scholarly journals The balancing act of Nipponites mirabilis (Nostoceratidae, Ammonoidea): managing hydrostatics during a complex ontogenetic trajectory

2020 ◽  
Author(s):  
David J. Peterman ◽  
Tomoyuki Mikami ◽  
Shinya Inoue
Keyword(s):  
Late Cretaceous ◽  
Vertical Axis ◽  
3D Models ◽  
Low Energy ◽  
Soft Body ◽  
Neutral Buoyancy ◽  
Ontogenetic Stages ◽  
Ontogenetic Trajectory ◽  
Mode Of Life

AbstractNipponites is a heteromorph ammonoid with a complex and unique morphology that obscures its mode of life and ethology. The seemingly aberrant shell of this Late Cretaceous nostoceratid seems deleterious. However, hydrostatic simulations suggest that this morphology confers several advantages for exploiting a quasi-planktic mode of life. Virtual, 3D models of Nipponites mirabilis were used to compute various hydrostatic properties through 14 ontogenetic stages. At each stage, Nipponites had the capacity for neutral buoyancy and was not restricted to the seafloor. Throughout ontogeny, horizontally facing to upwardly facing soft body orientations were preferred. These orientations were aided by the obliquity of the shell’s ribs, which were parallel to former positions of the aperture during life. Static orientations were somewhat fixed, inferred by stability values that are slightly higher than extant Nautilus. The initial open-whorled, planispiral phase is well suited to horizontal backwards movement with little rocking. Nipponites then deviates from this coiling pattern with a series of alternating U-shaped bends in the shell. This modification allows for proficient rotation about the vertical axis, while possibly maintaining the option for horizontal backwards movement by redirecting its hyponome. These particular hydrostatic properties likely result in a tradeoff between hydrodynamic streamlining, suggesting that Nipponites assumed a low energy lifestyle of slowly pirouetting in search for planktic prey. Each computed hydrostatic property influences the others in some way, suggesting that Nipponites maintained a delicate hydrostatic balancing act throughout its ontogeny in order to facilitate this mode of life.

A method to the madness: Ontogenetic changes in the hydrostatic properties of Didymoceras (Nostoceratidae: Ammonoidea)

Paleobiology ◽  
2020 ◽  
Vol 46 (2) ◽  
pp. 237-258 ◽  
Author(s):  
David J. Peterman ◽  
Margaret M. Yacobucci ◽  
Neal L. Larson ◽  
Charles Ciampaglio ◽  
Tom Linn
Keyword(s):  
Vertical Axis ◽  
3D Models ◽  
Juvenile Stage ◽  
Ontogenetic Changes ◽  
Neutral Buoyancy ◽  
Juvenile Dispersal ◽  
Directional Movement ◽  
Stability Change ◽  
Upward Direction ◽  
Two Stages

AbstractThe seemingly aberrant coiling of heteromorphic ammonoids suggests that they underwent more significant changes in hydrostatic properties throughout ontogeny than their planispiral counterparts. Such changes may have been responses to different selective pressures at different life stages. The hydrostatic properties of three species of Didymoceras (D. stevensoni, D. nebrascense, and D. cheyennense) were investigated by creating virtual 3D models at several stages during growth. These models were used to compute the conditions for neutral buoyancy, hydrostatic stability, orientation during life, and thrust angles (efficiency of directional movement). These properties suggest that Didymoceras and similar heteromorphs lived low-energy lifestyles with the ability to hover above the seafloor. The resultant static orientations yielded a downward-facing aperture in the hatchling and a horizontally facing aperture throughout most of the juvenile stage, before terminating in an upward direction at maturity. Relatively high hydrostatic stabilities would not have permitted the orientation of Didymoceras to be considerably modified with active locomotion. During the helical phase, Didymoceras would have been poorly suited for horizontal movement, yet equipped to pirouette about the vertical axis. Two stages throughout growth, however, would have enhanced lateral mobility: a juvenile stage just after the formation of the first bend in the shell and the terminal stage after completion of the U-shaped hook. These two more mobile phases in ontogeny may have improved juvenile dispersal potential and mate acquisition during adulthood, respectively. In general, life orientation and hydrostatic stability change more wildly for these aberrantly coiled ammonoids than their planispiral counterparts.

