1,721,145 research outputs found
The evolution of Eocene planktonic foraminifera Dentoglobigerina
Full text linkDentoglobigerina is a diverse genus of planktonic foraminifera ranging from the Eocene to Recent. However, the ancestry of Dentoglobigerina has been controversial. A growing body of evidence indicates that the genus Dentoglobigerina was spinose in life and evolved from Eocene Subbotina, whilst others have suggested its origins stem from Acarinina. Here we explore whether Subbotina or Acarinina is the ancestor of Dentoglobigerina by examining 35 specimens, evaluating their morphology and their occurrences through the middle to late Eocene, from localities worldwide. We find that Dentoglobigerina evolved ∼4 million years earlier than previously documented, with the species Dentoglobigerina pseudovenezuelana and ‘Dentoglobigerina’ eotripartita recorded in middle Eocene, Zone E9. Morphological convergences between Dentoglobigerina and Subbotina were found with D. galavisi and D. pseudovenezuelana, and between Dentoglobigerina and Acarinina with ‘D.’ eotripartita. Spine holes were observed in D. galavisi and D. pseudovenezuelana, though not uniformly found in all forms. Our findings suggest that there are two distinct lineages: (1) Dentoglobigerina, encompassing the species D. pseudovenezuelana and D. galavisi as a descendant of Subbotina; and (2) ‘Dentoglobigerina’ (including ‘D.’ eotripartita) as a descendant of Acarinina. Our results contribute to a better understanding of Dentoglobigerina biostratigraphy, phylogeny and evolution, and have implications for taxonomy
Size and shape data of Globigerinoidesella fistulosa, Trilobatus sacculifer and intermediate specimens from ODP Site 1115
No full textPlanktonic foraminifera are extremely well-suited to study evolutionary processes in the fossil record due to their high-resolution deposits and global distribution. Species are typically conservative in their shell morphology with the same geometric shapes appearing repeatedly through iterative evolution, but the mechanisms behind the architectural limits on foraminiferal shell shape are still not well understood. To understand when and how these developmental constraints can be overcome, we study morphological change leading up to the origination of the unusually ornate species Globigerinoidesella fistulosa. Our results show that the origination of G. fistulosa from the Trilobatus sacculifer plexus involved an amalgamation of three different heterochronic expressions: addition of chambers (hypermorphosis), earlier onset of protuberances (pre-displacement), and steeper allometric slope (acceleration) as compared to its ancestor. We argue that the protuberances unique to G. fistulosa were necessary to sustain a surface-area: volume ratio that could host sufficient numbers of photosymbionts. Our work provides a case study of the complex combination of processes required to produce unusual shell shapes and highlights the importance of developmental processes in evolutionary origination.</span
Data report: Miocene planktonic foraminifers Dentoglobigerina and Globoquadrina from IODP Sites U1489 and U1490, Expedition 363
Full text linkInternational Ocean Discovery Program Expedition 363 Sites U1489 and U1490, located in the Western Pacific Warm Pool, con- tain diverse assemblages of planktonic foraminifers. We examined and imaged specimens of Miocene Dentoglobigerina and Globo- quadrina to determine the presence or absence of spine holes and pustules in their wall texture. A total of 15 specimens were observed across six species, including Dentoglobigerina baroemoenensis, Dentoglobigerina binaiensis, Dentoglobigerina globosa, Dentoglobi- gerina globularis, Dentoglobigerina tripartita, and Globoquadrina dehiscens. Here we present scanning electron microscope and z- stacking light microscope images in three views, including illustra- tions of their wall texture
Bridging the extant and fossil record of planktonic foraminifera: implications for the <i>Globigerina</i> lineage
No full textWe conducted a morphometric study and wall texture analysis on extant and fossil specimens of the planktonic foraminifera Globigerina falconensis plexus. Our global data reveal morphological inconsistencies between fossil and extant populations. Our results are significant as G. falconensis is widely used in palaeoceanographic studies in conjunction with its sister taxon G. bulloides. Morphologically these two species are similar, with the main difference being the distinctive apertural lip present in G. falconensis. We selected cores covering the entire stratigraphic range of G. falconensis, from the early Miocene to current day, spanning sites from high latitudes in the North Atlantic Ocean and the southern Indian Ocean to sites in equatorial regions. The morphology found in the modern ocean is not consistent with the Miocene holotype of Globigerina falconensis Blow described from lower Miocene sediments in Venezuela. A more lobate morphology evolved in the late Miocene, thus, a new name is required for this morphotype, coexisting in the modern oceans with G. falconensis s.s. We thus describe the new morphospecies, G. neofalconensis for the more lobate forms which evolved in the late Miocene and inhabit the modern oceans. Additionally, we report a pseudocancellate wall texture present in the G. falconensis plexus. We use the molecular sequences from the PR2 database to explore the generic attribution of the G. falconensis lineage, confirming its close relationship with G. bulloides and its retention in the genus Globigerina
