362 research outputs found
β-diversity of deep-sea holothurians and asteroids along a bathymetric gradient (NE Atlantic)
No full textMeasuring and understanding patterns of ?-diversity remain major challenges in community ecology. Recently, ?-diversity has been shown to consist of 2 distinct components: (1) spatial turnover and (2) species loss leading to nestedness. Both components structure deep-sea macrofaunal assemblages but vary in importance among taxa and ocean basins and with energy availability. Here, we present the first evidence for turnover and nestedness along a bathymetric gradient in 2 major megafaunal taxa, holothurians and asteroids. Turnover is the dominant component of ?-diversity throughout bathyal and abyssal zones in both taxa, despite major differences in ?-diversity and trophic composition. High spatial turnover suggests a role for evolutionary adaptation to environmental circumstances within depth bands. This pattern differs fundamentally from those in some macrofaunal groups in low-energy environments where abyssal nestedness is high and diversity low, with diversity maintained partly by source-sink dynamics
Tyrannosaurus rex Osborn 1905
No full textWhether Tyrannosaurus rex was likely to have found food primarily by predation or scavenging has been debated for close to a century without resolution (Erickson et al. 1996; Erickson 1999). Much of this debate has used arguments based on jaw morphology and dentition. Here, we use calculations of energy gains and losses to estimate the minimum carrion productivity an ecosystem must provide in order to support an obligate scavenger of the 6 tonne (6000 kg) mass of T. rex. Our estimates suggest that carrion productivity equivalent to the current Serengeti would have been sufficient to support such a scavenger. Hence, we argue on the basis of physiological ecology that T. rex need not have been an active predator and could have found sufficient food to support itself purely by scavenging. Our hypothesis is that the key constraint for scavengers is generally their ability to find food items. This is in contrast to predators, where capturing rather than discovering prey is the key constraint, and herbivores, where processing consumed food is often the key restriction on energy gain rate. We assume that the scavenger spends a constant fraction (a) of its time searching for food items that are distributed with a constant uniform density (f). If, when active, the scavenger searches out area at a rate V, then it finds food items at a rate a fV. We assume that it extracts an amount of energy E from each food item found. Hence, the rate of energy gathering (E in) is a f VE. We assume that the individual has a resting metabolic rate R, but that searching for food requires extra energy investment at rate S. Thus, the rate of energy expenditure (E o ut) is given by R + a S, and scavengers attempt to optimize net energy gain (E net) given by E n et = E in ‾ E o ut = a(f VE ‾ S) ‾ R. (2.1) If we demand that E net be positive then we can rearrange equation (2.1) as a restriction on the energy density of food available for scavenging: for a positive energy budget we demand that the density of food energy available to a scavenger is greater than a critical value given by a S + R f E m in =. a V (2.2) The right-hand side of this is the minimum energy density that an ecosystem needs to have to support a scavenger. We will now estimate this for a scavenging T. rex and compare this with the energy density of carrion in the extant Serengeti. We will assume that restrictions owing to nightfall, bad weather and sleep mean that on average the scavenger can actively seek food for 50% of the 24 hour day, so we set a = 0.5. The relationship between the mass M of a reptile in kilograms and the resting metabolic rate R in watts has been described by Schmidt-Nielson (1984) R = 0.38 M 0.83. (2.3) There have been various estimates of the live mass of a full-sized T. rex, ranging from 3000 to 8000 kg (Farlow et al. 1995; Christiansen 1997; Seebacher 2001). Recent papers seem to be converging towards estimates close to 6 tonnes, so we will use a value of 6000 kg throughout this paper. Substituting this into equation (2.3) gives a value for R of 520 W. The relationship between the mass M of an ectotherm (in kg), the speed of travel v (in m s ‾1) and the extra cost of travel S (in W) has been suggested by Bennett (1982) to be S = 10.3 vM 0.64. (2.4) Reptiles can sustain a speed equivalent to 10% of their maximum speed (Bennett & Ruben 1979). The maximum speed of equivalent-sized