Presence of the vomeronasal system in aquatic salamanders

Previous reports have indicated that members of the proteid family of salam anders lack a vomeronasal system, and this absence has been interpreted as representing the ancestral condition for aquatic amphibians. I examined the anatomy of the nasal cavities, nasal epithelia, and forebrains of members of the proteid family, mudpuppies (Necturus maculosus), as well as members of the amphiumid and sirenid families (Amphiuma tridactylum and Siren inter media). Using a combination of light and transmission electron microscopy, I found no evidence that mudpuppies possess a vomeronasal system, but found that amphiuma and sirens possess both vomeronasal and olfactory systems. A mphiumids and sirenids are considered to be outgroups relative to proteids; therefore, these data indicate that the vomeronasal system is generally pr esent in salamanders and has been lost in mudpuppies. Given that the vomero nasal system is generally present in aquatic amphibians, and that the last common ancestor of amphibians and amniotes is believed to have been fully a quatic, I conclude that the vomeronasal system arose in aquatic tetrapods a nd did not originate as an adaptation to terrestrial life. This conclusion has important implications for the hypothesis that the vomeronasal organ is specialized for detection of non-volatile compounds.