A review of active hot-spring analogues of Rhynie: environments, habitats and ecosystems

Abstract

The Lower Devonian Rhynie chert formed as silica sinter entombed an early terrestrial ecosystem. Silica sinter precipitates only from water flowing from alkali-chloride hot springs and geysers, the surface expression of crustal-scale geothermal systems that form low-sulfidation mineral deposits in the shallow subsurface. Active alkali-chloride hot springs at Yellowstone National Park create a suite of geothermally influenced environments; vent pools, sinter aprons, run-off streams, supra-apron terrace pools and geothermal wetlands that are habitats for modern hot-spring ecosystems. The plant-rich chert, which makes Rhynie internationally famous, probably formed in low-temperature environments at the margins of a sinter apron where frequent flooding by geothermal water and less frequent flooding by river waters created ephemeral to permanent wetland conditions. Here, the plants and associated microbes and animals would be immersed in waters with elevated temperature, brackish salinity, high pH and a cocktail of phytotoxic elements which created stresses that the fossil ecosystem must have tolerated. The environment excluded coeval mesophytic plants, creating a low-diversity hot-spring flora. Comparison with Yellowstone suggests the Rhynie plants were preadapted to their environment by life in more common and widespread environments with elevated salinity and pH such as coastal marshes, salt lakes, estuaries and saline seeps.This article is part of a discussion meeting issue 'The Rhynie cherts: our earliest terrestrial ecosystem revisited'.

Neofunctionalisation of basic helix−loop−helix proteins occurred when embryophytes colonised the land

“…It is hypothesised that plants then underwent morphological diversification during and after the colonisation of the dry continental surfaces (Graham et al ., ; Delaux et al ., ; Harrison, ). These adaptations to life on the land contributed to the establishment of the first complex terrestrial ecosystems by 407 Ma and led to the terrestrial ecosystems that exist today (Gibling & Davies, ; Lenton et al ., ; Channing, ; Wellman, ).…”

An alternative model for the earliest evolution of vascular plants

“…), where the preservation of the fossils is exquisite. The earliest preserved terrestrial ecosystem of Rhynie was indeed formed in a hot‐spring environment (Channing ; Edwards et al . ), which results in a unique and exceptional anatomical preservation of the early land plants, among other organisms.…”

“…Most of them are known in great detail because they come from the Early Devonian (mid-Pragian-?earliest Emsian, Wellman 2006) Rhynie Lagerst€ atte, Aberdeenshire, in Scotland (see Kidston & Lang 1917, 1920aEdwards et al 2017), where the preservation of the fossils is exquisite. The earliest preserved terrestrial ecosystem of Rhynie was indeed formed in a hot-spring environment (Channing 2017;Edwards et al 2017), which results in a unique and exceptional anatomical preservation of the early land plants, among other organisms. Consequently, four Rhynie chert plants (Aglaophyton, Horneophyton, Rhynia and Asteroxylon), showing different grades of complexity of water-conducting cells, occupy key steps in current plant phylogeny (Kenrick 2000;Ligrone et al 2012).…”

Palaeontology: The Rhynie Chert Is the Gift that Keeps on Giving

“…They are, essentially, preserved siliceous sinters deposited by hot springs. Rather remarkably, the sinter-forming siliceous liquids emanating from the hot springs appear to have rapidly entombed the surrounding biota, preserving it in situ with remarkable fidelity [3].…”

“…But at Rhynie there are no signs of fish fossils, either in the cherts that preserved the ponds or even in the river and lake deposits that comprise the vast majority of rock sequence. When we ponder on how modern the Rhynie chert aquatic biotas appear, we must remember that we are dealing with a very strange environment indeed [3]. The Rhynie deposits accumulated in a volcanically active region with the associated lava flows of volcanos and the sinter deposits of hot springs.…”