The fossil algaChaetocladus gracilisrevisited: new material from the Silurian of Sweden

Abstract

In 2006, a new species of non-calcified dasycladalean alga, Chaetocladus gracilis, from the upper Silurian of Skåne (Scania), southernmost Sweden, was erected. The original description was based on a single incomplete fossil recovered from the abandoned limestone quarry at Bjärsjölagård, a classic geologic locality in Scania. Here we present four additional and, importantly, more complete specimens from this same site and type stratum. This new material largely corroborates the general anatomical features of C. gracilis, but also adds some intricate details, most notably with regards to the external sheet-like phytoleim and organisation of the laterals. Elemental mapping confirmed an expected carbonaceous composition of the fossils, which are embedded in a calcareous mudstone. These additional fossils show that the originally described specimen was not a singular occurrence at this locality. Based on the state of preservation of our algal fossils, we note that the mudstone facies of the Ludlow Bjärsjölagård Limestone Member of the Klinta Formation (Öved-Ramsåsa Group), from which all C. gracilis have been recovered, share characteristics with deposits typically referred to as "algal-Lagerstätten".

Coexistence of algae and a graptolite-like problematicum: a case study from the late Silurian of Podolia (Ukraine)

“…The studied fossil assemblage fits well into the category of a thallophytic-algal community, in which the dominant components are the noncalcified alga Voronocladus gen. nov. and benthic graptolite-like Podoliagraptus gen. nov. The present observations and numerous descriptions of similar Silurian communities, where algae and independently living benthic graptolites occurred (Kenrick and Vinther 2006;LoDuca and Tetreault 2017;Pettersson et al 2020), indicate that these two groups of organisms co-occurred in the same environment. Other fossils in the assemblage are represented mostly by Campylitestype tubes and gastropods, sometimes several centimetres long.…”

“…In the Swedish sections in Skania, 'algal-Lagerstätten' have been found in the inter-biostromal mudstone succession, in a generally lagoonal setting. A rapid burial of fossils during storms has been underlined in this case (Kenrick and Vinther 2006;Pettersson et al 2020).…”

“…The findings of noncalcified specimens are rare and are mostly linked with the Ordovician and Silurian successions of Laurentia (e.g., LoDuca et al 2013LoDuca 2019). In the last twenty years, however, numerous new records have been reported also from the shelves of Baltica (e.g., Kenrick and Vinther 2006;Mastik and Tinn 2015;Tinn et al 2015;Pettersson et al 2020).…”

Not dasycladalean alga, but an Odyssey of the earliest Phanerozoic animal reef-builders

“…In non-calcified dasycladalean fossils, the thalli are often composed of bush-like, branching filaments and sometimes bear reproductive structures such as cysts and gametophores 19–25 . These compressions are enriched with carbon and sulfur but are depleted with iron and phosphorus 26,27 . Although some dasycladaleans form a so-called “pseudocortex” by the inflation of the distal tip of the laterals (Fig.…”

“…In non-calcified dasycladalean fossils, the thalli are often composed of bush-like, branching filaments and sometimes bear reproductive structures such as cysts and gametophores [19][20][21][22][23][24][25] . These compressions are enriched with carbon and sulfur but are depleted with iron and phosphorus 26,27 .…”