"A look at sauropod dinosaurs as we know them today requires that we relegate the brontosaur, once thought to be one of the largest sauropods, to welterweight or at most middleweight status. " The author made the distinction quite clearly at the very beginning of his article and the term 'Brontosaurus' is still in use today - watch the film 'Jurassic Park"

The term is still in use informally, but as I said, no self-respecting paleontologist would use it. Furthermore, Jurassic Park is itself over a decade old, is based on a novel which is even older, and is hardly a definitive authority on the subject of dinosaurs. To name only one of the film's many factual errors, in the scene where Nedry plunders the embryo storage containers, "stegosaurus" is spelled wrong.

I still hold that the paper shows no interest in staying abrest of the current developments in paleontology, and thus, cannot be considered an authoritative source of such information. I stand by my statement that it is a very poor peice of scholarship and cannot add anything of substance to the debate.

-Pilgrim

From: http://microlnx.com/dinosaurs/OriginOfDino...AndMammals.html

Skeletal Scaling in Reduced Gravity
It is true that we can seldom test a paleontological hypothesis with a live experiment. What we can do is perform 'thought experiments.' We can erect hypotheses, deduce their consequences, and then we can see whether these consequences are borne out by the fossil data.

– Steven M. Stanley1

Although gravity is a universal force measured in absolute terms, its tangible influence on living things can and does vary. Aquatic animals, such as fishes and whales, are essentially 'immune' to gravity's influence because their buoyancy in water offsets their weight. All land-living animals, however, are subject to gravitational stress. Yet even on land, gravity's influence is variable. The relative influence of gravity (and most other physical forces) varies with size and scale; forces dominant at one scale of nature become inconsequential at another. Extremely small animals less than 1 mm in length, for example, inhabit a Gibbsian world dominated by cohesive forces; larger animals live in a Newtonian world dominated by gravity.2 The insect kingdom straddles gravity's frontier.

In terrestrial vertebrates, the skeleton provides structural support against the crushing stress of weight. With increasing body size, body weight increases at a faster rate that the weight-supporting capacity of the skeleton. Body weight is proportional to volume, and volume is proportional to the cube of linear dimensions. The strength of bone, on the other hand, is proportional to its cross-sectional area, and area is proportional to the square of linear dimensions. Thus, if linear dimensions l are doubled, body weight will increase by a factory of eight – 2l3 – while bone strength increases only by a factor of four – 2l2. Accordingly, with increasing body size, animals will devote a larger fraction of their body mass to the skeleton.

A change in relative bone dimensions and bone mass with increasing body size is a prime example of scaling, which has been described as "the structural and functional consequences of changes in size and scale among otherwise similar organisms."3 Galileo may have been the first to realize that an increase in body size makes it "necessary to change the ratio between [bone] thickness and length either by increasing the thickness or by diminishing the length."4 On the assumption that static strength is the primary determinant of relative bone dimensions, Galileo concluded that bones are scaled for constant-stress similarity, according to which bone length l is related to diameter d as l d1/2.

Although the general idea behind Galileo's reasoning is valid, his scaling formula turned out to be rather inaccurate in detail. Bones typically are somewhat thinner than constant-stress scaling would predict. In order to improve upon Galileo's insight, some recent workers have suggested that scaling is based on "elastic rather than strength criteria."5 According to the principle of elastic similarity, bones "should be scaled in such a way as to deform under gravity in a geometrically similar fashion."6 In other words, the ratio of bone-deformation-to-bone-length will remain constant with increasing size. The principle of elastic similarity yields a proportionality of l d2/3. Thus, bones scaled for elastic similarity would be thicker that geometrically similar bones – l d1 – and thinner that bones scaled for constant-stress similarity – l d1/2.

Characteristic General Formula Similarity Formulas
Geometric Elastic Constant-
Stress
Proportions ldx X = 1 X = 2/3 X = 1/2
Bone lengths lMx/(x+2) lM1/3 lM1/4 lM1/5
Bone diameters dM1/(x+2) dM1/3 dM3/8 dM2/5
Skeletal Mass sld2 (M1/3)(M1/3)2 (M1/4)(M3/8)2 (M1/5)(M2/5)2
MSkels MSkelM3/3 MSkelM8/8 MSkelM5/5

Table 1 – Comparison of Similarity Formulas7

Each of these scaling formulas can, within limited domains, account for the known facts, but none of them is universally valid. Leg dimensions in adult ungulates, for example, seem to be scaled for elastic similarity but those of mammals in general are not. (Mammalian leg lengths correspond more closely to the value predicted by geometric similarity.) In many cases, different bones within the same animal are scaled differently. In ground-running birds, such as quails and ostriches, the vertical leg bones (tibiotarsus and tibiometatarsus) are much longer than any of the scaling formulas would predict but come closest to the values predicted by geometric similarity. The horizontal bones (femur and toes), on the other hand, fall in between the values predicted by geometric and elastic similarity. Yet in both sets of bones the diameters correspond exactly with the values predicted by constant-stress similarity.8 At best, this bewildering situation suggests that individual bones are scaled according to the types of stress they are most likely to encounter; at worst, it proves that bone scaling defies rigorous analysis.

Another shortcoming of all of these scaling formulas is their unanimous prediction of isometric skeletal scaling. (See Table 1.) In fact, as mentioned above, animals devote a relatively larger fraction of their mass to the skeleton as body size increases.

It seems obvious that a reduction in gravity, and the consequent reduction in body weight, should have some affect on relative bone dimensions. But it is not at all clear from these scaling formulas what affect, if any, a gravity (and weight) reduction would have on relative bone dimensions. If bone dimensions are a function of mass (as shown in Table 1), then a change in gravity would have no effect. If, on the other hand, they are a function of weight (mass times gravity), then a gravity reduction would result in thinner and shorter bones, and therefore an overall reduction in body size. Both conclusions seem wrong. Galileo based his scaling principle on the capacity of bones to support their own weight: a reduction in gravity therefore would permit thinner bones. But that inference is not implicit in the above formulations. And with respect to elastic similarity, bones are proportioned so that they will deform in a geometrically similar fashion irrespective of body weight. Clearly, a reduction in gravity would have no effect on bone elasticity.

The problem of bone scaling has perplexed and so far eluded some of the most outstanding minds. Perhaps the best we can hope for is a scaling formula based on empirical similarity.9 But even a strictly empirical approach cannot account for the differences in relative bone dimensions found among different species and indeed within individual animals.

Fortunately, the scaling of the skeleton as a whole offers more promise. It is well known that the percentage of body mass devoted to the skeleton increases with size.10 In mammals, the statistically derived allometric scaling formula11 is

MSkel = 0. 0343 mBody1.083 (1)

For birds, the formula is

MSkel = 0. 0406 mBody1.068 (2)

Stated simply, Equations (1) and (2) indicate that the skeleton of a one-gram mammal should account for 3.43% of its total body mass, and it should account for 4.06% of body mass in a one-gram bird. An exponent greater than one indicates non-isometric scaling: the fraction of body mass devoted to the skeleton will increase with increasing body size.

A comparison of Equations (1) and (2) belies the common assumption that birds, as an adaptation for flight, have lighter skeletons than mammals. In fact, these empirical regressions indicate that birds actually devote a slightly larger fraction of their body mass to the skeleton than do mammals, especially at the low end of the scale. With increasing body size, however, the skeletal mass of mammals approaches and, above 100 kg in body mass, surpasses that of birds. Nevertheless, the two formulas yield very similar values between 10 kg (at which size a mammal would devote 7.2% of its mass to the skeleton and a bird 7.6%) and 1000 kg (10.6% for mammals and 10.3% for birds). Above one metric ton, the two formulas diverge but this is considerably larger than any living bird and is at the upper end of the mammalian size range.

Although Equation (1) represents a 'best fit' regression of available terrestrial mammal data, and includes animals ranging in size from a 3.5-gram shrew to a 6.6 metric ton elephant, it is rather inaccurate when applied to large-scale mammals. It predicts, for example, that a 6.6 ton elephant will devote 13% of its body mass to the skeleton when in fact the value is closer to 27%.12 (The two equations predict, respectively, that a mammal with 27% bone mass would weight 65 kilotons, and a similarly proportioned bird 1.3 megatons!) This gap between theory and fact does not invalidate the basic method: it merely reflects skewing toward the low end of the scale and demonstrates the pitfalls of extrapolating beyond the sample range.

On the assumption that the need for structural support is most acute in large-scale animals, Equation (1) can be adjusted to achieve a closer agreement between the predicted and actual skeletal mass for large-scale mammals. Based on a trial-and-error method, the following allometric formula was found to predict that a 10 kg dog would have 14% skeletal mass, a 67 kg human 17% skeletal mass, and a 6. 6 ton elephant 27% skeletal mass, all of which are approximately correct.13

MSkel = 0.0584 mBody1.098 (3)

The revised exponent (1.098) in Equation (3) is still within the range of statistical error of the Equation (1) exponent (1.083 ± 0. 021) but the revised coefficient (0.0584) is considerably larger than the Equation (1) coefficient (0.0343). This means that instead of devoting 3.43% of body mass to the skeleton, a 1-gram animal would devote 5.84%. Accordingly, Equation (3) is least accurate with respect to very small animals (a 6.3-gram shrew has 4.8% skeletal mass. Equation (1) predicts 4.0% skeletal mass and Equation (3) 7.0%) but it is much more accurate than Equation (1) for animals above 10 kg.

