Exploring the palaeoneurology of the extinct spiny rat Eumysops chapalmalensis (Hystricognathi: Echimyidae): a comparative phylogenetic analysis of brain size and shape.

This study focuses on the brain morphology of the extinct South American Echimyidae rodent *Eumysops chapalmalensis* from the Pliocene, using virtual endocasts and comparisons with extant echimyid species. Analyses reveal that *Eumysops* exhibits low encephalization but high spatial packing of the brain, with a distinctive brain shape characterized by strong flexion, posterolateral expansion of the neocortex, and large petrosal lobules. Phylogenetic comparative analyses indicate a low phylogenetic signal for brain shape but a significant influence of ecological factors, suggesting adaptive pressures related to its terrestrial to fossorial habits and occupation of open environments shaped its unique brain morphology. These findings highlight *Eumysops* as occupying a niche not exploited by living echimyids, emphasizing the role of fossils in understanding evolutionary diversity and specialization within the family.