The scale of ontogenetic morphological transformation in Tyrannosauridae was first explored by

60 Rozhdestvesnky (1965). He observed that several specimens initially regarded as separate

61 species ( novojilovi, Gorgosaurus lancinator, efremovi, and

62 bataar) represented a single taxon, for which the proper name was Tarbosaurus

63 bataar. Morphological distinctions beyond body size, such as changes in hindlimb proportion

64 and a shift from relatively ziphodont (blade-like) maxillary and dentary teeth in the smaller

65 “species” versus incrassate (inflated) teeth in the adult, had led previous authors to consider as

66 separate taxa what were in fact a continuous growth . Subsequently similar changes were

67 observed in other Asian and North American tyrannosaurids, with recognition that some

68 previously proposed species were parts of ontogenetic sequences (Carr 1999, 2020; Currie 2003;

69 Carr and Williamson 2004).

3 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 4 of 91

70

71 Given these anatomical transitions at different classes, the question of the possibility of

72 substantial shifts in functional anatomy and ecology through ontogeny in tyrannosaurids has

73 been speculated upon by a number of authors (Holtz 2004a, 2004b; Snively et al. 2006; Bates

74 and Falkingham 2012; Woodward et al. 2020; Carr 2020). Indeed, an ontogenetic niche shift

75 would be unavoidable in an animal that underwent a multiple order of magnitude increase in size

76 from hatching to adulthood (Taylor 1979; Auffenberg 1981; Tucker et al. 1996; Purwanda et al.

77 2016), barring provisioning by an adult throughout the entire growth series or membership in a

78 gregarious social group responsible for all food acquisition (but see Currie and Eberth (2010) for

79 the possibility for gregariousness in the Early Maastrichtian tyrannosaurid

80 sarcophagus.) Draft

81

82 How might these ontogenetic niche shifts be reflected in the structure of the communities of

83 carnivorous dinosaurs, and do communities in which tyrannosaurids are the largest (presumably

84 apex) predators differ from those in which the largest members are other theropod clades?

85 Theropod dinosaurs first appeared in the Late (Sereno 1999; Holtz and Osmólska 2004)

86 but were not the dominant predators until the loss of their competitors (primarily loricatan

87 pseudosuchians: Zanno et al. 2015) in the Triassic-Jurassic event (Olsen et al. 2002).

88 During the subsequent 135 million , theropods were the primary large-bodied flesh-eaters in

89 terrestrial ecosystems.

90

91 As such, the assemblage of theropods in a given faunal community can be considered an

92 ecological guild. As originally described by Root (1967), a guild comprises “a group of species

4 © The Author(s) or their Institution(s) Page 5 of 91 Canadian Journal of Earth Sciences

93 that exploit the same class of environmental resources in a similar way.” Therefore, members of

94 a guild are expected to be in principle each other’s most likely competitors, resulting in character

95 displacement (Brown and Wilson 1956; Van Valkenburgh 1988, 1994; Henderson 2000): the

96 selection for anatomical and behavioral adaptations that reduce the overlap of specific ecological

97 parameters for each taxon.

98

99 Aspects of theropod guild structure has been the subject of several previous studies. For

100 example, Henderson (2000) examined the functional differences in cranial form of sympatric

101 large theropods of the . Van Valkenburgh and Molnar (2002) compared the

102 assemblages of theropods of the Morrison, Dinosaur Park, and Nemegt Formations with

103 communities of carnivorous fromDraft various communities. Farlow and Pianka

104 (2003) observed the overlap in body size and form among the tyrannosaurids of the Dinosaur

105 Park Formation. Carbone et al. (2011) utilized theoretical ecology and the observed size

106 distribution of dinosaurs to test the possibility of obligate scavenging in

107 Tyrannosaurus rex. More recently Torices et al. (2018) examined the functional differences in

108 morphology for sympatric theropod species of western Canada. Frederickson et al. (2018)

109 studied niche partitioning in theropod dinosaurs in terms of diet and habitat preference in the

110 Mussentuchit Member of the .

111

112 One significant observation about Mesozoic theropod guilds is the qualitative difference between

113 Jurassic and assemblages relative to the later Late Cretaceous assemblages of

114 western and eastern and central Asia (Foster et al. 2001; Farlow and Holtz 2002;

115 Holtz 2004a, 2004b). While the former communities show a diversity of theropod lineages

5 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 6 of 91

116 represented among the larger , the latter contain only members of Tyrannosauridae.

117 This transition occurred sometime after the (Zanno and Makovicky 2013; Zanno et al.

118 2019; Nesbitt et al. 2019) and before the middle (Loewen et al. 2013) in North

119 America. A similar pattern is observed in Asia, where the tyrannosauroid Timurlengia of the

120 Turonian is a mid-sized predator (Brusatte et al. 2016), while a larger

121 carcharodontosaurid has recently been reported from the same unit (Tanaka et al. 2020). The

122 slightly stratigraphically younger Turonian- Upper Bayan Shireh Formation of

123 and Santonian of (Averianov and Sues 2012)

124 lack evidence at present of carcharodontosaurids, although in the former the large dromaeosaurid

125 Achillobator rivals the sympatric tyrannosauroid cf. in size (Perle et al. 1999). In

126 the post-Santonian no large carnivorousDraft theropods other than tyrannosaurids are observed in this

127 region.

128

129 The cause of the transition from carcharodontosaurid- to tyrannosaurid-dominated theropod

130 guilds in Asiamerica is still not understood. The disappearance of previous apex theropod clades

131 such as and between the Turonian and the Campanian may be due

132 to out-competition by the newly evolved Tyrannosauridae, loss of the primary prey of these older

133 taxa, or other environmental changes, but poor sampling of the interval involved leaves the cause

134 of this transformation (and the similar event in ) unresolved at present.

135

136 The present study seeks to compare tyrant-dominated and non-tyrant-dominated theropod guilds

137 through a number of different parameters. “Tyrant” in this context refers to Tyrannosauridae

138 proper as well as other large-bodied immediate outgroups (such as and

6 © The Author(s) or their Institution(s) Page 7 of 91 Canadian Journal of Earth Sciences

139 : Brusatte and Carr 2016): taxa typically of 1000 kg or more with powerful

140 jaws and laterally expanded (incrassate) teeth, reduced forelimbs ending in a didactyl manus, and

141 elongate hindlimbs terminating in an arctometatarsus (Holtz 2004a). The more inclusive

142 contains Jurassic and Early-to-early Late Cretaceous groups of smaller-bodied

143 taxa including , Proceratosauridae (although at least two genera of this group achieved

144 tyrannosaurid sizes, and : Ji et al. 2009; Xu et al. 2012), and

145 Stokesosauridae. These early tyrannosauroids were more typically middle-sized predators in

146 their respective guilds. Some Early-to-early Late Cretaceous tyrannosauroids of North America

147 and Asia such as , Moros, and Suskityrannus demonstrate that some of the

148 anatomical traits characteristic of Tyrannosauridae evolved in the context of smaller body size

149 (Li et al. 2010; Zanno et al. 2019; NesbittDraft et al. 2019).

150

151 INSTITUTIONAL ABBREVIATIONS

152 AMNH, American Museum of Natural History, New York City, New York, USA; BMRP,

153 Burpee Museum of Natural History, Rockford, Illinois, USA; FMNH, Field Museum of Natural

154 History, , Illinois, USA; PIN, Paleontological Institute, Russian Academy of Sciences,

155 Moscow, Russia; ROM, Royal Ontario Museum, Toronto, Canada.a

156

157 METHODS AND MATERIALS

158 Statistics for this study were calculated using the PAST 4.03 software package (Hammer et al.

159 2001; 2020).

160

7 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 8 of 91

161 Theropods range in size from Mellisuga hellenae (the bee hummingbird) to 14 m long, 8 tonne

162 or more giants including Tyrannosaurus rex, carolinii, and

163 aegyptiacus (Mazzetta et al. 2004; Holtz and Osmólska 2004; Persons et al. 2020; Campione and

164 Evans 2020). Even removing the avialian () component of this clade, the known lower end of

165 Mesozoic theropod range includes 50-cm long taxa such as and zhaoianus.

166 Consequently, size represents a parameter in which the guild of carnivorous dinosaurs might

167 easily partition the niche of flesh-eaters, especially as predator body size is positively associated

168 with maximum prey body size and total range of prey sizes (Van Valkenburgh and Hertel 1998;

169 Meers 2002; Radloff and Du Toit 2004).

170

171 Size estimates for individual theropod specimensDraft are derived primarily from the supplementary

172 data of Benson et al. (2018) and Campione and Evans (2020); for taxa not included in those

173 previous analyses, size class was assigned based on those of other theropod species with the most

174 similar femoral, tibial, or length. The size classes used in this study are: size class 1, 10 kg

175 or less; size class 2, 11-50 kg; size class 3, 51-100 kg; size class 4, 101-500 kg; size class 5, 501-

176 1000 kg; size class 6, 1001-5000 kg; and size class 7, greater than 5000 kg. These broad

177 categories, rather than particular estimated masses, are employed to reduce the uncertainties

178 resulting from differences in mass estimation techniques, inaccurate models, incomplete

179 preservation of the specimens, and variability within the taxon (Campione and Evans 2020).

180 Where possible, the size of the largest known individual of that species was used as the best

181 approximation of adult body size, with the recognition that our limited data set for most dinosaur

182 species might not currently include fully adult individuals (Hone et al. 2016). Carbone et al.

183 (1999) found a transition in extant mammalian predators between those which fed on small prey

8 © The Author(s) or their Institution(s) Page 9 of 91 Canadian Journal of Earth Sciences

184 (less than ½ predator mass) to large prey (near predator mass) at 21.5-25 kg. This inflection point

185 is within size class 2 in this study. At present it is uncertain where the equivalent inflection point

186 would be in Mesozoic theropods (or indeed if there is such an inflection rather than a gradual

187 transition). Thus, the scheme used here is admittedly a simplification.

188

189 For purposes of comparison, this study seeks to examine sympatric communities of organisms:

190 that is, those which actually inhabited the same geographical region at the same time. Almost

191 assuredly most carnivorous theropod species had ranges that extended beyond a single

192 depositional basin (Farlow 1993), but most species of dinosaur are currently known from only a

193 single stratigraphic unit. The question as to the degree of intracontinental and

194 provincialization in dinosaurian faunas remainsDraft a matter of debate (Sampson et al. 2010; Vavrek

195 and Larsson 2010; Lucas et al. 2016; Whitlock et al. 2018). While there may be some interaction

196 between faunal assemblages in different neighboring regions that are currently unrecognized due

197 to low levels of sampling (Vavrek and Larsson 2010), the present study takes the conservative

198 approach in using only taxa presently observed in the same stratigraphic units as being

199 sympatric. In at least the case of one individual of hadrosaurid from the

200 it was found that the total geographic range based on strontium isotopic data was only on the

201 scale of a few 100 kms (Terrill et al. 2020), potentially justifying the restriction of faunas to

202 single depositional basins.