Aerodynamic and aeroacoustic performance investigations on modified H-rotor Darrieus wind turbine

2021 ◽  
pp. 0309524X2110039
Author(s):  
Amgad Dessoky ◽  
Thorsten Lutz ◽  
Ewald Krämer
Keyword(s):  
Wind Turbine ◽  
High Speed ◽  
Cfd Simulation ◽  
Vertical Axis ◽  
3D Models ◽  
Power Coefficient ◽  
Design Parameters ◽  
Second Phase ◽  
Vertical Axis Wind Turbine ◽  
Guide Vanes

The present paper investigates the aerodynamic and aeroacoustic characteristics of the H-rotor Darrieus vertical axis wind turbine (VAWT) combined with very promising energy conversion and steering technology; a fixed guide-vanes. The main scope of the current work is to enhance the aerodynamic performance and assess the noise production accomplished with such enhancement. The studies are carried out in two phases; the first phase is a parametric 2D CFD simulation employing the unsteady Reynolds-averaged Navier-Stokes (URANS) approach to optimize the design parameters of the guide-vanes. The second phase is a 3D CFD simulation of the full turbine using a higher-order numerical scheme and a hybrid RANS/LES (DDES) method. The guide-vanes show a superior power augmentation, about 42% increase in the power coefficient at λ = 2.75, with a slightly noisy operation and completely change the signal directivity. A remarkable difference in power coefficient is observed between 2D and 3D models at the high-speed ratios stems from the 3D effect. As a result, a 3D simulation of the capped Darrieus turbine is carried out, and then a noise assessment of such configuration is assessed. The results show a 20% increase in power coefficient by using the cap, without significant change in the noise signal.

Developmental regulation and morphological saltation in the heteromorph ammonite Nipponites

Paleobiology ◽  
1988 ◽  
Vol 14 (3) ◽  
pp. 272-286 ◽  
Author(s):  
Takashi Okamoto
Keyword(s):  
Developmental Regulation ◽  
Shell Growth ◽  
Growth Direction ◽  
Intermediate Form ◽  
Free Living ◽  
Neutral Buoyancy ◽  
Life Orientation ◽  
Sea Bottom ◽  
Mode Of Life ◽  
Lower Limits

Nipponites, a Late Cretaceous nostoceratid ammonite, shows a peculiar meandering shell growth in the middle-late stage. Assuming neutral buoyancy, and a constant aperture angle relative to the sea bottom, meandering growth of this ammonite was modeled by computer simulation. In this model, the meandering shell growth is controlled by regulation of life orientation. The remarkable similarity in the coiling modes and rib obliquity patterns between the computer-simulated and actual specimens strongly suggests a free living mode of life in Nipponites with an approximately neutral buoyancy. The simulation also suggests that morphological saltation from a simple helicoid form like Eubostrychoceras japonicum to a meandering shell form like Nipponites occurred abruptly without any intermediate form by minor change of the upper and lower limits of growth direction.

