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Dinosaur size and our own growth


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#31    frogfish

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Posted 06 January 2007 - 12:11 AM

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Lions do consider Elephants viable prey and they hunt and kill them regularly

No, lions rarely attack elephants.

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#32    Mattshark

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Posted 06 January 2007 - 12:29 AM

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No, lions rarely attack elephants.

It had them doing so on the program, made by BBC Wildlife, the most reputable wildlife documentry makers around in a program by my personal hero Sir David Attenbourgh.
They attacked an adult African elephant in a "super pride" which apparently specialised in elephant hunting.

Edited by Mattshark, 06 January 2007 - 12:32 AM.

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#33    capeo

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Posted 06 January 2007 - 12:38 AM

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Actually the BBC series Planet Earth showed lions attacking a fully grown elephant at night and killing and eating it.


Doing a little research on this it turns out that a pride in Savuti Botswana have begun specializing in killing elephants.  That's something I've never seen before.  This is something only this pride does.  Here's an excerpt, I'm trying to find the actual full article:

"Over the 4 years, we observed a total of 74 elephants killed by lions, including eleven elephants in 1993, seventeen in 1994, nineteen in 1995, and 27 in 1996, suggesting an increasing hunting success rate. All the elephants killed, with one exception, were from breeding herds (females and young). The exception was an adult bull, previously wounded by another bull, who remained alive for several days before eventually being killed by the lions. The great majority of the young elephants killed were males, and two-thirds of the kills were of elephants in the age range 4-15 years, with highest hunting success achieved for elephants aged 4-9 years (Table 1). The animals killed were commonly on the periphery of, or straggling behind, the breeding herds, with nearly half killed more than 50 m away from the main herd. Hunts were less commonly attempted on calves which were under the age of 4 years, which remained more closely associated with their mothers. Hunting success for elephants older than 4 years apparently doubled from 33% (n = 9) in 1993 to 62% (n = 61) in 1996. Many attempts to kill adults bulls were made in
1996, when we saw lions attacking elephant bulls almost nightly although only one hunt was successful. All except one of the kills were made at night, and hunts occurred more commonly on dark moon nights than when the moon was bright."

I wonder what caused them to change up their hunting tactics?  Here's a bit about them with video of a kill:

http://darrennaish.blogspot.com/2006/11/gi...n-in-lions.html

Well, though usually unheard of, this pride are specialists in hunting lions.

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#34    frogfish

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Posted 06 January 2007 - 12:38 AM

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They attacked an adult African elephant in a "super pride" which apparently specialised in elephant hunting.

It doesn't mean all lions hunt elephants...Lions are very induvidualistic. There are a pride of "swamp cats" that hunt purely in the waters of the Okavango Swamp.

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#35    Mattshark

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Posted 06 January 2007 - 12:45 AM

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Doing a little research on this it turns out that a pride in Savuti Botswana have begun specializing in killing elephants.  That's something I've never seen before.  This is something only this pride does.  Here's an excerpt, I'm trying to find the actual full article:

"Over the 4 years, we observed a total of 74 elephants killed by lions, including eleven elephants in 1993, seventeen in 1994, nineteen in 1995, and 27 in 1996, suggesting an increasing hunting success rate. All the elephants killed, with one exception, were from breeding herds (females and young). The exception was an adult bull, previously wounded by another bull, who remained alive for several days before eventually being killed by the lions. The great majority of the young elephants killed were males, and two-thirds of the kills were of elephants in the age range 4-15 years, with highest hunting success achieved for elephants aged 4-9 years (Table 1). The animals killed were commonly on the periphery of, or straggling behind, the breeding herds, with nearly half killed more than 50 m away from the main herd. Hunts were less commonly attempted on calves which were under the age of 4 years, which remained more closely associated with their mothers. Hunting success for elephants older than 4 years apparently doubled from 33% (n = 9) in 1993 to 62% (n = 61) in 1996. Many attempts to kill adults bulls were made in
1996, when we saw lions attacking elephant bulls almost nightly although only one hunt was successful. All except one of the kills were made at night, and hunts occurred more commonly on dark moon nights than when the moon was bright."

I wonder what caused them to change up their hunting tactics?  Here's a bit about them with video of a kill:

http://darrennaish.blogspot.com/2006/11/gi...n-in-lions.html

Well, though usually unheard of, this pride are specialists in hunting lions.


