The Eocene larger foraminifer Lepidocyclina ariana Cole and Ponton, from the so-called Polylepidina gardnerae horizon at Little Stave Creek, Alabama

1997 ◽  
Vol 71 (1) ◽  
pp. 1-5 ◽  
Author(s):  
Edward Robinson
Keyword(s):  
Gulf Coast ◽  
Middle Eocene ◽  
Lower Horizon ◽  
Preliminary Research ◽  
Larger Foraminifers

Recent sampling for larger foraminifers in the so-called Polylepidina gardnerae horizon in the middle Eocene Lisbon Formation of the Little Stave Creek section, southwest Alabama, did not produce any examples of the lepidocyclinid foraminifer Polylepidina gardnerae Cole, but several specimens of the stratigraphically younger species, Lepidocyclina ariana Cole and Ponton, were recovered. Although the P. gardnerae horizon is named on nearly all figures of this important Gulf Coast section published since 1944, preliminary research has also failed to turn up a published basis for the identification of P. gardnerae at this locality. As L. ariana and P. gardnerae are not normally found together, it is the writer's opinion that true P. gardnerae probably has not been collected from any part of the Lisbon Formation at Little Stave Creek. If it does occur, it should be found at a lower horizon than that indicated in the literature.

Rise and fall of rotaliids in the Paleocene-Eocene: the influence of climate and trophic competition

2021 ◽  
Author(s):  
Andrea Benedetti ◽  
Cesare Andrea Papazzoni ◽  
Francesca Romana Bosellini
Keyword(s):  
Middle Eocene ◽  
Ecological Niches ◽  
Trophic Conditions ◽  
Significant Drop ◽  
Abrupt Decrease ◽  
Faunal Turnover ◽  
Number Of Species ◽  
Early Eocene Climatic Optimum ◽  
Climatic Optimum ◽  
Larger Foraminifers

<p>It is largely accepted that climate plays a pivotal role in the diversification of shallow-water communities, with special regards to larger foraminifera (LF), also because increase of surface water temperatures is often accompanied by change in trophic conditions. The shift from widespread eutrophic to oligotrophic conditions in shallow seas probably contributed to the LF differentiation during Paleocene-Eocene times. However, there are few recent attempts to quantify the changes in biodiversity and to correlate them with the global climatic events of the Paleogene. We concentrated our attention on the group of rotaliids, resilient taxa that partially survived after the mass extinction occurred at the end of the Cretaceous.</p><p>Our data show that their differentiation at genus level was very rapid, reaching its maximum already in the late Danian SB2 Zone. Specific diversification, instead, culminated in late Thanetian SB4 Zone. A second peak in specific diversity is recorded during the Cuisian (upper part of the Ypresian), then rotaliid diversity steadily declined, as long as other groups of larger foraminifers, especially <em>Alveolina </em>and <em>Nummulites</em>, became more competitive and proliferated with a large number of species up to the Bartonian SB17 Zone, when a significant drop in rotaliid biodiversity is recorded.</p><p>Differently to other taxonomic groups, i.e., alveolinids and nummulitids, for which a single genus during the whole Eocene generated numerous species, rotaliid genera are usually characterized by a low number of species, possibly due to the re-opening of ecological niches after the abrupt decrease of diversity that followed the PETM event. The competition with other K-strategist LF probably contributed to the decline of rotaliids in the middle Eocene up to the MECO event, where a last dramatic drop is recorded.</p><p>The major changes appear strictly linked to warming events such as the Late Danian Event (LDE, starting of the generic diversification of rotaliids), Paleocene Eocene Termal Maximum (PETM, faunal turnover followed by abrupt decrease in both generic and specific diversity), Early Eocene Climatic Optimum (EECO, increase in number of K-strategists under widespread oligotrophic conditions) and Middle Eocene Climatic Optimum (MECO, ultimate drop in diversity and competition with other larger foraminifers).</p><p>This study was funded by the Italian Ministry of Education and Research (MIUR), funds PRIN 2017: project “Biota resilience to global change: biomineralization of planktic and benthic calcifiers in the past, present and future” (prot. 2017RX9XXY).</p>

scholarly journals Differing histories of Eocene angiosperm diversity in eastern North America and western Europe: dependence on paleogeography

1992 ◽  
Vol 6 ◽  
pp. 105-105
Author(s):  
Norman O. Frederiksen
Keyword(s):  
North America ◽  
Western Europe ◽  
Environmental Heterogeneity ◽  
Gulf Coast ◽  
Middle Eocene ◽  
Late Eocene ◽  
Middle Part ◽  
Eastern North America ◽  
Climatic Fluctuations ◽  
Angiosperm Pollen

