Staurikosaurus

Abstract: The dinosaur record of the Santa Maria beds of Rio Grande do Sul (Mid–Late Triassic; south Brazil) includes the herrerasaur Staurikosaurus pricei, and two basal members of the sauropodomorph lineage: Saturnalia tupiniquim and Unaysaurus tolentinoi. The most enigmatic of the saurischian taxa is, however, Guaibasaurus candelariensis, previously regarded as either a basal theropod or a basal sauropodomorph. This study provides a detailed anatomical revision of all specimens originally referred to G. candelariensis by Bonaparte and co-authors, including its type-series and a more recently excavated partial postcranium. Although coming from different sites, these specimens share a unique combination of traits, and at least one possible autapomorphic feature of the pelvis, which support the inclusivity and uniqueness of the species. G. candelariensis was a medium-sized (nearly 2 m long) biped with an intriguing mix of plesiomorphic and derived (eusaurischian/theropod) features. Phylogenetic studies reveal weak support for the nesting of G. candelariensis within Theropoda, but this affinity is bolstered by various traits it shares with neotheropods. The Norian age of G. candelariensis corroborates previous studies that suggest the continuous radiation of more basal dinosauromorphs until the end of the Triassic, after the appearance of the three main dinosaur clades.

Abstract: The controversial dinosauriform Teyuwasu barberenai Kischlat, 1999 (Fig. 1B) is based on a right femur (BSPG AS XXV 53) and tibia (BSPG AS XXV 54), formerly referred to the pseudosuchian ‘Hoplitosuchus raui’ (= Hoplitosaurus raui) Huene, 1938 (see also Huene, 1942). This material comes from a classic Late Triassic (Carnian) locality in southern Brazil (Fig. 1A), the Cerro da Alemoa outcrop on the Alemoa complex, that has yielded several noteworthy tetrapod specimens (see Garcia et al., 2019, for a complete list of references). When reviewing these abovementioned materials, Kischlat (1999) considered it to belong to a “robust saurischian dinosaur”, but later this taxon was considered to be a nomen dubium (Langer et al., 2010; Ezcurra, 2012). Foremost, the initial description of this taxon is problematic, because Kischlat (1999) presented it in a symposium abstract which does not constitute a published work [which is not allowed under the Art. 9.10 of the International Commission on Zoological Nomenclature (ICZN)]. Moreover, the author did not list traits that clearly differentiated Teyuwasu from other coeval dinosauriforms (cf. Art. 13 of the ICZN, see further below). In particular, it was not adequately distinguished from Staurikosaurus pricei Colbert, 1970 (Fig. 1B), which also comes from the same Alemoa complex, but from another nearby outcrop (Sanga Grande/Sanga de Baixo) considered equivalent in stratigraphic level and horizon with the lower levels of the Cerro da Alemoa site (Huene, 1942; Colbert, 1970; see also Garcia et al., 2019) (Fig. 1A). However, Huene (1942) did not clearly specify that the materials (femur and tibia) later assembled by Kischlat (1999) into the holotype of Teyuwasu were found in close association, although Huene (1942) cited that they come from the same stratigraphical level and horizon, and to our interpretation, their morphology and preservational features are compatible. Still, assigning these bones as part of a single individual is tentative.

Abstract: Palaeosaurus (?) diagnosticus Huene from the Stubensandstone (Upper Triassic, Norian) of Nordwurttemberg, Germany is made the type species of a new genus of prosauropod dinosaurEfraasia, which is referred to the family Anchisauridae. The anatomy ofEfraasia diagnostica is conservative and it was an ideal ancestor for the later and more specializedAnchisaurus polyzelus of North America. The slenderness of the manus and pes ofEfraasia andAnchisaurus is matched amongst prosauropods only by the feet ofGyposaurus capensis andThecodontosaurus antiquus. Staurikosaurus pricei Colbert from the Upper Triassic of Brazil is probably a very primitive theropod dinosaur.

Abstract: Spondylosoma absconditum (Ladinian, Middle Triassic) lacks certain Dinosauriformes-Dinosauria characters (sigmoid curve and epipophyses in neck, distally placed deltopectoral crest on humerus) and those present (accessary hyposphene-hypantra vertebral articulations, three sacral vertebrae, elongate pubis) also occur in the Rauisuchia (Crurotarsi, Suchia, Rauisuchiformes).Spondylosoma is tentatively referred to the Rauisuchidae because, as indicated by the ventrolaterally directed sacral ribs, the ilium was held obliquely (and not vertically as in the Poposauridae).Staurikosaurus pricei (Carnian, Upper Triassic), one of the oldest dinosaurs, possesses autapomorphies of Dinosauriformes, Dinosauria, Saurischia, and Herrerasauridae, but it retains certain plesiomorphic characters (subcircular distal end to tibia, ?proximally placed deltopectoral crest, axially unshortened neural spine to sacral 1, ?scapular spine unreduced distally) not present inHerrerasaurus (Carnian, Ischigualasto Formation, Argentina). However, the femur is more derived in the loss of the trochanteric shelf and reduction of the lesser trochanter (as also occurs in some prosauropods). The two vertebrae sacrum ofStaurikosaurus is a plesiomorphic character for Dinosauria (also in other herrerasaurids, German Upper Triassic prosauropodSellosaurus gracilis — ?males), to which was added either a caudosacral (e.g. Santa Maria prosauropodSaturnalia, Sellosaurus gracilis — ?females) or a dorsosacral (e.g. Ischigualasto theropodEoraptor and prosauropodRiojasaurus). Agrosaurus (Upper Triassic, Durdham Down, England — not Australia) is not a herrerasaurid; it is referred to the prosauropod dinosaurThecodontosaurus antiquus (Upper Triassic, Durdham Down).