Much more than their fangs: Macroscopic anatomy of the brain of Bothrops moojeni Hoge 1966 (Squamata, Serpentes, Viperidae).

Neuroanatomical research has progressed considerably in several vertebrate lineages, yet studies of reptilian brain morphology remain markedly underdeveloped. Here we provide the first description of macroscopic brain anatomy and its ontogeny in the viperid Bothrops moojeni, based on a sample of seven individuals. Our results indicate that brain morphology undergoes significant size-related reshaping during growth: absolute measures revealed strong positive scaling of brain length, cerebral hemisphere length, cerebellum length, and medulla oblongata length with body and head size. However, when expressed relative to overall brain dimensions, most regions exhibited weak or no association with size, indicating relatively stable proportional relationships, while the olfactory bulbs and medulla oblongata became relatively more developed in adults. These relative increases likely reflect increased demands for chemosensory processing and autonomic regulation as individuals shift from consuming ectothermic to endothermic prey. In contrast, structures such as the cerebellum width, posterior colliculi, and epiphysis remained stable across ontogeny, suggesting conserved functional roles. Collectively, these findings reveal a mosaic pattern of brain development in females of B. moojeni, in which certain regions expand preferentially while others remain constrained, underscoring that encephalic growth is shaped by functional priorities and evolutionary trade-offs, consistent with patterns described in other vertebrates.