LETTER doi:10.1038/nature14307 An enigmatic plant-eating theropod from the Late Jurassic period of Chile Fernando E. Novas1,2, Leonardo Salgado1,3,4, Manuel Sua´rez5, Federico L. Agnolı´n2,6, Martı´n D. Ezcurra7, Nicola´s R. Chimento2, Rita de la Cruz8, Marcelo P. Isasi1,2, Alexander O. Vargas9 & David Rubilar-Rogers9,10 Theropod dinosaurs were the dominant predators in most Mesozoic following unique combination of characters: dentary deeper anteriorly era terrestrial ecosystems1. Early theropod evolution is currently than posteriorly; cervicals with septate and paired pleurocoels; pubic interpreted as the diversification of various carnivorous and curs- apron transversely narrow; ischia connected through a proximodistally orial taxa, whereas the acquisition of herbivorism, together with the extended medial lamina (‘ischial apron’); femoral greater trochanter secondary loss of cursorial adaptations, occurred much later among anteroposteriorly expanded, astragalar ascending process lower than advanced coelurosaurian theropods1,2. A new, bizarre herbivorous astragalar body; calcaneum subtriangular in distal view; metatarsal I basal tetanuran from the Upper Jurassic of Chile challenges this robust, elongate, and proximally compressed transversely; metatarsal II conception. The new dinosaur was discovered at Ayse´n, a fossil transversely wider than the other metatarsals; pedal digit I large. locality in the Upper Jurassic Toqui Formation of southern Chile Isolated skull material (including premaxilla, maxillae, frontals, (General Carrera Lake)3,4. The site yielded abundant and exquisitely postorbital, squamosal, basicranium, ectopterygoid and dentary; preserved three-dimensional skeletons of small archosaurs. Several Extended Data Fig. 2), suggests a proportionally small head for articulated individuals of Chilesaurus at different ontogenetic stages Chilesaurus. The premaxilla is short and deep, with a rugose rostral have been collected, as well as less abundant basal crocodyliforms, margin that suggests a ramphotheca (Fig. 2). Frontals are elongate and and fragmentary remains of sauropod dinosaurs (diplodocids and narrow and participate extensively in the orbital margin. The basi- titanosaurians). sphenoidal recess is deep. The dentary is short and deep, with a down- turned symphyseal region but a straight alveolar margin. Dentary teeth Theropoda Marsh, 1881 are tall, leaf-shaped, and procumbent, with small serrations restricted Tetanurae Gauthier, 1986 to the crown apex (Fig. 2). Chilesaurus diegosuarezi gen. et sp. nov. Cervical vertebrae are long and low, forming a slender neck. Cervical and anterior dorsal vertebrae possess a pair of septate pleur- Etymology. In reference to Chile, and honoring Diego Sua´rez, who at ocoels, which are absent posterior to the pectoral region (Fig. 1g). the age of 7, discovered the first bone remains in the Toqui Formation. ‘Pectoral’ vertebrae bear prominent hypapophyses. Holotype. Servicio Nacional de Geologı´a y Minerı´a, Chile (SNGM)- The scapular blade (Extended Data Fig. 3) is elongate and slightly 1935 consists of a nearly complete, articulated skeleton, approximately anteroposteriorly expanded distally, as in basal averostrans5.Thecor- 1.6 m long (Fig. 1, Supplementary Information and Extended Data acoid is subquadrangular and lacks theropod characteristics such as the Fig. 1). Holotype specimen was skeletally immature at the time of its posteroventral process and biceps tuberosity1. It is notably thick trans- death, as evidenced by the incomplete fusion of neurocentral sutures. versely, contrasting with the delicate anterodorsal and dorsal margins This ontogenetic inference agrees with the size of the holotype, which of most dinosaurs. The limb bones are stout, as in sauropodomorphs, represents 50% the length of the larger specimen SNGM-1888 (ref. 3). and forelimb length is 56% that of hind limbs. The humerus is prox- Paratypes. Postcranial skeletons of four individuals, corresponding to imodistally short and transversely wide (Extended Data Fig. 3). The different ontogenetic stages, ranging approximately from 1.2 to 3.2 m single proximal carpal is large, with a transversely convex proximal in total length (Extended Data Table 1). Several specimens referred to articular surface. Metacarpals I–III are present, but only manual digits I as indeterminate theropods and tetanurans previously3 are here and II are well developed (Fig. 1d–f). Metacarpal I is stout, and phalanx referred to as Chilesaurus diegosuarezi. 