Sebastián Apesteguía, Nathan D. Smith, Rubén Juárez Valieri & Peter J. Makovicky, 2016, An Unusual New Theropod with a Didactyl Manus from the Upper Cretaceous of Patagonia, Argentina, PLoS ONE 11 (7), pp. 1-41: 5-30
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gen. et sp. nov.
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Holotype. MPCN PV 0 0 0 1, 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 1 View Figure A). Much of the specimen had been lost to erosion when discovered, but the preserved parts including the forelimb, dorsal vertebrae, gastralia, and feet were articu- lated. Specimen measurements are provided in Table 1.
Provenance. The specimen came from a sandstone layer in a section of alternating sand- and mudstones (see S 1 Fig) that make up the Cenomanian to Turonian aged Huincul Forma- tion  exposed along the northern flank of the Meseta de la Rentería, Río Negro Province, Argentina ( Fig 1 View Figure B and 1 C). 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 com- plies with all relevant regulations.
Differential diagnosis. 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-ossi- fied 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; fib- ula 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 ); pedal unguals with single claw
sheath grooves that define small spur or tuber near proximal end.
Etymology. 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 ani- mals 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 13 th, 2007 (see S 1 Fig).
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 View Figure ). 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 2 View Figure C), 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 , ceratosaurs like Masiakasaurus  and Elaphrosaurus (MB.R. unnumbered), and also in the
megaraptoran Siats . Poorly preserved pneumatic openings are present on all three centra ( Fig 2 View Figure BAbout B). 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 ( FMNHAbout FMNH PRAbout PR 2716) and Aerosteon 
(MCNA-PV- 3137), but are absent in non-abelisaurid ceratosaurs with elongate dorsal centra such as Spinostropheus  and Masiakasaurus , as well as in coelophysoids , 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 2 View Figure B), though this is partially obscured by taphonomic distortion.
Three caudal vertebrae from the middle of the tail are preserved ( Fig 3 View Figure ). 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.
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 3 View Figure A– 3 D). 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 3 View Figure E– 3 H) 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 ( UMNHAbout UMNH VP 5278), Masiakasaurus  and Carnotaurus  (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 . The bifid condition is observed in many basal tetanuran lineages and is potentially a synapomorphy of a
monophyletic Carnosauria . 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 3 View Figure I– 3 K) 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 , megaraptorans , and some other theropod groups , multiple arches are fused at the midline. At least six arches exhibit midline fusion in MPCN PV 0 0 0 1, with fusion between elements observed in one anterior arch, and also in the five most posterior arches ( Fig 4 View Figure ). 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.
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 . 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 , 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 .
Pectoral girdle. The majority of the left scapula and coracoid are preserved ( Fig 5 View Figure ), 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 , and Mapusaurus , but also Allosaurus  and Deltadromeus
(SGM-Din 2). Following Rauhut , Carrano et al.  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 , though the dorsal-most portion of the blade is not preserved in
Masiakasaurus . Unlike most tetanurans , 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 , Limusaurus  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 View Figure
5 C). 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  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 . 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
(MUCPv-Ch 1), Mapusaurus , and Acrocanthosaurus , but not Megaraptor ( MUCPvAbout MUCPv 341), Allosaurus , and Sinraptor . 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.
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 5 View Figure B and 5 C). The scapula contributes about two thirds of the glenoid articulation, whereas the coracoid contributes the remaining third ( Fig 5 View Figure A). 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 5 View Figure B). Similar lips are present in many ceratosaur taxa including Elaphrosaurus ( MBAbout MB. RAbout R. unnumbered), Masiakasaurus , and Carnotaurus ( MACNAbout MACN Ch 895), but also are observed in the megaraptoran Aerosteon  (MCNA-PV- 3137). Unlike Elaphrosaurus ( MBAbout MB. RAbout 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 5 View Figure A– 5 C). 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 , Deltadromeus (SGM Din 2), and many Megalosaurians , but in contrast to the condition in most tetanurans, which possess an oblique ridge-like tubercle . 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 ( MUCPvAbout MUCPv 341). A well-developed posterovental process is only present in Masiakasaurus  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 . 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 5 View Figure AAbout A) that is present in megaraptoran taxa .
