Structural details of Early Devonian dipnoans

Abstract

The evolution of the Dipnoi is displayed in the Early Devonian in south-eastern Australia. The main points at issue are as follows. (a) The development of the tubercles in the two-layered rostral region of the skull. (b) The nerves ophthalmicus profundus V and opthalmicus superficialis VII, and their sensory function. (c) The abundance of fine tubules between these tubules and the dermal plates of the skull roof extending posterior to the pineal region. (d) The massive pterygoids and the restriction of the parasphenoids to a small posterior position. (e) The position of the bucco-hypophysial canal running to a buccal opening near the posterior of the pterygoids. (f) The presence of a rostral region, misnamed the ‘dentary’, in the mandible, with abundant tubercles serving sensory systems. (g) The presence of an anterior furrow in the mandible. Dipnoans form a separate evolutionary lineage that began in the Early Devonian. Diabolepis and associated genera are not Dipnomorphs, but are isolated genera formed by gene regulation in the early Devonian.