Big meal and elephants have terrible night vision, it can support a large group and they may like the taste.


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#36    Mattshark

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Posted 06 January 2007 - 12:46 AM

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It doesn't mean all lions hunt elephants...Lions are very induvidualistic. There are a pride of "swamp cats" that hunt purely in the waters of the Okavango Swamp.

It does not mean all lions hunt elephants, but some do, that is all I was alluding to, I doubt elephants will be replaceing wildebeast or yebra on the lions diet anytime soon.

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#37    frogfish

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Posted 06 January 2007 - 12:47 AM

Like I said, lots of lion prides specialize yes.gif Diet can drastically vary from place to place...

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#38    Mattshark

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Posted 06 January 2007 - 12:50 AM

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Like I said, lots of lion prides specialize yes.gif Diet can drastically vary from place to place...

Over such a large range it is no suprise. You eat what is available around you, you only get pick when it is busy.

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#39    frogfish

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Posted 06 January 2007 - 01:08 AM

They are very opportunistic predators

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#40    fantazum

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Posted 12 January 2007 - 08:06 PM

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You're forgetting a major factor, and that's weight distribution.  Sauropods walked with their legs directly below their bodies with a long massive tail outstretched and had large flat feet akin to an elephants.  With a similar gait as an elephant the weight distribution would be just fine for walking through marsh land just as elephants have no problem waking through mud.  No matter what the weight so long as there is sufficient area to distribute you can get around it.  Take a pyramid for example, if you could concievably turn it upside down and balance it on its point it would drive itself into the ground.  Sat on its base, it has no problem.  Physiologically there is no issue with sauropods.  Paleontologists estimate the weights based on how much weight the bones could handle.
Even with poles melted the water wouldn't have close to covering most of earth land surface.  I can find you the actual numbers.
This period was exceeding lush, far more so than any period since, and there was no issue with food.  The abundance of food was a primary factor in their size.


Based on footsize of male Elephant weighing an average 8 tons: An 80 ton Sauropod would need a foot the base of which would need to cover 16 sq feet in order for it to traverse the same type of marsh as an Elephant of 8 tons.An Elephant misjudging the depth of a swamp become completely stuck if the depth of mud rises above the animal's knee.

According to you, food availability is key to size. In which case how come humans living in an environment of unlimited food availability do not increase in height? and of course we must not forget that for any animal species to attain unlimited growth because of unlimited food supply actually conflicts with evolutionary laws.

Should both poles melt sea levels would increase by an estimated 200 feet. Add all the ice locked up in glaciers in both hemispheres and that level increases another 4 feet. This would reduce land surface area by an estimated one third.

Picture of the footrpint of an elephant estimated to weigh 6 tons. http://jmason.org/watchcam/2002_May_in_Nep...t_footprint.gif

Picture of the footrpint from a Sauropod weighing an estimated 30 tons: http://www.utexas.edu/tmm/exhibits/trackway/index.html

You can see how the elephant's foot is designed to splay out and distribute the animal's weight, but not so with the Sauropod - even though there would have been 7.5 tons of weight on that one foot, there is no sign of splaying in fact it appears that the foot hardly has any weight on it at all.

Edited by fantazum, 12 January 2007 - 08:14 PM.


#41    capeo

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Posted 12 January 2007 - 10:01 PM

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Based on footsize of male Elephant weighing an average 8 tons: An 80 ton Sauropod would need a foot the base of which would need to cover 16 sq feet in order for it to traverse the same type of marsh as an Elephant of 8 tons.An Elephant misjudging the depth of a swamp become completely stuck if the depth of mud rises above the animal's knee.


See below, because I'm not sure how you arrived at those numbers but they don't jive with studies I've read.

Quote

According to you, food availability is key to size. In which case how come humans living in an environment of unlimited food availability do not increase in height? and of course we must not forget that for any animal species to attain unlimited growth because of unlimited food supply actually conflicts with evolutionary laws.


That doesn't conflict with evolutionary laws.  In truth that isn't thought to be the prevalent factor though.  The largest factor was predatory pressure from what I've been reading.  The food rich environment simply allowed for runaway growth.  We've never since seen that amount of flaura rich environments.  Humans don't, and haven't really, increase in height because there's no selective pressure where a gain in height or mass  would be advantageous.  Also, there also seems to a be a mass where an animal couldn't, in a land environment, move enough heat from its core to its outer body fast enough to stop overheating and subsequent death, so the largest sauropods might have hit an upper limit but this is still being studied.      