203

204 For some very well-sampled dinosaur-bearing strata, recent work has provided detailed

205 biozonation of the individual species, reducing the chance of including taxa that did not actually

206 exist at the same time. Fowler (2017) provides a comprehensive overview of this for dinosaurs of

9 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 10 of 91

207 the Santonian through Maastrichtian of the Western Interior of North America. Examples of

208 specific Western North American formations for which such data are available include the

209 - Morrison Formation (Foster 2003), the middle-to-upper Campanian

210 Dinosaur Park Formation (Mallon 2019), and the Horseshoe Canyon Formation of the late

211 Campanian-early Maastrichtian (Eberth and Kamo 2019). These works additionally show that

212 individual dinosaur species were often present for relatively short geologic durations, shorter that

213 the of the formations in which they were present. Thus, including all the species

214 recovered in a single formation as being part of the same faunal community may be exaggerating

215 the diversity, transforming successions of taxa into one . However, detailed biostratigraphic

216 work has not been conducted or published for many dinosaur bearing strata. Consequently, the

217 study here may be combining taxa whichDraft did not actually interact in life for these formations.

218

219 The focus of this analysis is theropods as hypercarnivorous specialists feeding on other

220 dinosaurs. As such, regarding “carnivorous theropods” as a guild (a group of species that exploit

221 the same class of environmental resources in a similar way) rather than a clade (an ancestor and

222 all of its descendants), the highly derived pygostylians (Confusciusornis, enantiornithine, and

223 more derived : Cau 2018) are excluded from this particular study. None of the currently

224 known Mesozoic members of this clade are likely to have competed over the primary resource of

225 significance here, namely dead dinosaurs. The skull, and consequently the feeding ecology, of

226 the large probable ornithurine bird Gargantuavis remains unrecovered (Buffetaut and Angst

227 2020); however, barring discovery that this was a Maastrichtian phorusrhacid-mimic it will be

228 omitted as a dinosaur-eating theropod.

229

10 © The Author(s) or their Institution(s) Page 11 of 91 Canadian Journal of Earth Sciences

230 Similarly, the size class 1 theropods are excluded from the calculations in this study, as taxa of

231 such body size are more likely feeding on and microvertebrates and again would

232 not be competing for comparable resources (Hirt et al. 2020). Additionally, several theropod

233 clades (including elaphrosaurine noasaurids, ornithomimosaurs, therizinosaurs, and

234 oviraptorosaurs) evolved away from the ancestral hypercarnivorous diet, instead incorporating

235 foods such as and (Zanno and Makovicky 2011); these non-predaceous theropods

236 are excluded from the histogram analysis but are included in the total dinosaurian diversity

237 portion of the study. While some of them may have consumed , these were likely

238 restricted to small , , mammals, and ; it is unlikely that any of these taxa

239 routinely killed and ate other dinosaurs, except for and hatchlings.

240 Draft

241 The of the peculiar bahariasaurid (Motta et al. 2016; Porfiri et al. 2018; Lamana et al.

242 2020) theropods agilis and Bahariasaurus ingens of early Late Cretaceous

243 northern and shinyae and Aoniraptor liberatem of comparable age in

244 lack cranial material, and it is possible that these represent large-bodied elaphrosaurine-like

245 noasaurids similar to the much-smaller non-carnivorous (Ibrahim et al. 2020). If so,

246 they should not be included among the predatory forms. However, they are here conservatively

247 assumed to have retained the ancestral carnivorous diet.

248

249 Other contemporaneous carnivorous taxa, including mammals (Hu et al. 2005), squamates (Wick

250 et al. 2015), and crocodyliforms (Boyd et al. 2013; Sellés et al. 2020) competed with theropods,

251 especially in the smaller size classes. However, the limited size and/or mobility of these taxa

252 compared to predatory dinosaurs meant they were likely only a minor portion of the terrestrial

11 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 12 of 91

253 predator guild where larger-bodied dinosaurs were concerned (but see Dal Sasso et al. 2017 for a

254 case of a substantial-sized terrestrial crocodyliform which may have served as the

255 of its community.) These non-dinosaurian carnivores are not included here either

256 as members of the predatory guild nor in the count of prey items.

257

258 Adult body size distribution histograms of each community (or potential community) of

259 carnivorous dinosaurs were assembled. Previous work (for example, Travouillon and Legendre

260 2009) has used this technique in comparing mammalian faunas. Longrich and Currie (2009) and

261 Carbone et al. (2011) have used this method in a limited fashion for a single theropod fauna

262 each, while Mallon (2019) used it to compare the Dinosaur Park Formation dinosaurian

263 assemblage to a series of Cenozoic mammalianDraft communities.

264

265 This study only examines faunal assemblages of the Jurassic and Cretaceous. While theropods

266 (Zahner and Brinkmann 2019; Marsh and Parker 2020; Müller 2020) and non-theropod

267 herrerasaurids (Pacheco et al. 2019) were part of the guild of medium-sized terrestrial carnivores

268 in the , the largest predators (as well as the most abundant and morphologically

269 disparate) in these faunal assemblages were pseudosuchian (Brusatte et al. 2008;

270 Zanno et al. 2015). Future research to compare the carnivorous guilds of the Triassic with those

271 of the Jurassic and Cretaceous is planned but is not part of the present set of analyses.

272

273 The following parameters were used to evaluate whether a particular faunal assemblage was

274 included. At least three distinguishable carnivorous theropod taxa in size classes 2 upwards had

275 to have been confirmed. Additionally, a total of at least six distinguishable dinosaurian taxa (in

12 © The Author(s) or their Institution(s) Page 13 of 91 Canadian Journal of Earth Sciences

276 this case, including size class 1 carnivorous theropods, non-carnivorous theropods of any size,

277 and ornithischian and sauropodomorph dinosaurs) must be documented from this assemblage. In

278 determining total faunal diversity, instantaneous diversity counts were used rather than time-

279 binning: for instance, stratigraphically successive species within subclades of Centrosaurinae in

280 the same faunal zone in the Dinosaur Park Formation (Mallon 2019) would be considered as a

281 single species present at a given time, rather than two species for that fauna. (Whether these are

282 actually chronospecies or represent the termination of a lineage and a replacement from outside

283 this depositional basin is not considered in this analysis.) Woodruff (2019) highlighted some of

284 the difficulties in determining horizon-based species diversity in large dinosaurian taxa.

285

286 As a consequence, some particular faunasDraft in a sequence may be excluded even if those

287 stratigraphically above or below were part of the analysis. For instance, the uppermost

288 of the Horseshoe Canyon Formation, containing the triceratopsin Eotriceratops xerinsularis, was

289 not included as total dinosaurian diversity was too low (Eberth and Kamo 2019). Similarly,

290 Morrison Zone 1 (the lowermost biozone of that unit) was excluded as lacking sufficient number

291 of diagnosable theropod taxa (Foster 2003). The Middle-to- Yanliao biota of the

292 Daohugou Formation (Xu et al. 2013) and the Early Cretaceous Jehol biota of the Yixian and

293 Jiufotang Formations (Zhao 2014) were excluded as well: although exceptionally diverse in

294 terms of smaller-bodied (size classes 1 and 2) dinosaurian taxa, the depositional setting of these

295 Lagerstätten preferentially excludes common preservation of larger-bodied organisms and hence

296 these assemblages are not broadly comparable samples to more typical fluviolacustrine and

297 deltaic dinosaur-bearing formations. In the case of the among

298 hypercarnivorous dinosaurs there is none currently described between the various (all size class

13 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 14 of 91

299 1) species of Microraptor and the proceratosaurid tyrannosauroid (size class 6) Sinotyrannus

300 kazuoensis: consequently, there is only that latter carnivorous theropod in the study range and

301 this assemblage fails to meet the “three or more diagnosable size 2 or larger carnivorous

302 theropod” criterion. A few of the Yixian hypercarnivorous coelurosaurs (the primitive

303 tyrannosauroid Dilong paradoxus and the compsognathids Huaxiangnathus orientalis and

304 gigas) reach size class 2. The first two of these are from the Liujiatun Bed,

305 while Sinocalliopteryx is from the older Jianshangou Bed and consequently nearly 1 Myr older.

306 Unfortunately, the stratigraphic level (and indeed most of the relevant geologic context) of the

307 one known giant theropod within the 8 Myr duration of the (Chang et al.

308 2009), namely Yutyrannus huali (size class 6), is not presently described (Xu et al. 2012). This

309 hinders our ability to put this proceratosauridDraft in its proper faunal assemblage with regards to the

310 stratigraphically better constrained smaller bodied taxa.

311

312 It is recognized that the parameters chosen for the criteria are ultimately arbitrary and not

313 necessarily informed by some biological or sampling reality. They represent an intentional

314 compromise between restricting the study only to the small number of faunal assemblages that

315 have been subjected to substantial multi-decadal research on the one and the desire to

316 include as extensive a geographic and stratigraphic range of dinosaurian communities as

317 possible. Potentially future iterations of this or similar work might refine the methodology from

318 its initial version here.

319

320 A total of 60 faunal assemblages were recognized, from the Toarcian Cañadon Asfalto

321 Formation of Argentina (Pol et al. 2020) and the Bajocian- Xiashaximiao Formation

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322 (Lower Shaximiao Formation, or - assemblage), of Sichuan and Yunnan

323 Basins, (Li et al. 2011) through latest Maastrichtian upper Hell Creek Formation fauna of

324 the North American Western Interior (Fowler 2017). Twenty-nine of these (mostly from the later

325 Late Cretaceous of Asia and western North America: the Asiamerican landmass of that interval)

326 represent assemblages in which tyrannosaurids and their immediate outgroups were the apex

327 predators; the remaining 31 (representing the Jurassic through early Late Cretaceous, as well as

328 the Gondwanan landmasses of the late Late Cretaceous) had other taxa as their largest predators.

329 These faunal assemblages are described in Tables 1, S1, and S2.

330

331 Tyrannosauridae is not presently represented in any fauna in which that clade is not the apex

332 predator; however, earlier tyrannosauroidsDraft such as coelurids, proceratosaurids, and

333 stokesosaurids are present in communities with other theropods as the largest forms. These

334 earlier tyrannosauroids are so indicated on their respective histograms. In the present study

335 megaraptorids are not listed as being members of Tyrannosauroidea. However, some recent

336 analyses, such as Delcourt and Grillo (2018), Cau (2018), and Lamanna et al. (2020), find this

337 clade to represent a lineage within Tyrannosauroidea phylogenetically close to Tyrannosauridae.

338 Regardless of their phylogenetic affinity, the long slender snouts, ziphodont dentition, and large

339 grasping forelimbs with exceedingly large unguals of megaraptorids (Lamanna et al. 2020)

340 indicates a different style of prey acquisition in Megaraptoridae relative to Tyrannosauridae. The

341 presence or absence of members of Tyrannosauroidea other than Tyrannosauridae in the non-

342 tyrant faunas is not a factor of the analysis, but the position of these taxa as smaller predators in

343 earlier dinosaurian communities is shown of the histograms.

