be active). It is possible that other theriodonts lost this due to the evolution of either endothermy, intrinsically photosensitive retinal ganglion cells in the eyes—in tandem with the loss of colour vision and a shift to nocturnal life–or both. Nocturnal behaviour has long been assumed to have originated in mammals (nocturnal bottleneck), but the large orbit size and presence of sclerotic rings in many early synapsids, stretching as far back as the Carboniferous, would suggest that the ability to venture out in low-light conditions evolved much earlier. Based on these aspects, the specimen SAM-PK-K10034 may have had mesopic vision, and Cyonosaurus scotopic or photopic vision. The diameters of the sclerotic rings for the small Viatkogorgon are proportionally large, with an inner diameter of and outer diameter of , compared to a diameter of for the orbit itself, which suggests it made predominantly nocturnal excursions. Among gorgonopsians, the rubidgeine Clelandina has unusually small sclerotic rings, indicating it had photopic vision and was strictly diurnal; Kammerer suggested that niche partitioning among rubidgeines (as there have been as many as seven different taxa coexisting in an area), in part, took the form of different species being active at different times of the day, but the sclerotic rings of only Clelandina among this subfamily have been identified, making this hypothesis highly speculative. Gorgonopsians have a rather short nasal cavity, like pelycosaurs, but it features abundant longitudinal ridges behind the internal nostrils (which connect the nasal cavity to the throat); because respired air would not have passed through them, these are typically interpreted as having been olfactory turbinates, and would have given gorgonopsians a rather highly developed sense of smell. Gorgonopsians possessed a vomeronasal organ ("Jacobson's organ")—a part of the accessory olfactory system–which would have been placed at the base of the nasal septum; unlike dicynodonts and therocephalians, there seems to have been a canal connecting the organ with the mouth, indicating it was functional in gorgonopsians. Early theriodonts (including gorgonopsians) may have possessed an eardrum, unlike earlier pelycosaurs, indicated by the reduction of the connection between the quadrate bone (at the jaw hinge) and the pterygoid bone (at the palate), allowing the quadrate to independently vibrate to a degree. This may have allowed the detection of air-borne sounds with a low amplitude of less than , but the eardrum would have been supported by cartilage or ligaments instead of bone. If correct, then the