scholarly journals Major features of protistan evolution: controversies, problems and a few answers

2006 ◽  
Vol 29 (1) ◽  
pp. 55-80
Author(s):  
Jere H Lipps
Keyword(s):  
Fossil Record ◽  
Molecular Data ◽  
Trophic Levels ◽  
Early Earth ◽  
Huge Number ◽  
Geologic Time ◽  
Earth History ◽  
Important Development ◽  
Fossil Evidence

The major features of protist evolution are fraught with controversies, problems and few answers, especially in early Earth history. In general they are based on molecular data and fossil evidence that respectively provide a scaffold and details of eukaryotic phylogenetic and ecologic histories. 1. Their origin, inferred from molecular sequences, occurred very early (>;3Ga). They are a chimera of different symbiont-derived organelles, including possibly the nucleus. 2. The initial diversification of eukaryotes may have occurred early in geologic time. Six supergroups exist today, each with fossils known from the Proterozoic and Phanerozoic. 3. Sex, considered an important development, may have been inherited from bacteria. 4. Precambrian protists were largely pelagic cyst-bearing taxa, but benthic forms were probably quite diverse and abundant. 5. Protists gave rise to animals long before 600 Ma through the choanoflagellates, for which no fossil record exists. 6. Acritarchs and skeletonized protists radiated in the Cambrian (544-530 my). From then on, they radiated and became extinct at all the major events recorded in the metazoan fossil record. 7. Protists dominated major environments (shelves and reefs) starting with a significant radiation in the Ordovician, followed by extinctions and other radiations until most died out at the end of the Permian. 8. In the Mesozoic, new planktic protozoa and algae appeared and radiated in pelagic environments. 9. Modern protists are important at all trophic levels in the oceans and a huge number terrestrial, parasitic and symbiotic protists must have existed for much of geologic time as well. 10. The future of protists is likely in jeopardy, just like most reefal, benthic, and planktic metazoans. An urgent need to understand the role of protists in modern threatened oceans should be addressed soon.

scholarly journals Thai amber: insights into early diatom history?

2020 ◽  
Vol 191 ◽  
pp. 23
Author(s):  
Vincent Girard ◽  
Simona Saint Martin ◽  
Eric Buffetaut ◽  
Jean-Paul Saint Martin ◽  
Didier Néraudeau ◽  
...  
Keyword(s):  
Early Cretaceous ◽  
Late Cretaceous ◽  
Fossil Record ◽  
Late Jurassic ◽  
Molecular Data ◽  
Early Jurassic ◽  
Coastal Environments ◽  
Potential Bias ◽  
Fossil Evidence ◽  
History Of

The origin of the diatoms still remains enigmatic. Their fossil record is scarce until the Late Cretaceous and great divergences exist between molecular data and the earliest fossil evidence. While molecular data indicate an origin during the Triassic or Early Jurassic, early fossil evidence is only from the Late Jurassic-Early Cretaceous. The discovery of diatoms in French mid-Cretaceous amber by the end of the 2000s already suggested a potential bias in the diatom fossil record as it made older many diatom lineages, the record of which hitherto began at the end of the Cretaceous. The Jurassic/Early Cretaceous fossil record of diatoms is extremely sparse and any new occurrence is important for retracing the evolutionary, palaeogeographical and palaeoenvironmental history of diatoms. Thai amber has yielded a new diatom specimen that has been attributed to the genus Hemiaulus. Fossil assemblages and sedimentological data indicate that Thai amber and its Hemiaulus specimen are Late Jurassic in age. This discovery represents the oldest hitherto known specimen of Hemiaulus and so extends the fossil record of the bipolar diatoms and of the genus Hemiaulus by several dozens of millions of years and brings closer the fossil evidence and molecular data (that estimated an origin of the bipolar diatoms about 150 Ma ago). It reinforces the hypothesis of a pre-Cretaceous fossil diatom records and also supports an origin of the diatoms in shallow coastal environments.

scholarly journals Chemical Stability of FeOOH at High Pressure and Temperature, and Oxygen Recycling in Early Earth History

2021 ◽  
Author(s):  
Egor Koemets ◽  
Timofey Fedotenko ◽  
Saiana Khandarkhaeva ◽  
Maxim Bykov ◽  
Elena Bykova ◽  
...  
Keyword(s):  
High Pressure ◽  
Chemical Stability ◽  
Early Earth ◽  
High Pressure And Temperature ◽  
Earth History

Chemical stability of FeOOH at high pressure and temperature, and oxygen recycling in early Earth history

2021 ◽  
Author(s):  
Egor Koemets ◽  
Timofey Fedotenko ◽  
Saiana Khandarkhaeva ◽  
Maxim Bykov ◽  
Elena Bykova ◽  
...  
Keyword(s):  
High Pressure ◽  
Chemical Stability ◽  
Early Earth ◽  
High Pressure And Temperature ◽  
Earth History

Did Ground Cover Change Over Geologic Time?

