Abstract Amphisbaenians are fossorial squamates characterized by extreme cranial specialization, particularly in snout morphology. Whether variation in external rostral form predicts internal cranial anatomy remains poorly understood. We present the first large-scale comparative analysis of amphisbaenian endocranial morphology, using three-dimensional landmark data from endocasts of 50 species representing all major families and snout morphotypes. Endocasts within Amphisbaenia share general squa