226 research outputs found
The Organization, Operation, and Benefits of A Regional Industrial Council: A Model in Western Kentucky
No full textDr. Galloway is Chairman and Professor, Department of Management, College of Business and Public Affairs, Murray State University
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 Hymn Rex sanctorum angelorum in Notated Missal ms. 387 and its Partial Meaning in the Search of the Provenance of the Manuscript
No full textHymn Rex sanctorum angelorum w missale notatum sygn. rkp. 387 i jego znaczenie w poszukiwaniu proweniencji rękopisu
Hymn Rex sanctorum angelorum jest śpiewem Wigilii Paschalnej przeznaczonym na błogosławieństwo wody przed chrztem katechumenów. Obecność tego śpiewu w średniowiecznych rękopisach nie jest powszechna. W Missale notatum zanotowano go również na wigilię uroczystości Zesłania Ducha Świętego. Jego wersja różni się jednak od większości przebadanych manuskryptów. W porównaniu z nimi rkp. 387 zachowuje w większym stopniu tradycję niemiecką. Biorąc pod uwagę niektóre zawarte w nim obrzędy, np. związane z chrztem dziecka, wielce prawdopodobne jest duńskie pochodzenie tego rękopisu.Amongst the 18 notated manuscripts (today located in Slovak depositories as part of our precious cultural heritage), we can find Notated Missal ms. 387 from the former Evangelical College Library in Bratislava. It is preserved in the Central Library of the Slovak Academy of Sciences in Bratislava. Currently it is the subject of deeper research. Its most disputable aspect is its provenance. According to many scholars, it dates back to the 13th century, because it does not include the Feast of Corpus Christi. On the basis of a later note in the calendar (f. 5) we may also assume that the manuscript was written (or, at least, utilised) in the city of Lund, Sweden. For confirmation or refutation of such a hypothesis, the author will take into account the considerations regarding the hymn Rex sanctorum angelorum, that may represent one of the clues in order to get closer to the truth
Cold war theology: a controversial religious image of King James VI & I in England and on the Continent in 1603
No full textA former student of James Cameron’s, Ian Hazlett contributes a paper very much in the spirit of his teacher. It considers the afterlife of the King’s (or Negative) Confession, commissioned by James VI of Scotland in 1581 as a clear statement of his Calvinist credentials. By the time he gained the crown of England in 1603 however, his evolving religious views meant it had become a document he sought to distance himself from. Both Protestant and Catholic propagandists and publishers, keen to give a particular picture of the theological sympathies of the new English king, subsequently produced a surprisingly varied selection of versions of the Confession. These sources and what they can tell us about the theology and politics of the day are considered here for the first time in a scholarly study.Publisher PD
Semiometrics: producing a compositional view of influence
No full textHigh-impact academic papers are not necessarily the most cited. For example, Einstein's 'Special Relativity' paper from 1905 received (and continues to receive) fewer citations from other papers than his 'Brownian Motion" paper of the same year, despite the former radically changing the course of an entire scientific discipline to a much greater extent. Similarly, 'impact' metrics using citation count alone are, it is argued, not adequate for determining the scientific influence of papers, authors or small groups of authors. Although valid, they remain controversial when used to determine influence of larger groups or journals. While the term 'impact' has become closely linked to a journal's citation-based Journal Impact Factor score, this thesis uses the term 'influence' to describe the wider effectiveness of research, combining citation and metadata analysis to allow richer calculations to be performed over large-scale document networks. As a result, more qualitative influence ratings can be determined and a broader outlook on scientific disciplines can be produced. These ratings are best applied using an ontology-based data source, allowing more efficient inference than under a traditional RDBMS system, and allowing easier integration between heterogeneous data sources. These metrics, termed 'Semantic Bibliometrics' or 'Semiometrics', can be applied at a variety of levels of granularity, allowing a compositional framework for impact and influence analysis. This thesis describes the process of data preparation, systems architecture, metric value and data integration for such a system, introducing novel approaches at all four stages, thereby creating a working semiometrics system for determining influence at different semantic levels of granularity
