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1 doi: /nature Occurrence, age, and preservation of the holotype and referred specimens of Chilesaurus diegosuarezi gen. et sp. nov. The holotype and referred specimens of Chilesaurus were collected from beds of the Toqui Formation, which crops out in the mountains flanked by the Maitenes and Horquetas rivers, south to the Lago General Carrera. The succession of clastic sedimentary rocks with intercalated tuffs is m thick. The dinosaur fossils occur in an approximately 100 m succession of alternating green volcaniclastic pebbly sandstones and sandy sedimentary breccias, with intercalations of lapilli tuffs and red ignimbrites with eroded tops 1 3. The sandstones are coarse-grained, frequently passing into conglomerates formed by andesites, rhyolites, basalts, and zircons, among other components. The sedimentary breccias are tuffaceous, mainly with volcanic clasts of 2 8 mm in diameter. These rocks experienced low-grade metamorphism of prehnitepumpellyite facies 4. These sedimentary beds resemble braided river deposits. The U-Pb SHRIMP age of 147 ± 1.0 Ma was obtained from zircon samples from the ignimbrite that immediately underlies the fossil-bearing levels, indicating a Tithonian age (latest Jurassic) for Chilesaurus and its associated fauna 5. Analytical procedures of the dating followed those summarized in Williams 6 and the results are interpreted as representing magmatic ages 3. Extraction of the specimens was conducted by some of the authors (M.P.I, L.S., M.S., R.C., F.L.A., N.R.C) and their preparation was completed by professionals at the MACN under the supervision of the senior author (F.E.N.). The specimens were found and collected articulated in the field (Extended Data Fig. 1), but subsequently separated into different blocks during preparation to facilitate the study of the specimens. The different blocks fit well to each other, allowing the assemblage of large part of the 1

2 articulated skeletons. All of the blocks, bearing the different specimens, are composed of a greenish matrix with identical lithology. Several specimens, including the holotype, were found in natural articulation (Extended Data Fig. 1), demonstrating that the different specimens described by Salgado et al. 3 pertained to a single species. The natural articulation of the holotype and several referred specimens of Chilesaurus rule out the possibility of mixture between different species (i.e. chimeric taxon) in the hypodigm of the new dinosaur. Referred specimens. SNGM-1937, associated forelimbs and left tibia and fibula, and complete foot, and incomplete right distal end of tibia and fibula; SNGM-1936, nearly complete left ilium, incomplete right ilium, both pubes and ischia, and forelimbs, right astragalus and right metatarsals; SNGM-1938, both forelimbs with incomplete hands, left and right scapulocoracoids, nearly complete dorsal vertebral series and articulated ribs; SNGM-1889, right ilium; SNGM-1895, proximal end of left tibia; SNGM-1888, partial left pes, comprising articulated distal end of tibia and fibula, astragalus and calcaneum, distal tarsal IV, metatarsals II-IV and many articulated phalanges; SNGM-1901, distal end of right tibia; SNGM-1894, SNGM-1898, SNGM- 1900, SNGM-1903, incomplete and isolated dorsal vertebrae; SNGM-1887, partial left manus (see 3 ). 2. Phylogenetic analyses In order to investigate the phylogenetic position of Chilesaurus, we coded the new dinosaur into four different data matrixes with samplings focused on basal dinosauriforms (Nesbitt et al. 7 ), basal sauropodomorphs (Otero & Pol 8 ) and basal theropods (Carrano et al.9; a modified version of Smith et al. 10 ) (see below). 2

3 Analysis protocol. All the data matrixes were analyzed under equally weighted parsimony using TNT A heuristic search of 100 replications of Wagner trees (with random addition sequence) followed by TBR branch swapping (holding 10 trees per replicate) was performed. The best trees obtained at the end of the replicates were subjected to a final round of TBR branch swapping. Zero length branches among all of the recovered MPTs were collapsed (i.e. rule 1 of Coddington & Scharff 12 ). Node supports were calculated using decay indexes (Bremer support) and absolute and GC bootstrap frequencies calculated after 10,000 pseudoreplicates. The following multistate characters were treated as additive in each data matrix: Modified version of Smith et al. 10 : 3, 7, 10, 12, 37, 65, 67, 70, 98, 111, 136, 148, 166, 182, 188, 192, 193, 207, 280, 291, 303, 309, 316, 325, 328, 334, 335, 336, 340, 364, 373, 375, 387, and Nesbitt et al. 7 : 17, 30, 67, 128, 174, 184, 213, 219, 231, 236, 248, 253, 254, and Otero & Pol 8 : 8, 13, 19, 23, 40, 57, 69, 92, 102, 108, 117, 121, 134, 144, 147, 149, 150, 157, 167, 170, 171, 177, 205, 207, 222, 227, 242, 251, 254, 277, 294, 299, 336, 342, and 349. Carrano et al. 9 : none. Changes in the original datasets. Chilesaurus was scored into the data matrixes of Nesbitt et al. 7 and Carrano et al. 9 without changes in the original datasets. A single scoring was changed and one taxon was added (Tawa) in the data matrix of Otero & Pol 9 (the scoring of the character 250 in Chromogisaurus was changed from [1] to [0]). 3

4 The original data set published by Smith et al. 10 was deeply modified with the addition of 59 characters and four new terminals (Tawa, Aerosteon, Falcarius, Chilesaurus). Plateosaurus and NMV P were not included in the new version of the data matrix because of the morphological gap present between the very early sauropodomorphs present in the data set (e.g. Saturnalia) and Plateosaurus, and the low number of characters that can be scored in the Australian specimen. Characters 61, 62, 70, 278 and 333 of Smith et al. 10 were modified. Additionally, several taxa were deeply rescored based on new available data (e.g. Eoraptor lunensis 13 ; Megaraptor namunhuaiquii 14 ). The final matrix is composed of 60 taxa and 412 characters (see TNT file below). Results. The results of the four analyses are detailed below, but all of them agree in the position of Chilesaurus as a tetanuran theropod. Features supporting the theropodan position of Chilesaurus include: pleurocoelous cervical and cranial dorsal vertebrae; hypapophyses on pectoral vertebrae; preacetabular wing of ilium dorsoventrally expanded; femoral fourth trochanter semicircular; and tibia distally expanded and with lateral malleolus extending strongly laterally. Tetanuran characteristics present in Chilesaurus are: scapular blade elongate and strap-like; distal carpal semilunate; and manual digit III reduced. The basal position of Chilesaurus within Tetanurae conflicts with the presence of several highly derived coelurosaurian features (e.g., opisthopubic pelvis, large supratrochanteric process on ilium, reduced supracetabular crest) which are present in combination with a number of surprisingly plesiomorphic traits present in basal sauropodomorphs (e.g., stout construction of the limb bones, the absence of an adductor fossa and mediodistal crest on distal end of femur, a tibia lacking a fibular crest, the presence of a low, thick ascending process on the astragalus and a robust and triangular 4