Forelimb. Parts of both forelimbs were collected with MPCN PV 0 0 0 1, including a complete left forelimb. The right forelimb is represented by the radius and ulna. The humerus is almost straight with only a slight laterally convex bow ( Fig 5 View Figure A and 5 BAbout B). The distal condyles are twisted laterally about 15 degrees relative to the humeral head ( Fig 6 View Figure CAbout C and 6 D), which is mediolaterally elongate, unlike the spherical humeral head of many ceratosaurs  including Deltadromeus (SGM-Din 2) and Elaphrosaurus ( MBAbout MB. RAbout R. unnumbered). There is a very weak cleft between the head and the pointed internal tuberosity ( Fig 6 View Figure BAbout B). The internal tuberosity is distinctly thinner than the head in proximal view. There is no evidence of a deep, longitudinal furrow on the caudomedial side of the proximal humerus, as is present in Australovenator , Fukuiraptor , Chilantaisaurus , and Megaraptor . Although this feature has also been suggested to be present in tyrannosaurids , this is based on misinterpretation of a pathology in one specimen of Tyrannosaurus rex [42, 43] ( FMNHAbout FMNH PR 2081). Two broad depressions are present on the anterior face of the humerus, though these are slightly accentuated by crushing of the element. The proximal depression is just below the humeral head and is mediolaterally elongate, extending across the breadth of the bone. The distal depression is more elongate and situated in the middle of the bone just medial to the deltopectoral crest. The
deltopectoral crest is set perpendicular to the long axis of the humeral head ( Fig 6 View Figure A and 6 B), as in a majority of theropods with the exception of some megalosaurians that have an
anterolaterally directed deltopectoral crest . It is proximodistally elongate and spans approximately one quarter the length of the humerus. Among theropods, a deltopectoral crest with such a limited proximodistal extent is only seen in Deltadromeus (SGM Din- 2) and Ornithomimosauria , although Masiakasaurus  and Elaphrosaurus (MB.R. unnumbered)
approach this condition. It tapers to a thin (and abraded) edge proximally, but its apex is thickened mediolaterally into a lobate tuberosity that is a proximodistally elongate ellipse in anterior aspect. A distinctly offset and lobate apex on the deltopectoral crest is widespread among allosauroid species including Acrocanthosaurus , Neovenator , and Fukuiraptor , but is not observed in megalosauroids , ceratosaurs (e.g., Ceratosaurus UMNHAbout UMNH VP 5278), coelophysoids ( Dilophosaurus UCMPAbout UCMP 37302), and coelurosaurs (e.g., Compsognathus MB.R. 2003.2; Guanlong IVPPAbout IVPP VAbout V 14531). There is a small, circular divot on the posterior surface of the humerus ( Fig 6 View Figure BAbout B), just below the midpoint of the head that is located in a topologically identical position to a large fossa on the humerus of Acrocanthosaurus ( NCSMAbout NCSM 14345). This part of the humerus likely serves as an insertion point for m. scapulohumeralis posterior, as in modern birds [46, 47].
The humeral shaft is relatively straight and cylindrical below the level of the deltopectoral crest, and lacks the distinct curvature seen in many tetanurans including Piatnitzkysaurus (MACN-CH 895), Allosaurus , and Torvosaurus . There is a broad but very shallow brachial fossa on the anterior face of the distal end of the humerus that is far less developed than in most tetanuran taxa. The distal condyles exhibit no mediolateral expansion, nor are any epicondylar tubers present. The distal articular end is somewhat flattened and slightly abraded. There is no strong cleft or separation into distinct condyles, except for a small notch on the rostral aspect of the distal end ( Fig 6 View Figure D). The lateral condyle is much more robust and expanded anteroposteriorly than the medial condyle.
The proximal left ulna is broken, but the right element retains most of a modestly sized, rounded olecranon process, the medial portion of which is broken away. The proximal end is only slightly caudally expanded relative to the shaft, which is straight unlike the strongly curved ulna seen in most tetanurans such as Allosaurus  and Concavenator . The midshaft is subcircular in cross section, and there are faint striations extending down the anterior to anteromedial surface of the ulnar shaft, which may mark the separation between the origin of m. abductor pollicis longus medial to the striations from the insertion of m. anconeus lateral to the striations . The distal end is weakly expanded mediolaterally. As in most tetanurans, the distal articulation is flattened, unlike the derived, convex condition observed in abelisaurids .
The radial shaft is comparable in diameter to the ulna ( Fig 6 View Figure EAbout E – 6 IAbout I). The distal end is slightly expanded and medially offset from the main axis of the shaft. The distal articular surface is weakly triangular in distal aspect. Longitudinal striations extend throughout the shaft, but are faint and not well developed. There is a small, one centimeter long linear tuberosity located approximately five centimeters from the distal end of the radius, that projects laterally slightly above the shaft. The proximal face of the radius is better preserved on the right element and is rounded and globular, with a slight divot on one edge.
