Bringing planktonic crinoids back to the bottom: Reassessment of the functional role of scyphocrinoid loboliths

Paleobiology ◽  
2019 ◽  
Vol 46 (1) ◽  
pp. 104-122
Author(s):  
Przemysław Gorzelak ◽  
Dorota Kołbuk ◽  
Mariusz A. Salamon ◽  
Magdalena Łukowiak ◽  
William I. Ausich ◽  
...  
Keyword(s):  
Theoretical Calculations ◽  
Distal Portion ◽  
Unconsolidated Sediments ◽  
Ecological Niches ◽  
Filter Feeder ◽  
Recumbent Posture ◽  
Distal Side ◽  
Middle Paleozoic ◽  
Long Stem ◽  
Gas Leaks

AbstractLiving crinoids are exclusively passive suspension feeders and benthic as adults. However, in the past they adapted to a broad range of ecological niches. For instance, the stratigraphically important middle Paleozoic scyphocrinoids are hypothesized to have been planktonic, employing their inferred gas-filled globular, chambered structure at the distal end of the stem, the so-called lobolith, as a buoyancy device with the crinoid calyx suspended below it. Here, we evaluate this hypothesis using evidence from skeletal micromorphology and theoretical biomechanical modeling. Lobolith walls are typically composed of ossicles, which are exclusively composed of constructional labyrinthic stereom. In plates from the distal side of the lobolith, this stereom extends into microperforate stereom layer, forming wavy ridges and spines. No microscale adaptations for preventing gas leaks and/or ingress of water (such as internal and external imperforate stereom layers) are known. Furthermore, theoretical calculations suggest that the scyphocrinoid tow-net mode of feeding would have resulted in small relative velocities between the towed filter and the ambient water, thus making it an ineffective passive filter feeder. We suggest that the lobolith of these crinoids acted as a modified holdfast rather than as a floating buoy. Its globular shape and distally positioned microspines served as adaptations for living in unconsolidated sediments, analogous to iceberg- and snowshoe-like strategies used by some mollusks and brachiopods. Like modern isocrinids, scyphocrinoids could have maintained an upright feeding posture by extending the distal portion of the stalk along the bottom. In this recumbent posture, the distal part of the stalk with the lobolith might have functioned as a drag anchor. As a consequence of the ~3-m-long stem, even with this posture, the benthic scyphocrinoids could have risen to the highest epifaunal tier in the Paleozoic.

scholarly journals Vertebrate fauna genesis in the Middle Paleozoic Podolian paleobasin

2020 ◽  
pp. 195-208
Author(s):  
Victor Voichyshyn
Keyword(s):  
Shallow Water ◽  
Sharp Increase ◽  
Evolutionary Development ◽  
Ecological Niches ◽  
Early Devonian ◽  
Vertebrate Fauna ◽  
High Ranking ◽  
Middle Paleozoic ◽  
Local Endemic

The formation of the Early Devonian ichthyofauna occurred under the combined influence of historical, paleogeographic and paleoecological factors. A consequence of evolutionary development at the beginning of the Devonian period arose a number of high-ranking taxa of sea vertebrates, which actively colonized the shallow water basins of new continent Laurussia. For representatives of local endemic faunas there was an opportunity to expand their habitats. There were exchanges of migrants between neighboring regional faunas. All this was accompanied by the evolution of ecosystems, the formation and development of new ecological niches. Early Devonian for most groups of vertebrates was marked by a sharp increase in the number of taxonomic units. The formation of Podillya regional ichthyofauna illustrates these trends of global biotic changes in that time.

XUV Absorption Spectra of Carbon Ions

1988 ◽  
Vol 102 ◽  
pp. 71-73
Author(s):  
E. Jannitti ◽  
P. Nicolosi ◽  
G. Tondello
Keyword(s):  
Absorption Spectra ◽  
Cross Section ◽  
Theoretical Calculations ◽  
Photoionization Cross Section ◽  
Carbon Ions

AbstractThe photoabsorption spectra of the carbon ions have been obtained by using two laser-produced plasmas. The photoionization cross-section of the CV has been absolutely measured and the value at threshold, σ=(4.7±0.5) × 10−19cm2, as well as its behaviour at higher energies agrees quite well with the theoretical calculations.

