The spores of arbuscular mycorrhizal fungi (Glomeromycota) in the Early Devonian Rhynie ecosystem served as a habitat for a diversity of other fungi, only a few of which have been studied in detail so far. Rhizophydites shutei nov. sp. occurs in planar assemblages and tuft-like clusters comprised of thalli in various stages of development on Archaeosporites rhyniensis-like acaulospores. The presence of multiple individuals on several closely spaced hosts allows a thorough depiction of this fungus. Thalli are monocentric and characterized by an ovoid, narrowly to broadly citriform, bulb-shaped, or globose inoperculate zoosporangium 10–35(–38) μm high and 7–33 μm wide, and an endobiotic rhizoidal system reaching into the host lumen. The sporangium can be epibiotic or interbiotic (stalked), or located between the wall layers of the host spore. Mature sporangia have a pronounced apical papilla. Similarities with the modern chytrid genera Rhizophydium and Phlyctochytrium are used to suggest that the fossil belongs to the Chytridiomycota, and to place it in the genus Rhizophydites, which accommodates chytrid-like fossils that are morphologically similar or even identical to present-day Rhizophydium. This discovery contributes to our understanding of the various roles mycorrhizal fungi had in early terrestrial ecosystems.

Algae from the Lower Devonian Rhynie chert: Populations of a probable saccoderm desmid (Mesotaeniaceae, Zygnematales) preserved in a microbial mat

The Early Devonian Rhynie chert preserves the earliest terrestrial ecosystem and informs our understanding of early life on land. However, our knowledge of the 3D structure, and development of these plants is still rudimentary. Here we used digital 3D reconstruction techniques to produce the first well-evidenced reconstruction of the structure and development of the rooting system of the lycopsid Asteroxylon mackiei, the most complex plant in the Rhynie chert. The reconstruction reveals the organisation of the three distinct axis types - leafy shoot axes, root-bearing axes, and rooting axes - in the body plan. Combining this reconstruction with developmental data from fossilised meristems, we demonstrate that the A. mackiei rooting axis - a transitional lycophyte organ between the rootless ancestral state and true roots - developed from root-bearing axes by anisotomous dichotomy. Our discovery demonstrates how this unique organ developed and highlights the value of evidence-based reconstructions for understanding the development and evolution of the first complex vascular plants on Earth.

The Early Devonian fungus Mycokidstonia sphaerialoides from the Rhynie chert is a member of the Ambisporaceae (Glomeromycota, Archaeosporales), not an ascomycete

Deciphering interfungal relationships in the 410-million-yr-old Rhynie chert: Brijax amictus gen. et sp. nov. (Chytridiomycota) colonizing the walls of glomeromycotan acaulospores

Deciphering interfungal relationships in the 410 million-year-old Rhynie chert: Glomoid spores under attack

The Early Devonian Rhynie and Windyfield cherts remain a key locality for understanding early life and ecology on land. They host the oldest unequivocal nematode worm (Nematoda), which may also offer the earliest evidence for herbivory via plant parasitism. The trigonotarbids (Arachnida: Trigonotarbida) preserve the oldest book lungs and were probably predators that practiced liquid feeding. The oldest mites (Arachnida: Acariformes) are represented by taxa which include mycophages and predators on nematodes today. The earliest harvestman (Arachnida: Opiliones) includes the first preserved tracheae, and male and female genitalia. Myriapods are represented by a scutigeromorph centipede (Chilopoda: Scutigeromorpha), probably a cursorial predator on the substrate, and a putative millipede (Diplopoda). The oldest springtails (Hexapoda: Collembola) were probably mycophages, and another hexapod of uncertain affinities preserves a gut infill of phytodebris. The first true insects (Hexapoda: Insecta) are represented by a species known from chewing (non-carnivorous?) mandibles. Coprolites also provide insights into diet, and we challenge previous assumptions that several taxa were spore-feeders. Rhynie appears to preserve a largely intact community of terrestrial animals, although some expected groups are absent. The known fossils are (ecologically) consistent with at least part of the fauna found around modern Icelandic hot springs.This article is part of a discussion meeting issue 'The Rhynie cherts: our earliest terrestrial ecosystem revisited'.

