Wall structures in selected Paleozoic lagenide foraminifera

Groves J., Rettori R., Altiner D.

JOURNAL OF PALEONTOLOGY, vol.78, no.2, pp.245-256, 2004 (SCI-Expanded) identifier


Paleozoic lagenide foraminifera are strikingly similar morphologically to Mesozoic and Cenozoic Lagenida, but because benthic foraminifers suffered a catastrophic reduction in diversity during the end-Permian mass extinction, it is unclear whether the similarities of Paleozoic lagenides and younger unquestioned Lagenida link them evolutionarily or are the product of convergence. Seven species representing five families of Paleozoic lagenide foraminifers were examined and found to possess mostly monolamellar hyaline-radial walls, as in extant nodosariid Lagenida. Exceptions are Protonodosaria rauserae Gerke, 1959, whose wall is not optically radial, and Syzrania amazonica Altiner and Savini, 1997, whose hyaline-radial wall may or may not be accompanied by a secreted inner microgranular layer. The inner microgranular layer is an element that is thought to have been inherited from the ancestral Fusulinida. Its absence in all but the earliest and morphologically simplest Paleozoic lagenides indicates more advanced wall structure than generally has been ascribed to this group. The wall in Pachyphloia spp. is secondarily thickened, suggesting plesio- or ortho-monolamellar construction, whereas other examined species exhibit atelo-monolamellar wall structure. These types of lamellarity are common among modern nodosariids. Thus, on the basis of not only morphologic similarity but also similar wall structure, we strongly suspect evolutionary continuity of lagenides across the Permian-Triassic boundary. The question is not completely resolved, however, because lagenides have not yet been recovered from lowest Triassic rocks.