Fossil chondrichthyan and placoderm remains from the Middle devonian South Blue Range, Victoria, Australia: biostratigraphic implications

Fossil fishes were first discovered in the South Blue Range (SBR), near Mansfield, in the mid 1930s, and described by Hills (1936). First thought by Hills to be Late Devonian, later studies on the placoderms suggested the deposit to be older, probably Givetian in age. This site has yielded the placoderms Bothriolepis sp., Austrophyllolepis edwini, and Groendlandaspis sp. (Long 1989) plus the stem tetrapod fish Owensia chooi (Holland 2009). Chondrichthyan teeth are here described from a new site located in the upper section of the Middle Devonian Kevington Creek Formation in the South Blue Range, near Mansfield, Victoria (Cas et al. 2003). The teeth include a new species of McMurdodus with coarse serrations, supporting a possible late Eifelian-early Givetian age for the unit, as this genus is otherwise known only from the early Middle Devonian Cravens Peak beds of central Australia (Turner & Young 1987, Emsian-Eifelian boundary) and from the lowermost units of the Aztec Silstone (Givetian-Eifelian) in Antarctica. Other chondrichthyan taxa in the same fauna include Aztecodus sp. and Antarctilamna prisca, also known from the Aztec Siltstone fauna of Antarctica (Young 1982; Long & Young 1995). Remains of the antiarchs Bothriolepis sp. and ?Venezuelepis are consistent with this being a faunal assemblage with a wider Gondwanan aspect. The younger occurrence of the genus McMurdodus in the Aztec Siltstone of Antarctica (Eifelian-Givetian) and the presence of Aztecodus sp. and Antarctilamna sp. in the Kevington Creek fauna would also support an older age for the whole South Blue Range Devonian succession. This implies the unconformity between the Devonian succession demarcated by the Mt. Kent Conglomerate (conformable with the Early Carboniferous Devils Plain Formation) could be chronologically longer than previously estimated.