Quote

Should both poles melt sea levels would increase by an estimated 200 feet. Add all the ice locked up in glaciers in both hemispheres and that level increases another 4 feet. This would reduce land surface area by an estimated one third.


Yep, that's what I found too, about one third of the current land mass.  Obviously this is enough land mass to support large populations.

Quote

Picture of the footrpint of an elephant estimated to weigh 6 tons. http://jmason.org/watchcam/2002_May_in_Nep...t_footprint.gif

Picture of the footrpint from a Sauropod weighing an estimated 30 tons: http://www.utexas.edu/tmm/exhibits/trackway/index.html

You can see how the elephant's foot is designed to splay out and distribute the animal's weight, but not so with the Sauropod - even though there would have been 7.5 tons of weight on that one foot, there is no sign of splaying in fact it appears that the foot hardly has any weight on it at all.



Actually, I think your mixing up the tracks.

http://www2.brevard.edu/reynoljh/FTWeb/Ass...lenRoseDino.jpg

Same site.  You can see the sauropod tracks on the right.  The three toed tracks in the pic you linked to are the therapod.  As you can see the sauropod tracks are quite similar to an elephant as they are broad and flat.  Here's some pics of trackways:

http://palaeo.gly.bris.ac.uk/Palaeofiles/T...5/egtracks.html

Here's a cool little paper comparing sauropods to elephants:

http://www.projectexploration.org/jobaria/...TheElephant.pdf

The largest factor in Sauropod locomotion is the ridiculous mass of their bones which allowed such size:

"The faster an animal runs, the greater the forces its feet exert on the ground and the stronger its legs need to be. The reason is, at higher speeds each foot is on the ground for a smaller fraction of the stride, so it has to exert peak force - the maximum force that occurs while the foot is on the ground - to make a complete stride balance and carry the body weight. The forces exerted by the feet of various creatures led to a greater understanding of dinosaur motion. The use of a force plate to measure the forces on the feet of people, dogs etc enabled us to calculate the stresses imposed on the animals' leg bones. The same approach used for dinosaurs would have involved elaborate calculations and a good deal of imagination. As a result, a quicker and easier way, using the concept of dynamic similarity and insights from structural engineering is preferred.

Forces that act on the ends of bones setting up stresses can be broken down into their components : axial force (Fax), acts along the long axis of the bone, and transverse force (Ftrans) acts at right angles to it. Fax sets up a uniform stress, -Fax/ A, where A is a cross section of the bone and the minus sign indicates a compressive stress. Added to this force are the stresses caused by F trans. These transverse stresses vary across the thickness of the bone from -Ftrans x /Z at one end of the bone to +Ftransx /Z at the other. x is the distance of the cross section from the end of the bone, and Z is the section modulus. Calculations for the leg bones of running and jumping modern animals showed that the stress Fax x/ Z was generally much greater than the stress Faxx/A. This difference tells us that transverse forces are a much more serious threat to bones than axial ones. So the less important Fax can be ignored.

For animals running dynamically in a similar fashion, the forces on the bones are proportional to body weight, W. The stresses they cause (Ftrans x/Z) are proportional to W x/Z. The stresses in the leg bones of two similar animals of different sizes in comparison, will be less in whichever animal has lower values of W x/Z, indicating that its bones are stronger than the other animals' bones.

By changing the expression just slightly, the reciprocal Z/Wx, a value for a strength indicator can be arrived at. The greater the value of Z/Wx, the more athletic an animal can be expected to be. More precisely, the expression, Z/aWx can be used, where a is the fraction of body weight supported by the forelegs or hindlegs, as is appropriate. This weight distribution enables comparison between elephants and dinosaurs. Once the strength indicator is determined, we could conclude that a dinosaur could have been as athletic as any modern mammal with similar strength indicators. The conclusion depended on the assumption that the bones of different animals can stand about the same stresses. It also depended on the assumption that evolution has adjusted the strengths of bones of different animals to give them equal safety factors. The process of arriving at the values for the strength indicators for the dinosaurs is not as straight forward as the conclusions imply. The first step is to calculate the value of the section modulus, or Z, of their bones. Detailed measurements of cross sections at known distances, x, from the end of the bones was obtained from accurate drawings published by earlier paleontologists. The calculation of the strength indicators becomes complete with the weight, W, of the dinosaur and if quadruped, the fraction, a, of that weight carried by each pair of feet. To calculate the distribution of weight between the feet, centre of gravity of each dinosaur must be found. In the real animals, the bones are distributed along the whole length of the body, which did not affect the centre of gravity too much. The models that were selected for studying had to contain a hole, bored through, representing the approximate volume where the lungs would have been.

