Evolutionary Signal and Development of the Foramen Dorsum Sellae (Nov.) Across Primates.

The sella turcica, a small depression within the sphenoid bone in mammal skulls, exhibits notable morphological variation across primates, including the occasional presence of accessory openings. We investigated one such foramen within the posterior wall of the sella turcica that has been variably described in humans and other primates. We scored foramen presence in humans (N = 114) and 30 genera of non-human primates (N = 1468), tested its phylogenetic signal, conducted human and macaque dissections, and tracked its developmental onset with newborn and infant baboons. The foramen was present in 12% of humans and 33% of non-human primates, occurring most frequently among hylobatids (77%) and non-human great apes (59%) and least among strepsirrhines (4%), revealing a significant phylogenetic signal (p < 0.001). Phylogenetic generalized least squares showed a strong signal with presence regressed on cranial base angle (CBA), a measure of cranial flexion. Genera with lower presence were more likely to have larger CBAs (Pagel's λ = 0.891), though this signal was strongly driven by Homo. Neither dissections nor developmental histology revealed foramen neurovasculature. However, one fetal and one infant baboon showed spatial constraints by the neurohypophysis, which may compress the sella and delay or prevent local endochondral ossification. We propose formalizing the foramen dorsum sellae and suggest its formation relates to developmental variation in dorsum sellae ossification and remodeling.