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THE PECTORAL GIRDLE and FORELIMB ANATOMY of the STEM-SAUROPODOMORPH SATURNALIA TUPINIQUIM (UPPER TRIASSIC, BRAZIL) by MAX C

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THE PECTORAL GIRDLE and FORELIMB ANATOMY of the STEM-SAUROPODOMORPH SATURNALIA TUPINIQUIM (UPPER TRIASSIC, BRAZIL) by MAX C [Special Papers in Palaeontology 77, 2007, pp. 113–137] THE PECTORAL GIRDLE AND FORELIMB ANATOMY OF THE STEM-SAUROPODOMORPH SATURNALIA TUPINIQUIM (UPPER TRIASSIC, BRAZIL) by MAX C. LANGER*, MARCO A. G. FRANC¸A* and STEFAN GABRIEL *FFCLRP, Universidade de Sa˜o Paulo (USP), Av. Bandeirantes, 3900, Ribeira˜o Preto 14040–901, SP, Brazil; e-mails: [email protected]; [email protected] School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK; e-mail: [email protected] Typescript received 24 February 2006; accepted in revised form 27 October 2006 Abstract: Description of the pectoral girdle (scapulocora- Although less clear than previously suggested, some traits coid) and forelimb (humerus, radius and ulna) elements of S. tupiniquim, such as a long deltopectoral crest and a of two specimens of Saturnalia tupiniquim, a stem-sauro- broad distal humeral end, are indicative of its sauropodo- podomorph from the Upper Triassic Santa Maria For- morph affinity. The taxon also bears several features previ- mation, southern Brazil, reveals a distinctive set of ously regarded as autapomorphic of Herrerasaurus plesiomorphic, derived and unique traits, which shed light ischigualastensis, alluding to their broader distribution on the function and phylogenetic significance of these skel- among basal dinosaurs. Variations within S. tupiniquim are etal elements within early dinosaurs. Autapomorphic fea- mainly robustness-related and do not necessarily imply tures of S. tupiniquim include, among others, an unusually taxonomic distinctions. long olecranon process of the ulna. Its function is still unclear, but it might have helped to sustain a quadrupedal Key words: Saturnalia tupiniquim, Dinosauria, Brazil, Trias- gait, as inferred from the structure of the entire forearm. sic, pectoral girdle, forelimb, anatomy. THE shoulder girdle and forelimb osteology of early tupiniquim is available (Langer 2003). Among the other dinosaurs is poorly known. Apart from the relatively elements resulting from preparation of two of the skele- abundant material referred to Herrerasaurus ischiguala- tons are partial shoulder girdles and forelimbs, which are stensis (Reig 1963; Novas 1986; Brinkman and Sues 1987; the subject of the present contribution. Sereno 1993), and the still undescribed skeleton of Eorap- Until now, because of the abundance of its material, tor lunensis (Sereno et al. 1993), most of the reported Herrerasaurus has been the main basis on which the remains are incomplete. A nearly complete scapulocora- anatomy of the shoulder girdle and forelimb of basal coid is part of the holotype of Guaibasaurus candelariensis dinosaurs was assessed. The constraint of using the con- (Bonaparte et al. 1999), but only scapula fragments and a dition in a single taxon, with its own set of derived and dubious proximal humerus were assigned to Staurikosau- unique features, as almost the sole window on the ples- rus pricei (Galton 2000; Bittencourt 2004). Within other iomorphic anatomy of a clade as diverse as the Dinosau- putative Triassic dinosaurs, incomplete scapula and fore- ria might lead to significant biases. The data available limb elements are among the material referred to Saltopus for S. tupiniquim is believed to alleviate this bias, adding elginensis (von Huene 1910), Spondylosoma absconditum morphological diversity to produce a better picture of (Galton 2000) and Agnosphitys cromhallensis (Fraser et al. the general anatomy of the shoulder girdle and forelimb 2002). of basal dinosaurs in general, and basal saurischians in In the austral summer of 1998, fieldwork conducted by particular. the Museu de Cieˆncias e Tecnologia, Pontifı´cia Universi- dade Cato´lica do Rio Grande do Sul, collected three partial Institutional abbreviations. BMNH, the Natural History Museum, skeletons of a basal dinosaur in the red mudstone that London, UK; MACN, Museo Argentino de Ciencias Naturales typically crops out on the outskirts of Santa Maria (Text- ‘Bernardino Rivadavia’, Buenos Aires, Argentina; MB, Museum fig. 1), in south Brazil (Langer et al. 1999; Langer 2005a). fu¨r Naturkunde, Berlin, Germany; MCN, Fundac¸a˜o Zoobotaˆnica The material is only partially prepared, but a comprehen- do Rio Grande do Sul, Porto Alegre, Brazil; MCP, Museu de Cieˆncias e Tecnologia PUCRS, Porto Alegre, Brazil; PVL, sive description of the pelvis and hindlimb of Saturnalia ª The Palaeontological Association 113 114 SPECIAL PAPERS IN PALAEONTOLOGY, 77 TEXT-FIG. 1. Map showing the fossil-bearing sites on the eastern outskirts of Santa Maria, Rio Grande do Sul, Brazil. Shaded parts indicate urban areas. GS: ‘Grossesanga’, type locality of Staurikosaurus pricei Colbert, 1970; WS: ‘Waldsanga’, type locality of Saturnalia tupiniquim. Fundacı´on Miguel Lillo, Tucuma´n, Argentina; PVSJ, Museo de Ciencias Naturales, San Juan, Argentina; QG, National Museum of Natural History, Harare, Zimbabwe; SMNS, Staatlisches Museum fu¨r Naturkunde, Stuttgart, Germany. MATERIAL AND METHODS 45° The shoulder girdle and forelimb elements of the holo- 110° type of Saturnalia tupiniquim (MCP 3844-PV) include a nearly complete right scapulocoracoid, humerus and radius, and a right ulna lacking its distal third. Additional material belongs to one of the paratypes (MCP 3845-PV), 140° and includes two nearly complete scapulocoracoids, a 100° partial right humerus and the proximal portion of the right ulna. No carpals, metacarpals or phalanges have been recovered, and there is also no trace of any of the dermal elements of the shoulder girdle. If not explicitly TEXT-FIG. 2. Saturnalia tupiniquim, Santa Maria Formation, mentioned, the described features and elements are shared Rio Grande do Sul, Brazil. Lateral view of the right pectoral by both specimens. girdle and partial forelimb reconstructed based mainly on MCP Directional and positional terms used herein are those 3844-PV. Bones assembled in two different poses, corresponding defined in Clark (1993) and the dinosaur compendium of to maximum angles of limb retraction and forearm extension, Weishampel et al. (2004). Considering the rather uncer- and limb protraction and forearm flexion. Shaded (see-through) tain, although most probably oblique (Colbert 1989), area represents the missing distal part of the ulna, and orientation of the shoulder girdle in basal dinosaurs scapulocoracoid long axis is at an angle of about 25 degrees to (Text-fig. 2), it is treated as vertical for descriptive purpo- the horizontal. ses (Nicholls and Russell 1985). Accordingly, the coracoid lies ventral to its articulation with the scapula, whereas (Romer 1966; Coombs 1978; Gauthier 1986). Regarding the scapula blade expands dorsally. This orientation is the forelimb, the arm and forearm are described with chosen, rather than one that more closely reflects avian their long axes orientated vertically (Sereno 1993), and anatomy (Ostrom 1974), because it is plesiomorphic for with the long axis of the elbow joint being orthogonal to archosaurs (Romer 1956) and also more traditional the sagittal plane. This does not reflect their natural posi- LANGER ET AL.: PECTORAL GIRDLE AND FORELIMB OF SATURNALIA TUPINIQUIM 115 tion (see Text-fig. 2), but should render the description SYSTEMATIC PALAEONTOLOGY easier to follow. Hence, the deltopectoral crest expands cranially from the humerus and the forearm moves cau- DINOSAURIA Owen, 1842 dally during extension. SAURISCHIA Seeley, 1887 The remains of S. tupiniquim are well preserved (Lan- EUSAURISCHIA Padian, Hutchinson and Holtz,1999 ger 2003) and lack evidence of major taphonomic distor- stem SAUROPODOMORPHA von Huene, 1932 tions. This allows the recognition of various osteological traces left by the attachments of major muscle groups, Genus SATURNALIA Langer, Abdala, Richter and and some insights on pectoral girdle and limb myology Benton,1999 are presented here (Text-fig. 3). The tentative identifica- tion of the musculature corresponding to these traces Saturnalia tupiniquim Langer, Abdala, Richter and Benton, represents inferences based on a ‘phylogenetic bracket’ 1999 approach (Felsenstein 1985; Bryant and Russell 1992; Wit- Text-figures 2–9, Tables 1–3 mer 1995; Hutchinson 2001). Crocodiles and birds are evidently the main elements of comparison, because they Referred specimens. The type series is composed of the holotype are the only extant archosaurs and the closest living rela- (MCP 3844-PV) and two paratypes (MCP 3845-PV and 3846- tives of S. tupiniquim. PV) (Langer 2003). A BCD H EF I G J TEXT-FIG. 3. Saturnalia tupiniquim, Santa Maria Formation, Rio Grande do Sul, Brazil. Muscle attachment areas on A–B, right scapulocopracoid, C–F, humerus, G–H, partial ulna, I, radius, and J, distal part of radius, reconstructed based mainly on MCP 3844- PV, in lateral (A, C, G, J), medial (B, E, H–I), caudal (D), and cranial (F) views. Light shading indicates areas of muscle origin and dark shading their insertion areas. b., biceps; br., brachialis; cbr.b.d., coracobrachialis brevis pars dorsalis; cbr.b.v., coracobrachialis brevis pars ventralis; cbr.l., coracobrachialis longus; delt.s., deltoideous scapularis; delt.s.i., deltoideous scapularis inferior; e.c.r., extensor carpi radialis; e.c.u., extensor carpi ulnaris; e.d.c., extensor digitorum communis; f.c.u., flexor carpi ulnaris; f.d.l., flexor digitorum longus; f.u., flexor ulnaris; h., humeroradialis; l.d. latissimus dorsi; p. pectoralis; pr.q., pronator quadratus; s., supinator; sc., supracoracoideus; sbs., subscapularis; sh.a., scapulohumeralis
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