The above procedures and data supplied the information needed to calculate the strength indicators. Z/aWx for different dinosaur limbs. Obtaining large values to compare elephants and Apatosaurus, commonly known as brontosaur, suggests that despite Apatosaurus' huge size, it could have been about as athletic as an elephant. Diplodocus, a more slender sauropod, seems to have a lower strength indicator and was therefore probably less agile, able to walk on land, possibly unable to run. Considerable doubt exists about the mass of Diplodocus and Triceratops because measurements have been made in each case on a skinny model and a stout one - it seems uncertain which model is more accurate. The higher values of strength indicators of Triceratops suggests it may have been more athletic. The conclusions reached for Apatosaurus, Diplodocus and Triceratops are tentative, and more so, for Tyrannosaurus, because all modern bipeds are so very much smaller.

Finally, the calculations that allowed us to assess the agility of dinosaurs are firmly based on physics and engineering. Although large dinosaurs walked slowly, most were capable of quite a quick run and none needed to live in water or to rely on buoyancy for support.

(Condensed From R McNeill Alexander, Sci. Am., 62, (1991))"


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#42    fantazum

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Posted 13 January 2007 - 12:19 AM

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See below, because I'm not sure how you arrived at those numbers but they don't jive with studies I've read.
That doesn't conflict with evolutionary laws.  In truth that isn't thought to be the prevalent factor though.  The largest factor was predatory pressure from what I've been reading.  The food rich environment simply allowed for runaway growth.  We've never since seen that amount of flaura rich environments.  Humans don't, and haven't really, increase in height because there's no selective pressure where a gain in height or mass  would be advantageous.  Also, there also seems to a be a mass where an animal couldn't, in a land environment, move enough heat from its core to its outer body fast enough to stop overheating and subsequent death, so the largest sauropods might have hit an upper limit but this is still being studied.      
Yep, that's what I found too, about one third of the current land mass.  Obviously this is enough land mass to support large populations.
Actually, I think your mixing up the tracks.

http://www2.brevard.edu/reynoljh/FTWeb/Ass...lenRoseDino.jpg

Same site.  You can see the sauropod tracks on the right.  The three toed tracks in the pic you linked to are the therapod.  As you can see the sauropod tracks are quite similar to an elephant as they are broad and flat.  Here's some pics of trackways:

http://palaeo.gly.bris.ac.uk/Palaeofiles/T...5/egtracks.html

Here's a cool little paper comparing sauropods to elephants:

http://www.projectexploration.org/jobaria/...TheElephant.pdf

The largest factor in Sauropod locomotion is the ridiculous mass of their bones which allowed such size:

"The faster an animal runs, the greater the forces its feet exert on the ground and the stronger its legs need to be. The reason is, at higher speeds each foot is on the ground for a smaller fraction of the stride, so it has to exert peak force - the maximum force that occurs while the foot is on the ground - to make a complete stride balance and carry the body weight. The forces exerted by the feet of various creatures led to a greater understanding of dinosaur motion. The use of a force plate to measure the forces on the feet of people, dogs etc enabled us to calculate the stresses imposed on the animals' leg bones. The same approach used for dinosaurs would have involved elaborate calculations and a good deal of imagination. As a result, a quicker and easier way, using the concept of dynamic similarity and insights from structural engineering is preferred.

Forces that act on the ends of bones setting up stresses can be broken down into their components : axial force (Fax), acts along the long axis of the bone, and transverse force (Ftrans) acts at right angles to it. Fax sets up a uniform stress, -Fax/ A, where A is a cross section of the bone and the minus sign indicates a compressive stress. Added to this force are the stresses caused by F trans. These transverse stresses vary across the thickness of the bone from -Ftrans x /Z at one end of the bone to +Ftransx /Z at the other. x is the distance of the cross section from the end of the bone, and Z is the section modulus. Calculations for the leg bones of running and jumping modern animals showed that the stress Fax x/ Z was generally much greater than the stress Faxx/A. This difference tells us that transverse forces are a much more serious threat to bones than axial ones. So the less important Fax can be ignored.

