This is the accepted version of the article: Vila, Bernat; Sellés, Albert G; Moreno Azanza, Miguel; [et al.]. «A titanosaurian sauropod with Gondwanan affinities in the latest Cretaceous of Europe». Nature Ecology & Evolution, (February 2022). DOI 10.1038/s41559-021-01651-5 This version is available at https://ddd.uab.cat/record/254843 under the terms of the license A titanosaurian sauropod with Gondwanan affinities in the latest Cretaceous of Europe Bernat Vila*1,2, Albert Sellés1,2, Miguel Moreno-Azanza3,4,5, Novella L. Razzolini1,2, Alejandro Gil-Delgado2,6, José Ignacio Canudo5, Àngel Galobart1,2 1. Institut Català de Paleontologia Miquel Crusafont, Universitat Autònoma de Barcelona, Carrer Escola Industrial 23, 08201 Sabadell (Barcelona), Catalonia, Spain. 2. Museu de la Conca Dellà, Carrer del Museu, 4, Isona (Lleida), Catalonia, Spain. 3. GEOBIOTEC, Department of Earth Sciences, NOVA School of Science and Technology, Universidade Nova de Lisboa, 2829-516, Caparica, Portugal. 4. Espaço NovaPaleo, Museu de Lourinhã, Rua João Luís de Moura 95, 2530-158, Lourinhã, Portugal. 5. Grupo Aragosaurus-IUCA, Paleontología, Facultad de Ciencias, Universidad de Zaragoza, Calle Pedro Cerbuna, 12, 50009 Zaragoza, Spain. 6. Departament de Geologia, Facultat de Ciències, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès (Barcelona), Spain. Corresponding author: bernat.vila@icp.cat ORCID IDs: BV, 0000-0002-5935-1732; AGS, 0000-0002-4637-6084; MMA, 0000- 0002-7210-1033; NR, 0000-0002-2234-8935; AG-D, 0000-0001-5147-5426; JIC, 0000-0003-1732-9155; AG, 0000-0003-1508-4561. 1 1 ABSTRACT 2 The origin of the last sauropod dinosaur communities in Europe and their evolution 3 during the final 15 million years of the Cretaceous has become a complex 4 phylogenetic and palaeobiogeographic puzzle characterized by the controversy on 5 the alleged coexistence of immigrant, Gondwana-related taxa alongside relictual and 6 insular clades. In this context, we describe a new titanosaurian sauropod dinosaur, 7 Abditosaurus kuehnei gen. et sp. nov., from the Upper Cretaceous (Maastrichtian) 8 Tremp Group of Catalonia (Spain). Phylogenetic analyses recover Abditosaurus 9 separately from other European titanosaurs, within a clade of otherwise South 10 American and African saltasaurines. The affinity of the new taxon with southern 11 landmasses is reinforced by spatiotemporal co-occurrence with Gondwanan 12 titanosaurian oospecies in southern Europe. The large size and the lack of 13 osteohistological features potentially related to insular dwarfism or size reduction 14 support the idea that Abditosaurus belongs to an immigrant lineage, unequivocally 15 distinct from some of the the island dwarfs of the European archipelago. The arrival 16 of the Abditosaurus lineage to the Ibero-Armorican island is hypothesized to have 17 occurred during the earliest Maastrichtian (70.6 Ma), probably as a result of a global 18 and regional sea-level drop that reactivated ancient dispersal routes between Africa 19 and Europe. The arrival of large-bodied titanosaurs to the European archipelago 20 produced dramatic changes in its insular ecosystems and important evolutionary 21 changes in its dinosaur faunas, especially with respect to the ‘island rule’ effect. 22 2 23 INTRODUCTION 24 At the very end of the Cretaceous, Europe was an extensive island archipelago in 25 which titanosaurian sauropods were integral components of terrestrial ecosystems. 26 In the large Ibero-Armorican Island (which included the current areas of south- 27 western France, Spain, and Portugal), the evolution of sauropod communities was 28 shaped by the “Maastrichtian Dinosaur Turnover”, a major faunal change in which 29 the late Campanian–early Maastrichtian (LC–EM) pre-turnover dinosaur 30 communities were replaced by early–late Maastrichtian post-turnover assemblages1– 3 31 . The pre-turnover titanosaur assemblage included small-sized species such as 32 Lirainosaurus astibiae, Atsinganosaurus velauciensis, and Garrigatitan meridionalis4– 6 33 , and moderate-sized species such as Ampelosaurus atacis and Lohuecotitan 34 pandafilandi 7,8, some of which have been interpreted to have lowered metabolic 35 rates6,9–11. Reduction of body size and shifts in growth rate relative to their 36 contemporaneous sister taxa from continental landmasses may have resulted from 37 selective pressures under insular, limited-resource environments – an evolutionary 38 process known as insular dwarfism12,13. In contrast, the post-turnover forms are 39 apparently larger in size but still taxonomically undescribed14,15, and their first 40 appearance on the island co-occurs with a specific group of oospecies of 41 Gondwanan affinity. Recent phylogenetic analyses distinguish two distinct clades: a 42 relictual core of endemic titanosaurs, and a clade of immigrants with African 43 affinities11. This partially supports a previously-postulated biotic interchange, 44 including sauropod faunas, between the archipelago – mostly and particularly with 45 the Ibero-Armorican Island16 – and the neighbouring landmasses during the latest 46 Cretaceous17–21. 