Endocast of the Late Triassic (Carnian) dinosaur Saturnalia tupiniquim: implications for the evolution of brain tissue in Sauropodomorpha

Abstract

The evolutionary history of dinosaurs might date back to the first stages of the Triassic (c. 250–240 Ma), but the oldest unequivocal records of the group come from Late Triassic (Carnian – c. 230 Ma) rocks of South America. Here, we present the first braincase endocast of a Carnian dinosaur, the sauropodomorph Saturnalia tupiniquim, and provide new data regarding the evolution of the floccular and parafloccular lobe of the cerebellum (FFL), which has been extensively discussed in the field of palaeoneurology. Previous studies proposed that the development of a permanent quadrupedal stance was one of the factors leading to the volume reduction of the FFL of sauropods. However, based on the new data for S. tupiniquim we identified a first moment of FFL volume reduction in non-sauropodan Sauropodomorpha, preceding the acquisition of a fully quadrupedal stance. Analysing variations in FFL volume alongside other morphological changes in the group, we suggest that this reduction is potentially related to the adoption of a more restricted herbivore diet. In this context, the FFL of sauropods might represent a vestigial trait, retained in a reduced version from the bipedal and predatory early sauropodomorphs.

New Specimen Sheds Light on the Anatomy and Taxonomy of the Early Late Triassic Dinosauriforms from the Chañares Formation, NW Argentina

“…The PSC is strongly bowed posteriorly in dorsal view (Figs. L and L: psc), as also occurs in Saturnalia tupiniquim (Bronzati et al ., ). In contrast, the PSC is only slightly posteriorly bowed in Euparkeria capensis (Sobral et al ., ) and Triopticus primus (Stocker et al ., ).…”

“…Like in other archosaurs, the floccular recess is equally formed by the supraoccipital and prootic (Nesbitt, ). The size and depth of this recess, projecting into the space of the semi‐circular canals of the inner ear, indicates the presence of a relatively large cerebellar flocculus and associated soft tissue, as occurs in the holotype of Lewisuchus admixtus (PULR 01), Marasuchus lilloensis (PVL 3872), Silesaurus opolensis (ZPAL Ab III/364/1), and early dinosaurs (e.g., Saturnalia tupiniquim : Bronzati et al ., ; Herrerasaurus ischigualastensis : Stocker et al ., , Supporting Information Fig. S1).…”

“…S1). In contrast, the dorsoventral asymmetry between the ASC and PSC is more pronounced in the nonarchosaurian archosauriform Triopticus primus (Stocker et al ., ), the early dinosaurs Saturnalia tupiniquim (Bronzati et al ., ) and Herrerasaurus ischigualastensis (Stocker et al ., , Supporting Information Fig. S1), and the neotheropods Sinosaurus triassicus (Xing et al ., ) and Majungasaurus crenatissimus (Sampson and Witmer, ).…”

Peer Review #3 of "The braincase of Mesosuchus browni (Reptilia, Archosauromorpha) with information on the inner ear and description of a pneumatic sinus (v0.2)"

“…The thickness, curvature and angulation of the semicircular canals have all been used to infer these abilities (Boistel et al, 2011). Likewise, the size of the floccular fossa has also been used as a parameter for assessing gaze stabilization mechanisms (Bronzati et al, 2017, Witmer et al, 2003.…”

Dinossauromorfos triássicos do sul do Brasil e padrões biogeográficos da irradiação dos dinossauros

“…e Bagualosaurus agudoensis . Ao contrário de outros membros mais recentes da linhagem que eram herbívoros, de grandes dimensões, e pesando várias toneladas, estes primeiros sauropodomorfos eram pequenos animais com cerca de 1 metro de comprimento e adaptados para a faunivoria Bronzati et al 2017;.…”