Origination and early evolution of Involutinida in the aftermath of the end-Permian mass extinction: Praetriadodiscus n. gen., and two new species

In this study, we describe as the earliest representatives of involutinids a new population comprising one new genus (Praetriadodiscus) and two new species (P. zaninettiae and P. tappanae) from the Great Bank of Guizhou in the Nanpanjiang Basin of south China. This new population appears to have diverged from an undetermined pseudoammodiscid ancestor in the late Smithian, during the second phase of foraminiferal recovery from the end-Permian mass extinction. The new genus exhibits a two-layered wall, inner microgranular and outer hyaline, fibrous and aragonitic, and a planispirally coiled, lenticular test with one lamella for one complete whorl of the deuteroloculus. The genus Triadodiscus, which may represent the last common ancestor of the Order Involutinida, is potentially the direct descendant of this new population characterized by a two-layered wall.