Gualicho, a Spanish name derived from the Gennaken (günün-a-künna or northern Tehuelche language) watsiltsüm, for a goddess who was considered the owner of animals and later, following the introduction of Christianity, reinterpreted as a demonic entity. She is now considered a source of misfortune by rural settlers (gauchos) of the Southern Cone. The name was chosen to reflect the difficult circumstances surrounding the discovery and study of the specimen, and its contentious history following excavation. The specific name honors Ms. Akiko Shinya, Chief Fossil Preparator at the Field Museum, for her many contributions to paleontology including discovery of the holotype of Gualicho on February 13th, 2007 (see S1 Fig ).

Gualicho shinyae is distinguished by a unique combination of character states, which otherwise optimize as derived traits of very disparate theropod groups (see Description and Discussion ). Posterior dorsal vertebrae very elongated and with slit-like pneumatic openings; scapular blade narrow with sinuous rostral margin marked by a shallow notch between the acromion process and blade; forelimb foreshortened with reduced muscle attachments and articulations and functionally didactyl; first and second metacarpals co-ossified proximally, third metacarpal reduced to a splint; pubes with little or no pubic apron and blade-like boot; femur with mediodorsally inclined head; reduced femoral distal condyles; fibula with large fossa and accessory flange on proximocaudal corner; ridge-like m. iliofibularis tubercle of fibula; third metatarsal with expanded proximal articulation with posterior edge wider than rostral edge (antarctometatarsal condition [ 8 ]); pedal unguals with single claw sheath grooves that define small spur or tuber near proximal end.

The specimen came from a sandstone layer in a section of alternating sand- and mudstones (see S1 Fig ) that make up the Cenomanian to Turonian aged Huincul Formation [ 25 ] exposed along the northern flank of the Meseta de la Rentería, Río Negro Province, Argentina ( Fig 1B and 1C ). Exact locality data are on file with the authors. Permission was obtained by the senior author for this study from the Agencia Cultura de Río Negro, and complies with all relevant regulations.

(A) Map of Rio Límay region of northern Patagonia, showing where the holotype of Gualicho shinyae was discovered (star) (B) Schematic stratigraphic column of lower part of Neuquén Group (Upper Cretaceous) strata exposed in the Neuquén Basin with approximate level at which the holotype of Gualicho shinyae was collected from the base of the Huincul Formation. See S1 Fig for excavation photos. (C) Skeletal reconstruction of Gualicho shinyae showing recovered elements in white and missing elements in grey shading. Artwork by J. González.

MPCN PV 0001, comprising four articulated centra from the dorsal vertebral column, an articulated gastral basket, a section of the tail distal to the transition point, the left scapulocoracoid and forelimb, the distal end of both pubes including the pubic boot, and parts of both hind limbs ( Fig 1A ). Much of the specimen had been lost to erosion when discovered, but the preserved parts including the forelimb, dorsal vertebrae, gastralia, and feet were articulated. Specimen measurements are provided in Table 1 .

Description and comparisons

Axial column. Three dorsal centra are preserved in articulation, though the last one is missing the posterior half of its centrum (Fig 2). The absence of both parapophyses and ventral keels suggest they are from the caudal section of the dorsal series. The articular facets are flat, and the rims of the facets exhibit distinct longitudinal striations around the entire rims (Fig 2C), which are often present in the posterior dorsals of theropods. The centra are spool-shaped with elliptical articular faces, and are slightly compressed dorsoventrally. The centra are very elongate, roughly 2.5 times as long as the articular facets are dorsoventrally high. Such proportions are unusual among theropods, but are approached in some coelophysoids [26], ceratosaurs like Masiakasaurus [27] and Elaphrosaurus (MB.R. unnumbered), and also in the megaraptoran Siats [28]. Poorly preserved pneumatic openings are present on all three centra (Fig 2B). They are extremely elongate and slit-shaped, being dorsoventrally shallow, yet extending axially along the spool-portion of the centrum body. The left pneumatic opening of the first vertebra in the series is the best preserved, and indicates that the openings are confined to the centrum body, but rims are difficult to make out on the other elements. Unfortunately the poor preservation does not allow for an assessment of their depth, nor whether they deeply invade the centra. Dorsoventrally narrow pneumatic openings are observed on the dorsal vertebrae of some carcharodontosaurians such as Siats (FMNH PR 2716) and Aerosteon [29] (MCNA-PV-3137), but are absent in non-abelisaurid ceratosaurs with elongate dorsal centra such as Spinostropheus [30] and Masiakasaurus [27], as well as in coelophysoids [31], and other outgroups. A few fragments of bone that are likely from the neural arch of the first vertebra in the series are still connected by matrix, but little detail regarding their morphology can be discerned. An isolated partial centrum of another posterior dorsal is preserved, but was crushed considerably dorsoventrally. This element exhibits a tight fit with the block of three centra and constitutes the fourth element in the series. It also bears an elongate, slit-like pneumatic foramen (Fig 2B), though this is partially obscured by taphonomic distortion. PPT PowerPoint slide

