scholarly journals Early Permian glacio-marine thecamoebian assemblages from the northwest Himalayas, India

2011 ◽  
Vol 30 (1) ◽  
pp. 75-89 ◽  
Author(s):  
Arun Kumar ◽  
Anjum Farooqui ◽  
Neerja Jha
Keyword(s):  
Late Carboniferous ◽  
Marine Environments ◽  
Early Permian ◽  
Geological Time ◽  
Morphological Comparison ◽  
Shallow Marine ◽  
Northwestern Margin ◽  
Extinction Events ◽  
Northwest Himalayas ◽  
Mass Extinction Events

Abstract. Diverse assemblages of thecamoebians are reported here from the Early Permian Manjir Formation of the northwest Himalaya in India. These thecamoebian tests were found in palynological preparations and are assigned an Early Permian age based on co-occurrence of age-diagnostic palynomorphs. Several of them show very close morphological affinity with extant thecamoebian genera, such as Amphitrema, Arcella, Centropyxis, Cyclopyxis, Cucurbitella, Difflugia and Trinema. This fauna lived in shallow-marine environments during the Early Permian deglacial phase of the widespread Late Carboniferous–Early Permian glaciation of Gondwana. The extant forms used for morphological comparison with the fossil forms were recorded from lakes and ponds in various parts of India. This study supports the current hypothesis of minimal evolution in thecamoebian lineages through geological time, and this group of protists has survived through long geological time and several mass extinction events without any significant morphological change. Stratigraphical and palaeontological evidence indicates that this fauna lived in the shallow-marine environments along the northwestern margin of Indian Gondwana during the deglacial phase of Late Carboniferous–Early Permian glaciation.

scholarly journals The origins of modern biodiversity on land

2010 ◽  
Vol 365 (1558) ◽  
pp. 3667-3679 ◽  
Author(s):  
Michael J. Benton
Keyword(s):  
Regional Scale ◽  
Global Scale ◽  
Scale Model ◽  
Time Range ◽  
Geological Time ◽  
New Methods ◽  
Evolution Of Life ◽  
History Of ◽  
Extinction Events ◽  
Mass Extinction Events

Comparative studies of large phylogenies of living and extinct groups have shown that most biodiversity arises from a small number of highly species-rich clades. To understand biodiversity, it is important to examine the history of these clades on geological time scales. This is part of a distinct ‘phylogenetic expansion’ view of macroevolution, and contrasts with the alternative, non-phylogenetic ‘equilibrium’ approach to the history of biodiversity. The latter viewpoint focuses on density-dependent models in which all life is described by a single global-scale model, and a case is made here that this approach may be less successful at representing the shape of the evolution of life than the phylogenetic expansion approach. The terrestrial fossil record is patchy, but is adequate for coarse-scale studies of groups such as vertebrates that possess fossilizable hard parts. New methods in phylogenetic analysis, morphometrics and the study of exceptional biotas allow new approaches. Models for diversity regulation through time range from the entirely biotic to the entirely physical, with many intermediates. Tetrapod diversity has risen as a result of the expansion of ecospace, rather than niche subdivision or regional-scale endemicity resulting from continental break-up. Tetrapod communities on land have been remarkably stable and have changed only when there was a revolution in floras (such as the demise of the Carboniferous coal forests, or the Cretaceous radiation of angiosperms) or following particularly severe mass extinction events, such as that at the end of the Permian.

scholarly journals Meteorites that produce K-feldspar-rich ejecta blankets correspond to mass extinctions

2021 ◽  
pp. jgs2021-055
Author(s):  
M. J. Pankhurst ◽  
C. J. Stevenson ◽  
B. C. Coldwell
Keyword(s):  
Cloud Microphysics ◽  
Ice Nucleation ◽  
Mass Extinctions ◽  
Geological Time ◽  
Content Type ◽  
Meteorite Impacts ◽  
Cloud Dynamics ◽  
Supplementary Material ◽  
Extinction Events ◽  
Mass Extinction Events

