Precambrian micro‐organisms and evolutionary events prior to the origin of vascular plants
TL;DR: The nature of the early Palaeozoic life was a fertile subject for speculation as mentioned in this paper, however, evidence of this development remained largely undeciphered ; the nature of Precambrian life was also fertile subject to speculation.
Abstract: The nature of the Precambrian biota-its antiquity. composition and evolutionand the well-known faunal discontinuity near the beginning of the Palaeozoic. have long been recognized as particularly puzzling problems in palaeontology . The evolutionary continuum well-documented in Phanerozoic sediments and the diversity and complexity of the early Palaeozoic biota augur well for a substantial period of Precambrian evolutionary development . Until recently. however. evidence of this development remained largely undeciphered ; the nature of Precambrian life was a fertile subject for speculation. essentially unfettered by the poorly known fossil record . The past few years have witnessed a renewed interest in these classic problems and a marked proliferation of available data; this increased activity has resulted in the
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TL;DR: It is argued that the essentially autogenous origins of most eukaryotic cell properties (phagotrophy, endomembrane system including peroxisomes, cytoskeleton, nucleus, mitosis and sex) partially overlapped and were synergistic with the symbiogenetic origin of mitochondria from an alpha-proteobacterium.
Abstract: Eukaryotes and archaebacteria form the clade neomura and are sisters, as shown decisively by genes fragmented only in archaebacteria and by many sequence trees. This sisterhood refutes all theories that eukaryotes originated by merging an archaebacterium and an alpha-proteobacterium, which also fail to account for numerous features shared specifically by eukaryotes and actinobacteria. I revise the phagotrophy theory of eukaryote origins by arguing that the essentially autogenous origins of most eukaryotic cell properties (phagotrophy, endomembrane system including peroxisomes, cytoskeleton, nucleus, mitosis and sex) partially overlapped and were synergistic with the symbiogenetic origin of mitochondria from an alpha-proteobacterium. These radical innovations occurred in a derivative of the neomuran common ancestor, which itself had evolved immediately prior to the divergence of eukaryotes and archaebacteria by drastic alterations to its eubacterial ancestor, an actinobacterial posibacterium able to make sterols, by replacing murein peptidoglycan by N-linked glycoproteins and a multitude of other shared neomuran novelties. The conversion of the rigid neomuran wall into a flexible surface coat and the associated origin of phagotrophy were instrumental in the evolution of the endomembrane system, cytoskeleton, nuclear organization and division and sexual life-cycles. Cilia evolved not by symbiogenesis but by autogenous specialization of the cytoskeleton. I argue that the ancestral eukaryote was uniciliate with a single centriole (unikont) and a simple centrosomal cone of microtubules, as in the aerobic amoebozoan zooflagellate Phalansterium. I infer the root of the eukaryote tree at the divergence between opisthokonts (animals, Choanozoa, fungi) with a single posterior cilium and all other eukaryotes, designated 'anterokonts' because of the ancestral presence of an anterior cilium. Anterokonts comprise the Amoebozoa, which may be ancestrally unikont, and a vast ancestrally biciliate clade, named 'bikonts'. The apparently conflicting rRNA and protein trees can be reconciled with each other and this ultrastructural interpretation if long-branch distortions, some mechanistically explicable, are allowed for. Bikonts comprise two groups: corticoflagellates, with a younger anterior cilium, no centrosomal cone and ancestrally a semi-rigid cell cortex with a microtubular band on either side of the posterior mature centriole; and Rhizaria [a new infrakingdom comprising Cercozoa (now including Ascetosporea classis nov.), Retaria phylum nov., Heliozoa and Apusozoa phylum nov.], having a centrosomal cone or radiating microtubules and two