344

15 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 16 of 91

345 After histogram construction, the number of size classes in which adult predaceous theropods are

346 not currently discovered was assessed. Size class 1 (<10 kg) was excluded, as was size class 7

347 (>5000 kg) as only a few theropod lineages achieved this size. In some assemblages no size

348 classes were missing; in others all size classes between 2 and 7 were unoccupied (and thus 4

349 classes were missing.)

350

351 RESULTS

352 Some representative histograms from the better sampled tyrant faunas are shown in Fig. 2, and

353 from non-tyrant faunas in Fig. 3.

354

355 Box-and-whisker plots of the representativeDraft classes of fauna are shown as Fig. 4. For the tyrant

356 assemblages the mean number of missing cells was found to be 2.9±0.8 and a median of 3, while

357 for the non-tyrant assemblages this mean was 1.8±1.2 and a median of 2 (full statistics for this

358 and other analyses available in Table S3). To test to see if these represent statistically significant

359 distributions, Student t-tests testing for equal means and Mann-Whitney U-tests for distributions

360 around equal medians were conducted. These two classes were found to have statistically distinct

361 means (p = 0.000077) and medians (p = 0.00024). Thus, there is a quantitative difference in the

362 size distribution of theropods in communities in which tyrannosaurids are present versus those in

363 which tyrants are absent.

364

365 It is recognized that not all formations have been equally well surveyed. Some have only been

366 explored for a few field seasons, while others have had multiple teams engaged in field work

367 every field season for multiple decades. Nevertheless, this difference in fieldwork does not seem

16 © The Author(s) or their Institution(s) Page 17 of 91 Canadian Journal of Earth Sciences

368 to be the sole or even primary reason for missing medium-sized theropods in the tyrant-

369 dominated assemblages. While it is true that some of the Campano-Maastrichtian Asiamerican

370 strata have only been explored for a few field seasons, other tyrant-bearing formations such as

371 the Hell Creek, Horseshoe Canyon, Dinosaur Park, Nemegt, and Kaiparowits are among the

372 most intensely surveyed dinosaur-bearing units known, rivaled by very few others (e.g., the

373 Morrison). Thus, we would expect on average a better knowledge of theropods of all sizes within

374 these formations compared to more poorly sampled ones, and yet intermediate-sized taxa are rare

375 or absent in these well-studied units. In contrast, less well-studied units such as the Cañadón

376 Asfalto and Huincul Formations of Argentina have already yielded a high diversity of medium-

377 to-large carnivorous theropods (in the first case, the allosauroid Asfaltovenator vialidadi, the

378 megalosauroids floresiDraft and Condorraptor currumili, and the abelisauroid

379 Eoabelisaurus mefi, and in the second the carcharodontosaurids rosea and

380 Taurovenator violantei, the abelisaurids Skorpiovenator bustingorryi,

381 aguadagrandensis, and Tralkasaurus cuyi, and the ?bahariasaurids Gualicho shinyae and

382 Aoniraptor liberatem.)

383

384 One possibility that might explain this difference would be if the potential prey diversity were

385 lower in the tyrant-dominated assemblages, so that there was less opportunity for niche

386 partitioning among the carnivores and thus lower overall spread of theropod sizes. Recognizing

387 that not all theropods would have eaten dinosaurs of all size classes (Hone and Rauhut 2010), in

388 principle we might expect a more diverse food resource base to support a broader variety of

389 carnivores and thus more extensive niche partitioning. Additionally, all the prey taxa had to pass

390 through the smaller size classes on their way to adulthood, and thus were potentially prey for

17 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 18 of 91

391 smaller theropods while they were hatchlings and juveniles (e.g., even and

392 were potential food for ).

393

394 Fig. 5A shows the plot of carnivorous theropod diversity against total faunal size; no clear

395 distinction between the two classes is apparent. Box-and-whisker plots of these data are shown in

396 Fig. 5B. The mean number of dinosaurian taxa in the tyrant-dominated assemblages is 13.9±5.8

397 and a median of 14. In contrast the non-tyrant mean is in fact slightly lower, with a mean of

398 12.4±4.3 and a median of 12. This slight difference is statistically insignificant, however, as

399 analysis fails to reject the null hypothesis for either the mean (p = 0.28) or the median (p = 0.47).

400

401 A related issue to consider is the effect ofDraft the presence or absence of sauropod dinosaurs within

402 the community. Such exceedingly large-bodied prey, often greatly exceeding the predator mass

403 in the same faunal assemblage (Sander et al. 2010), could conceivably serve as food items for the

404 entire predatory theropod guild between their eggs to adulthood. The same tyrant dominated

405 Asiamerican communities, or more specifically most of the western North American

406 (Laramidian) component of these, are noteworthy in being among the very few Jurassic and

407 Cretaceous dinosaurian faunal assemblages in which sauropods were absent (D’Emic et al.

408 2010). Among the faunas in this study, only the Bissekty Formation (Turonian of )

409 among the non-tyrant assemblages lacks a known sauropod presence, while among the tyrant

410 assemblages sauropods are known at present only from the Iren Dabasu, Bayan Shireh, and

411 Nemegt Formations of Mongolia and the Javelina Formation and Naashoibito Member of the

412 of the late Maastrichtian of the American Southwest (D’Emic et al. 2010).

413

18 © The Author(s) or their Institution(s) Page 19 of 91 Canadian Journal of Earth Sciences

414 In order to see if the presence of sauropods is reflected in the number of missing size classes,

415 another iteration of comparisons was conducted (Fig. 6). The mean number of missing sizes in

416 sauropod faunas was a mean of 1.9±0.2 and a median value of 2, while those lacking sauropods

417 had a mean of 2.9±0.2 and a median value of 3. Similar to the comparison of tyrant vs. non-

418 tyrant faunas, it was found that these classes were found to have statistically distinct means (p =

419 0.0021) and medians (p = 0.0059). Thus, this reinforces the observation that the dinosaurian

420 faunas of Campano-Maastrichtian Laramidia (at least) show a different observed guild structure

421 than typical Jurassic-Cretaceous theropod communities.

422

423 DISCUSSION

424 Might the apparent lack of middle-sizedDraft (50-1000 kg) predatory dinosaurs in many communities

425 of the Campanian and Maastrichtian of Asiamerica be the product of undersampling? This seems

426 unlikely, as these include some of the best studied dinosaurian assemblages in the world (e.g.,

427 Lyson and Longrich 2011; Horner et al. 2011; Larson and Currie 2013; Fowler 2017; Mallon

428 2019; Eberth and Kamo 2019).

429

430 That is not to say that middle-sized predatory dinosaurs are entirely absent in these assemblages.

431 DePalma et al. (2015) document the existence of steini, a size class 4 (101-500 kg)

432 dromaeosaurid in the upper Hell Creek community. However, its remains are apparently rare

433 enough that its presence was not recovered at all in major census studies of the Hell Creek

434 Formation (Lyson and Longrich 2011; Horner et al. 2011). The troodontid Latenivenatrix

435 mcmasterae is a size class 3 (50-100 kg) theropod distributed in both Megaherbivore Zones 1

436 and 2 within the Dinosaur Park Formation (van der Reest and Currie 2017). Holtz et al. (1998)

19 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 20 of 91

437 proposed that at least some of the troodontids were omnivorous rather than strictly herbivorous,

438 and it might be that they fed on smaller-bodied dinosaurs than comparable-sized

439 eudromaeosaurs; this would be consistent with Torices et al.’s (2018) estimation that troodontids

440 favored softer, smaller, or immobile prey. Potentially Latenivenatrix may have effectively been a

441 “smaller” predator than its body size would suggest. Similarly, in the the

442 enigmatic theropod Bagaraatan ostromi is a size class 3 carnivore (Osmólska 1996). However,

443 the latter is known from a single incomplete skeleton at present. Additionally, there is a size class

444 4 tyrannosaurid ( altai) in that community, as well as the apex predator Tarbosaurus

445 bataar (at size class 5).

446

447 However, as the histogram studies show,Draft this situation is in contrast to that seen in typical

448 Jurassic and Early Cretaceous dinosaurian communities, where middle sized taxa (including

449 ceratosaurids, piatnitzkysaurids, metriacanthosaurids, neovenatorids, megaraptorids, and early

450 tyrannosauroids such proceratosaurids and stokesosaurids) occupied these intermediate sizes

451 below the apex predators.

452

453 If the distinction of the missing middle-sized portion of the theropod communities is indeed an

454 actual attribute of these assemblages and not simply a taphonomic sampling issue, what might

455 this imply about dinosaurian ecosystems of the Campanian and Maastrichtian of Asiamerica?

456 One possibility briefly suggested previously by Holtz (2004a, 2004b) is that the younger

457 individuals of tyrannosaurids might have occupied these middle-sized niches. That is while the

458 earlier growth stages of (for example Tarbosaurus bataar) were not actually distinct taxa such as

459 “Gorgosaurus novojilovi’ and “Gorgosaurus lancinator”, but that they were ecologically

20 © The Author(s) or their Institution(s) Page 21 of 91 Canadian Journal of Earth Sciences

460 functioning as distinct predators in their communities. Ontogenetic niche shifts have recently

461 been proposed on isotopic evidence in the Early Cretaceous dromaeosaurid

462 antirrhopus (Frederickson 2020).

463

464 Consider small-bodied tyrannosaurid individuals such as juvenile Tyrannosaurus rex BMRP

465 2002.4.1 or the juvenile Gorgosaurus libratus AMNH 5664 or ROM 1247 (size class 5

466 individuals). At this size their bite forces are an order of magnitude smaller than the adult

467 individuals (Bates and Falkingham 2012; Gignac and Erickson 2017; Therrien et al. this issue),

468 while their agility as measured by the ability to turn quickly was considerably higher (Snively et

469 al. 2019). At less than 1000 kg these individuals would still be in a size range in which their

470 elongate distal limb proportions would provideDraft a net benefit in maximal speed relative to shorter

471 limbed (Dececchi et al. 2020). Such an individual would be functionally distinct from

472 adults of the same species. It might be easier for these partially grown individuals to acquire and

473 dispatch smaller and more agile prey such as ornithomimids, thescelosaurids, and

474 pachycephalosaurids than it would be for the more massive adult relatives. Indeed, Codron et al.

475 (2013) argued that very large theropods may have found such small prey insufficient to supply

476 their meat requirements. In contrast, young tyrannosaurid individuals would likely lack sufficient

477 force to take down the large prey animals such as adult hadrosaurids and ceratopsids known to

478 have been fed upon by fully grown tyrannosaurids (Gignac and Erickson 2017; Therrien et al.