5 calcaneum, as well as a metatarsal II that is proximally thicker than the remaining metatarsals) 8,13. This combination of derived Coelurosaurian and Prosauropod-like traits specifically recalls the plant-eating Laurasian therizinosaurs 26. This posits Chilesaurus as a possible member of this clade of peculiar maniraptorans, sharing the presence of a leafshaped dentition, an opisthopubic pelvis, a large supratrochanteric process on ilium, and a tetradactyl foot. Nevertheless, this set of general characteristics contrasts with the 18 derived features absent in Chilesaurus that are usually recognized as uniting therizinosaurs with derived coelurosaurs, including: anterior cervicals with prezygapophyses that are ventrally flexed at their distal tip; anterior caudal centra that are subrectangular and box-like; a shelf-like brevis fossa; a peg and socket iliac-ischial articulation; an ischium with an obturator process that is offset proximally by a notch and with a tapering distal end; a tibia that lacks bracing for the ascending process of the astragalus; and a metatarsal III that is hourglass-shaped in proximal view. Moreover, Chilesaurus exhibits important differences from therizinosaurs in the plesiomorphic morphology of its astragalus and calcaneum, the elongate and rod-like shape of the ischium, the extensive pubic aprons, and the simple carpal structure, which differs from the unusual distal carpal row typical of therizinosaurs 26. Furthermore, under constrained suboptimal topologies, 11 additional steps are necessary to force the position of Chilesaurus as a therizinosaur. This set of anatomical distinctions implies a phylogenetic position for Chilesaurus outside Therizinosauria, Maniraptora and Coelurosauria. Apart from typically saurischian and theropodan characters, Chilesaurus also shows several potential apomorphies of ornithischians or subclades thereof. Unfortunately, very few basal ornithischians are currently known from good materials. The data matrix of Nesbitt et al includes Scutellosaurus, Lesothosaurus, Eocursor, Heterodontosaurus and Pisanosaurus, and thus provides as good a taxon 5

6 sample as is available, This matrix discards that Chilesaurus is an ornithischian (see below). Adding further ornithischians would consider taxa that are either very fragmentary, or derived (well nested within Ornithischia). Thus, it is unlikely they would alter the result. Nesbitt et al. 7 data matrix The analysis recovered six most parsimonious trees (MPTs) of 917 steps with a consistency index (CI) of and a retention index (RI) of The best score was hit 66 times out of the 100 replications. Chilesaurus is found deeply nested within Theropoda, as the sister taxon of Velociraptor. However, the addition of the new dinosaur resulted in a topology within Averostra that contradicts all recent theropod phylogenies, in which an Allosaurus+Piatnitzkysaurus clade is the sister taxon of a node including Ceratosaurus and Velociraptor. This controversial result is probably a result of the highly homoplastic anatomy of Chilesaurus and the poor taxonomic sampling of this data set in this part of the theropod tree. Accordingly, the phylogenetic position of Chilesaurus should be considered as evidence of averostran affinities, but not as evidence of a coelurosaur affiliation. The rest of the topology is almost identical to that recovered by Nesbitt et al. 7, with the exception of some topologies within Ornithischia and at the base of Neotheropoda. The theropodan signal of Chilesaurus in this data set is considerably high, with the presence of some rather well supported nodes within Theropoda (e.g. Tawa+Neotheropoda, Neotheropoda, Averostra) (Fig. S1). Indeed, under constrained suboptimal topologies, 15 additional steps are necessary to force Chilesaurus to be the sister-taxon of Neotheropoda, 18 to be at the base of Theropoda, 16 to be nested within 6

7 Sauropodomorpha (sister taxon of Plateosaurus), and 14 to be nested within Ornithischia (either as the most basal ornithischian or sister-taxon of Heterodontosaurus). 20 additional steps are necessary to find Chilesaurus outside Dinosauria. The lower numbers of steps that are necessary to force the position of Chilesaurus within Sauropodomorpha and Ornithischia rather than within Theropoda are a result of the multiple homoplasies with the former clades that are present in this bizarre new dinosaur. Synapomorphies of Theropoda present in Chilesaurus: 161-1, 173-1, Synapomorphy of the clade including Eoraptor and more derived theropods present in Chilesaurus: Synapomorphies of the clade including Tawa and more derived theropods present in Chilesaurus: 125-1, Synapomorphies of Neotheropoda present in Chilesaurus: 144-1, 175-1, 192-1, 196-2, 201-1, 249-1, 256-1, Synapomorphy of the Dilophosaurus + Aversotra clade present in Chilesaurus: Synapomorphies of Averostra present in Chilesaurus: 120-1, 146-1, 189-0, 236-0, 273-2, 274-1, Synapomorphies of the Ceratosaurus + Velociraptor clade present in Chilesaurus: 252-0, Synapomorphies shared between Chilesaurus and Velociraptor: 172-0, 204-1, 217-0, 220-0,

8 Figure S1. Phylogenetic position of Chilesaurus based on the data matrix of Nesbitt et al. 7. Numbers above the nodes represent Bremer support, and absolute and GC bootstrap frequencies, respectively. Character scorings for Chilesaurus in Nesbitt et al. 7 data set:???????????????????0???1???????????????00????????????????????????????????????1??????????????01110???????? ????01?1? [12] ??011?1 10?1?? ?0111?11?111??1???0001??

