A New and Open CoiledValvata(Gastropoda) from the Pliocene Koobi Fora Formation of the Turkana Basin, Northern Kenya

2010 ◽  
Vol 84 (5) ◽  
pp. 996-1002 ◽  
Author(s):  
Henning Scholz ◽  
Matthias Glaubrecht
Keyword(s):  
New Species ◽  
Environmental Stress ◽  
Environmental Conditions ◽  
Lake Level ◽  
Shell Morphology ◽  
Koobi Fora ◽  
Northern Kenya ◽  
Turkana Basin ◽  
High Level ◽  
Stratigraphic Interval

New field collections allow the study and description ofValvata juliaenew species from the Pliocene upper Burgi Member of the Koobi Fora Formation of Kenya. The shell morphology of this species varies from trochospiral to planispiral to open coiled. The species is restricted to a short stratigraphic interval.Valvata juliaeis considered as an invader of the Turkana Basin during a lacustrine transgression event. The open coiling of the species is interpreted as an ecophenotypic response to a high level of environmental stress caused by lake level fluctuations and emergence of delta systems. These environmental conditions broughtValvata juliaeto extinction soon after it invaded the Turkana Basin.

Shell and operculum taphonomy of the bithyniid gastropodGabbiellain the Pleistocene Turkana Basin, North Kenya

2013 ◽  
Vol 87 (1) ◽  
pp. 84-90
Author(s):  
Henning Scholz ◽  
Matthias Glaubrecht
Keyword(s):  
Relative Abundance ◽  
Fossil Record ◽  
Mesh Size ◽  
Koobi Fora ◽  
Morphological Comparison ◽  
Northern Kenya ◽  
Turkana Basin ◽  
Systematic Paleontology ◽  
Preservation Potential ◽  
Mollusk Assemblages

Shells and opercula of bithyniid gastropods assigned toGabbiellaare found in high abundance in the Pleistocene upper Burgi and KBS Members of the Koobi Fora Formation, Turkana Basin, northern Kenya. The systematic paleontology of the Turkana BasinGabbiellais revised herein based on morphological comparison with the opercula of other Recent African bithyniids. The fossils from the upper Burgi and KBS Members are here assigned toGabbiella roseaMandahl-Barth, 1968, a species not known from the Turkana fossil record before, but extant in this lake today. A sampling and taphonomic bias is identified which influences the relative abundance ofGabbiellashells and opercula, as a mesh size of 0.63 mm or less is necessary to capture all opercula preserved in the sediments. Accordingly, opercula were found to be significantly more abundant than shells, indicating a different preservation potential of shells and opercula, as the calcitic operculum is more robust than the aragonitic shell. In contrast to previous arguments that most shellbeds in the Turkana Basin sequence represent undisturbed life assemblages, a taphonomic bias is clearly evident reducing the fidelity of the Turkana Basin mollusk assemblages.

scholarly journals Similarities and contrasts between the patterns of survival and recovery following the Cenomanian-Turonian (Upper Cretaceous) and the Cretaceous-Tertiary mass extinctions

1992 ◽  
Vol 6 ◽  
pp. 121-121
Author(s):  
Peter J. Harries
Keyword(s):  
New Species ◽  
Environmental Conditions ◽  
Mass Extinction ◽  
Range Data ◽  
Mass Extinctions ◽  
Temporary Reduction ◽  
Abundance And Diversity ◽  
Forcing Mechanisms ◽  
High Level ◽  
Extinction Events