479 this issue). At least some subadult tyrannosaurids were feeding on large-sized food sources

480 (Peterson and Daus 2019), but whether they were scavenging or took down this large prey cannot

481 be determined. Even the mode of prey acquisition and manipulation would be expected to be

482 different in juvenile and sub-adult tyrannosaurids relative to adults. For instance, in some

21 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 22 of 91

483 tyrannosaurid taxa the smaller individuals have proportionately longer arms (compare 660 kg

484 Tyrannosaurus rex BMRP 2002.4.1 with a 0.39 times the estimated length of the ,

485 to 0.29 for the same ratio in the ten-times larger specimen FMNH PR2081); the proportionately

486 longer forelimb of younger and weaker-jawed Tyrannosaurus might have served in a form of

487 prey capture or manipulation which was lost or greatly reduced in later growth stages.

488

489 While some workers consider certain tyrannosaurid specimens (including BMRP 2002.4.1) of

490 the Hell Creek Formation as representing a distinct taxon Nanotyrannus lancensis (Bakker et al.

491 1988; Larson 2013; Persons and Currie 2018), the observation would still remain that younger

492 individuals of Tyrannosaurus rex would necessarily pass through these intermediate size ranges.

493 Furthermore, the published specimens ofDraft this proposed taxon demonstrate juvenile histological

494 (Woodward et al. 2020) and morphological (Carr 2020) traits, so that even if it is its own species

495 the adult form would presumably be a larger animal.

496

497 Brett-Surman (1989, 1997) proposed the concept of “niche assimilation”: the observation that

498 large dinosaurs, as terrestrial animals which went through multiple orders of magnitude size

499 growth during ontogeny, were functionally equivalent to what would be in large mammals

500 several successive niches occupied by separate species. For instance, an individual of

501 annectens was hatched as a dik-dik (Madoqua spp.) sized small browser but as

502 an adult equaled or exceeded the size of Loxodonta africana, and thus throughout its life cycle

503 operates as the functional ornithischian equivalent of the Serengeti’s entire size range of hoofed

504 mammals.

505

22 © The Author(s) or their Institution(s) Page 23 of 91 Canadian Journal of Earth Sciences

506 As proposed here, the “tyrannosaurid niche assimilation hypothesis” is the concept that juvenile

507 and subadult members of Tyrannosauridae were the functional equivalent of earlier middle-sized

508 theropod carnivores. Of course, all theropods of size classes 6 and 7 would have occupied these

509 smaller size classes during their growth from hatching to maturity, and thus broadly speaking

510 went through the same general niche shifts as tyrannosaurids. However, species in communities

511 with closer packing of niches might be suspected as being under a different set of selective

512 pressures than those experienced by a species which was the only member of the guild

513 occupying those sizes. Thus, from this hypothesis several predictions can be made.

514

515 1) Transitions from one phase of niche occupation to the next might involve rapid transitions or

516 transformations rather than simple gradualDraft allometric trends. Imansyah et al. (2008) and

517 Purwanda et al. (2016) have demonstrated such transformations in anatomy and life habits in

518 Varanus komodoensis. Ecological thresholds concerning (for instance) size of prey and style of

519 prey acquisition may be relatively abrupt with increasing size, as described by Carbone et al.

520 (1999), Randolff and Du Toit (2004), and Hirt et al. (2020) (although these authors were

521 concerned with predatory taxa of different sizes rather than different sized individuals of the

522 same species.) Carr (2020), in the most thorough analysis of Mesozoic theropod ontogeny so far,

523 has demonstrated that in Tyrannosaurus rex in particular a “secondary metamorphosis” from

524 juvenile to subadult forms, evidenced in nearly every portion of the skeletal anatomy he studied.

525 Additional comparable work on the ontogeny of other large theropods species may demonstrate

526 to what degree this was unique to Tyrannosaurus rex, or if were more widespread among

527 tyrannosaurids, or if it were present in theropods in more closely packed guilds. Cullen et al.

528 (2020) demonstrated in a single individual of large bodied carcharodontosaurid from the Huincul

23 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 24 of 91

529 Formation that it showed a much more gradual growth pattern rather than the accelerated growth

530 phase as seen in tyrannosaurids; whether this attribute is present in other non-tyrannosaurids

531 remains to be discovered.

532

533 2) In faunas with multiple middle-to-large bodied predatory theropod species, niche partitioning

534 would favor the rapid achievement of adult body size to reduce competition with other sized

535 sympatric theropod species. In contrast, under the tyrannosaurid niche assimilation hypothesis

536 such a pressure might be relaxed for tyrant dinosaurs, such that the energy available from small-

537 to-middle sized prey might be more effectively exploited by the predatory species before it grew

538 too large to acquire such food resources.

539 Draft

540 The study of ontogeny has been greatly enhanced by histologically based within-species growth

541 curve analysis (Erickson et al. 2001; Erickson 2014; Woodward et al. 2015). Tyrannosaurids

542 have been among the first and most extensively dinosaurian taxa so studied (Erickson et al. 2004,

543 2006, 2010). While the best or preferred specific methodology for growth curve fitting remains

544 debated (Lee and Werning 2008; Erickson 2014; Myhrvold 2016), age of somatic maturity can

545 generally be assessed by the onset of the external fundamental (EFS). Previous work has

546 found that tyrannosaurids have among the latest such onset among non-sauropod dinosaurs. For

547 instance, Erickson et al. (2004) found the EFS appeared in tyrannosaurids around ages 14-16 for

548 Albertosaurus, Gorgosaurus, and Daspletosaurus and 18.5 for Tyrannosaurus; in contrast, full

549 somatic maturity was found to be achieved at 9 years in the hadrosaurid (Woodward

550 et al. 2015) and estimated at 10-15 years in the larger hadrosaurid Edmontosaurus (Vanderven et

551 al. 2014).

24 © The Author(s) or their Institution(s) Page 25 of 91 Canadian Journal of Earth Sciences

552

553 However, at present while the data for tyrannosaurids can compared to small-bodied theropods

554 and to herbivorous dinosaur species, there are few published studies of other large-bodied

555 theropods for comparison. Despite a large sample size examined no specimen of the Jurassic

556 allosauroid fragilis has been found with an EFS (Bybee et al. 2006; Lee and Werning

557 2008), suggesting we may not have a fully-grown specimen of this commonly recovered

558 theropod species or alternatively that this species did not have determinate growth. (The large

559 sympatric allosaurid maximus may in fact be the fully adult form of Allosaurus,

560 but this has yet to be assessed histologically.) Thus, we are not currently in a situation to

561 compare growth history patterns of tyrannosaurids to most other large theropods. Such data

562 would be extremely useful in determiningDraft if theropods in closely packed ecosystems had growth

563 patterns similar to tyrannosaurids (perhaps achieving full body size earlier) or not. Indeed,

564 Cullen et al. (2020) found the opposite of the prediction here, and instead that the growth of an

565 unnamed carcharodontosaurid was more gradual and extended than in

566 tyrannosaurids. Future studies will help to see if this is a typical pattern among non-

567 tyrannosaurid giant theropods.

568

569 3) Similar patterns of niche assimilation may be present in later Late Cretaceous Gondwanan

570 theropod guilds. While earlier Late Cretaceous southern continent theropod guilds typically

571 included members of both the ceratosaurian group and the enigmatic coelurosaur

572 clade Megaraptoridae, the latter clade is not known to extend beyond the Santonian or early

573 Campanian in northern , while giant megaraptorids are present and abelisaurids

574 apparently absent in Campano-Maastrichtian southern South America (Porfiri et al. 2018;

25 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 26 of 91

575 Lamanna et al. 2020). Thus, just as the Tyrannosauridae would have been the sole large-bodied

576 theropods of late Campanian and Maastrichtian, the Abelisauridae and Megaraptoridae may have

577 been in the same situation for their respective regions of Gondwana in the same time interval.

578 Thus, they would have had a similar release from the selective pressure of niche partitioning and

579 might have assimilated the niches once occupied by middle-sized theropods in a comparable

580 fashion. If so, we might similarly predict comparable rapid transformations in morphology

581 during ontogeny and/or delays in achievement of somatic maturity as hypothesized for

582 Tyrannosauridae.

583

584 As is typical for dinosaurian studies, however, we are hindered by the small sample size of

585 individuals and a dearth of relevant specimens.Draft Future discoveries of growth series of

586 abelisaurids, allosauroids, and other large-bodied theropods, including documentation of their

587 anatomical transformations and histologically assessed chronological ages, will bring our

588 understanding of these other groups of carnivorous dinosaurs to a comparable state as that

589 achieved for tyrannosaurids.

590

591 CONCLUSIONS

592 All large-bodied carnivorous theropod dinosaurs necessarily passed through a wide range of

593 body sizes from hatching to adulthood. Consequently, unless they were provisioned throughout

594 growth, the of any given individual shifted throughout its lifetime. For Jurassic

595 through early Late Cretaceous this transition occurred in the context of ecosystems in which the

596 juveniles and subadults potentially competed with other theropod species with medium adult

597 body sizes. As shown here, however, there is an observed quantitative distinction between the

26 © The Author(s) or their Institution(s) Page 27 of 91 Canadian Journal of Earth Sciences

598 theropod guilds of Campano-Maastrichtian Asiamerica and most of the rest of theropod-

599 dominated communities. In the former, tyrannosaurid juveniles and subadults represent most or

600 all of the intermediate-sized carnivorous forms, as medium-sized predatory taxa of other clades

601 are rare or absent. This distinction is independent of the total diversity of potential dinosaurian

602 prey. The cause of this ecological isolation of Tyrannosauridae in Campano-Maastrichtian

603 Asiamerica compared to the rather more ecologically densely packed guilds of other dinosaurian

604 communities remains unresolved. It is noteworthy that in Campanian and early Maastrichtian

605 Laramidia at least these same tyrant-dominated communities are also absent any confirmed

606 sauropod dinosaurs, which might serve throughout their own ontogeny to serve as prey for

607 theropods of all size classes; that said, sauropods are present in at least some Asian tyrant-

608 dominated communities and in the AmericanDraft southwest during the late Maastrichtian.

609

610 The absence of potential mid-sized competitors in Campano-Maastrichtian Asiamerica may be a

611 factor in some evolutionary transformations in Tyrannosauridae not yet documented in other

612 large-bodied theropod clades. In particular, tyrannosaurids show profound transitions in potential

613 prey acquisition and dispatch adaptations such as bite force and agility, and recent work on the

614 ontogeny of tyrant dinosaurs demonstrates that in at least some of these species these ontogenetic

615 transformations occurred quite rapidly and dramatically. This might reflect selection in

616 tyrannosaurid evolution favoring distinctly different ecomorphologies and prey selection at

617 different ontogenetic phases as this lineage assimilated the otherwise missing niches of the

618 theropod predatory guilds.

619

620 ACKNOWLEDGEMENTS

27 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 28 of 91

621 I would like to thank the editors for the invitation to contribute to this volume. Dale Russell was

622 among the first professional paleontologists outside my graduate committee to advise

623 me and support my research in its early days. Conversations with him about dinosaur ecology

624 and ontogeny were among the initial inspiration for the research that led to this study. Even more

625 so, Dale emphasized to me (and to all scientists) the importance of speculation, creativity, and

626 wonder in our examination of the natural world; I hope that some of that encouragement is

627 reflected here.

