The Lagerstätte of algal flora from the Silurian of Estonia

The Palaeozoic fossil record of macroscopic algae contains mostly taxa with calcified thalli; knowledge of non-calcareous algae is poor. A diverse flora of non-calcareous thallophytic algae was recovered in the Kalana Quarry, central Estonia. The fossils occur in a shallowing upward sequence of shelf carbonates of the early Aeronian, in interbeds of brown organic-rich, microlaminated limestones alternating with micritic limestones. Algae are preserved as brown kerogenous and black-coloured carbonized compressions, being represented by compacted ‘stems’ and sporangia, but occasionally also by laterals or entire thalli. Over ten morphological groups (species) can tentatively be assigned to the Rhodophyta and Chlorophyta, representing several previously known and new genera. Only 14 species of noncalcified thallophytic algae have previously been reported from the entire Silurian System, and Kalana is far the richest Silurian Lagerstätte of thallophytes. Most abundant is Leveilleites (?) hartnageli (Rhodophyta, corallinaceans?). A species with leaflike/phylloid thallus, 2–5 mm wide, shows occasionally groups of ovoid structures (about 50x100 µm) interpreted as reproductive structures. In our interpretation there are male plants bearing spermatangia formed on spermatangial mother cells and female plants (carposporophytes) bearing carposporangia. Some taxa are assigned to formerly reported genera of Chlorophyte order Dasycladales (Inopinatella sp., Chaetocladus sp., Medusaegraptus sp.).