mammals and reptiles is similar (Bennett & Ruben 1979). The following relationship between mass M (in kg) and maximum speed v m ax (in m s ‾1) has been proposed by Alexander (1977): v m ax = 8.5 M ‾ 0.08. (2.5) Substituting M = 6000 in equation (2.5) gives a maximum speed for a T. rex of 4.2 m s ‾ 1. This compares well with a recent estimate of 5 m s ‾1 based on T. rex ’s limb mor- * Author for correspondence ([email protected]). phology (Hutchinson & Garcia 2002). We will assume that sustained travelling speed, v, is 10% of our estimate, i.e. 0.42 m s ‾ 1. If we substitute for v and M in equation (2.4), then this gives an added cost of travel S of 1100 W. The rate at which an area is swept, V, is simply the sustained travel speed v multiplied by twice the distance at which food can be detected, which we will denote d. That is V = 0.84 d. (2.6) Substituting the parameter values derived in equation (2.6) into equation (2.2) gives an equation for the minimum energy density of carrion (in J m ‾2) that could sustain an animal (fE m in) in terms of the distance at which it could detect carrion (d) as follows: 2550 f E m in =. d (2.7) This relationship is plotted for a range of d values from 10 m to 10 km in figure 1. To give us something to compare this against, we can estimate the energy density of carrion available each day from ungulate herbivores in the modern Serengeti ecosystem. It has been estimated that a total weight of 4´ 107 kg of ungulates die in the Serengeti each year (Houston 1979). Assuming that these have an mass-specific energy content of 7´ 106 J kg ‾1 (Peters 1983), and that the Serengeti stretches over 25 000 km 2 (Sinclair & Norton-Griffiths 1979). This gives a mean energy density of 31 J m ‾ 2 d ‾1. When we compare this value with figure 1, we see that even if we make the conservative assumption that animals that die only remain available to T. rex for 24 hours (before spoiling or being consumed by other scavengers), then, if it is able to monopolize all the food it finds and can detect food at a range of 80 m, an ecosystem of similar productivity to the current Serengeti would provide sufficient food for such a scavenger. One reason for caution in the interpretation of our results is that the allometric relations used are based on data from extant reptiles, and consequently very few of the species used to generate the relations would have a mass approaching even 1% of our estimated mass for T. rex. Of our estimates, the sustainable travel speed of 0.42 m s ‾ 1 seems rather low for a bipedal animal with 2.5 m legs (see Fitzgerald (2002) and references therein). If we repeat our calculations assuming a sustainable running speed of 2.1 m s ‾ 1, then this changes equation (2.7) to 1600 f E m in =. d (2.8) The faster running speed increases the area that can be swept for food faster than it increases the total energetic requirements of that animal, and so this leads to a reduction in the food density required to sustain the scavenger. Thus, our initial assumption of a low running speed can be seen as conservative, making a scavenging lifestyle challenging to maintain. Some scientists consider that mammals (rather than reptiles) are a more appropriate model for dinosaurs (e.g. Bakker 2001). It is possible to repeat our calculations under such an assumption. Schmidt-Nielson (1984) suggests that this would change our equation for R to R = 0.38 M 0.83, (2.9) increasing R substantially to 2300 W for our 6000 kg animal. Calder (1996) suggests that, for a mammal, the equation for S becomes S = 10.7 vM 0.68. (2.10) Bennett & Ruben (1979) suggest that the sustainable speed of mammals is 50% of their maximum speed, hence we will assume that v is 2.1 m s ‾1. If we finally assume that a is unchanged at 0.5, then (using mammals rather than reptiles as a model) changes equation (2.7) to 3100 f E m in =. d (2.11) Hence, we see that substantial compensation for higher resting and movement costs in a mammal-like T. rex may come from a mammalian physiology allowing a higher sustainable rate of movement. The consequence of this is that the minimum food density required by our scavenger is only slightly increased if a mammalian model rather than a reptilian model is assumed. 