Two carpals are preserved with the left forelimb. The larger of the two is the compound semilunate carpal and is attached by matrix, though not co-ossified with, the left ulna ( Fig 6 View Figure EAbout E – 6 GAbout G). Its distal surface was discovered in articulation with the proximal articular surfaces of metacarpals IAbout I and II. It has a semilunate shape in lateral view, with a convex proximal surface and a flatter distal one. The proximal aspect is partly covered by the matrix connecting it to the ulna, but the exposed rostral section reveals a broad, shallow sulcus as in Allosaurus [33, 50], and Sinraptor . The distal articulation is elliptical in end view with notches at the rostral and caudal ends that correspond to the termini of the longitudinal sulcus along the proximal surface. Its surface is kinked into a smaller rostral and a larger caudal area, again resembling the condition in Allosaurus  and other neotetanurans . The medial face of the carpal is much smaller than the lateral one.
The second carpal is smaller and flatter than the first ( Fig 7 View Figure EAbout E and 7 FAbout F). In distal view, it has an irregular elliptical outline that is weakly constricted. Because no element was found lateral to this carpal, it is likely the scapholunare. It does not resemble the large kidney shaped scapholunare reported in Australovenator , but the presence of a slight notch or constriction is similar to Allosaurus , and Acrocanthosaurus .
The unusual, didactyl manus of Gualicho is dominated by a robust metacarpal IAbout I that is about twice the mediolateral width of metacarpal II ( Fig 7 View Figure AAbout A and 7 BAbout B). The proximal end bears a slightly expanded, shallowly concave articular facet that is rectangular rather than triangular in end view ( Fig 7 View Figure D). The dorsal border of the articulation is straight, but the ventral (palmar) rim is gently concave, though not to the degree observed in either Australovenator or Acrocanthosaurus . An expanded proximomedial process as occurs in Australovenator  is absent. The width across the distal condyles is greater than that of the proximal articulation ( Fig 7 View Figure BAbout B). The distal articulation is not twisted relative to the proximal surface. Of the two hemicondyles, the medial one is much deeper in distal aspect, though both hemicondyles are roughly equal in mediolateral width ( Fig 7 View Figure CAbout C). AAbout A shallow sulcus separates them distally. AAbout A small tuber is present on the medial surface of the medial hemicondyle in place of a collateral ligament pit, though it is uncertain whether this represents an autapomorphy, or perhaps, a pathology.
Metacarpal II is proximally fused with metacarpal IAbout I and their shafts are closely appressed to each other throughout ( Fig 7 View Figure AAbout A and 7 D). The proximal surface of MCAbout MC II is very abraded, but is slightly angled relative to that of MCAbout MC I. Unlike carcharodontosaurian taxa, such as
Acrocanthosaurus  and Megaraptor , the base of metacarpal II is not broadly expanded, and the shaft is cylindrical and relatively slender overall, especially when compared with metacarpal I ( Fig 7 View Figure A and 7 B). There is a broad but very shallow fossa on the anterior surface of the shaft, just below the proximal end. A teardrop-shaped extensor fossa is also present distally on the anterior surface. The distal hemicondyles are roughly equal in size and mediolateral width, though the medial condyle is distinctly deeper than the lateral one.
Metacarpal III is reduced to a thin splint probably lacking a distal articulation, as in tyrannosaurids ( Fig 7 View Figure A and 7 B). Its proximal end is slightly expanded, but very abraded. The shaft is weakly elliptical in cross section, being slightly broader anteroposteriorly than mediolaterally. It is nearly straight with only a weak curvature in the anteroposterior plane. Metacarpal III is broken distally, but the preserved portion is just slightly shorter than MC IAbout I. The small cross section of bone at the distalmost preserved portion of MCAbout MC III argues against the presence of a distal articulation for any phalanges.
As with the metacarpals, the phalanx and ungual of digit IAbout I are roughly twice as large as those of digit II ( Fig 8 View Figure ). The ventral surface of I- 1 is round and lacks a sulcus as is seen in megaraptoran theropods such as Megaraptor  and Australovenator [39; 53]. AAbout A tab-like ridge on the posterior edge of the proximal articular surface is canted slightly laterally, rather than being in the middle of the posterior edge. The distal articulation bears deep, symmetrical collateral ligament pits, and the hemicondyles are approximately equally developed ( Fig 8 View Figure AAbout A – 8 CAbout C). However, a distinct tuberosity is present on the posterior surface just proximal to the medial condyle that is not as well developed on the lateral condyle.