The important point here is that skeletal mass increases out of proportion to body mass, which suggests that the need for skeletal support increases with body size. The fact that gravitational stresses also increase with size implies that weight (mass times gravity) is the crucial factor in the hyperallometric scaling of skeletal mass. This notion is borne out in whales. The body mass of a whale is buoyantly supported in water, which relieves much of the stress on its skeleton. Accordingly, the skeletal scaling exponent in whales is much lower that in terrestrial mammals and, indeed, approaches isometry:14

MSkel MBody1.024 (4)

The fact that the skeleton of whales seems to "scale strictly in proportion to body size… [s]uggests that when there is no need to support the body in a gravitational field, the skeleton is not required to scale out of proportion to body size."15

If gravitational stress is responsible for the hyperallometric skeletal scaling of land-living animals, then the complete absence of gravitational stress (zero g) should permit isometric scaling. In zero g, skeletal mass should increase in direct proportion to body mass: “In the absence of gravity… geometric similarity must be obeyed. ”16 This, in turn, implies that in reduced gravity, the allometric exponent would fall between the 1 g value of 1.098 (Equation (3)) and the hypothetical zero g value of 1.000. Thus, for example, at . 75 g, the exponent would be 1.0735, while at .25 g it would be 1.0245. Because we are dealing with exponents, these seemingly negligible differences yield very substantial results.



Three Predicted Consequences of a Gravity Reduction
If the skeletal scaling exponent is a function of gravity, then a reduction in gravity will have three important consequences (all else being equal):

Animals adapted to low gravity should have less bone mass than animals of equal mass adapted to normal gravity.
In reduced gravity, bones of a given length would tend to be thinner and bones of given thickness, longer.
If there is a limit on the amount of body mass that can be devoted to the skeleton, then a gravity reduction should permit a considerable increase in size and mass of the very largest land animals.
The first prediction – that animals adapted to low gravity should have less bone mass than an animal of equal mass in normal gravity – follows from the assumed dependency of skeletal scaling on gravity. The second prediction – that bones would become thinner and longer – follows the first prediction and from the fact that bone dimensions are related to skeletal mass as ld2MSkel. Since the proportionality of bone diameter to bone length is dlx (where x > 1), a reduction in skeletal mass will result in a reduction in the scaling exponent x. In other words, all else being equal, bones of given length would tend to be thinner, and bones of given thickness, longer. Both of these expectations are supported by biomedical space research: bone thinning and an overall reduction in bone mass is one of the best-known side effects of weightlessness.

Bones are quite sensitive to changes in gravitational stress.17 Upon entering zero g (or, more accurately, micro g), bone growth slows down immediately and eventually ceases altogether. In laboratory rats sent into space, the rate of bone formation dropped to half the control rate in earth-bound rats even though total body mass remained constant." Without exception, each rat formed more bone after than during flight." Since "the greatest changes occur in weight bearing bones, changes in mechanical loading are undoubtedly important."18 Similarly, in astronauts and cosmonauts, "the first reaction to a decrease in stress is decalcification." There is a significant increase in urinary and fecal calcium and other bone-related minerals; the rate of calcium loss is about 0.5% of the total calcium content per month.19 "These results are indicative of an alteration in bone structure, as confirmed by an increase in urinary hydroxyproline, a degradation product of bone collagen."20

Bone thinning and the loss of bone mass in zero g are not at all surprising. Since the skeleton must be strong enough (at least) to support body weight, the complete absence of body weight in zero g means that the need for weight is also completely absent; as a result, the bones and skeleton degenerate. A similar thing happens to bed-ridden invalids: their bones and muscles atrophy from lack of use. Because of the complete elimination of mechanical stress, prolonged exposure to zero g creates symptoms not unlike osteoporosis, a degenerative bone malady." "Theoretically, it seems possible that bone could be reduced and decalcified so far that a return to terrestrial conditions and normal body weight would increase the stresses… so much that they would go beyond the upper tolerance level."21

The third predicted consequence of a reduction in gravity is closely related to the first two. If there is a limit on the amount of body mass that can be devoted to the skeleton, and skeletal scaling is a function of gravity, then a gravity reduction should permit a considerable increase in maximum body size. In reduced gravity, animals will be able to achieve body sizes not possible under normal 1 g conditions because they can devote a smaller fraction of their body mass to the skeleton. Assuming that animals cannot exceed 27% bone mass (the value for elephants), a 20% reduction in gravity would permit roughly an order of magnitude increase in body size. Applying the gravity reduction conversion method described above to Equation (3), the skeletal scaling formula at 0. 8 g would be:

MSkel = 0.0584 mBody 1.079 (5)

Using this formula, the mass of an animal with an elephant-like skeleton (27% of body mass) would be 250 metric tons; a human-like animal (17% skeletal mass) would be 750 kg and a dog-like animal (14% skeletal mass) would be 65 kg. These surprising results indicate that even a small reduction in gravity will have a huge effect on skeletal mass, especially in large-scale animals.



Vertebrate Evolution in Reduced Gravity
What affect, then, would a gravity reduction have on vertebrate evolution? Basic skeletal design, of course, is genetically determined; and since modern evolutionary theory denies the inheritability of acquired traits, the loss of bone mass experienced by an individual exposed to low gravity would not be transmitted to its offspring.22 However, if it is beneficial for animals to have the lowest possible bone mass23, then evolution in reduced gravity should favor those varieties with a genetic tendency toward lightweight skeletons: animals with low bone mass (perhaps expressed as a low genetically-encoded skeletal growth allometry) would have a competitive edge over animals equipped with more massive skeletons. Moreover, because such animals would devote relatively less body mass to the skeleton, they should be able to grow much larger than animals with more robust skeletons and there should be an increase in the size of the very largest land animals. Because of its magnified effect on large animals, a 20% reduction in gravity would, in effect, foster the evolution of giants – animals with the skeleton of an elephant but the mass of a whale.

If there was a reduction in gravity during the Middle-to-Late Triassic, then the animals that evolved afterwards should have been more gracile and lightly constructed than those that had gone before, and they should have been able to grow much larger. Both predictions are borne out by the fossil evidence.


--------------------------------------------------------------------------------

1 Stanley, 1981.

2 Went, 1968.

3 Schmidt-Nielsen, 1984.

4 Galilieo, 1638, 1954 edition.

5 McMahon, 1973; Rashevsky, 1960.

6 Alexander, 1982a.

7 After Calder, 1984.

8 Calder 1984.

9 Alexander, 1982a.

10 Prange, et al., 1979.

11 As modified by Schmidt-Nielsen, 1984.

12 Prange et al., 1979.

13 Prange et al., 1979.

14 Schmidt-Nielsen, 1984.

15 Ibid.

16 Economos, 1983.

17 See Smith, 1975, for an excellent review of "gravitational biology."

18 Morey and Baylink, 1978.

19 Shapland and Rycroft, 1984.

20 Lenfant and Chiang, 1982.

21 Kummer, 1972.

22 Cf. Smith, 1975.

23 Calder, 1984.

From: http://microlnx.com/dinosaurs/OriginOfDino...AndMammals.html


Dinosaur Giantism
The sauropods began their long evolutionary history as giants; one might say that geologically speaking they became instantaneous giants, because the first of these great dinosaurs is found in rocks of very early Jurassic age.

– Edwin H. Colbert1

Barapasaurus, from the Early Jurassic, was one of the first true sauropods. At twenty-five meters in length2, Barapasaurus was the largest animal that had yet evolved. Prior to the Mesozoic, the largest land animals were herbivorous pelycosaurs from the Permian, sprawling quadrupeds that rarely exceeded four or five meters in length. The very existence of Barapasaurus demonstrates that powerful selection pressures favoring giantism were at work during the Mesozoic, pressures that simply were not operative during the Paleozoic. But more important, the appearance of Barapasaurus so early in the age of dinosaurs belies the notion that the evolution of dinosaur giantism was a protracted and incremental process, à la Cope's Law.3 Although dinosaur giantism did not reach its zenith until the Late Jurassic, gigantic dinosaurs appeared quite early.

Every schoolchild knows that dinosaurs were the largest land animals that ever lived. Yet professional paleontologists are forever pointing out that 'not all dinosaurs were giants.' And indeed, Compsognathus, from the Late Jurassic, was quite small, about the size of a chicken. But for the most part, dinosaurs were big – very big. Estimates of median dinosaur mass range from 500 kg to 5 metric tons; and a safe estimate, perhaps a bit conservative, would be one ton. The biggest finds on record may well have exceeded 100 tons, about the size of a Blue Whale. And given the astronomical odds against the fossil preservation of any given animal, it is nearly certain that larger dinosaurs existed but were not preserved or have not yet been found.

During the Jurassic Period, giant dinosaurs were the rule not the exception. Eighty percent of the biomass from the Late Jurassic Morrison formation of the western United States consisted of stegosaurs and sauropods; the latter average 20 tons.4 Nevertheless, everything about these giants belies their enormous size: "Surprisingly, the joint surfaces of the [sauropods] limbs are poorly defined, and there must have been a good deal of cartilage in the carpus and tarsus as well. The capacity for the cartilage to yield under pressure and conform to a shape that would most effectively distribute the force produced by the weight of the body was apparently more important than the greater per unit strength of bone."5

The bipedal theropods were of course much smaller than the giant sauropods. But many of these 'small' dinosaurs were still quite large. Until recently, Tyrannosaurus, from the Late Cretaceous, was thought to be the biggest biped, but other theropods of equal or even larger size from the Late Jurassic have been unearthed.6 The mass of these 'small' dinosaurs was 'only' four or five tons.