Tyrannosaurus rex Osborn 1905
No full textAfter the publication of its discovery from the famous Hell Creek Formation (HCF) in 1905, the carnivorous dinosaur Tyrannosaurus rex (1) was met with intense scientific interest and public popularity, which persists to the present day (2). Numerous hypotheses concerning T. rex biology and behavior result from decades of research primarily focused on skeletal morphology and biomechanics [e.g., (3) and references therein]. Only within the past 15 years has bone histology been applied to investigate the aspects of T. rex life history inaccessible from gross examinations, addressing questions concerning ontogenetic age, growth rate, skeletal maturity, and sexual maturity. In 2004, two teams independently assessed the growth dynamics of T. rex using osteohistology. Their results suggest that T. rex had an accelerated growth rate compared with other tyrannosaurids and achieved adult size in approximately two decades (4, 5). The teams focused on growth curves, rather than on detailed analyses or interpretations of bone tissue microstructures. However, osteohistology is critical for establishing a baseline against which skeletal maturity and growth changes in cortical morphology related to life events in this taxon can be tested. Identifying the timing of growth acceleration and empirically quantifying juvenile T. rex growth rates are of special importance because the juvenile growth record is lost in older individuals because of bone remodeling and resorption (4, 5). Here, we examine the femur and tibia bone microstructure of two tyrannosaur skeletons of controversial taxonomic status recovered from the HCF: BMRP (Burpee Museum of Natural History) 2002.4.1, a largely complete specimen composed of nearly the entire skull and substantial postcranial material, and BMRP 2006.4.4, a more fragmentary specimen. Respectively, we estimate these specimens to be 54 and 59% the body length of FMNH (Field Museum of Natural History) PR 2081 (“Sue”) (6, 7), one of the largest known T. rex. The ontogenetic age of BMRP 2002.4.1 was previously reported by Erickson (8) as 11 years based on fibula osteohistology. However, because the fibula grows more slowly than the weight-bearing femur and tibia, it does not reflect annual increases in body size or relative skeletal maturity as accurately [e.g., (9)]. We use femur and tibia data to (i) provide detailed comparative intra- and interskeletal histological descriptions, (ii) quantify the ontogenetic age and relative skeletal maturity of these specimens, and (iii) allow empirical observation of annual growth rate, with emphasis on variability during the life history of tyrannosaurs (10). Moreover, by histologically quantifying the ontogenetic age of BMRP 2002.4.1 and BMRP 2006.4.4 and inferring skeletal maturity, we present new data that can be used to evaluate competing taxonomic hypotheses regarding these and other mid-sized tyrannosaur specimens discovered in the HCF, specifically whether BMRP 2002.4.1 (and by proxy other specimens) represents an adult “pygmy” genus of tyrannosaurid, “ Nanotyrannus.” RESULTS For detailed, orientation-specific histology descriptions, refer to the Supplementary Materials. In general, the femur and tibia cortical bones of BMRP 2002.4.1 and BMRP 2006.4.4 can be classified as a wovenparallel complex. Vascularity and osteocyte lacuna density are uniformly high throughout (Figs. 1 and 2). In the femora, the primary and secondary osteons surrounding vascular canals are frequently isotropic in the transverse section (Fig. 1, A and B) and anisotropic in the longitudinal section (Fig. 1C). Also in the transverse section, femur primary tissue exhibits moderate anisotropy regionally and weak anisotropy locally, corresponding to a loose arrangement of mineralized fibers in parallel (e.g., Fig. 1, A and B, and fig. S3B). 