Meteorite impacts load the atmosphere with dust and cover the Earth's surface with debris. They have long been debated as a trigger of mass extinctions through Earth's history. Impact winters generally last <100 years, whereas ejecta blankets persist for 103-105 years. Here we show that only meteorite impacts that emplaced ejecta blankets rich in K-feldspar (Kfs) correlate to Earth system crises (n=11, p<0.000005). Kfs is a powerful ice-nucleating aerosol yet is normally rare in atmospheric dust mineralogy. Ice nucleation plays an important role in cloud microphysics, which modulates global albedo. A conceptual model is proposed whereby the anomalous prevalence of Kfs is posited to have two key effects on cloud dynamics: 1) reducing the average albedo of mixed-phase cloud, which effected a hotter climate; 2) weakening of the cloud albedo feedback, which increased climate sensitivity. These mechanisms offer an explanation as to why this otherwise benign mineral is correlated so strongly with mass extinction events: every K-feldspar-rich ejecta blanket corresponds to a severe extinction episode over the past 600 Myr. This model may also explain why many kill mechanisms only variably correlate with extinction events through geological time: they coincide with these rare periods of climate destabilization by atmospheric Kfs.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5690646

Modeling Extinction

2003 ◽  
Author(s):  
M. E. J. Newman ◽  
R. G. Palmer
Keyword(s):  
Evolutionary Biology ◽  
Large Scale ◽  
Competitive Exclusion ◽  
Applied Mathematics ◽  
Santa Fe ◽  
New Approach ◽  
Self Organized ◽  
Self Organized Criticality ◽  
Extinction Events ◽  
Mass Extinction Events

Developed after a meeting at the Santa Fe Institute on extinction modeling, this book comments critically on the various modeling approaches. In the last decade or so, scientists have started to examine a new approach to the patterns of evolution and extinction in the fossil record. This approach may be called "statistical paleontology," since it looks at large-scale patterns in the record and attempts to understand and model their average statistical features, rather than their detailed structure. Examples of the patterns these studies examine are the distribution of the sizes of mass extinction events over time, the distribution of species lifetimes, or the apparent increase in the number of species alive over the last half a billion years. In attempting to model these patterns, researchers have drawn on ideas not only from paleontology, but from evolutionary biology, ecology, physics, and applied mathematics, including fitness landscapes, competitive exclusion, interaction matrices, and self-organized criticality. A self-contained review of work in this field.

Effects of microalgal communities on reflectance spectra of carbonate sediments in subtidal optically shallow marine environments

2003 ◽  
Vol 48 (1part2) ◽  
pp. 535-546 ◽  
Author(s):  
F. Carol Stephens ◽  
Eric M. Louchard ◽  
R. Pamela Reid ◽  
Robert A. Maffione
Keyword(s):  
Reflectance Spectra ◽  
Carbonate Sediments ◽  
Marine Environments ◽  
Shallow Marine

Middle Ordovician Fish-bearing Beds from the St. Lawrence Lowlands of Quebec

1973 ◽  
Vol 10 (6) ◽  
pp. 954-960 ◽  
Author(s):  
Leslie S. Eliuk
Keyword(s):  
Lower Portion ◽  
Quebec City ◽  
Marine Environments ◽  
European Standard ◽  
Shallow Marine ◽  
Vertebrate Fauna ◽  
Middle Ordovician ◽  
Fish Remains ◽  
Black River Group

Ostracoderm tubercles were recovered from the lower portion of two Black River Group sections between Montreal and Quebec City. Some of these fish remains seem identical to tubercles of Astraspis desiderata from the Harding Sandstone of Colorado. The age of the Quebec remains is questionably earliest Blackriveran or basal Caradocian of the European standard. The remains were found in sandy carbonates probably laid down in the supratidal to shallow marine environments. It is concluded that these remains may represent part of a continent-wide, biostratigraphically useful vertebrate fauna and that bulk sampling and acid residuing might be a technique whereby sparse, fragmentary, earliest Paleozoic fish remains could be found.

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