Algae with siliceous structures are proposed to have originated following the Permian-Triassic extinction or even earlier, but there have been no robust fossil records to indicate their existence before the Jurassic–Cretaceous Periods. Recently, abundant chrysophyte (classes Chrysophyceae and Synurophyceae) cyst fossils were discovered in a Late Triassic lacustrine stratum deposited ∼228–235 m.y. ago in the Ordos Basin, China. The high morphological variety of the discovered cyst fossils suggests that the chrysophytes were remarkably diversified, and that their common ancestors emerged even earlier. This discovery provided fossil records of the early evolution of algae with siliceous structures. The cyst fossils formed thin laminations in organic-rich shale, reflecting variable environmental conditions in the ancient lake basin.

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