1 Department of Anatomy and Cell Biology, Oklahoma State University Center for Health Sciences, 1111 W.17th St., Tulsa, OK 74104, USA. 2 Department of Earth Science, Montana State University, P.O. Box 173480, Bozeman, MT 59717, USA. 3 Museum of the Rockies, Montana State University, 600 W.Kagy Blvd., Bozeman, MT 59717, USA. 4 Paleontology, North Carolina Museum of Natural Sciences, 11 W. Jones St., Raleigh, NC 27601, USA. 5 Department of Biological Sciences, North Carolina State University, 3510 Thomas Hall, Campus Box 7614, Raleigh, NC 2769, USA. 6 Chapman University, 1 University Dr., Orange, CA 92866, USA. 7 Intellectual Ventures, 3150 139th Avenue Southeast, Bellevue, WA 98005, USA. *Corresponding author. Email: [email protected], holly.n.woodward@ gmail.com In the tibia transverse section of BMRP 2002.4.1 (Fig. 2A and fig. S4), longitudinal primary osteons are isotropic in circularly polarized light (CPL), but fibers of primary osteons encircling laminar, circular, and plexiform vascular canals are anisotropic. In contrast, primary osteons in the tibia of BMRP 2006.4.4 are frequently isotropic regardless of vascular canal orientation. Because of its proximal sampling location, the cortical shape of the tibia from BMRP 2006.4.4 in transverse section differs from that of BMRP 2002.4.1 and incorporates the fibular crest on the lateral side (figs. S2D and S8, A and F). Highly vascularized reticular woven tissue is present on the anterior and anterolateral periosteal surfaces (Fig. 2C). In both individuals, the thickest tibial cortex is located anteriorly. Of special note, within the medullary cavity of the femur and tibia of BMRP 2006.4.4, isotropic, vascularized, primary tissue is separated from the cortex by a lamellar endosteal layer. These features are morphologically consistent with medullary bone (11); however, additional studies on the systemic nature of this tissue throughout BMRP 2006.4.4 and biochemical tests on this tissue are necessary to test this hypothesis. Cyclical growth marks (CGMs), resembling tree rings in transverse thin section, were observed in the femora and tibiae of both BMRP specimens. Studies on extant vertebrates demonstrate that CGMs result from brief interruptions in osteogenesis, occurring with annual periodicity and typically coinciding with the nadir (12). The annual pauses in bone apposition are recorded as CGMs in cortical microstructure as either pronounced lines of arrested growth (LAGs) or diffuse annulus rings. On the basis of counting CGMs, BMRP 2002.4.1 was at least 13 years old at death (13 CGMs in the femur and 10 CGMs in the tibia), and BMRP 2006.4.4 was at least 15 years old at death (15 CGMs in the femur and 13 to 18 CGMs in the tibia). Typically, vertebrate long bone cortices will exhibit widely spaced CGMs within the cortex when young, corresponding to high annual osteogenesis. In subadults, CGMs become more closely spaced as osteogenesis decreases approaching adult size [e.g., (10)]. In contrast to these frequently observed patterns, the spacing of CGMs was unexpectedly variable throughout the femur and tibia cortices of both BMRP specimens. In the femur of BMRP 2006.4.4, there is an annulus at the periosteal surface on the medial side (Fig. 1D), but when followed posteriorly, the annulus is within the outer cortex, while fibrolamellar tissue makes up the cortex of the periosteal surface (Fig. 1E). Within the innermost cortex on the anterolateral side, six LAGs are closely spaced (Fig. 2D). Because of resorption from the medullary drift, these LAGs are absent within the innermost cortex of the posterior and lateral sides. Prondvai et al. (13) demonstrated that inaccurate bone microstructure interpretations are possible if the mineralized tissue is observed in only a single plane; specifically, the more slowly formed parallel-fibered mineral arrangement could be mistaken for the rapidly deposited woven-fibered mineral arrangement, which has direct bearing on growth rate interpretations. Therefore, the femur of BMRP 2006.4.4 was longitudinally sectioned in an anterolateral-posteromedial plane, and the tibia of BMRP 2002.4.1 was sectioned in a medial-lateral plane to accurately assess tissue organization and associated relative growth rates (Figs. 1C and 2B, and figs. S2, B and C, S5, and S7). In the femur of BMRP 2006.4.4, vascular canals are arranged parallel to the plane of section and to the shaft of the long bone. Adjacent to the vascular canals, bone fibers are highly anisotropic in CPL and contain osteocyte lacunae with long axes arranged parallel to the vascular canals and plane of section. Tissue of the laminae between primary osteons varies locally in degree of isotropy, with corresponding variable shape in osteocyte lacunae. On the medial side of the longitudinal section through the tibia of BMRP 2002.4.1, vascular canals are arranged obliquely with numerous communications (fig.S5B). From the mid- to the outer cortex, vascular canals are more uniformly parallel to the bone shaft, with fewer transverse Volkmann’s canals (fig. S5C). Adjacent to vascular canals, fibers of the primary osteons are anisotropic in CPL with