For animals running dynamically in a similar fashion, the forces on the bones are proportional to body weight, W. The stresses they cause (Ftrans x/Z) are proportional to W x/Z. The stresses in the leg bones of two similar animals of different sizes in comparison, will be less in whichever animal has lower values of W x/Z, indicating that its bones are stronger than the other animals' bones.

By changing the expression just slightly, the reciprocal Z/Wx, a value for a strength indicator can be arrived at. The greater the value of Z/Wx, the more athletic an animal can be expected to be. More precisely, the expression, Z/aWx can be used, where a is the fraction of body weight supported by the forelegs or hindlegs, as is appropriate. This weight distribution enables comparison between elephants and dinosaurs. Once the strength indicator is determined, we could conclude that a dinosaur could have been as athletic as any modern mammal with similar strength indicators. The conclusion depended on the assumption that the bones of different animals can stand about the same stresses. It also depended on the assumption that evolution has adjusted the strengths of bones of different animals to give them equal safety factors. The process of arriving at the values for the strength indicators for the dinosaurs is not as straight forward as the conclusions imply. The first step is to calculate the value of the section modulus, or Z, of their bones. Detailed measurements of cross sections at known distances, x, from the end of the bones was obtained from accurate drawings published by earlier paleontologists. The calculation of the strength indicators becomes complete with the weight, W, of the dinosaur and if quadruped, the fraction, a, of that weight carried by each pair of feet. To calculate the distribution of weight between the feet, centre of gravity of each dinosaur must be found. In the real animals, the bones are distributed along the whole length of the body, which did not affect the centre of gravity too much. The models that were selected for studying had to contain a hole, bored through, representing the approximate volume where the lungs would have been.

The above procedures and data supplied the information needed to calculate the strength indicators. Z/aWx for different dinosaur limbs. Obtaining large values to compare elephants and Apatosaurus, commonly known as brontosaur, suggests that despite Apatosaurus' huge size, it could have been about as athletic as an elephant. Diplodocus, a more slender sauropod, seems to have a lower strength indicator and was therefore probably less agile, able to walk on land, possibly unable to run. Considerable doubt exists about the mass of Diplodocus and Triceratops because measurements have been made in each case on a skinny model and a stout one - it seems uncertain which model is more accurate. The higher values of strength indicators of Triceratops suggests it may have been more athletic. The conclusions reached for Apatosaurus, Diplodocus and Triceratops are tentative, and more so, for Tyrannosaurus, because all modern bipeds are so very much smaller.

Finally, the calculations that allowed us to assess the agility of dinosaurs are firmly based on physics and engineering. Although large dinosaurs walked slowly, most were capable of quite a quick run and none needed to live in water or to rely on buoyancy for support.

(Condensed From R McNeill Alexander, Sci. Am., 62, (1991))"



Here is a clearer pic of a Sauropod foot print:http://www.dinoruss.com/utah2kweb/morrision_j/morrison_j_sltwashvert3.jpeg
Again what you see here doesnt make sense as the print is believed to be that of a creature weighing some thirty tons but the imprint shows that the size of the pad of the foot to be not much larger than a fully grown Elephant's.

You state that the larger Dinosaurs were agile and capable of running. This indicates a high metabolic rate and if true ,conflicts with the idea that Dinosaurs were reptiles. A high metabolic rate also indicates fast growth which reinforces the research that points to higher oxygen levels during the period of the Jurassic but this research is somewhat in dispute by fresher research that has claimed the opposite to be true - in which case what drove such rapid growth and increased metabolic rate?