Ungual I- 2 is slightly longer than phalanx I- 1, though its distal tip is missing. The proximal articular surface is less than twice as high anteroposteriorly as broad mediolaterally, in contrast to the transversely narrow proportions that are a synapomorphy of some neovenatorids,
including Australovenator , Chilantaisaurus , Fukuiraptor , and Megaraptor [7; 38]. The claw is highly recurved such that with the proximal articulation oriented vertically, the tip of the ungual reaches well below the flexor tubercle ( Fig 8 View Figure AAbout A and 8 BAbout B). The length of the ungual is over twice as great as its height, similar to the condition present in Baryonyx , Chilantaisaurus , Megaraptor , Suchomimus , and Torvosaurus . Single, symmetrical vascular grooves are present on both sides. The flexor tubercle is robust and mound-shaped, but less than half the height of the proximal articular facet.
Phalanx II- 1 is slightly (~ 1cm) longer than both phalanges II- 2 and II- 3, but is shorter than all the metacarpals ( Fig 8 View Figure GAbout G – 8 OAbout O). In ventral view the proximal end of the shaft is asymmetric with the lateral edge more expanded than the medial one. The same asymmetry in the tuberosities above the distal condyles on the posterior face present in phalanx I- 1 is also present here (i.e. with the medial tuberosity larger). Both collateral ligament pits are present but abraded. Phalanx II- 2 has the same asymmetry in the development of the medial and lateral edges just below the proximal articular surface as in phalanx II- 1. There is some amount of crushing on the posterior face of the bone in this area and just distal to it. Ungual II- 3 is partially broken and missing its distal tip ( Fig 8 View Figure IAbout I, 8 LAbout L and 8 OAbout O). It is similar to ungual I- 2 in having a broad proximal articulation and single vascular grooves on each side, but is notably less recurved.
Pelvic girdle. Only the distal pubes, including the boot, are preserved ( Fig 9 View Figure ). AAbout A small portion of the proximalmost left pubic shaft is broken, but articulates cleanly with the larger piece. The shaft is robust and elliptical in cross section with the long axis oriented anterolaterally-posteromedially, and a narrow pubic apron extending from its posteromedial edge. The lateral face is round throughout its length. Although the medial edges of the shafts are broken, it appears that the pubic apron was open medially for the proximal half of the preserved elements, where the shafts are converging on each other in a broad V-shape. Further distally, where the pubic shafts are more parallel, the two sides contact along their posteromedial edges, leaving a deep but narrow rostral groove between the conjoined elements ( Fig 9 View Figure BAbout B). The distal portions of the pubes are conjoined medially as in all averostrans , but a distal pubic foramen, as present in tetanurans , is absent in Gualicho . As the pubic shafts converge they also twist laterally about their long axes, such that where the shafts contact they are now mediolaterally elongate ellipses in cross section. Though slightly distorted, the pubic shafts are relatively straight throughout their length, with only a slight anterior convexity (accentuated by the pubic boot) at their distal ends.
The edges of the pubic boot are poorly preserved, but it is clearly expanded both anteriorly and posteriorly, though the anterior expansion is only observable on the right pubis ( Fig 9 View Figure A). The boot is fully fused and compressed mediolaterally, and would not have been broadly expanded ventrally as seen in a number of tetanurans including Giganotosaurus ( MCFAbout MCF Pv Ch 1), Aerosteon (MCNA-PV- 3137), and Torvosaurus . A mediolaterally compressed pubic boot with a narrow ventral edge is observed in Deltadromeus (SGM-Din 2; note that the element originally identified as the pubic boot  is actually the ischiadic symphysis ), and some coelurosaurs (e.g., Ornithomimus RTMPAbout RTMP 95.110.1), and was recovered as a potential coelurosaurian synapomorphy . The posterodorsal edge of the boot forms a sharp edge that diverges rostrally into two ridges, each one reaching a short distance up the caudal surface of a pubic shaft. A deep conical depression invades the dorsal aspect of the boot between the pubic shafts, but is closed off rostrally, resembling the condition described for Masiakasaurus , and also observed in taxa as diverse as Deltadromeus (SGM-Din 2) and Coelurus ( YPMAbout YPM 1993).