9 ?11??? ?0?01???211101? ?0???????? Otero and Pol 8 data matrix The analysis recovered 50 MPTs of 1414 steps with a consistency index (CI) of and a retention index (RI) of The best score was hit 76 times out of the 100 replications. Chilesaurus is found in the strict consensus tree as part of a politomy composed of the theropods taxa Tawa, Chindesaurus and Neotheropoda (Figure S2). The rest of the topology of the strict consensus tree is congruent with that recovered y Otero and Pol 8. Under constrained suboptimal topologies, five additional steps are necessary to force the inclusion of Chilesaurus within Sauropodomorpha (as the most basal member of the clade), 11 additional steps to be the sister-taxon of Ornithischia, and 22 to lie outside Dinosauria (as its sister-taxon). Accordingly, the result of this analysis corroborates the exclusion of Chilesaurus from Sauropodomorpha and bolsters its inclusion within Theropoda. Bremer supports and bootstrap frequencies are very low for Theropoda and surrounding nodes among basal saurischians (Fig. S2). 1. Synapomorphies of Dinosauria present in Chilesaurus: 132-1, 145-1, 260-1, 319- Synapomorphies of Saurischia present in Chilesaurus: 157-1, 221-2, Synapomorphies of Eusaurischia present in Chilesaurus: 277-1, Synapomorphies of Theropoda present in Chilesaurus:

10 Synapomorphies of Theropoda and less inclusive nodes, excluding Agnosphitys, present in Chilesaurus: 177-1/2, 178-1, 235-1, 246-1, 248-1, 250-1, 251-3, 255-2, Figure S2. Phylogenetic position of Chilesaurus based on the data matrix of Otero and Pol 8. Numbers above the nodes represent Bremer support, and absolute and GC bootstrap frequencies, respectively. 10

11 Character scorings of new taxa in the data matrix of Otero and Pol 8 : Chilesaurus?0???????0????????????????????????????????001?1?????000???????????????????????????????1???????0???1?1???????1? [12]??????? ?00101?0000?10? ?00?00-0???21??0????00????????? ? [01]0--? ?? ?000?00?0? ? Tawa 0?1?000?? ?11110?0?00---?? ?0?101?1?1010???0[01]00101??10????0????0?0?????????? ???1?? ?1?????110?10?????????????0????0?????[12]?????????00????00??00??????????0?0?10100?0000??1010????1???????020??0??1?-- 0?0? ?00??? ?1??????2???????????0?0?0?0110?1?1?0????10??01??????????0?1???0?11?11??0?0???00?0?10????0?????0?0?????11?1 Smith et al. 10 data matrix The analysis recovered eight MPTs of 1210 steps with a consistency index (CI) of and a retention index (RI) of The best score was hit 36 times out of the 100 replications. Chilesaurus is found as the most basal tetanuran, being the sister taxon of the (Piatnitzkysaurus+Condorraptor)+Neotetanurae clade. Under constrained suboptimal topologies, two additional steps are necessary to force the position of Chilesaurus as the sister-taxon of Neotheropoda, three steps to be the most basal 11

12 Coelurosauria, eight steps to be the sister-taxon of Averostra or the most basal Ceratosauria or Megalosauroidea, nine steps to be the most basal member of Allosauroidea, and 11 steps to be the sister-taxon of Falcarius (i.e. a therizinosaurian). The low number of additional steps necessary to find Chilesaurus as the sister-taxon of Neotheropoda is not surprising because of the multiple features that share the new dinosaur with basal saurischians. However, the four independent phylogenetic data matrix favours a position as a neotheropod, and particularly as a basal tetanuran. The overall topology of the strict consensus tree mostly resembles that recovered by Smith et al. 10, but there are some clear differences that result from the new information added here (i.e. new taxa, characters, scoring revisions) that deserve discussion. The early dinosaur Eoraptor was recovered in the present analysis as a member of Sauropodomorpha, in agreement with the result of Martínez et al. 15, rather than the sister-taxon of Eusaurischia (contra Smith et al. 10 ). The other early dinosaur Herrerasaurus was recovered as the most basal theropod, being the sister-taxon of Tawa (absent in the original data set of Smith et al. 10 ) + Neotheropoda. The changes in topology among non-neotheropod dinosaurs are likely a result of the deep changes in the scorings of Eoraptor (following Sereno et al. 13 ) and the addition of Tawa. The latter taxa possesses a combination of herrerasaurid and neotheropod features (Nesbitt et al. 7 ) that probably resulted in the migration of Herrerasaurus to the base of Theropoda. The new analysis also differs from the result recovered by Smith et al. 10 in the presence of a paraphyletic Dilophosauridae (i.e. Dilophosaurus wetherilli, Dracovenator, Cryolophosaurus and Dilophosaurus sinensis). In our analysis dilophosaurids represent successive outgroups of Averostra. In particular, the position 12

13 of Cryolophosaurus and Dilophosaurus sinensis as more closely related to averostran than to Dilophosaurus wehterilli is in agreement with the result of Carrano et al. 9, but these authors recovered the latter species as the most basal member of Coelophysoidea. Within Neoceratosauria or Ceratosauria (depending on the phylogenetic positions of Ceratosaurus), Elaphrosaurus was recovered as its most basal member, being the sister taxon of Ceratosaurus and Abelisauroidea. This result is in agreement with the most recent phylogenies focused on ceratosaur theropods 16,17. One of the most heated debated topics of theropod phylogeny in the last years has been the high-level position of megaraptorans. Smith et al. 18 found megaraptorans (represented only at that time by Megaraptor) as members of Allosauroidea and nested within Carcharodontosauridae. Subsequently, Smith et al. 10 found megaraptorans as member of Megalosauroidea. Benson et al. 19 recognized for the first time a megaraptoran clade and found them as the sister-taxon of Carcharodontosauridae, within Allosauroidea. Finally, Novas et al. 20 conducted a new phylogenetic analysis and found megaraptorans as basal coelurosaurs and probably deeply nested members of Tyrannosauroidea. The latter hypothesis has been recently bolstered by a new juvenile specimen of Megaraptor that preserves a partial skull 14. We revised the scorings of Megaraptor based on the new information published by Porfiri et al. 14 and first hand observation on the new specimen, and we also added the megaraptoran Aerosteon to the taxonomic sample of the data matrix. The taxonomic sampling of the present phylogeny represents a good test for the high level position of Megaraptora within Tetanurae, because of the presence of multiple megalosauroids, allosauroids and coelurosaurs (but much more work is needed for a strong test of megaraptoran affinities, for example including more basal allosauroids and tyrannosauroids than in the present sample). The current modified version of Smith et al. 10 data matrix found megaraptorans as basal 13