Taxonomy, biostratigraphy, and phylogeny of Oligocene Subbotina
No full textThe taxonomy, biostratigraphy, and phylogeny of Oligocene Subbotina is discussed and reviewed. We include forms that have teeth extending into the umbilicus. A total of nine species are accepted as distinct, namely Subbotina angiporoides (Hornibrook), Subbotina corpulenta (Subbotina), Subbotina eocaena (Gümbel), Subbotina gortanii (Borsetti), Subbotina linaperta (Finlay), Subbotina minima (Jenkins), Subbotina projecta Olsson, Pearson and Wade n. sp., Subbotina tecta Pearson and Wade, and Subbotina utilisindex (Jenkins and Orr)
Morphology of <i>Pulleniatina </i>(planktonic foraminifera) from optical microscopy, micro-CT, and SEM investigations
No full textPulleniatina is a genus of planktonic foraminifera that is widely used in biostratigraphic and palaeoceanographic studies. In our taxonomy, it comprises six morphospecies, alphabetically P. finalis, P. obliquiloculata, P. praecursor, P. praespectabilis, P. primalis, and P. spectabilis. Standard methods of taxonomic discrimination rely on descriptive characteristics of the adult test, such as the shape of the chambers, the shape and position of the primary aperture, the number of chambers per whorl, the height of the spire, the degree of involution, and the irregularity of coiling (“streptospirality”). Here, we illustrate representative specimens of each morphospecies and the likely ancestor, Neogloboquadrina acostaensis, from International Ocean Discovery Program (IODP) Site U1488 (Eauripik Rise, western equatorial Pacific Ocean) using light microscopy and X-ray microcomputed tomography (micro-CT). For each specimen, we provide multifocus light microscope images in three standard orientations, a set of up to 2000 X-radiographs, and a rendered three-dimensional (3D) model that can be viewed externally, internally, and in any cross-section using widely available freeware. We also include labelled images distinguishing each successive chamber and quantify the chamber volumes, the rate of size increase, the aspect ratios, and the angles at which they are added. A second set of specimens was crushed and imaged using scanning electron microscopy (SEM) to further study the internal morphology and wall texture. We use these observations to document the comparative ontogeny and test structure of the six Pulleniatina morphospecies in the context of an evolutionary model involving two diverging species lineages
Heterochrony in the evolution of the planktonic foraminifer Globigerinoidesella fistulosa from the <i>Trilobatus sacculifer</i> plexus
No full textPlanktonic foraminifera are extremely well-suited to study evolutionary change in the fossil record due to their high-resolution deposits and global distribution. Species are typically conservative in their shell morphology with the same geometric shapes appearing repeatedly through iterative evolution, but the mechanisms behind the architectural limits on foraminiferal shell shape are still not well understood. To understand when and how these developmental constraints evolve, we study morphological change leading up to the origination of the unusually ornate species Globigerinoidesella fistulosa. We measured the size and circularity of over 900 specimens of G. fistulosa, its ancestor Trilobatus sacculifer and intermediate forms from a site in the Western Equatorial Pacific. Our results show that the origination of G. fistulosa from the Trilobatus sacculifer plexus involved a combination of two heterochronic expressions: earlier onset of protuberances (pre-displacement) and steeper allometric slope (acceleration) as compared to its ancestor. Our work provides a case study of the complex morphological and developmental changes required to produce unusual shell shapes and highlights the importance of developmental changes in evolutionary origination
Rediscovering Globigerina bollii Cita and Premoli Silva 1960
Full text linkGlobigerina bollii Cita and Premoli Silva was described from the historical Langhian-type section
in Langhe, Piedmont (Italy). Due to its peculiar compact morphology, it was set apart from all the other globigerinids
typical of the coeval Mediterranean fauna, and it was only reported for a short and limited stratigraphic
range. The taxon became a first-order marker for the local biostratigraphy with its own Globigerina bollii Zone
within the Langhian stage. However, the species was later synonymised with Globigerina falconensis Blow, ending
its use in biostratigraphic schemes, and it was no longer utilised by authors working in the Mediterranean area
and Paratethys. We present a reassessment of Globigerina bollii, showing for the first time a full collection of
high-quality scanning electron and optical microscope images of the type series of specimens and a comparative
study with Mediterranean individuals from the Langhian of the Cretaccio Section (Italy) and extra-Mediterranean
individuals from Ocean Drilling Program Site 747 in the Kerguelen Plateau (Indian Ocean). The stratigraphic
ranges of all the occurrences cited in the scientific literature from 1960 to the present day and all the references
including images of the taxon are compiled.We compare G. bollii to other four-chambered morphospecies
inhabiting the oceans during the Miocene, providing a detailed discussion of their morphological differences,
which allows us to retain G. bollii as a valid taxon and to disclaim its synonymy with Globigerina falconensis.
