Early development of the head and pharynx of Neoceratodus with a consideration of its phylogeny

The development of the head and pharynx of larvae of Neoceratodus (ranging in length from 11.5 to 34. 5 mm) was investigated form microscopic transverse serial sections. The structures studied included the chondrocranium and visceral arches, ossifications, cranial and anterior spinal nerves, musculature and vascular system. These components of Neoceratodus are compared with similar ones, likewise investigated, in Rana temporaria and Rana esculenta (33 and 26 mm long, respectively), and in various genera of Urodela, either previously investigated by the author or by reference to the earlier literature. Some new homologues of the various morphological components of the head and pharynx of these groups are suggested. On the basis of the larval structure an assessment is made of the classical view of a close phylogenetic relationship between Neoceratodus and the two amphibian groups. it is concluded that they share a common derivation from pro‐dipnoan‐amphibian stock—of crossopterygian ancestry—in the early Devonian: a conclusion which supports an earlier somewhat similar view of Goodrich. It is further considered that there is evidence of a quasi parallel evolution between Neoceratodus and Urodela, though some assumed similarities in larval structure are spurious; nevertheless, in some ways, they are more similar than are Neoceratodus and members of the Anura. A common origin of Neoceratodus (Dipnoi) and the amphibian groups supports the vie of a monophyletic derivation of the Tetrapoda.