Swimming speed estimation of extinct marine reptiles: energetic approach revisited

Paleobiology ◽  
2002 ◽  
Vol 28 (2) ◽  
pp. 251-262 ◽  
Author(s):  
Ryosuke Motani

Cruising speeds of Mesozoic marine reptiles have been estimated in the past by using a mathematical model of energetic equilibrium during steady swimming. This method suffered from a significant tendency to overestimate speeds of extant cetaceans for no clear reason, which raised questions about the validity of the approach itself. The present study identifies the factors that caused this shortcoming and proposes corrections and some additional modifications. These include the use of more accurate body shape models, updated metabolic rate models, and optimal rather than critical swimming speeds. The amended method successfully approximates published optimal speeds of several extant marine vertebrates, including cetaceans, showing that the basic framework of the energetic approach is valid. With this confirmation, the method was applied to Mesozoic marine reptiles, by assuming three different metabolic rate categories known in extant swimming vertebrates (i.e., average ectothermic, raised ectothermic, and marine endothermic levels). The results support previous inferences about the relative cruising capabilities of Mesozoic marine reptiles (i.e., ichthyosaurs > plesiosaurs > mosasaurs). Stenopterygius, a thunniform ichthyosaur, was probably capable of cruising at a speed at least comparable to those reported for some extant thunniform teleosts with similar diets (~1 m/second).

Paleobiology ◽  
1988 ◽  
Vol 14 (2) ◽  
pp. 187-205 ◽  
Author(s):  
Judy A. Massare

Body shape and mode of swimming were major factors that affected the swimming capabilities of Mesozoic marine reptiles. By estimating the total drag and the amount of energy available through metabolism, the maximum sustained swimming speed was calculated for 115 marine reptile specimens. Calculated sustained swimming speeds range from 1.8 to 2.7 m/sec, but are probably too high by as much as a factor of two. Mesozoic marine reptiles were probably much slower than modern toothed whales. The diversification of fast, agile teleost fish in the Cretaceous may have therefore contributed to the decline of the marine reptiles.Long-bodied reptiles appear to have had slower sustained swimming speeds than deep-bodied forms of the same length. For a given length, ichthyosaurs were probably faster sustained swimmers than plesiosaurs, and plesiosaurs were probably faster sustained swimmers than crocodiles and mosasaurs. This suggests that the long-bodied forms probably used an ambush technique to capture prey, to maximize the range of possible prey and to minimize competition with the faster pursuit predators.


2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Dror Malul ◽  
Tamar Lotan ◽  
Yizhaq Makovsky ◽  
Roi Holzman ◽  
Uri Shavit

AbstractJellyfish locomotion and orientation have been studied in the past both in the laboratory, testing mostly small jellyfish, and in the field, where it was impossible to control the seawater currents. Utilizing an outdoor water flume, we tested the locomotion of jellyfish when swimming against and with currents of up to 4.5 cm s−1. We used adult jellyfish from two of the most abundant species in the eastern Mediterranean, Rhopilema nomadica and Rhizostoma pulmo, and measured their pulsation frequency and swimming speed relative to the water. While pulsation frequency was not affected by the water velocity, jellyfish swam faster against the current than with it. This finding suggests that jellyfish possess a sensory ability, whose mechanism is currently unknown, enabling them to gauge the flow and react to it, possibly in order to reduce the risk of stranding.


2012 ◽  
Vol 512-515 ◽  
pp. 1227-1230
Author(s):  
Miao Sheng Chen ◽  
Yung Tse Tsai

In the past, energy authorities attempted to prevent potential entrants from participating in the energy market. This study posits that this two-stage game theory is insufficient to describe the modern-day situation. Ware (1984) modified the Dixit (1980) model to develop a three-stage game structure. We use this mathematical model to analyze the optimal cost of an energy authority and the strategy of excess capacity.


2015 ◽  
Vol 2015 ◽  
pp. 1-5 ◽  
Author(s):  
Tianshu Jiang ◽  
Mengzhe Zhou ◽  
Bi Shen ◽  
Wendi Xuan ◽  
Sijie Wen ◽  
...  

