Erik Jarvik - Theories On Amphibian Phylogeny

Theories On Amphibian Phylogeny

Jarvik proposed partly controversial hypotheses about the principal structure of the vertebrate head and the origin of the tetrapods. He thus held, on the basis of detailed analyses of the snout and nasal capsule structures as well as the intermandibular, neuroepiphysial, and occipital regions, that Tetrapoda was biphyletic. In his view, the anatomical details of the Caudata (salamanders) bound them to the primitive porolepiform fishes, while all other tetrapods (“eutetrapods”) – apodans possibly excepted – were descended from primitive osteolepiforms. Thus Amphibia had arisen twice.

On the basis of his findings, he argued that Amphibia should be split, with salamanders (and possibly caecilians) in one class (the Urodelomorpha), and the frogs as a separate class, the Batrachomorpha. The Lepospondyli was thought as possible Urodelomorphans, while the other Labyrinthodonts were thought to be Batracomorphs. Jarvik's ideas was never widely accepted, though Friedrich von Huene did include his system in systematic treatment og tetrapods. Few other supported his ideas, and today it has been abandoned by vertebrate paleontologists. The term "Batrachomorpha" is however sometimes used in an cladistic sense to denote Labyrinthodonts more closely related to modern amphibians than to amniotes.