"Hundreds of slices from bones of all types of dinosaurs have now been examined and all show:
1) Woven bone typical of rapid bone growth
2) Vascular canals equivalent to those of birds
3) Generally poor growth rings but more obvious in teeth
ie in all regards they resemble warm-blooded rather than cold-blooded animals. However, continuing studies have complicated the interpretation of these results. Many small mammals and birds do not show either Haversian canals or fibrolamellar bone, and at least one turtle has been found with a dense Haversian bone. Dinosaurs do appear to differ from other reptiles in their ability to deposit fibrolamellar bone continuously instead of periodically.
In 1993 a comparative study was made of the long bone growth plate of a chicken (bird), dog (mammal) and monitor lizard (cold-blooded reptile) with juvenile Maiasaura bone. In longitudinal section, the line between cartilage and newly formed bone was straight in the dog and monitor, but undulating in the bird and dinosaur. As well as reinforcing the close relationship between dinosaur and bird, the authors conclude that the different bone formation processes that cause the wavy line indicate rapid growth and are consistent with a high metabolic rate ."
Source: http://www.dinoruss.com/de_4/5c51dbb.htm

So far as Oxygen levels during the Jurassic:

"Recent evidence suggests that oxygen levels were suppressed worldwide 175 million to 275 million years ago and fell to precipitously low levels compared with today's atmosphere, low enough to make breathing the air at sea level feel like respiration at high altitude.

Now, a University of Washington paleontologist theorizes that low oxygen and repeated short but substantial temperature increases because of greenhouse warming sparked two major mass-extinction events, one of which eradicated 90 percent of all species on Earth.

In addition, Peter Ward, a UW professor of biology and Earth and space sciences, believes the conditions spurred the development of an unusual breathing system in some dinosaurs, a group called Saurischian dinosaurs that includes the gigantic brontosaurus. Rather than having a diaphragm to force air in and out of lungs, the Saurischians had lungs attached to a series of thin-walled air sacs that appear to have functioned something like bellows to move air through the body.

Ward, working with UW biologist Raymond Huey and UW radiologist Kevin Conley, believes that breathing system, still found in today's birds, made the Saurischian dinosaurs better equipped than mammals to survive the harsh conditions in which oxygen content of air at the Earth's surface was only about half of today's 21 percent.

"The literature always said that the reason birds had sacs was so they could breathe when they fly. But I don't know of any brontosaurus that could fly," Ward said. "However, when we considered that birds fly at altitudes where oxygen is significantly lower, we finally put it all together with the fact that the oxygen level at the surface was only 10 percent to 11 percent at the time the dinosaurs evolved.

"That's the same as trying to breathe at 14,000 feet. If you've ever been at 14,000 feet, you know it's not easy to breathe," he said.

Ward believes low oxygen and greenhouse conditions caused by high levels of methane from intense volcanic activity are likely culprits in mass extinctions that occurred about 250 million years ago, at the boundary between the Permian and Triassic periods, and about 200 million years ago, at the boundary between the Triassic and Jurassic periods. He will make a presentation on the topic Tuesday at the American Geological Society annual meeting in Seattle.

The Permian-Triassic extinction is believed to have eradicated 90 percent of all species, including most protomammals, a group of mammal-like reptiles that were the immediate ancestors of true mammals. The Triassic-Jurassic extinction killed more than half the species on Earth, with mammal-like reptiles and true mammals, which evolved during the Triassic Period, hit particularly hard. But dinosaurs, which also evolved between the two extinctions, had little problem with conditions during the Triassic-Jurassic extinction.

"The seminal observation is that dinosaurs skated across the second of these mass extinctions, actually increasing in number as they went along, while everything else was dropping around them," Ward said.

Scientists know of five mass extinction events in Earth's history, but a cause has been widely agreed upon for only one -- the episode at the end of the Cretaceous Period 65 million years ago, when the impact of an asteroid is believed to have brought the demise of the dinosaurs. Such impact also has been suggested as the cause of the Permian-Triassic and Triassic-Jurassic extinctions, but geologists have yet to unearth any indisputable evidence of such an impact, and there is no conclusive evidence of what caused either of the events.

Ward said mass spectrometer readings on fossil material, as well as the extinction pattern for fossils in rock outcrops collected from the time of the two extinctions, indicates the events were drawn-out affairs and did not happen suddenly, as they would have with an asteroid impact.

In addition, he said it is known which types of creatures, and which breathing systems, best survived the extinction events. The same breathing systems are still present in birds, which are known to fare well at high altitudes, where oxygen levels are substantially lower than at the surface.

"The reason the birds developed these systems is that they arose from dinosaurs halfway through the Jurassic Period. They are how the dinosaurs survived," he said.