Affinities of the alleged earliest Cambrian gastropod Aldanella

2013 ◽  
Vol 91 (12) ◽  
pp. 914-923 ◽  
Author(s):  
Jerzy Dzik ◽  
Dawid Mazurek
Keyword(s):  
Shell Morphology ◽  
Skewed Distribution ◽  
Phylogenetic Position ◽  
Soft Body ◽  
Middle Cambrian ◽  
Small Shelly Fossils ◽  
Embryonic Shell ◽  
Mode Of Life ◽  
Early Palaeozoic ◽  
Mature Size

Unlike true Palaeozoic gastropods, but similar to some coeval hyoliths, the cup-like hemispherical embryonic shell of Aldanella attleborensis (Shaler and Foerste, 1888) from the earliest Cambrian (early Tommotian) Erkeket Formation of northern Siberia bears a mucro. Also, the pattern of mortality, with right-skewed distribution and a peak at about 1.0 mm diameter, is not similar to that of early Palaeozoic gastropods; there is no evidence of metamorphosis that would end the pelagic larval stage of ontogeny. Specimens of larger size are rare in samples of phosphatized “small shelly fossils” but are known in related species of the genus, of up to 3–5 mm diameter. A phosphatized soft body is preserved in a few specimens of A. attleborensis, one bearing possible chaetae of about 5 μm diameter. Such bunches of chaetae arming locomotory organs were earlier identified in the genus Pelagiella Matthew, 1895, a more derived member of the same lineage. It shares with the genus Aldanella Vostokova, 1962 also the mucronate embryonic shell and acicular aragonitic shell wall microstructure. The presence of chaetae-bearing organs suggests pelagic mode of life of pelagiellids at maturity. Middle Cambrian Pelagiella shells reached 7 mm in diameter, suggesting evolutionary increase in mature size. Embryonic shell morphology, wall microstructure, and the presence of locomotory organs with a fan of chaetae contradicts gastropod, and even conchiferan affinity of the pelagiellids, but together with the pattern of ontogeny conforms to the enigmatic Palaeozoic hyoliths. They differ in having opercula closing the shell apertures and in lacking evidence of chaetae. The helens, paired apertural appendages of possible locomotory function occurring in apertures of some of them, do not reveal any similarity to chaetae in their development. We propose classifying the order Pelagiellida in the class Hyolitha rather than in the class Gastropoda, until its phylogenetic position is clarified. Such understood hyoliths may represent the earliest stage in evolution of molluscs, immediately following initial diversification of the spiralians (lophotrochozoans) into phyla.

Paleomagnetic determinations of vertical-axis tectonic rotations from Late Cretaceous and Paleocene strata of Bolivia

Geology ◽  
1995 ◽  
Vol 23 (9) ◽  
pp. 799 ◽  
Author(s):  
R. F. Butler ◽  
D. R. Richards ◽  
T. Sempere ◽  
L. G. Marshall
Keyword(s):  
Late Cretaceous ◽  
Vertical Axis

Large recent counterclockwise rotations in the Tajik Basin and implications on the Pamir salient formation

2021 ◽  
Author(s):  
Lin Li ◽  
Guillaume Dupont-Nivet ◽  
Pierrick Roperch ◽  
Yani Najman ◽  
Mustafa Kaya ◽  
...  
Keyword(s):  
Late Cretaceous ◽  
Late Miocene ◽  
Vertical Axis ◽  
Mantle Lithosphere ◽  
North Central ◽  
Combined Analysis ◽  
Lateral Extrusion ◽  
Axis Rotation ◽  
Early Late

<p>Contrasting models have been proposed to explain the formation of the Pamir salient: either largely inherited from a Mesozoic arcuate structure or recently formed by Indian northward indentation and possibly related to syn-orogenic lateral extrusion. The vertical-axis counterclockwise rotations observed in the Tajik Basin are key constraints on testing these models, but the timing of these rotations remains hindered by poor age control on the basin sediments. We report a combined analysis of vertical-axis rotation and magnetostratigraphic dating of a long sedimentary section in the eastern Tajik Basin, which yields strong counterclockwise rotations (~56°) in early Late Cretaceous to late Miocene strata. This result suggests that rotation in the Tajik Basin occurred after ~8 Ma, much later than previously suggested. Combining with a regional compilation of previous paleomagnetic studies as well as structural and GPS constraints including Pamir and Tarim, we explore potential implications on models of the Pamir salient. We infer that after 8 Ma (probably even later), the Pamir (North, Central, and South) began to overthrust west- and northwest-ward, causing counterclockwise rotations in the Tajik Basin. This reconstruction allows for ~150 km of post-8 Ma northwestward indentation into the Tajik Basin, in agreement with coeval underthrusting of the Indian mantle lithosphere into Asia.</p>

