Early Devonian Rhynie Chert Research Articles

An evidence-based 3D reconstruction of Asteroxylon mackiei, the most complex plant preserved from the Rhynie chert.

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

Glomeromycotan propagules (spores) are morphologically diverse in the Early Devonian Rhynie chert; however, only relatively few of these fossils have been documented and critically evaluated. This study re-examines propagules previously described informally as ‘reproductive unit 1’, and identified as glomeromycotan acaulospores borne within the neck of a sporiferous saccule. Size and morphology, spore wall structure, and the close association of specimens in land plant axes with small glomoid spores, are solid arguments for affinities of ‘reproductive unit 1’ to the Ambisporaceae (Archaeosporales). Moreover, the acaulospores correspond morphologically to Mycokidstonia sphaerialoides, a Rhynie chert fossil originally interpreted as an ascomycete perithecium that, consequently, is redefined here as a member of the Glomeromycota conspecific with ‘reproductive unit 1’. The diagnosis for M. sphaerialoides is emended to be compliant with glomeromycotan taxonomy; features of the saccule, acaulospore wall, and associated glomoid spores are included. An epitype is also designated. Mycokidstonia sphaerialoides adds to an increasing body of fossil data depicting Devonian Glomeromycota as a diverse fungal lineage which is likely to have been an ecologically important constituent of early terrestrial ecosystems.

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

Glomeromycotan spores from the Early Devonian Rhynie chert frequently contain evidence of colonization by other fungi. However, relatively few of these relationships have been described and evaluated. Brijax amictus gen. et sp. nov., a probable chytrid (Chytridiomycota) associated with certain thick-walled archaeosporalean acaulospores from the Rhynie chert, develops largely within the host spore wall. Thalli are eucarpic, monocentric, 16.5–40(−50) μm high, and consist of an inoperculate sporangium (zoosporangium or resting spore stage) located in the outer, ephemeral spore wall component, and a rhizoidal system that extends into the persistent spore wall. Sporangia that, at maturity, are completely surrounded by the host spore wall develop a prominent discharge tube, whereas ones not covered by the host wall have simple openings or pores. Thallus morphology resembles certain present-day species of Rhizophydium (Rhizophydiales) and Phlyctochytrium (Chytridiales); however, the systematic affinities of B. amictus remain unresolved. This discovery contributes to the understanding of the various levels of interfungal relationship that existed in early terrestrial ecosystems.

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

Various types of other fungi colonize glomeromycotinan (Mucoromycota) spores in the Early Devonian Rhynie chert. However, relatively few of these associations have been described and evaluated in detail. One particular type of glomoid spore located in degrading land plant axes from the Rhynie chert provides evidence of (simultaneous) interaction with three different fungi. Massive callosities occur around the intrusion filaments of a chytrid-like parasite with epibiotic sporangia, while the hyphae of a delicate mycelial fungus extend into the spore lumen without triggering a recognizable host response. Several spores show large numbers of inwardly directed projections, which are regularly distributed and consist of a short hyphal branch encased in host wall material. The projections represent the penetration sites of a distinctive, mycelial fungus that forms a mantle-like hyphal sheath around the spores. This type of fungal interaction with glomeromycotinan spores has not previously been reported, and thus expands our knowledge of the numerous interfungal relationships that existed in early continental ecosystems.

Organs and tissues of Rhynie chert plants.

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'.

Whole-Plant Regeneration via Epidermal Cells in the Axis of the Early Devonian Rhynie Chert PlantRhynia gwynne-vaughaniiKidston et Lang

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 underst...