For more information, contact Ward at (206) 543-2962 or argo@u.washington.edu

Source: http://uwnews.washington.edu/ni/article.asp?articleID=2205







#43    capeo

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Posted 16 January 2007 - 03:24 PM

Quote

Here is a clearer pic of a Sauropod foot print:http://www.dinoruss.com/utah2kweb/morrision_j/morrison_j_sltwashvert3.jpeg
Again what you see here doesnt make sense as the print is believed to be that of a creature weighing some thirty tons but the imprint shows that the size of the pad of the foot to be not much larger than a fully grown Elephant's.


Again you must realize that the area required to support a weight is not geometric, so it won't just double with the doubling of a weight.  How the weight above it is distributed plays a crucial role.  The vast tails and necks of these creatures were supported with musculature running along the spine akin to a suspension bridge which helps to redistribute weight with each step.  As you see by the link I provided ther can shocking little wieght on an elephants leg at any given moment even though it weighs eight tons.  The same hold true for a larger animal, not to mention the massive increase in bone size to carry that weight.  The simple fact of the matter though is that it's obvious they had no problem walking because there are many trackways showing them walking.  

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You state that the larger Dinosaurs were agile and capable of running. This indicates a high metabolic rate and if true ,conflicts with the idea that Dinosaurs were reptiles. A high metabolic rate also indicates fast growth which reinforces the research that points to higher oxygen levels during the period of the Jurassic but this research is somewhat in dispute by fresher research that has claimed the opposite to be true - in which case what drove such rapid growth and increased metabolic rate?


The research I cited says it and it says the most massive of sauropods may not have been able to run though juveniles could.  But some upwards of 50 tons do seem to be able to run for short times based on computer modeling of their skeletons.

The idea that most dinosaurs were reptiles, as we classify reptiles today, was discarded a while back due to the precise type of research you mention below.  Most are classified as Dinosauria (or something like that).  Though direct ancestors of reptiles (Dimetradon for an early example) existed.

Quote

"Hundreds of slices from bones of all types of dinosaurs have now been examined and all show:
1) Woven bone typical of rapid bone growth
2) Vascular canals equivalent to those of birds
3) Generally poor growth rings but more obvious in teeth
ie in all regards they resemble warm-blooded rather than cold-blooded animals. However, continuing studies have complicated the interpretation of these results. Many small mammals and birds do not show either Haversian canals or fibrolamellar bone, and at least one turtle has been found with a dense Haversian bone. Dinosaurs do appear to differ from other reptiles in their ability to deposit fibrolamellar bone continuously instead of periodically.
In 1993 a comparative study was made of the long bone growth plate of a chicken (bird), dog (mammal) and monitor lizard (cold-blooded reptile) with juvenile Maiasaura bone. In longitudinal section, the line between cartilage and newly formed bone was straight in the dog and monitor, but undulating in the bird and dinosaur. As well as reinforcing the close relationship between dinosaur and bird, the authors conclude that the different bone formation processes that cause the wavy line indicate rapid growth and are consistent with a high metabolic rate ."
Source: http://www.dinoruss.com/de_4/5c51dbb.htm

So far as Oxygen levels during the Jurassic:

"Recent evidence suggests that oxygen levels were suppressed worldwide 175 million to 275 million years ago and fell to precipitously low levels compared with today's atmosphere, low enough to make breathing the air at sea level feel like respiration at high altitude.

Now, a University of Washington paleontologist theorizes that low oxygen and repeated short but substantial temperature increases because of greenhouse warming sparked two major mass-extinction events, one of which eradicated 90 percent of all species on Earth.

In addition, Peter Ward, a UW professor of biology and Earth and space sciences, believes the conditions spurred the development of an unusual breathing system in some dinosaurs, a group called Saurischian dinosaurs that includes the gigantic brontosaurus. Rather than having a diaphragm to force air in and out of lungs, the Saurischians had lungs attached to a series of thin-walled air sacs that appear to have functioned something like bellows to move air through the body.


To sustain a high metabolic rate the food just needs to be there.  Nobody questions that there was sufficient food to support them.  Also, as you can see, research suggest that they had evolved to deal with a lower oxygen environment.  


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#44    Roj47

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Posted 17 January 2007 - 01:13 PM

Whilst scouting through my favourite webpages I came across this article which sheds some light on my initial question -

http://www.livescience.com/animalworld/070...ttle_lions.html

Carnivores Can't Get Much Bigger

By Robin Lloyd
Senior Editor
posted: 16 January 2007
07:55 am ET



Lions and tigers and bears are about as terrifying, size-wise, as it’s going to get in the wild world of mammals, new research shows.

