Phylogenetic relationships of the largest lungless tetrapod (Gymnophiona, Atretochoana) and the evolution of lunglessness in caecilians

摘要

Atretochoana eiselti is the largest extant lungless tetrapod. This species is one of the fully aquatic caecilian amphibians of the family Typhlonectidae. It is unique within Gymnophiona in lacking lungs and having sealed choanae, a snake-like postoccipital jaw articulation, and some other greatly divergent features. Phylogenetic relationships of the five typhlonectid genera have been estimated only once previously, in an analysis of morphological data. Here we infer for the first time integrating molecular and morphological data, the relationships of all typhlonectid genera. Although Atretochoana and Potomotyphlus share several derived character states in morphology, some of which linked to a reduction of the pulmonary importance in respiration, Potomotyphlus is more closely related to Typhlonectes than to Atretochoana. Consequently, we conclude that evolutionary loss of lungs or gradual reduction of their importance in respiration in Atretochoana and Potomotyphlus was convergent within this poorly known group of amphibians.