3. CONCLUSIONS Our calculation suggests that T. rex would be able to gather enough food to survive as a pure scavenger if a number of conditions are met. One is that the ecosystem yields the same density of carrion as the current Serengeti. Estimates of primary productivity at the place and time appropriate to T. rex vary widely but encompass values similar to that of the present-day Serengeti (Beerling & Woodward 2001). Any given primary productivity would have supported a greater biomass of ectothermic dinosaurs compared to the endothermic mammals that dominate the extant Serengeti (Farlow 1990). This higher biomass will more than compensate for the lower turnover rate per unit biomass that one would predict if dinosaurian herbivores had longer lifespans than the mammalian herbivores of the extant Serengeti, on account both of their larger size and probably lower specific metabolic rates. Another condition is that T. rex can detect carcasses at a distance of 80 m. Given the performance of polar bears in detecting seals over distances of kilometres (Stirling 1977) and the ability of turkey vultures to find 80% of experimentally provided chicken carcasses in tropical rainforest within 12 hours of presentation (Houston 1986), this seems likely to have been comfortably within T. rex ’s compass. Brochu (2000) argues, on the basis of computed tomographic analysis of a fossil skull, that T. rex had greatly enlarged olfactory bulbs, suggestive of high olfactory acuity. Farlow (1994) suggests that the upright stance of T. rex could have aided carrion location, both by visual and olfactory pathways. We also assumed that the fallen carcass was only detectable to T. rex for a period of 24 hours. Little is known about how long a carcass is accessible to vertebrate scavenges. Small (chicken) carcasses in tropical African forests were totally consumed by maggots within 3 days (Houston 1987). Hence, our assumption that prey is only available for 1 day seems entirely reasonable, and if anything on the low side. Our final assumption that our focal T. rex individual is able to find all the carcasses that fall in areas where it searches seems less plausible. It is likely that our T. rex would experience competition from other species and from other members of its own species. However, if we arbitrarily assume that our focal individual is only able to access 25% of the carcasses that fall, so that the ecosystem has effectively only 25% of the carrion density of the Serengeti (7.75 J m ‾2), then (from figure 1) we see that T. rex would have to be able to detect prey at a distance of 330 m to balance its energy budget. This is more challenging, but still seems within the bounds of the possible, especially if, like many extant reptiles (Zug et al. 2001), T. rex had an effective sense of smell. Hence, our conclusion is that an energy budget analysis suggests that a reptile as large as T. rex could have survived using a purely scavenging lifestyle, providing that competition for carrion was low. This conclusion leads to the obvious question, why is there not a T. rex- like scavenger on the Serengeti today? Or generally, we must ask why vultures are the only extant vertebrates that have a predominantly scavenging lifestyle. The answer may be that an avian scavenger can outcompete a terrestrial one because, as mentioned in § 1, the key requirement for a scavenger is to minimize energy expenditure while searching. Compared to terrestrial locomotion, even powered flying is faster and much less energetically expensive per distance covered (Schmidt- Nielson 1984), and birds like vultures that make extensive use of soaring have dramatically lower energy expenditure than any terrestrial scavenger could have. If T. rex was a scavenger, then this was probably only possible because avian radiation had yet to have a substantial effect on ecosystems. It may well be, as suggested by Farlow (1994), that T. rex was an opportunist flesh eater, combining scavenging carrion with active predation. That said, our calculations suggest that total (or near total) dependence on carrion (in the manner of extant vultures) may at least have been feasible. a S + R f E m in =. a V (2.2) The right-hand side of this is the minimum energy density that an ecosystem needs to have to support a scavenger. We will now estimate this for a scavenging T. rex and compare this with the energy density of carrion in the extant Serengeti. We will assume that restrictions owing to nightfall, bad weather and sleep mean that on average the scavenger can actively seek food for 50% of the 24 hour day, so we set a = 0.5. The relationship between the mass M of a reptile in kilograms and the resting metabolic rate R in watts has been described by Schmidt-Nielson (1984) R = 0.38 M 0.83. (2.3) There have been various estimates of the live mass of a full-sized T. rex, ranging from 3000 to 8000 kg (Farlow et