2000 ◽  
Vol 6 ◽  
pp. 171-182 ◽  
Author(s):  
Ben A. LePage ◽  
Hermann W. Pfefferkorn
Keyword(s):  
Fossil Record ◽  
Ground Cover ◽  
The Other ◽  
Detailed Account ◽  
Geologic Time ◽  
The Past ◽  
Other Hand ◽  
Plant Fossil

When one hears the term “ground cover,” one immediately thinks of “grasses.” This perception is so deep-seated that paleobotanists even have been overheard to proclaim that “there was no ground cover before grasses.” Today grasses are so predominant in many environments that this perception is perpetuated easily. On the other hand, it is difficult to imagine the absence or lack of ground cover prior to the mid-Tertiary. We tested the hypothesis that different forms of ground cover existed in the past against examples from the Recent and the fossil record (Table 1). The Recent data were obtained from a large number of sources including those in the ecological, horticultural, and microbiological literature. Other data were derived from our knowledge of Precambrian life, sedimentology and paleosols, and the plant fossil record, especially in situ floras and fossil “monocultures.” Some of the data are original observations, but many others are from the literature. A detailed account of these results will be presented elsewhere (Pfefferkorn and LePage, in preparation).

Stereotactic Radiosurgery: Adjacent Tissue Injury and Response after High-Dose Single Fraction Radiation—Part II: Strategies for Therapeutic Enhancement, Brain Injury Mitigation, and Brain Injury Repair

Neurosurgery ◽  
2007 ◽  
Vol 60 (5) ◽  
pp. 799-814 ◽  
Author(s):  
Bryan C. Oh ◽  
Charles Y. Liu ◽  
Michael Y. Wang ◽  
Paul G. Pagnini ◽  
Cheng Yu ◽  
...  
Keyword(s):  
Brain Injury ◽  
Tissue Injury ◽  
Whole Brain Radiotherapy ◽  
Molecular Data ◽  
Phase Iii ◽  
High Dose ◽  
Whole Brain ◽  
Brain Radiotherapy ◽  
Axonal Regrowth

Abstract IN THE FIRST part of this series, we reviewed the histological, radiographic, and molecular data gathered regarding the brain parenchymal response to radiosurgery and suggested future studies that could enhance our understanding of the topic. With this article, we begin by addressing methods of potentiating the effect of radiosurgery on target lesions of the central nervous system. Much of the work on potentiating the effects of cranial radiation has been performed in the field of whole-brain radiotherapy. Data from Phase III trials evaluating the efficacy of various agents as radiosensitizers or radioenhancers in whole-brain radiotherapy are reviewed, and trials for investigating certain agents as enhancers of radiosurgery are suggested. The roles of gene therapy and nanotechnology in enhancing the therapeutic efficacy of radiosurgery are then addressed. Focus is then shifted to a discussion of strategies of protecting healthy tissue from the potentially deleterious aspects of the brain's response to radiosurgery that were presented in the first article of this series. Finally, comments are made regarding the role of neural progenitor or stem cells in the repair of radiation-induced brain injury after radiosurgery. The importance of both the role of the extracellular matrix and properly directed axonal regrowth leading to appropriate target reinnervation is highlighted.

scholarly journals Molecular and Biological Characterisation of Turnip mosaic virus Isolates Infecting Poppy (Papaver somniferum and P. rhoeas) in Slovakia

Viruses ◽  
2018 ◽  
Vol 10 (8) ◽  
pp. 430 ◽  
Author(s):  
Miroslav Glasa ◽  
Katarína Šoltys ◽  
Lukáš Predajňa ◽  
Nina Sihelská ◽  
Slavomíra Nováková ◽  
...  
Keyword(s):  
Mosaic Virus ◽  
Phylogenetic Analyses ◽  
Molecular Data ◽  
Turnip Mosaic Virus ◽  
Biological Assays ◽  
Genetic Complexity ◽  
The World ◽  
History Of ◽  
Virus Isolates

In recent years, the accumulated molecular data of Turnip mosaic virus (TuMV) isolates from various hosts originating from different parts of the world considerably helped to understand the genetic complexity and evolutionary history of the virus. In this work, four complete TuMV genomes (HC9, PK1, MS04, MS15) were characterised from naturally infected cultivated and wild-growing Papaver spp., hosts from which only very scarce data were available previously. Phylogenetic analyses showed the affiliation of Slovak Papaver isolates to the world-B and basal-B groups. The PK1 isolate showed a novel intra-lineage recombination pattern, further confirming the important role of recombination in the shaping of TuMV genetic diversity. Biological assays indicated that the intensity of symptoms in experimentally inoculated oilseed poppy are correlated to TuMV accumulation level in leaves. This is the first report of TuMV in poppy plants in Slovakia.

