alan Channing

The first avian fossil recovered from high-temperature hot spring deposits is a three-dimensional external body mould of an American coot (Fulica americana) from Holocene sinters of Yellowstone National Park, Wyoming, USA. Silica encrustation of the carcass, feathers and colonizing microbial communities occurred within days of death and before substantial soft tissue degradation, allowing preservation of gross body morphology, which is usually lost under other fossilization regimes. We hypothesize that the increased rate and extent of opal-A deposition, facilitated by either passive or active microbial mediation following carcass colonization, is required for exceptional preservation of relatively large, fleshy carcasses or softbodied organisms by mineral precipitate mould formation. We suggest physico-chemical parameters conducive to similar preservation in other vertebrate specimens, plus distinctive sinter macrofabric markers of hot spring subenvironments where these parameters a...

The Canaries have recently served as a test-bed island system for evaluating newly developed parametric biogeographical methods that can incorporate information from molecular phylogenetic dating and ages of geological events. To use such information successfully, knowledge of geological history and the fossil record is essential. Studies presenting phylogenetic datings of plant groups on oceanic islands often through necessity, but perhaps inappropriately, use the geological age of the oldest island in an archipelago as a maximum-age constraint for earliest possible introductions. Recently published papers suggest that there is little chance of informative fossil floras being found on volcanic islands, and that nothing could survive violent periods of volcanic activity. One such example is the Roque Nublo period in Gran Canaria, which is assumed to have caused the extinction of the flora of the island (c. 5.3–3.7 Ma). However, recent investigations of Gran Canaria have identified numerous volcanic and sedimentological settings where plant remains are common. We argue, based on evidence from the Miocene–Pliocene rock and fossil records, that complete sterilization of the island is implausible. Moreover, based on fossil evidence, we conclude that the typical ecosystems of the Canary Islands, such as the laurisilva, the Pinus forest and the thermophilous scrubland, were already present on Gran Canaria during the Miocene–Pliocene. The fossil record we present provides new information, which may be used as age constraints in phylogenetic datings, in addition to or instead of the less reliable ages of island emergences or catastrophic events. We also suggest island environments that are likely to yield further fossil localities. Finally, we briefly review further examples of fossil floras of Macaronesia.

RESUMEN En 1997 se descubrió un yacimiento excepcional con fósiles de plantas en los sedimentos del interior de la Caldera de Taburiente, que fueron originados en un ambiente lacustre durante el Pleistoceno su-perior. Este yacimiento está situado en las inmediaciones del camino que da acceso al Parque Nacional, hecho que aumenta las amenazas por expolio. Además, este lugar de interés geológico tiene una alta vulnerabilidad ante los frecuentes procesos erosivos de la ladera sobre la que se sitúa. En el año 2012 el Servicio de Patrimonio del Cabildo Insular de La Palma fue informado de la existencia y valor científico de estos fósiles y se tomaron medidas para la protección física del yacimiento. Esta medida ha contri-buido eficazmente para la disminución de las amenazas externas. Paralelamente, se ha emprendido un plan para su investigación paleontológica y se han realizado actividades de divulgación desde el Museo Benahoarita de Los Llanos de Aridane. Palabras clave: Caldera de Tabu...

[摘要]: 正Hot springs active at Rhynie during the Lower Devonian were the surface expression of a low-sulphidation (alkali-chloride) epithermal system (Channing, 2003). Little evidence has been observed that indicates any modification of this subsurface water chemistry prior to eruption. Wetland habitats are common at Rhynie and Windyfield and include active and dormant vent-pools, wet sinter-aprons, run-off streams, geothermal

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 salinit...

Siliceous hot spring deposits form at Earth's surface above terrestrial hydrothermal systems, which create low-sulphidation epithermal mineral deposits deeper in the crust. Eruption of hot spring waters and precipitation of opal-A create sinter apron complexes and areas of geothermally influenced wetland. These provide habitat for higher plants that may be preserved in situ, by encrustation of their surfaces and permineralization of tissues, creating T0 plant assemblages. In this study, we review the fossil record of hot spring floras from subfossil examples forming in active hot spring areas, via fossil examples from the Cenozoic, Mesozoic and Palaeozoic to the oldest known hot spring flora, the Lower Devonian Rhynie chert. We demonstrate that the well-known megabias towards wetland plant preservation extends to hot spring floras. We highlight that the record of hot spring floras is dominated by plants preserved in situ by permineralization on geothermally influenced wetlands. Angiosperms (members of the Cyperaceae and Restionaceae) dominate Cenozoic floras. Equisetum and gleicheniaceous ferns colonized Mesozoic (Jurassic) geothermal wetlands and sphenophytes and herbaceous lycophytes late Palaeozoic examples. Evidence of the partitioning of wetland hydrophytic and dryland mesophytic communities, a feature of active geothermal areas, is provided by well-preserved and well-exposed fossil sinter apron complexes, which record flooding of dryland environments by thermal waters and decline of local forest ecosystems. Such observations from the fossil record back-up hypotheses based on active hot springs and vegetation that suggest removal of taphonomic filtering in hot spring environments is accompanied by an increase in ecological and ecophysiological filtering. To this end we also demonstrate that in the hot spring environment, the wetland bias extends beyond broad ecology. We show that ecosystems preserved from the Cenozoic to the Mesozoic provide clear evidence that the dominant plants preserved in situ by hot spring activity are also halophytic, tolerant of high pH and high concentrations of heavy metals. By extension, we hypothesize that this is also the case in Palaeozoic hot spring settings and extended to the early land plant flora of the Rhynie chert.

