A description of the head, mandible, pectoral girdle, humerus, medial fins and their supports, and the dissociated vertebral column has been prepared for Onychodus jandemarrai n. sp. from the Gogo Formation (Frasnian) of Western Australia. This is the most completely known species of the genus. The feature influencing most of the head morphology is the retractable parasymphysial tusk whorls. Their presence has caused a reorganisation of the braincase, palate (including the loss of the vomers), and lateral displacement of the nasal capsules. The extensive mandibular articulation is in cartilage, and the mandibular symphysis is weak. This makes for a kinetic skull. There is a single submandibular on each side. The vertebral column is poorly ossified, consisting of intercentra which have no ventral contact, and pleurocentra. The neural arches have no longitudinal ligament, have unequal sides, and asymmetrical placing of the dorsal and ventral nerve root foramina. Each arch has an anterior surface that often attaches to the next anterior arch. The caudal fin is almost diphycercal; all the medial fins have strong support structures. An attempt is made to discuss the functional morphology of many features of the skeleton.

The axial skeleton and fin supports of the Middle Devonian lungfish Dipterus are described from a range of specimens from the Orcadian Basin of Scotland. The axial skeleton of the trunk region consists of intercentra, relatively short ribs, and neural arches bearing two rows of supraneural spines; posteriorly, the intercentra are replaced by haemal arches. The notochord seems to have been essentially unconstricted. There may have been two pairs of cranial ribs. In general terms the vertebral column resembles that of Neoceratodus but is more fully ossified. The only known paired fin support of Dipterus is an archipterygial structure resembling those of Neoceratodus, with at least seven mesomeres and jointed pre- and postaxial radials. The pectoral fin is rotated as in modern lungfishes. The median fin supports all consist of basal plates supporting radials. In the posterior dorsal fin support the posterior radials form a branched structure. The heterocercal tail is supported by segmental radials. A new body reconstruction is presented.

The characters possessed by Dipterus offer support for a lungfish–porolepiform sistergroup relationship. All known lungfishes fit into a single cumulative series of postcranial morphologies. The evidence for a paedomorphic trend in lungfish phylogeny is interesting but inconclusive.