An unusual historic dicynodont specimen (Therapsida: Dicynodontia) from the Dinodontosaurus Assemblage Zone of the Santa
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RESEARCH PAPER
An unusual historic dicynodont specimen (Therapsida: Dicynodontia) from the Dinodontosaurus Assemblage Zone of the Santa Maria Formation (Middle Triassic) of Rio Grande do Sul, Brazil Michael W. Maisch1 Received: 26 January 2020 / Accepted: 22 June 2020 © Paläontologische Gesellschaft 2020
Abstract An unusual dicynodont specimen from the historical collection of von Huene and Stahlecker (1928/1929) is described from the Middle Triassic Dinodontosaurus Assemblage Zone of the Santa Maria Formation of Chiniquá, Rio Grande do Sul, Brazil. Hitherto only two dicynodont species, the stahleckeriid Stahleckeria potens and the more basal kannemeyeriiform Dinodontosaurus turpior, were recorded from this faunal assemblage. The specimen consists of an isolated partial brain case and intertemporal skull roof, a left nasal and a preparietal. In contrast to Stahleckeria, a preparietal is present, the intertemporal skull roof is extremely narrow and the postorbitals are short posteriorly. In contrast to Dinodontosaurus, the interparietal is narrow and intrudes far onto the intertemporal skull roof, the tabular is separately ossified and the entire intertemporal region is extremely narrow. The form represents a rare, hitherto unrecorded component of the fauna. Comparison to other known Middle Triassic dicynodonts shows that it cannot be referred to any known taxon, showing a unique combination of characters. Close resemblance is found to some other South American taxa, particularly to Jachaleria candelariensis from the Riograndia Assemblage Zone of the Caturrita Formation. Keywords Dicynodontia · Kannemeyeriiformes · Diversity · Middle Triassic · Santa Maria Formation · Rio Grande do Sul
Introduction The Triassic deposits of southern Brazil have yielded a diverse tetrapod fauna (Beltrão 1965; Bonaparte 1970; Barberena et al. 1985a, b; Langer et al. 2007; Martinelli et al. 2017). Investigation of these fossils commenced at the beginning of the twentieth century (Woodward 1907, 1908; von Huene 1926, 1928, 1929; Tupí-Caldas 1936). A major pioneering contribution was made by German paleontologists Friedrich von Huene and Rudolf Stahlecker, who visited Rio Grande do Sul in 1928 and 1929, conducting extensive excavations in the Middle Triassic deposits of the Santa Maria Formation (Fig. 1) and discovering an entire new fauna of Triassic tetrapods. The material collected during this expedition was later split between the Handling Editor: Irina Ruf. * Michael W. Maisch maisch@uni‑tuebingen.de 1
Albstadt‑Tailfingen, Germany
Paleontological Department of Tübingen University, which holds the majority of therapsid and rhynchosaur material, and the Bayerische Staatssammlung für Paläontologie und Geologie Munich, where most of the archosaur material was deposited. The results of the expedition were published from 1935 to 1942 in a series of monographs (von Huene 1935, 1936, 1942a, b), which covered the majority of finds. Nonetheless, a substantial part of von Huene’s collection remains undescribed to the present day. The
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