longitudinally flattened osteocyte lacunae. Fibers within the primary laminae vary locally in isotropy and osteocyte lacuna orientation (Fig. 2B). The lateral cortex is thinner than the medial cortex, and vascular canals are more closely spaced with fewer communicating canals (fig. S5D). DISCUSSION Limb bones exhibit moderate growth rates and tension loading Comparison of BMRP 2002.4.1 and BMRP 2006.4.4 bone fiber organization in the transverse and longitudinal sections using CPL confirms that primary tissue is generally poorly organized parallel fibered to weakly woven. Dense osteocyte lacunae and poor bone fiber organization, in combination with a rich vascular network of reticular, laminar, and plexiform primary osteons, are characteristics that empirically correspond to elevated osteogenesis ranging from 5 to 90 μ m/day (10). Nonetheless, the frequency of longitudinal vascularity, as well as regionally prevalent poorly organized parallel fiber bundles within the transverse sections, suggests that annual growth rates were nearer the lower bound (10). The BMRP individuals did, however, experience occasional periods of faster growth indicated by bands of regionally isotropic woven laminae with reticular vascularity (e.g., Figs. 1E and 2C, and figs. S6D and S8, C and D) (10). In both BMRP specimens, the majority of primary osteons as well as some secondary osteons were isotropic in the transverse section. Corresponding anisotropy in longitudinal examination confirms that the fiber bundles within osteons are longitudinally arranged (Figs. 1C and 2B, and fig. S5, B to D). Studies on long bone response to loading show that longitudinal collagen fiber orientation within secondary osteons is commonly found in habitually tension-loaded regions (14), which may also apply to primary osteon collagen fiber orientation. As such, future studies on tyrannosaurid locomotion biomechanics may benefit from incorporation of osteohistology. Relative skeletal maturity Rather than exhibiting an external fundamental system (EFS) (Fig. 3), a woven-parallel complex extends to the periosteal surface in both tyrannosaurid specimens. Thus, histology supports morphological observations that BMRP 2002.4.1 and BMRP 2006.4.4 were skeletally immature individuals at death (10). In lieu of epiphyseal fusion, which most reptile taxa lack, an EFS is the only way to conclusively confirm attainment of asymptotic adult body length from the long bones of a vertebrate. When present, the EFS occupies the periosteal surface as either closely spaced LAGs (separated by micrometers) (Fig. 3A) or as a thick, primarily avascular annulus (Fig. 3B) (10). CGMs close to the periosteal surface can sometimes be mistaken for an EFS. In the case of BMRP 2006.4.4, an annulus is present at the periosteal surface of both the femur (Fig. 1D) and tibia (fig. S8E), but when the annulus is followed around the cortex, in both cases it becomes embedded within the outer cortex and superseded by woven primary tissue (Figs. 1E and 2C). The proximity of the annulus to the periosteal surface instead suggests that BMRP 2006.4.4 died soon after growth resumed following the annual hiatus and that cortical osteogenesis was directional. Ontogenetic age On the basis of femur CGM count, BMRP 2002.4.1 was>13 years old at death, which is 2 years older than the original estimate by Erickson (8) based on fibula CGM count. The slightly larger BMRP 2006.4.4 was>15 years old. The number of CGMs missing due to medullary expansion is unknown, precluding an exact age at death for BMRP 2002.4.1 and BMRP 2006.4.4. Although the number of missing CGMs could be predicted on the basis of innermost zonal thicknesses and a process of retrocalculation [e.g., (5, 10)], the variable spacing between CGMs observed in BMRP 2002.4.1 and BMRP 2006.4.4 and other tyrannosaurs (15) renders the technique unreliable in this case, and it was not attempted. Within the innermost cortex of BMRP 2006.4.4, there is a tight stacking of six CGMs (Fig. 2D). Because the CGMs remain parallel about the cortex and do not merge, they either represent a single hiatus in which growth repeatedly ceased and resumed (totaling 13 years of growth) or up to 6 years where relatively little growth occurred annually (totaling up to 18 years of growth) (9, 16). This tight stacking of six CGMs is not observed in the femur of BMRP 2006.4.4, which preserves 15 CGMs. The CGM count from the partial tibia of BMRP 2006.4.4 is questionable because the proximal sampling location away from midshaft incorporates the fibular crest, introducing associated regions of remodeling and directional