microtubular roots and a soft surface, frequently with reticulopodia. Corticoflagellates comprise photokaryotes (Plantae and chromalveolates, both ancestrally with cortical alveoli) and Excavata (a new protozoan infrakingdom comprising Loukozoa, Discicristata and Archezoa, ancestrally with three microtubular roots). All basal eukaryotic radiations were of mitochondrial aerobes; hydrogenosomes evolved polyphyletically from mitochondria long afterwards, the persistence of their double envelope long after their genomes disappeared being a striking instance of membrane heredity. I discuss the relationship between the 13 protozoan phyla recognized here and revise higher protozoan classification by updating as subkingdoms Lankester's 1878 division of Protozoa into Corticata (Excavata, Alveolata; with prominent cortical microtubules and ancestrally localized cytostome--the Parabasalia probably secondarily internalized the cytoskeleton) and Gymnomyxa [infrakingdoms Sarcomastigota (Choanozoa, Amoebozoa) and Rhizaria; both ancestrally with a non-cortical cytoskeleton of radiating singlet microtubules and a relatively soft cell surface with diffused feeding]. As the eukaryote root almost certainly lies within Gymnomyxa, probably among the Sarcomastigota, Corticata are derived. Following the single symbiogenetic origin of chloroplasts in a corticoflagellate host with cortical alveoli, this ancestral plant radiated rapidly into glaucophytes, green plants and red algae. Secondary symbiogeneses subsequently transferred plastids laterally into different hosts, making yet more complex cell chimaeras--probably only thrice: from a red alga to the corticoflagellate ancestor of chromalveolates (Chromista plus Alveolata), from green algae to a secondarily uniciliate cercozoan to form chlorarachneans and independently to a biciliate excavate to yield photosynthetic euglenoids. Tertiary symbiogenesis involving eukaryotic algal symbionts replaced peridinin-containing plastids in two or three dinoflagellate lineages, but yielded no major novel groups. The origin and well-resolved primary bifurcation of eukaryotes probably occurred in the Cryogenian Period, about 850 million years ago, much more recently than suggested by unwarranted backward extrapolations of molecular 'clocks' or dubious interpretations as 'eukaryotic' of earlier large microbial fossils or still more ancient steranes. The origin of chloroplasts and the symbiogenetic incorporation of a red alga into a corticoflagellate to create chromalveolates may both have occurred in a big bang after the Varangerian snowball Earth melted about 580 million years ago, thereby stimulating the ensuing Cambrian explosion of animals and protists in the form of simultaneous, poorly resolved opisthokont and anterokont radiations.
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Cites background from "Precambrian micro‐organisms and evo..."
...Origin of sex: cell fusion and syngamy Whether sex was necessary, important (as often assumed, e.g. Schopf, 1970) or relatively trivial for the origin of eukaryotes is unclear to me....
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TL;DR: It is hypothesized that terrestrial plants are the product of an ancient and continuing symbiosis of a semi-aquatic ancestral green alga and an aquatic fungus-an oomycete that were equipped to cope with the problems of desiccation and starvation associated with terrestrial existence.
Abstract: It is hypothesized that terrestrial plants are the product of an ancient and continuing symbiosis of a semi-aquatic ancestral green alga and an aquatic fungus-an oomycete. The Siluro-Devonian "explosive" colonization of land, and indeed the very evolution of plants, was possible only through such mutualistic partnerships-partnerships that were equipped to cope with the problems of desiccation and starvation associated with terrestrial existence.
615 citations
TL;DR: Comparisons of dated pollen floras of other regions indicate that one major subgroup of angiosperms, tricolpate-producing dicots (i.e., excluding Magnoliidae of Takhtajan) originated in the Aptian of Africa-South America at a time of increasing aridity and migrated poleward into Laurasia and Australasia.