Bank crisis is grabbing more serious attention as several financial turmoils have broken out in the past several decades, which leads to a number of researches in this field. Comparing with researches carried out on basis of degree distribution in complex networks, this paper puts forward a mathematical model constructed upon dynamic systems, for which we mainly focus on the stability of critical point. After the model is constructed to describe the evolution of the banking market system, we devoted ourselves to find out the critical point and analyze its stability. However, to refine the stability of the critical point, we add some impulsive terms in the former model. And we discover that the bank crisis can be controlled according to the analysis of equilibrium points of the modified model, which implies the interference from outside may modify the robustness of the bank network.


2005 ◽  
Vol 84 (3) ◽  
pp. 221-229 ◽  
Author(s):  
A.R. Dutchak

AbstractAigialosaurs have been recognised as a group of semi-aquatic marine reptiles for over one hundred years. While the taxonomic status of aigialosaurs has changed little in the past century, the interfamilial relationships have been modified considerably making the phylogenetic relationships between aigialosaurs, mosasaurs, dolichosaurs, coniasaurs, varanids and other squamates a topic of much debate. The monophyly of the family Aigialosauridae has been contested by recent studies and remains highly questionable. The higher-level relationships of mosasauroids within Squamata remain problematic with studies placing mosasauroids outside of Varanidae, Varanoidea and even Anguimorpha. These findings conflict with earlier views that aigialosaurs (and by association mosasaurs) were closely related to Varanus. This study concludes that further descriptions of aigialosaur taxa are needed, and several key flaws need to be addressed in the data matrices that have been used in previous studies. This should facilitate the clarification of aigialosaur systematic relationships both within Mosasauroidea and Squamata.


2011 ◽  
Vol 51 (4) ◽  
pp. 327 ◽  
Author(s):  
Werner T. Flueck ◽  
Jo M. Smith-Flueck

Early explorers described huemul (Hippocamelus bisulcus) as stocky, massive and short-legged deer of mountains, comparing them to ibex (Cabra ibex), chamois (Rupicapra rupicapra), mountain sheep (Ovis canadensis) and mountain goats (Oreamnos americanus). Subsequent key paleontological work also claimed that huemul are mountain deer. However, all these comparisons of huemul to other ungulates were done without any supporting data. These historic events lead to: (i) the continued prevailing claim that huemul are mountain deer; and (ii) that their natural range is the Andean mountains, as evidenced by the current distribution. We found that early writings about huemul generally reported their rareness, disappearance or near extinction. References to stocky and short-legged huemul were casual remarks made about deer found mainly in refuge areas. Paleontological comparisons were based on a new fossil labelled as mountain deer which, however, has been shown to be a construct and declared a ‘nomen nudum’. Behaviour like the aggressive horseshoe stance and thick long hair dissimulate stockiness by distorting body shape. Comparing leg morphometrics of huemul and 12 other ungulates revealed that huemul cannot be associated with rock climbing species. Intraspecific proportional leg length is not static and is influenced by ecogeography, nutrition, physiology and factors affecting exercise. Thus, climate, altitudinal hypoxia and locomotor pattern employed according to terrain, predation and forage affect the appendicular skeleton. Nutritional deficiencies occurring in Andean mountains are notorious for affecting bone development, causing osteopathology and altering body shape. Frequent underdeveloped huemul antlers and high incidence of osteopathology support the effect from mineral deficiencies. Skeletal proportions are affected by numerous factors, causing large intraspecific variation. Relative metapodial length varies up to 70% in better studied cervids, and populations from different environments can be clearly distinguished. Huemul morphology does not overlap with rock climbing species previously considered analogous, but falls within the range of other cervids. We caution against the rigid application of modern huemul occurrences in interpreting past habitat use. The few historic extra-Andean accounts cannot be considered abnormal outliers. Huemul ecology must be interpreted in terms of first principles rather than applying direct analogues from the present. This allows us to begin to use the past to understand the present instead of repeating the fallacy of imposing the present on the past. Current efforts to recover remaining huemul are distinctly based on the assumption that huemul foremost belong in rugged mountains, because of their supposed special adaptions and resemblance to stereotype ungulates, also erroneously believed to only occur in rugged mountains elsewhere. We conclude that the present empirical comparisons support many other lines of evidence that huemul existed in treeless habitat and colonised Andean forests and higher altitudes secondarily. Habitat breath of huemul is thus more like that found in other closely related Odocoilines, promising tremendous new opportunities for recovery efforts.