Mass extinctions have played a significant role in the Phanerozoic evolutionary history. Not only have they resulted in the relatively rapid loss of numerous, ecologically and genetically diverse taxa, but, in most cases, they have culminated in the radiation of new lineages, communities and ecological structure based not only on the evolution of new taxa, but also on changes in dominance of surviving taxa. The hypothesis that these biotic crises may be periodic and caused by similar forcing mechanisms has generated the need to compare mass extinction survival and recovery intervals. The ultimate test of this hypothesis lies in the fossil record. For this study, the Cenomanian-Turonian (C-T) and Cretaceous-Tertiary (K-T) boundary intervals are analyzed. These boundaries are interesting for a number of reasons: 1) they both are well-studied at a high level of resolution at a number of localities; 2) the K-T event follows the C-T event by approximately 26 My reflecting the proposed extinction periodicity; 3) they represent two different levels of extinction intensity with the K-T affecting a far greater percentage of taxa; and 4) they occurred under very different environmental conditions. Initial analyses of generic and species range data for epifaunal and infaunal bivalves, ammonites, brachiopods, benthic and planktic foraminifers, ostracodes, and nannoplankton suggest that the basic patterns of survival and recovery are similar for C-T and K-T extinctions. Both extinction events show an initial survival interval in most groups, during which most of the species present represent survivors (including “Lazarus taxa”) or new species within surviving lineages. This gives way to a recovery interval characterized by an increasing number of new species within new lineages. Based on the rapidity with which new species evolve, these repopulation intervals suggest that the degree of survivorship among diverse groups must be far greater than generally believed, because the evolutionary rates appear to be too rapid to be accounted for by rapid radiation solely from generalist stocks. Although the general patterns appear to be quite similar between these two extinction-repopulation intervals, there are significant differences. The C-T mass extinction affected primarily epifaunal bivalves, benthic foraminifers, and ammonite taxa severely, while the K-T event resulted in a pronounced extinction among planktic foraminifers and infaunal bivalves. This suggests that at least the proximate causes of extinction for the two intervals were substantially different. Despite the greater overall magnitude of the K-T extinctions, the repopulation occurred more rapidly following this event. This suggests that the degree of vacated niches was greater and/or the environmental conditions returned to more favorable levels more rapidly. The C-T repopulation may have been delayed due to the deleterious background conditions which existed throughout much of the mid-Cretaceous. Finally, the K-T extinctions resulted in the disappearance of significant elements of the pre-extinction faunas and communities, such as the ammonites, inoceramids, and rudists, whereas the C-T event resulted in the temporary reduction in abundance and diversity in these groups, but they rapidly reobtained their dominance.

Rock varnish record of the African Humid Period in the Lake Turkana basin of East Africa

The Holocene ◽  
2021 ◽  
pp. 095968362110116
Author(s):  
Tanzhuo Liu ◽  
Christopher J Lepre ◽  
Sidney R Hemming ◽  
Wallace S Broecker
Keyword(s):  
East Africa ◽  
Lake Level ◽  
Drainage System ◽  
Early Holocene ◽  
Lake Turkana ◽  
Moisture Condition ◽  
Turkana Basin ◽  
Rock Varnish ◽  
Geomorphic Features ◽  
Humid Period

Rock varnish is a manganiferous dark coating accreted on subaerially exposed rocks in drylands. It often contains a layered microstratigraphy that records past wetness variations. Varnish samples from latest Pleistocene and Holocene geomorphic features in the Lake Turkana basin, East Africa display a regionally replicable microstratigraphy record of Holocene millennial-scale wetness variability and a broad interval of wetter conditions during the African Humid Period (AHP). Three major wet pulses in the varnish record occurred during the generally wet interval of the early Holocene (11.5–8.5 ka) when the lake attained its maximum high stand (MHS) at 455–460 m. A >23 m drop from the MHS occurred between 8.5 and 8 ka. Subsequently two additional wet pulses occurred during the early to middle Holocene (8–5 ka) when the lake occupied its secondary high stand at 445 m. Collectively, these five wet phases represent an extended wet interval coincident with the AHP in the region. One moderate wet phase occurred during the subsequent climatic transition from the humid to arid regime (5–4.3 ka) after the lake level dropped rapidly from 445 m to <405 m. Five minor wet phases took place during the overall arid period of the late Holocene (4.3–0 ka) when the lake level oscillated below 405 m. These findings indicate that the AHP terminated rapidly around 5 ka in the Turkana basin in terms of lake level drop, but the regional shift in relative humidity from the AHP mode to its present-day condition lagged for about 700 years until 4.3 ka, hinting at a gradual phasing out in terms of moisture condition. These findings further suggest that Lake Turkana overflowed intermittently into the Nile drainage system through its topographic sill at 455–460 m during the early Holocene and has become a closed-basin lake thereafter for the past 8 ky.