The typically large size of the dinosaurs, and the comparatively small size of modern mammals, has been quantified by Nicholas Hotton.7 Based on 63 dinosaur genera, Hotton's data yield an average generic mass in excess of 850 kg (about the size of a grizzly bear) and a median generic mass of nearly 2 tons (comparable to a giraffe). This contrasts sharply with extant mammals (788 genera) whose average generic mass is 863 grams (a large rodent) and a median mass of 631 grams (a smaller rodent). The smallest dinosaur was bigger than two-thirds of all living mammals; the majority of dinosaurs were bigger than all but 2% of living mammals.

Robert Bakker believes that Hotton has overstated the size difference.8 Bakker maintains that the modern fauna – dominated by very small mammals and devoid of very large ones – is atypical in the history of mammals. Yet even when all of the mammals smaller than the smallest dinosaur (4 kg) are excluded from Hotton's data set, the size gap between the mammals and dinosaurs is only marginally reduced: the average generic mass of mammals is raised to 36 kg (a large dog) and median mass is raised to 25 kg (a smaller dog). Both values are still orders of magnitude less than dinosaurs.

In order to balance the scales, as it were, Bakker compared Late Jurassic dinosaurs with mammals from the Miocene and Pliocene, which Bakker characterized as "the Age of Mammal Giants."9 But Bakker's histograms (which, incidentally, do not include any mammals under 1 kg) still reveal a significant in difference in size.10 A comparison of Miocene mammals with Late Jurassic dinosaurs (from the Tendagaru formation) yields a median mass of 316 kg for both mammals and dinosaurs, but an average specimen mass of 125 kg for the mammals versus 418 kg for the dinosaurs. The size difference is much more pronounced when comparing Pliocene mammals with Morrison dinosaurs. The average and median mass of Pliocene mammal species was about 300 kg and 316 kg, respectively, versus an 1895 kg average mass and 3162 kg median mass for Jurassic dinosaurs from the Morrison formation When compared to the modern fauna, the Mio-Pliocene may have been an age of giants, but it pales in comparison to the Late Jurassic.

Bakker's desire to narrow the size gap between mammals and dinosaurs stems, in part, from his personal belief that dinosaurs were ecologically and physiologically similar to mammals. Hotton, by contrast, rejects dinosaur endothermy as unnecessary and untenable. He argues that size alone could have enabled dinosaurs to maintain a constant body temperature (mass homeothermy). But quite apart from the problem of dinosaur physiology (discussed later), no one on either side of the debate has been able to explain why dinosaurs grew so large, or why animals of dinosaurian dimensions were limited to the Mesozoic.

Accustomed with the typically large size of dinosaurs, most scientists take dinosaur giantism for granted. As a result, they tend to ignore or belittle the very real mechanical problems associated with size. But to early workers, the large size of the 'terrible lizards' was a problem of the first order. William Buckland, who lived in the mid-nineteenth century, believed the earliest known dinosaurs, Megalosaurus, Iguanodon, and Hylaeosaurus, which he and his wife discovered, were "the most gigantic of all quadrupeds that have ever trod upon this planet."11 Acutely aware of the problems of size and unjaded by familiarity with the dinosaurs, the Victorians reconstructed these dinosaurs as heavily muscled sprawling quadrupeds. Yet, as we now know, the dinosaurs in question were only medium-sized, and they were bipeds to boot.

When the first sauropod was discovered in the 1840s, Richard Owen believed it to be much too large to live on land and therefore decided that it must have been a marine lizard. His name for it – Cetiosaurus, or 'whale-lizard' – reflected this belief. However, the discovery of weight-bearing limbs proved that Cetiosaurus was in fact a land dweller, a notion that Owen found difficult to accept. Accordingly, he decided that Cetiosaurus must have spent its life in lagoons and swamps, where its enormous mass could be supported buoyantly in water.12 Thus was born the amphibian theory of sauropods.

Many leading paleontologists have subscribed to the amphibian theory. "The legs of sauropods were large," wrote A.S. Romer in 1966, "but even so, it seems doubtful whether they could have borne so many tons of weight. For his reason [and others], it appears probable that the sauropods were amphibious types that spent most of their lives in lowland swamps and lagoons where they were buoyed up by the water, and the problems of support and locomotion were greatly simplified."13 Bjorn Kurten concurred: "It must be assumed that the sauropods normally dwelt in water, where their weight would cause no trouble, since it was buoyed up by the water."14

This amphibian theory of sauropods was held almost universally until Bakker convincingly demonstrated that sauropods did not live in water but were actually land-dwellers, more like high-browsing giraffes than wallowing hippos.15 The long erect limbs and deep rib cage of sauropods are similar to those of elephants and other large terrestrial mammals, and quite unlike the short, stubby limbs and barrel-shaped torso of hippos, which spend most of their lives in water. Moreover, sauropod fossils are typically found in well-drained floodplain or fluvial deposits, and not in lakes or swamps.

Bakker believes that dinosaurs were the Mesozoic analogues of modern terrestrial mammals, with sauropods being the dinosaur equivalent of giraffes. He makes a convincing case. But in solving the problem of sauropod ecology and behavior, Bakker has unwittingly reopened the problem of dinosaur giantism. In removing these giants to dry land, Bakker has thrown out the sauropods with the swamp water, for the raison d'être of amphibian sauropods – the reason they were relegated to the swamps in the first place – was their gigantic size. Bakker, of course, maintains that sauropods were not anomalously large and hence denies that there is any problem at all. Calculations of sauropod bone strength by Alexander lend support to this view,16 but Alexander's conclusions are only as good as his estimates of dinosaur mass, which I suspect are probably low. For example, Colbert estimated that Brachiosaurus had a mass in excess of eighty tons17 whereas Alexander's estimate is less than fifty.18

Perhaps the most relevant analysis of terrestrial giantism is by Economos.19 Citing centrifugal hypergravity experiments, Economos noted that "small mammals could adapt and survive for extended periods of time in stronger fields than large mammals. If terrestrial gravity is expresses as 1G, a mouse tolerates 7G, a rat 5G, a dog and chicken 3G; the approximate value for man is about 1.7G. Conceivably, as the magnitude of the tolerable field or 'gravitational tolerance' decreases with increasing body mass, an upper limit for body size would be reached, that 'largest' mammal having a gravitational tolerance equal to terrestrial gravity." From these data, Economos derived the following power-law function that relates body mass m (in kg) to gravitational tolerance Gmax.

Gmax = 4 m-0.14 (6)

Based on Equation (6), Economos calculated that the maximum possible body size for land mammals – where Gmaxequals one – "is found to be about 20,000 kg, which agrees with the estimated body mass of Baluchitherium."

At 20 tons, Baluchitherium, a rhinoceros from the late Oligocene and early Miocene, was the largest of all land mammals, living or extinct. Compared to a modern rhino or elephant, Baluchitherium was truly gigantic. But according to Bakker, 20 tons was only the average size of Morrison sauropods. Larger sauropods, of 50 or even 100 tons, are known to have lived. How did they support themselves? Economos, together with an earlier generation of paleontologists, opted for the amphibian solution: "Apparently, the buoyancy of water has made possible the evolution of sea mammals much larger than the largest land species. (This was also true of dinosaurs.)"20 Bakker, however, has shown that sauropods were land-dwellers; hence, they could not rely on buoyancy to support their bulk. Thus, we have a paradox: either 20 tons is the maximum size for a land animal, in which case Bakker is wrong about the terrestrial habits of sauropods, or else Economos is wrong and land animals larger than 20 tons can exist.

There is, of course, a simple solution to this paradox, a solution that validates Bakker's empirical findings without violating Economos's theoretical analysis. Reduced gravity during the Jurassic would have permitted land animals to achieve body sizes not possible under present-day conditions. In a previous section, it was argued based on the skeletal scaling Equation (3) that a 20% reduction in gravity would permit an order of magnitude increase in body mass of the very largest land animals without any increase in the fraction of body mass devoted to the skeleton. The mass of the largest sauropods was probably about 100 tons. It is therefore worth noting that for Gmax= 0.8G, Economos's Equation (6) yields a maximum body size of about 100 metric tons.


--------------------------------------------------------------------------------

1 Colbert, 1983.

2 Galton, 1986.

3 Bakker, 1980.

4 Bakker, 1980.

5 Carroll, 1988.

6 Geotimes, Feb. 1990.

7 Hotton, 1980.

8 Bakker, 1980.

9 Ibid.

10 Both Hotton (1980) and Bakker (1980) depicted their data on log-vs-linear histograms, with body mass given as the log values. Hotton split his sizes into 0.1 log ranges; Bakker lumped his data into 1-log ranges. My numbers are extrapolated from these histograms. With respect to Bakker’s histograms, I assigned a median value for each size class – thus, animals in the size range 102 – 103 grams were assigned a mass of 102.5 grams.

11 Quoted in Desmond, 1976.

12 Desmond, 1976.

13Romer, 1966.

14 Kurten, 1968.

15 Bakker, 1971b.

16Alexander, 1985; Alexander, 1989.

17 Colbert, 1962.

18Alexander, 1989.

19 Economos, 1981.

20 Ibid.

From: http://microlnx.com/dinosaurs/OriginOfDino...AndMammals.html
Locomotion in Reduced Gravity
Practically all the work done in walking and running is against gravity.

– Rodolfo Margaria1

When American astronauts went to the Moon in the late 1960s and early 1970s, they discovered that walking and running, the normal bipedal gaits of humans on Earth, were ineffective on the Moon where gravity is 1/6 that of Earth. But the astronauts discovered that by modifying their locomotive behavior, and shifting to a skipping or hopping gait, they could move about quickly with relatively little effort or exertion. The Apollo astronauts adapted to lunar gravity by changing gait. Dimensional analysis, based on the principle of dynamic similarity, helps explain why they did this and provides a simple and elegant approach to the problem of gait selection.