Floating the Vrancea slab and tectonic reconstruction of the collapse of the PalaeoPannonian Basin

2021 ◽  
Author(s):  
Jack Muston ◽  
Wim Spakman ◽  
Gordon Lister
Keyword(s):  
Large Scale ◽  
Pannonian Basin ◽  
Vertical Axis ◽  
3D Models ◽  
Fault System ◽  
Slab Geometry ◽  
Lower Velocity ◽  
Tomographic Images ◽  
Model Interpretation ◽  
Tectonic Reconstruction

<p>Here we present the first 4D tectonic reconstruction that models the Vrancea slablet and incorporates the floated slab as a constraint on the magnitude of slab rollback during collapse of the Palaeo-Pannonian Basin. Seismic tomographic images provide insight into the geometry and tectonic history of subducted slabs. High velocity anomalies can be interpreted as ‘cold’ lithosphere penetrating ‘warmer’ lower velocity asthenosphere, and 3D models created using the <em>SKUA-GOCAD</em> modelling software. Combined with information from the 3D distribution of earthquake hypocentres, we thereby obtain a simple approximation to slab geometry beneath the Vrancea region. The resultant DXF was imported into the <em>Pplates</em> tectonic reconstruction software, and floated back to the Earth’s surface. The method utilised assumes no significant deformation (stretching, buckling, folding, shortening) during or after subduction, so that the obtained geometry estimates the pre-subduction configuration. The resultant floated slab is then incorporated as a constraint on 2D + time tectonic reconstructions. We apply a double-saloon-door rollback model, which involves propagation of a slab tear along the mid-Hungarian lineament. Each saloon-door rolls back independently of the other and this leads to two epochs of extension. AlPaCa is ‘pulled’ eastwards and rotated counter-clockwise as the western saloon-door rolls back. The Tisza-Dacia unit is then ‘pulled’ eastward, and rotated, but in a clockwise sense as the eastern saloon-door rolls back. Once the subduction hinge reached the East European Platform, the slab was left hanging. Gravitational forces then drove slab-boudinage and detachment in a similar fashion as occurs today beneath the Hindu Kush. This model explains the large opposing-sense vertical-axis rotations that occurred during convergence of the AlPaCa and Tisza-Dacia terranes. The zipper fault model rotates the microplates without requiring large-scale thrusting. Interpretation of the Mid-Hungarian lineament as a zipper-fault system is also consistent with the geodynamic effects expected because of tearing in a subducting plate leading to a double-saloon-door rollback. The vertical extent of the slab is roughly 300 km, which only fills half of the basin, consistent with the double-saloon-door roll-back model interpretation.</p>

Form and function in Thylacocephala, Conchyliocarida and Concavicarida (?Crustacea): a problem of interpretation

1985 ◽  
Vol 76 (2-3) ◽  
pp. 391-399 ◽  
Author(s):  
W. D. Ian Rolfe
Keyword(s):  
Compound Eye ◽  
Neutral Buoyancy ◽  
Low Contrast ◽  
Linear Pattern ◽  
Form And Function ◽  
Mode Of Life ◽  
And Function ◽  
Food Substrate