2021 ◽  
Author(s):  
SENAI Goitom SEREKE ◽  
SEMHAR Eyob BERHE ◽  
Felix Bongomin

Background: With the introduction of effective antiretroviral therapy (ART), descriptions of body shape abnormalities, such as central fat accumulation and peripheral fat loss emerged among persons living with human immunodeficiency virus (HIV). We aimed to determine the prevalence of lipodystrophy and associated risk factors among patients on ART at Orotta National Referral Hospital (ONRH), Asmara, Eritrea. Methods: A single center, retrospective study was conducted at the ONRH, reviewing records of HIV-infected patients commenced on ART between January 2007 and December 2012. Results: Records of 250 eligible patients were reviewed. Most were female (59.2%, n=148) with a median age of 35 (IQR-20-63) years. Forty-three (17.2%) participants had body fat abnormalities. 42 (97.6%) had lipoatrophy and 1 (2.4%) buffalo hump. Of the 43 patients with lipodystrophy 34 (79%) were on Stavudine (d4T)/Lamivudine (3TC)/Nevirapine (NVP) regimen, 6 (14%) on Zidovudine (AZT)/3TC/NVP, 2 (4.7%) on d4T/3TC/Efavirenz (EFV) and 1(2.3%) on AZT, 3TC, EFV. EFV- based regimen was significantly associated with lipodystrophy (p< 0.01). Conclusion: We report a high prevalence of lipodystrophy. Four drug regimens were incriminated in the development of lipodystrophy. EFV-based regimen was significantly associated with the lipodystrophy.


2018 ◽  
Author(s):  
Ronan Duchesne ◽  
Anissa Guillemin ◽  
Fabien Crauste ◽  
Olivier Gandrillon

AbstractThe in vivo erythropoiesis, which is the generation of mature red blood cells in the bone marrow of whole organisms, has been described by a variety of mathematical models in the past decades. However, the in vitro erythropoiesis, which produces red blood cells in cultures, has received much less attention from the modelling community. In this paper, we propose the first mathematical model of in vitro erythropoiesis. We start by formulating different models and select the best one at fitting experimental data of in vitro erythropoietic differentiation. It is based on a set of linear ODE, describing 3 hypothetical populations of cells at different stages of differentiation. We then compute confidence intervals for all of its parameters estimates, and conclude that our model is fully identifiable. Finally, we use this model to compute the effect of a chemical drug called Rapamycin, which affects all states of differentiation in the culture, and relate these effects to specific parameter variations. We provide the first model for the kinetics of in vitro cellular differentiation which is proven to be identifiable. It will serve as a basis for a model which will better account for the variability which is inherent to experimental protocol used for the model calibration.


2016 ◽  
Vol 4 (1) ◽  
Author(s):  
Mu-Fa Chen

AbstractThe main topic of this talk is the speed estimation of stability/instability. The word “various” comes with no surprising since there are a lot of different types of stability/instability and each of them has its own natural distance to measure. However, the adjective “unified” is very much unexpected. The talk surveys our recent progress on the topic, made in the past five years or so.


2001 ◽  
Vol 58 (6) ◽  
pp. 1104-1112 ◽  
Author(s):  
D J McKenzie ◽  
E Cataldi ◽  
P Romano ◽  
S F Owen ◽  
E W Taylor ◽  
...  

Specific growth rates, exercise respirometry, and swimming performance were compared in young-of-the-year Adriatic sturgeon (Acipenser naccarii) maintained in freshwater (FW) or acclimated to brackish water (BW) that was slightly hypertonic to sturgeon plasma, at a salinity of 11 g·L–1. Specific growth rate was significantly (17%) lower in BW than in FW. Sturgeon in BW also had a significantly (30%) higher standard metabolic rate than those in FW. In both groups, the relationship between swimming speed and oxygen uptake was described equally well by a linear or exponential equation, with a power relationship between swimming speed and net cost of locomotion and a linear relationship between tailbeat frequency and swimming speed. However, sturgeon in BW exhibited higher mean total oxygen uptake, net costs, and tailbeat frequencies than the FW group at any given swimming speed. There were, however, no differences in aerobic scope or maximum sustainable swimming speed between the FW and BW groups because the BW group exhibited a compensatory increase in active metabolic rate and maximum tailbeat frequency. The results indicate that FW is a more suitable environment than mildly hypertonic BW for young-of-the-year Adriatic sturgeon.


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