Dynamic similarity is an application of the pendulum principle – the interaction between gravity and inertia. "Motions are said to be dynamically similar if they could be made identical by uniform changes of the scales of length and time."2 Thus, two pendulums of different lengths but identical angular amplitude are dynamically similar. Likewise, two running animals with different leg lengths but the same ratio of stride-length-to-leg-length are also dynamically similar. Mathematically, pendulums (and running animals) are dynamically similar if they have equal Froude numbers – u2/gl – where u is a characteristic speed, g the acceleration of gravity, and l a characteristic length. When Froude numbers are applied to animal locomotion, u refers to forward velocity and l to leg length.

It has been found that animals ranging in size from small rodents to horses use similar gaits and equal values of (stride length/leg length) at any given Froude number. More to the point, gait transitions tend to occur at particular Froude numbers. "Men break into a run and kangaroos and crows change from walking to hopping at Froude number around 0.6, about the same as the Froude numbers at which quadrupedal mammals change from walking to a faster symmetrical gait."3 In order to achieve maximum speed, quadrupeds will shift from a symmetrical gait, such as a trot, to an asymmetrical gait, such as a gallop. Thus gait transition occurs at Froude numbers between 2 and 3.

Dimensional analysis of gait transition helps explain the problems encountered by the Apollo astronauts when they attempted to walk and run in lunar gravity, and why they found skipping and hopping to be so effective. Gravity is one of the Froude number variables. If gait transition occurs within a narrow range of Froude numbers, then a reduction in gravity will necessary lower the speed at which a human astronaut (or any other animal) shifts to a higher gait.



The Mechanics, Dynamics and Energetics of Animal Locomotion
These considerations are brought into sharper focus by understanding the mechanics, dynamics and energetics of animal locomotion. Bipeds are capable for four distinct gaits: walking, running, ‘skipping’, and hopping. Adult humans normally employ the first two gaits, but children, because of their high energy and low mass, frequently shift to a ‘skipping’ gait at intermediate speeds. Hopping is unnatural for humans but is quite common in small mammals and birds and, of course, kangaroos. Quadrupeds on the other hand, have a much larger repertoire of gaits: walk, amble, trot, pace, canter, transverse gallop, rotary gallop, bound and pronk.4 For our purposes, these nine gaits can be reduced to four – walk, trot, gallop, and bound. Hind limb movement in these quadrupedal gaits is mechanically similar to the four bipedal gaits.

Bipeds Quadrupeds Temporal Spacing
of Footfalls Leg-pair swing Characteristic
Phase Relative Stride
Rate Length
Walk Walk Symmetrical Alternating Supported Low



High Short








Long
Amble
Run Trot Suspended
Pace
'Skip' Canter Asymmetrical Synchronized Medium
Gallop High
Hop Bound Aerial Low
Pronk

Table 2 – A Comparison of Bipedal and Quadruped Gaits

As shown in Table 2, these four gaits differ with respect to footfall sequence, characteristic phase, stride rate, and stride length. Walking and running (trotting) employ alternating leg swings; they are said to be symmetrical gaits because the spacing of footfalls is evenly distributed through time. The two gaits differ in that walking is a supported gait – at least one foot is on the ground at all times – while running (trotting) is a suspended gait – all feet are off the ground momentarily while the body is suspended in midair between footfalls. Skipping (galloping) also employs a suspended phase; but unlike running (trotting), skipping is an asymmetrical gait: footfalls are unevenly distributed through time and leg-pair motion is synchronized. Finally, hopping (bounding) is an asymmetrical gait characterized by an aerial phase, which is simply a prolonged suspended phase when the animal is propelled high off the ground.

For any gait, animals tend to move at their most ‘comfortable’ or economical speed. They change gait for energetic reasons.5 Changing gait minimizes the metabolic cost of locomotion at higher speeds, much as shifting to higher gears in an automobiles lowers engine speed and conserves fuel.

Walking, the slowest form of locomotion, is also the most economical. It relies on gravity as its primary energy source.6 The gravitational potential energy acquired at the beginning of each step, when the body is raised through the leverage action of the legs and feet, is converted into kinetic energy (forward motion) during the second (downward) phase as the body falls forward under gravity. This is known as 'ballistic walking.'7 Walking is a supported gait: balance and stability are maintained by keeping at least one foot on the ground at all times.

Because ballistic walking is powered by gravity, muscular exertion is kept to a minimum with obvious energy-saving benefits. The optimum speed of ballistic walking – the most comfortable and efficient speed – is probably dictated by the natural frequency of the pendulum-like limbs. Swinging the legs faster or slower than their natural frequency requires the application of muscle power. Otherwise, muscles need only provide enough energy to help support the body, overcome inertia when beginning to walk, raise the body at the beginning of each step, and lift the feet between steps. Because it uses gravity and inertia instead of muscles and metabolism, walking is very efficient at low speeds.

The speed of locomotion is the product of stride length times stride rate. In walking, stride length is limited by leg length and the arc swept out by the legs swinging from the hips. Consequently, stride length cannot be increased without introducing a suspended phase, i.e. by shifting to a running gait. The only way to walk faster than normal is by increasing stride rate. But swinging the legs faster than their natural frequency requires muscular exertion. Therefore, as walking speed increase, there comes a point at which ballistic walking is no longer practical. The muscles are doing most of the work so the economies provided by ballistic walking no longer apply. Moreover, the application of muscle power enables the animal to propel itself forward and float momentarily between steps – the suspended phase – which effectively increases stride length. At this point, a biped will abandon walking and begin to run, and a quadruped will begin to trot.

With respect to energetics, walking and running are radically different gaits. Whereas a walking biped falls forward under gravity, a running biped propels itself forward by applying muscular (i.e. metabolic) energy to its leg-levers. Running speed can be raised by increasing stride rate, stride length, or both. Stride rate is increased by swinging the legs faster than their normal frequency (by applying additional muscle power to the legs) and by bending the legs (shortening their length) during the recovery stroke when the feet are off the ground.8 Stride length is increased by introducing a suspended phase: a running or trotting animal will ‘leap’ from one step to the next and ‘float’ forward momentarily between steps when both feet are off the ground. The suspended phase is the characteristic dynamic state of running. But the application of muscle power to the legs in order to increase stride rate and stride length requires metabolic input and naturally incurs an oxygen debt. Hence, a walker will always outdistance a runner; the latter will eventually ‘run out of gas.’

Gravitational potential energy is effectively wasted when an animal runs or gallops.9 Nevertheless, a vertical component is required to elevate the animal high enough off the ground to enable it to move its legs forward during the suspended phase. In suspended gaits, the vertical component is equal to body weight; the animal’s center-of-mass remains at a relatively constant elevation above the ground. If, however, the vertical component exceeds body weight, the animal will be propelled vertically as well as forward: the center-of-mass follows a parabolic ballistic path between footfalls. When this occurs, the animal has shifted to an aerial gait, i.e. hopping in bipeds, and bounding or pronking in quadrupeds.

In many respects, hopping is a blend of walking and running; it combines the best of both worlds. Like walking, it converts the gravitational potential energy acquired at the height of each jump into the kinetic energy of forward motion. (In specialized hoppers, such as kangaroos, much of this gravitational energy is converted into elastic energy stored in tendons upon impact, and then converted into kinetic energy during the next power phase.10 More on this in the next chapter.) Like running, hopping employs a suspended phase (or, more accurately, an aerial phase), with both feet off the ground, in order to increase stride length. However, this protracted aerial phase reduces the duty factor (i.e. the fraction of each step cycle when the feet are on the ground) and therefore requires a reduction in stride rate that, as in walking, approaches the natural frequency of the limbs; the limbs swing leisurely back and forth between footfalls. The reduction in stride rate is more than offset by the enormous increase in stride length.

But hopping is also quite different than walking and running. Walking and running are symmetrical gaits: footfalls alternate – first one foot, then the other – to ensure stability and balance. Hopping, however, is an asymmetrical gait and footfalls are concurrent which permits the two legs to apply their power simultaneously. This has two benefits. First, it minimizes lateral displacements in the center-of-gravity and helps maintain inertial stability during the aerial phase when the feet are off the ground. It also allows the animal to land squarely on both feet in preparation for the next step. Second, having both legs kick simultaneously creates a much more forceful power stroke. Thus, whereas a running biped must apply a downward force that is approximately equal to body weight, a hopping biped can apply a force with no real limit, and well in excess of body weight.

For obvious reasons, aerial gaits are generally limited to small, lightweight animals such as birds, kangaroo rats, squirrels and dik-diks. (The one notable exception, the kangaroo, is discussed in the next two chapters.) Because aerial gaits require a vertical component that exceeds body weight, only the very smallest and lightest animals have the requisite power (relative to body weight) to propel their bodies off the ground.

This rather lengthy analysis of tetrapod locomotion helps explain why the Apollo astronauts abandoned walking and running in favor of skipping and hopping. In reduced gravity, the decrease in gravitational potential energy requires a corresponding decrease in kinetic energy and hence a reduction in forward velocity. Reduced gravity also makes the limb-pendulums swing more slowly: "at reduced gravity, such as on the surface of the Moon, the period of the system increases and the step frequency correspondingly decreases."11 Accordingly, walking speed on the Moon is much lower than it is on Earth and does not exceed 2 km/hr.