14 members of Coelurosauria, being the sister-taxon of Tyrannosauroidea + more derived coelurosaurs. This result is very interesting because represents an intermediate position between those suggested by Benson et al. 19 and Novas et al. 20, and definitely deserves further testing. Synapomorphies of selected nodes including Chilesaurus (character-states in bold are present in Chilesaurus): Dinosauria/Saurischia 39(1 0): Position of the apicobasally highest tooth crowns in the maxilla and dentary placed in the anterior portion of the tooth row (unknown in Chilesaurus). 166(0 1): Axial epipophysis present and small. 303(0 1/2): Iliac acetabular wall partially open or fully open. 314(1 0): Pubic shaft subequal or anteroposteriorly broader than that of the ischium at mid-length (reversed in Chilesaurus). 325(0 1/2): Ischium with pubic and iliac facets separated from each other. 326(0 1): Ischium shaft rod-like. 342(0 1): Oblique ligament groove on posterior surface of femoral head deep and bounded medially by a well-developed posterior lip. 406(2 0): Metatarsal V with rounded distal articular facet (unknown in Chilesaurus). 14

15 Theropoda 42(1 0): Teeth with mesiodistal constriction between crown and root: absent (reversed in Chilesaurus). 84(1 0): Postorbital with convex posterior margin of the ventral process (reversed in Chilesaurus). 320(0 1): Strongly expanded pubic boot (reversed in Chilesaurus). 392(2 1): Metatarsus with ratio between transverse width of the distal end of metatarsal I and width of the distal end of metatarsal II of (reversed in Chilesaurus). Tawa + Neotheropoda 8(0 1): Premaxillary body in front of external nares longer than body below the nares and angle less than 70 degrees (unknown in Chilesaurus). 11(0 1): Premaxillary tooth row ends anterior to naris (unknown in Chilesaurus). 12(0 1/2): Subnarial process of the premaxilla strongly reduced (unknown in Chilesaurus). 48(0 1): Lateral surface of anterior end of nasal along the posterior margin of the external naris with concave fossa. 56(0 1): Absence of a lateral ridge longitudinally traversing the rostral and caudal processes of the jugal (unknown in Chilesaurus). 125(0 1): Anterior tympanic recess in the braincase (unknown in Chilesaurus). 15

16 169(0 1): Pleurocoels in cervical vertebrae. 298(0 1): Iliac postacetabular length > acetabulum length. 343(0 1): Lesser trochanter spike-like or developed as trochanteric shelf (Chilesaurus possesses the derived additive condition). 364(0 1): Distal articular surface of tibia subrectangular with small lateral process (Chilesaurus possesses the derived additive condition). 365(0 1): Anteroposterior breadth of medial margin of distal tibia broader than the lateral margin (reversed in Chilesaurus) 385(0 1): Calcaneum with a ventromedial tuberosity fitting into a notch on the ventrolateral margin of the astragalus incipient or absent. 386(1 0): Fossa or groove on lateral surface of calcaneum absent or shallow (reversed in Chilesaurus). 406(0 1): Metatarsal V strongly reduced and lacking distal articular facet (unknown in Chilesaurus). Neotheropoda 16(0 1): Nasal process of the premaxilla with a posterior tip that extends posterior to the posterior tip of the posterolateral premaxillary process (unknown in Chilesaurus). 18(0 1): Premaxilla-nasal suture on internarial bar W-shaped (unknown in Chilesaurus). 16

17 27(0 1): Maxillary antorbital fossa shallow, margins formed by low ridges, and a sharp rim may be present only in front of the promaxillary foramen (unknown in Chilesaurus). 29(0 1): Depth of the ventral antorbital fossa much greater than the depth of the maxilla below the ventral margin of the antorbital fossa (unknown in Chilesaurus). 71(0 1): Prefrontal ventral process short and subtriangular or absent. 92(0 1): Squamosal lateral surface of main body separated from the ventral process by a sub-horizontal shelf. 122(0 1): Basisphenoid recess present between basispenoid and basioccipital (unknown in Chilesaurus). 144(0 1): Dentary rostral end dorsally raised over the distance of the first three to four alveoli (reversed in Chilesaurus). 149(0 1): Enlarged, fang-like teeth in the anterior part of the dentary (reversed in Chilesaurus). 192(0 1): Pleurocoels in dorsal vertebrae present in anterior dorsals ( pectorals ) (reversed in Chilesaurus). 207(1 2): More than three sacral vertebrae. 269(0 1): Distal end of metacarpal I with strongly asymmetrical condyles, with lateral condyle extending further distally than the medial condyle. 271(0 1): Shaft of MC III considerably more slender than MC II (less than 70 percent of the width of MC II) (polymorphic in Chilesaurus). 17

18 275(0 1): Third finger of the manus shorter than second finger. 302(1 0): Ilium without tuberosity contacting preacetabular process with supraacetabular crest. 307(0 1): Iliac supraacetabular crest hood-like and extensive, extending laterally and also curving ventrally, to cover the dorsal portion of the acetabulum in lateral view (supraacetabular crest absent in Chilesaurus). 309(1 2): Brevis fossa very strongly expanded posteriorly (reversed in Chilesaurus). 346(0 1): Dorsolateral trochanter on proximal femur reduced or absent. 349(0 1): Femur with mediodistal crest in the distal end (reversed in Chilesaurus). 358(0 1): Ridge on lateral side of tibia for connection with fibula (reversed in Chilesaurus). 360(0 1): Tibial lateral malleolus tabular (reversed in Chilesaurus). 362(0 1): Tibia with ventral extension of the lateral malleolus distinctly ventral to the level of the ventral margin of the medial malleolus and separated by an inflexion. 366(0 1): Tibia with concave posterolateral surface of the distal end (reversed in Chilesaurus). 369(0 1): Deep groove on medial side of proximal end of fibula and medial side of fibula bearing distinct fossa (reversed in Chilesaurus). 18