Ecologists at the Zoological Society of London modeled the energy budgets of land-dwelling carnivores and arrived at a 1-ton limit as the maximum sustainable mass for these meat-eating mammals.

After that, there is a huge pay-off for each kill made by a large predator, but it takes too much lumbering energy for the behemoths to hunt the vast quantities of meat required to carry on across evolutionary time, said Chris Carbone, lead author of the new research published in the journal PLoS Biology.

At least four terrestrial, carnivorous mammals that Carbone puts near the 1-ton mark have gone extinct: the short-faced bear; North American lion; South American sabercat; and Megistotherium osteothlastes (a wolf-like carnivore that lived 25 million years ago in Africa).

Today’s large carnivorous land mammals, including the record-setting polar bears—which usually weigh around half a ton but can grow to weigh nearly a ton, are threatened in part because of the energy intake-and-expenditure equation, Carbone told LiveScience.

“By being a carnivore that specializes on hunting big prey, it potentially can make you vulnerable to the process of extinction,” he said. “It’s more costly to feed on these larger prey, so it’s more energy demanding. And you’re more reliant on prey. If you can’t meet those energy costs, you’re no longer viable over time.”

Hunting strategies

Carbone’s model also explains some of the hunting strategies used by carnivorous mammals and how they vary depending upon the size of the carnivore and whether they tend to prey on invertebrates (such as insects) and smaller animals or larger vertebrates, such as deer, antelopes and their relatives.

Carnivores travel over some of the widest distances of all land-based mammals for their size. The long travels, plus chasing, pulling down and pulling apart of prey costs a lot of energy.

For carnivores that feed on rodents, small reptiles or insects, most of the energy cost comes simply from getting to and from prey, Carbone said. “They might chase and eat it, but it’s dispatched easily.”

Lolling about and naps are ways big carnivores make up for the energy costs, Carbone and his co-authors surmise in the research.

Mid-size carnivores around the size of a lynx, jackal or termite-eating aardwolf, a hyena-like carnivore that lives in Africa, have a cross-over advantage energetically, Carbone said. They have low metabolic rates that allow them to conserve energy and can hunt both small and large prey.

For instance, Eurasian lynxes can feed happily on rabbits and smaller prey, but due to their size, they can also take down medium-sized antelopes. In the absence of large prey, such animals can always resort to rodent-killing, Carbone said.

The difficulty of catching and killing larger animals costs twice as much energy (even though the payoff is greater too). But massive, large-prey predators have no small-prey options—those meals are too small to be worthwhile. Massive mammals must hunt the big prey that require huge amounts of energy to locate, catch and take down. “There is no where else to go, and then you’re kind of stuck,” Carbone said.

Animal 'ground rules'

Paleobiologists will find Carbone's model useful, said John A. Finarelli, a University of Chicago paleontologist who studies all dog-like carnivores. In the past, some scientists have looked at the minimum mass limits for warm-blooded animals, and even stated that North American mammals never approached maximum mass limit.

"However, in light of (Carbone's) findings, it could very well be the case that carnivorous mammals do not play by the same set of rules that other mammals do," Finarelli said.

The largest known land-dwelling carnivores of all time were lower-metabolism dinosaurs such as Spinosaurus (about 8 tons), Giganotosaurus (about 8 tons) and Tyrannosaurus (about 6 tons).

And then there was the15-ton Indricothere—but that extinct mammal was an herbivore.

“Carnivores, because of the cost of hunting, can never achieve the sizes and intake rate of prey of the largest herbivores,” Carbone said. “It’s costly to be a big carnivore. The weaponry required to take down big prey adds to cost in terms of movement and maintenance. Ultimately that limits your ability to hunt, which again limits your size.”



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#45    frogfish

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Posted 17 January 2007 - 08:38 PM

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The idea that most dinosaurs were reptiles, as we classify reptiles today, was discarded a while back due to the precise type of research you mention below. Most are classified as Dinosauria (or something like that). Though direct ancestors of reptiles (Dimetradon for an early example) existed.


Dinosaurs were not reptiles. They are archosaurs. They have an extra chamber of the heart, and are most likely warm-blooded. Who said they couldn't of been ambush predators?

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