The reason that running on the Moon proved so difficult is less obvious but is still basically the same. The forceful application of leg power in the running gait not only propelled the astronauts forward but also launched them high off the surface, which effectively disrupted the rhythm of their normal symmetrical gait. In other words, because of their high stride rate, the astronauts’ legs and feet were positioned for the next step before their bodies had floated back to the surface. In reduced gravity, therefore, the aerial hopping gait was doubly beneficial: it enabled the astronauts to take advantage of their high power-to-weight ratio and permitted a lower stride rate as well.



The Affect of a Gravity Reduction on the Evolution of Animal Locomotion
What affect, then, would a gravity reduction have on the evolution of tetrapod locomotion? Dimensional analysis indicates that a gravity reduction will lower the speed of gait transition and thus enable animals to shift to higher gaits at lower speeds. At the same time, a reduction in gravity will tend to favor lower stride rates. This suggests that when shifting from a walk to a higher gait, animals may bypass the suspended gaits (running, trotting and galloping), which employ high stride rates, and go directly to aerial gaits (hopping, bounding or pronking) for which a high stride rate is not necessary. The reduction in body weight would make aerial gaits all the more attractive. The experience of the Apollo astronauts supports these expectations.

The astronauts, of course, were already bipedal when they went to the Moon. Their morphology was such that shifting to a bipedal hopping gait required merely a minor change in behavior. But early archosaurs were quadrupeds; the shift to an obligatory bipedal gait involved fundamental changes in body structure. In the next chapter, we will discuss archosaur locomotion and limb mechanics and the possible role played by a gravity reduction in the evolution of archosaur locomotion and morphology.


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1 Margaria, 1976.

2 Alexander, 1982a.

3 Alexander and Jayes, 1983.

4 Hildebrand, 1985.

5 Alexander, 1982b; Bennett, 1985.

6 Margaria, 1976; Alexander, 1982b; McMahon, 1984.

7 McMahon, 1984.

8 Gray, 1968.

9 Margaria, 1976.

10 Dawson, 1977.

11 Margaria, 1976; see also McMahon, 1984.

I am pleased that you have finally found a source worthy of discussion.

This still does not solve the fundamental problems of reduced gravity on the environment - lower atmospheric pressure, the change of atmospheric composition, the fact that its predictions about dinosaur locomotion are not borne out by fossil tracks, and, of course, the catastrophic loss of the moon.

These three atricles collectively represent a SINGLE interesting source (all were pulled from various portions of the same page) but they by no means prove the thesis due to their inability to address these fundamental issues. It also fails to offer up any plausible mechanism by which the earth's gravity could have shrunk during the Triassic and then expanded in the Jurassic; it simply asserts that earth's radius was different.

Therefore, while it raises some interesting questions, I still hold that the evidence for such reduced gravity is lacking.

-Pilgrim

Upon further reading, I must again raise the issue of the validity of the sources used in this article. Some are quite good and respected; however, much like the previous article, there is no single source sighted which is less than fifteen years old. Many deal with the issue of the warm blooded/cold blooded dinosaur debate, in which enormous strides have been made in the past decade and a half. Furthermore, modelling techniques for dinosaur gait, posture, size, and mass have likewise undergone considerable revision as technology improves.

While the author here clearly displays a willingness and, indeed, an eagerness to present a firm argument, the use of old sources remains a point of contention. While the older source material is by no means useless to a modern argument, the failure to address more current source material is a severe handicap as it ignores the numerous strides made in the field since the source books were written. This, combined with my earlier comments as to the failure to address the more fundamental problems with the hypothesis, lead me to conclude most firmly that the author's position cannot be validated.

-Pilgrim

vulcanism on a cataclysmic scale can change the earth's gravitational field as was proven during the Mount Loa eruption.. It is now suspected that the earth has been subjected to numerous cataclysmic seismic events thru its existance and these events may have taken place at regular intervals. But where is the ground zero for these events? was it the earth's molten core suddenly becoming unstable and venting out thru the mantle and crust thus creating massive tectonic shift and crustal displacement? or was it violent tectonic plate shift? We know that silicon is being drawn from the crust and mantle to the core and perhaps being used as fuel. Is this extraction of material occasionally excessive creating instability within the molten core?

Mount Loa gravit shift: Gravity Changes on Mauna Loa Volcano

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"Johnson, D.J., Gravity changes on Mauna Loa Volcano, in Mauna Loa Revealed: Structure, composition, History and Hazards, Geophysical Monograph 92, edited by J.M. Rhodes and John P. Lockwood, pp. 127-143, AGU, Washington, D.C., 1995.

Copyright 1995 American Geophysical Union. Further electronic distribution is not allowed.

Order the whole book directly from AGU. This 360-page volume contains 20 articles about Mauna Loa.


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Abstract. Gravity observations made on Mauna Loa Volcano Hawaii, before and after the March 25-April 14, 1984 eruption indicate that a magma reservoir, centered 3630200 m below the summit area, lost 136(50)x10^9 kg of magma mass during the event. Comparison of the reservoir mass loss figure (M) with the volume change by surface subsidence of the edifice (Ve) gives M/ Ve=2033 kg/m^3, consistent with the ratio predicted for magma withdrawal from a reservoir containing degassed, CO2-poor magma. The net reservoir mass loss is insufficient to entirely account for the mass of erupted lava and dike intrusion. A proposed explanation is that a pulse of magma flow from depth, concurrent with the eruption, may have replaced reservoir magma lost to eruption. With this model, magma resupply to the shallow Mauna Loa reservoir is episodic and is associated with eruption; during repose, extensive CO2 degassing and a low rate of magma resupply minimizes the CO2 content of stored reservoir magma.



INTRODUCTION


Accelerating rates of seismicity and ground surface displacement observed at Mauna Loa Volcano led to a published statement in September 1983 of an increased probability of eruption within the following 2 years [Decker et al., 1983]. Baseline gravity observations on Mauna Loa were made February 13-14, 1984 in anticipation of the eruption. Fortuitously an eruption began on March 25 at 01:25 HST [Lockwood et al., 1985] within just 6 weeks of the initial gravity observations. Additional measurements were begun 8 hours after the first sighting of lava, and continued at intervals of 1-6 days for the duration of the 3 week eruption. Analysis of these data give a unique perspective on how Mauna Loa works.

A classic view of the eruptive behavior of Hawaiian volcanoes is that they contain a shallow magma reservoir, located below the summit, that gradually fills with mantle-derived magma during repose. Then, on eruption, previously stored magma is rapidly expelled from the reservoir to the surface or into rift zone intrusions [Dzurisin, et al., 1984; Decker et al., 1983]. This view is reinforced by observation of surface uplift during periods of repose and subsidence of the edifice during eruption, indicating filling and draining of a subsurface magma storage zone.

An unresolved issue of the 1984 eruption is a disparity between the volume of edifice contraction and the volume of erupted lava [Dvorak et al, 1985]. Previous estimates of the volume of edifice collapse are 110x10^6 m^3 [Okamura et al., 1984], 100(30)x10^6 m^3 [Lockwood et al., 1985], and 55(15)x10^6 m^3 [Dvorak et al., 1985]. Approximately 220x10^6 m^3 of lava, which has an estimated density of 2000 kg/m^3, reached the surface during the eruption [Lipman and Banks, 1987]. This is equivalent to 170x10^6 m^3 of magma with density 2600 kg/m^3 - still more than the volume of collapse. Consider also that a significant volume of magma was delivered to the inferred 22 km-long intrusive dike that bisected the summit and rift zones. Perhaps 75x10^6 m^3 of magma (dike roughly estimated 0.75 m wide, 5000 m high, and 20 km long) ended up stored within the rift zone dike. The total of dike and lava flow volumes gives 245x10^6 m^3, far in excess of the subsidence volumes given above.

Okamura et al. [1984], states that the volume discrepancy between subsidence and erupted lava might be due to: (1) eruption of magma stored within the rift zone since the previous eruption in 1975, (2) subsidence restricted by crustal rigidity, and (3) vesiculation of stored reservoir magma. The first process may be minor, as geochemical analyses of 1984 lava samples presented by Rhodes [1988] do not indicate a significant proportion of rift zone-derived lavas. The remaining two processes are shown by Johnson [1992] to be important at neighboring Kilauea Volcano during a recent phase of frequent, low-volume eruptions. The idea is that the shear strength of the edifice limits the amount of downward sagging of the crust overlying the draining magma reservoir, while the space left by the expelled magma is claimed by decompressional expansion of magma and CO2, as well as CO2 exsolution.

Dvorak et al. [1985] proposed that additional magma reservoirs may also have contributed to the eruption, explaining limited subsidence with respect to the volume of lava observed at the surface. Such reservoirs may have been beyond the perimeter of the geodetic network, or possibly located deep enough that surface displacement was not detectable.

Johnson [1992] presented theoretical arguments and a suite of gravity and geodetic observations from Kilauea Volcano that show that it is not strictly necessary for the collapse volume to equal the volume of magma removed. This is because the volume change observed at the surface is the sum of the volume change due to removal of mass (i.e. magma), bulk compression of the magma resident in the reservoir, volatile (mainly CO2) compression, exsolution, and migration, and lastly volume change due to density redistribution of the crust. For example, while magma is being removed from the reservoir during eruption, decreasing internal pressure causes exsolution of CO2 plus volumetric decompression of exsolved gas and magma. All of these factors mitigate reservoir contraction [Johnson, 1992, equation 8]. Concurrently, the volume change of the edifice is 1.5 times the change in size of the reservoir cavity as a consequence of the crustal density change associated with deformation [Johnson, 1992, equation 9, with a Poisson's ratio of 0.25 typical of crustal material]. While the processes internal and external to the reservoir have opposite influence on the ratio of edifice volume change to internal reservoir mass change, Johnson [1992] shows that at Kilauea the internal processes may at times dominate. Comparison with observations from Kilauea are useful in the analysis of Mauna Loa.