628

629 In additional to Dale Russell, other researchers whose discussions and conversations led to my

630 initial exploration of the topics here include Michael Brett-Surman, Thomas Carr, Phil Currie,

631 Jim Farlow, and Ralph Molnar. I am indebtedDraft to the two anonymous reviewers and to the editors

632 of this issue for their suggestions and corrections which greatly improved this research. In

633 particular, one of the reviewers and (assuming said reviewer was not him) Roger Benson

634 encouraged the iteration of the analysis exploring sauropod versus non-sauropod communities.

635

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1098 Paleobiology, 28: 527-543.

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1100 Van der Reest, A.J., and P.J. Currie. 2017. Troodontids (Theropoda) from the Dinosaur Park

1101 Formation, Alberta, with a description of a unique new taxon: implications for deinonychosaur

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1104

1105 Vanderven, E., M.E. Burns, and P.J. Currie. 2014. Histologic growth dynamic study of

1106 (Dinosauria: Hadrosauridae) from a bonebed assemblage of the Upper

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1109

1110 Vavrek, M.J., and H.C.E. Larsson. 2010. Low beta diversity of Maastrichtian dinosaurs of North

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1114 Whitlock, J.A., K.C. Trujillo, and G.M. Hanik. 2019. Assemblage-level structure in Morrison

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1117 Draft

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1125 112.

1126

1127 Woodward, H.N., E.A. Freedman-Fowler, J.O. Farlow, and J.R. Horner. 2015. Maiasaura, a

1128 model organism for extinct vertebrate population biology: a large sample statistical assessment

1129 of growth and survivorship. Paleobiology 41: 503-527. doi: 10.1017/pab.2015.19.

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1131 Woodward, H.N., K. Tremaine, S.A. Williams, L.E. Zanno, J.R. Horner, and N. Mhyrvold. 2020.

1132 Growing up Tyrannosaurus rex: osteohistology refutes the pygmy “Nanotyrannus” and supports

1133 ontogenetic niche partitioning in juvenile Tyrannosaurus. Science Advances 6: eaax6250. doi:

1134 10.1126/sciadv.aax6250.

1135

1136 Xu, X., K. Wang, K. Zhang, Q. Ma, L. Xing, C. Sullivan, D. Hu, S. Cheng, and S. Wang. 2012.

1137 A gigantic from the Lower Cretaceous of China. Nature 484: 92-95. doi:

1138 10.1038/nature10906.

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1140 Xu, X., Z. Zhou, C. Sullivan, Y. Wang, Draftand D. Ren. 2016. An updated review of the Middle-Late

1141 Jurassic Yanliao Biota: chronology, , paleontology and paleoecology. Acta Geologica

1142 Sinica 90: 2229-2243. doi: 10.1111/1755-6724.13033.

1143

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1145 the early evolution of dinosaurs. Nature Ecology & Evolution 3: 1146-1152. doi:

1146 10.1038/s41559-019-0941-z.

1147

1148 Zanno, L.E., and P.J. Makovicky. 2011. Herbivorous ecomorphology and specialization patterns

1149 in theropod dinosaur evolution. Proceedings of the National Academy of Sciences 108: 232-237.

1150 doi: 10.1073/pnas.1011924108.

1151

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1152 Zanno, L.E., and P.J. Makovicky. 2013. Neovenatorid theropods are paex predators of the Late

1153 Cretaceous of North America. Nature Communications 4: 2827. doi: 10.1038/ncomms3827.

1154

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1156 top tier predator diversity during the rise of dinosaurs. Scientific Reports 5: 9276. doi:

1157 10.1038/srep09276.

1158

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1160 Diminutive fleet-footed tyrannosauroid narrows the 70-million-year gap in the North American

1161 fossil record. Communications Biology 2: 64. doi: 10.1038/s42003-019-0308-7.

1162 Draft

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1164 implications. National Science Review 1: 543-559. doi: 10.1093/nsr/nwu055.

52 © The Author(s) or their Institution(s) Page 53 of 91 Canadian Journal of Earth Sciences

1165 TABLES

1166

1167 TABLE 1. List of theropod guilds

1168

1169 Faunas within each category listed in stratigraphic order. Tyrannosauroid taxa denoted by

1170 asterisk (*). Size classes: 1 = <10 kg; 2 = 11-50 kg; 3 = 51-100 kg; 4 = 101-500 kg; 5 = 501-

1171 1000 kg; 6 = 1001-5000 kg; 7 = >5000 kg. Correlations for Western Interior Formations from

1172 Fowler (2017).

1173

1174

1175 Draft

1176 Tyrant-dominated communities

1177

1178 Hell Creek Formation, Upper (latest Maastrichtian; Montana, South , North

1179 Dakota, USA)

1180 Carnivorous Theropods:

1181 Size class 7 Tyrannosaurus rex*

1182 Size class 6 --

1183 Size class 5 --

1184 Size class 4 Dakotaraptor steini

1185 Size class 3 --

1186 Size class 2 Acheroraptor temertyorum, cf. gilmorei, Pectinodon

1187 bakkeri

53 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 54 of 91

1188 Size class 1 --

1189 Non-carnivorous Dinosaurs: 10 spp.

1190

1191 Hell Creek Formation, Middle (late Maastrichtian; Montana, , ,

1192 USA)

1193 Carnivorous Theropods:

1194 Size class 7 Tyrannosaurus rex*

1195 Size class 6 --

1196 Size class 5 --

1197 Size class 4 --

1198 Size class 3 -- Draft

1199 Size class 2 Acheroraptor temertyorum, cf. Richardoestesia gilmorei, Pectinodon

1200 bakkeri

1201 Size class 1 --

1202 Non-carnivorous Dinosaurs: 11 spp.

1203

1204 Hell Creek Formation, Lower (late Maastrichtian; Montana, South Dakota, North Dakota,

1205 USA)

1206 Carnivorous Theropods:

1207 Size class 7 Tyrannosaurus rex*

1208 Size class 6 --

1209 Size class 5 --

1210 Size class 4 --

54 © The Author(s) or their Institution(s) Page 55 of 91 Canadian Journal of Earth Sciences

1211 Size class 3 --

1212 Size class 2 Acheroraptor temertyorum, cf. Richardoestesia gilmorei, Pectinodon

1213 bakkeri

1214 Size class 1 --

1215 Non-carnivorous Dinosaurs: 11 spp.

1216

1217 (late Maastrichtian; Alberta, Canada)

1218 Carnivorous Theropods:

1219 Size class 7 Tyrannosaurus rex*

1220 Size class 6 --

1221 Size class 5 -- Draft

1222 Size class 4 --

1223 Size class 3 --

1224 Size class 2 Dromaeosauridae indet., cf. Richardoestesia gilmorei, indet.

1225 Size class 1 --

1226 Non-carnivorous Dinosaurs: 7 spp.

1227

1228 (late Maastrichtian; Saskatchewan, Canada)

1229 Carnivorous Theropods:

1230 Size class 7 Tyrannosaurus rex*

1231 Size class 6 --

1232 Size class 5 --

1233 Size class 4 --

55 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 56 of 91

1234 Size class 3 --

1235 Size class 2 Acheroraptor sp., Troodontidae indet.

1236 Size class 1 --

1237 Non-carnivorous Dinosaurs: 4 spp.

1238

1239 (late Maastrichtian; , USA)

1240 Carnivorous Theropods:

1241 Size class 7 Tyrannosaurus rex*

1242 Size class 6 --

1243 Size class 5 --

1244 Size class 4 -- Draft

1245 Size class 3 --

1246 Size class 2 Acheroraptor sp.., Richardoestesia sp., Pectinodon bakkeri

1247 Size class 1 --

1248 Non-carnivorous Dinosaurs: 11 spp.

1249

1250 Naashoibito Member, Ojo Alamo Formation (late Maastrichtian; New Mexico, USA)

1251 Carnivorous Theropods:

1252 Size class 7 Tyrannosaurus sp.*

1253 Size class 6 --

1254 Size class 5 --

1255 Size class 4 --

1256 Size class 3 --

56 © The Author(s) or their Institution(s) Page 57 of 91 Canadian Journal of Earth Sciences

1257 Size class 2 Dineobellator notohesperus, Richardoestesia sp., Troodontidae indet.

1258 Size class 1 --

1259 Non-carnivorous Dinosaurs: 8 spp.

1260

1261 Javelina Formation (late Maastrichtian; Texas, USA)

1262 Carnivorous Theropods:

1263 Size class 7 Tyrannosaurus sp.*

1264 Size class 6 --

1265 Size class 5 --

1266 Size class 4 --

1267 Size class 3 -- Draft

1268 Size class 2 Saurornitholestinae indet., Troodontidae indet.

1269 Size class 1 --

1270 Non-carnivorous Dinosaurs: 4 spp.

1271

1272 Nemegt Formation (early Maastrichtian; Bayankhongor, Ömnögovi, Övörkhangai,

1273 Mongolia)

1274 Carnivorous Theropods:

1275 Size class 7 --

1276 Size class 6 Tarbosaurus bataar

1277 Size class 5 --

1278 Size class 4 Alioramus altai

1279 Size class 3 Bagaraatan ostromi

57 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 58 of 91

1280 Size class 2 mongoliensis, nemegtensis, gracilicrus,

1281 Zanabazar junior

1282 Size class 1 --

1283 Non-carnivorous Dinosaurs: 22 spp.

1284

1285 Horseshoe Canyon Formation, Middle (early Maastrichtian; Alberta, Canada)1

1286 Carnivorous Theropods:

1287 Size class 7 --

1288 Size class 6 Albertosaurus sarcophagus*

1289 Size class 5 --

1290 Size class 4 -- Draft

1291 Size class 3 --

1292 Size class 2 Dromaeosauridae indet., Richardoestesia sp., Troodontidae indet.

1293 Size class 1 --

1294 Non-carnivorous Dinosaurs: 12 spp.

1295

1296 Horseshoe Canyon Formation, Lower (late Campanian; Alberta, Canada)2

1297 Carnivorous Theropods:

1298 Size class 7 --

1299 Size class 6 Albertosaurus sarcophagus*

1300 Size class 5 --

1301 Size class 4 --

1302 Size class 3 --

58 © The Author(s) or their Institution(s) Page 59 of 91 Canadian Journal of Earth Sciences