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

Branchiopod crustaceans are represented by fairy, tadpole, and clam shrimps (Anostraca, Notostraca, Laevicaudata, Spinicaudata), which typically inhabit temporary freshwater bodies, and water fleas (Cladoceromorpha), which live in all kinds of freshwater and occasionally marine environments [1, 2]. The earliest branchiopods occur in the Cambrian, where they are represented by complete body fossils from Sweden such as Rehbachiella kinnekullensis [3] and isolated mandibles preserved as small carbonaceous fossils [4-6] from Canada. The earliest known continental branchiopods are associated with hot spring environments [7] represented by the Early Devonian Rhynie Chert of Scotland (410 million years ago) and include possible stem-group or crown-group Anostraca, Notostraca, and clam shrimps or Cladoceromorpha [8-10], which differ morphologically from their modern counterparts [1, 2, 11]. Here we report the discovery of an ephemeral pool branchiopod community from the 365-million-year-old Strud locality of Belgium. It is characterized by new anostracans and spinicaudatans, closely resembling extant species, and the earliest notostracan, Strudops goldenbergi [12]. These branchiopods released resting eggs into the sediment in a manner similar to their modern representatives [1, 2]. We infer that this reproductive strategy was critical to overcoming environmental constraints such as seasonal desiccation imposed by living on land. The pioneer colonization of ephemeral freshwater pools by branchiopods in the Devonian was followed by remarkable ecological and morphological stasis that persists to the present day.

A fungal reproductive unit from the Lower Devonian Rhynie chert (Aberdeenshire, Scotland) that demonstrates an unusual hyphal investment pattern

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.

Macro to micro aspects of the plant preservation in the Early Devonian Rhynie cherts, Aberdeenshire, Scotland

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.

Microfossils With Suggested Affinities To The Pyramimonadales (Pyramimonadophyceae, Chlorophyta) From The Lower Devonian Rhynie Chert

AbstractAn 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 Sordariomycete (Ascomycota, Diaporthales) from the Lower Cretaceous of Vancouver Island, British Columbia, Canada

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.

A mechanical preparation of Rhynie Chert fossils.

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 arachnid with a ricinuleid-like pedipalpal claw

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.

Microanatomy of Early Devonian book lungs

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.

A prasinophycean alga of the genus Cymatiosphaera in the Early Devonian Rhynie chert

Spherical phycomata of prasinophycean algae are preserved in the Early Devonian Rhynie chert. Because they display a surface reticulum composed of muri oriented perpendicular to the vesicle surface, they are assigned to the genus Cymatiosphaera (Cymatiosphaeraceae, Pyramimonadales). We interpret the size range of the phycomata (24 to 48 μm in overall diameter) as reflecting continued metabolic activity and growth of the alga during the phycoma stage. The phycomata from the Rhynie chert represent the earliest account of the genus Cymatiosphaera in a freshwater paleoecosystem, and broaden our knowledge about the ecological diversity of Early Devonian prasinophycean algae.

A filamentous cyanobacterium showing structured colonial growth from the Early Devonian Rhynie chert

This paper describes a new aquatic filamentous-colonial fossil cyanobacterium from the Early Devonian Rhynie chert that grows on sediment and submerged plant parts. It is associated with the formation of microbial mats, and occurs in structured colonies, in which the individual filaments are aligned more or less parallel into flat, irregular stands, or united radially into hemispherical aggregates; it may also form elongate, fan-shaped tufts. Individual filaments are ∼ 3 μm in diameter, and consist of uniseriate trichomes composed of barrel-shaped cells enveloped in a thin but distinct sheath. Heterocysts and akinetes have not been observed, which suggests that the cyanobacterium belongs to the cyanobacterial subsection III (Oscillatoriales). This is the first account for sessile, structured colonial growth in cyanobacteria from the Rhynie chert.

Fungal endophytes in a 400‐million‐yr‐old land plant: infection pathways, spatial distribution, and host responses

The Early Devonian Rhynie chert has been critical in documenting early land plant-fungal interactions. However, complex associations involving several fungi that enter into qualitatively different relationships with a single host plant and even interact with one another have not yet been detailed. Here, we studied petrographic thin sections of the Rhynie chert plant Nothia aphylla. Three fungal endophytes (co)occur in prostrate axes of this plant: narrow hyphae producing clusters of small spores; large spherical spores/zoosporangia; and wide aseptate hyphae that form intercellular vesicles in the cortex. Host responses on attack include bulging of infected rhizoids, formation of encasement layers around intracellular hyphae, and separation of infected from uninfected tissues by secondarily thickened cell walls. A complex simultaneous interaction of N. aphylla with three endophytic fungi was discovered. The host responses indicate that some of the mechanisms causing host responses in extant plants were in place 400 million yr ago. Anatomical and life history features of N. aphylla suggest that this plant may have been particularly susceptible to colonization by fungi.

