Lack of a pheromonal sense in phytosaurs and other archosaurs, and its implications for reproductive communication

The vomeronasal (VN) system is a pheromone-processing sensory system of tetrapods. Tetrapods use pheromones to communicate territorial boundaries, reproductive status, sex, and species identity. Presumed impressions of VN bulbs on phytosaur frontals led to a claim that phytosaurs possessed the VN system. However, in extant crocodilians, which lack the VN system, the corresponding impressions are associated not with cerebral tissue but with the ophthalmic nerves. Phytosaur head morphology was not conducive to pheromone collection. The extant phylogenetic bracket suggests that all extinct archosaurs, including phytosaurs, lacked the VN system. Without the pheromonal sense, they would not have used chemical means to convey territorial boundaries, reproductive status, sex, and species identity. Instead, they would have used visual, acoustic, and tactile cues, as in extant archosaurs and other tetrapods in which the VN sense is reduced or absent.