Alan Channing

Equisetum thermale sp. nov. (Equisetales) from the Jurassic San Agustín hot spring deposit, Patagonia: Anatomy, paleoecology, and inferred paleoecophysiology

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. from the Upper Jurassic San Agustín hot spring deposit were collected and studied with the use of polished blocks, thin sections, and light microscopy. KEY RESULTS Equisetum thermale exhibits all the morphological and anatomical characteristics of the extant crown group Equisetum. It shows a mixture of features present in the two extant subgenera, e.g., superficial stomata typical of subgenus Equisetum allied with infrequently ramifying stems typical of subgenus Hippochaete. This appears to ally E. thermale with the least derived extant species in the genus Equisetum bogotense (sister species to the two subgenera). Its association of hydromorphic and xeromorphic characters allowed it to grow as an emergent aquatic in physically and chemically stressed geothermally influenced wetlands, where it formed dense monospecific stands. Equisetum thermale, because it is preserved in situ with intact anatomy, provides clear paleoecological, biological, plus inferred paleoecophysiological evidence of adaptations known in extant species. CONCLUSIONS As the earliest unequivocal member of the genus, E. thermale supports the hypothesis of a Mesozoic origin. Its inferred tolerance of a similar range of stresses (e.g., high salinity, alkalinity, and heavy metal concentrations) to that seen in extant Equisetum suggests early evolution and subsequent maintenance of ecophysiological innovations in the genus.

Experimental taphonomy: silicification of plants in Yellowstone hot-spring environments

During experiments conducted within the vent pool of Medusa Geyser, Norris Geyser Basin, Yellowstone National Park, USA, amorphous opaline silica (opal-A) was deposited on/within plant tissues within 30 days of immersion. Initially, deposition created inter/intra-cellular films which lined cell walls plus intercellular colloid suspensions (sols) of opal-A nano/microspheres. By 330 days, opal-A deposition created a robust external and internal matrix that stabilised tissues against collapse and replicated plant structure. Opal-A films increased to micron-order thicknesses and intracellular sols were created. Systematic variation of opal-A fabric between tissues comprising living/dead cells at the time of deposition indicate that cell function, architecture and shape influence fabric development. Heterogeneity of opal-A fabric within adjacent cells of similar structure/function indicates spatially/temporally fluctuating physicochemical conditions and the presence of intraorganic microenvironments. Early deposition of opal-A films suggests a period of low silica supersaturation and slow opal-A deposition. In contrast, intracellular sols suggest high levels of supersaturation, and rapid opal-A deposition. Shell-like microsphere growth suggests cyclic variation of silica supersaturation, and alternations between rapid and slower opal-A deposition. Microsphere growth to the upper limit of colloidal stability and colloidal crystal structures indicate prolonged sol stability, whilst floc-like microsphere networks indicate localised sol instabi

Yellowstone hot spring environments and the palaeo-ecophysiology of Rhynie chert plants: towards a synthesis

Background: The Rhynie chert, Aberdeenshire, encapsulates the ecophysiological and anatomical information on all components, including plants, animals and micro-organisms, of an early terrestrial ecosystem as it existed some 400 million years ago (Early Devonian), as preserved by siliceous waters emanating from a hot spring system. Aims: This paper concentrates on the higher plants (tracheophytes) and brings together information on the habitats of the plants and the environmental pressures that they endured to answer issues relating to their endemism and their ecophysiology. Methods & Results: The synthesis includes detailed information on the palaeo-environments recorded in the chert, plus anatomical and autecological data from the plants themselves, and makes comparisons with the abiotic and biotic data obtained from an extant analogue, the alkali–chloride geothermal systems at Yellowstone National Park. Particular attention is paid to the physiological basis and evolution of osmotic and chemical tolerance of halophytes, the dominant colonisers of Yellowstones wetlands and, to a lesser extent, metallophytes. Conclusions: The Rhynie plants colonised wetlands at the low temperature fringes of a hot spring system and were versatile, but physiologically highly specialised, capable of withstanding osmotic and chemical stresses in a dynamic environment, but were probably out-competed by mesophytic vegetation elsewhere.

Silicification of higher plants in geothermally influenced wetlands: Yellowstone as a Lower Devonian Rhynie analog

Abstract Silicification of higher plants associated with active, alkali-chloride hot springs in Yellowstone National Park, Wyoming, USA, occurs dominantly in areas of geothermally influenced wetlands. Plants grow in an environment with many of the characteristics of an oligosaline marsh and are subjected to brackish salinity and high pH, temperature, silica, and heavy metal concentrations. As such, the plants undergoing silicification at Yellowstone are predominantly those more typically found colonizing widespread evaporation-driven inland waters and coastal salt marshes (e.g., Eleocharis rostellata, Triglochin maritimum) and are in some ways preadapted to hot-spring settings. This paper documents hydrochemistry and physical parameters in a typical geothermally influenced wetland at Big Blue Hot Spring, Elk Park in Yellowstone and records the taphonomic processes involved in silicification of the most common wetland plant Eleocharis rostellata. Silicification of plants in situ results in the three-dimensional preservation of tissues and cells characteristic of plants preserved around the Lower Devonian Rhynie chert hot-spring system. Sinter deposition at active and fossil hot-spring areas is typically associated with alkali-chloride springs above low-sulfidation epithermal systems. As mineralogical and geological evidence indicates that such a system was responsible for preservation of the Rhynie plants, it is hypothesized that they too, at least periodically, withstood comparable physiological stresses to the modern analogs.

