Foraminiferal organic linings: Functional and phylogenetic challenges
Jarosław Tyszka, Karolina Godos, Jan Goleń, Wiesława Radmacher
Abstract
Foraminifera are commonly applied as essential tools for relative time control and reconstructions of paleo/environmental conditions. These single-celled organisms leave in the sedimentary rocks two types of fossil records represented by mineralized shells (tests) and their organic linings. Although both types require different preparation methodologies, they should be treated complementary as they represent the same specimens. Unfortunately, this is not the case, and the foraminiferal fossil record is highly biased towards mineral shells. The fossil archive of acid resistant organic linings is highly fragmentary and limited to accessory components within palynological preparations of marine sediments. Surprisingly, meta-analysis of the overall published record of linings from the Paleozoic till today indicates that nearly all foraminiferal linings reveal globular chambers that tend to show minimized distances between apertures. These two morphologic features classify them into the same Globothalamea class (sensu Pawlowski et al., 2013). The question therefore is why there is nearly no record of fossil linings belonging to other foraminiferal classes. Do all foraminiferal classes produce organic linings? Are they compositionally and structurally similar? What is their taphonomic potential? If the foraminiferal lining is phylogenetically significant, it might be involved in specific functions associated with different morphogenetic and biomineralization patterns. All these questions encourage novel interdisciplinary investigations on organic linings as a crucial research target.