INHERITANCE OF RESISTANCE TO NET BLOTCH IN BARLEY. I. FACTORS AFFECTING THE PENETRANCE AND EXPRESSIVITY OF GENE(S) CONDITIONING HOST RESISTANCE

1969 ◽  
Vol 11 (3) ◽  
pp. 587-591 ◽  
Author(s):  
T. N. Khan
Keyword(s):  
Environmental Conditions ◽  
Net Blotch ◽  
Host Reaction ◽  
Susceptible Parent ◽  
Breeding Programs ◽  
Genetic Studies ◽  
Factors Affecting ◽  
Drechslera Teres ◽  
Resistant Varieties ◽  
High Level

Variability in the host-reaction of barley to infection by Drechslera teres was examined in the parents and progeny of selected crosses under different environmental conditions of testing.The Ethiopian variety C.I. 5791 exhibits a consistently high level of resistance under a range of environmental conditions, which is in contrast to the Manchurian variety C.I. 2330. The sensitivity of the genes for resistance possessed by these varieties to environmental modifications is considered to depend upon their respective genetic backgrounds. Furthermore, variability of host reaction in the progeny of these resistant varieties was shown to be influenced by the genetic background of the susceptible parent used.The implications of these findings in the conduct and interpretation of genetic studies and in backcross breeding programs is discussed.

An Electrophoretic and Morphological Examination of Bothriembyron kendricki (Pulmonata: Bulimulidae), a New Species previously Considered Conspecific with B. bulla (Menke)

1983 ◽  
Vol 31 (2) ◽  
pp. 227 ◽  
Author(s):  
A Hill ◽  
MS Johnson ◽  
H Merrifield
Keyword(s):  
New Species ◽  
Shell Morphology ◽  
Morphological Examination ◽  
A New Species

Bothriembryon bulla (Menke) has previously been thought to include pale and melanic morphs. Studies of morphology and allozymes reveal that the two forms are reproductively isolated. The melanic is herein referred to as B. kendricki, sp. nov. Both species show large amounts of variation among populations for both shell morphology and allozymes, emphasizing the need for comprehensive geographic sampling in studies of the genus Bothriembryon.

scholarly journals Stepwise drying of Lake Turkana at the end of the African Humid Period: an example of forced regression modulated by solar activity?

2016 ◽  
Author(s):  
Alexis Nutz ◽  
Mathieu Schuster
Keyword(s):  
Solar Activity ◽  
Lake Level ◽  
Controlling Factors ◽  
Lake Turkana ◽  
Turkana Basin ◽  
Orbital Precession ◽  
Forced Regression ◽  
Humid Period

Abstract. Although timing of the termination of the African Humid Period (AHP) is relatively well-established now, modes and controlling factors are still being determined. Here, through a geomorphological approach, we characterize the evolution of the final regression of Lake Turkana at the end of the African Humid Period. We show that lake level fall during this period was not constant, yet rather stepwise consisted of five periods marked by rapid rates of lake level fall separated by periods of lower rates of lake level fall. Even the overall regressive trend is associated with regional decreased precipitations due to reduced insolation controlled by orbital precession, we discuss the origin of the five periods of accelerated rates of lake level fall. Finally, we propose that accelerations are associated with periods marked by solar activity minima that locally resulted in the repeated westward displacement of the Congo Air Boundary (CAB), thereby reducing rainfall across the Lake Turkana basin.