Relative Intensities in ED Patterns From Thin Gold Films

1972 ◽  
Vol 30 ◽  
pp. 636-637
Author(s):  
R. H. Morriss ◽  
J. D. C. Peng ◽  
C. D. Melvin
Keyword(s):  
Theoretical Calculations ◽  
Diffraction Theory ◽  
Gold Films ◽  
Reasonable Accuracy ◽  
Experimental Conditions ◽  
Crystal Perfection ◽  
Heavy Atoms ◽  
Fine Focus ◽  
Convergent Beam ◽  
Beam Diffraction

Although dynamical diffraction theory was modified for electrons by Bethe in 1928, relatively few calculations have been carried out because of computational difficulties. Even fewer attempts have been made to correlate experimental data with theoretical calculations. The experimental conditions are indeed stringent - not only is a knowledge of crystal perfection, morphology, and orientation necessary, but other factors such as specimen contamination are important and must be carefully controlled. The experimental method of fine-focus convergent-beam electron diffraction has been successfully applied by Goodman and Lehmpfuhl to single crystals of MgO containing light atoms and more recently by Lynch to single crystalline (111) gold films which contain heavy atoms. In both experiments intensity distributions were calculated using the multislice method of n-beam diffraction theory. In order to obtain reasonable accuracy Lynch found it necessary to include 139 beams in the calculations for gold with all but 43 corresponding to beams out of the [111] zone.

Effects of Higher-Order Laue Zone reflections on structure images

1993 ◽  
Vol 51 ◽  
pp. 450-451
Author(s):  
H. S. Kim ◽  
S. S. Sheinin
Keyword(s):  
Wave Vector ◽  
Theoretical Calculations ◽  
Reciprocal Lattice ◽  
Image Plane ◽  
Bloch Wave ◽  
Dynamical Theory ◽  
Higher Order ◽  
Lattice Image ◽  
Lattice Vector ◽  
Image Position

The importance of image simulation in interpreting experimental lattice images is well established. Normally, in carrying out the required theoretical calculations, only zero order Laue zone reflections are taken into account. In this paper we assess the conditions for which this procedure is valid and indicate circumstances in which higher order Laue zone reflections may be important. Our work is based on an analysis of the requirements for obtaining structure images i.e. images directly related to the projected potential. In the considerations to follow, the Bloch wave formulation of the dynamical theory has been used.The intensity in a lattice image can be obtained from the total wave function at the image plane is given by: where ϕg(z) is the diffracted beam amplitide given by In these equations,the z direction is perpendicular to the entrance surface, g is a reciprocal lattice vector, the Cg(i) are Fourier coefficients in the expression for a Bloch wave, b(i), X(i) is the Bloch wave excitation coefficient, ϒ(i)=k(i)-K, k(i) is a Bloch wave vector, K is the electron wave vector after correction for the mean inner potential of the crystal, T(q) and D(q) are the transfer function and damping function respectively, q is a scattering vector and the summation is over i=l,N where N is the number of beams taken into account.

REDUKSI KADAR LOGAM BERAT DALAM KIJING TAIWAN Anodonta woodiana AGAR MENJADI BAHAN PANGAN KONSUMSI YANG AMAN

2013 ◽  
Vol 3 (1) ◽  
pp. 184-192
Author(s):  
Sata Yoshida Srie Rahayu ◽  
Erni Rustiani
Keyword(s):  
Filter Feeder ◽  
Anodonta Woodiana

Kijing Taiwan (Anodonta woodiana) termasuk salah satu jenis kerang air tawar yang telah dikonsumsi oleh masyarakat. Salah satu bahan pencemar yang sering terdapat pada hewan filter feeder seperti kijing adalah logam berat. Logam-logam berat berbahaya yang sering mencemari lingkungan antara lain merkuri (Hg), cadmium (Cd), dan timbal (Pb). Tujuan penelitian ini adalah mengetahui kandungan logam berat Hg, Cd, dan Pb daging Kijing Taiwan selama periode dua bulan (Maret dan Mei) serta menerapkan perlakuan depurasi sebagai usaha untuk mengurangi kandungan logam berat. Penelitian dilakukan dengan cara mengiventarisasi wilayah pengambilan sampel, analisis karakteristik kijing, melakukan depurasi, dan analisis kandungan logam berat Hg, Cd, dan Pb daging kijing. Sampel Kijing Taiwan diambil dari perairan Darmaga di, Bogor. Kandungan proksimat daging kijing yang diukur adalah kadar air 81,5%, protein 8,9%, lemak 1,0%, abu 3,1%, dan karbohidrat 5,4%. Rendemen daging kijing sebesar 20,1% (sebelum depurasi), 19,6% (setelah 10 hari depurasi), dan 18,9% (setelah 20 hari depurasi). Kijing Taiwan di perairan Darmaga menunjukkan kandungan logam berat merkuri dan kadmium yang sangat kecil pada daging selama periode dua bulan (Maret dan Mei). Kandungan timbal bulan Maret lebih tinggi dibandingkan bulan Mei. Rata-rata kandungan timbal di perairan Darmaga selama dua periode adalah sebesar 1,4 ppm. Perlakuan depurasi selama 20 hari dapat menurunkan kandungan timbal pada kijing sebesar 0,05 ppm (setelah 10 hari depurasi) dan 0,08 ppm (setelah 20 hari depurasi).Kata kunci: Anodonta woodiana, Cd, depurasi, Hg, perairan Darmaga, Pb.

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