The purpose of this paper is to use the gravity data collected before and after the 1984 eruption to examine the observed volume disparity between edifice contraction and lava flow at Mauna Loa. The utility of the gravity method with respect to monitoring a subsurface magma reservoir is that it is sensitive to mass change, whereas geodetic methods (such as leveling, tilt, trilateration, GPS) detect surface displacement only. An apparent volume change detected by geodetic methods may reflect expansion/contraction of existing crust and reservoir material as well as addition/ subtraction of magma from the system. Analysis of gravity data may thus help sort out these kinds of volume ambiguities. The first goal is to determine the actual mass of magma removed from the known summit magma reservoir and determine if this amount is sufficient to explain the mass of the eruptive products. Secondly, the relationship between mass removed and the resulting summit collapse will be analyzed to learn more about the shear strength of the edifice and the compressibility of the magma reservoir itself.


THE 1984 ERUPTION


Mauna Loa, like neighboring Kilauea Volcano, contains a central subcaldera magma reservoir which is recharged by magma during repose [Decker et al., 1983; Rhodes, 1988]. With time, this filling produces a measurable distention of the edifice. Analysis of surface displacement patterns prior to the 1984 eruption by Decker et al. [1983] placed the region of filling roughly 3 km below the southeast rim of the summit caldera Mokuaweoweo.

The events of the March 1984 eruption have been described by Lockwood et al. [1985]. The first phase of eruption saw the propagation of an eruptive fissure to the floor of Mokuaweoweo at 01:25 HST on March 25. Over the next several hours the eruptive fissures migrated out of the caldera, into both the southwest and the northeast rift zones. By 07:00 HST fountaining was restricted to a portion of the upper northeast rift zone at an elevation of 3700 m. The eruption migrated down the northeast rift zone through the first day in a series of jumps; as new fountains appeared downrift, activity farther uprift waned. At 16:41 HST venting began near 2900 m elevation and continued in that vicinity for the remainder of the 3-week eruption.


Observations


As the eruption progressed, subsidence of the ground surface above the reservoir was monitored by frequent geodetic surveys [Lockwood et al., 1985; Dvorak and Okamura, 1987]. Subsidence is attributed to magma removal from the reservoir; some of this magma was intruded as dikes into both of Mauna Loa's rift zones while a large volume was erupted to the surface [Lockwood et al., 1985]. Locations of geodetic and gravity observation sites on Mauna Loa are shown in Figure 1, and measured tilt and leveling changes are illustrated in Figure 2. The area of maximum subsidence, as indicated by the orientation of ground tilting and the vertical movement of leveling benchmarks, was located southeast of Mokuaweoweo Caldera (Figure 2), at a location similar to the area of previous uplift [Decker et al., 1983].

Leveling surveys to third-order standards were done on June 27, 1983 and May 7-8, 1984 [Okamura et al., 1984; Dvorak, et al., 1985] on a route that traverses the summit area of Mauna Loa. A maximum subsidence of 574 mm relative to site ML7 was measured along the southeast rim of Mokuaweoweo caldera. Most likely neither end of the leveling traverse was distant enough from the apex of subsidence to escape subsidence. An estimate of the amount of subsidence of the reference benchmark, or "float" of the level line, will thus be made in the following section.

Occupation of the entire inventory of spirit-level tilt sites located around the rim of Mokuaweoweo caldera and the upper slopes of Mauna Loa was done between July 12-August 24, 1983 and April 23-27, 1984. These data are considered to have a precision of 12 urad [Dvorak and Okamura, 1987]. The changes (Figure 2) define an inward tilt, towards a common focus at the southeast rim of Mokuaweoweo.

A complete survey of gravity sites C1, ML1, ML3, and ML8 was done on February 13-14 and May 2, 1984. Gravity readings are corrected for tidal effects [Longman, 1959]. Calibration functions with linear and periodicterms were determined from calibration ranges and applied to the data. Gravity data were reduced using JOSH v. 3 [unpublished, 1994] which inputs data from an unlimited number of individual runs and calculates a least squares solution of second-order polynomials to approximate time-dependent changes in the reading level of the gravimeters (gravimeter drift), offsets of the reading level (tares) as needed, and relative gravity g at each surveyed station. A run comprises a sequence of gravity readings made using a particular gravimeter. Separate runs, which may be made during the same day or on multiple days, are combined to make a survey. In this study, gravity surveys were done using two gravimeters run over closed loops between the base station SAS and monitoring sites using helicopter transport. The February survey comprised two loops over both days and reduced values have standard errors of from 8 to 12 Gal. The May survey comprised three loops on the same day and values have std. errors of about 7 Gal. Observed gravity changes between the complete surveys, bracketing the 1984 eruption, are given in Table 1 along with corresponding elevation changes.

During the course of the 1984 eruption gravity measurements were occasionally made at station ML1 to record the chronology of gravity change. These surveys were accomplished by closing two loops between SAS and ML1 with two gravimeters. The exception was the March 26 survey, when only one loop could be completed because helicopter support was unavailable. A time plot of ML1 gravity is given in Figure 3. First impressions of the ML1 data are that the pattern of change closely follows the exponentially diminishing rates of tilt change and horizontal strain [Lockwood, et al., 1985]. Also, the positive sign of the change is consistent with a strong contribution of an increase due to the decreased height of the observation point (the free-air change), which is both greater and of opposite sign to the component due to the subsurface magma mass loss.

As a part of the gravimeter calibration procedure, a gravity tie was made between base station SAS and GC7, located 16 km north of SAS on the lower slope of neighboring Mauna Kea Volcano. Measured gravity change at SAS between pre- and post-eruption surveys on February 21 and May 15, 1984 is .611.2 Gal relative to GC7. The absence of a significant gravity change at SAS diminishes the probability that this station moved up or down.


REVIEW OF MODEL EQUATIONS


Model for Deformation from Reservoir Volume Change


The principles of deformation and gravity analysis presented here are a foundation for the analysis that follows. These generalized equations enable inferences to be made about the nature of mass and volume changes at depth associated with the gravity and surface displacement anomalies. However, because of the dramatic topography of Mauna Loa which is not anticipated in the derivation of the principles, they should be used with some caution.

Deformation resulting from the inflation and deflation of the summit reservoir of Mauna Loa is simulated using a model first applied to volcanology by Mogi [1958]. This model gives deformation of an elastic body having one free surface as a function of pressure change within a spherical cavity inside the body. Surface uplift is given as


(1)


where Z is the source depth, X is the radial distance of the point from the source epicenter, P is the pressure change, Vr is the volume of the source and and u are the Poisson's ratio and shear modulus of the body [modified from Hagiwara, 1977]. The change in radius, a, of the source of radius a is given by Hagiwara [1977] as:


(2)


As long as a is large relative to a, the volume change Vr of the spherical source may be estimated as the surface area of the sphere (4a2) times the change in radius (equation 2), or


(3)


[Johnson, 1987, with volume relation 3Vr/4=a3 substituted]. Integration of equation (1) over the surface of the body gives


(4)


which is the volume change of the body due to displacement, h, of the free surface. Division of equation (4) by (3) gives


(5)


which is the volume change of the body as a function of volume change of the imbedded spherical source. Notice that for a Poisson's ratio of 0.25, typical of crustal rock, equation (5) predicts dilation, or expansion, of the crust equal to 50% of the volume change of the source. The volume of surface uplift would equal the volume change of the source only if the Poisson's ratio were 0.5; media with such a Poisson's ratio include rubber and fluids.

To the gravity modeler, the significance of crustal dilation predicted by equation (5) is the implied density change, which has a direct effect on the measured gravity field. The variation in density at a point located within the body at depth D below the surface is


(6)


where Z is the depth of burial of the spherical source, and X is the horizontal distance between source and observation point [modified from Hagiwara, 1977]. Notice, again, that equation (6) predicts a changing density distribution within the body, except in the special case that =0.5.

To the volcanologist seeking to estimate the magma budget of a volcano by monitoring surface uplift, the significance of equations (5) and (6) is that a portion of the volume of expansion or contraction of a volcanic edifice is the consequence of crustal density change, not magma accumulation. Analyses that have assumed that one unit volume of uplift is equivalent to one unit volume of reservoir magma accumulation (of which there are many) are thus in error.

Model for Gravity Change from Reservoir Volume Change


The problem of modeling gravity change associated with an altered density distribution of the crust has been treated by Hagiwara [1977], Rundle [1978], Walsh and Rice [1979], and Savage [1984] for the case of a spherical source. The consensus is that deformation of the crust caused solely by the volume change of a spherical source does not produce a net gravity change. Previous gravity studies of Kilauea Volcano [Jachens and Eaton, 1980; Dzurisin et al., 1980; Johnson, 1987; Johnson, 1992] have made the explicit assumption that crustal deformation yields no gravity change. (Some gravity change, however, is expected due to related vertical movement of the observation site with respect to the mass of the Earth plus any change in the mass of magma contained within the source.)

It is useful to review some details of the Hagiwara [1977] study of deformation-induced gravity change for a spherical source model. Hagiwara [1977] separated the deformation into three components and solved the gravity change for each separately: (1) the volume change of the spherical source cavity, (2) the surface uplift, and (3) the crustal density change. I have modified the original equations to reduce the number of elastic constants to only the Poisson's ratio and to use a source volume change term Ve rather than a pressure change.

