Evolution of Trochamminoids (Trochospiral Organic-Cemented Agglutinated Foraminifera): Examples from the Lower Permian of Western Australia

Abstract

Abstract Trochamminids are the oldest trochospiral group of foraminifera. An exceptionally well-preserved assemblage, found in the Lower Permian (Sakmarian, ∼294–290 Ma) of Western Australia, includes Trochammina geoffplayfordi n. sp., Trochammina gloveri n. sp., Trochamminopsis teicherti n. sp., and Tritaxis crespinae n. sp. Verispira holmesorum n. sp. seems related to broader Trochamminoidea. These represent the oldest known well-preserved representatives of the superfamily. By the Sakmarian, trochamminids, remarkably like modern species, had developed in a shallow-water interior sea with muddy substrate; some may have lived in the flocculent surface layer of the mud, and some were epibionts. No potential trochospiral ancestor is known among calcareous foraminifera of the Late Paleozoic. Triassic Duostomina seems to be the oldest calcareous taxa with simple trochospiral coiling (also having an inner organic lining). Molecular analyses of modern species suggest that morphotypes like the Permian Trochammina lie at some genetic distance from Trochammina inflata (type species of the genus).