1303 Size class 2 marshalli, Richardoestesia sp., Albertavenator curriei

1304 Size class 1 --

1305 Non-carnivorous Dinosaurs: 10 spp.

1306

1307 De-na-zin Member, (late Campanian; New Mexico, USA)

1308 Carnivorous Theropods:

1309 Size class 7 --

1310 Size class 6 Bistahieversor sealeyi*

1311 Size class 5 --

1312 Size class 4 --

1313 Size class 3 -- Draft

1314 Size class 2 sullivani, Troodontidae indet.

1315 Size class 1 --

1316 Non-carnivorous Dinosaurs: 8 spp.

1317

1318 Kaiparowits Formation, Middle (late Campanian; Utah, USA)

1319 Carnivorous Theropods:

1320 Size class 7 --

1321 Size class 6 Teratophoneus curriei*

1322 Size class 5 --

1323 Size class 4 --

1324 Size class 3

1325 Size class 2 indet., Richardoestesia sp.

59 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 60 of 91

1326 Size class 1 --

1327 Non-carnivorous Dinosaurs: 7 spp.

1328

1329 Dinosaur Park Formation, Megaherbivore Assemblage Zone 2b (late Campanian; Alberta,

1330 Canada)3

1331 Carnivorous Theropods:

1332 Size class 7 --

1333 Size class 6 Daspletosaurus sp.*

1334 Size class 5 --

1335 Size class 4 --

1336 Size class 3 Latenivenatrix mcmasteraeDraft

1337 Size class 2 albertensis, Richardoestesia sp.

1338 Size class 1 elizabethae

1339 Non-carnivorous Dinosaurs: 9 spp.

1340

1341 Dinosaur Park Formation, Megaherbivore Assemblage Zone 2a (late Campanian; Alberta,

1342 Canada)3

1343 Carnivorous Theropods:

1344 Size class 7 --

1345 Size class 6 Gorgosaurus libratus*, Daspletosaurus sp.*

1346 Size class 5 --

1347 Size class 4 --

1348 Size class 3 Latenivenatrix mcmasterae

60 © The Author(s) or their Institution(s) Page 61 of 91 Canadian Journal of Earth Sciences

1349 Size class 2 Dromaeosaurus albertensis, Richardoestesia gilmorei

1350 Size class 1 Hesperonychus elizabethae

1351 Non-carnivorous Dinosaurs: 12 spp.

1352

1353 Kaiparowits Formation, Lower (late Campanian; Utah, USA)

1354 Carnivorous Theropods:

1355 Size class 7 --

1356 Size class 6 Teratophoneus curriei*

1357 Size class 5 --

1358 Size class 4 --

1359 Size class 3 Talos sampsoni Draft

1360 Size class 2 Paronychodon indet., Richardoestesia sp.

1361 Size class 1 --

1362 Non-carnivorous Dinosaurs: 3 spp.

1363

1364 Dinosaur Park Formation, Megaherbivore Assemblage Zone 1b (late Campanian; Alberta,

1365 Canada)3

1366 Carnivorous Theropods:

1367 Size class 7 --

1368 Size class 6 Gorgosaurus libratus*, Daspletosaurus sp.*

1369 Size class 5 --

1370 Size class 4 --

1371 Size class 3 Latenivenatrix mcmasterae

61 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 62 of 91

1372 Size class 2 Dromaeosaurus albertensis, Saurornitholestes langstoni, Richardoestesia

1373 gilmorei, inequalis

1374 Size class 1 Hesperonychus elizabethae

1375 Non-carnivorous Dinosaurs: 17 spp.

1376

1377 Dinosaur Park Formation, Megaherbivore Assemblage Zone 1a (late Campanian; Alberta,

1378 Canada)3

1379 Carnivorous Theropods:

1380 Size class 7 --

1381 Size class 6 Gorgosaurus libratus*

1382 Size class 5 -- Draft

1383 Size class 4 --

1384 Size class 3 Latenivenatrix mcmasterae

1385 Size class 2 Dromaeosaurus albertensis, Saurornitholestes langstoni, Richardoestesia

1386 gilmorei, Stenonychosaurus inequalis

1387 Size class 1 Hesperonychus elizabethae

1388 Non-carnivorous Dinosaurs: 16 spp.

1389

1390 , Upper (middle Campanian; Montana, USA)

1391 Carnivorous Theropods:

1392 Size class 7 --

1393 Size class 6 Daspletosaurus horneri*, Gorgosaurus sp.*

1394 Size class 5 --

62 © The Author(s) or their Institution(s) Page 63 of 91 Canadian Journal of Earth Sciences

1395 Size class 4 --

1396 Size class 3 --

1397 Size class 2 Saurornitholestes sp., Richardoestesia sp., Troodon sp.

1398 Size class 1 feinbergorum

1399 Non-carnivorous Dinosaurs: 10 spp.

1400

1401 (middle Campanian; Montana, USA)

1402 Carnivorous Theropods:

1403 Size class 7 --

1404 Size class 6 Tyrannosauridae indet.*.

1405 Size class 5 -- Draft

1406 Size class 4 --

1407 Size class 3 --

1408 Size class 2 Dromaeosaurus albertensis, Saurornitholestes sp., Troodon formosus

1409 Size class 1 --

1410 Non-carnivorous Dinosaurs: 6 spp.

1411

1412 , Upper (middle Campanian; Alberta, Canada)

1413 Carnivorous Theropods:

1414 Size class 7 --

1415 Size class 6 Daspletosaurus torosus*

1416 Size class 5 --

1417 Size class 4 --

63 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 64 of 91

1418 Size class 3 --

1419 Size class 2 Dromaeosaurus albertensis, Saurornitholestes langstoni, Richardoestesia

1420 sp., Troodontidae indet.

1421 Size class 1 Hesperonychus elizabethae

1422 Non-carnivorous Dinosaurs: 13 spp.

1423

1424 Oldman Formation, Lower (middle Campanian; Alberta, Canada)

1425 Carnivorous Theropods:

1426 Size class 7 --

1427 Size class 6 Daspletosaurus torosus*

1428 Size class 5 -- Draft

1429 Size class 4 --

1430 Size class 3 --

1431 Size class 2 Dromaeosaurus albertensis, Saurornitholestes langstoni, Richardoestesia

1432 sp., Troodontidae indet.

1433 Size class 1 Hesperonychus elizabethae

1434 Non-carnivorous Dinosaurs: 2 spp.

1435

1436 Two Medicine Formation, Lower (middle Campanian; Montana, USA)

1437 Carnivorous Theropods:

1438 Size class 7 --

1439 Size class 6 Tyrannosauridae indet.*

1440 Size class 5 --

64 © The Author(s) or their Institution(s) Page 65 of 91 Canadian Journal of Earth Sciences

1441 Size class 4 --

1442 Size class 3 --

1443 Size class 2 Dromaeosaurus sp., Saurornitholestes sp.

1444 Size class 1 --

1445 Non-carnivorous Dinosaurs: 4 spp.

1446

1447 Hunter Wash Member, Kirtland Formation (middle Campanian; New Mexico, USA)

1448 Carnivorous Theropods:

1449 Size class 7 --

1450 Size class 6 Bistahieversor sealeyi*

1451 Size class 5 -- Draft

1452 Size class 4 --

1453 Size class 3 --

1454 Size class 2 Dromaeosauridae indet., Troodontidae indet.

1455 Size class 1 --

1456 Non-carnivorous Dinosaurs: 5 spp.

1457

1458 Fruitland Formation (middle Campanian; New Mexico, USA)

1459 Carnivorous Theropods:

1460 Size class 7 --

1461 Size class 6 Tyrannosauridae indet*

1462 Size class 5 --

1463 Size class 4 --

65 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 66 of 91

1464 Size class 3 --

1465 Size class 2 Dromaeosauridae indet., Troodontidae indet.

1466 Size class 1 --

1467 Non-carnivorous Dinosaurs: 4 spp.

1468

1469 Aguja Formation (middle Campanian; Texas, USA)

1470 Carnivorous Theropods:

1471 Size class 7 --

1472 Size class 6 Tyrannosauridae indet*

1473 Size class 5 --

1474 Size class 4 -- Draft

1475 Size class 3 --

1476 Size class 2 cf. Dromaeosaurus sp., Richardoestesia sp., Troodontidae indet.

1477 Size class 1 --

1478 Non-carnivorous Dinosaurs: 8 spp.

1479

1480 (early Campanian; Ömnögovi, Mongolia)

1481 Carnivorous Theropods:

1482 Size class 7 --

1483 Size class 6 --

1484 Size class 5 Tyrannosauridae indet.*

1485 Size class 4 --

1486 Size class 3 --

66 © The Author(s) or their Institution(s) Page 67 of 91 Canadian Journal of Earth Sciences

1487 Size class 2 mongoliensis, mangas, Gobivenator mongoliensis,

1488 Saurornitholestes mongoliensis, jaffei

1489 Size class 1 Archaeornithoides deinosauriscus, , Almas ukhaa

1490 Non-carnivorous Dinosaurs: 15 spp.

1491

1492 Iren Dabasu Formation (Santonian; Nei Mongol, China)

1493 Carnivorous Theropods:

1494 Size class 7 --

1495 Size class 6 --

1496 Size class 5 Alectrosaurus olseni*

1497 Size class 4 -- Draft

1498 Size class 3 --

1499 Size class 2 indet., Troodontidae indet.

1500 Size class 1 --

1501 Non-carnivorous Dinosaurs: 12 spp.

1502

1503 Bayan Shireh Formation, Upper (late Turonian-late Santonian; Dornogovi, Ömnögovi,

1504 Mongolia)

1505 Carnivorous Theropods:

1506 Size class 7 --

1507 Size class 6 --

1508 Size class 5 cf. Alectrosaurus*, Achillobator giganticus

1509 Size class 4 --

67 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 68 of 91

1510 Size class 3 --

1511 Size class 2 Velociraptorinae indet.

1512 Size class 1 --

1513 Non-carnivorous Dinosaurs: 12 spp.

1514

1515 Non-tyrant-dominated communities

1516 (late Maastrichtian; Madhya Pradesh, , Maharashtra, )

1517 Carnivorous Theropods:

1518 Size class 7 --

1519 Size class 6 Indosaurus matleyi, narmadensis, Rahiolisaurus gujaratensis

1520 Size class 5 -- Draft

1521 Size class 4 --

1522 Size class 3 --

1523 Size class 2 indicus

1524 Size class 1 --

1525 Non-carnivorous Dinosaurs: 5 spp.

1526

1527 (Maastrichtian; Mahajanga, Madagascar)

1528 Carnivorous Theropods:

1529 Size class 7 --

1530 Size class 6 --

1531 Size class 5 crenatissimus

1532 Size class 4 --

68 © The Author(s) or their Institution(s) Page 69 of 91 Canadian Journal of Earth Sciences