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larger image TIFF original image Download: Fig 2. Articulated dorsal vertebral centra of Gualicho shinyae. A series of articulated posterior dorsal vertebral centra of the holotype specimen of Gualicho shinyae (MPCN PV 0001) in (A) left lateral, (B) right lateral, (C) ventral, and (D) anterior views. Abbreviation: pnf, pneumatic foramen. https://doi.org/10.1371/journal.pone.0157793.g002 Three caudal vertebrae from the middle of the tail are preserved (Fig 3). The articular facets are circular in end view and concave and the centra are spool-shaped and elongate, varying from about 1.5 to 2.0 times as long as the dorsoventral height of the articular facets. No sulci or ridges are observed on the ventral faces of the centrum bodies in the first two caudals. However, the last caudal, which is also the most axially elongated of the three, bears a faint midline ventral sulcus that is confined to the anterior half of the centrum body. PPT PowerPoint slide

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larger image TIFF original image Download: Fig 3. Preserved caudal vertebrae of Gualicho shinyae. Three mid-caudal vertebrae of the holotype of Gualicho shinyae. Anteriormost caudal in (A) posterior view, (B) anterior view, (C) right lateral and (D) dorsal views. Middle of the three caudals in (E) posterior, (F) anterior, (G) left lateral, and (H) ventral views. Posteriormost of the three caudals in (I) right lateral, (J) left lateral, and (K) dorsal views. Abbreviations: ns, neural spine; prz, prezygapophysis; pz, postzygapophysis; trp, transverse process. https://doi.org/10.1371/journal.pone.0157793.g003 The largest of the three caudals is also the most complete. It retains transverse processes in the form of axially elongated, elliptical projections on the sides of the neural arch, slightly posterior to its midpoint, indicating it is close to or at the transition point (Fig 3A–3D). The prezygapophyses are stalked and project well beyond the anterior articular facet, further than the postzygapophyses, which only extend slightly past the posterior articular facet. The prezygapophyses are incomplete distally, and are angled anterodorsally rather than anteriorly. Stout ridges extend from the posterior base of the neural spine out to the tips of the postzygapophyses, which are canted with articular facets facing ventrolaterally. A strong ridge of bone also connects the lateral edge of the postzygapophysis to the middle of the lateral face of the neural arch. Only the posterior opening of the neural canal is visible and is rectangular and slightly wider than tall. A small depression is present dorsal to the neural canal, between the bases of the medial edges of the postzygapophyses. The base of a short neural spine is present, but is abraded and broken posteriorly. Another caudal (Fig 3E–3H) exhibits even more reduced transverse processes, which are represented by low ridges on the sides of the neural arch. The neural spine is shallow, rectangular and axially elongate, unlike the tall, strap-like spines of many ceratosaurs including Ceratosaurus (UMNH VP 5278), Masiakasaurus [27] and Carnotaurus [32] (MACN-CH 894), but similar to the basal ceratosaur Elaphrosaurus (MB.R. unnumbered). The dorsal border of the spine has a weakly concave dorsal margin, giving it a saddle-shaped appearance in lateral aspect, though not to the degree that it appears bifid, as in e.g., Allosaurus [33]. The bifid condition is observed in many basal tetanuran lineages and is potentially a synapomorphy of a monophyletic Carnosauria [26]. Both pre- and postzygapophyses are broken in this specimen, but a low ridge spanning across the lateral face of the arch connects the base of the prezygapophysis to that of the postzygapophysis on each side. The third caudal (Fig 3I–3K) is missing the posterior half of the centrum and postzygapophyses. The neural arch bears no trace of transverse processes suggesting this element represents a posterior caudal. The indented dorsal margin of the rectangular neural spine is below the level of the dorsal edges of the prezygapophyses. The prezygapophyses are relatively short and lobate in lateral aspect, and are significantly shorter than the length of the centrum.

