2,508 research outputs found
The late Middle Devonian fauna of Red Hill I, Nevada, and its paleobiogeographic implications
<i>Eurycormus</i> – <i>Eurypoma</i>, two Jurassic actinopterygian genera with mixed identity
Scale morphology and specialized dorsal scales of a new teleosteomorph fish from the Aptian of West Gondwana
Scales of a new species of Teleosteomorpha from the continental Aptian of
the south of South America are studied. These neopterygians are from the La
Cantera Formation in central Argentina, and were previously identified as
Pholidophoriformes. They present ganoid scales; most of them are rhombic
with well-developed peg-and-socket articulations and possessing a smooth
surface. They have a straight posterior margin, but occasionally, some
scales of the flank have a sinuous posterior margin with one or two
serrations. The shape of the scales varies along the body from large,
rectangular and deeper than long scales behind the head to the preanal
region to smaller and rhomboidal scales in the caudal region. There are a
few horizontal rows along the flank and about 32 lateral line scales. Thick,
round ganoid scales are present in the prepelvic region close to the ventral
margin. The round and rhombic scales present growth lines, which form
concentric ridges on the external side. A characteristic row of deep scales
forms the dorsal margin on each side of the body; a row of median ridge
scales is not present. This is a unique feature of the studied fishes.
Scutes covered with unornamented ganoine precede the pelvic, dorsal, and
anal fins, as well as the dorsal and ventral margins of the caudal fin. The
posterior margin of the dorsal lobe of the caudal fin is formed by a single
line of scales, which continues and covers the base of the first principal
caudal ray. Histological studies reveal a lepisosteoid-scale type with
multiple ganoine layers, lack of dentine, and the presence of canaliculi of
Williamson. The macro- and micromorphology of the scales shows features that
are found in other teleosteomorphs, but also in other neopterygians
A Porolepiform Rhipidistian from the Lower Devonian of the Canadian Arctic
A holoptychiid fish is described from the Lower Devonian of Arctic Canada. The new form is distinct from other holoptychiids by the presence of a large supraorbital bone and a boomerang-shaped tabular. Nasogaluakus n. gen. is the oldest and most primitive holoptychiid based on a phylogenetic analysis of porolepiforms and their closest relatives. The sequence of the genera corresponds to their stratigraphic appearance.
Ein Holoptychiide aus dem Unterdevon der kanadischen Arktis wird beschrieben. Er unterscheidet sich durch ein großes Supraorbitale und die Bumerang-Form des Tabulare von allen übrigen Holoptychiiden. Nasogaluakus n. gen. ist der älteste und primitivste Holoptychiide, was durch eine phylogenetische Analyse der Porolepiformes belegt wird. Die Abfolge der Gattungen in diesem Verwandtschaftsschema stimmt mit ihrem zeitlichen Auftreten überein.
doi:10.1002/mmng.20000030106</a
Sarcopterygian and other Fishes from the Marine Upper Devonian of Colorado, U.S.A.
The fish fauna of Upper Devonian deposits of SW Colorado is described and compared with those of Central Colorado. The osteolepidid Litoptychus is redescribed including skull roof, cheek, palatoquadrate, cleithrum and postcranial elements. A second osteolepidid with cosmine-covered scales and bones is recognized in the Upper Devonian deposits of Colorado. A skull roof and a parasphenoid formerly attributed to Litoptychus, and a pterygoid, cleithrum, ribs and scales are assigned to dipnoans, partly to long-snouted dipnoans cf. Soederberghia. Comparison of the Late Devonian fish fauna of Colorado with that of Arizona places the fishes of Colorado into a coastal marine depositional environment.
Die oberdevonische Fischfauna von SW Colorado ist beschrieben und mit der von Zentral-Colorado verglichen. Die osteolepidide Gattung Litoptychus ist neu beschrieben einschließlich Schädeldach, Wangenreigion, Palatoquadratum, Cleithrum und postkranialer Elemente und diagnostiziert. Ein zweiter Osteolepidide mit Kosmin bedeckten Schuppen und Knochen wird von Litoptychus (ohne Kosmin) abgetrennt. Ein Schädeldach und ein Paraschenoid, die früher zu Litoptychus gestellt wurden, und ein Pterygoid, ein Cleithrum, Rippen und Schuppen werden zu Lungenfischen gestellt, z. T. zu langschnauzigen Lungenfischen cf. soederberghia. — Der Vergleich der spätdevonischen Fischfauna von Colorado mit der von Arizona deutet auf eine küstennahe marine Lebenswelt der Colorado-Fische hin.