3 47 Here we present a new titanosaurian sauropod dinosaur from the Late Cretaceous 48 (Maastrichtian) of Catalonia that represents the most complete, semi-articulated 49 titanosaur skeleton thus far discovered in Europe. Phylogenetic analyses of this 50 informative taxon provide an opportunity to test hypotheses of phylogenetic 51 relationships among European titanosaurs and shed light on palaeobiogeographic 52 events between the southern islands of the European archipelago and the northern 53 regions of the African landmass. Further, the new taxon is substantially larger-bodied 54 than any species within the late Campanian–early Maastrichtian titanosaur 55 assemblage, probably indicating an eventual decrease of the alleged insular 56 dwarfism or the so-called ‘island rule’ effect in Ibero-Armorican sauropod faunas. 57 58 RESULTS 59 Nomenclatural acts 60 61 Systematic palaeontology 62 DINOSAURIA Owen, 1842 63 SAURISCHIA Seeley, 1887 64 SAUROPODA Marsh, 1878 65 TITANOSAURIA Bonaparte and Coria, 1993 66 SALTASAURIDAE Bonaparte and Powell, 1980 67 SALTASAURINAE Bonaparte and Powell, 1980 68 Abditosaurus kuehnei, gen. et sp. nov. 69 4 70 The Life Science Identifiers (LSIDs) for this publication are: 71 urn:lsid:zoobank.org:act:C9CDB600-42D3-4448-910F-5630DEA64A90; 72 urn:lsid:zoobank.org:act:D9EFD886-7FE2-440C-AAC2-C8C88DF035A3 73 74 Etymology – ‘Abditus’, Latin, concealed, because the skeleton was concealed from 75 science for 60 years; ‘sauros’, Greek, lizard. ‘kuehnei’ honours Professor Walter 76 Georg Kühne (1911–1991), the discoverer of the specimen. 77 Holotype – An associated, semi-articulated, partial skeleton consisting of isolated 78 teeth, 12 articulated and partial cervical vertebrae, cervical ribs, seven nearly 79 complete or fragmentary anterior and middle dorsal vertebrae, six complete or 80 almost complete dorsal ribs and fragments of others, three chevrons, the right 81 scapula, posterior end of the left scapular blade, right coracoid, left sternal plate, a 82 sternal rib, proximal half of the left humerus, distal half of the right humerus, partial 83 right radius, fragment of the left ilium, part of the proximal half of the right femur, right 84 tibia, right fibula, and distal half of the left fibula with the adhered calcaneum (see 85 Supplementary Section 2.1 for a list of materials with repository numbers). We 86 consider these elements to represent a single titanosaurian individual because they 87 formed a partially articulated skeleton within an accumulation area of 6 m by 4 m at 88 the same stratigraphic level. No duplicated elements were found (Fig. 1). 89 Type locality – Orcau-1, approximately 6 km east of Tremp, Pallars Jussà county, 90 Catalonia, Spain (Fig. 1; coordinates: 42º 9’ 34.1424” N, 0º 58’ 22.631” E). The 91 locality (formerly known as “Barranco de Orcau” or “Orcau”) was discovered in 1954 92 by Walter Georg Kühne during fieldwork in the Suterranya-Orcau area (see 93 Supplementary Section 2.1). 5 94 Horizon – Lower portion of the Tremp Group, basalmost strata of the Conques 95 Formation3. Other fossils identified at the Orcau-1 locality include shed 96 crocodylomorph teeth (MCD-6752), plant remains, and Lychnus gastropod casts. 97 Two isolated, shed dromaeosaurid teeth (MCD-6994, MCD-6740) and scattered 98 eggshells (Fusioolithus baghensis; IPS5913322) were found in a stratigraphic level 99 immediately above the sauropod skeleton. 100 Age and distribution – ca. 70.5 Ma, early Maastrichtian (C31r), Late Cretaceous3. 101 Diagnosis – Abditosaurus kuehnei is diagnosed by a unique combination of 102 characters not seen in other titanosaurs as well as 14 autapomorphies (marked with 103 an asterisk): anterior dorsal vertebrae with anterior centrodiapophyseal lamina (acdl) 104 not reaching centrum but intersecting centroprezygapophyseal lamina (cprl)*; 105 anterior and first middle dorsal vertebrae with diapophyses ventral to 106 postzygapophyses*, absence of centroprezygapophyseal lamina (cprl)*, and long 107 axes of zygapophyses at low angle relative to horizontal plane (the latter character 108 shared with Argentinosaurus23); middle dorsal vertebrae with oblique, 109 posterodorsally oriented accessory lamina dividing parapophyseal 110 centrodiapophyseal fossa (pacdf)*, secondary prezygodiapophyseal lamina (prdl) 111 dividing prezygapophyseal paradiapophyseal fossa (prpadf)*, posterior 112 centrodiapophyseal lamina (pcdl) dorsally penetrated by large pneumatic foramen 113 (shared with Rapetosaurus24, Lohuecotitan8, and Saltasaurus25), abundant 114 pneumatic foramina in spinopostzygapophyseal (spof)*, centropostzygapophyseal 115 (cpof)*, and postzygapophyseal centrodiapophyseal (pocdf)* fossae, pneumatized 116 centropostzygapophyseal lamina (cpol) (shared with Rapetosaurus24), and absence 117 of postspinal laminae (posl) (shared with Overosaurus26, Muyelensaurus27, and 118 Isisaurus28); anterior dorsal ribs without pneumatic foramina on anterolateral and 6 119 posteromedial surfaces*; second dorsal ribs with anteroposterior thickening or bulge 120 on posterior margin of distal end*; scapula with co-occurrence of posteroventral 121 process or tubercle on medial margin of acromial plate, subtle process on 122 anteroventral