Hind limb. The right femur of MPCN PV 0 0 0 1 is almost complete ( Fig 10 View Figure ), whereas the left is only represented by an extremely crushed distal end. The femoral head is incomplete, with the medial half of the head missing, precluding observations on the presence and form of the posterior sulcus. A proximal articular sulcus on the proximal surface of the head as is found in silesaurids, some basal sauropodomorphs and coelophysoids  is likely absent, as in most avetheropods , because at least the lateralmost extent of this sulcus should be visible on the preserved portion of the femoral head if it were present ( Fig 10 View Figure E). The femoral head is angled primarily medially relative to the orientation of the distal condyles, with only a minor anterior angle, though this impression may be accentuated by the missing medial portion of the femoral head. It also appears to be canted slightly proximally as well ( Fig 10 View Figure C), similar to the condition in Deltadromeus (SGM-Din 2), though to a lesser degree than in carcharodontosaurids [7, 57].
The femur bears an extensive lesser trochanter that is blade-like and broken at its proximal tip, but appears unlikely to have reached the level of the femoral head proximally ( Fig 10 View Figure A and 10 B and 10 D). An enlarged accessory trochanter projects from it at midheight ( Fig 10 View Figure A).
Although large, it is not as prominent as in Neovenator . The anterior trochanteric border slopes gradually into the femoral shaft below it. There is a very weak cleft between the proximalmost portion of the lesser trochanter and the femoral shaft. The fourth trochanter is
reduced and projects weakly from the femoral shaft ( Fig 10 View Figure C). It is a low, proximodistally elongate ridge several millimeters thick that begins just below the level of the lesser trochanter and extends distally for about 12 centimeters. The femoral shaft is mediolaterally compressed and gracile, with a gentle, anteriorly convex curvature. The proximal portion of the shaft at the
level of the fourth trochanter has been crushed on its lateral side. The anterior surface of the shaft is poorly preserved at the distal end, but the area preserved is very flat and appears to lack an extensive extensor fossa ( Fig 10 View Figure D), which is present in nearly all tetanurans  with the exception of the possible basal members Cryolophosaurus  ( FMNHAbout FMNH PR 1821) and Chuandongocoelurus ( CCGAbout CCG 20010). The base of a medial epicondylar crest is preserved, though most of the distal portion of the crest is broken. Based on the proximal portion of the crest, and the preserved distal part of the left femur, it is weakly developed and far less prominent than in, for example, Coelophysis  and Liliensternus (MB R. 2175). It is clear that the crest did not project far proximally, and was restricted to the distal one-fifth of the femur. There are relatively thick longitudinal striations on the medial surface of the femoral shaft in the area of the epicondylar crest that likely correlate with the origin of m. femorotibiales internus (medialis) .
The distal condyles are not mediolaterally expanded beyond the borders of the shaft ( Fig View Figure
and Sinraptor . A distinct and robust horizontal ridge of bone extends between the medial condyle and the crista tibiofibularis on the posterior side closing off the ventral end of the popliteal fossa, and may mark the insertion for the cruciate ligaments ( Fig 10 View Figure F). Such a ridge is
proximodistally elongate tuberosity projects about 2 cm posteriorly from the middle of this
bridge, but is a widespread structure observed in numerous taxa including Sinraptor , Acrocanthosaurus , and Deltadromeus (SGM Din 2). There is a small depression in the middle of the distal surface of the femur, just proximal to the cruciate bridge and between the proximal ends of the medial condyle and the crista tibiofibularis. A deep popliteal fossa is present on the posterior side of the distal femur. It creates a depression on the proximal side of the cruciate bridge and is deepest in this area, just between the proximal ends of the medial condyle and the crista tibiofibularis. The fossa extends up the femoral shaft about 12 centimeters before grading smoothly into the femoral shaft. The lateral condyle is bulbous and well rounded, projecting primarily laterally, but slightly anteriorly from the distal end of the femur ( Fig 10 View Figure C and 10 F). The crista tibiofibularis is slightly less robust than the medial condyle. It is compressed strongly mediolaterally, particularly at its proximal end, which is blade-like. The proximal portion of the medial condyle is also compressed mediolaterally and its tip is similarly blade-like. The lateral face of the crista tibiofibularis is not circumscribed by a prominent groove as is observed in Dilophosaurus ( UCMPAbout UCMP 37302), some other coelophysoids , and Masiakasaurus .
The distal portion (~ 30cm) of the left femur is also preserved, though its entire anterior side has been crushed and sheared medially, and both condyles are crushed and extremely abraded. The medial edge is slightly distorted, but well preserved, and confirms that the medial epicondylar ridge is very reduced and not flange-like in morphology.