1533 Size class 3 --

1534 Size class 2 knopfleri

1535 Size class 1 ostromi

1536 Non-carnivorous Dinosaurs: 3 spp.

1537

1538 (middle Campanian-early Maastrichtian; Rio Negro, Neuquèn, La

1539 Pampa, Argentina)

1540 Carnivorous Theropods:

1541 Size class 7 --

1542 Size class 6 --

1543 Size class 5 -- Draft

1544 Size class 4 Quilmesaurus curriei, cabazai

1545 Size class 3 Niebla antiqua

1546 Size class 2 --

1547 Size class 1 --

1548 Non-carnivorous Dinosaurs: 11 spp.

1549

1550 (late Santonian-early Campanian; Mendoza, Rio Negro, Neuquèn,

1551 Argentina)

1552 Carnivorous Theropods:

1553 Size class 7 --

1554 Size class 6 Abelisaurus comahuensis, riocoloradensis

1555 Size class 5 garriodi

69 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 70 of 91

1556 Size class 4 --

1557 Size class 3 --

1558 Size class 2 --

1559 Size class 1 --

1560 Non-carnivorous Dinosaurs: 5 spp.

1561

1562 Bajo de la Carpa Formation (middle-late Santonian; Rio Negro, Neuquèn, Argentina)

1563 Carnivorous Theropods:

1564 Size class 7 --

1565 Size class 6 Tratayenia rosalesi

1566 Size class 5 Viavenator exxoniDraft

1567 Size class 4 --

1568 Size class 3 --

1569 Size class 2 unicus

1570 Size class 1 --

1571 Non-carnivorous Dinosaurs: 7 spp.

1572

1573 (late Turonian-early ; Mendoza, Rio Negro, Neuquèn,

1574 Argentina)

1575 Carnivorous Theropods:

1576 Size class 7 --

1577 Size class 6 namunhuaiquii

1578 Size class 5 --

70 © The Author(s) or their Institution(s) Page 71 of 91 Canadian Journal of Earth Sciences

1579 Size class 4 --

1580 Size class 3 comahuensis

1581 Size class 2 argentinus

1582 Size class 1 Pamparaptor micros

1583 Non-carnivorous Dinosaurs: 6 spp.

1584

1585 Bissekty Formation (middle-late Turonian; Uzbekistan)

1586 Carnivorous Theropods:

1587 Size class 7 --

1588 Size class 6 Unnamed carcharodontosaurid4

1589 Size class 5 Timurlengia euoticaDraft*

1590 Size class 4 --

1591 Size class 3 --

1592 Size class 2 Itemirus medullarius, Euronychodon asiaticus, Urbacodon sp.

1593 Size class 1 --

1594 Non-carnivorous Dinosaurs: 7 spp.

1595

1596 Bajo Barreal Formation (middle -Turonian; Chubut, Santa Cruz, Argentina)

1597 Carnivorous Theropods:

1598 Size class 7 --

1599 Size class 6 bonapartei, indet.,

1600 Megaraptoridae indet.

1601 Size class 5 --

71 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 72 of 91

1602 Size class 4 --

1603 Size class 3 --

1604 Size class 2 Aniksosaurus darwini, Dromaeosauridae indet.

1605 Size class 1 --

1606 Non-carnivorous Dinosaurs: 6 spp.

1607

1608 Huincul Formation (late Cenomanian; Mendoza, Rio Negro, Neuquèn, Argentina)

1609 Carnivorous Theropods:

1610 Size class 7 Mapusaurus rosae

1611 Size class 6 Skorpiovenator bustingorryi, Taurovenator violantei

1612 Size class 5 Ilokelesia aguadagrandensis,Draft Gualicho shinyae, Aoniraptor liberatem

1613 Size class 4 Tralkasaurus cuyi

1614 Size class 3 --

1615 Size class 2 --

1616 Size class 1 Overoraptor chimentoi

1617 Non-carnivorous Dinosaurs: 7 spp.

1618

1619 (early Cenomanian; Mendoza, Rio Negro, Neuquèn, Argentina)

1620 Carnivorous Theropods:

1621 Size class 7 Giganotosaurus carolinii

1622 Size class 6 novasi

1623 Size class 5 --

1624 Size class 4 --

72 © The Author(s) or their Institution(s) Page 73 of 91 Canadian Journal of Earth Sciences

1625 Size class 3 --

1626 Size class 2 argentina, gonzalezorum

1627 Size class 1 --

1628 Non-carnivorous Dinosaurs: 5 spp.

1629

1630 (early Cenomanian; Western Desert, )

1631 Carnivorous Theropods:

1632 Size class 7 Spinosaurus aegyptiacus, saharicus, Bahariasaurus

1633 saharicus

1634 Size class 6 Deltadromeus agilis

1635 Size class 5 Rugops sp. Draft

1636 Size class 4 --

1637 Size class 3 --

1638 Size class 2 Dromaeosauridae indet.

1639 Size class 1 --

1640 Non-carnivorous Dinosaurs: 3 spp.

1641

1642 Aoufous Formation (early Cenomanian; Errachidia, Morocco)

1643 Carnivorous Theropods:

1644 Size class 7 Spinosaurus cf. S. aegyptiacus, Sigilmassasasaurus brevicollis (?=

1645 Spinosaurus), Carcharodontosaurus saharicus

1646 Size class 6 Sauroniops pachytholus, Deltadromeus agilis

1647 Size class 5 Rugops sp.

73 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 74 of 91

1648 Size class 4 --

1649 Size class 3 --

1650 Size class 2 indet., Dromaeosauridae indet.

1651 Size class 1 --

1652 Non-carnivorous Dinosaurs: 3 spp.

1653

1654 Echkar Formation (late -early Cenomanian; Agadez, )

1655 Carnivorous Theropods:

1656 Size class 7 Spinosaurus sp., Carcharodontosaurus iguidiensis, Bahariasaurus sp.

1657 Size class 6 --

1658 Size class 5 Rugops primus Draft

1659 Size class 4 --

1660 Size class 3 --

1661 Size class 2 --

1662 Size class 1 --

1663 Non-carnivorous Dinosaurs: 2 spp.

1664

1665 Mussentuchit Member, Cedar Mountain Formation (early Cenomanian; Utah, USA)

1666 Carnivorous Theropods:

1667 Size class 7 --

1668 Size class 6 meekerorum

1669 Size class 5 --

1670 Size class 4 --

74 © The Author(s) or their Institution(s) Page 75 of 91 Canadian Journal of Earth Sciences

1671 Size class 3 Moros intrepidus*, Dromaeosauridae indet.

1672 Size class 2 cf. Richardoestesia, Troodontidae indet.

1673 Size class 1 --

1674 Non-carnivorous Dinosaurs: 7 spp.

1675

1676 Elrhaz Formation (late -early Albian; Niger)

1677 Carnivorous Theropods:

1678 Size class 7 --

1679 Size class 6 tenerensis, Eocarcharia dinops

1680 Size class 5 Kryptops palaios

1681 Size class 4 -- Draft

1682 Size class 3 --

1683 Size class 2 Afromimus tenerensis

1684 Size class 1 --

1685 Non-carnivorous Dinosaurs: 5 spp.

1686

1687 Cloverly Formation (Aptian-Albian; Wyoming, Montana, USA)

1688 Carnivorous Theropods:

1689 Size class 7 --

1690 Size class 6 sp.

1691 Size class 5 --

1692 Size class 4 Tyrannosauroidea indet.*

1693 Size class 3 Deinonychus antirrhopus

75 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 76 of 91

1694 Size class 2 --

1695 Size class 1 --

1696 Non-carnivorous Dinosaurs: 8 spp.

1697

1698 Cat & Poison Strip Members, Cedar Formation (-early Aptian; Utah,

1699 USA)

1700 Carnivorous Theropods:

1701 Size class 7 --

1702 Size class 6 --

1703 Size class 5 ostrommaysi

1704 Size class 4 -- Draft

1705 Size class 3 --

1706 Size class 2 Yurgovuchia doellingi, Geminiraptor suarezorum

1707 Size class 1 --

1708 Non-carnivorous Dinosaurs: 12 spp.

1709

1710 (Barremian; Thailand)

1711 Carnivorous Theropods:

1712 Size class 7 --

1713 Size class 6 Siamosaurus suteethorni

1714 Size class 5 isanensis, Phuwiangovenator yaemniyomi

1715 Size class 4 Vayuvenator nongbualamphuensis

1716 Size class 3 --

76 © The Author(s) or their Institution(s) Page 77 of 91 Canadian Journal of Earth Sciences

1717 Size class 2 --

1718 Size class 1 Compsognathid indet.

1719 Non-carnivorous Dinosaurs: 2 spp.

1720

1721 (late -Barremian; Dorset, , UK)

1722 Carnivorous Theropods:

1723 Size class 7 --

1724 Size class 6 walkeri, salierii

1725 Size class 5 Tyrannosauroidea indet.*5, Basal tetanurine5

1726 Size class 4 lengi*

1727 Size class 3 Thecocoelurus daviesiDraft

1728 Size class 2 pussilis, Calamosaurus foxi, Dromaeosauridae indet.

1729 Size class 1 Ornithodesmus cluniculus, bitholus

1730 Non-carnivorous Dinosaurs: 10 spp.

1731

1732 Upper Dinosaur Member, (Tithonian; Lindi, Tanzania)

1733 Carnivorous Theropods:

1734 Size class 7 --

1735 Size class 6 Ostafrikasaurus crassiserratus, Basal tetanurine6

1736 Size class 5 Basal ceratosaur6

1737 Size class 4 --

1738 Size class 3 --

1739 Size class 2 --

77 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 78 of 91

1740 Size class 1 --

1741 Non-carnivorous Dinosaurs: 8 spp.

1742

1743 Lourinhã Formation (Kimmeridgian-Tithonian; Lourinhã, )

1744 Carnivorous Theropods:

1745 Size class 7 --

1746 Size class 6 gurneyi, Allosaurus europaeus

1747 Size class 5 sp., Abelisauridae indet.

1748 Size class 4 antunesi

1749 Size class 3 Lusovenator santosi

1750 Size class 2 Aviatyrannis jurassica,Draft cf. Richardoestesia

1751 Size class 1 --

1752 Non-carnivorous Dinosaurs: 13 spp.

1753

1754 Morrison Formation, Zone 6 (early Tithonian; Western Interior, USA)7

1755 Carnivorous Theropods:

1756 Size class 7 --

1757 Size class 6 Allosaurus fragilis

1758 Size class 5 Ceratosaurus nasicornis

1759 Size class 4 --

1760 Size class 3 --

1761 Size class 2 Koparion douglassi

1762 Size class 1 --

78 © The Author(s) or their Institution(s) Page 79 of 91 Canadian Journal of Earth Sciences