19 381(1 0): Astragalus without proximally facing basin posterior to the base of the ascending process (reversed in Chilesaurus). 393(0 1): Metatarsal I does not contact the ankle joint (unknown in Chilesaurus). extension. 394(1 0): Shaft of metatarsal I contacting metatarsal II along its entire 395(0 1): MT I length < 50% MT II length (unknown in Chilesaurus). 404(0 1): Distal articular surface of metatarsal IV taller dorsoplantarlly than broad mediolaterally (reversed in Chilesaurus). Zupaysaurus + Averostra 3(0 1): Tooth row ends at the anterior rim of the orbit (unknown in Chilesaurus). 58(0 1): Lacrimal fenestra present (unknown in Chilesaurus). 102(0 1): Quadratojugal fused to quadrate in adults (unknown in Chilesaurus). 103(0 1): Quadratojugal-quadrate suture exposed laterally and with a sharp lateral flange running anterodorsally on the quadratojugal (unknown in Chilesaurus). 157(0 1): Well-developed anterior wall to lateral glenoid on surangular, resulting in a lateral glenoid fossa that is at least weakly U-shaped in lateral aspect (unknown in Chilesaurus). 19

20 160(0 1): Retroarticular process of the mandible broadened, as wide mediolaterally as long anteroposteriorly or wider, often with groove posteriorly for the attachment of the M. depressor mandibulae (unknown in Chilesaurus). 375(0 1): Ascending process of astragalus higher than the astragalar body, typically covering only lateral half of anterior surface of distal tibia. Dilophosaurus wetherilli + Averostra 1(0 1): Dorsoventrally elongated orbit (reversed in Chilesaurus). 46(0 1): Antorbital fossa extending onto the lateroventral side of the nasals (unknown in Chilesaurus). 51(0 1): Lacrimal contributes to posterior margin of nasal crest (unknown in Chilesaurus). 81(0 1): Postorbital facet for articulation with the laterosphenoid present and harboured by a distinct medial process (reversed in Chilesaurus). 153(0 1): Anterior portion of the surangular more than half the height of the mandible at the level of the mandibular fenestra (unknown in Chilesaurus). 387(0 1): Calcaneum with small tibial facet on posteromedial corner. Cryolophosaurus + Averostra 9(1 0): Ventral process at the posterior end of premaxillary body absent (unknown in Chilesaurus). 20

21 26(0 1): Ascending process of the maxilla offset from anterior rim of maxillary body, with anterior projection of maxillary body shorter than high (unknown in Chilesaurus). Dilophosaurus sinensis + Averostra 45(0 1): Pneumatic foramen in the nasals (unknown in Chilesaurus). Averostra 23(1 0): Constriction between articulated premaxillae and maxillae absent (unknown in Chilesaurus). 24(1 0): Premaxilla and maxilla in contact at alveolar margins (unknown in Chilesaurus). 29(1 0): Depth of the ventral antorbital fossa less than or subequal to the depth of the maxilla below the ventral margin of the antorbital fossa (unknown in Chilesaurus). 50(1 0): Nasal crest as midline sagittal crest (unknown in Chilesaurus). Tetanurae 92(1 0): Squamosal lateral surface of main body continuous with ventral process (reversed in Chilesaurus). 21

22 240(0 1): Scapula with circular tuberosity immediately anterior to the glenoid fossa (reversed in Chilesaurus). 268(0 1): MC I closely appressed to proximal half of MC II. 274(0 1): Metacarpal IV absent. 308(0 1): Antitrochanter posterior to acetabulum absent or poorly developed. 309(2 1): Brevis fossa narrow and with subparallel margins. 335(0 1): Femur with ratio between maximum transverse width of the distal end and total length of the bone of (0 1): Femoral head horizontally directed. femur. 351(0 1): Well-developed extensor groove present on anterior side of distal 356(0 1): Tibia with lateral condyle of the proximal end anteriorly displaced from the posterior margin of the medial condyle but well on the posterior half of the bone in proximal view. 357(0 1): Tibia with deep and broad notch separating the posterior condyles of the proximal end. 358(1 2): Ridge on lateral side of tibia for connection with fibula present and clearly separated from proximal articular surface. 22

23 Chilesaurus is excluded from less inclusive tetanuran clades by the following synapomorphies: 74(0 1): Relative length of associated frontals as wide as long, or wider. 83(0 1): Postorbital in lateral view with frontal process that curves anterodorsally and dorsal border of temporal bar is dorsally concave (present in therizinosaurians). 167(0 1): Axial neural spine anteroposteriorly reduced and rod-like. 180(0 1): Prezygapophyses in anterior postaxial cervicals anteroposteriorly convex, flexed ventrally anteriorly (present in therizinosaurians). 182(1 2): Epipophyses in postaxial anterior cervical vertebrae pronounced, strongly overhanging the postzygapophyses and expanded dorsally. process. 204(0 1): Parapophyses in posteriormost dorsals distinctly below transverse 205(1 0): Parapophyses of posterior trunk vertebrae flush with neural arch. 215(0 1): Anterior caudal centra subrectangular and box-like (present in therizinosaurians). 253(0 1): Olecranon process of ulna strongly reduced or absent. 270(0 1): Medial side of MC II not expanded proximally. 297(0 1): Posterior end of ilium rectangular (present in therizinosaurians). 301(1 2): Posterior end of cuppedicus fossa ( preacetabular fossa of Hutchinson, 2001) on anterior end of pubic peduncle, anterior to acetabulum. 23