corner, and very prominent bulge on dorsomedial margin of blade, and 123 two oval lateral fossae on posterior end of blade*; coracoid with elliptical foramen 124 that twists its orientation from lateral through to medial surface*; sternal plate without 125 anteroventral ridge on ventral surface (shared with Mnyamawamtuka29); presence of 126 sternal ribs; humerus with a medially projected deltopectoral crest (shared with 127 Gondwanatitan30, Nullotitan31, and Jainosaurus32) and articular surface of radial 128 condyle facing anterodistally (shared with Saltasaurus33 and Paralititan34); radius 129 with oblique ridge on posterodistal surface*; tibia with anteriorly projected cnemial 130 crest (shared with Gondwanatitan30) and small prominent bulge at posterior margin 131 of proximal end (shared with Neuquensaurus35); fibula with distal end beveled 132 posteriorly 20º with respect to long axis of shaft*; presence of ossified calcaneum 133 (shared with Neuquensaurus36 and presumably with Elaltitan37). 134 135 Osteological description and comparisons – The cervical vertebrae (Fig. 2a) 136 have opisthocoelous, internally pneumatized centra with ventral surfaces lacking a 137 ventral keel or ventrolateral ridges, thus differing from all or some of the cervical 138 centra of most titanosaurs such as Lohuecotitan8, Rapetosaurus24, Saltasaurus25, 139 and Overosaurus26, which bear some of these structures. Unlike most titanosaurs, 140 the posterior cervical centra bear large, oval, and deep pleurocoels. The 141 parapophyses extend half the anteroposterior length of the centrum, project laterally, 142 and are located on the anterior margin of the centrum, as in most titanosaurs. The 143 neural spine is estimated to be short. Cervical ribs are fused in nine of the 12 7 144 cervical vertebrae and project far laterally from the centrum (Fig. 2a). The anterior 145 process has a projection that curves medially, resembling a characteristic ‘batwing’ 146 shape, and extends to the level of the anterior margin of the condyle. The posterior 147 process is elongate and thins distally, overlapping 2.5 more posterior centra. The 148 dorsal vertebrae are described with the neural canal oriented horizontally. They are 149 strongly opisthocoelous, have camellate internal tissue, and become shorter from the 150 anterior to the middle vertebrae (Fig. 2b and c). All centra lack a ventral keel, and the 151 lateral pleurocoels are oval and undivided. In the anterior and first middle dorsal 152 vertebrae, the transverse processes are low (with the ventral edge approximately 153 level with the dorsal edge of the posterior cotyle) and laterally directed, as in 154 Lohuecotitan8 and other titanosaurs23,24,28. In the anterior dorsal vertebrae, the 155 anterior centrodiapophyseal lamina does not reach the centrum because it intersects 156 the centroprezygapophyseal lamina. The neural spine is large and triangular, 157 moderately tall, and angled posterodorsally (Fig. 2b), like those of the middle dorsal 158 vertebrae of most European titanosaurs and others. The surfaces of the 159 spinopostzygapophyseal, centropostzygapophyseal, and postzygapophyseal 160 centrodiapophyseal fossae are autapomorphically pneumatized by scattered 161 foramina. The intrapostzygapophyseal and postspinal laminae are absent, as in 162 Overosaurus26. The long axes of the zygapophyses are at a low angle relative to the 163 horizontal plane, as in Argentinosaurus23, and the diapophyses are laterally directed 164 and located at level with the prezygapophyses. Abditosaurus is unique in having the 165 diapophyses ventral to the postzygapophyses in the anterior and first middle dorsal 166 vertebrae (first, second, and third dorsals) (Fig. 2b). A secondary 167 prezygodiapophyseal lamina in the first middle dorsal and a parapophyseal 168 centrodiapophyseal fossae internally divided by an oblique, posterodorsally-oriented 8 169 accessory lamina in the middle dorsals are two autapomorphies of Abditosaurus. 170 Unlike in other Ibero-Armorican species and many other titanosaurs, the 171 centroprezygapophyseal lamina is absent. The posterior centrodiapophyseal lamina 172 bears a dorsal and elliptical pneumatic foramen (Fig. 2b,c), a character shared with 173 Lohuecotitan8, Rapetosaurus 24, and Saltasaurus25. The capitulum and tuberculum of 174 the dorsal ribs (Fig. 2d) are oriented at a right angle and united by a thin 175 capitulotubercular web that shows camellate texture. The web lacks pneumatic 176 foramina, unlike most titanosauriforms38, a feature that we regard as a local 177 autapomorphy of Abditosaurus. The rib head bears a proximodistally elongate and 178 narrow ridge (outstandingly pronounced in the third rib) that extends distally from the 179 tuberculum onto the rib shaft. The rib shaft has a plank-like, asymmetric, D-shaped 180 cross-section. The second through fourth ribs show a distal spoon-like expansion. In 181 the third dorsal rib, this expansion produces a distal peduncle where the rib 182 articulates with the sternal plates. Autapomorphically, the posterior surface of the 183 distal end of the second ribs bears a striated anteroposterior thickening or bulge. 