The Lower Devonian Rhynie chert is one of the most important rock deposits yielding comprehensive information on early continental plant, animal and microbial life. Fungi are especially abundant among the microbial remains, and include representatives of all major fungal lineages except Basidiomycota. This paper surveys the evidence assembled to date of fungal hyphae, mycelial cords and reproductive units (e.g. spores, sporangia, sporocarps), and presents examples of fungal associations and interactions with land plants, other fungi, algae, cyanobacteria and animals from the Rhynie chert. Moreover, a small, chytrid-like organism that occurs singly, in chain-like, linear arrangements, planar assemblages and three-dimensional aggregates of less than 10 to [Formula: see text] individuals in degrading land plant tissue in the Rhynie chert is formally described, and the name Perexiflasca tayloriana proposed for the organism. Perexiflasca tayloriana probably colonized senescent or atrophied plant parts and participated in the process of biological degradation. The fungal fossils described to date from the Rhynie chert constitute the largest body of structurally preserved evidence of fungi and fungal interactions from any rock deposit, and strongly suggest that fungi played important roles in the functioning of the Early Devonian Rhynie ecosystem.This article is part of a discussion meeting issue 'The Rhynie cherts: our earliest terrestrial ecosystem revisited'.

The Early Devonian Rhynie chert and the nearby Windyfield chert contain the oldest in situ preserved terrestrial ecosystem. Two of the seven species of anatomically preserved land plants had naked axes, one an axis with a more or less regular pattern of short-longitudinal ribs, two species had spiny axes and one species had small leaf-like appendages. All plants mainly consist of parenchymatous tissues. In some species, conducting elements comprise uniformly thickened thick-walled cells resembling hydroids of larger bryophytes, whereas others have real tracheids with annular and/or spiral secondary wall thickenings. True phloem has never been demonstrated but in all species the thick-walled water-conducting cells are encircled by a zone of thin-walled cells without intercellular spaces. The cortex is differentiated into two or three zones and forms the major part of the axes; in one species the cells of the middle cortex are sclerified. Some species have a hypodermis. In all species the epidermis is covered by a well-developed cuticle. Sporangia are known from all species. Sporangia are spindle-shaped, lobed or kidney-shaped and attached terminally or laterally with a short stalk. Gametophytes of four species have been described. Gametophytes are unisexual, isomorphic but much smaller than the sporophytes.This article is part of a discussion meeting issue 'The Rhynie cherts: our earliest terrestrial ecosystem revisited'.

Photoautotrophic microorganisms were likely abundant in the Early Devonian Rhynie ecosystem;however, documented evidence of these life forms is rare. Hagenococcus aggregatus nov. gen. et sp. occurs in the Rhynie chert matrix as solitary cells, dyads, triads, linear, decussate, and isobilateral tetrads, sarcinoid packets, short filaments, irregular aggregations, and colonies. Individual cells are 15-40(->55) mu m in diameter. While it cannot be ruled out that H. aggregatus is a large cyanobacterium, affinities to the Chlorophyta or Streptophyta are far more likely. Some of the cells contain a prominent, spheroid inclusion which might represent the pyrenoid. Hagenococcus aggregatus expands our knowledge of the diversity of primary producers in Paleozoic non-marine ecosystems.

Premise of research. The Early Devonian Rhynie chert is an invaluable source for studying the morphology, ecology, and life cycles of early land plants, but information regarding morphological development in the Rhynie chert plants is sorely lacking.Methodology. Serial petrographic thin sectioning of the Rhynie chert reveals asexual propagules developing from the epidermal cells in the axes of the plant Rhynia gwynne-vaughanii. Three distinct developmental stages recording the formation of stomata, rhizoids, apical growth, and vascular tissue were observed. Similar propagules are also found developing from hemispherical projections, also on the axes of Rhynia.Pivotal results. The developmental pattern resembles that seen in somatic embryogenesis, a form of asexual reproduction that occurs naturally in extant plants as well as in in vitro, producing nutritionally independent plantlets from somatic plant cells.Conclusions. Our new observations on these propagules significantly contribute to a better understanding of how the tissues and organs of one of the earliest land plants formed. They allow us to compare the ontogeny of R. gwynne-vaughanii with that of extant land plant groups and demonstrate a form of asexual reproduction conserved over millions of years of plant evolution.