24 311(0 1): Brevis fossa shelf-like (present in therizinosaurians). 313(0 1): Iliac-ischial articulation formed by peg (iliac peduncle) and socket (ischium) joint (present in therizinosaurians). 315(0 1): Pubic tubercle extended cranially as a crest or spine (=preacetabular tubercle of Aves) (present in therizinosaurians). 329(0 1): Obturator process on ischium offset from pubic peduncle by a distinct notch (present in therizinosaurians). 330(0 1): Obturator process located distally, near middle or end of ischiadic shaft (present in therizinosaurians). 332(1 0): Ischium with ventromedial lamina extended along more of the half of the length of the bone (present in therizinosaurians). 333(0 2): Distal end of ischium tapering (present in therizinosaurians). 345(1 2): Posterior M. iliofemoralis insertion on proximal femur developed as a lateral ridge. 347(0 1): Fourth trochanter on the femur reduced to a feeble, low ridge or absent (present in therizinosaurians). 351(1 0): Extensor groove present on anterior side of distal femur absent (present in therizinosaurians). 353(0 1): Fibular condyle on proximal end of tibia strongly offset from cnemial crest (present in therizinosaurians). 24

25 361(0 1): Bracing for ascending process of astragalus on anterior side of distal tibia absent (present in therizinosaurians). 375(1 2): Height of ascending process of astragalus more than twice the height of astragalar body (present in therizinosaurians). 386(1 0): Deep fossa or groove on lateral surface of calcaneum absent or shallow (present in therizinosaurians). 398(0 1): Outline of proximal articular surface of metatarsal III hourglassshaped (present in therizinosaurians). 25

26 Figure S3. Phylogenetic position of Chilesaurus based on the modified version of the data matrix of Smith et al. 10. Numbers above the nodes represent Bremer support, and absolute and GC bootstrap frequencies, respectively. Character list of the modified version of the data matrix of Smith et al. 10. Characters taken or modified from: Benton et al. 21, Gauthier 22, Wilson & Sereno 23, 26

27 Bonaparte 24, Carrano et al. 25, Rauhut 26, Sereno 27, Sampson et al , Sereno et al. 29, Yates 30, Tykoski & Rowe 31, Bakker et al. 32, Langer & Benton 33, Tykoski 34, Harris 35, Sereno et al. 36, Sues 37, Rowe & Gauthier 38, Sereno et al. 39, Carpenter 40, Sereno et al. 41, Chiappe et al. 42, Sereno 43, Butler et al. 44, Ezcurra 45, Sereno 46, Tykoski 47, Smith et al. 18, Holtz 48, Yates 49, Sereno & Novas 50, Holtz 51, Molnar et al. 52, Russell & Dong 53, Currie 54, Britt 55, Allain 56, Yates 57, Forster 58, Coria & Currie 59, Canale et al. 60, Novas 61, Irmis et al. 62, Carrano et al. 63, Carrano & Sampson 64, Rauhut 65, Currie & Carpenter 66, Coria & Currie 67, Makovicky & Sues 68, Currie & Zhao 69, Novas 70, Ostrom 71, Barsbold et al. 72, Novas et al. 73, Brusatte & Sereno 74, Perez-Moreno et al. 75, Rowe 76, Makovicky 77, Britt 78, Coria & Salgado 79, Novas 80, Allain 81, Rauhut 82, Chen et al. 83, Xu et al. 84, Perez- Moreno et al. 85, Novas and Puerta 86, Novas 87, Sereno et al. 88, Currie and Russell 89, Hutchinson 91, Bakker & Galton 92, Norell and Makovicky 94, Rauhut 95, Smith & Galton 96, Novas 97, Ezcurra & Novas 99, Mader & Bradley 100, Welles & Long 101, Smith & Pol 102, Paul 103, Sereno et al. 104, Sampson et al. 105, Novas & Bandyopadhyay Orbit round in lateral or dorsolateral view (0); or dorsoventrally elongate (1) (TWiG). 2. Skull length relative to femur length: > 0.5 (0); < 0.5 (1) (Benton et al. 2000). 3. Tooth row: extends posteriorly to approximately half the length of the orbit (0); ends at the anterior rim of the orbit (1); completely antorbital, tooth row ends anterior to the vertical strut of the lacrimal (2) (Gauthier 1986). ORDERED. 4. External naris, anteroposterior length versus anteroposterior length of orbit in adults: <35% (0); => 35% (1) (modified from Wilson & Sereno 1998). 5. Infratemporal fenestra: smaller than or subequal in size to orbit (0); strongly enlarged, more than 1.5 times the size of the orbit (1) (Bonaparte 1991). 27

28 6. Skull, interdental plates: present (0); absent (1) (Carrano et al. 2002). 7. Height:length ratio of premaxilla below external naris: < 0.5 (0), (1), or > 1.25 (2) (modified from Carrano et al. 2002, Rauhut 2003). ORDERED. 8. Premaxillary body in front of external nares: shorter than body below the nares and angle between anterior margin and alveolar margin more than 75 degrees (0); longer than body below the nares and angle less than 70 degrees (1) (Rauhut 2003). 9. Ventral process at the posterior end of premaxillary body: absent (0); present (1) (Rauhut 2003). 10. Number of premaxillary teeth: premaxillary teeth absent (0); three (1); four (2); five (3); more than five (4) (Rauhut 2003). ORDERED. 11. Premaxillary tooth row ends: ventral (0); anterior (1) to naris (Sereno 1999). 12. Subnarial process of the premaxilla: wide; plate-like, broadly contacting the nasals and excluding the maxilla from the external nares (0); strongly reduced in width, but still contacting the nasals (1); strongly reduced process does not contact the nasals, and the maxilla forms part of the posteroventral border of the external nares (2) (modified from Gauthier 1986; Rauhut 2003). ORDERED. 13. Maxillary/palatal process of premaxilla: large flange (0); blunt triangle (1) (Sampson et al. 1998). 14. Foramen on the medial side of the premaxillary body, below the narial margin: absent (0); present (1) (modified from Sereno et al. 2004; Yates 2005). 15. Slot-shaped foramen on the lateral face of the premaxilla, located at the base of the nasal process: absent (0); present (1) (Yates 2005). 28