1-I is short and strongly twisted along its main axis, as in basal saur- Locality and horizon. Central Patagonian Cordillera, Ayse´n (Chile; opodomorphs6. The ungual of digit I is shorter than metacarpal II and approximately 46u S); Toqui Formation3,4, Tithonian, latest Jurassic. less curved than most basal tetanurans5,7. Metacarpal II is the longest, Diagnosis. Chilesaurus differs from other dinosaurs in the following and its digit presents strongly shortened pre-ungual phalanges, as in combination of autapomorphies: premaxilla short and deep, with some ceratosaurians8. Metacarpal III is much more slender than in prominent plate-like postnarial process; teeth leaf-shaped, being finely basal theropods, and its digit comprises a single minute phalanx. denticulate only on the crown apex of erupting teeth; coracoid sub- The ilium is dolichoiliac, typical for Theropoda1 (Fig. 1b). The pubic quadrangular in side view and with transversely thick margins; manual pedicle is elongate (as in sauropods, ornithischians and therizino- digit II with short pre-ungual phalanges; manual digit III atrophied; saurs2,9), and the ischiadic peduncle is bulbous, as in ornithischians iliac blade with posterodorsal prominence; ischiadic peduncle of ilium and alvarezsaurid coelurosaurs10. A prominent supratrochanteric pro- robust; supracetabular crest absent; pubis fully retroverted; pubic cess is present on the posterodorsal corner of the ilium, similar to those shaft rod-like and distally unexpanded; femoral mediodistal crest of sauropods, therizinosaurs, paravians, and some ornithischians11–13. absent; tibia without fibular crest. In addition, Chilesaurus shows the The acetabular roof is transversely narrow and a supracetabular crest 1Conicet, Museo Argentino de Ciencias Naturales ‘‘B. Rivadavia’’, Av. A´ ngel Gallardo 470 (C1405DJR), Buenos Aires, Argentina. 2Museo Argentino de Ciencias Naturales ‘‘B. Rivadavia’’, Av. A´ ngel Gallardo 470 (C1405DJR), Buenos Aires, Argentina. 3Conicet, Instituto de Investigacio´n en Paleobiologı´a y Geologı´a, Universidad Nacional de Rı´o Negro, General Roca 1242, General Roca (8332), Rı´o Negro, Argentina. 4Instituto de Investigacio´n en Paleobiologı´a y Geologı´a, Universidad Nacional de Rı´o Negro, General Roca 1242, General Roca (8332), Rı´o Negro, Argentina. 5Universidad Andres Bello, Geologı´a, Facultad de Ingenierı´a, Sazie 2315, Santiago, Chile. 6Fundacio´n de Historia Natural Fe´lix de Azara, Universidad Maimo´nides, Hidalgo 775 (C1405BDB), Buenos Aires, Argentina. 7School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK. 8Servicio Nacional de Geologı´a y Minerı´a, Avenida Santa Marı´a 0104, Santiago 8330177, Chile. 9Red Paleontolo´gica U-Chile. Laboratorio de Ontogenia y Filogenia, Departamento de Biologı´a, Facultad de Ciencias, Universidad de Chile, Santiago 7800003, Chile. 10A´ rea Paleontologı´a, Museo Nacional de Historia Natural de Chile, casilla 787, Santiago, Chile. 18 JUNE 2015 | VOL 522 | NATURE | 331 G2015 Macmillan Publishers Limited. All rights reserved RESEARCH LETTER b c c d e poz prz mtc I mtc III 2 cm f g ppl is 2 cm isa p ps 2 cm I a II I m mt III mt IV l mt II k mt I 50 cm mt I 0.5 cm h i ap j ast ap calc I IV IV I II b 2 cm 0.5 cm III III II Figure 1 | Skeletal anatomy of Chilesaurus diegosuarezi gen. et sp. nov. posterior view. g, Articulated pubes (SNGM-1936) in anterior view. a, Reconstructed skeleton (SNGM-1935). b, Fourth cervical vertebra (SNGM- h, Proximal tarsals (SNGM-1888) in distal view. i, j, Left astragalus (SNGM- 1935) in right lateral view, with a close-up of tabicated anterior pleurocoel. 1936) in proximal (l) and anterior (m) views. k–m, Left pes (SNGM-1937) in c, d, Composite reconstruction of right hand (carpals, metacarpals, and non- dorsal (k), medial (l) and proximal (m) views. ap, ascending process; ast, ungual phalanges of digits I and II are from specimen SNGM-1935; ungual astragalus; b, basin; c, carpal; calc, calcaneum; ia, ischiadic apron; is, ischium; phalanges I and II are from specimen SNGM-1937; metacarpal III is from mtc, metacarpal; p, pubis; poz, postzygapophysis; pps, posterior pleurocoel; prz, specimen SNGM-1887) in dorsal (c) and medial (d) views. e, Pelvic girdle prezygapophysis; ps, pubic symphysis; I, II, III, IV, digits first to fourth. (SNGM-1936) in right lateral view. f, Articulated ischia (SNGM-1936) in is absent, as occurs in derived coelurosaurs and ornithopods1,11,13. basal ornithischians, and differs from the subtriangular crest The pubis (Fig. 1b, c) closely resembles that of basal ornithischians, present in most basal theropods1,15. As in sauropodomorphs, and therizinosaurs and dromaeosaurid paravians in being fully retroverted, unlike most theropods, the proximal end of the tibia lacks a fibular with a reduced proximal end bearing a posteriorly open obturator crest1. Like theropods, the distal end of the tibia is anteroposteriorly notch1,2. The pubic apron is transversely narrow and the pubis has a compressed with a laterally extending