al. 1995; Christiansen 1997; Seebacher 2001). Recent papers seem to be converging towards estimates close to 6 tonnes, so we will use a value of 6000 kg throughout this paper. Substituting this into equation (2.3) gives a value for R of 520 W. The relationship between the mass M of an ectotherm (in kg), the speed of travel v (in m s ‾1) and the extra cost of travel S (in W) has been suggested by Bennett (1982) to be S = 10.3 vM 0.64. (2.4) Reptiles can sustain a speed equivalent to 10% of their maximum speed (Bennett & Ruben 1979). The maximum speed of equivalent-sized mammals and reptiles is similar (Bennett & Ruben 1979). The following relationship between mass M (in kg) and maximum speed v m ax (in m s ‾1) has been proposed by Alexander (1977): v m ax = 8.5 M ‾ 0.08. (2.5) Substituting M = 6000 in equation (2.5) gives a maximum speed for a T. rex of 4.2 m s ‾ 1. This compares well with a recent estimate of 5 m s ‾1 based on T. rex ’s limb mor- * Author for correspondence ([email protected]). phology (Hutchinson & Garcia 2002). We will assume that sustained travelling speed, v, is 10% of our estimate, i.e. 0.42 m s ‾ 1. If we substitute for v and M in equation (2.4), then this gives an added cost of travel S of 1100 W. The rate at which an area is swept, V, is simply the sustained travel speed v multiplied by twice the distance at which food can be detected, which we will denote d. That is V = 0.84 d. (2.6) Substituting the parameter values derived in equation (2.6) into equation (2.2) gives an equation for the minimum energy density of carrion (in J m ‾2) that could sustain an animal (fE m in) in terms of the distance at which it could detect carrion (d) as follows: 2550 f E m in =. d (2.7) This relationship is plotted for a range of d values from 10 m to 10 km in figure 1. To give us something to compare this against, we can estimate the energy density of carrion available each day from ungulate herbivores in the modern Serengeti ecosystem. It has been estimated that a total weight of 4´ 107 kg of ungulates die in the Serengeti each year (Houston 1979). Assuming that these have an mass-specific energy content of 7´ 106 J kg ‾1 (Peters 1983), and that the Serengeti stretches over 25 000 km 2 (Sinclair & Norton-Griffiths 1979). This gives a mean energy density of 31 J m ‾ 2 d ‾1. When we compare this value with figure 1, we see that even if we make the conservative assumption that animals that die only remain available to T. rex for 24 hours (before spoiling or being consumed by other scavengers), then, if it is able to monopolize all the food it finds and can detect food at a range of 80 m, an ecosystem of similar productivity to the current Serengeti would provide sufficient food for such a scavenger. One reason for caution in the interpretation of our results is that the allometric relations used are based on data from extant reptiles, and consequently very few of the species used to generate the relations would have a mass approaching even 1% of our estimated mass for T. rex. Of our estimates, the sustainable travel speed of 0.42 m s ‾ 1 seems rather low for a bipedal animal with 2.5 m legs (see Fitzgerald (2002) and references therein). If we repeat our calculations assuming a sustainable running speed of 2.1 m s ‾ 1, then this changes equation (2.7) to 1600 f E m in =. d (2.8) The faster running speed increases the area that can be swept for food faster than it increases the total energetic requirements of that animal, and so this leads to a reduction in the food density required to sustain the scavenger. Thus, our initial assumption of a low running speed can be seen as conservative, making a scavenging lifestyle challenging to maintain. Some scientists consider that mammals (rather than reptiles) are a more appropriate model for dinosaurs (e.g. Bakker 2001). It is possible to repeat our calculations under such an assumption. Schmidt-Nielson (1984) suggests that this would change our equation for R to R = 0.38 M 0.83, (2.9) increasing R substantially to 2300 W for our 6000 kg animal. Calder (1996) suggests that, for a mammal, the equation for S becomes S = 10.7 vM 0.68. (2.10) Bennett & Ruben (1979) suggest that the sustainable speed of mammals is 50% of their maximum speed, hence we will assume that v is 2.1 m s ‾1. If we finally assume that a is unchanged at 0.5, then (using mammals rather than reptiles as a model) changes equation (2.7) to 3100 f E m in =. d (2.11) Hence, we see that substantial compensation for higher resting and movement costs in a mammal-like T. rex may come from a mammalian physiology allowing a higher sustainable rate of movement. The consequence of this is that the minimum food density required by our scavenger is only slightly increased if a mammalian model rather than a reptilian model is assumed. 