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

Abstract

With 4 plates and 42 figures in the text)The development of the head and pharynx of larvae of Neoceratodus (ranging in length from 11.5 to 34.5 nun) was investigated from 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 Neocerarodus and the two amphibian groups. It is concluded that they share a common derivation from pro-dipnoan-amphibian stockof 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 view of a monophyletic derivation of the Tetrapoda.

Cephalic muscle development in the Australian lungfish,Neoceratodus forsteri

“…A retractor mandibulae as described by Fox () ‐ spanning between the posteroventral surface of Meckel's cartilage and the lateral surface of the ceratohyal ‐ could not be identified in our study and was not described by others (e.g., Bartsch, ; Edgeworth, ; Ericsson et al, ).…”

“…During development, the origin of the adductores mandibulae shifts posteriorly and they originate from the chondrocranium and covering bones (present study; Edgeworth, ; Fox, ). Diogo and Abdala () describe an A2, A2‐PVM, retractor anguli oris, and an A3' as present and hardly separable in adult lungfishes, presenting a figure modified from Bemis and Lauder () of the South American lungfish Lepidosiren paradoxa .…”

“…The dorsal end of the mandibular muscle anlage will contribute to the adductor mandibulae A3' (Edgeworth, ). Fox () alternatively suggested that the A3' and A2 derive from premandibular and mandibular mesoderm, respectively. The homology of the adductores mandibulae in N. forsteri and the levatores mandibulae in Lissamphibia was established by Edgeworth () and Pusey ().…”

“…The levator hyoideus in early stages of caudates develops into the depressor mandibulae, which is considered homologous to the levator hyoideus in lungfishes (Edgeworth, ; Forey, ; Fox, ). The levator hyoidei originates from the otic capsule and inserts onto the dorsal end of the ceratohyal in N. forsteri (e.g., present study; Ericsson et al, ).…”

“…In anurans and caudates, four levatores arcuum branchialium are followed by the dilatator laryngis (Edgeworth, ; Ziermann & Diogo, ; Ziermann & Olsson, ), which is similar to the observations in N. forsteri . Fox () suggests that his levatores arcuum branchialium 5 and 6 include fibers that are homologous to the dilatator laryngis and the cucullaris (protractor pectoralis) muscle. The latter develops in caudates from the most caudal levator (Edgeworth, ; Ziermann & Diogo, ).…”