Peat Moss–Like Vegetative Remains from Ordovician Carbonates

Abstract

Premise of research. Climatically favorable conditions correspond with fossil evidence for dramatic Ordovician marine biodiversification, but coeval terrestrial biodiversity is less well understood. Although diverse Middle and Late Ordovician microfossils are interpreted as reproductive remains of early bryophyte-like land plants (consistent with molecular data indicating pre-Ordovician embryophyte origin), the vegetative structure of Ordovician plants remains mysterious, as do relationships to modern groups. Because distinctive fungal microfossils indicating land plant presence were previously reported from Ordovician carbonate deposits in Wisconsin, we examined another nearby outcrop for additional evidence of terrestrial biodiversification. Methodology. Replicate collections were made from well-understood 455-454 Ma Platteville Formation carbonates of relatively low porosity and hydraulic conductivity. We employed measures to avoid contamination, and organic remains extracted by acid maceration were characterized by light and scanning electron microscopy and energy-dispersive X-ray spectroscopy. Pivotal results. Multicellular organic fragments displayed distinctive cellular features shared with modern vegetative peat mosses but differed from modern materials, e.g., fossil presence of mineral coatings, absence of epibionts. Biometric features of mosslike microfossils isolated from carbonates collected and macerated 12 yr apart by separate investigators did not differ. Putative peat moss remains occurred with foraminifera similar in frequency and thermal maturity to types previously described from the same formation. No diatoms, pollen, or other indicators of post-Ordovician environments were observed. Conclusions. The peat moss-like fragments described here are the oldest-known vegetative remains of land plants and the oldest fossils having distinctive features linking them to a modern plant group. These findings are consistent with peat moss recalcitrance properties that foster fossilization and molecular evidence that the peat moss lineage is 460-607 Ma of age. The new findings suggest that moss-dominated peatlandsrecognized for globally significant roles in modern terrestrial biodiversity and C and N cycling-were present hundreds of millions of years earlier than previously thought.

Range change evolution of peat mosses (Sphagnum) within and between climate zones

“…These are generally interpreted as evidence for the existence of embryophyte land plants (i.e., "bryophytes" [mosses, liverworts, hornworts] and vascular plants). Cardona-Correa et al (2016) recently described a remarkably well-preserved fossil with the diagnostic morphological features of Sphagnopsida from the Ordovician Period in what would now be Wisconsin. Cardona-Correa et al (2016) recently described a remarkably well-preserved fossil with the diagnostic morphological features of Sphagnopsida from the Ordovician Period in what would now be Wisconsin.…”

“…Although mosses in general have a relatively poor fossil record, the Sphagnopsida are represented by four genera in the Paleozoic (Permian) Protosphagnales (Maslova, Ignatiev, Mosseichik, & Ignatov, 2015;Maslova, Mosseichik, Ignatiev, Ivanov, & Ignatov, 2012;Neuburg, 1960). Cardona-Correa et al (2016) recently described a remarkably well-preserved fossil with the diagnostic morphological features of Sphagnopsida from the Ordovician Period in what would now be Wisconsin. It is not possible to assign this fossil to any one of the four genera in this class, but it does corroborate molecular phylogenetic inferences that peat mosses in the broad sense are an ancient group.…”

“…Furthermore, the very ancient Ordovician Sphagnopsida fossil(Cardona-Correa et al, 2016) was unknown at the time of our previous study. This hypothesis could be tested with increased molecular sampling to resolve with greater precision relationships among derived tropical latitude species.…”

“…Cardona-Correa et al, 2016). Details about the first four fossils can be found inLaenen et al (2014).…”

The Sphagnome Project: enabling ecological and evolutionary insights through a genus‐level sequencing project

“…Molecular phylogenies suggest the Sphagnopsida diverged from other mosses > 250–350 million years ago (mya) (Shaw et al ., ), and fossils of peat moss‐like fragments, which are the oldest known land plant macrofossils to date, have been found in the Ordovician rocks ( c . 500 mya, Cardona‐Correa et al ., ). Fossil Sphagnum and close relatives are recognized by the unique cell pattern in leaves.…”