A NEW DINICHTHYID FISH (PLACODERMI ARTHRODIRA) FROM THE UPPER DEVONIAN OF WESTERN AUSTRALIA, WITH A DISCUSSION OF DINICHTHYID INTERRELATIONSHIPS

WA Museum Records and Supplements | Updated 1 decade ago

Abstract
A new dinichthyid arthrodire, Westralichthys uwagedensis gen. et sp. nov. is described from the Upper Devonian carbonates of the Canning Basin, Western Australia. Although the exact location of the specimen is unknown an associated conodont fauna indicates a mid-Famennian (toIIB) age, and suggests that the specimen may have come from the Virgin HiJ.ls Formation. Westralichthys, known from one incomplete skull roof, is characterised by having a skull roof pattern with a broad trapezoidal nuchal plate, weakly trilobate centrals and very elongated marginal and postorbital plates, whilst lacking dermal ornamentation. The visceral surface has massive nuchal and lateral thickenings, deep mesial pits on the paranuchals, and well developed ventral postocular processes. The braincase had a well developed supraorbital process. Westralichthys is regarded as more derived than Eastmanosteus and Golshanichthys in possessing elongated postorbitals, a broad nuchal plate, lacking dermal ornamentation and in having well developed inframarginal laminae, and is placed as the sister taxon to Dunkleosteus plus higher dinichthyids. Paedomorphosis may have played a role in the evolution of the dinichthyids from the Middle Devonian coccosteomorphs.