29 16. Length of the nasal process of the premaxilla: posterior tip level with the posterior tip of the posterolateral premaxillary process (0); posterior tip extends posterior to the posterior tip of the posterolateral premaxillary process (1) (Yates 2005). 17. Premaxillary posterodorsal process contributes to a blade-like nasal crest: no (0); yes (1) (Smith et al. 2008). 18. Premaxilla-nasal suture on internarial bar: V-shaped (0); W-shaped (1) (Sereno et al. 2004). 19. Serrations on premaxillary teeth: present (0); absent (1) (Rauhut 2003). 20. Premaxillary teeth cross-sections: elliptical (0); subcircular (1); D-shaped in cross-section (modified from Carrano et al. 2002; TWiG; Tykoski & Rowe 2004; Yates 2005). 21. Labiolingual symmetry of premaxillary teeth: symmetrical (0); asymmetrical (1); (Bakker et al. 1988). 22. Rostroventral narial fossa: absent or shallow (0); expanded, welldeveloped fossa on the premaxilla in the rostroventral corner of the naris (1) (modified from Sereno 1999; Langer & Benton 2006). 23. Constriction between articulated premaxillae and maxillae: absent (0); present (1). (Rauhut 2003). 24. Premaxilla and maxilla in contact at alveolar magins (0), or alveolar margins do not contact (1) (Tykoski 2005). 25. Orientation of the maxillae towards each other in dorsal view: acutely angled (0); subparallel (1) (Harris 1998). 26. Ascending process of the maxilla: confluent with anterior rim of maxillary body and gently sloping posterodorsally (0); offset from anterior rim of 29

30 maxillary body, with anterior projection of maxillary body shorter than high (1); offset from anterior rim of maxillary body, with anterior projection of maxillary body as long as high or longer (2) (Sereno et al. 1996). 27. Maxillary antorbital fossa: deep, and with sharp margins (0); shallow, margins formed by low ridges, a sharp rim may be present only in front of the promaxillary foramen (1) (Sues 1997). 28. Maxillary antorbital fossa in front of the internal antorbital fenestra: 25 percent or less of the length of the external antorbital fenestra (0); more than 40 percent of the length of the external antorbital fenestra (1) (Sereno et al. 1996). 29. Depth of the ventral antorbital fossa: less than or subequal to the depth of the maxilla below the ventral margin of the antorbital fossa (0); or much greater than the depth of the maxilla below the ventral margin of the antorbital fossa (1) (Yates 2005). 30. Horizontal ridge on the maxilla: absent (0); present (1) (Rowe & Gauthier 1990). 31. Maxillary fenestra: absent (0); present (1) (Gauthier 1986). 32. Maxillary fenestra situated at rostral border of antorbital fossa (0); or situated posterior to rostral border of fossa (1) (TWiG). 33. Pneumatic excavation/antrum in maxillary anterior ramus: absent (0); present (1) (Sereno et al. 1994). 34. Promaxillary fenestra: absent (0); present (1) (Carpenter 1992). 35. Palatal process of maxilla: ridged flange (0); reduced, simple process (1); long, and plate-shaped (2) (modified from Sereno et al. 1998; Carrano et al. 2002). 30

31 36. Secondary palate formed by premaxilla only (0); or by premaxilla, maxilla, and vomer (1) (TWiG). 37. Maxillary tooth count: < 12 (0); (1); > 20 (2); (modified from Carrano et al. 2002; Tykoski 2005). ORDERED. 38. Maxillary and dentary teeth: serrated (0); some or all without serrations (1) (modified from Chiappe et al. 1996; Rauhut 2003; TWiG). 39. Teeth, position of the apicobasally highest crowns in the maxilla and dentary: placed in the anterior portion of the tooth row (0); placed in the central portion of the tooth row (1); all crowns subequal in height (2) (Sereno 1986; Butler et al. 2007; Ezcurra 2012). 40. Teeth, denticles: perpendicular to the main axis of the crown (0); oblique (ca. 45º) to the main axis of the crown (1) (Benton et al. 2000). 41. Teeth, longitudinal ridges and grooves on the labial surface of the crown: absent (0); present (1) (Sereno et al. 1996, 1998). 42. Teeth, mesiodistal constriction between crown and root: absent (0); present in at least some teeth (1) (Sereno 1984). 43. Medial surface of paradental plates: smooth (0); striated (1) (Sampson et al. 1998). 44. Nasal, internarial bar: transversely broad (transverse width subequal or greater than the anteroposteiror length) (0); transversely narrow (transverse width lower than the anteroposteiror length) (1) (Gauthier 1986). 45. Pneumatic foramen in the nasals: absent (0); present (1) (Rauhut 2003). 46. Dorsal extent of antorbital fossa: dorsal rim of antorbital fossa below nasal suture, or formed by this suture (0); antorbital fossa extending onto the lateroventral side of the nasals (1) (Sereno et al. 1994). 31

32 47. Nasals: unfused (0); partially or fully fused (1) in adults (Sereno 1999). 48. Lateral surface of anterior end of nasal along the posterior margin of the external naris: flat (0); concave fossa (1); laterall convex hood covering posterior part of external naris (2) (modified from Tykoski 1998, 2005; Carrano et al. 2002). 49. Nasals: flat or gently convex, lacking crest (0); expanded into sagittal or parasagittal crests (1) (Rauhut 2003; Smith et al. 2007). 50. Nasal crest (when present): midline sagittal crest (0); parasagittal crests (1) (Rauhut 2003). 51. Construction of nasal crest: formed from the nasals only (0); lacrimal contributes to posterior margin of crest (1) (Holtz 2000; Smith et al. 2007). 52. Caudolateral process on the nasal that envelops part of the rostral ramus of the lacrimal: no (0); yes (1) (modified from Yates 2003; Langer & Benton 2006). 53. Sublacrimal part of the jugal: tapering (0); triradiate anterior end (1); strongly expanded anteriorly, overlapping most of the ventral portion of the lacrimal (2) (Rauhut 2003). 54. Pneumatization of the jugal: absent (0); jugal pneumatized by a foramen in the posterior rim of the jugal antorbital fossa (1) (Sereno et al. 1996). 55. Medial jugal foramen present on medial surface ventral to postorbital bar: absent (0) or present (1) (TWiG). 56. Lateral ridge longitudinally traversing the rostral and caudal processes of the jugal: present (0), absent (1) (modified from Sereno & Novas 1993; Tykoski 1998). 32