A new arthropod from the early Devonian Rhynie chert, Aberdeenshire (Scotland), with a remarkable filtering device in the mouthparts

A new arthropodSaccogulus seldeni n. gen. n. sp. is described from the Early Devonian Rhynie cherts, Aberdeenshire, Scotland, UK. Although an incomplete thin section preparation, this enigmatic fossil differs substantially in overall shape and in various morphological details from previous named discoveries at Rhynie. A remarkable feature is what appears to be a very thick cuticle, albeit with a curious spongiform texture and ducts running through it. Secondly, associated with the mouth is a unique, elongate, steeply-rising structure comprising filamentous or platelet-like projections. This probably acted as some sort of post-oral (?) filtering device and implies a terrestrial animal; a liquid-feeder that practised preoral digestion. Affinities of this new fossil remain equivocal, but preoral digestion implies an arachnid. Indeed the overall outline present in the thin section and, perhaps, the filtering device show some intriguing similarities to spiders (Araneae).

Fossils explained 51

The Earth???s oldest terrestrial ecosystems date from the Late Silurian period, about 414 million years ago. Amongst primitive plants lived the first land-based animals; invertebrate invaders of a new world, some 30 million years before vertebrates made the very same transition. The fossil record suggests many early land animals were arthropods, belonging to subgroups such as Myriapoda (e.g. millipedes and centipedes) and Arachnida (e.g. spiders, scorpions, mites, etc.). Trigonotarbids belong to the latter. They are appar- ently primitive arachnids, superficially similar in ap- pearance to spiders, but lacking the ability to produce silk. Their presence at Ludford Lane in the Welsh Borderlands in the UK (P??\'{\i}dol\'{\i}, Late Silurian) places the group amongst the earliest terrestrial animals, and their anatomy is well known from exception- ally preserved, silicified fossils in the slightly younger Early Devonian Rhynie Chert of Scotland (Fig. 1). By the Late Carboniferous, trigonotarbids seem to have been amongst the most abundant arachnids; at least their fossils are relatively common throughout the Coal Measures deposits of Europe and North America. They have also been recorded in South America. Such success didn???t last???the group became extinct in the Permian.

Perithecial ascomycetes from the 400 million year old Rhynie chert: an example of ancestral polymorphism

We describe a perithecial, pleomorphic ascomycetous fungus from the Early Devonian (400 mya) Rhynie chert; the fungus occurs in the cortex just beneath the epidermis of aerial stems and rhizomes of the vascular plant Asteroxylon. Perithecia are nearly spherical with a short, ostiolate neck that extends into a substomatal chamber of the host plant; periphyses line the inner surface of the ostiole. The ascocarp wall is multilayered and formed of septate hyphae; extending from the inner surface are elongate asci interspersed with delicate paraphyses. Asci appear to be unitunicate and contain up to 16 smooth, uniseriate-biseriate ascospores. The method of ascospore liberation is unknown; however, the tip of the ascus is characterized by a narrow, slightly elevated circular collar. Ascospores appear 1–5 celled, and germination is from one end of the spore. Also present along the stems and interspersed among the perithecia are acervuli of conidiophores that are interpreted as the anamorph of the fungus. Conidiogenesis is thallic, basipetal and probably of the holoarthric-type; arthrospores are cube-shaped. Some perithecia contain mycoparasites in the form of hyphae and thick-walled spores of various sizes. The structure and morphology of the fossil fungus is compared with modern ascomycetes that produce perithecial ascocarps, and characters that define the fungus are considered in the context of ascomycete phylogeny.