Article: Early Ordovician trilobites, Nora Formation, central Australia

This is the first detailed account of the trilobites from the platformal carbonate/clastic Nora Formation of central Australia. The fauna records a remarkable, endemic radiation of the Family Asaphidae, producing forms with inflated, tuberculate frontal glabellar lobes unlike any other asaphids, but with a general resemblance to certain unrelated trilobites which lived in former epeiric habitats. The fauna is probably of mid-late Arenig age. The generic composition indicates that Australia lay in equatorial latitudes during the early Ordovician, attached or close to the Gondwanaland of the time and well-removed from other continents spanning the palaeoequator. The fauna includes eighteen species, of which four are left under open nomenclature. The concept of the Leiostegiidae is reviewed to include Annamitella, formerly regarded as a bathyurid. The classification of trinucleine trilobites is briefly reviewed. The peculiar blind trilobite Prosopiscus, hitherto considered an aberrant cheiruracean, is reclassified in the Phacopina, and for its reception a separate family, Prosopiscidae nov., is proposed. The following new taxa are described: Annamitella strigifrons, A. brachyops; Norasaphus, N. (Norasaphus) skalis, Norasaphites, Norasaphus (Norasaphites) monroeae, N. (N.) vesiculosus; Lycophron, L. rex; Fitzroyaspis irritans, Hungioides acutinasus, Nambeetella embolion, Gogoella brevis, and Prosopiscus praecox. On the basis of the trilobite fauna two assemblage zones are defined in the Nora Formation.