1763 Non-carnivorous Dinosaurs: 12 spp.

1764

1765 Morrison Formation, Zone 5 (late Kimmeridgian-early TIthonian; Western Interior,

1766 USA)7

1767 Carnivorous Theropods:

1768 Size class 7 Saurophaganax maximus

1769 Size class 6 Torvosaurus tanneri, Allosaurus fragilis

1770 Size class 5 Ceratosaurus nasicornis

1771 Size class 4 bicentissimus

1772 Size class 3 clevelandi*

1773 Size class 2 fragilis*Draft

1774 Size class 1 --

1775 Non-carnivorous Dinosaurs: 9 spp.

1776

1777 Middle Dinosaur Member, Tendaguru Formation (late Kimmeridgian; Lindi, Tanzania)

1778 Carnivorous Theropods:

1779 Size class 7 --

1780 Size class 6 Veterupristatisaurus milneri

1781 Size class 5 Basal ceratosaur6

1782 Size class 4 --

1783 Size class 3 --

1784 Size class 2 Abelisauroid2, Basal tetanurine2

1785 Size class 1 --

79 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 80 of 91

1786 Non-carnivorous Dinosaurs: 8 spp.

1787

1788 Morrison Formation, Zone 4 (late Kimmeridgian; Western Interior, USA)7

1789 Carnivorous Theropods:

1790 Size class 7 --

1791 Size class 6 Torvosaurus tanneri, Allosaurus fragilis

1792 Size class 5 Ceratosaurus nasicornis

1793 Size class 4 --

1794 Size class 3 --

1795 Size class 2 --

1796 Size class 1 HesperornithoidesDraft miessleri

1797 Non-carnivorous Dinosaurs: 13 spp.

1798

1799 Morrison Formation, Zone 3 (middle Kimmeridgian; Western Interior, USA)7

1800 Carnivorous Theropods:

1801 Size class 7 --

1802 Size class 6 Torvosaurus tanneri, Allosaurus fragilis

1803 Size class 5 Ceratosaurus nasicornis

1804 Size class 4 Marshosaurus bicentissimus

1805 Size class 3 --

1806 Size class 2 --

1807 Size class 1 --

1808 Non-carnivorous Dinosaurs: 11 spp.

80 © The Author(s) or their Institution(s) Page 81 of 91 Canadian Journal of Earth Sciences

1809

1810 Morrison Formation, Zone 2 (middle Kimmeridgian; Western Interior, USA)7

1811 Carnivorous Theropods:

1812 Size class 7 --

1813 Size class 6 Allosaurus fragilis

1814 Size class 5 Ceratosaurus nasicornis

1815 Size class 4 --

1816 Size class 3 Stokesosaurus clevelandi*

1817 Size class 2 Coelurus fragilis*, topwilsoni*, Ornitholestes hermanni

1818 Size class 1 --

1819 Non-carnivorous Dinosaurs: 14 spp. Draft

1820

1821 Shangshaximiao Formation (?; Sichuan, China)

1822 Carnivorous Theropods:

1823 Size class 7 --

1824 Size class 6 shangyouensis

1825 Size class 5 Szechuanosaurus campi, Yangchuanosaurus hepingensis

1826 Size class 4 --

1827 Size class 3 --

1828 Size class 2 --

1829 Size class 1 --

1830 Non-carnivorous Dinosaurs: 12 spp.

1831

81 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 82 of 91

1832 , Upper (Callovian-Oxfordian; , China)

1833 Carnivorous Theropods:

1834 Size class 7 --

1835 Size class 6 --

1836 Size class 5 dongi

1837 Size class 4 wucaii*

1838 Size class 3 --

1839 Size class 2 salleei

1840 Size class 1 --

1841 Non-carnivorous Dinosaurs: 12 spp.

1842 Draft

1843 Xiashaximiao Formation (Bajocian-Callovian; Xinjiang, China)

1844 Carnivorous Theropods:

1845 Size class 7 --

1846 Size class 6 --

1847 Size class 5 Leshansaurus qianweiensis, Yangchuanosaurus zigongensis

1848 Size class 4 Kiajiangosaurus lini, qilixiaensis

1849 Size class 3 constructus

1850 Size class 2 Chuandongocoelurus primitivus

1851 Size class 1 --

1852 Non-carnivorous Dinosaurs: 11 spp.

1853

1854 Cañadon Asfalto Formation (Toarcian8; Chubut, Argentina)

82 © The Author(s) or their Institution(s) Page 83 of 91 Canadian Journal of Earth Sciences

1855 Carnivorous Theropods:

1856 Size class 7 --

1857 Size class 6 --

1858 Size class 5 Asfaltovenator vialidadi

1859 Size class 4 Eoabelisaurus mefi, Piatnitzkysaurus floresi

1860 Size class 3 Condorraptor currumili

1861 Size class 2 --

1862 Size class 1 --

1863 Non-carnivorous Dinosaurs: 3 spp.

1864

1865 Draft

1866 1The altispinus- osborni Dinosaur Macrofossil Assemblage Zone of

1867 Eberth et al. (2013).

1868 2The Edmontosaurus regalis- canadensis Dinosaur Macrofossil Assemblage

1869 Zone of Ebert et al. (2013).

1870 3Megaherbivore Assemblage Zones and subdivisions from Mallon et al. (2012) and Mallon

1871 (2019)

1872 4Bissekty Formation carcharodontosaurid reported in Tanaka et al. (2020).

1873 5Wessex Formation theropods after Naish et al. (2001).

1874 6Tendaguru Formation theropods after Rauhut (2005, 2011).

1875 7Morrison Formation biozonation from Foster (2003).

1876 8Toarcian age for the Cañadón Asfalto Formation from Pol et al. (2020).

1877

83 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 84 of 91

1878 FIGURE CAPTIONS

1879

1880 Fig. 1. Hypothetical hatchling albertosaurine tyrannosaurid, from Russell (1970). Reproduced by

1881 permission: Dale Russell © Canadian Museum of Nature. Femur length 100 mm. Although

1882 other researchers have estimated somewhat different proportions for these individuals (Currie

1883 2003), this reconstruction emphasizes the different morphology, and consequently different

1884 ecological role, of young tyrant dinosaurs compared to the adult stages.

1885

1886 Fig. 2. Histogram of theropod size distribution in selected tyrant-dominated guilds. Solid bars

1887 represent non-tyrant taxa; bars with diagonal pattern represent tyrannosauroids. Data from Table

1888 1. Draft

1889

1890 Fig. 3. Histogram of theropod size distribution in selected non-tyrant-dominated guilds. Solid

1891 bars represent non-tyrant taxa; bars with diagonal pattern represent tyrannosauroids. Data from

1892 Table 1.

1893

1894 Fig. 4. Box-and-whisker plot of number of missing size classes for tyrant and non-tyrant guilds.

1895 Data from Table 1. Silhouettes of Teratophoneus curriei and Allosaurus fragilis from

1896 PhyloPic.org, by Scott Hartman and reproduced under CCA-NC-SA 3.0 Unported License: For

1897 Teratophoneus curriei: http://phylopic.org/image/ad05ef4a-3533-4b30-b1ff-3d1faf393337/

1898 Allosaurus fragilis: http://phylopic.org/image/a3fe8af3-8bcf-469a-b3d8-08bc0f071c98/

1899

84 © The Author(s) or their Institution(s) Page 85 of 91 Canadian Journal of Earth Sciences

1900 Fig. 5. A, Scatter plot of number of carnivorous theropod taxa against total number of dinosaur

1901 species in faunal assemblages. Crosses, tyrant-dominated faunas; open circles, non-tyrant-

1902 dominated faunas. B, Box-and-whisker plot of total number of dinosaurian species in faunal

1903 assemblages for tyrant and non-tyrant-dominated faunas. Data from Table 1. Silhouettes of

1904 Teratophoneus curriei and Allosaurus fragilis from PhyloPic.org, by Scott Hartman and

1905 reproduced under CCA-NC-SA 3.0 Unported License: For Teratophoneus

1906 curriei: http://phylopic.org/image/ad05ef4a-3533-4b30-b1ff-3d1faf393337/

1907 Allosaurus fragilis: http://phylopic.org/image/a3fe8af3-8bcf-469a-b3d8-08bc0f071c98/

1908

1909

1910 Fig. 6. Box-and-whisker plot of numberDraft of missing size classes in theropod guilds for

1911 dinosaurian faunas in which sauropods were present and absent. Data from Table 1. Silhouette of

1912 supremus from PhyloPic.org, by Mathew Wedel and reproduced under CCA-NC-

1913 SA 3.0 Unported License: http://phylopic.org/image/7a99b167-b719-4233-946c-addf3ef1c06c/

1914

85 © The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 86 of 91

Draft

Fig. 1. Hypothetical hatchling albertosaurine tyrannosaurid, from Russell (1970). Reproduced by permission: Dale Russell © Canadian Museum of Nature. Femur length 100 mm. Although other researchers have estimated somewhat different proportions for these individuals (Currie 2003), this reconstruction emphasizes the different morphology, and consequently different ecological role, of young tyrant dinosaurs compared to the adult stages.

© The Author(s) or their Institution(s) Page 87 of 91 Canadian Journal of Earth Sciences

Draft

Fig. 2. Histogram of theropod size distribution in selected tyrant-dominated guilds. Solid bars represent non- tyrant taxa; bars with diagonal pattern represent tyrannosauroids. Data from Table 1.

© The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 88 of 91

Draft

Fig. 3. Histogram of theropod size distribution in selected non-tyrant-dominated guilds. Solid bars represent non-tyrant taxa; bars with diagonal pattern represent tyrannosauroids. Data from Table 1.

© The Author(s) or their Institution(s) Page 89 of 91 Canadian Journal of Earth Sciences

Draft

Fig. 4. Box-and-whisker plot of number of missing size classes for tyrant and non-tyrant guilds. Data from Table 1. Silhouettes of Teratophoneus curriei and Allosaurus fragilis from PhyloPic.org, by Scott Hartman Silhouettes of Teratophoneus curriei and Allosaurus fragilis from PhyloPic.org, by Scott Hartman and reproduced under CCA-NC-SA 3.0 Unported Licence: For Teratophoneus curriei: http://phylopic.org/image/ad05ef4a-3533-4b30-b1ff-3d1faf393337/ Allosaurus fragilis: http://phylopic.org/image/a3fe8af3-8bcf-469a-b3d8-08bc0f071c98/

© The Author(s) or their Institution(s) Canadian Journal of Earth Sciences Page 90 of 91

Draft

Fig. 5. A, Scatter plot of number of carnivorous theropod taxa against total number of dinosaur species in faunal assemblages. Crosses, tyrant-dominated faunas; open circles, non-tyrant-dominated faunas. B, Box- and-whisker plot of total number of dinosaurian species in faunal assemblages for tyrant and non-tyrant- dominated faunas. Data from Table 1. Silhouettes of Teratophoneus curriei and Allosaurus fragilis from PhyloPic.org, by Scott Hartman Silhouettes of Teratophoneus curriei and Allosaurus fragilis from PhyloPic.org, by Scott Hartman and reproduced under CCA-NC-SA 3.0 Unported Licence: For Teratophoneus curriei: http://phylopic.org/image/ad05ef4a-3533-4b30-b1ff-3d1faf393337/ Allosaurus fragilis: http://phylopic.org/image/a3fe8af3-8bcf-469a-b3d8-08bc0f071c98/

© The Author(s) or their Institution(s) Page 91 of 91 Canadian Journal of Earth Sciences

Draft

Fig. 6. Box-and-whisker plot of number of missing size classes in theropod guilds for dinosaurian faunas in which sauropods were present and absent. Data from Table 1. Silhouette of Camarasaurus supremus from PhyloPic.org, by Mathew Wedel and reproduced under CCA-NC-SA 3.0 Unported Licence: http://phylopic.org/image/7a99b167-b719-4233-946c-addf3ef1c06c/

© The Author(s) or their Institution(s)