The Palaeobiogeography of Eastern Australian lower carboniferous corals

Abstract

Eastern Australian Lower Carboniferous (EALC) corals are characterized by high endemism, with ende‐mism indices of 50 in the Tournaisian and 44 in the Visean. The most closely related coral faunas occur in the Akiyoshi and Kitakami Terranes of Japan. Less robust faunal linkages exist with southeast Asia, south China, northern Siberia and Kazakhstan, suggesting east to north Tethyan linkages on most tectonic reconstructions. Amygdalophyllum appears to have originated in the eastern Australian‐Japanese region and then migrated throughout the Palaeotethys during the late Tournaisian and early Visean. Eastern Australian taxa that lacked such a widespread distribution during the Tournaisian did not spread throughout the Palaeotethys during the Visean. EALC coral distributions can be explained by a palaeobiogeographical model wherein: 1) shallow‐water coral faunas were largely depleted following the Frasnian/Famennian extinction event; 2) dispersal occurred during the late Famennian to early Tournaisian from an oceanic centre to the northeast, in western Panthalassa; 3) eastern Australian coral faunas were isolated from the north by the prevailing southerly current direction and possible coastal upwelling in northernmost Australia and New Guinea, and from the south by cooler high latitudes; 4) endemic taxa arose by vicariance subsequent to geographic isolation. Sampling of EALC corals is incomplete owing to the restriction of most taxa to shallow carbonate facies, which have very limited geographic and stratigraphic distributions. Hence, EALC coral diversity is probably controlled largely by sample density. Better sampling will be required before coral data can be used to independently constrain EALC palaeolatitude, but the limited incidence of coral‐bearing facies may preclude a definitive analysis. High EALC coral endemism is puzzling in light of the apparently cosmopolitan nature of co‐occurring shallow benthos. Hence, either EALC corals were particularly subject to genetic isolation for ecological and/or other reasons, or other EALC invertebrates may prove to have higher levels of endemism than has been assumed. Increased emphasis on detailed reconstruction of phylogenies, and the recognition of homo‐plasy, in particular, in other EALC benthic invertebrates suggest that they may be less cosmopolitan than is currently accepted.