3. CONCLUSIONS Our calculation suggests that T. rex would be able to gather enough food to survive as a pure scavenger if a number of conditions are met. One is that the ecosystem yields the same density of carrion as the current Serengeti. Estimates of primary productivity at the place and time appropriate to T. rex vary widely but encompass values similar to that of the present-day Serengeti (Beerling & Woodward 2001). Any given primary productivity would have supported a greater biomass of ectothermic dinosaurs compared to the endothermic mammals that dominate the extant Serengeti (Farlow 1990). This higher biomass will more than compensate for the lower turnover rate per unit biomass that one would predict if dinosaurian herbivores had longer lifespans than the mammalian herbivores of the extant Serengeti, on account both of their larger size and probably lower specific metabolic rates. Another condition is that T. rex can detect carcasses at a distance of 80 m. Given the performance of polar bears in detecting seals over distances of kilometres (Stirling 1977) and the ability of turkey vultures to find 80% of experimentally provided chicken carcasses in tropical rainforest within 12 hours of presentation (Houston 1986), this seems likely to have been comfortably within T. rex ’s compass. Brochu (2000) argues, on the basis of computed tomographic analysis of a fossil skull, that T. rex had greatly enlarged olfactory bulbs, suggestive of high olfactory acuity. Farlow (1994) suggests that the upright stance of T. rex could have aided carrion location, both by visual and olfactory pathways. We also assumed that the fallen carcass was only detectable to T. rex for a period of 24 hours. Little is known about how long a carcass is accessible to vertebrate scavenges. Small (chicken) carcasses in tropical African forests were totally consumed by maggots within 3 days (Houston 1987). Hence, our assumption that prey is only available for 1 day seems entirely reasonable, and if anything on the low side. Our final assumption that our focal T. rex individual is able to find all the carcasses that fall in areas where it searches seems less plausible. It is likely that our T. rex would experience competition from other species and from other members of its own species. However, if we arbitrarily assume that our focal individual is only able to access 25% of the carcasses that fall, so that the ecosystem has effectively only 25% of the carrion density of the Serengeti (7.75 J m ‾2), then (from figure 1) we see that T. rex would have to be able to detect prey at a distance of 330 m to balance its energy budget. This is more challenging, but still seems within the bounds of the possible, especially if, like many extant reptiles (Zug et al. 2001), T. rex had an effective sense of smell. Hence, our conclusion is that an energy budget analysis suggests that a reptile as large as T. rex could have survived using a purely scavenging lifestyle, providing that competition for carrion was low. This conclusion leads to the obvious question, why is there not a T. rex- like scavenger on the Serengeti today? Or generally, we must ask why vultures are the only extant vertebrates that have a predominantly scavenging lifestyle. The answer may be that an avian scavenger can outcompete a terrestrial one because, as mentioned in § 1, the key requirement for a scavenger is to minimize energy expenditure while searching. Compared to terrestrial locomotion, even powered flying is faster and much less energetically expensive per distance covered (Schmidt- Nielson 1984), and birds like vultures that make extensive use of soaring have dramatically lower energy expenditure than any terrestrial scavenger could have. If T. rex was a scavenger, then this was probably only possible because avian radiation had yet to have a substantial effect on ecosystems. It may well be, as suggested by Farlow (1994), that T. rex was an opportunist flesh eater, combining scavenging carrion with active predation. That said, our calculations suggest that total (or near total) dependence on carrion (in the manner of extant vultures) may at least have been feasible.Published as part of Ruxton, Graeme D. & Hou
The Oedipus Casebook Reading Sophocles' Oedipus the King