184 Caudal chevrons (Fig. 2e) are dorsally open and ‘Y-shaped’ with rounded to oval 185 articular facets. The middle chevron has two dorsal articular subfacets, but unlike 186 Lohuecotitan8 they lack a distinct groove between them. 187 The scapula is described with the scapular blade oriented horizontally. The acromion 188 and acromial ridge are oriented perpendicular to the long axis of the blade and dorsally 189 expanded to twice the dorsoventral breadth of the posterior end (Fig. 2f). The scapular 190 blade has a nearly ‘D’-shaped cross section at its anterior end and lacks a ventral 191 ridge on the medial surface, unlike Atsinganosaurus11, Lirainosaurus39, 192 Ampelosaurus40, Mansourasaurus16, and Opisthocoelicaudia41. Posteriorly, the 193 posterodorsal expansion is more pronounced than the posteroventral expansion, as 9 194 in several titanosaurs but differing from Lirainosaurus39 and Ampelosaurus40, among 195 others. The posterior end of the scapular blade bears two autapomorphic lateral 196 fossae or depressions. The co-occurrence of a posteroventral process on the medial 197 margin of the acromial plate, a subtle process on the anteroventral corner, and a very 198 prominent bulge on the dorsomedial margin of the scapular blade is unique to 199 Abditosaurus. The scapula contributes more to the glenoid than does the coracoid, 200 differing from Lirainosaurus (coracoid contributes more than scapula39) and 201 Opisthocoelicaudia (scapula and coracoid contributes subequally41), but similar to 202 Mansourasaurus16. The coracoid is described with the glenoid surface oriented 203 posteroventrally (Fig. 2g). It is longer than tall and has a quadrangular outline, a 204 character shared with several titanosaurs, and as in many of these sauropods it lacks 205 a ridge originating near the midpoint of the anterodorsal border of the lateral surface. 206 The coracoid foramen is far from the scapular articulation, as in several titanosaurs, 207 but differing from Atsinganosaurus11, Lirainosaurus39, Ampelosaurus40, and some 208 other derived titanosaurs16,24,42. The foramen is elliptical and autapomorphically twists 209 its orientation from the lateral through to the medial surface. In articulation with the 210 scapula, the dorsal margin of the coracoid is situated below the level of that of the 211 scapular acromial plate. The sternal plate (Fig. 2h) is semilunar, with a strongly 212 concave lateral surface, as in other titanosaurs43,44. Unlike most titanosaurs6, 213 however, it lacks an anteroventral ridge on the ventral surface (as in 214 Mnyamawamtuka29). The ratio of the length of the sternal plate to that of the humerus 215 is 0.68 in Abditosaurus, which falls very close to the value seen in saltasaurids 216 (>0.7)44. The sternal rib (Fig. 2i) is elongate and rod-like and challenges the 217 assumption that the loss of ossified sternal ribs might be a synapomorphy of 218 Titanosauriformes45. The presence of this element in Abditosaurus is considered a 10 219 local autapomorphy within the clade. The ossification of at least one sternal rib in the 220 new form might be related to the very advanced ontogenetic age of the holotypic 221 individual. 222 The humerus (Fig. 2j and k) is robust and remarkably different from the more gracile 223 humeri of Ibero-Armorican and many other titanosaurs. The mediolateral 224 development of the proximal end is similar to those described in Saltasaurus33, 225 Neuquensaurus australis35, and Opisthocoelicaudia41. The deltopectoral crest is 226 robust and strongly expanded mediolaterally to reach the central axis of the shaft, as 227 in several titanosaurs, but differs from the unexpanded or moderately expanded 228 crests of all other Ibero-Armorican taxa and many other titanosaurs. It projects 229 unambiguously medially, similar to Gondwanatitan30, Nullotitan31, and Jainosaurus32. 230 Unlike other Ibero-Armorican titanosaurs, the Abditosaurus humerus exhibits a 231 distally expanded deltopectoral crest, a synapomorphy of Saltasauridae44,46 shared 232 with Opisthocoelicaudia41, Saltasaurus47, N. australis48, and Alamosaurus49. The 233 distal condyles are clearly divided as in saltasaurids44,46, and the articular surface of 234 the radial condyle faces anterodistally, as in Paralititan34 and Saltasaurus47. The 235 radius (Fig. 2l) has a mediolaterally expanded distal end that is beveled 236 posterolaterally more than 20º relative to the long axis of the shaft and a well-defined 237 interosseus ridge, as in other lithostrotian titanosaurs44. The interosseous ridge 238 extends proximodistally and is laterally emarginated, as in Opisthocoelicaudia41. 239 Unlike the rounded shape of Rapetosaurus24 or Dreadnoughtus50, the distal surface 240 is elliptical and anteroposteriorly asymmetrical, as in N. australis48. 241 Autapomorphically, Abditosaurus presents a small, oblique ridge on the posterodistal 242 surface of the radius. 