Contributions to the sensory paleobiology of Sauropodomorpha from the study of the endocranium of the Early Jurassic eusauropod Bagualia alba

Abstract

Most palaeoneurological studies of sauropodomorphs have focused on neosauropods, while very little is known about Triassic and Early Jurassic taxa. We examined the palaeoneurology of the basal eusauropod Bagualia alba from the Lower Jurassic of Patagonia, based on the digital reconstruction of its brain and inner ear. The temporal and phylogenetic position of Bagualia enables us to identify neuroanatomical and sensory changes that occurred during the evolution of Sauropodomorpha, from small-bodied Triassic forms to eusauropods weighing over 10 tonnes. The hypertrophied pituitary gland in Bagualia suggests that this feature appeared early in the evolution of eusauropods. Additionally, the poorly developed floccular lobe and the shortened semicircular canals of the inner ear in Bagualia may be related to its obligatory quadrupedal posture and columnar limbs, which probably contributed to low agility in responding to external stimuli, particularly in terms of eye and head movements. Based on its encephalization quotient, Bagualia has greater brain volume than expected for taxa of similar body size, and this quotient was not correlated with body size in the sauropodomorphs studied. In contrast, a sense of smell was important in Bagualia, but not as crucial as in small-bodied, faunivorous early sauropodomorphs from the Late Triassic; this may be related to its bulk herbivorous diet. This study demonstrates that the sensory evolution of sauropods is likely to have occurred gradually and was slower than changes in body mass, with dietary shifts playing a partial role in the long evolutionary history of the group.