No full textIntro -- Contents -- Preface, by Mark R. Anspach -- Acknowledgments -- Sophocles, Oedipus Tyrannus, Greek text edited and annotated by H. Lloyd-Jones and N. G. Wilson, translated into English by Wm. Blake Tyrrell -- Part One. The Ritual Background -- Greek Tragedy and Sacrificial Ritual, by Walter Burkert -- Scapegoat Rituals in Ancient Greece, by Jan Bremmer -- The Exposed Infant, by Marie Delcourt -- Part Two. King and Victim -- Imitating Oedipus, by Mark R. Anspach -- Oedipus and the Surrogate Victim, by René Girard -- Excerpt from Sweet Violence, by Terry Eagleton -- Ambiguity and Reversal: On the Enigmatic Structure of Oedipus Rex, by Jean-Pierre Vernant -- Oedipus as Pharmakos, by Helene Peet Foley -- Part Three. Oedipus on Trial -- Excerpt from Wrong-Doing, Truth-Telling, by Michel Foucault -- The Murderers of Laius, by William Chase Greene -- The Murderers of Laius, Again (Soph. OT 106-7), by Rick M. Newton -- Who Killed Laius? by Karl Harshbarger -- Lêistas Ephaske: Oedipus and Laius' Many Murderers, by Sandor Goodhart -- An Anonymous Namer: The Corinthian's Testimony, by Frederick Ahl -- IndexDescription based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
Tyrannosaurus rex
No full text<p> Stemming from more than a century of investigation, considerable understanding of tyrannosaurid osteology 4, myology 5, neurology 6, behaviour 7, 8, physiology 3, 9, physical capabilities 10, 11 and phylogeny 12, 13 have been gained. Lacking are empirical data on tyrannosaurid life history such as growth rates, longevity and somatic maturity (adult size) from which the developmental possibilities for how <i>T. rex</i> attained gigantism can be formally tested.</p> <p> Recent advances in techniques for determining the ages at death of dinosaurs by using skeletal growth line counts 3, 14, coupled with developmental size estimates 3, make quantitative growth-curve reconstructions for dinosaurs feasible. These methods have been used to study growth rates in two small theropods, a small and a large ornithischian and a medium-sized and a gigantic sauropodomorph 3. These data were used to derive a regression of body mass against growth rate and to generalize broadly about non-avian dinosaur growth 3. However, because of the phylogenetically disparate nature of these data (that is, none are close outgroups to one another) it has not been possible to use them to infer how specific cases of size change occurred within dinosaurian sub-clades such as the Tyrannosauridae. Such an understanding requires multi-species sampling at low taxonomic levels (that is, among closely related species) and access to growth series spanning juvenile through adult stages, a rarity among extinct dinosaurs 15. Furthermore, it requires the capacity to account for growth line losses due to medullar cavity hollowing and cortical remodelling 16, two processes that are pervasive in the major weight-bearing bones from large theropods such as tyrannosaurids.</p> <p> The sampling problem has been overcome in North American tyrannosaurids. A flurry of recent discoveries has greatly increased the number of substantially complete specimens representing various growth stages available for study. For example, more than 30 <i>T. rex</i> specimens are known 4, 17, compared with only 11 reported in 1993 (ref. 18; see Supplementary Information). Recent work has broadened the developmental representation of these animals by showing that several purported ‘dwarf’ tyrannosaur species are juveniles of larger, previously recognized forms such as <i>T. rex</i> 12, 13, 19, 20. Finally, preliminary analyses for this research revealed that several non-weight-bearing bones in tyrannosaurids (for example pubes, fibulae, ribs, gastralia and postorbitals) did not develop hollow medullar cavities and showed negligible intracortical remodelling during their entire life history (Fig. 1). Like major long bones, these elements are effective for assessing longevity in living reptiles (Fig. 1) 21, 22 and hence provide a viable alternative method for determining the age at death of extinct reptiles such as tyrannosaurids.