Article: Biology and evolution of the nasal region in trematopid amphibians

Postmetamorphic ontogeny of the nasal region in trematopid amphibians (Temnospondyli: Dissorophoidea) from the Lower Permian of Texas is characterized by the early appearance of a narial flange which is identical to that of an adult. Subsequent ontogenetic changes are the posterior expansion of the external naris, positive allometric growth of rostral length, and the development of caniniform teeth on the premaxillae and maxillae. It is hypothesized that the narial flange of dissorophoids, regardless of the details of its morphology, was an adaptation for terrestriality, and probably acted in a manner analogous to the primary concha of reptiles to enhance olfactory receptivity and improve the efficiency of moisture reclamation from exhaled air. Evolution of caniniform teeth in the Trematopidae apparently localized and increased cranial stresses in the rostrum during eating. Consequently, the plesiomorphic dissorophoid narial flange was modified in trematopids to fulfil an additional role of cranial reinforcement. Expansion of the external naris was a subsequent event, and probably a result, rather than a cause, of any alterations to cranial stresses. Existence of a salt gland in the expanded external naris is equivocal and not necessary for an interpretation of trematopids as terrestrial amphibians.