Abstract: Morphological, stratigraphic, and sedimentological analyses of Early Cretaceous pollen and leaf sequences, especially from the Potomac Group of the eastern United States, support the concept of a Cretaceous adaptive radiation of the angiosperms and suggest pathways of their initial ecological and systematic diversification. The oldest acceptable records of angiosperms are rare monosulcate pollen grains with columellar exine structure from probable Barremian strata of England, equatorial Africa, and the Potomac Group, and small, simple, pinnately veined leaves with several orders of reticulate venation from the Neocomian of Siberia and the basal Potomac Group. The relatively low diversity and generalized character of these fossils and the subsequent coherent pattern of morphological diversification are consistent with a monophyletic origin of the angiosperms not long before the Barremian. PatuxentArundel floras (Barremian-early Albian?) of the Potomac Group include some pollen and leaves with monocotyledonous features as well as dicotyledonous forms. Patuxent angiosperm pollen is strictly monosulcate and has exine sculpture indicative of insect pollination. Rare Patuxent-Arundel angiosperm leaves are generally small, have disorganized venation, and are largely restricted to sandy stream margin lithofacies; the largest are comparable to and may include ancestors of woody Magnoliidae adapted to understory conditions. Patapsco floras (middle to late Albian?) contain rapidly diversifying tricolpate pollen and several new complexes of locally abundant angiosperm leaves. Ovate-cordate and peltate leaves in clayey pond lithofacies may includeancestors of aquatic Nymphaeales and Nelumbonales. Pinnatifid and later pinnately compound leaves with increasingly regular venation which are abundant just above rapid changes in sedimentation are interpreted as early successional “weed trees” transitional to but more primitive than the modern subclass Rosidae. Apparently related palmately lobed, palinactinodromous leaves which develop rigidly percurrent tertiary venation and become abundant in uppermost Potomac stream margin deposits (latest Albian-early Cenomanian?) are interpreted as riparian trees ancestral to the order Hamamelidales. Comparisons of dated pollen floras of other regions indicate that one major subgroup of angiosperms, tricolpate-producing dicots (i.e., excluding Magnoliidae of Takhtajan) originated in the Aptian of Africa-South America at a time of increasing aridity and migrated poleward into Laurasia and Australasia. However, the earlier (Barremian) monosulcate phase of the angiosperm record is represented equally in Africa-South America and Laurasia before marked climatic differentiation between the two areas. These trends are considered consistent with the hypothesis that the angiosperms originated as small-leafed shrubs of seasonally arid environments, and underwent secondary expansion of leaf area and radiated into consecutively later successional stages and aquatic habitats after entering mesic regions as riparian “weeds,” as opposed to the concept that they arose as trees of mesic forest environments.
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411 citations
TL;DR: Action spectra and relative quantum efficiency measurements demonstrated the existence of both Photosystem I and Photosystem II in membrane fragments which contained chlorophyll a as the only significant light-absorbing pigment.
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628 citations
TL;DR: In this paper, a study was made of the reasons for isotopic fractionation in photosynthesis and various factors controlling it, and the effects of high light intensities on the fractionation factors of photosynthesis were studied.
521 citations
Journal Article•
TL;DR: In this article, 30 new species, representing 24 new genera, of green algae, blue-green algae, colonial bacteria, fungus-like filaments, and possible pyrrophytes, are described from the bedded carbonaceous cherts of the late Precambrian Bitter Springs formation, Ross river area, central Australia.
Abstract: Thirty new species, representing 24 new genera, of green algae, blue-green algae, colonial bacteria, fungus-like filaments, and possible pyrrophytes, are described from the bedded carbonaceous cherts of the late Precambrian Bitter Springs formation, Ross river area, central Australia. Chemical data and petrologic evidence indicate that the organisms are geochemically altered but are morphologically intact. The age of the microflora is considered to be approximately 1000 m.y.
488 citations
TL;DR: Analysis of chemical fractions from several plant phyla show that in all cases the lipid fraction is enriched in C/sup 12/ compared to the whole plant, which may be explained if selective preservation of plant lipids occurred during the sedimentation process.
Abstract: C/sup 13//C/sup 12/ ratio analyses of chemical fractions from several plant phyla show that in all cases the lipid fraction is enriched in C/sup 12/ compared to the whole plant. The C/sup 13//C/sup 12/ r atio of the plant lipids corresponds roughly to the C/sup 13//C/sup 12/ ratio of petroleums. The C/sup 12/ enrichment in petroleums a compared to present day plants can be explained if selective preservation of plant lipids occurred during the sedimentation process. The degree of C/sup 12/ enrichment in the plant lipid fraction is inversely related to the amount of lipid in the plant. The C/sup 12/ enrichment which occurs in plant lipids may be balanced by the C/sup 13/ enrichment which occurs in respired CO/sub 2/. Isotope selection at the level of acetate or pyruvate is a possible mechanism for explaining our results. (auth)
366 citations