Our taxonomical observations also allow us to reassign Globigerina bollii to the genus Globoturborotalita, due
to its strong affinities with other members of that genus, such as G. eolabiacrassata Spezzaferri and Coxall,
and G. ouachitaensis (Howe and Wallace). We present a direct visual comparison with the other representatives
of middle Miocene globoturborotaliids. An additional comparison is also discussed with Globigerina bollii
lentiana Rögl, a species endemic in the Paratethys. We conclude that the presence of G. bollii in the Mediterranean
Basin during such a confined stratigraphic interval (Mediterranean Subzone MMi4c–MMi4d), might be
a palaeogeographical indicator of the intermittent opening of the eastern gateway with the Paratethys, affecting
the Mediterranean faunas during the Langhian and their migration from oceanic realms into the Paratethys and
Mediterranean
Did Photosymbiont Bleaching Lead to the Demise of Planktic Foraminifer Morozovella at the Early Eocene Climatic Optimum?
Full text linkThe symbiont-bearing mixed-layer planktic foraminiferal genera Morozovella and Acarinina were among the most important calcifiers of early Paleogene tropical–subtropical oceans. A marked and permanent switch in the abundance of these genera is known to have occurred at low-latitude sites at the beginning of the Early Eocene Climatic Optimum(EECO), such that the relative abundance of Morozovella permanently and significantly decreased along with a progressive reduction in the number of species; concomitantly, the genus Acarinina almost doubled its abundance and diversified. Here we examine planktic foraminiferal assemblages and stable isotope compositions of their tests at Ocean Drilling Program Site 1051 (northwest Atlantic) to detail the timing of this biotic event, to document its details at the species level, and to test a potential cause: the loss of photosymbionts (bleaching). We also provide stable isotope measurements of bulk carbonate to refine the stratigraphy at Site 1051 and to determine when changes in Morozovella species composition and their test size occurred. We demonstrate that the switch in Morozovella and Acarinina abundance occurred rapidly and in coincidence with a negative carbon isotope excursion known as the J event (~53 Ma), which marks the start of the EECO.We provide evidence of photosymbiont loss after the J event from a size-restricted δ13C analysis. However, such inferred bleaching was transitory and also occurred in the acarininids. The geologically rapid switch in planktic foraminiferal genera during the early Eocene was a major evolutionary change within marine biota, but loss of photosymbionts was not the primary causal mechanism
Atmospheric carbon dioxide through the Eocene–Oligocene climate transition
No full textGeological and geochemical evidence1, 2, 3 indicates that the Antarctic ice sheet formed during the Eocene–Oligocene transition4, 33.5–34.0 million years ago. Modelling studies5, 6 suggest that such ice-sheet formation might have been triggered when atmospheric carbon dioxide levels () fell below a critical threshold of 750 p.p.m.v., but the timing and magnitude of relative to the evolution of the ice sheet has remained unclear. Here we use the boron isotope pH proxy7, 8 on exceptionally well-preserved carbonate microfossils from a recently discovered geological section in Tanzania9, 10 to estimate before, during and after the climate transition. Our data suggest that a reduction in occurred before the main phase of ice growth, followed by a sharp recovery to pre-transition values and then a more gradual decline. During maximum ice-sheet growth, was between 450 and 1,500 p.p.m.v., with a central estimate of 760 p.p.m.v. The ice cap survived the period of recovery, although possibly with some reduction in its volume, implying (as models predict11) a nonlinear response to climate forcing during melting. Overall, our results confirm the central role of declining in the development of the Antarctic ice sheet (in broad agreement with carbon cycle modelling12) and help to constrain mechanisms and feedbacks associated with the Earth's biggest climate switch of the past 65 Myr
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