The component of gravity change due to the volume change Vr of the source is


(7)


where c is the crustal density. The value of is 6.67x10-11 Nm2kg-2. Included is an allowance for mass, such as magma, of density 0 which replaces displaced crustal material. If no matter moves into or out of the source to balance Vr, then 0=0. The magnitude of (7) is essentially the gravitational attraction of a spherical shell that represents the mass gained or lost by a change in diameter of the source. For example, expansion of an empty reservoir would result in a spherical shell where empty space of density 0=0 has displaced crustal rock of density c. This would give a negative gravity change component.

The component of gravity change due to surface uplift is


(8)


To illustrate this component, consider a gravimeter fixed in space above the Earth's surface. An increase in Vr results in surface uplift - uplift moves mass upward and displace air with a thin layer of crustal material. This layer has an area equal to the uplift anomaly, and a variable thickness depending on the local uplift. The gravimeter located above the uplifted area would record a gravity increase due to this component of deformation.

Finally, an outcome of deformation is variation in the density of the crust within the deformed region. The gravity change component due to density variation is


(9)


Notice that only in the unrealistic case of a Poisson's ratio of 0.5 does the density change term vanish. Otherwise, for a typical Poisson's ratio of 0.25, the effect of this term for inflation, as an example, is a gravity decrease corresponding to the net density decrease of the deformed crust.

Considering only the deformation-induced components of the gravity change (by setting 0=0 to reflect no inflow or outflow of matter from the source sphere), the uplift component (1) is exactly offset by the sum of the source volume change and crustal density change components (02). In other words, the net gravity change due to deformation caused by a point source is nil as stated by Hagiwara [1977], Rundle [1978], Walsh and Rice [1979], and Savage [1984].

The residual gravity change, g' using the notation of Johnson [1992], is defined as the sum of the above components, including the mass of material flowing into or out of the source, but not including the free-air change. Summing (7), (8), and (9) above gives............"

for the rest go to this site:http://www.volcanic.com/library/agumonograph/agumonograph.html

yes its interesting isnt it? a creature with a 12m wingspan wieghing perhaps upto 100kilos (we cant really get an accurate wieght at present) could fly as perfectly as the Albatross with a body weight of 8-12kilos and a wingspan of 3.5metres.
There are several problems here, firstly, the Abatross has feathered wings and a shoulder lock. The feathers allow the wings to flap up and down thus creating lift. A wing composed of a skin membrane, however thin,having a surface area of perhaps 8sq metres,could not be made to flap effectively because the air pressure above the wing on the upward stroke cannot be relieved which means simply that the creature would require enormous wing muscles....which we know it didnt have. The other problem is that the creature in question has not been found to have a shoulder lock - a sheet of tendon - that allows the wings to be locked in position for gliding.

Firstly, the creature in question almost certainly did not weigh 100 kg, which is a very high estimate. Indeed, if the creature did weigh 100 kg as you have suggested, and was able to fly in 20% reduced gravity (adjusted weight of approximately 175 pounds), then it almost certainly could fly in normal gravity with a more accurate weight estimate of 70 kg (roughly 155 pounds). Secondly, you are assuming that the wings are covered in skin and skin alone. This is not the case. Evidence suggests that Pterosaurs were covered in fur. Fur can act in much the same way as feathers (though not as effectively), as is amply demonstrated in bats, some of which have wingspans in excess of 2 meters - smaller than an albatros, certainly, but clealry quite large in their own right.

The lack of evidence of a shoulder lock is not surprising given that tendons do not fossilize. However, even if the shoulder lock was absent, there is no question - even under your own model of a lighter gravitational pull - that the creature did in fact glide. The shoulder lock is an energy-saving mechanism, but gliding without it is by no means impossible, even under standard gravity.

As for the other article, it is my understanding that the gravity in the vicinity of Mount Loa was reduced, as a result of the eruption. It does NOT claim that worldwide gravitational force was changed, and indeed, seems to state quite the opposite, that the change was entirely due to magma displacement and was strictly local. Such localized changes are predicted by existing models of volcanism, and is not evidence that volcanism could account for a worldwide reduction in gravity. While gravity at Mount Loa was reduced by a small amount, the lost mass did not vanish, it was simply redeposited elsewhere.

Even if volcanism could account for a major reduction in worldwide gravity, a point which I contest, it still cannot account for the other difficulties related to a reduced gravity, which I have already mentioned numerous times and feel no need to repeat again.

-Pilgrim

"Quetzalcoatlus was a flying reptile whose wing-span was just under 36 feet wide (10.96 m). It was the largest flying animal ever found. It had hollow bones, was lightly built, and had a small body. Even though it was very big, it probably weighed only about 300 pounds (135 kg). It had toothless jaws and a long, thin beak. The neck was 10 feet (3 m) long. The legs were over 7 feet (2.1 m) in length, as was the long head. "
for the rest go to this site or any one of a million others that all seem to agree that the weight of this creature was in the region of at least 100kgs or more.
http://www.enchantedlearning.com/subjects/...alcoatlus.shtml

Now if you go to this site you will see clearly the difference between the bone structure of a Bat's wing and the wing of a Quetzalcoatlus. The Bat's wing is structured entirely differently and is designed to collapse or fold on the upward stroke very rapidly.......now if you observe the wing of the Quetzalcoatlus you will see that the bone structure could not possibly have allowed this considering the surface area of the wing. Dont forget that a Bat's heart beat can increase from 100 beats a minute at rest to over 1,000 beats a minute when in flight. Is it feasible to assume that the much larger heart of the Quetzalcoatlus would act in the same way?
Whether or not the wing was covered in fur is irrelevant as fur over a skin membrane would would only have the effect of keeping it insulated.
The wing of the Quetzalcoatlus simply was not designed to operate in the same way....so if the wing could not fold on the upward stroke rapidly, then how could it have possibly flown?
this site shows the difference between the wing structure of a Bat and a Quetzalcoatlus very clearly: http://science.howstuffworks.com/bat1.htm

So far as the Mount Loa gravitational change is concerned: yes the effect was localised to the immediate vicinity of the eruption which is as one would expect. But what would the effects be should a series of eruptions on a cataclysmic scale occur at the same time over the entire surface of the earth?
What changes would be made to the shape and size of the earth and its molten gravity generating core from an event that not only releases vast quantities of magma onto the surface but also vast quantities of water from beneath the crust and mantle?

Now ...so fas as the atmosphere is concerned: we know that the atmosphere is retained in place by gravity. We also know that oxygen levels have increased at intervals in the prehistoric past. A 20% reduction in the earth's gravitational field would not be sufficient to allow the atmosphere to leak out into space. It would need at least a 50% drop, and any small loss of atmosphere would be more than compensated by those increases in oxygen levels.

I am well aware of how a bat's wing is different from a pterodon, I simply posed it as an example of how fur can aid in flight. As this debate is growing tiresome I will leave it to someone else to discuss the flight properties of pterodons, particularly since the arguments you seem to be posing are equally problematic under reduced gravity. I still hold that the generally accepted weights of these creatures is nowhere near 100 kg, and if necessary, I can provide sources.

As for the Mount Loa question, you appear to be laboring under the misaprehension that the gravity was reduced absolutely - that is, that a small amount of gravity simply vanished. It did not. A large amount of gravity-producing mass was spewed out over a wide area. In other words, the gravity did not go away, it simply moved to a different place. Earth's overall gravitational pull was not changed. Thus, a global volcanic cataclysm would not reduce the earth's gravity because it cannot reduce the earth's mass.

As for the increased oxygen levels and atmospheric change, I am not suggesting that our atmosphere would vanish entirely. However, reduced gravity will cause lighter gasses to leak out, substantially changing the atmospheric composition. Oxygen is one of the lightest gasses present in any great quantities and would among the first to be lost.

I have yet to see a remotely plausible explanation as to how the earth's gravity could be changed; of how the ensuing environmental catastrophe could escape detection; or of how the earth's moon could possibly exist in the stable orbit it now does were such radical changes to have occured a scant 65 million years ago. Given these massive failings, I can only conclude that there is nothing to this theory, that science was right to reject it 70 years ago, and that its continued rejection is fully warrented.

However, it seems clear that this debate will continue despite all logic, and thus, my continued refutations are falling upon deaf ears. If anyone has anything significant to add - perhaps something addressing the numerous glaring failures which I have mentioned - I will be glad to examine their evidence in turn, however, I have no intention to spend any more of my time researching an issue which was definitively settled in the first half of the previous century.

-Pilgrim

the moon is not in a stable orbit....its actually moving away from the earth. You keep claiming that fur aids flight ...which is just crap. You obviously didnt read the article I posted re Mount Loa....if you had you would not be calling me a liar. The first dinosaur remains were only discovered in the latter half of the 19th century and its a science that has barely developed. There is a great deal of evidence to support the theory of cataclysmic changes in the earth's structure and environment....the k-t extinction being one such example.

Since you have not provided me with anything worth discussing, I will limit myself to two points. The first is that I did not call you a liar, I said I believed you were mistaken, which is hardly the same thing (and yes, I did read the article, and I stand by my assessment). The second is that we are now living in the 21st century, not the 20th. I also mentioned that science discarded the expanding earth theory 70 years ago, which would be the first half of the previous century and NOT the first half of the 19th century.