The proximal part of a right tibia is preserved, broken approximately 14 cm distal to the end of the fibular crest ( Fig 11 View Figure ). The proximal surface is heavily abraded and the medial surface of the cnemial crest is lost to erosion. The medial condyle is considerably more robust than the lateral condyle, and it projects proximally to a level above the proximal extents of both the lateral condyle and the cnemial crest ( Fig 11 View Figure E and 11 F). The medial condyle also extends farther posteriorly than the lateral condyle ( Fig 11 View Figure H). Most of the proximal articular surface is rugose, but is also abraded and still has some matrix attached. A deep notch separates the medial and lateral condyles posteriorly, as is typical of tetanurans [7, 26]. Both condyles grade relatively
smoothly into the tibial shaft distally, and do not form pronounced hoods or shelves. A low, but distinct (~ 2cm across) tuberosity projects into the incisura tibialis ( Fig 11 View Figure F), just anterior to the articular surface of the lateral condyle and may be homologous to the "anterolateral process"  (= "craniolateral process" and "ventral process"). Benson et al.  noted a
strongly ventrally curving anterolateral process of the lateral condyle in both Australovenator and Neovenator , but it is also present in Deltadromeus (SGM Din 2). A very low ridge of bone extends anteromedially and slightly proximally from this tuberosity and runs across the lateral face of the cnemial crest. This low ridge divides the incisura tibialis (located distal to the ridge), from a smaller, weakly concave, triangular fossa proximal to the ridge. Just below the anterolateral tuberosity, the lateral edge of the tibial shaft extends down toward the fibular crest. The cnemial crest projects primarily anteriorly and does not rise very high proximally, barely clearing the proximal articular surface. It thus differs from the rectangular and strongly anterodorsally oriented cnemial process diagnostic of abelisauroids like Majungasaurus [8, 61], and also from the anterodorsally pointed cnemial crests of some allosauroids including Sinraptor  and Giganotosaurus ( MUCP Pv CH 1). It exhibits a strong lateral curl to its anterior end ( Fig 11 View Figure G), such that its tip reaches the level of the anterolateral edge of the tibial shaft in anterior aspect. There is no evidence of a "posteroventral ridge"  on the lateral face of the apex of the cnemial crest, though the tip of the crest is broken. The medial face of the cnemial crest that still preserves the outermost cortical bone is covered by thick striations for soft tissue attachment. The crest extends distally and grades into the tibial shaft just below the level of the proximal end of the fibular crest.
The fibular crest does not project far lateral to the tibial shaft ( Fig 11 View Figure D– 11 F), but is proximodistally extensive. It grades smoothly into the tibial shaft proximally, but exhibits a more abrupt, tab-like distal border. Unlike a number of coelophysoid and ceratosaurian species, in which the fibular crest extends proximally to about the level of the lateral condyle , the fibular crest arises well below the lateral condyle in Gualicho . The edge of the fibular crest is slightly thickened and more rugose than the base of the crest. The posterior face is more heavily striated than the anterior one. The tibial shaft is an anterolaterally-posteromedially elongate ellipse in cross section. The anteromedial face of the tibial shaft is flattened, whereas the posterolateral face is rounded.
The proximal section of the right fibula is preserved, but most of the shaft distal to the m. iliofibularis tubercle is missing ( Fig 11 View Figure A– 11 C). Its proximal articular surface is an anteroposteriorly elongate ellipse, with a weak saddle-shaped concavity in the middle. A strong tab-like triangular flange projects posteriorly and slightly ventrally from the posterior edge of the proximal articular facet ( Fig 11 View Figure A). This flange is rounded and rugose proximally, and separated from the main articular facet by a shallow cleft. Distally, this flange grades smoothly into the posterior edge of the fibular shaft as a sharp ridge. The medial face of this flange bears a shallow sulcus that runs parallel to the much larger and more expansive medial fibular fossa. A similar sulcus is also present in Giganotosaurus ( MUCP Pv CH 1). This shallow sulcus terminates distally before the ridge attenuates. Opposite this, the lateral side of the ridge is also marked by a proximodistally elongate fossa that is shallow and may be a site of muscle attachment.
The medial fibular fossa is extremely large and deep, and takes up almost the entire medial surface of the fibula, though it does not appear to invade any part of the robust posterior flange ( Fig 11 View Figure A). The medial fossa is deepest proximally, and grades out onto the medial shaft of the fibula slightly above the level of the m. iliofibularis tubercle. The proximal rim of the fossa is sharp and forms a hood over a portion of the fossa. Unlike non-tetanuran theropods such as Syntarsus , Masiakasaurus , and Ceratosaurus , there is no oblique ridge bordering the proximal rim of the medial fossa.
