The Late Triassic dinosauromorph Sacisaurus agudoensis (Caturrita Formation; Rio Grande do Sul, Brazil): anatomy and affinities

Abstract

Silesauridae is an exclusively Triassic group of dinosauromorphs, knowledge on the diversity of which has increased dramatically in the last few years. Silesaurid relationships are still contentious, as a result in part of different homology statements, particularly regarding the typical edentulous mandible tip of these animals. One of the most complete silesaurids yet discovered is Sacisaurus agudoensis from the Caturrita Formation (Late Triassic: Norian) of Rio Grande do Sul, Brazil, represented by numerous isolated bones recovered from a single site. The anatomy of S. agudoensis is fully described for the first time here, and comparisons are provided to other basal dinosauromorphs. S. agudoensis is a small-bodied animal (less than 1 m in length) that possesses a dentition consisting of leaf-shaped crowns with large denticles in the carinae, a plesiomorphic propubic pelvis with an almost fully closed acetabulum, elongate distal hindlimbs suggesting well-developed cursorial ability, and a laterally projected outer malleolus in the tibia. All previous numerical phylogenies supported a non-dinosaur dinosauromorph affinity for Silesauridae, but the reanalysis of one of those studies suggests that a position within Dinosauria is not unlikely, with silesaurids forming the basal branch of the ornithischian lineage.

A juvenile sauropodomorph tibia from the 'Botucaraí Hill', Late Triassic of Southern Brazil

“…This morphology contrasts with that observed in lagerpetids, many silesaurids (e.g. Asilisaurus kongwe Nesbitt et al, 2010, Silesaurus opolensis, and Sacisaurus agudoensis), herrerasaurids, and theropods, in which both condyles are positioned at the caudal margin of the proximal end of the tibia (Dzik, 2003;Langer & Benton, 2006;Nesbitt et al, 2010;Langer & Ferigolo, 2013). A shallow intercondylar notch ( Figures 1C, E) separates both condyles of MMACR-PV-028-T caudally.…”

The femoral anatomy of Pampadromaeus barberenai based on a new specimen from the Upper Triassic of Brazil

“…The femoral morphology of CAPPA/UFSM 0027 does not match that of basal ornithischians due the following features: (i) presence of the posteromedial tuberosity (Langer and Benton 2006); (ii) anterior trochanter not wing-like (Langer and Ferigolo 2013); (iii) presence of a well-developed trochanteric shelf, which is absent or present just as a discrete scar in basal ornithischians (Langer and Benton 2006) and (iv) the fourth trochanter that is not pendant (Ezcurra 2012). These traits suggest an early saurischian affinity for CAPPA/UFSM 0027, which is fully supported by the present phylogenetic analyses.…”

“…The proximal portion of the anterior trochanter is fully connected to the shaft, as in the holotype of Pampadromaeus barberenai (Figure 3(B)) and Tawa hallae. In Saturnalia tupiniquim, the proximal tip is separated from the shaft by a small cleft (Figure 3(C)) (Langer and Ferigolo 2013), as seen in Coelophysis bauri and in some silesaurids (Ezcurra 2006;Langer and Ferigolo 2013). The extreme condition (known as 'winglike') is present in ornithischians and Jurassic theropods, where the anterior trochanter is well pronounced with a large cleft between its anterior portion and the femoral shaft (Langer and Ferigolo 2013).…”

“…In Saturnalia tupiniquim, the proximal tip is separated from the shaft by a small cleft (Figure 3(C)) (Langer and Ferigolo 2013), as seen in Coelophysis bauri and in some silesaurids (Ezcurra 2006;Langer and Ferigolo 2013). The extreme condition (known as 'winglike') is present in ornithischians and Jurassic theropods, where the anterior trochanter is well pronounced with a large cleft between its anterior portion and the femoral shaft (Langer and Ferigolo 2013). In contrast, Staurikosaurus pricei bears only a rugose surface on the corresponding (Bittencourt and Kellner 2009).…”

Wachholz, a new exquisite dinosaur-bearing fossiliferous site from the Upper Triassic of southern Brazil

“…At first, Sacisaurus was interpreted as an ornithischian dinosaur, however subsequent authors placed it within Silesauridae (Brusatte et al, 2010;Nesbitt et al, 2010;Benton and Walker, 2011;Nesbitt, 2011;Kammerer et al, 2012;Martínez et al, 2013;Peecook et al, 2013). Langer and Ferigolo (2013) redescribed Sacisaurus, reinstating its ornithischian affinities. (Cisneros and Schultz, 2003), the lepidosauriform Cargninia enigmatica (Bonaparte et al, 2010a), the sphenodontian Clevosaurus riograndensis (Bonaparte and Sues, 2006), an indeterminate phytosaur (Kischlat and Lucas, 2003), the putative pterosaur Faxinalipterus minima (Bonaparte et al, 2010b), some indeterminate archosaur teeth (Dornelles, 1990), the dicynodont Jachaleria candelariensis (Araújo et al, 1980), and the small cynodonts Riograndia guaibensis (Bonaparte et al, 2001), Brasilodon quadrangularis (Bonaparte et al, 2003), Brasilitherium riograndensis (Bonaparte et al, 2003), Irajatherium hernandezi (Martinelli et al, 2005) and Minicynodon maieri (Bonaparte et al, 2010a).…”