Coralline red algae from the Silurian of Gotland indicate that the order Corallinales (Corallinophycidae, Rhodophyta) is much older than previously thought

Abstract

Aguirrea fluegelii gen. et sp. nov. (Corallinales, Corallinophycidae, Rhodophyta) is described from the mid-Silurian of Gotland Island, Sweden (H€ ogklint Formation, lower Wenlock). The holotype is of dimerous construction and includes a uniporate conceptacle with a sporangium, thus providing evidence that taxa of the Corallinales/Corallinaceae existed at least 300 million years earlier than previously documented. Aguirrea fluegelii cannot be unequivocally placed in any of seven currently recognized lineages/subfamilies/groups of the Corallinaceae as not all diagnostic characters are preserved, and thus is accorded incertae sedis status within the family Corallinaceae and order Corallinales. Extant evolutionary history studies of Corallinophycidae involving molecular clocks now require updating using new calibration points to take account of the much earlier unequivocal mid-Silurian record of uniporate conceptaclebearing taxa of Corallinales/Corallinaceae as well as the parallel record of Graticula, a genus attributed to the Sporolithales.

A possible link between coral reef success, crustose coralline algae and the evolution of herbivory

“…While CCA have existed at least since the Silurian 61 , pre-Cretaceous occurrences are scarce. We downloaded data on all reefs occurring from the earliest Cretaceous (Berriasian stage, 145.5 Ma) to the Late Pleistocene (0.01 Ma) and having corals as the main reef builders from the PaleoReefs Database (PARED, www.paleo-reefs.pal.uni-erlangen.de ) in May 2018.…”

Radiation of the coralline red algae (Corallinophycidae, Rhodophyta) crown group as inferred from a multilocus time-calibrated phylogeny

“…However, both studies agreed that the radiation of the crown group took place in the Lower Cretaceous, which coincides with our analyses. The consistent diversification during the Lower Cretaceous requires a reappraisal of the nature and classification of a number of fossil red algae ranging from the Neoproterozoic to the Triassic that have been considered as either possibly related to modern corallines or as true corallines (Riding et al, 1998;Riding, 1998, 2000;Senowbari-Daryan et al, 2002;Cózar and Vachard, 2003;Smith and Butterfield, 2003;Riding and Braga, 2005;Senowbari-Daryan and Velledits, 2007;Teichert et al, 2019) (Fig. 5).…”

“…are considered non-calcified ancestors of modern coralline red algae based on the resemblance in vegetative structure (Xiao et al, 2004). Additional taxa, both calcified and non-calcified forms, gathered from Paleozoic and Triassic rocks have been claimed to be related with modern corallines or to be included within the order Corallinales Riding, 1998, 2000;Riding et al, 1998;Senowbari-Daryan et al, 2002;Riding and Braga, 2005;Senowbari-Daryan and Velledits, 2007;Smith and Butterfield, 2013;Teichert et al, 2019). Nonetheless, whether these taxa belong to the stem group of the modern corallines or are true corallines requires an indepth evaluation (see Discussion).…”

A possible erect coralline alga from the Ediacaran Dengying Formation in the Zhenba area of South China

“…Recently, fossils of the order Corallinales were identified from the Silurian of Gotland (Teichert et al, 2019), over 300 million years earlier than the age previously estimated based on molecular data (Aguirre et al, 2010;Yang et al, 2016;Rösler et al, 2017). The difference in divergence time of coralline algae estimated by molecular data is probably because those putative ancestral coralline fossils were not used as calibration points.…”

“…In South China, the Ediacaran Doushantuo phosphorous deposits yield numerous and diverse phosphatized specimens of multicellular algae (Zhang, 1989;Zhang and Yuan, 1992;Yuan et al, 1993;Zhang, 1996;Yuan and Hofmann, 1998;Zhang et al, 1998;Xiao et al, 1999;Zhou et al, 2004). These specimens, preserved with complex pseudoparenchymatous construction and possible reproductive structures, were interpreted as uncalcified stem-group coralline algae , which was of great significance in indicating a soft-bodied (uncalcified) evolutionary history in the Neoproterozoic, given that Phanerozoic and living coralline algae were almost all calcified (Johansen, 1981;Riding, 1998, 2000;Riding et al, 1998;Luchinina and Terleev, 2008;Chatalov et al, 2015;Teichert et al, 2019). The Doushantuo specimens also demonstrate the significant potential of Ediacaran phosphatized fossil assemblages to explore the origins and early evolution of coralline algae.…”