Depth distribution and convergent evolution of microboring organisms

Abstract

Traces of microbial euendoliths have been recognized as convenient indicators of ancient depositional depths, particularly in ranges that lack physical evidence of actions of waves and currents. The paleobathymetric indication value is sought in recognizing the distinction between traces made by phototrophic microorganisms, which are expected to be restricted to the illuminated portions of the ocean, and organotrophic ones, which are light-independent and may occur at any depth. Our findings show that unrelated organisms often use similar solutions to solve similar problems, resulting in convergent evolution of body shapes and their functions, also expressed in the traces of phototrophic and organotrophic, which limits their recognition and indication value. The relationship between microboring organisms and their traces can only be studied in modern environmental settings, followed by comparisons with traces in the fossil record. Examples of convergent evolution between phototrophic and organotrophic euendoliths that resulted in similar morphological features of their trace morphologies are illustrated ways to improve the distinction between light-independent and light-dependent microboring forms are discussed.