That "the Proteidae constitute the most primitive of the Urodeles" (Holmes, 1906) is generally accepted as an established fact. But here and there one finds dissenting opinions from this particular view. Kingsbury (1905) has given some very instructive and suggestive comparisons, chiefly of skeletal features, between Necturus and typical Urodela showing that Necturus and the larval stages of Spelerpes have so many characters in common that the similarities must stand for some degree of close relationship.
Proceedings of the Iowa Academy of Science
©1911 Iowa Academy of Science, Inc.
Norris, H. W.
"The Rank of Necturus among the Tailed Amphibians as Indicated by the Distribution of Its Cranial Nerves,"
Proceedings of the Iowa Academy of Science, 18(1), 137-143.
Available at: https://scholarworks.uni.edu/pias/vol18/iss1/29