33 57. Anterior end of jugal participates in internal antorbital fenestra: yes (0); no (1) (modified from Holtz 1994; Rauhut 2003). 58. Lacrimal fenestra: absent (0); present (1) (Molnar et al. 1990). 59. Lacrimal horn : absent (0); dorsal crest above orbit (1) (Russell & Dong 1993). 60. Posterior dorsal process of lacrimal: absent (0); present, lacrimal T - shaped in lateral view (1) (Currie 1995). 61. Configuration of lacrimal and frontal: lacrimal separated from frontal by prefrontal (0); lacrimal contacts frontal (1) (Rauhut 2003). 62. Contact between lacrimal and postorbital: absent (0); present (1) (Sampson et al. 1998). 63. Lacrimal, shape in lateral view: blocky-shape or subtriangular (0); inverted L-shaped (1) (Gauthier 1986). 64. Lacrimal, height of the ventral process versus maximum preorbital height of the skull: <45% (0); => 45% (1) (modified from Rauhut 2003). Excluding skull roof crests if present. 65. Lacrimal anterior ramus length: > 65% ventral ramus length (0), < 65% ventral ramus length (1); lacrimal anterior ramus strongly reduced and almost non-existent (2); (Sereno et al. 1998). ORDERED. 66. Suborbital process of lacrimal: absent (0); present (1) (Sampson et al. 1998). 67. Lateral blade (sensu Britt 1991) of lacrimal overhangs antorbital fenestra: absent (0); present, overlapping only part of the antorbital fossa (1); present, overlapping the posterodorsal border of the antorbital fenestra (2) (modified from Britt 1991; Allain 2002) ORDERED. 33

34 68. Ventral ramus of lacrimal: broadly triangular, articular end nearly twice as wide anteroposteriorly as lacrimal body at juncture between anterior and ventral ramus (0); bar- or strut-like, roughly same width anteroposteriorly throughout ventral ramus (1) (Sereno 1999). 69. Orientation of the long axis of the lacrimal ventral process: strongly sloping anterodorsally (0); erect or nearly vertical (1); strongly sloping posterodorsally (2) (Yates 2007). 70. Prefrontal: exposed dorsally on the anterior rim of the orbit in lateral view (0); excluded from the anterior rim of the orbit in lateral view, being displaced posteriorly and/or medially; but dorsal exposure similar to that of lacrimal (1); excluded from the anterior rim of the orbit in lateral view, being displaced posteriorly and/or medially; and greatly reduced in size (2); absent (3) (modified from Rauhut 2003; TWiG). ORDERED. 71. Prefrontal, ventral process: long and slender along the posteromedial rim of the lacrimal (0); short and subtriangular or absent (1) (modified from Rauhut 2003; TWiG). Inapplicable if taxon has state 61(2-3). 72. Prefrontal, posterior process: articulates laterally to the frontal (0); fits into a notch in the frontal (1) (New carácter). 73. Anterior edge of associated frontals: rectangular anteriorly (0); triangular wedge-shaped anteriorly (1); triangular notch at the median line (2) (modified from Holtz 1994). 74. Relative length of associated frontals: longer than wide (0); as wide as long, or wider (1) (Allain 2002). 75. Frontal contribution to midline nasal crest: no (0); yes (1) (Smith et al. 2007). 34

35 76. Frontals and parietals: separate (0); fused (1) in adults (Forster 1999). 77. Median fossa in saddle shaped depression overlapping frontal-parietal contact: absent (0); present (1) (Sampson et al. 1998). 78. Supratemporal fossa: extends onto posterodorsal surface of frontal (0); restricted by overhanging frontoparietal shelf (1) (Coria & Currie 2002). 79. Supratemporal fenestrae: face dorsally (0); face anterodorsally (1) (Coria & Currie 2002). 80. Postorbital, orientation of anterior process: anterodorsal (0); subhorizontal (1) (Currie 1995). 81. Postorbital, facet for articulation with the laterosphenoid: absent or not harbored by a distinct process (0); present and harboured by a distinct medial process (1) (Ezcurra 2012). 82. Distinct anterior spur indicating the lower delimitation of the eyeball present on jugal process of the postorbital: no (0); yes (1) (Rauhut 2003). 83. Postorbital in lateral view with straight or anteroventrally curved anterior (frontal) process (0); or frontal process curves anterodorsally and dorsal border of temporal bar is dorsally concave (1) (TWiG). 84. Postorbital, posterior margin of the ventral process: convex (0); slightly concave or straight (1) (Canale et al. 2009). 85. Cross-section of the ventral process of the postorbital: triangular (0); U- shaped (1) (Sereno et al. 1994, 1996). 86. Ventral extent of postorbital substantially above ventral margin of orbit: yes (0); no (1); no and postorbital process of jugal reduced or absent (2) (Allain 2002). 35

36 87. Long axis of postorbital: dorsal-ventral (0); anteroventral-posterodorsal (1) (Novas 1989). 88. Stepped-down ventrolateral fossa on postorbital: absent (0); present (1) (Sampson et al. 1998). 89. Supratemporal fenestrae: separated by a horizontal plate formed by the parietals (0); contact each other posteriorly, but separated anteriorly by an anteriorly widening triangular plate formed by the parietals (1); confluent over the parietals; parietals form a sagittal crest (2) (Molnar et al. 1990). 90. Nuchal wedge and parietal alae: small (0); hypertrophied and elevated (1) (Forster 1999). 91. Tounge-like process of parietals overlapping the supraoccipital knob: absent (0); present (1) (Coria & Currie 2002). 92. Squamosal, lateral surface of main body: continuous with ventral process (0); separated from the ventral process by a sub-horizontal shelf (1) (New character). 93. Squamosal contribution to broad, arching nuchal crest: absent (0); present (1) (modified from Novas 1989; Sampson et al. 1998). 94. Squamosal, orientation of the ventral process with respect to the anteroposterior axis of the postorbital region of the skull: mainly vertical (0); mainly anteroventrally oriented (1) (modified from Rauhut 2003; Irmis et al. 2007; Ezcurra 2012). 95. Supratemporal fenestra bounded laterally and posteriorly by the squamosal (0); or supratemporal fenestra extended as a fossa on to the dorsal surface of the squamosal (1) (TWiG). 36