Oxygen isotope analysis of fossil organic matter by secondary ion mass spectrometry

A 365-Million-Year-Old Freshwater Community Reveals Morphological and Ecological Stasis in Branchiopod Crustaceans

The Early Devonian Rhynie chert has yielded the oldest evidence of hyphal investments (= mantles) in fungal reproductive units, with four different investment morphologies documented to date. This paper describes an unusual fungal reproductive unit from the Rhynie chert that is spheroid–elongate in outline, up to 60 μm in diameter, and consists of a thin-walled central cavity enveloped in a plectenchymatous or pseudoparenchymatous investment of tightly abutting, interwoven hyphae; pores extend through the investment. Several specimens contain a single spherical structure in the cavity. Because the structure of the investment differs from that seen in all other fossil fungal reproductive units, the new genus Scepasmatocarpion and species S. fenestrulatum are proposed for the new form. The systematic affinities of S. fenestrulatum remain unresolved. Nevertheless, the fossils support the hypothesis that the diversity of the fungi that produced hyphal envelopes was extensive by the Early Devonian.

ABSTRACTMaterial excavated from a trench dug to expose the Rhynie Cherts Unit of the Dryden Flags Formation included blocks of Rhynie chert up to 50 cm thick and comprising the full thickness of plant-bearing chert beds. These blocks, and others collected as float, display a variety of macro-textures typical of silicification at the terrestrial surface and in shallow water. On sandy terrestrial surfaces, autochthonous and allochthonous plant debris and plant rhizomes are well preserved, but aerial axes generally decayed prior to silicification. In shallow water, clonal plants, particularlyRhynia, are preserved with aerial axes in growth position, supported by microbial mats and meshworks. Preservation of such delicate fabrics required the creation of a load-bearing framework early in the silicification process, to prevent crushing during early burial.On the microscale, plant taphonomy reveals characteristic features due to plant decay prior to silicification in both wet and dry conditions, and also during the silicification process. Silicification of plants was frequently very rapid, preserving delicate transient features such as spore germination and ejection of sperm cells from antheridia. In situations where plant tissue continued to decay during silicification, the process was slower.

Abstract An assemblage of unusual microfossils occurs within an accumulation of plant debris, hyphae, and various types of propagules in the Early Devonian Rhynie chert. Specimens consist of a vesicle with one or more prominent wings (alae) arising from the surface; one wing forms a rim around the equator of the vesicle. The microfossils are interpreted as phycomata of a prasinophycean green alga based on morphological similarities to Pterospermella, a microfossil similar to phycoma stages of the extant Pterosperma (Pyramimonadales). This report represents the third record of phycomata in the Rhynie chert, suggesting that this Early Devonian ecosystem served as habitat to a variety of prasinophyte algae. Moreover, the new microfossils add to the inventory of fossil freshwater representatives of this predominantly marine group of algae.

