Cretaceous Records of Diatom Evolution, Radiation, and Expansion

Abstract

New information and discussions regarding Mesozoic diatoms presented over the last decade advanced our knowledge of their origin and early history. The oldest confirmed centric diatom fossils are presented here from the earliest Cretaceous, and araphid and raphid pennate diatoms now date from the Late Cretaceous; all from terrestrial sediments. Molecular sequencing helped clarify relationships between diatom lineages, and verify the position of diatoms within the heterokontophytes. Molecular clock approaches estimate a diatom origin near ~135 Ma, but not before 240 Ma. Biomarkers in marine sediments are able to trace a diatom presence back to the mid-Cretaceous, even when siliceous fossils are absent. Seasonal growth and encystment cycles in Late Cretaceous planktonic marine diatoms are now well documented. A biostratigraphic framework for the Late Cretaceous Arctic will aid regional and global biostratigraphic correlations. The systematic position of many new taxonomic groups is now included within a more natural classification scheme that better reflects phylogenetic relationships evident in molecular data and affirmed by biostratigraphic micropaleontology. Discussions regarding the impact of diatoms on several global systems are maturing, as more information becomes available. Four stages in diatom evolution are proposed to explain the history of radiation, extinction, and expansion into new environments and habitats during the Mesozoic.

Spermatogenesis and auxospore structure in the multipolar centric diatom Hydrosera

“…Similar valves have also been recovered from a Korean deposit dating to the earliest part of the Cretaceous, although in this case the frustules found were heterovalvar, the thimble‐like valves being linked to planar valves in what were probably resting spores (Harwood et al. , Chang and Park ). Sometime during the Mesozoic, diatoms seem to have expanded their morphogenetic repertoire, producing not only the circles and ellipses made previously, but also more complex shapes: triangles, squares, leaf‐like shapes, and even twisted or spiral forms.…”

A comprehensive study of sterols in marine diatoms (Bacillariophyta): Implications for their use as tracers for diatom productivity

“…Not surprisingly, diatoms are an important link in the food web and a major source for organic matter in marine environments, especially in coastal areas. Despite their current abundance, it was only relatively recently in geologic history that diatoms occupied their dominant position; molecular clock calculations suggest that diatoms originated during the Early Jurassic (Sorhannus 2007;Rampen et al 2009b), and this is in accordance with findings of Late Jurassic and Early Cretaceous diatom fossils (Harwood et al 2007). It was not until the Eocene (40,000-35,000 kyr) that diatoms became significant in numbers (Kooistra et al 2007) and marine planktonic diatom diversity reached its peak at or immediately before the Eocene-Oligocene transition (Rabosky and Sorhannus 2009).…”

A Molecular Genetic Timescale for the Diversification of Autotrophic Stramenopiles (Ochrophyta): Substantive Underestimation of Putative Fossil Ages

“…These new results suggest that the diatom lineage evolved sometime near the Devonian-Carboniferous transition, and that the fossils of many diatom groups (e.g. ‘pennate’ diatoms) could be much older than the currently known paleontological record has indicated [66], [71]. Despite our results indicating that representatives of Bacillariophyceae may already have existed in the early Paleozoic, modern looking diatoms reported by Sieminska and Kwiecinska [26], [27] from this time period are likely to be ‘contaminants’ from younger strata because the earliest known diatoms are morphologically rather different from modern diatoms.…”