Ordovician Rhipidognathidae (Conodonta) from Australia and Iran
Five species of rhipidognathid conodonts, including Appalachignathus delicatulus Bergström et al., 1974, Bergstroemognathus extensus (Graves and Ellison, 1941), B. hubeiensis An, 1981, B. kirki Stait and Druce, 1993, and Rhipidognathus yichangensis (Ni, 1981), are described and revised in terms of multielement morphology, based on specimens from Australia and Iran. All three genera comprising the Rhipidognathidae are interpreted as having a septimembrate apparatus, partially confirmed by bedding plane assemblages of B. extensus from Victoria. Occurrence of A. delicatulus in allochthonous limestones (about the Middle-Upper Ordovician boundary) of central New South Wales is the first record of the species outside North America. Recognition of Rhipidognathus yichangensis (a senior synonym of Honghuayangnathus Ni 1981) in Early Ordovician strata of the Canning Basin, reinforces biogeographic affinities of Australia and South China. The three species described of Bergstroemognathus are restricted to late Early Ordovician strata. Bergstroemognathus extensus is widely distributed in North America, western Argentina (Precordillera), China, and Australia. Bergstroemognathus hubeiensis, described from east-central Iran, has been previously recorded only from China, while the slightly younger B. kirki seems endemic to central and northern Australia. Apart from B. kirki, which was restricted to shallow, warm water environments, rhipidognathids appear to have inhabited a variety of water temperatures and depths. The widespread occurrences of these species greatly enhances their potential for long-range correlation, and indicates biogeographic links between Australia, China, Iran, and western Argentina, particularly during the Early Ordovician.