scholarly journals An abundance of developmental anomalies and abnormalities in Pleistocene people

2018 ◽  
Vol 115 (47) ◽  
pp. 11941-11946 ◽  
Author(s):  
Erik Trinkaus
Keyword(s):  
Fossil Record ◽  
Elevated Level ◽  
Developmental Disorders ◽  
Upper Paleolithic ◽  
Developmental Changes ◽  
Single Factor ◽  
Developmental Abnormalities ◽  
Low Probability ◽  
Developmental Variants

Diverse developmental abnormalities and anomalous features are evident in the PleistoceneHomofossil record, varying from minor but rare dental, vertebral, and carpal variants to exceptional systemic disorders. There are currently 75 documented anomalies or abnormalities from 66 individuals, spanning the Pleistocene but primarily from the Late Pleistocene Middle and Upper Paleolithic with their more complete skeletal remains. The expected probabilities of finding these variants or developmental disorders vary from <5% to <0.0001%, based on either recent human incidences or relevant Pleistocene sample distributions. Given the modest sample sizes available for the skeletal or dental elements in question, especially if the samples are appropriately limited in time and geography, the cumulative multiplicative probability of finding these developmental changes is vanishingly small. These data raise questions regarding social survival abilities, differing mortuary treatments of the biologically unusual, the role of ubiquitous stress among these Pleistocene foragers, and their levels of consanguinity. No single factor sufficiently accounts for the elevated level of these developmental variants or the low probability of finding them in the available paleontological record.

scholarly journals The role of climatic and geological events in generating diversity in Ethiopian grass frogs (genus Ptychadena )

2017 ◽  
Vol 4 (8) ◽  
pp. 170021 ◽  
Author(s):  
Megan L. Smith ◽  
Brice P. Noonan ◽  
Timothy J. Colston
Keyword(s):  
Habitat Complexity ◽  
Molecular Data ◽  
Cryptic Diversity ◽  
Horn Of Africa ◽  
Climatic Fluctuations ◽  
Divergence Dating ◽  
Evolutionary Radiation ◽  
Novel Taxa ◽  
Climatic History

Ethiopia is a world biodiversity hotspot and harbours levels of biotic endemism unmatched in the Horn of Africa, largely due to topographic—and thus habitat—complexity, which results from a very active geological and climatic history. Among Ethiopian vertebrate fauna, amphibians harbour the highest levels of endemism, making amphibians a compelling system for the exploration of the impacts of Ethiopia's complex abiotic history on biotic diversification. Grass frogs of the genus Ptychadena are notably diverse in Ethiopia, where they have undergone an evolutionary radiation. We used molecular data and expanded taxon sampling to test for cryptic diversity and to explore diversification patterns in both the highland radiation and two widespread lowland Ptychadena . Species delimitation results support the presence of nine highland species and four lowland species in our dataset, and divergence dating suggests that both geologic events and climatic fluctuations played a complex and confounded role in the diversification of Ptychadena in Ethiopia. We rectify the taxonomy of the endemic P. neumanni species complex, elevating one formally synonymized name and describing three novel taxa. Finally, we describe two novel lowland Ptychadena species that occur in Ethiopia and may be more broadly distributed.

Hybrid crinoids in the fossil record (Early Mississippian, Phylum Echinodermata)

Paleobiology ◽  
1994 ◽  
Vol 20 (3) ◽  
pp. 362-367 ◽  
Author(s):  
William I. Ausich ◽  
David L. Meyer
Keyword(s):  
Fossil Record ◽  
Evolutionary Process ◽  
Parent Species ◽  
Probable Explanation ◽  
South Central ◽  
Most Probable Explanation ◽  
The Impact

Potential hybrid fossil crinoids, Eretmocrinus magnificus x Eretmocrinus praegravis, are identified from the Lower Mississippian Fort Payne Formation of south-central Kentucky. These are the first fossil hybrid crinoids identified, and one of very few examples of hybrids recognized in the fossil record. Eretmocrinus magnificus x E. praegravis specimens have shapes and calyx plate sculpturing that are morphologically intermediate between well-defined, distinct parent species. Suspected hybrids occur at localities where parent species co-occur and where the parent species are the most abundant; the hybrids occur at what may have been the distributional margins of the parent species; and the mixture of characters on suspected hybrids seems to be morphogenetically partitioned. Parent species are derived from separate lineages within Eretmocrinus, and hybridization is the most probable explanation for these morphologically intermediate specimens. This example highlights the need to consider hybridization as a potential interpretation of intermediate morphologies among fossils and raises questions concerning the impact of hybridization for our interpretation of the fossil record and the role of hybridization in the evolutionary process.

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