A new species of the genus Rapturella (Gastropoda: Acteonidae) from southeast Brazil

Zootaxa ◽  
2018 ◽  
Vol 4521 (1) ◽  
pp. 125 ◽  
Author(s):  
CARLO M. CUNHA ◽  
LUIZ RICARDO L. SIMONE
Keyword(s):  
New Species ◽  
Continental Shelf ◽  
Deep Water ◽  
Shell Morphology ◽  
Southwest Pacific ◽  
Southeast Brazil ◽  
Pacific Waters ◽  
A New Species ◽  
High Diversity

Acteonidae d'Orbigny, 1843 is the largest family within the superfamily Acteonoidea (Bouchet et al. 2017) and includes small gastropods typical of infralittoral environments. Most acteonids living on the continental shelf or in deep water have been described on the basis of shell morphology alone (Simone 2006; Valdés 2008; Cunha 2011; Salvador & Cunha 2016), because little material with soft parts has been collected and examined. Consequently, little is known about the ecology of the species.  Recently, many new species of the genus Acteon Montfort, 1810 have been described from tropical Southwest Pacific waters (Valdés 2008), suggesting that a high diversity of acteonid species may await discovery in other deep water environments, including those of Brazil. 

Experimental Investigation on the Active Range of Sulfate-Reducing Bacteria for Geological Disposal

1994 ◽  
Vol 353 ◽  
Author(s):  
S. Fukunaga ◽  
H. Yoshikawa ◽  
K. Fujiki ◽  
H. Asano
Keyword(s):  
Experimental Investigation ◽  
Environmental Conditions ◽  
Desulfovibrio Desulfuricans ◽  
Sulfate Reducing Bacteria ◽  
Geological Disposal ◽  
Sulfate Reducing ◽  
Buffer Material ◽  
Ph Range ◽  
High Level ◽  
Reducing Bacteria

AbstractThe active range ofDesulfovibrio desulfuricans. a species of sulfate-reducing bacteria, was examined in terms of pH and Eh using a fermenter at controlled pH and Eh. Such research is important because sulfate-reducing bacteria (SRB) are thought to exist underground at depths equal to those of supposed repositories for high-level radioactive wastes and to be capable of inducing corrosion of the metals used in containment vessels.SRB activity was estimated at 35°C, with lactate as an electron donor, at a pH range from 7 to 11 and Eh range from 0 to -380 mV. Activity increased as pH approached neutral and Eh declined. The upper pH limit for activity was between 9.9 and 10.3, at Eh of -360 to -384 mV. The upper Eh limit for activity was between -68 and -3 mV, at pH 7.1. These results show that SRB can be made active at higher pH by decreasing Eh, and that the higher pH levels of 8 to 10 produced by use of the buffer material bentonite does not suppress SRB completely.A chart was obtained showing the active range ofDesulfovibrio desulfuricansin terms of pH and Eh. Such charts can be used to estimate the viability of SRB and other microorganisms when the environmental conditions of a repository are specified.

scholarly journals Descriptions of four new dextral land snails of the genus Camaena (Gastropoda, Eupulmonata, Camaenidae) from south China

ZooKeys ◽  
2020 ◽  
Vol 996 ◽  
pp. 37-58
Author(s):  
Pei Wang ◽  
Mei-Ling Hu ◽  
Jun-Hong Lin ◽  
Hai-Fang Yang ◽  
Xiao-Jing Li ◽  
...  
Keyword(s):  
New Species ◽  
South China ◽  
Dna Sequences ◽  
Reproductive System ◽  
Phylogenetic Analyses ◽  
Morphological Characteristics ◽  
Land Snails ◽  
Shell Morphology ◽  
Molecular Phylogenetic ◽  
Living Environments

In this study, four new dextral camaenid from China are reported, based on shell morphology, reproductive system anatomy, and molecular phylogenetic analyses: Camaena funingensis Zhou, Wang &amp; Lin, sp. nov., Camaena gaolongensis Zhou, Wang &amp; Lin, sp. nov., Camaena maguanensis Zhou, Wang &amp; Hu, sp. nov., and Camaena yulinensis Zhou, Wang &amp; Hu, sp. nov. Detailed descriptions of the morphological characteristics including shells and genitalia, DNA sequences, and living environments of the four new species are provided, with further comparisons with congeners.

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