-Pilgrim

The fact is that we have only began to understand the force of gravity and outer space, and there is a billion times more knowledge that we don't know than that we know.So we cannot draw conclusions on wether gravity was diffrent in the past or not, after all we berely know what causes gravity, but probbably gravity has something to do with mass after all jupitar is the largest planet in our solar system has the shortest day in the solar system ,about 16 hours if memory serves.

The MOON has no atmoshere so any meteore that hits it becomes a part of it's mass and it gets hit multiple times a year. Now imagine afer million's of years it would get covered many times with meteores and it's mass would have probbably incresed and so it's gravity would have probbably incresed as WELL!!!!

even if the moon keeps getting bigger there is a low chance that it's gravity will get big.The Moon core is so small and made mostly in solid iron.

as for the topic. maybe in the earlier days of the earth which the dinosaurs have flew and lived. the earth gravity was still in it's early stage that it's still weak compared today.

Hello everyone, it seems I'm late in joining this paleogravity discussion. First off, I will say that Fantazum raised the question in his very first entry (Oct 25, 2005) that:



You have realized that a CONTRACTING Earth, which shrinks in size but retains its same mass will cause the gravity felt AT THE SURFACE to INCREASE. I have had the toughest time getting people to understand that. Have you ever been to dinotheorist.com? I know you said that you hadn't heard of Bakker till this discussion and I quoted him a few times, so I guess you haven't. If you go to http://www.dinox.org and check out the "links to other sites" listed by Stephen Hurrell, that'll show you what pages have been out there for a number of years.



What reason do we have to believe that a contraction would be Earth-shattering? I am one paleogravity theorist who agrees with Bakker on the pace of the K-T extinction event. "thousands and even millions of years." (D. Heresies, pg 435) A contracting Earth could well fit the gradualist extinction model. Let me ask you this: does anyone refute that the interior of the Earth has cooled down and contracted since it congealed out of hot space dust, and was a flaming ball of magma? Hardly. So, we are talking about whether that, by the time animals appeared on land, the cooling and contracting process was completely finished for the rest of Earth's geologic history. Then, one might ponder whether the Earth one day will cool off inside to the point that its residual heat (or nuclear-driven heat, not that anyone even knows) will be gone, and how small (and dense) will the earth be then? Of course, scientists have considered all that, ruled on it, and projected the easily predictable effects into Earth's geologic future. Haven't they?

No, they haven't. It has always been assumed that the Earth settled into its current size and stayed that way for all practical purposes. EVEN THOUGH the K-T was right about the same time that the continents started drifting apart, as if there was a sudden need for their heavy granite plates to be more evenly distributed around the planet.

Fantazum posted an article about a localized reduction in gravity observed in connection with an eruption in Hawaii. I think the more significant point about this "hot spot" volcano is WHERE it is. Those granite continental plates have a long way to go before they balance themselves on their planetary sea of tectonic basalt. It is gravity which would dictate that new land should form in the middle of the world's largest ocean void.

An Earth contraction event would not have to occur all on one day, and be "cataclysmic." It could happen over an extended period of time, and there would be an increase in the frequency of the same things we have now: sea floor subduction, volcanism, and earthquakes. It would have to occur in periodic, accellerated phases to fit what happened at the end of the Cretaceous, AND the Jurrassic. Perhaps I'm in a chatroom full of catastrophists and I don't know it yet.

Pilgrim said something about atmospheric pressure at reduced gravity; that it would be thinner, and that the increased gravity would not affect specialized fliers like pterodactyls because it would give them thicker air in which to flap or glide. Is there a cost-benefit ratio so that we know how much the flier weight/atmospheric pressure issues would be mutually cancelling?

Anyway, there's one thing that I know would offset the change in atmospheric pressure from lower to higher ambient gravity: the change in ratio of O2 to N2. Even though that ratio has changed from the Mesozoic till now, I think that (as with living ecosystems) nobody has even considered O2/N2 to be gravitationally defined, even though the trend has been exactly what we would expect to see. O2 is a little heavier than N2. Lower gravity would mean a higher retention of the heavier gas in the atmosphere. I'm sure that the CO2 atmosphere of Mars helps it to have more of an atmosphere than it would if oxygen was all there was over there. Heck, it doesn't have the gravity to retain oxygen. What if algae were ever to evolve on Mars, and convert its CO2 to oxygen? Then we would have an even tougher time when we go to colonize the place, having to build shelters that can hold up in a total vacuum. Say -- maybe algae did evolve on Mars and that's exactly how it lost its atmosphere. Naah!

Anyway, somewhere between the gravity level we now experience and the gravity that would allow dinosaurs to float around like party balloons, a lot of questions are answered and everybody can be right.

Dinosaurs appear to have been too heavy to support their body weight... They appear to be lower-gravity animals. These are equivalent statements, worded differently.

There seems to be no 'evidence' that dinosaurs were too big to support their own weight in a 1g Earth, as this article indicates.

Without the 'evidence' of dinosaurs size being an issue it would also seem the idea that gravity was less at the surface of the Earth due to it being larger is unsupported as well.

Seems anatomists, physiologists and paleontologists do not agree with you. Of course we can always go with the famous "I reject your reality and substitute my own!"
I find that often works best when attempting to make up your own histories.

"That article" specifically refutes Ted Holden's arguments for lower-gravity dinosaurs. That makes me so jealous. I think that my statements are just as worthy of intelligent critical feedback as his are! Oh, well.

very very interesting..........................

Gravity is one the most understood forces in science and is described by some the simplest and most elegant equations out there. It works everywhere in the universe the same, as has been proven by countless experiments, and acts exactly as we would expect. This why we can put things in orbit, send things to mars, describe orbits in massive detail and predict the flight of everything we catalog in space. The amount of mass the moon picks up from space debris is negligable and the earth picks up far, far more but it too is negligable in the scheme of things.

The earth always had the same gravity as it always had the same mass since the formation of the moon. By the time of the dinosaurs tidal effects were negligable as well. The reason insects and dinosaurs could grow so big is a combination of an extremely oxygen rich atmosphere and a level a flora that is basically inconcievable today but well evidenced by the fossil record and amounts of coal in the earth's crust.

Here's something you might find interesting:



http://biology.plosjournals.org/perlserv?r...al.pbio.0040248

So how big would dinosaurs be now if they were still around? And if humans lived at the time of dinosaurs would we too be bigger?

I think they were pushing the limit already, so I doubt if they would be any larger.

I'm not sure you can make a direct comparison between dinosaurs and mammals, you can't even make a direct comparison between dinosaurs because they were so diverse, but I think if the model for inertial homeothermy is correct, our largest land mammals may already be at their maximum size.

If I understand it correctly, should they get much larger their internal body temperature would be too high, and without a means of cooling they would perish.

Have I got that right ?

Of course, my arguments do not hinge upon mass homeothermy, nor upon a change of gravity of the Earth as a planet. The surface gravity of a planet can increase due to core cooling and contraction, leaving the lunar orbit alone -- as well as that of the Earth around the sun.



In a way, dinosaurs are still around. Birds and crocodiles share so many of their features that it could be said, "What was to stop birds and crocs from evolving into large, dinosaur-like land animals after the Cretaceous? It seems like they had their chance. But I know that in the case of birds, the largest species to evolve anywhere seem to have been only in isolated places to where the major mammal species could not swim: Madagascar, New Zealand, and South America before it was connected to North America. Why should that be?

Birds and crocodilians are doing the best job of representing dinosaurs that any animal can in today's gravity. Crocodilians spend much of their lives enjoying the benefit of the neutral buoyancy of fresh water. There are a few crocodilians which evolved the ability to live as land predators after the dinosaurs, proving that it was possible for them to do so. But by the same token, what stroke of bad luck kept them from rising to dinosaurian glory? My argument is that it wasn't bad luck at all. It is no longer "profitable" enough for a dinosaur-like animal to "make its living" as a large land animal -- at least, not against the contemporary mammal competition. The increase in surface gravity at the K-T caused the paradigm of what was profitable to go from being that which the dinosaurs had, to that which the mammals had.

If the gravity environment of humans today were to revert to Cretaceous levels, the death rates for obesity and circulatory problems would go down. Large-bodied, muscular people such as Arnold Schwartzenegger would be able to run farther and faster without their bodies overheating as quickly as in modern gravity. (This is also to address Shaftsbury, as lower gravity would help with the internal body heat problem.) If bringing home our dinner and defending our territories involved such primitive activities as bashing other organisms in our daily lives, and surviving famines, then evolutionary pressures would favor more muscled and chubby people in the succession of generations. But, we are so into using our minds and using tools that it is hard to say just how lower gravity would affect us.

http://www.associatedcontent.com/article/7..._the_earth.html

http://news.bbc.co.uk/2/hi/science/nature/1761407.stm

On another note of feeding quantity. I have always been under the impression plants grew at a faster rate in dinosaur times than today and bamboo type plants were more predominant.

http://www.ncsu.edu/news/press_releases/04_01/026.htm

“Research has shown that elevated carbon dioxide levels result in higher productivity, faster photosynthetic and growth rates, and greater rates of carbohydrate synthesis,” she says. “My work involves measuring how modern ginko trees react to Cretaceous-like atmospheres, and how the higher levels of oxygen and carbon dioxide affect the leaves’ nutritive value and digestibility. We’re also comparing these experimental ginko leaves with fossilized ginko leaves from the Cretaceous period to help verify our work.”

Oooh. Yer gonna make the global warming people upset with you!

http://www.msnbc.msn.com/id/7285683/

T-Rex blood was recovered and DNA testing was done.
Apparently they look like they could be related to birds, therefore they may have had the lighter mass allowing them to be so big.

Some are even thinking that dinosaurs have evolved out of their massiveness, and be