Non-Potluck Blog Post, but relevant topic: The timescale of early land plant evolution

When did the first land plant appear?

A group of researchers from the UK think they have a solid timescale estimate that differs from the fossil land plant record.

The researchers, Morris and colleagues, write that at present the land plant fossil record is unreliable method to understand early plant emergence due to the lack of early land megafossils found. However, they also underscore the importance of needing a timescale of the emergence of land plants to understand the “coevolution of land plants and Earth’s System”.

To get around this issue the authors took a molecular clock approached looking at the living bryophytes--non-vascular land plants--and tracheophytes--land plants whose tissue conducts water and minerals. However, the authors admit to this method having issues as well due to the current unresolved issue of the evolutionary relationship between living bryophytes and tracheophytes.

To ameliorate this issue, Morris and her colleagues, created a timescale that combines the uncertainty of the bryophytes and tracheophytes evolutionary by investigating the competing hypotheses of bryophyte−tracheophyte relationships with other variables (topology, dataset size, and dating methods) to develop a divergence timescale estimate.

The seven completing bryophyte and tracheophyte evolutionary relationship hypotheses. From Morris et al. 2018.

The authors organized 37 land plant fossils for calibrations using a best practice approach and a Bayesian--probability of an event based on available information--relaxed molecular clock analysis to determine the probability of land plant evolution. Two phylogenomic dataset of Embryophyta, green plant (eg ferns, etc.), and Viridiplantae, green algae and land plants that emerged with the green algae, from the published nucleotide alignments was also used.

The authors determine that a Cambrian origin of Embryophyta had the highest probability in all of their analysis as well as indicating non-vascular land plants emerged in the middle Cambrian−Early Ordovician and vascular plants during the Late Ordovician−Silurian interval.

This also study suggest an early land plants appeared to have emerged around the same time as the first appearance of terrestrial animals.  

Link to the PNAS article here.

Morris, J. L., Puttick, M. N., Clark, J. W., Edwards, D., Kenrick, P., Pressel, S., ... & Donoghue, P. C. (2018). The timescale of early land plant evolution. Proceedings of the National Academy of Sciences, 115(10), E2274-E2283.

-Kristen Tuosto

Kristen's 2nd PNAS Journal update.