11 243 The ilium has a preacetabular process that projects anterolaterally, as in 244 Garrigatitan6 and Lohuecotitan8 but differing from Lirainosaurus39. Internally, it is 245 pneumatized, as in most Ibero-Armorican titanosaurs6,8,11,39, Alamosaurus51, 246 Saltasaurus, and Neuquensaurus52, among others. The femur exhibits a prominent, 247 proximally located, lateral bulge as well as a posterior accessory ridge. The 248 eccentricity index of the shaft is >185%, as in most titanosaurs53. The tibia (Fig. 2m) 249 is gracile, and its proximal end is less mediolaterally compressed than in 250 Atsinganosaurus11 and Lirainosaurus39, but also contrasting with the rounded shape 251 of Lohuecotitan8 and Ampelosaurus40. A small but prominent bulge at the posterior 252 margin of the proximal end is also observed in Neuquensaurus35, and the cnemial 253 crest projects anteriorly, as in Gondwanatitan30. The distal end is longer 254 mediolaterally than anteroposteriorly, as typical for titanosaurs43,54. The anteromedial 255 ridge is more pronounced than in Lirainosaurus39, Atsinganosaurus11, and 256 Lohuecotitan8. The sigmoid shape of the fibula (Fig. 2n) is a character shared with 257 most Campanian–Maastrichtian titanosaurs, and the presence of a prominent lateral 258 trochanter is a synapomorphy of Saltasaurinae48. The fibula of Abditosaurus is 259 unique in having its distal end beveled posteriorly 20º with respect to the long axis. 260 The distal articular surface is triangular, as in Rapetosaurus24, Lirainosaurus39, 261 Alamosaurus55, and Laplatasaurus56. The calcaneum (Fig. 2o) is a small, convex, 262 and oval element, as in Euhelopus57 and the purported calcaneum reported in 263 Elaltitan37. The ossification of the calcaneum (and a sternal rib) in the Abditosaurus 264 holotype is exceedingly rare in Titanosauria, and therefore their presence in this 265 senescent individual might indicate that the preservation of these elements is related 266 to its advanced ontogenetic stage. 267 12 268 DISCUSSION 269 Phylogenetic and palaeobiogeographic analyses 270 We assessed the phylogenetic affinities of Abditosaurus kuehnei using both 271 parsimony and Bayesian methods with the dataset of Gorscak and O’Connor29 (see 272 Methods and Supplementary Section 1.6). In both analyses, Abditosaurus kuehnei is 273 recovered as a saltasaurid lithostrotian titanosaur on the basis of the following 274 synapomorphies: coracoid with rectangular anteroventral margin; humerus with 275 strong posterolateral bulge around level of deltopectoral crest apex; humeral 276 deltopectoral crest expanded distally; humeral distal condyles divided; and radius 277 with distal end beveled ca. 20º proximolaterally relative to shaft43. More specifically, 278 Abditosaurus is positioned within a clade of Late Cretaceous saltasaurines from 279 South America and Africa (Fig. 3). Within this otherwise South American–African 280 clade, Abditosaurus and Paralititan are sister taxa, and the Abditosaurus + 281 Paralititan clade is the sister taxon of Maxakalisaurus. The (Abditosaurus + 282 Paralititan) + Maxakalisaurus clade is the sister taxon of the South American 283 saltasaurins (Saltasaurus + Neuquensaurus). The South American–African clade as 284 a whole (that is, [Paralititan + Abditosaurus] + Maxakalisaurus and Saltasaurus + 285 Neuquensaurus) is supported by two synapomorphies (anterior and middle caudal 286 centra wider than tall; divided humeral distal condyles) and is sister to 287 Opisthocoelicaudiinae59, a Pan-American, African, and Eurasian clade that 288 comprises most of the rest of the Ibero-Armorican taxa as well as the North 289 American Alamosaurus, the South American Dreadnoughtus, and the Asian 290 Opisthocoelicaudia, among others. 291 The phylogenetic and palaeobiogeographic analyses (Fig. 3) indicate that 292 Abditosaurus is a derived member of a distinct immigrant clade of otherwise South 13 293 American and African saltasaurine titanosaurs that reached Europe via a dispersal 294 event from Africa during the post-Cenomanian, very probably during the early 295 Maastrichtian. Further, the direct association of the Abditosaurus skeleton with 296 Fusioolithus baghensis, an oospecies with in-ovo titanosaur embryos60 and an 297 otherwise Gondwanan (South America, India, Africa) distribution (see 298 Supplementary Section 2.4), reinforces the southern origin of the clade. The 299 dispersal event from Africa is hypothesized to have occurred during the KMa2 300 regressive event (70.6 Ma, early Maastrichtian), a eustatic event61 that affected the 301 central Tethyan margin and northern Africa. With the subaerial exposure of various 302 carbonate platforms, the Europe–Africa connection was reestablished, and Early 303 Cretaceous migratory routes62-64 were probably reactivated, facilitating the dispersal 304 of titanosaurian taxa (Fig. 4; Supplementary Section 2.6). 