Gastral basket. A near-complete and articulated gastral basket comprising 16 or 17 gastral rows was collected with the holotype. As in carcharodontosaurids [2], megaraptorans [29], and some other theropod groups [34], multiple arches are fused at the midline. At least six arches exhibit midline fusion in MPCN PV 0001, with fusion between elements observed in one anterior arch, and also in the five most posterior arches (Fig 4). These last five fused arches exhibit a progressively more acute angle between their rami posteriorly suggesting they are approaching the pubic boot. Notably, midline gastralia from the posterior portion of the gastral series found in contact with the pubic boot of Deltadromeus (SGM-Din 2) do not appear to be fused. PPT PowerPoint slide

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larger image TIFF original image Download: Fig 4. Posterior gastral arches of Gualicho shinyae. Last four preserved gastral arches of the holotype specimen of Gualicho shinyae (MPCN PV 0001) in dorsal view. Abbreviations: lg, lateral gastralia; mg, medial gastralia. https://doi.org/10.1371/journal.pone.0157793.g004 The rostralmost gastralia are thicker in girth than more posterior ones and also meet at a much shallower angle on the midline, as is typical for theropods [34]. More posterior elements are hooked at the midline where they form an expanded but flattened surface for fusion with the opposite medial element. Unlike some tyrannosaurid specimens [34], pronounced medioventral or mediodorsal facets for articulation with adjacent gastral rows are not observed in the holotype of Gualicho. The medial gastralia taper toward their lateral ends and some exhibit shallow grooves for articulation with lateral gastralia. Fragments of lateral gastralia are preserved in articulation with two of the medial rows, but none are complete so it is unknown whether lateral elements were shorter than medial ones, or vice versa. None of the gastral elements, whether fused or not, exhibit pneumatic openings such as those described in Aerosteon [29].

Pectoral girdle. The majority of the left scapula and coracoid are preserved (Fig 5), though the distal tip of the scapula is broken off, rendering its total length uncertain. The blade is strap-like, with a preserved scapular length more than 10 times the width at the narrowest point of the blade, a proportion similar to that observed in carcharodontosaurids including Acrocanthosaurus [35], and Mapusaurus [2], but also Allosaurus [7] and Deltadromeus (SGM-Din 2). Following Rauhut [26], Carrano et al. [7] found this elevated ratio to be a synapomorphy of some carcharodontosaurids, and possibly also Allosauridae, as well as of Coelurosauria. In contrast to these taxa, however, the blade appears short and less than twice the length of the acromion-glenoid distance in Gualicho, resembling Deltadromeus (SGM-Din 2) and Masiakasaurus [27], though the dorsal-most portion of the blade is not preserved in Masiakasaurus [27]. Unlike most tetanurans [26], the blade does not exhibit a subequal width throughout most of its length, and rather appears to taper distally from its base as in Masiakasaurus [27], Limusaurus [36] and Deltadromeus (SGM-Din 2). The blade is weakly convex laterally throughout its length implying low curvature of the rib cage. The lateral surface is weakly rounded while the medial surface is almost completely flat, and the ventral edge is slightly thicker than the dorsal edge. Near the base of the blade, the dorsal edge expands dorsally, but then arcs weakly back ventrally adjacent to the base of the expanded acromion process (Fig 5C). This sinuous margin creates a weak, rostrocaudally elongate flange along the dorsal edge that is separated from the base of the acromion process anteriorly by a broad and shallow indentation along the dorsal margin. A sinuous dorsal margin of the scapula adjacent to the acromion process defining a low flange is also observed in the African theropod Deltadromeus (SGM-Din 2), which also shares the presence of a relatively short, narrow, and distally tapering scapular blade with Gualicho. The scapula of Limusaurus [36] exhibits a deep, semicircular embayment of the rostral edge of the scapula at the transition between the acromion process and blade. Rostral to this indentation, the scapular margin expands smoothly dorsally to define the acromion process. The angle between the acromion process and the scapular blade is oblique, in contrast to the derived, perpendicular orientation seen in Allosauria and Coelurosauria [7]. Only the very base of the acromion process retains a natural edge, with the rest of the edges broken. However, the preserved edge is extremely thin, and likely did not continue much further, so that the outline of the preserved process is close to its original shape. The acromion process appears to have been shallow as in Deltadromeus (SGM-Din 2), Giganotosaurus (MUCPv-Ch 1), Mapusaurus [2], and Acrocanthosaurus [35], but not Megaraptor (MUCPv 341), Allosaurus [33], and Sinraptor [37]. The base of the coracoid process of the scapula is preserved with the scapular blade, but the glenoid portion is broken off and preserved with the coracoid. PPT PowerPoint slide

