All About That Base: Dietary Plasticity, Basicranial Flexion and Sphenoid Form

OBJECTIVES: The mammalian sphenoid is a morphologically and embryologically complex bone bridging the cranial vault and face. Sphenoid phenotypic diversity has been attributed to the coaction of natural selection and developmental variation in adjacent cranial organs and bones. These associations underscore enduring interest in the evolutionary, ontogenetic, and clinical importance of the sphenoid. We address key gaps regarding several structural and adaptive factors that differentially characterize postnatal ontogeny when brain growth is negligible and has a correspondingly diminished impact. MATERIALS AND METHODS: We employ microCT data from a well-known rabbit model of long-term dietary plasticity to address variation in two putative influences on the sphenoid: face length on basicranial flexion and osteogenesis in the pterygoid plates and sphenoid joints. Examining the roles of cyclical loading and feeding modality on basicranial flexion and sphenoid robusticity contributes uniquely to understanding the multifactorial nature of skull growth and form in mammals. RESULTS: Postnatal increases in facial length do not drive corresponding decreases in basicranial flexion, suggesting that flexion is primarily established during prenatal development due to changes in encephalization. Sphenoid joints and pterygoid plates exhibit diet-related plasticity, highlighting adaptive changes due to elevated cyclical loading and feeding modality that vary depending on the bony site as well as the hierarchical level of a given region of interest. DISCUSSION: Our findings highlight the importance of cyclical loading and feeding modality in shaping postnatal craniofacial development, necessitating the consideration of these factors in studies of structure and function across extant and extinct mammalian taxa.