ABSTRACTDifferences in the preservation of Jurassic thylacocephalans and conchyliocarids have given rise to different interpretations of the form of these fossils, and thus their mode of life. When evidence from these two groups is combined with that derived from Palaeozoic concavicarids, it becomes possible to unify the several interpretations of this one group of organisms, the Thylacocephala. The group ranges from at least the Silurian to the Cretaceous.A review is given of how these differences of interpretation have arisen, and some resolution is attempted. If the thylacocephalan “anterior structure” is reinterpreted by analogy with hyperiid amphipods as a paired compound eye occupying most of the surface of the head, it explains its bilobed nature and the position of the stomach within the structure, but it raises the difficulty of a post-cephalic origin for the carapace. The simpler solution is preferred of regarding this structure as discrete paired eyes with a smooth cornea and subjacent crystal cones.The raptorial appendages are post-oral and post-adductor in insertion. They are therefore tentatively identified as the maxillae and maxilliped, but verification of the mandible's position is needed to test this. The postero-ventral battery of “body somites” is reinterpreted as paired protopods of abdominal limbs. A respiratory current is deduced to have entered a branchiostegal chamber ventrally, and left it posterodorsally. It is speculated that the looped linear pattern of intra-cuticular spheres in Paraostenia are photophores. The large eyes with small interommatidial angles were probably used to discern low contrast prey or carrion against a dim background. By analogy with hyperiid amphipods, it is suggested that at least some thylacocephalans were mesopelagic predators. They may have attained neutral buoyancy from their food substrate of shark and coleoids.

Rail Passenger Vehicle Crashworthiness Simulations Using Multibody Dynamics Approaches

2017 ◽  
Vol 12 (4) ◽  
Author(s):  
Yan Quan Sun ◽  
Maksym Spiryagin ◽  
Colin Cole
Keyword(s):  
Multibody Dynamics ◽  
Three Dimensional ◽  
3D Models ◽  
Low Energy ◽  
Passenger Vehicle ◽  
Passenger Car ◽  
Passenger Train ◽  
Simulation Results ◽  
Vehicle Crashworthiness

Multibody dynamics approaches have nowadays been an essential part in examining train crashworthiness. A typical passenger train structure has been investigated on its crashworthiness using three-dimensional (3D) models of a single passenger car and multiple cars formulated using multibody dynamics approaches. The simulation results indicate that the crush length or crush force or both of the crush mechanisms in the high and low energy (HE and LE) crush zones of a passenger train have to be increased for the higher crash speeds. The results on multiple cars (up to ten cars) show that the design of HE and LE crush zones is significantly influenced by the number of cars. The energy absorbed by the HE zone is reasonably consistent for train models with more than four cars at the crash speed of 35 km/h. The comparison of simulations can identify the contribution of the number of cars to the head-on crash forces. The influence of train mass on the design of both HE and LE crush zones, and the influence of design of the crush zones on the wheel-rail contacts are examined.

scholarly journals New evidence from exceptionally “well-preserved” specimens sheds light on the structure of the ammonite brachial crown

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
C. P. A. Smith ◽  
N. H. Landman ◽  
J. Bardin ◽  
I. Kruta
Keyword(s):  
Late Cretaceous ◽  
Large Family ◽  
Soft Body ◽  
Evolutionary Origins ◽  
Data Analyses ◽  
Tomographic Data ◽  
First Time ◽  
New Evidence ◽  
Topological Data

AbstractAmmonite soft body remains are rarely preserved. One of the biggest enigmas is the morphology of the ammonite brachial crown that has, up till now, never been recovered. Recently, mysterious hook-like structures have been reported in multiple specimens of Scaphitidae, a large family of heteromorph Late Cretaceous ammonites. A previous examination of these structures revealed that they belong to the ammonites. Their nature, however, remained elusive. Here, we exploit tomographic data to study their arrangement in space in order to clarify this matter. After using topological data analyses and comparing their morphology, number, and distribution to other known cephalopod structures, in both extant and extinct taxa, we conclude that these hook-like structures represent part of the brachial crown armature. Therefore, it appears that there are at least three independent evolutionary origins of hooks: in belemnoids, oegospids, and now in ammonites. Finally, we propose for the first time a hypothetical reconstruction of an ammonite brachial crown.

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