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larger image TIFF original image Download: Fig 5. Left scapulocoracoid of Gualicho shinyae. Scapulocoracoid of the holotype specimen of Gualicho shinyae (MPCN PV 0001) in (A) posterolateral oblique (B) lateral, and (C) medial views. Dotted line indicates boundary between scapula and coracoid. Abbreviations: cf, coracoid foramen; gl, glenoid; nab, notch between scapular blade and acromion process. https://doi.org/10.1371/journal.pone.0157793.g005 The scapula and coracoid are fused but not completely co-ossified, and a line of fusion can still be discerned on both sides, though it is more visible on the medial side (Fig 5B and 5C). The scapula contributes about two thirds of the glenoid articulation, whereas the coracoid contributes the remaining third (Fig 5A). The articular surface of the glenoid is angled outward slightly, such that it faces ventrolaterally. A small lip is formed by the scapula and coracoid at the dorsal and ventral margins of the glenoid, respectively. These lips are not laterally everted, and instead project caudally (Fig 5B). Similar lips are present in many ceratosaur taxa including Elaphrosaurus (MB.R. unnumbered), Masiakasaurus [27], and Carnotaurus (MACN Ch 895), but also are observed in the megaraptoran Aerosteon [29] (MCNA-PV-3137). Unlike Elaphrosaurus (MB.R. unnumbered), the glenoid lips do not merge to form a rim around the entire glenoid, but rather are restricted to the ventral and dorsal limits of the articulation. A large, oval coracoid foramen is present about eight centimeters anterior to the glenoid (Fig 5A–5C). The majority of the coracoid is weakly convex laterally, with the exception of a small area just dorsal to the coracoid foramen and anterior to the suture between the scapula and coracoid that is shallowly depressed. A coracoid (= 'biceps') tubercle is absent, as is the case in Masiakasaurus [25], Deltadromeus (SGM Din2), and many Megalosaurians [7], but in contrast to the condition in most tetanurans, which possess an oblique ridge-like tubercle [7]. The posteroventral process of the coracoid is hooked and extends far ventral to the glenoid, to a degree similar to that seen in Deltadromeus (SGM-Din 2), and Megaraptor (MUCPv 341). A well-developed posterovental process is only present in Masiakasaurus [27] and Elaphrosaurus (MB.R. unnumbered) within Ceratosauria, and in these two taxa, the process is not as extensive as in Gualicho. Within Tetanurae, a pronounced posteroventral process is absent in basal members such as 'Dilophosaurus' sinensis, Torvosaurus, Megalosaurus, and Yangchuanosaurus hepingensis, but is a synapomorphy of Allosauria [7]. Its posterior edge below the glenoid is also everted slightly laterally, much like the glenoid articulation. This everted edge is widest just below the glenoid, and it thins ventrally along the posteroventral process. This area of the posteroventral process also lacks the distinct fossa (Fig 5A) that is present in megaraptoran taxa [38].