Paul K. Strother

New evidence for land plants from the lower Middle Ordovician of Saudi Arabia

Macerations of Middle Ordovician (Llanvirnian) shales from Saudi Arabia yield an assemblage of spores of probable land plants (cryptospores), acritarchs, and chitinozoa. The production of sporopollenin-containing, sporelike tetrads is considered a fundamental character of the embryophytes, because no extant algae produce spores of this type. No trilete spores were found at this horizon, reinforcing previous assertions that obligate meiotic tetrads predate the earliest trilete spores. Sporomorph tetrads and dyads, in conjunction with cuticlelike fragments, were probably derived from terrestrial plants at a bryophyte grade. Although there are reports of possibly older cryptospores, the Hanadir assemblage described herein clearly establishes their presence by Llanvirnian time.

Plant microfossils from Llandoverian and Wenlockian rocks of Pennsylvania

Abstract Macerations of greenish shales from the Tuscarora Formation (Llandoverian) and Clinton? strata (Wenlockian) in central and eastern Pennsylvania yield a remarkable assemblage of spores and probable spores, dyads, spore tetrads, tubular and cuticle‐like structures. These are considered as remains of a pre‐vascular plant, terrestrial flora and are discussed according to this interpretation. Although this study is preliminary in nature, we have described the following new taxa: Rugosphaera tuscarorensis (n.gen., n.sp.), Tetrahedraletes medinensis (n.gen., n.sp.), Nodospora burnhamensis (n.gen., n.sp.), Nodospora rugosa (n.sp.), Nodospora oyleri (n.sp.), Dyadospora murusattenuata (n.gen., n.sp.) and Dyadospora murusdensa (n.sp.).

Earth’s earliest non-marine eukaryotes

The existence of a terrestrial Precambrian (more than 542 Myr ago) biota has been largely inferred from indirect chemical and geological evidence associated with palaeosols, the weathering of clay minerals and microbially induced sedimentary structures in siliciclastic sediments. Direct evidence of fossils within rocks of non-marine origin in the Precambrian is exceedingly rare. The most widely cited example comprises a single report of morphologically simple mineralized tubes and spheres interpreted as cyanobacteria, obtained from 1,200-Myr-old palaeokarst in Arizona. Organic-walled microfossils were first described from the non-marine Torridonian (1.2–1.0 Gyr ago) sequence of northwest Scotland in 1907. Subsequent studies found few distinctive taxa—a century later, the Torridonian microflora is still being characterized as primarily nondescript “leiospheres”. We have comprehensively sampled grey shales and phosphatic nodules throughout the Torridonian sequence. Here we report the recovery of large populations of diverse organic-walled microfossils extracted by acid maceration, complemented by studies using thin sections of phosphatic nodules that yield exceptionally detailed three-dimensional preservation. These assemblages contain multicellular structures, complex-walled cysts, asymmetric organic structures, and dorsiventral, compressed organic thalli, some approaching one millimetre in diameter. They offer direct evidence of eukaryotes living in freshwater aquatic and subaerially exposed habitats during the Proterozoic era. The apparent dominance of eukaryotes in non-marine settings by 1 Gyr ago indicates that eukaryotic evolution on land may have commenced far earlier than previously thought.

Distribution and diagenesis of microfossils from the lower Proterozoic Duck Creek Dolomite, Western Australia.

Two distinct generations of microfossils occur in silicified carbonates from a previously undescribed locality of the Lower Proterozoic Duck Creek Dolomite, Western Australia. The earlier generation occurs in discrete organic-rich clasts and clots characterized by microquartz anhedra; it contains a variety of filamentous and coccoidal fossils in varying states of preservation. Second generation microfossils consist almost exclusively of well-preserved Gunflintia minuta filaments that drape clasts or appear to float in clear chalcedony. These filaments appear to represent an ecologically distinct assemblage that colonized a substrate containing the partially degraded remains of the first generation community. The two assemblages differ significantly in taxonomic frequency distribution from previously described Duck Creek florules. Taken together, Duck Creek microfossils exhibit a range of assemblage variability comparable to that found in other Lower Proterozoic iron formations and ferruginous carbonates. With increasing severity of post-mortem alteration, Duck Creek microfossils appear to converge morphologically on assemblages of simple microstructures described from early Archean cherts. Two new species are described: Oscillatoriopsis majuscula and O. cuboides; the former is among the largest septate filamentous fossils described from any Proterozoic formation.

A classification schema for the cryptospores

Abstract The cryptospores are a class of sporomorphs which is distinct from trilete and monolete spores, pollen grains and acritarchs. These spore‐like palynomorphs are similar in many respects to spores of embryophytes. Because immediate biological affinity is unknown for species of cryptospores, their classification is most effectively achieved through the construction of an artificial system. The schema presented here is an artificial one based on morphology and does not represent a phylogenetic classification which groups species on the basis of ancestor‐descendant relationships. One new species, Tetrahedraletes grayii is described as the oldest known permanent tetrad cryptospore from North America. Three species of dyads, Dicryptosporites radiatus gen. et sp. nov., D. minus, and Confossuspora reniforma gen. et sp. nov. are also described.