</p> <p> Here we exploit these findings to determine the pattern of growth in <i>T. rex</i> and three of its close tyrannosaurid relatives. We then use character optimization methods 23 to infer how <i>T. rex</i> attained giant proportions among tyrannosaurids. Finally, this new evidence is used to further our understanding of tyrannosaurid biology. In performing these analyses, we sampled several amedullar bones from adolescent, juvenile, sub-adult and adult representatives of the North American Late Cretaceous tyrannosaurids <i>Albertosaurus sarcophagus</i>, <i>Gorgosaurus libratus</i>, <i>Daspletosaurus torosus</i> and <i>T. rex</i>. Longevity in each of the 20 specimens was assessed from line counts in histological sections by using polarizing, dissecting and reflected-light microscopy (Fig. 1) 3, 14. Conservative estimates of body mass (see Supplementary Information) were made by using femoral circumference measures 24. Longevity and size data were plotted and least-squares regression was used to determine the first empirical growth curves for tyrannosaurids 3. The length and timing of the various developmental stages and the maximal growth rates for each taxon were compared 25. The results were examined in an evolutionary context 23 by using two competing phylogenetic hypotheses for the Tyrannosauridae 12, 13.</p> <p> Sampled longevities for <i>T. rex</i> ranged from 2 to 28 years and corresponding body mass estimates ranged from 29.9 to 5,654 kg (Table 1). The transition to somatic maturity in this taxon seems to have begun at about 18.5 years of age (Fig. 2). At least one individual (exemplified by FMNH (The Field Museum) PR 2081), showed evidence for prolonged senescence in the form of conspicuously narrow pericortical growth-line spacing (Fig. 1). Maximal growth rates in <i>T. rex</i> were 2.07 kg d <b>‾</b> 1 and such exponential rates were maintained for about 4 years (Fig. 2). The longevity estimates for <i>T. rex</i> outgroups ranged from 2 to 24 years and corresponding body sizes spanned from 50.3 to 1,791 kg (Table 1). Somatic maturity occurred at between 14 and 16 years in these taxa (Fig. 2). Like <i>T. rex</i>, at least some exceptionally large individuals of <i>A. sarcophagus</i> and <i>D. torosus</i> showed narrow pericortical growth-line spacing indicative of the onset of senescence. The maximal growth rates for the three smaller tyrannosaurid taxa ranged from 0.31 to 0.48 kg d <b>‾</b> 1 ; such exponential stage rates were also maintained for about 4 years (Fig. 2). Optimization of growth rates onto the two current phylogenetic hypotheses of tyrannosaurid relationships suggests that a 1.5-fold acceleration in maximal growth rate might diagnose Tyrannosaurinae (the clade comprising <i>Daspletosaurus and Tyrannosaurus</i> 13, 19, Fig. 2). A second substantial increase in growth rate optimizes as a physiological autapomorphy of <i>Tyrannosaurus</i> irrespective of phylogenetic hypothesis and optimization criterion.</p> <p> <i>T. rex</i> is notable for its great size, which is at least 15-fold greater than the largest living terrestrial carnivorous animals today and second only to <i>Giganotosaurus</i> 26 among theropod dinosaurs. How did it attain such great proportions within the Tyrannosauridae? From the two competing hypotheses of tyrannosaurid phylogeny it is most parsimonious to conclude that <i>T. rex</i> acquired the majority of its giant proportions after diverging from the common ancestor of itself and <i>D. torosus</i>, a species with an optimized body mass of about 1,800 kg. Direct comparison between the tyrannosaurid growth curves shows that the transition to the exponential and stationary phases of development occurred about 2–4 years later in <i>T. rex</i> (Fig. 2). However, such temporal post-displacement had little to do with the evolution of its gigantism because the exponential stage, during which most body size is accrued 25, was not extended beyond the ancestral, 4-year condition observed in other tyrannosaurids. Rather, the key developmental modification that propelled <i>T. rex</i> to giant proportions was primarily through evolutionary acceleration in the exponential stage growth rate and the transition zones bounding it. This is reflected in the regions of maximal slope on the growth curves depicted in Fig. 2 and holds true regardless of which evolutionary hypothesis is correct and how the maximum growth rates are optimized. Notably, this method of attaining gigantism contrasts with that in the largest crocodilians and lizards, where ancestral growth rates were retained and the exponential stages lengthened 27. How other dinosaurs attained gigantism within their respective sub-clades will serve as an interesting line of inquiry in the future. Does the same pattern of acceleratory growth seen here characterize the means by which all or most members of the Dinosauria attained great size?</p> <p>...................................................................................................................................................................................................................................................................................................................................................................