https://www.pnas.org/doi/10.1073/pnas.1517943113 https://www.pnas.org/doi/10.1073/pnas.1517943113 claims that lignin was being broken down even during coal-form

https://www.pnas.org/doi/10.1073/pnas.1517943113 https://www.pnas.org/doi/10.1073/pnas.1517943113 claims that lignin was being broken down even during coal-forming periods. I did not verify this article though.