Biogeographic and Biostratigraphic Implications of the Serratognathus bilobatus Fauna (Conodonta) from the Emanuel Formation (Early Ordovician) of the Canning Basin, Western Australia

Discovery of Serratognathus bilobatus in the Early Ordovician Emanuel Formation of the Canning Basin, Western Australia, has regional biogeographic and biostratigraphic implications. Distribution of Serratognathus indicates a close biogeographic link between Australia and adjacent eastern Gondwanan plates and terranes during the latest Tremadocian to early Floian (Early Ordovician), and the formation of the so-called Australasian Province, a distinctive biogeographic entity that existed throughout most of the Ordovician. The S. bilobatus fauna from the Canning Basin is much more diverse in comparison with those assemblages bearing Serratognathus from coeval Chinese Lower Ordovician successions and probably represents an assemblage inhabiting relatively deeper water (mid-outer shelf) environments. The Canning Basin fauna contains many pandemic forms, and bridges the gap in the regional correlation of this widely distributed fauna across eastern Gondwana. This well-preserved, diverse fauna includes Serratognathus bilobatus and 23 associated species: Acodus deltatus?, Acodus? transitans, Bergstroemognathus extensus, Cornuodus sp., Drepanodus arcuatus, Drepanoistodus sp. cf. D. nowlani, Fahraeusodus adentatus, Lissoepikodus nudus, Nasusgnathus dolonus, Paltodus sp., Paracordylodus gracilis, Paroistodus parallelus, Paroistodus proteus, Prioniodus adami, Protopanderodus gradatus, Protoprioniodus simplicissimus, Scolopodus houlianzhaiensis, Semiacontiodus sp. cf. S. cornuformis, Stiptognathus borealis, Triangulodus bifidus, Tropodus australis, gen. et sp. indet. A and gen. et sp. B. A P adami-S. bilobatus Biozone is defined within the middle and upper Emanuel Formation. Correlation of this biozone suggests an early Floian (late P proteus Biozone to possibly earliest P elegans Biozone) age for the middle and upper members of the Emanuel Formation.