The palaeobiogeography of Late Cretaceous and Cenozoic brachiopods from Western Australia

Recent research on the Late Cretaceous and Cenozoic fossil brachiopods from the Carnarvon, Perth, Bremer and Eucla sedimentary basins in Western Australia has added much to our understanding of their systematics and biodiversity. Fifty-eight species, including one new family, two new genera and 30 new species, have been described from these sources. Four, possibly five, genera and one species from the Late Cretaceous of Western Australia are common to the Late Cretaceous deposits of the Antarctic Peninsula. This evidence suggests that in the Late Cretaceous there was a continuous shelf environment extending from the Antarctic Peninsula to the Carnarvon Basin of Western Australia. These southern shelf environments formed the high latitude southern circum-Indo-Atlantic faunal province. In this area, brachiopods evolved genera and species differing from those of the northern hemisphere. Many subsequently dispersed into northern areas of the Indian, Atlantic and, finally, Pacific Oceans. Examination of Cenozoic material from the Carnarvon Basin indicates that there is a strong correlation with Cenozoic material from the Antarctic Peninsula. At least six brachiopod genera are common to the two areas. If the distribution of brachiopod genera in Australia and New Zealand is analysed, they first appear in the northwest of Western Australia. They then appear in chronological order in the south-western, south-eastern basins of Australia and finally New Zealand. The apparent migration of brachiopods south and then eastward was most likely due to the Proto-Leeuwin and Great Australian Bight Currents. Fifteen species are common to south-western Australia and south-eastern Australia. Brachiopods may well have used various migration mechanisms from the earliest breaching of the gap between Australia and Antarctica to be transported into the Tasman Sea and hence to New Zealand. This included attachment to living specimens and dead objects as well as possible extended larval life in lower temperature waters. Factors such as light avoidance, food availability and competition with bivalves may provide an explanation for the small number of species and specimens of brachiopods in some deposits.