305 306 Implications for titanosaur evolution in the European archipelago 307 Abditosaurus was a large titanosaur by Ibero-Armorican standards, representing a 308 very mature, senescent, individual estimated to be 17.5 m in length with a body 309 mass of 14,053 kg (see Supplementary Table 1). Overall, it was substantially larger 310 than any titanosaur species described from the region, being more than 70% larger 311 than the largest known adult Atsinganosaurus and Garrigatitan, more than twice the 312 size of the largest individuals attributed to Lirainosaurus or Lohuecotitan, and 20% 313 larger than the largest individual attributed to Ampelosaurus (Supplementary Table 314 1). The anatomical and osteohistological characters of the senescent Abditosaurus 315 do not indicate a reduction in growth rate nor a reduction in body size (see 316 Supplementary Section 2.3), two common traits found in Lirainosaurus9, 317 Ampelosaurus10, Atsinganosaurus11, and Magyarosaurus66. Indeed, the 14 318 Abditosaurus appendicular bones lack modified laminar bone, a bone tissue 319 potentially related to a reduction in metabolic rate and body size10 and interpreted as 320 evidence for possible insular dwarfism in sauropods9-11,20. Therefore, there is no 321 evidence for metabolic adaptations to insular settings in Abditosaurus, as are 322 present in other European titanosaurs13,66. Our results suggest that Abditosaurus 323 must be regarded as a member of a distinct immigrant clade of large titanosaurs that 324 reached Ibero–Armorica during the early Maastrichtian, and as a representative of 325 the post-turnover titanosaurian fauna of this island. 326 The scenario during the middle of the early Maastrichtian (lower part of C31r) of 327 large-bodied, post-turnover titanosaurs in the Ibero-Armorican island replacing small 328 late Campanian–early Maastrichtian forms might be mirrored in other islands of the 329 European archipelago, such as in the eastern Hațeg Island (in modern-day 330 Romania), where large taxa seem to appear later than dwarfed forms (e.g., 331 Magyarosaurus67), probably also by the middle of the early Maastrichtian (lower part 332 of C31r68). Accordingly, these new titanosaur faunas are expected to be associated 333 with fusioolithid oospecies in post-early Maastrichtian deposits. Hence, this proposed 334 titanosaurian faunal replacement might represent the decrease of the ‘island rule’ 335 effect on sauropod communities throughout Europe. 336 337 METHODS 338 Osteohistological analyses - Histological samples were taken from the humerus, 339 femur, and tibia, prepared as thin sections, and studied using a petrographic 340 microscope. Body mass and length estimates - We compiled a dataset of limb 341 bone measurements for the Ibero-Armorican titanosaur species (Supplementary 342 Table 1) for use in body mass (BM) and body length (BL) estimations with the 15 343 formulas of Campione and Evans69 based on femoral and humeral circumferences, 344 which were estimated following the allometric equation of González Riga et al.70 345 when necessary, and Seebacher71. Photogrammetric models – 3-D models of 346 fossil specimens were produced following photogrammetric protocols 72-74 and using 347 Agisoft Photoscan Pro (v. 1.2.4, www.agisoft.com), to perform scaling and alignment. 348 Phylogenetic and palaeobiogeographic analyses – We performed maximum 349 parsimony and Bayesian analyses. Maximum parsimony analyses used the dataset 350 of Gorscak and O’Connor29, which included the original 55 taxa plus Abditosaurus 351 scored for 272 independent characters that were treated as unordered in all the 352 analyses. Both equal weights and extended implied weighting analyses with different 353 concavity constants were explored. The Bayesian dataset29, which also included the 354 original 55 taxa plus Abditosaurus, was coded for a total of 272 variable characters 355 plus 260 autapomorphic, invariable characters. A non-clock analysis was carried out 356 using MrBayes 3.2.675, running in the CIPRES Science Gateway, using a model of 357 variable rates of character state change, sampled from a lognormal-distribution, 358 setting an exponential hyperprior of 1.0 for the rate of variation among characters. 359 Four independent runs of the Markov chain Monte Carlo (MCMC) ran for 10 million 360 generations with one hot and three cold chains. The chains sampled tree-space 361 every 1,000 generations and the first 25% of the posterior distribution was discarded 362 to eliminate the initial climbing phase. Convergence of independent runs was 363 assessed in Tracer 1.7 using effective sample size (ESS) for each parameter greater 364 than 200. We also performed a tip-dating Bayesian phylogenetic analysis to estimate 365 divergence dates and branch lengths based on the additional data in the form of 366 stratigraphic information. The assumed tree model for this set of analyses was the 367 birth-death-skyline-serial-sampling76. A relaxed clock was assumed under a 16 368 lognormal distribution of sampled rates. Rates of character change were tested 369 under variable (with an assumed gamma-distribution) assumptions. Four 370 independent runs of the MCMC persisted for 50 million generations with sampling of 371 tree-space occurring every 1,000 generations and the first 25% of the sample was 372 discarded. Stratigraphic ranges of each taxon (see Supplementary Section 1.6 and 373 Table 2) were sampled under a uniform distribution to account for stratigraphic 374 uncertainty. Again, convergence of independent runs was assessed in Tracer 1.7 375 using effective sample size (ESS) for each parameter greater than 200. A 376 palaeobiogeographic analysis following the methodology of Sallam et al.16 was 377 conducted using the R script BioGeoBEARS77 over the tip dating maximum clade 378 credibility tree. Three models (DEC, DIVALIKE, and BAYAREALIKE) and alternative 379 models with the additional + J parameter to facilitate long-distance dispersal events 380 alongside the assumptions of each model where evaluated. All figures were created 381 by the authors using Adobe Illustrator CC 2015 2.1. 