Early land plant debris (Hooker's "waifs and strays"?)

Information derived from Ordovician to Devonian phytodebris is discussed in terms of its utility in phylogenetic; bistratigraphic, paleoecologic and biogeographic studies. Several preparation techniques are described. Studies of latest Ordovician through Early Devonian land plant phytodebris have been important in addressing the origin of early land plants, in making taxonomic distinctions at the species through ordinal levels, and in documenting the phyletic radiation of early land plants

New species of Nematothallus from the Silurian Bloomsburg Formation of Pennsylvania

The early terrestrial fossil record contains numerous Siluro-Devonian problematic Thallophyta which have morphological and habitat characteristics intermediate between the algae and the embryophytic plant kingdom. Three new species of the genus Nematothallus Lang ( N. taenia, N. lobata , and N. elliptica ) are described from a coaly lens in the Bloomsburg Formation (Ludlow). They are included in the order Nematophytales, which is placed in a new informal taxonomic group, Paraphyta, intended to include enigmatic, terrestrial plant-like fossils. These species designations are based upon the gross morphology of carbonized thalli which consist of an underlying anatomy of flattened tubular elements. The association and attachment of cuticles and axes of ? Prototaxites to Nematothallus is clearly demonstrated in these collections. The morphological and anatomical variety expressed in the numerous fragments of thalli from the deposit implies moderate levels of organic diversity in a “flora” of nonvascular, terrestrial plant-like thallophytes which predates the adaptive radiation of the embryophytes.

Observations on the genus huroniospora barghoorn: Implications for paleoecology of the gunflint microbiota

Abstract Examination of exceptionally well-preserved thin-sections of Gunflint Chert reveals new morphological criteria which are utilized for a critical evaluation of the genus Huroniospora . The shape varies from spheroidal to ellipsoidal. One-third of the specimens examined have either simple circular apertures or breaks in the vessel wall. Wall structure and surface texture appear to vary with quality of preservation. These and other features lead to the conclusion that Huroniospora represents a spore or encysted cell rather than a vegetative cell. The presence of Huroniospora in the Schreiber Beach assemblage does not constitute direct evidence for the primary photosynthetic nature of the interlaminar community.

Enhanced cellular preservation by clay minerals in 1 billion-year-old lakes

Organic-walled microfossils provide the best insights into the composition and evolution of the biosphere through the first 80 percent of Earth history. The mechanism of microfossil preservation affects the quality of biological information retained and informs understanding of early Earth palaeo-environments. We here show that 1 billion-year-old microfossils from the non-marine Torridon Group are remarkably preserved by a combination of clay minerals and phosphate, with clay minerals providing the highest fidelity of preservation. Fe-rich clay mostly occurs in narrow zones in contact with cellular material and is interpreted as an early microbially-mediated phase enclosing and replacing the most labile biological material. K-rich clay occurs within and exterior to cell envelopes, forming where the supply of Fe had been exhausted. Clay minerals inter-finger with calcium phosphate that co-precipitated with the clays in the sub-oxic zone of the lake sediments. This type of preservation was favoured in sulfate-poor environments where Fe-silicate precipitation could outcompete Fe-sulfide formation. This work shows that clay minerals can provide an exceptionally high fidelity of microfossil preservation and extends the known geological range of this fossilization style by almost 500 Ma. It also suggests that the best-preserved microfossils of this time may be found in low-sulfate environments.

Aeroterrestrial Coleochaete (Streptophyta, Coleochaetales) models early plant adaptation to land

PREMISE OF THE STUDY The streptophyte water-to-land transition was a pivotal, but poorly understood event in Earth history. While some early-diverging modern streptophyte algae are aeroterrestrial (living in subaerial habitats), aeroterrestrial survival had not been tested for Coleochaete, widely regarded as obligately aquatic and one of the extant green algal genera most closely related to embryophytes. This relationship motivated a comparison of aeroterrestrial Coleochaete to lower Paleozoic microfossils whose relationships have been uncertain. METHODS We tested the ability of two species of the experimentally tractable, complex streptophyte algal genus Coleochaete Bréb. to (1) grow and reproduce when cultivated under conditions that mimic humid subaerial habitats, (2) survive desiccation for some period of time, and (3) produce degradation-resistant remains comparable to enigmatic Cambrian microfossils. KEY RESULTS When grown on mineral agar media or on quartz sand, both species displayed bodies structurally distinct from those expressed in aquatic habitats. Aeroterrestrial Coleochaete occurred as hairless, multistratose, hemispherical bodies having unistratose lobes or irregular clusters of cells with thick, layered, and chemically resistant walls that resemble certain enigmatic lower Paleozoic microfossils. Whether grown under humid conditions or air-dried for a week, then exposed to liquid water, aeroterrestrial Coleochaete produced typical asexual zoospores and germlings. Cells that had been air-dried for periods up to several months maintained their integrity and green pigmentation. CONCLUSIONS Features of modern aeroterrestrial Coleochaete suggest that ancient complex streptophyte algae could grow and reproduce in moist subaerial habitats, persist through periods of desiccation, and leave behind distinctive microfossil remains.