Jurassic geothermal landscapes and fossil ecosystems at San Agustín, Patagonia, Argentina

Abstract: An extensive, well-preserved, Late Jurassic (c. 150 Ma) geothermal system at San Agustín farm in the Deseado Massif, Patagonia, Argentina, is described. This deposit, along with others previously known from the same region, partially fills a considerable gap between Cenozoic and scattered Palaeozoic hot spring localities reported worldwide. The San Agustín deposit is novel because it represents a large (1.4 km2) and nearly complete geothermal landscape. Siliceous hot spring facies, both subaerial and subaqueous, are exposed side by side in their original spatial and geological context, set amongst intrusive rhyolite domes and fluviolacustrine sediments. The Jurassic hot springs have preserved an entire local ecosystem containing microbes, arthropods, gastropods and plants exhibiting Lagerstätten-style preservation. Plant preservation, in particular, ranges from decayed litter, to seedling sprouts, and to dense stands in life orientation with intact anatomy. The San Agustín deposit shares some ecological, taphonomic and sedimentological characteristics with modern hot springs. As it formed in a pre-angiosperm world, it is akin to the famous hot spring-related Devonian Rhynie cherts of Scotland. It differs in having excellent exposure, and thus will probably contribute to a better understanding of biosignal preservation in extreme environments in the geological record.

A new Middle–Late Jurassic flora and hot spring chert deposit from the Deseado Massif, Santa Cruz province, Argentina

We present an initial report of a well-preserved and relatively diverse Gondwanan plant assemblage from Bahia Laura Group, Chon Aike Formation strata of the Estancia Flecha Negra area, central-western region of the Deseado Massif, Santa Cruz province, Patagonia, Argentina. The locality contains the first richly fossiliferous chert with a diverse and well-preserved plant assemblage reported from the Mesozoic which is demonstrably associated with hot spring activity. A compression flora and petrified forest contained in associated clastic and volcaniclastic environments provide an indication of regional plant diversity during this as yet poorly represented stratigraphic interval.

FIRST REPORT OF FUNGI AND FUNGUS-LIKE ORGANISMS FROM MESOZOIC HOT SPRINGS

ABSTRACT Herein we provide the first report of the diversity of fungi and fungus-like organisms within a Mesozoic hot spring ecosystem. The Jurassic San Agustín hot spring deposit (Patagonia, Argentina), represents only the second known Phanerozoic hot spring ecosystem with an associated microflora and contains diverse, exceptionally preserved microorganisms. Preserved propagules include flask-shaped pycnidia produced by extant coelomycetes, shield-like and nearly round thyriothecia of extant Microthyriales in the ascomycetes, variously shaped spore-like bodies representing chytrid and chytrid-like zoosporangia and other life cycle forms, and additional fungal and fungus-like remains (spores, hyphal fragments, reproductive structures) of uncertain affinity. Many of these microorganisms are associated with variously decayed organic remains, most commonly of horsetails. This expands the fungal fossil record and provides a unique opportunity to learn about the biology of Mesozoic microorganisms.

A silicified bird from Quaternary hot spring deposits

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 soft-bodied 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 are met.

Preservation of protists within decaying plants from geothermally influenced wetlands of Yellowstone National Park, Wyoming, United States

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. Recorded physicochemical conditions in wetland pools reveal relatively high temperatures (often >35 °C), high pH (≤9.1), high conductivity (>3000 µS/cm−1), brackish salinity and elevated concentrations of toxic elements including antimony (Sb), thallium (Tl), mercury (Hg), and arsenic (As). This report contains the first observations of heliozoans and chrysophytes from intercellular sites within decaying plants and adds a previously unreported and extreme environment to their known habitats. Such settings are potential taphonomic windows for preservation of fossil protists.

First Glimpse of the Silicified Hot Spring Biota from a New Jurassic Chert Deposit in the Deseado Massif, Patagonia, Argentina

Abstract. Jurassic hot-spring chert deposits in the Deseado Massif, Patagonia, Argentina, have been known for over two decades, but the associated biota has only begun to be documented recently, and thus far only from a small number of localities. Here we report the discovery of a large complex of well-exposed Upper Jurassic epithermal siliceous deposits represented by organic-rich cherts preserved within the geothermal system from La Bajada, Santa Cruz, Argentina. The chert samples analyzed so far contain exceptionally well-preserved, in situ and transported, tri-dimensionally silicified plants, animals and microorganisms. Plants include equisetaleans (Equisetum thermale), ferns and gymnosperms. Among them, well-preserved in situ osmundaceous rhizomes in different developmental stages are the dominant component of the taphoflora. Conifers are represented by wood, seeds, leaves and pollen tentatively assigned to the families Araucariaceae and Cheirolepidiaceae. The assemblage also contains vegetative and reproductive structures of fungi, oomycetes, cyanobacteria, algae, testate amoebas, ciliates and numerous remains of unresolved taxonomic affinity. Microorganisms are preserved isolated in the chert matrix or directly associated with plants and other organic remains in mutualistic, parasitic and saprotrophic engagements. Also present are numerous coprolites and arthropod remains that, along with the named microorganisms, are indicative of trophic relationships in the ecosystem. Altogether, this fossil assemblage suggests that distal paleoenvironments within the geothermal system are preserved at La Bajada. The diversity, abundance, and exceptional preservation of fossils in the La Bajada ecosystem provides a unique window into the geological past that offers a substantial contribution to the reconstruction of middle Mesozoic terrestrial ecosystems.