Abstract• Premise of the study: Dated molecular phylogenies suggest a Cenozoic origin for the crown group of Equisetum. but compression fossil equisetaleans that are morphologically indistinguishable from extant Equisetum and recently discovered anatomically preserved examples strongly suggest an earlier Mesozoic initial diversification.• Methods: In situ samples of Equisetum thermale sp. nov.

Abstract Decaying and partially silica-permineralized subfossil plant stems collected from geothermally influenced wetlands of Yellowstone National Park contain evidence of colonization by protists, including heliozoa and chrysophytes. Wetland pools in which the plants and heliozoans occur represent an extreme environment characterized by steady influxes of hot-spring water.

The Canaries have recently served as a test-bed island system for evaluating newly developed parametric biogeographical methods that can incorporate information from molecular phylogenetic dating and ages of geological events. To use such information successfully, knowledge of geological history and the fossil record is essential. Studies presenting phylogenetic datings of plant groups on oceanic islands often through necessity, but perhaps inappropriately, use the geological age of the oldest island in an archipelago as a maximum-age constraint for earliest possible introductions. Recently published papers suggest that there is little chance of informative fossil floras being found on volcanic islands, and that nothing could survive violent periods of volcanic activity. One such example is the Roque Nublo period in Gran Canaria, which is assumed to have caused the extinction of the flora of the island (c. 5.3–3.7 Ma). However, recent investigations of Gran Canaria have identified numerous volcanic and sedimentological settings where plant remains are common. We argue, based on evidence from the Miocene–Pliocene rock and fossil records, that complete sterilization of the island is implausible. Moreover, based on fossil evidence, we conclude that the typical ecosystems of the Canary Islands, such as the laurisilva, the Pinus forest and the thermophilous scrubland, were already present on Gran Canaria during the Miocene–Pliocene. The fossil record we present provides new information, which may be used as age constraints in phylogenetic datings, in addition to or instead of the less reliable ages of island emergences or catastrophic events. We also suggest island environments that are likely to yield further fossil localities. Finally, we briefly review further examples of fossil floras of Macaronesia.

In 1997 a unique late Pleistocene fossil flora site was discovered in a lacustrine sedimentary rock sequence within the Caldera de Taburiente, La Palma. The fossiliferous beds, which are located adjacent to the road access into the National Park, is vulnerable to both natural and human removal of irreplaceable palaeontological data. The poorly-lithified rocks of the locality are particularly susceptible to rapid slope and gully erosion. In 2012 the Heritage Service of the Cabildo Insular de La Palma was alerted to the presence of the fossil resource and its scientific value. Initial infrastructure designed to physically protect the site has been installed. The fence has effectively contributed to decrease of external threats. In collaboration with Benahoarita Museum of Los Llanos de Aridane a plan for paleontological research has been devised and series of outreach activities conducted.

Silicification of plants by hot springs at Rhynie, Aberdeenshire during the Lower Devonian preserved abundant plant axes, in situ, erect and at the cellular level, conserving arguably the most important and informative evidence of early terrestrial ecosystems. Investigation of rate, timing and extent of tissue degradation and silica deposition in modern hot spring environments at Norris Geyser Basin, Yellowstone National Park, Wyoming, USA revealed that excellent preservation of parenchymatous and sclerenchymatous tissues occurs in hot, wet conditions intolerable by microbial decomposers. Sinter aprons, characterised by lower water temperatures and immersion frequency, allowed increased microbial degradation; plant preservation quality was correspondingly low. Wet sinter aprons with water temperatures below 45OC were sites of in situ preservation of sparse halophytic plants. Cooler peripheral wetlands were sites of abundant plant growth. Silica supersaturated geothermal fluids entering the wetlands caused cellular silicification of in situ emergent aquatic plants and plant litter. Silica permeation of plants occurred via rhizomes, stomata and the epidermis/cuticle. Within plants, silica nucleated and polymerised onto cell walls (creating films) and within intracellular/intercellular spaces, creating colloidal particle suspensions. Colloidal particle growth, aggregation and sedimentation formed distinctive intracellular silica fabrics. Particle coalescence and cementation occluded intracellular (and in compact tissues intercellular) porosity. Plants within pools were indurated by silica following eleven months immersion. Early silica deposition stabilised cell walls but did not isolate tissues from decay. Subfossil/fossil material indicated slow hydrolytic removal of organic frames and later infilling by silica. Secondarily thickened walls silicified by this means replicated organic structures crudely.
Comparison of modern/Holocene environments, sediments, plants and decay/silicification patterns with Palaeozoic examples, suggests that waterlogged/wetland conditions were common in Palaeozoic geothermal areas. Plants were possibly tolerant of waterlogging and low “soil” chemical potentials. Anomalous high preservation potentials of parenchymatous peripheral tissues in rhyniophytes are proposed to have arisen from in-life silicification.