A perithecial ascomycete, Spataporthe taylori gen. et sp. nov., represented by >70 sporocarps is preserved by cellular permineralization in marine carbonate concretions dated at the Valanginian-Hauterivian boundary (Early Cretaceous) from Vancouver Island, British Columbia, Canada. The spheroid perithecia with lumina 330–470 μm wide and 220–320 μm high are densely distributed and entirely immersed in the tissues of a coniferous leaf. The perithecial wall consists of an outer layer of large pseudoparenchyma and an inner layer of thin filamentous nature. Perithecial necks are incompletely preserved due to taphonomic abrasion; they have a bell-shaped chamber at the base and a narrow channel, with longitudinally aligned hyphae above. The basal chamber of the neck is filled with a plug of pseudoparenchyma, which subsequently disintegrates to form a peripheral collar; periphyses are present on the basal chamber walls. A pseudoparenchymatous hymenium lines the bottom of perithecia. Asci are clavate, with thinly tapered bases, and small (30–47 μm long and 12–20 μm wide at tip), ornamented with minute papillae. They become detached from the hymenium to float freely in the perithecium. No unequivocal ascospores were found, although smaller units are present in some of the asci. The combination of immersed perithecia with complex wall structure and a well-defined hymenium, absence of paraphyses, and persistent, detachable inoperculate asci is consistent with order Diaporthales of class Sordariomycetes. The small clavate asci are comparable to those found in family Gnomoniaceae. Perithecioid ascomata are rare in the fossil record, and bona fide perithecia are known with certainty only from the Early Devonian Rhynie Chert and Cenozoic amber. Spataporthe taylori contributes a well-characterized Early Cretaceous occurrence, which is also the oldest to date, to the scarce fossil record of the Sordariomycetes and a second taxon to the fungal flora of the locality, which also includes a basidiomycete. As the oldest representative of the Diaporthales, Spataporthe provides a minimum age (136 Ma) for the order and a direct calibration point for studies of divergence times in the ascomycetes.

The Early Devonian Rhynie cherts represent the surface deposits of a subaerial hot spring system. Historically palaeobotanists have studied the exceptionally preserved early land plants contained within the cherts by mounting thin sections of the rock on glass microscope slides. Investigation of plant morphology and life habitat has relied on reconstruction from consecutive serial sections with the inherent loss of information at the blade width scale. Here we detail the previously unrealised potential for some of the Rhynie chert beds to respond well to mechanical preparation. Recognition that some chert beds may be prepared in this way provides an additional technique for the continued investigation of the flora and fauna of this important fossil locality. The technique might find wider application in the investigation of other more recently discovered fossil-bearing sinters worldwide.

A fossil trigonotarbid (Arachnida: Trigonotarbida) assigned to Palaeocharinus sp. from the Early Devonian (c. 410 Ma) Rhynie cherts of Aberdeenshire, Scotland, UK is described, specifically for a previously unrecognised feature of the distal end of the pedipalp. This exhibits a small chela formed from a movable, unpaired apotele articulating against a slightly shorter, fixed projection from the inferior surface of the tarsus. Among other arachnids, this morphology has only previously been observed in the rare and enigmatic Carboniferous—Recent taxon Ricinulei. This character offers explicit support for a monophylum (Trigonotarbida + Ricinulei); a hypothesis previously based on opisthosomal characters which (if correct) would draw Ricinulei within the so-called Pantetrapulmonata clade (i.e. spiders and their closest relatives). Our data is not consistent with Ricinulei’s traditional position as sister-group of mites (Acari) and is an example of how considering extinct taxa may help to resolve the position of a ‘difficult’ living group.

The book lungs of an exceptionally preserved fossil arachnid (Trigonotarbida) from the Early Devonian (approx. 410 Myr ago) Rhynie cherts of Scotland were studied using a non-destructive imaging technique. Our three-dimensional modelling of fine structures, based on assembling successive images made at different focal planes through the translucent chert matrix, revealed for the first time fossil trabeculae: tiny cuticular pillars separating adjacent lung lamellae and creating a permanent air space. Trabeculae thus show unequivocally that trigonotarbids were fully terrestrial and that the microanatomy of the earliest known lungs is indistinguishable from that in modern Arachnida. A recurrent controversy in arachnid evolution is whether the similarity between the book lungs of Pantetrapulmonata (i.e. spiders, trigonotarbids, etc.) and those of scorpions is a result of convergence. Drawing on comparative studies of extant taxa, we have identified explicit characters (trabeculae, spines on the lamellar edge) shared by living and fossil arachnid respiratory organs, which support the hypothesis that book lungs were derived from a single, common, presumably terrestrial, ancestor.