</p> <p>FMNH, The Field Museum; RTMP, Royal Tyrrell Museum of Palaeontology; ICM, Indianapolis Children’s Museum; LACM, Los Angeles County Museum; AMNH, American Museum of Natural History; USNM, United States National Museum. R, rib; G, gastralia; F, fibula; P, pubis; C, dermal skull bones; OLB, other long bones; est., estimated; EFS, external fundamental system 16.</p> <p> Besides revealing how the evolution of <i>T. rex</i> gigantism was obtained, the data garnered here provide for a more comprehensive understanding of tyrannosaurid biology. For instance the presence of thin, tightly packed growth lines late in development (Fig. 1) shows that these animals, like nearly all (if not all) dinosaurs, had determinate growth 3, 14. They would not have gained an appreciably greater size than the largest specimens studied here and could spend nearly 30% of their lives as full-grown adults (Fig. 2). In addition, the maximal growth rates for these tyrannosaurid species are only 33–52% of the rates expected for non-avian dinosaurs of their size when compared with the more broadly sampled data of Erickson <i>et al.</i> 3. This provides the first evidence of its kind pointing to major differences in whole body growth rates among a non-avian dinosaur sub-clade. Such findings are not unexpected because similar patterns (for example primates within Eutheria) occur within living vertebrate groups 28. Our findings also have a bearing on the biomechanical capacities of tyrannosaurids. <i>T. rex</i> ’s capacity for ‘fast running’ was biomechanially infeasible after a body mass of about 1,000 kg was attained 11. This corresponds to a juvenile-sized animal just 13 years of age on the basis of our longevity data and conservative estimates of body mass (Fig. 2). If we assume that the same relationship held true for the smaller tyrannosaurid species studied here, such locomotory limitations would not have emerged until these animals were much closer to adult size (Fig. 2). Finally, a glimpse into the potential population age structure for a dinosaur is also afforded from these data. Currie 7 has described a catastrophic death assemblage consisting of eight or nine <i>A. sarcophagus</i> specimens thought to represent an entire pack or a subset of one. On the basis of femoral lengths, the age and developmental stage of each animal can now be estimated. The group seems to have consisted of two or three older adults ~21 or more years of age, one ~17-year-old young adult, four ~12–17- year-old sub-adults that were undergoing exponential stage growth at the time of death, and one ~10-year-old juvenile that was beginning the transition to exponential stage growth. A reopening of the site has revealed at least one more specimen (RTMP (Royal Tyrrell Museum of Palaeontology) 2002.45.46) shown here to be only 2 years old (Table 1). This indicates that <i>A. sarcophagus</i> groups, whether temporary or permanent, might have been composed of individuals spanning the age spectrum from adolescents to very old, senescent adults, a finding consistent with trackway evidence for other theropod dinosaurs 7.</p>Published as part of <i>Gregory M. Erickson, Peter J. Makovicky, Philip J. Currie, Mark A. Norell, Scott A. Yerby & Christopher A. Brochu, 2004, Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs, pp. 772-775 in Nature 430</i> on pages 772-774, DOI: 10.1038/nature02699, <a href="http://zenodo.org/record/3736475">http://zenodo.org/record/3736475</a>
The Effect of Own-Gender Juries on Conviction Rates
No full textLaborThe right to an impartial jury is the cornerstone of the U.S. justice system and is enshrined in the Bill of Rights, but are these juries truly impartial, or do they favor defendants who are similar to themselves? In PERC working paper 1803, PERC��������s Rex Grey Professor Mark Hoekstra and co-author Brittany Street study whether gender matches between jurors and defendants affect criminal conviction rates
MUTATION INDUCTION BY AND MUTATIONAL INTERACTION BETWEEN MONOCHROMATIC WAVELENGTH RADIATIONS IN THE NEAR‐ULTRAVIOLET AND VISIBLE RANGES
No full textBiological Interactions between Wavelengths in the Solar-UV Range: Implications for the Predictive Value of Action Spectra Measurements
No full textModulation of gene expression by the oxidative stress generated in human skin cells by UVA radiation and the restoration of redox homeostasis
No full text
- …