doi:10.1002/mmng.19980010104</a
The Influence of Length of Storage of Bovine Semen on Conception Rate under Field Conditions
It is the purpose of this study to determine whether under conditions of routine handling in artificial breeding associations there is a decline in semen fertility from day to day and also to determine the magnitude of this decline. Tabulation of such data will not only be of value in determining the effect of frequent semen collection on the over-all artificial breeding results but will also serve as a basis of comparison in investigational work directed toward increasing the efficiency of artificial breeding
On a remarkable new species of <i>Tharsis</i>, a Late Jurassic teleostean fish from southern Germany: its morphology and phylogenetic relationships
A complete morphological description, as preservation permits, is provided
for a new Late Jurassic fish species (Tharsis elleri) together with
a revision and comparison of some morphological features of Tharsis dubius, one of the most common species from the Solnhofen limestone,
southern Germany. An emended diagnosis of the genus Tharsis – now
including two species – is presented. The new species is characterized by a
combination of morphological characters, such as the presence of a complete
sclerotic ring formed by two bones placed anterior and posterior to the eye,
a moderately short lower jaw with quadrate-mandibular articulation below the
anterior half of the orbit, caudal vertebrae with neural and haemal arches
fused to their respective vertebral centrum, and parapophyses fused to their
respective centrum. A phylogenetic analysis based on 198Â characters and
43Â taxa is performed. Following the phylogenetic hypothesis, the sister-group
relationship Ascalaboidae plus more advanced teleosts stands above the node
of Leptolepis coryphaenoides. Both nodes have strong support among teleosts. The results
confirm the inclusion of Ascalabos, Ebertichthys and
Tharsis as members of this extinct family. Tharsis elleri
n. sp. (LSID urn:lsid:zoobank.org:act:6434E6F5-2DDD-48CF-A2B1-827495FE46E6,
date: 13 December 2018) is so far restricted to one Upper Jurassic German
locality – Wegscheid Quarry near Schernfeld, Eichstätt – whereas
Tharsis dubius is known not only from Wegscheid Quarry, but also
from different localities in the Upper Jurassic of Bavaria, Germany, and
Cerin in France.</p
Coherent control for the spherical symmetric box potential in short and intensive XUV laser fields
Coherent control calculations are presented for a spherically symmetric box
potential for non-resonant two photon transition probabilities. With the help
of a genetic algorithm (GA) the population of the excited states are maximized
and minimized. The external driving field is a superposition of three intensive
extreme ultraviolet (XUV) linearly polarized laser pulses with different
frequencies in the femtosecond duration range. We solved the quantum mechanical
problem within the dipole approximation. Our investigation clearly shows that
the dynamics of the electron current has a strong correlation with the
optimized and neutralizing pulse shape.Comment: 11 Pages 3 Figure
Testing models of dental development in the earliest bony vertebrates, Andreolepis and Lophosteus
Theories on the development and evolution of teeth have long been biased by the fallacy that chondrichthyans reflect the ancestral condition for jawed vertebrates. However, correctly resolving the nature of the primitive vertebrate dentition is challenged by a dearth of evidence on dental development in primitive osteichthyans. Jaw elements from the Silurian–Devonian stem-osteichthyans Lophosteus and Andreolepis have been described to bear a dentition arranged in longitudinal rows and vertical files, reminiscent of a pattern of successional development. We tested this inference, using synchrotron radiation X-ray tomographic microscopy (SRXTM) to reveal the pattern of skeletal development preserved in the sclerochronology of the mineralized tissues. The tooth-like tubercles represent focal elaborations of dentine within otherwise continuous sheets of the dermal skeleton, present in at least three stacked generations. Thus, the tubercles are not discrete modular teeth and their arrangement into rows and files is a feature of the dermal ornamentation that does not reflect a polarity of development or linear succession. These fossil remains have no bearing on the nature of the dentition in osteichthyans and, indeed, our results raise questions concerning the homologies of these bones and the phylogenetic classification of Andreolepis and Lophosteus
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