growth affecting apposition interpretations. Because of this and their absence in the femur, the observed grouping of six CGMs is conservatively interpreted as a single hiatus event. Similar instances of a single hiatus represented by narrowly spaced LAGs are reported in other tyrannosauroids (15). If this grouping of CGMs instead represents 6 years of protracted growth, then BMRP 2006.4.4 demonstrates the extent to which these individuals could adjust growth rate based on resource availability, in this case prolonging the ontogenetic duration of BMRP 2006.4.4 as a mid-sized carnivore. Bone tissue organization was similar across femora and tibiae, suggesting that both bones record annual increases in body size equally well. If the stacked CGMs of BMRP 2006.4.4 reflect a single hiatus, then each femur preserved more CGMs than the associated tibia. Previous studies demonstrated that intraskeletal inconsistencies in CGM counts are due to variable rates of medullary cavity expansion or cortical drift across elements (9, 17, 18) when sampled at midshaft. Therefore, our preliminary assessment of T. rex intraskeletal histology suggests that the femur is more informative than the tibia, despite regions of cortical remodeling from tendinous entheses about the cortex. Additional intraskeletal histoanalyses of tyrannosaurid specimens are necessary to test whether the femur is the preferred weight-bearing bone for simultaneous assessments of annual growth rates and skeletochronology. In addition to ontogenetic zonal thickness variability within the cortex, zonal thickness also changed with respect to cortical orientation. That is, zones were often much thinner relative to one another on one side of the transverse section and much thicker on another side (e.g., fig. S4, G and H). This pattern is particularly noticeable in the tibia of BMRP 2002.4.1 (medial cortical zones are thickest) and the femur of BMRP 2006.4.4 (posteromedial cortical zones are thickest). This observation implies that directional cortical growth occurred over ontogeny and stresses the necessity of complete transverse sections for histological analysis: Obtaining a fragment or core for study from one orientation may result in erroneous interpretations of growth rate and skeletal maturity. Variability in annual growth as a response to resource abundance Interpretations of relative maturity in nonavian dinosaurs often rely on reported trends in the thickness of cortical zones between CGMs from the inner to the outer cortex (10). Zone thickness is typically greatest within the innermost cortex, corresponding to rapid annual growth early in life. Zones become progressively thinner in the midto the outer cortex of older individuals, as annual growth rate decreases approaching asymptotic body length. These general trends provide the interpretive foundation for the two previous histologybased ontogenetic studies on Tyrannosaurus growth (4, 5). The spacing of CGMs within the outer cortices of BMRP 2002.4.1 and BMRP 2006.4.4 (Fig. 4) is narrower than between some CGMs deeper within the cortices, which suggests that, although not adults, the specimens were approaching a body length asymptote at about one-half the body length of FMNH PR 2081. However, annual zonal thicknesses between CGMs deeper within the cortices of BMRP 2002.4.1 (Fig. 4A) and BMRP 2006.4.4 (Fig. 4B) are variable, and zones do not consistently progress from widely spaced within the inner cortex to more closely spaced in the outer cortex. Because of unpredictable spacing within the cortex, reduced zonal thickness near the periosteal surface is likely an unreliable indicator of skeletal maturity in BMRP 2002.4.1 and BMRP 2006.4.4. Variable zonal thicknesses are, thus, likely to be observed in ontogenetically older T. rex individuals. To test this hypothesis, we examined femur and tibia thin sections from T. rex specimens USNM PAL (National Museum of Natural History) 555000, MOR (Museum of the Rockies) 1125, MOR 1128, MOR 1198, and CCM (Carter County Museum) V33.1.15. In all individuals, variability in annual zonal thicknesses was observed. In particular, compared to zone spacing within the mid-cortex, noticeably thinner zones are present within the innermost cortex of USNM PAL 555000 (Fig. 4C) and MOR 1128 (Fig. 4D). These results contradict the mathematically predictable zonal spacing in T. rex long bones reported by Horner and Padian (5), which used some of the same specimens reassessed in the present study. Results further suggest not only that BMRP 2002.4.1 and BMRP 2006.4.4 had not yet entered the accelerated growth period