Sensory lines and rostral skull bones in lungfish of the family Neoceratodontidae (Osteichthyes : Dipnoi)

Skull bones in early lungfish contain permanent insignia of the sensory lin es of the head, but osteological evidence of sensory lines in derived lungf ish is reduced to foramina for nerves to neuromasts, superficial grooves, o r elevated ridges on some bones. This is particularly evident in anterior b ones, making definition of these bones difficult, and creating problems for phylogenetic analyses. Despite a close association of the sensory lines wi th the bones of the developing skull in the Australian lungfish, Neoceratod us forsteri, few traces of the lines remain in the bones of the adult anima l. Among derived dipnoans, Mioceratodus, a genus of neoceratodont fossil lu ngfish from Tertiary deposits in central and northern Australia, is unusual because traces of the supraorbital sensory line are retained in the anteri or skull roofing bones of large specimens. Equivalent traces are absent fro m the rostral bones of N. forsteri, and from small specimens of Mioceratodu s. The supraorbital sensory line grooves in Mioceratodus bones pass over the p osterior surface of the rostral bone, and not the anterior process as in Ne oceratodus. The rostral bones of Mioceratodus may be formed from the fusion of different bones in the primitive dipnoan skull compared with those that formed the rostral (EQ) bone of N. forsteri. Alternatively, the associatio n between sensory lines and skull bones may not be constant.