Permian higher latitude bryozoan biogeography

Bryozoans from Gondwana and northern Eurasia are within the higher latitude Gondwana and Boreal Realms respectively and display a clear antitropical faunal distribution, with lower diversity than tropical realms. Within these realms however, faunas at highest latitudes are the least diverse and dominated by cosmopolitan genera. Further, separate geological and oceanographic developmental histories of the boreal and Gondwanan regions have resulted in the Boreal Realm showing much higher diversity than its southern counterpart.Gondwana was in a high-latitude position during the Permian experiencing the polar climatic conditions of the Late Palaeozoic Ice Age, and the distribution of bryozoans show a distinct diversity decrease towards cold-water high latitudes where the eurytopic fenestrates and trepostomes were the dominant groups. The eastern Australian margin, with the least diverse faunas of the Gondwanan realm, is oriented north–south as a narrow shelf, hindering the migration of taxa into the southern coldest environments. In contrast, northern hemisphere mid to high-latitude basins experienced cooling through the Permian as Pangaea moved northward and tectonics altered oceanographic circulation; however glaciomarine deposits were not widespread even at highest latitudes. The marine shelf of the northern Eurasian margin was broad and oriented west–east allowing establishment of widespread stable faunas in waters that became increasingly nutrient-fed through the Permian from cool-water upwelling from the Panthalassa Ocean in the west. This cool-water mid-latitude setting, west–east shelf, and nutrient enrichment resulted in a Boreal Realm bryozoan fauna of over 100 genera; more diverse than the Gondwanan Realm with only 61 genera.Antitropical taxa restricted to Boreal and Gondwanan Realms only include Diploporaria, Lyropora, and Metelipora, however, a number of other genera are more abundant outside the tropics even if they occur in all realms. These genera include Alternifenestella, Rectifenestella, Polypora, Polyporella, Shulgapora, Dyscritella, Stenopora, Streblascopora, Pinegopora, Maychella, Maychellina, Ramipora, Tabulipora and Hexagonella. The wide nutrient-fed mid-latitude shelf of the Boreal Realm also allowed development of a number of endemic taxa, or taxa that are rare elsewhere, including Permoheloclema, Timanodictya, Permofenestella, Lyrocladia, Wjatkella, Parafenestralia, Triznella and Gilmouropora. In southern Gondwana endemic taxa are limited to Crockfordia and Paramaychella, however, there is an abundance of Evactinostella, Etherella and Liguloclema that are distinctive of Western Australia.