The m. iliofibularis tubercle is formed as an elongate, triangular flange ( Fig 11 View Figure A and 11 B), as in Deltadromeus (SGM Din 2), Elaphrosaurus (MB.R. unnumbered), and Masiakasaurus . The rostral face of the flange bears a broad, shallow sulcus bordering the medial surface of the fibula. Distal to the m. iliofibularis tubercle, the shaft of the fibula is D-shaped in cross section and its lateral face is slightly convex, whereas its medial edge is flat.
The left third metatarsal is almost complete ( Fig 12 View Figure ). Its proximal articular surface is weakly concave, with raised anterior and posterior borders ( Fig 12 View Figure C and 12 D). It is weakly figure 8 -shaped in proximal view ( Fig 12 View Figure E), with slightly indented medial and lateral borders and convex rostral and caudal borders. The posterior edge of the proximal articulation is markedly wider than the anterior one and about as wide as the distal articulation, as seen in some ceratosaurs including Elaphrosaurus (MB.R. unnumbered) and Majungasaurus . By contrast, most tetanurans have a third metatarsal with an "hourglass" shape in proximal aspect, with a wider anterior edge, a pinched middle section, and a posterior edge that is narrower than the anterior one , though Acrocanthosaurus is a notable exception to this pattern . The raised anterior and posterior borders significantly overhang the shaft ( Fig 12 View Figure C and 12 D), with the caudal edge bordering a massive, squared-off posterior process ( Fig 12 View Figure A), similar to ones observed in Liliensternus (MB R 2175), and especially Elaphrosaurus (MB.R. unnumbered). This block is extremely robust and rugose, and forms a distinct shelf that abruptly transitions to the metatarsal shaft, which is heavily marked by striations below it.
The robust metatarsal shaft is slightly bowed medially, an effect that is accentuated by a distal medial flange on the anterior surface ( Fig 12 View Figure B). Approximately seven to eight centimeters below the proximal end there is a low circular tuberosity on the anterior face of the metatarsal shaft. The medial articular surface for Metatarsal II is much more distinct than the lateral articular surface for Metatarsal IV, and the former extends as a broad concavity over almost the
entire medial face of the shaft. The posteromedial edge of the metatarsal shaft forms a distinct ridge for insertion of the digital flexors ( Fig 12 View Figure A). A weaker ridge makes up the posterolateral edge of the metatarsal shaft, though it is not as extensive proximally. The posterior face of the shaft between these two ridges is mostly flat. The proximal end of the proximolateral ridge
curls across the lateral face of the metatarsal shaft moving proximally and does not make contact with the proximal end of the metatarsal. The anteromedial edge of the metatarsal shaft,
which marks the anterior border to the articular sulcus for metatarsal II, is not well developed proximally, but is better developed on the distal half of the metatarsal shaft and projects
strongly medially as a distinct flange in anterior aspect. The flange grades smoothly back into the metatarsal shaft distally, just proximal to the expansion of the distal articular end of the
metatarsal. A weak extensor fossa is present on the anterior face of the distal metatarsal ( Fig 12 View Figure E and 12 F). It is bounded laterally and medially by two marked tuberosities, as in many theropods including Allosaurus , Piatnitzkysaurus ( MACNAbout MACN CH 895), and Torvosaurus .
The lateral of these tuberosities is more robust and situated further proximally than the medial tuberosity. The distal end of the extensor fossa grades relatively smoothly onto the proximal end of the distal articular surface (i.e., the latter surface does not create a distinct proximal "shelf" connecting to the metatarsal shaft). Posteriorly, the transition from shaft to distal articular surface is slightly constricted.
The distal end of the metatarsal is transversely expanded, and the distal articulation is much broader than deep in distal aspect, a condition also observed in Elaphrosaurus (MB.R. unnumbered), Majungasaurus , and Torvosaurus  ( FMNHAbout FMNH PR 3060). The articular surface is smoothly rounded distally and lacks a distinct ginglymus and its exposure is triangular with a proximal apex ( Fig 12 View Figure A). Collateral ligament pits are well developed and appear to be relatively symmetrical in development, though both are still partially obscured by matrix.
The distalmost portion of the right metatarsal III is also preserved ( Fig 13 View Figure ). It is slightly larger than the left element, particularly in its mediolateral breadth. The overall morphology is similar to the left element with several notable exceptions. The collateral ligament pits in the right element are much deeper and more distinctly rimmed. Also, the proximolateral tuberosity bounding the extensor fossa is not present in the right element, though the smaller distomedial tuberosity is present.
