Ammobaculites (Foraminifera): Living fossils in southern western australian estuaries

Ammobaculites assemblages are recorded from five localities selected during reconnaissance sampling of shallow-water mud in the hyposaline reaches of Wellstead Estuary, Kalgan River, Frankland River, Walpole Inlet and Hardy Inlet. The aim of the study was to: (1) find potential living populations that in future could be the subject of biological, including molecular, investigations, and (2) describe the morphological variation in the recovered assemblages. In the geological record, Ammobaculites is one of the longest ranging multichambered genera within the Phylum Foraminifera, and is common in shallow-marine mudstone facies of Gondwanan/ Australian interior basins of the Late Paleozoic and Mesozoic. The southern Western Australian estuarine Ammobaculites are compared to five main morphotypes recognized in this genus among the global estuarine fauna. The most common form here is referred to Ammobaculites sp. ex. gr. A. exiguus; and another species, although related to one of the morphotype groups, does not appear to have close counterparts elsewhere. Species confirmation and comparisons to morphologically close forms in eastern Australian and on other continents must await future rDNA sequence study. The modern Ammobaculites are also compared to Australian continental fossil assemblages from the Permian, Triassic and Cretaceous, in which there are close morphological analogues. The modern types are living fossils whose future study could contribute to resolution of questions concerning the geological longevity of the genus, the morphological and potential genetic conservatism within the genus, and how such similar morphotypes that thrive in isolated ephemeral mud in marginal-marine environments can disperse across regions and continents in both space and time.