Revisiting the neuroanatomy of Massetognathus pascuali (Eucynodontia: Cynognathia) from the early Late Triassic of South America using Neutron Tomography

Abstract

This paper analyzes the paleoneurology (cranial endocast and maxillary canal) of Massetognathus pascuali, an iconic non-mammaliaform cynodont from the early Late Triassic of South America, using Neutron Tomography. The application of neutron tomography holds the potential for uncovering more refined anatomical and quantitative data. The newly examined cranial endocast shows a forebrain with a tubular shape without an interhemispheric fissure, presence of a pineal body (with a closed parietal foramen), and a marked unossified zone. In comparison with a smaller, putatively juvenile specimen previously studied (PVL 4016), the new endocast exhibits a similar degree of encephalization, indicating little change in relative brain size between both ontogenetic stages. In the context of cynognathian brain evolution, M. pascuali maintained a low encephalization quotient, typical of early cynognathians, contrasting with the higher values of some Late Triassic taxa. The maxillary canal of M. pascuali is described here for the first time. It is considerably ramified, although slightly less than in some early cynognathians, following the general pattern of non-probainognathians and suggesting the absence of a flexible rhinarium or mobile vibrissae. By integrating endocast data with the maxillary canal, this study offers enhanced insights into the neurosensory ecology of M. pascuali, thereby deepening our understanding of its biology and ecological interactions.