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When did the earliest unambiguous moss fossils appear?

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Thick green bryophyte moss covers the trunks of three oak trees in a forest, with fallen leaves on the ground. — Bryophyte Bryophyte moss growing on oak trees.

The earliest unambiguous moss fossils appear in the Permian Period, which occurred approximately 298.9 million to 251.9 million years ago.12

While evidence of other bryophytes, such as liverwort cryptospores, dates back to the Ordovician Period (about 473 million to 471 million years ago), the fossil record for mosses is less complete. Even within the Permian material, detailed evolutionary relationships remain unclear, and while the subclass Bryidae is the most likely classification, precise attribution is difficult.12