proposed for this taxon (4, 5) but also that the accuracy of the generalized T. rex body mass curve from Erickson et al. (4) would be affected by undetected individual variation in annual growth. Variable LAG spacing is reported in ornithomimids, ornithopods [(19) and references therein], and other tyrannosauroids (15) and may correlate with annual resource abundance (12, 19). Our data suggest that this trait also characterizes T. rex: Because the level of bone tissue organization within zones remained the same from the innermost cortex to the periosteal surface in the BMRP specimens, growth rates were within a similar range from year to year. To produce these extremes in annual bone apposition, the duration of the growth hiatus must have varied annually. On the basis of the larger T. rex specimens examined here for comparison, the adjustment of annual growth hiatus duration in response to resource abundance is a physiological characteristic observed throughout T. rex ontogeny. Regardless of cause, unpredictable CGM spacing observed here and in previous studies stresses caution when inferring relative maturity based on cortical LAG spacing (19). The observation of closely spaced CGMs within the innermost cortices of larger T. rex validates our interpretation that the thin zonal spacing observed in the outermost cortices of BMRP 2002.4.1 and BMRP 2006.4.4 are not reliable indicators of relative maturity when an EFS is absent. Implications for the Nanotyrannus hypothesis The bone microstructural interpretations discussed here not only provide insight into T. rex ontogeny but also have bearing on discussions concerning CMNH (Cleveland Museum of Natural History) 7541 and Nanotyrannus. CMNH 7541 consists of a small isolated skull 572 mm in length (20). Inferred to be sympatric with T. rex, it was originally named Gorgosaurus lancensis (21). In 1988, Bakker et al. (22) redescribed CMNH 7541 as an adult specimen of a new genus, Nanotyrannus. Using an extensive empirical dataset, Carr and Williamson (23) formally synonymized Nanotyrannus into Tyrannosaurus in 2004, supporting the interpretation of CMNH 7541 as a juvenile T. rex proposed by Rozhdestvensky in 1965 (24). Presently, most tyrannosaurid specialists consider CMNH 7541 and possible referred specimens to be juvenile T. rex based on morphological skull features shared with those found in undisputed juvenile individuals of other tyrannosaurid taxa [e.g., (2, 20, 23, 25 – 28)]. Nonetheless, several publications have since argued for the validity of Nanotyrannus based not only on morphological characters of the CMNH 7541 type skull but also on characters from the somewhat larger skull of BMRP 2002.4.1 (720 mm in length) [e.g., (29 – 33)], which some researchers have assigned to Nanotyrannus based on shared morphological characters they consider adult autapomorphies of the taxon [e.g., (29 – 33)]. Currently, BMRP 2002.4.1 is the only accessioned specimen with postcranial skeletal elements preserved that is specifically argued by proponents of Nanotyrannus as belonging to that genus [e.g., (29 – 32)]. Because CMNH 7541 lacks the postcranial skeleton and proponents of Nanotyrannus refer BMRP 2002.4.1 to that taxon, the limb bone histology of BMRP 2002.4.1 (and additionally BMRP 2006.4.4; see the Supplementary Materials for taxonomic discussion) reveals the life history of CMNH 7541 by proxy. Here, we provide histological data that can be used to reject the hypothesis that Nanotyrannus was erected
Properties of rubble-pile asteroid (101955) Bennu from OSIRIS-REx imaging and thermal analysis
No full text© 2019, The Author(s), under exclusive licence to Springer Nature Limited. Establishing the abundance and physical properties of regolith and boulders on asteroids is crucial for understanding the formation and degradation mechanisms at work on their surfaces. Using images and thermal data from NASA’s Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft, we show that asteroid (101955) Bennu’s surface is globally rough, dense with boulders, and low in albedo. The number of boulders is surprising given Bennu’s moderate thermal inertia, suggesting that simple models linking thermal inertia to particle size do not adequately capture the complexity relating these properties. At the same time, we find evidence for a wide range of particle sizes with distinct albedo characteristics. Our findings imply that ages of Bennu’s surface particles span from the disruption of the asteroid’s parent body (boulders) to recent in situ production (micrometre-scale particles)
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