Only the distal end of the right metatarsal II is preserved ( Fig 13 View Figure ). The shaft is quadrangular in cross section and deeper than wide. The anterior, medial, and posterior faces of the shaft are rounded, whereas the lateral border is flat throughout its preserved length. On the posterior face, a strong posterolateral edge that defines the posterior border of the flat articular surface for MT III is evident and is more pronounced along its distal half. There is no extensor fossa above the distal articular surface. The distal articulation is slightly asymmetrical and weakly canted medially. The anterior and distal portions of the distal articular surface are bulbous and undivided. The posterior hemicondylar rims are also asymmetrically developed on the distal surface ( Fig 13 View Figure A). The narrower medial hemicondyle extends further posteriorly and proximally than the lateral one, though the posteriormost tip of the lateral hemicondyle is broken off. The posterior end of the medial hemicondyle is everted slightly medially. A wide sulcus separates the hemicondyles in plantar view. The collateral ligament pits are asymmetrically developed. Both are deep and bear distinct rims, but the lateral pit is distinctly longer proximodistally and more teardrop-shaped, whereas the medial pit is largely circular.
All phalanges of the three principal digits of the right foot are preserved, though the tips of unguals II- 3 and IV- 5 are broken ( Fig 13 View Figure ). All preserved non-terminal phalanges with the exceptions of IV- 3 and IV- 4 are elongate and slender, with their shafts constricted between the expanded articular ends in dorsal view, unlike the short and stout phalanges of carcharodontosaurids [2, 35], and abelisaurids such as Majungasaurus . They also exhibit well-defined collateral ligament pits and extensor pits just proximal to the dorsal ends of the distal articulations ( Fig 13 View Figure B and 13 C). The unguals are short, curved and triangular rather than elliptical in cross section, and the ungual of pedal digit II is symmetrical unlike those of abelisauroids . Very weak flexor tubercles are present, but the claw sheath grooves are not caudally forked as in abelisauroids . The grooves are well defined and the proximal portion of their ventromedial and ventrolateral edges form little spurs on the ventral aspect of the ungual ( Fig 13 View Figure A) as in Beishanlong .
Addition of Gualicho and Deltadromeus to the Carrano et al.  character-taxon matrix resolves them as basal carcharodontosaurians and sister to the neovenatorid radiation ( Fig 14 A). This result is recovered whether the nine new characters are included or not. Whereas the phylogenetic position of these two fragmentary specimens appears well resolved, support is relatively low, with Bremer support  values of 1 for most nodes along the spine of the tetanuran radiation. However, the sister-taxon relationship between Gualicho and Deltadromeus is relatively robust (branch support = 3), despite the fact that both specimens are incomplete. Addition of Gualicho introduces some character conflict, with tree length increasing from 1044 to 1063 steps, and addition of both Deltadromeus and Gualicho increases tree length to 1075 steps. Comparison to the tree length increases associated with inclusion of other taxa as calculated with a modified version (see S 6 File) of the ‘Term_lengths’ script (http://phylo.wdfiles. com/local—files/tntwiki/Term_lengths.run) suggests that the tree length increments associated with Gualicho (9 steps) and Deltadromeus (10 steps) are well below increments associated with other taxa such as Dilophosaurus (29 steps), Ceratosaurus (19 steps), and Majungasaurus (25 steps). The conflict is borne in characters for which Gualicho , and more specifically, Deltadromeus , exhibit character states that are either plesiomorphic for tetanurans or shared with Ceratosauria. Indeed, if Gualicho is excluded from the analysis, Deltadromeus groups with
ceratosaurs, mirroring previously published results [8, 30]. Constraining these two taxa to both be ceratosaurs results in an increase in tree length to 1079 steps.
In the analysis of the modified Porfiri et al.  dataset, Gualicho was recovered near the base of Coelurosauria ( Fig 14 B), well removed from either didactyl tyrannosaurids, or the
megaraptoran clade it was close to in the Carrano et al.  dataset. Surprisingly, however, our reanalysis following changes to the matrix found Neovenator as sister taxon to a clade of coelurosaurs plus Gualicho and megaraptorans rather than as a member of Allosauroidea. We did not find support for megaraptorans as members of Tyrannosauroidea as previously reported [11, 12] after rescoring a number of characters in those analyses (see S 1 Text) and running all traits as unordered, although megaraptorans were found to be closer to tyrannosauroids than to the included carcharodontosaurids. The very different results of these two analyses are predicated on significant differences in both taxon- and character sampling, and only a more comprehensive analysis beyond the scope of this description can resolve the disagreement.
|Semilunate carpal (left)|
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