Studies of Eocene angiosperm pollen floras in eastern North America (my work, especially in the eastern Gulf Coast) and western Europe (Boulter, Krutzsch) have shown significant differences in floral diversities between the two regions: in western Europe, maximum diversity was in the early Eocene and it decreased thereafter, in eastern North America, maximum diversity was in the middle part of the middle Eocene. The hypothesis presented here is that paleogeography was an important control on the diversity histories in the two regions: eastern North America was part of a large terrestrial landmass, whereas the terrestrial depositional basins of western Europe were on islands or peninsulas surrounded by the sea. Migrations between eastern and western North America were relatively easy, but migrations within what is now western Europe involved island-hopping, which explains distinct diachroneity of some angiosperm first appearances among different basins there. Western European basins were in contact with a large land mass during late Paleocene time but became isolated and smaller during the middle to late Eocene marine transgression. These changes resulted in decreased genetic exchange and increased probabilities of extinction due to (1) greater competition among species because of a reduced number of niches and (2) presence of small, isolated species populations, leading to local variations in extinctions, which probably explain the observed diachronism of taxon last appearances in different areas of Europe. Terrestrial climatic cooling in western Europe may be linked to decreasing contact between the NW European Tertiary Basin and the warm Tethys Seaway during the middle and late Eocene. In short, some combination of low environmental heterogeneity, geographic isolation, and long-term climatic deterioration probably caused the decrease in angiosperm diversity during the middle and late Eocene in western Europe.Several factors encouraged increasing or stable diversity in eastern North America but were far less effective in western Europe: (1) Eastern North America underwent greater climatic fluctuations during the Eocene (thus, immigration of taxa with different climatic preferences took place at different times), whereas the islands and peninsulas of western Europe had more uniform, maritime climates. (2) Evolution and immigration of r-selected taxa in eastern North America were favored by distinct dry seasons at certain times during the Eocene and by repeated marine transgressions and regressions that created opportunities for evolution and immigration of r-selected plants on and to freshly exposed coastal plain. In contrast, the predominantly maritime climates of western Europe in the early and middle Eocene favored K-selected plants, which had fewer possibilities for evolution and which had greater difficulty in migrating because island-hopping taxa are mainly r-selected. (3) “Arcto-Tertiary” taxa adapted to cooler climates lived and evolved in the uplands of the Appalachian Mountains, whereas western Europe was relatively flat in the Eocene –another example of its relative lack of environmental heterogeneity.

II.—A Contribution to the Molluscan Fauna of the Laki and Basal Khirthar Groups of the Indian Eocene

1932 ◽  
Vol 57 (1) ◽  
pp. 25-92 ◽  
Author(s):  
L. R. Cox
Keyword(s):  
Middle Eocene ◽  
Reliable Information ◽  
Western India ◽  
Lower Eocene ◽  
North West ◽  
Lower Horizon ◽  
The North ◽  
Molluscan Fauna ◽  
North Western

The Tertiary geology of north-western India is of particular interest on account of the extensive development of richly fossiliferous rocks of Lower Eocene (including Palæocene) age. The monographs by Cossmann and Pissarro (1909a, 1927) and Vredenburg (1928) have familiarised us with the well-preserved molluscan fauna of the Upper Ranikot beds (Palæocene) of Sind, while Lt.-Col. L. M. Davies' collection of mollusca from a slightly lower horizon in the Samana Range, on the North-West Frontier, has recently been described by myself (1930). With the exception, however, of one family, the Gisortiidæ, dealt with by Vredenburg (1927) and Schilder (1930), the mollusea of the overlying Laki group (Ypresian), as well as of the Khirthar group (Middle Eocene), have been neglected by modern workers. The well-known monograph by D'Archiac and Haime (1853–54), moreover, in which some Laki species are described, has always been a source of confusion owing to the fact that fossils from all horizons from the Danian to the Miocene are grouped together as “Nummulitic,” and no reliable information as to their respective horizons has been available.

Early Tertiary radiation of marine molluscs and the long-term effects of the Cretaceous-Tertiary extinction

Paleobiology ◽  
1988 ◽  
Vol 14 (1) ◽  
pp. 37-51 ◽  
Author(s):  
Thor A. Hansen
Keyword(s):  
Gulf Coast ◽  
Middle Eocene ◽  
Late Eocene ◽  
Ecological Niches ◽  
Long Term Effects ◽  
Gamma Diversity ◽  
Time Diversity ◽  
Total Diversity ◽  
Radiation Phase

The Cretaceous–Tertiary (K–T) extinction reduced the gamma diversity of molluscs on the U.S. Gulf Coast from over 500 species in the late Maastrichtian to a little over 100 species in the early Danian. Gamma (total) diversity increased in a series of steps that generally tracked temperature, to a high of around 400 species in the late Middle Eocene, at which time diversity declined in the Late Eocene–Oligocene extinctions. The molluscan radiation occurred in at least two distinct phases: 1) an Initial Radiation Phase in which certain families underwent unusually high speciation, apparently filling ecological niches vacated by the extinction, followed by extinction of many of the species in these families in the late Danian; and, 2) a Secondary Radiation Phase where gamma diversity gradually increased and new genera gradually appeared. The fact that the gamma diversity of molluscs did not reach pre-extinction levels before the next extinction in the Late Eocene suggests that molluscan faunas may spend much of their evolutionary time recovering from these extinctions.

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