382 383 Data availability –This published work and the nomenclatural acts it contains have 384 been registered in ZooBank, the proposed online registration system for the 385 International Code of Zoological Nomenclature (ICZN). The ZooBank LSIDs (Life 386 Science Identifiers) can be resolved and the associated information viewed through 387 any standard web browser by appending the LSID to the prefix ‘‘http://zoobank.org/’’. 388 The authors declare that all other data supporting the findings of this study are 389 available within the paper and its Supplementary Information. 390 391 Acknowledgements – We thank J. Montané, E. Aguirre, A. Lacasa, and J.V. 392 Santafé for providing key information on early excavations, and U. Klebe and A. 17 393 Klebe for transcripts and translation of WGK’s field notes. We warmly thank R. 394 Gaete, J. González, E. Nieto, A. Vallès, and I. Fernández for logistics and fossil 395 preparation, and all colleagues who participated in the field campaigns. Eric Gorscak 396 kindly provided XML files for BEAST 2.1.3, B. F. Rotatori assisted with Bayesian 397 phylogenetic methods, and M. Belvedere assisted with photogrammetry techniques. 398 Urs and Anna Klebe gave permission to reproduce WGK and fieldnotes images in 399 Fig. 1 and Suppl. Fig. 2, B. González Riga gave permission to reproduce the skeletal 400 reconstruction in Fig. 1, R. Contreras provided the image for Suppl. Fig. 3, and R. 401 Glasgow reviewed the English. The authors would also like to thank M. C. Lamanna 402 and V. Díez Díaz for their helpful reviews and J. A. Wilson for his constructive 403 feedback on an early version of the manuscript. MNCN provided permissions for 404 study, sampling, and casting the MNCN specimens and Archivo MNCN-CSIC 405 provided permission to reproduce images for Suppl. Figs. 1 and 2. 406 This research is part of the project I+D+i/PID2020-119811GB-I00 funded by MCIN/ 407 AEI/10.13039/501100011033/ to B.V. Additional funding was provided by the 408 CERCA Programme and the project CLT009/18/00067 funded by the Generalitat de 409 Catalunya (to B.V. A.S, and A.G.), the Committee for Research and Exploration of 410 the National Geographic Society (grant 9148-12 to B.V.), MEIC, MCI, and MEC 411 (CGL2017-85038-P, CGL2016-77230-P, and CGL2011-30069-C02-01 to A.G., B.V., 412 A.S., and J.I.C.), and Fundação para a Ciência e a Tecnología (PTDC/CTA- 413 PAL/31656/2017, UIDB/04035/2020, and PTDC/CTA-PAL/2217/2021 to M.M.A.). 414 Fossil preparation was supported by the Servei de Museus–Departament de Cultura 415 of the Generalitat de Catalunya (grants 2015/104328, CLT005/16/00008, 416 CLT005/19/00045), and the Institut d’Estudis Ilerdencs (grant 201602412). 417 18 418 Author contributions 419 B.V. devised and directed the project and supervised the fieldwork; B.V., A.S., A.G., 420 N.L.R., and J.I.C. collected the fossils and taphonomic data in the field; B.V, A.S., 421 and A.G. supervised fossil preparation; B.V. described and measured the fossils, 422 and collected historical information; M.M.A. and B.V. performed phylogenetic and 423 biogeographic analyses; A.G.-D., A.S., and B.V. conducted histological analyses; 424 N.L.R. performed the photogrammetry and 3D modelling; B.V. wrote the paper with 425 substantial inputs of A.S., M.M.A., A.G-D., and N.L.R. B.V., A.S., and M.M.A. 426 designed the figures. B.V., A.S., M.M.A., N.L.R., A.G-D., A.G., and J.I.C. reviewed 427 and edited the original draft. 428 429 Competing interests – The authors declare no competing interests. 430 431 432 FIGURE CAPTIONS 433 434 Figure 1. Type locality of Abditosaurus kuehnei gen. et sp. nov. a, location of 435 the Orcau-1 locality in the southern Pyrenees (Catalonia, Spain). b, the discoverer, 436 Professor Walter Georg Kühne (1911–1991), during a lecture at the Palaeontological 437 Society of Berlin in 1959 (courtesy of Urs and Anna Klebe). c, site map showing the 438 skeletal disposition of the in situ skeletal elements recovered, mapped, and/or 439 collected during excavations since 1954. The position of the remains discovered in 440 the early excavations is based on sketches from Kühne’s notebook (see 441 Supplementary Section 2.1). D, schematic skeletal reconstruction in right lateral 442 view, with indication of the recovered elements (silhouette courtesy of Bernardo 443 González Riga). ?, indeterminate “flat bone”; ca, calcaneum; ch, chevron; co, 444 coracoid; cr, cervical rib; CV, cervical vertebra; dr, dorsal rib; DV, dorsal vertebra; f, 19 445 femur; fi, fibula; h, humerus; il, ilium; r, radius; sc, scapula; sp, sternal plate; sr, 446 sternal rib; t, tooth; ti, tibia. 447 448 Figure 2. Skeletal anatomy of Abditosaurus kuehnei gen. et sp. nov. a, anterior 449 dorsal and cervical vertebrae (MCD-9882) in ventral view; b, third dorsal vertebra 450 (MCD-6718) in posterior view; c, fourth and fifth dorsal vertebrae (MCD-6729, MCD- 451 6730) in right ventrolateral view; d, second left dorsal rib (MCD-6720) in anterolateral 452 view; e, anterior chevron (MNCN-62760) in caudal view; f, right scapula (from a cast 453 of MCD-6724) in medial view; g, right coracoid (MCD-6742) in lateral view; h, left 454 sternal plate (MCD-6716) in ventral view; i, sternal rib (MCD-6747) in longitudinal 455 view; j, left humerus (MNCN-79834) in anterior view; k, right humerus (MCD-6988) in 456 anterior view; l, right radius (MCD-6748) in posterior view; m, right tibia 457 (MNCN79837-79838-79848) in lateral view; n, right fibula (MCD-6723) in lateral 458 view; o, left fibula and adhered calcaneum (MNCN-79847) in medial view. acdl, 459 anterior centrodiapophyseal lamina; acpl, anterior centroparapophyseal lamina; al, 460 accessory lamina; ap, acromial plate; aspa, articular surface for ascending process 461 of astragalus; avp, anteroventral process; b, bulge; ca, calcaneum; cap, capitulum; 462 cc, cnemial crest; cdf, centrodiapophyseal fossa; cf, coracoid foramen (twisted 463 mediolaterally); cfo, cnemial fossa; cpof, centropostzygapophyseal fossa 464 (pneumatized); cpol, centropostzygapophyseal lamina; cprl, centroprezygapophyseal 465 lamina; cr, cervical rib; CV, cervical vertebra; d, diapophysis; de, distal end 466 (bevelled); dp, dorsal process; dpc, deltopectoral crest; dr, dorsal rib; DV, dorsal 467 vertebra; gl, glenoid; ior, interosseous ridge; lt, lateral trochanter; pa, parapophysis; 468 pacdf, parapophyseal centrodiapophyseal fossa; pc, pleurocoel; pcdl, posterior 469 centrodiapophyseal lamina; pdr, posterodistal ridge; pf, pneumatic foramen; po, 20 470 postzygapophysis; pocdf, postzygapophyseal centrodiapophyseal fossa 471 (pneumatized); podl, postzygodiapophyseal lamina; posdf, postzygapophyseal 472 spinodiapophyseal fossa; prcdf, prezygocentrodiapophyseal fossa; pvp, 473 posteroventral process; r, ridge; rac, radial condyle; scb, scapular blade; spdl, 474 spinodiapophyseal lamina; spof, spinopostzygapophyseal fossa; spol, 475 spinopostzygapophyseal lamina; tu, tuberculum; ulc, ulnar condyle. * indicates 476 autapomorphic character. Yellow shading in b indicates a dorsal rib fragment; blue 477 shading in a-c indicates neural arch fossae. Scale bars equal 10 cm. 478 479 Figure 3. Time-calibrated phylogenetic analysis and palaeobiogeographic 480 context of Abditosaurus kuehnei gen. et sp. nov. and other saltasaurid 481 titanosaurian sauropods. Plot based on the Maximum Clade Credibility Tree 482 inferred by the tip-dated Bayesian analysis; palaeobiogeographic analysis using the 483 BAYAREALIKE model under starting distribution multipliers. Letters in coloured 484 squares at the nodes indicate relative support for ancestral range reconstruction. 485 Light blue bars represent the 95% highest posterior density for the timing of 486 divergence date at each node. The colour-coded bars for each terminal taxon 487 indicate palaeogeographic range and the 95% highest posterior density of the 488 recorded stratigraphic range of that taxon. Green line indicates the timing of the final 489 breakup and separation between South America and Africa (see Supplementary 490 Section 2.6 for references). Global Polarity Time Scale (GPTS) after Ogg and 491 Hinnov58. A, Asia; E, Europe; F, Africa; N, North America; S, South America. 492 493 21 494 495 Figure 4. Chronostratigraphy and hypothesized dispersal route for 496 Abditosaurus kuehnei gen. et sp. nov. and other latest Cretaceous Ibero- 497 Armorican titanosaurs. a, chronostratigraphic range and positions of the Ibero- 498 Armorican titanosaurs and their holotype localities, respectively, correlated to the 499 global sea-level curve, with indication of the timing of the hypothesized dispersal 500 event from Africa to Europe during the KMa2 regressive event. b, palaeogeography 501 of the western Tethys Seaway in the early Maastrichtian, with hypothesized 502 migratory pathway (yellow arrow) through the ‘Apulian’ route to the Ibero-Armorican 503 island. Green and yellow boxes represent the chronostratigraphic ranges of the pre- 504 and post-turnover oospecies, respectively. Schemes in circles represent radial thin- 505 sections of Megaloolithus siruguei (green circle) and F. baghensis (yellow circle) 506 eggshells, taken from Vianey-Liaud et al.65. Brackets represent the 95% highest 507 posterior density of the recorded stratigraphic range for each taxon. Ab, 508 Abditosaurus kuehnei gen. et sp. nov.; Am, Ampelosaurus atacis; At, 509 Atsinganosaurus velauciensis; Li, Lirainosaurus astibiae; Lo, Lohuecotitan 510 pandafilandi. HI, Haţeg Island; IB-ARM, Ibero-Armorican Island; NW AFR, north- 511 western Africa. Global Polarity Time Scale (GPTS) after Ogg and Hinnov58. Global 512 sea-level curve and eustatic events after Haq61; sea-level (in m) on top, highstand 513 (left), lowstand (right). Palaeogeographic map based on R. Blakey. Titanosaur 514 silhouette modified from illustrations of O. Sanisidro. 515 516 REFERENCES 22 517 1. 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