A number of commonly accepted assumptions about large dinosaurs are not
compatible with scientific laws. For example, sauropods grazing from the
tops of trees were physiologically impossible, for blood flow reasons.
(A heart and circulatory system made of biological cellular tissues
cannot pump blood more than about seven vertical feet above the heart, or
bring blood back from legs and feet lower than about seven feet below it.).|
An early dinosaur fossil researcher (Marsh) found much of the fossilized bones of a brontosaurus (in 1879, at Como Bluff), but he did not find a skull. In an unbelievably un-scientific (and scientifically disgusting!) move, he found a skull at a considerable distance away, where no dinosaur fossils had been found, and he claimed that the skull belonged with the skeleton. (He certainly knew that was not true.) For a hundred years, all the display brontosaurs in museums worldwide showed that same (wrong) skull! It has only been in the past several decades that the error (or deception) has been uncovered.
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All this is meant to indicate how little absolute evidence actually exists regarding these very interesting creatures! Books, including textbooks, have always tried to make it seem that EVERYTHING is known about these creatures, where the reality is that very little is actually known! But progress seems to be rapidly progressing. In a valley in Montana, in the past few years, eight different T. Rex fossil sets have been found by an extensive team of researchers and college students. This is a good sign that future knowledge might soon improve!
In some related web-pages, I present a discussion about the necessary size of the mouth of a large dinosaur to be able to ingest enough food for enough energy audit for its size. Some truly huge sauropods are described as having rather tiny mouths, which seems to bring up interesting logical questions! Another related web-page discusses the necessary muscle and tendon strengths necessary in the Mechanical Engineering in a very long neck, when the head might have weighed nearly a ton. To cantilever out that much weight thirty or forty feet or more in front of front legs creates a number ofserious mechanical stresses, and they often seem to challenge current thinking in that the strongest biological muscles and tendons seem unlikely to be able to withstand those levels of stress. Even the vertebrae and the disks between them need some extensive study and explanation! As a consequence of these aspects of Physics, I concluded that the largest of the sauropods could not have been land-dwelling animals and they must have been nearly constantly submerged in a swamp or shallow lake environment to provide the needed temperature aspects of the energy audit. Fully warm-blooded is nearly impossible, but being in a relatively warm swamp or pond could make the energy audit possible.
Most of the following comments are only intended to apply to the very largest of the land-based(?) dinosaurs, called Brontosaurus (Apatosaurus is the same thing), Diplodocus, Brachiosaurus, and Camarasaurus, and a few others, collectively referred to as Sauropods. Few of these comments apply to any of the smaller dinosaurs like the velociraptors, Tyrannosaurus Rex, Stegosaurus, etc. The comments regarding blood pressures and flows might apply to T. Rex, because of the 18-foot tall height it would have had when fully erect. (In that regard, the recent findings of many T. Rex fossils in Montana now suggest that the posture of a T. Rex was not as upright as had been commonly thought, and its torso was more horizontal. This would greatly agree with the blood flow considerations described below.)
As an example, fossils of Brachiosaurus seem to imply that its trunk was around 12 feet in diameter and 20 feet long. Using the method suggested above, and thinking of its trunk as a cylinder, the volume V is given by (PI)*D2/4 * L or about 3.14 * 144/4 * 20 or about 2,260 cubic feet. At 64 pounds per cubic foot (the density of nearly all biological material, essentially that of water), that gives about 145,000 pounds. Add some more for its head, neck, tail and feet, and you have around the 80 tons mentioned above. (That's pretty much how the estimated weights were first identified by the experts!)
That enormous weight, in itself, is amazing but not impossible for a living creature. The modern day Great Blue Whale actually weighs more than this. There have been stories of Great Blues, which have become beached at low tide, and their ribs have allegedly broken under their own weight. This is reasonable. While floating, the buoyancy of the water supports most of its weight, so a moderate-sized bone structure can maintain stability and bodily integrity. But on land, without that buoyancy, it could not survive. This sort of argument has been used regarding the largest sauropods to suggest that they must have lived in swamps or very shallow seas, in order to support their weight.
Other scientists believe that these large dinosaurs lived on dry land, that their legs and muscles were actually strong enough to support and move around this vast weight. Such scientists may be overlooking the fact that the mass we are talking about is equivalent to about 50 automobiles! The leg bones and muscles necessary to support and move this huge weight on dry land would necessarily be near the absolute limits of cell and bone and muscle fiber strength. The estimated mass of the brachiosaurus is on the scale of 20 elephants. Elephants' legs are rather stout to support the several tons of their weight. The proposed dinosaur mass would require MUCH more stout legs, possibly to an unrealistic extent.
For a leg to support four times the weight (on dry land) the leg bones and leg muscles must each be twice as thick (so their cross-sectional areas are four times as great). It doesn't actually matter if those bones are round or oval or square, or if they are solid or hollow. In the case of a brachiosaur that had a body weight of 16 times that of a 10,000-pound elephant, those bones and muscles would all have to be four times the thickness (sixteen times the cross-sectional area) that is present in the elephant. Where the elephant's leg may be about a foot in diameter, the brachiosaurus' legs would therefore have to be about four feet in diameter (if it was to be mobile on land).
Existing fossils do not support such extremely thick legs. The fossils of leg bones are certainly thick, but they are not four times as thick. It is far more likely that the swamp hypothesis has more validity, and that these extremely large dinosaurs would have been susceptible to broken leg bones if they would ever attempt to walk on land. (Medium and small sized dinosaurs did not have this limitation and DEFINITELY were land creatures.)
If such a huge animal had a leg bone break, its possibility of survival would drop to nearly zero. It would no longer have the mobility to go to food sources and it would be immobile and easy prey for many carnivorous predators to attack and kill.
The large brachiosaurs appear, due to fossils, to have had feet that had around three square feet area, and at least two of them were probably always in contact with the ground while such a creature would have been walking. The 160,000 pounds of its weight would therefore be supported by six square feet of area of contact between feet and ground. This gives a pressure of around 27,000 pounds per square foot, almost 40 times that of a human and many times that of any known modern creature. Such an animal walking on soft or muddy ground probably wouldn't sink in 40 times as deeply as a person, but certainly very deeply. It is very likely that such footprints would be pits of more than a foot deep, in even moderately soft ground, because of the enormous pressure created from the weight of the creature.
Some fossilized footprints have been found that have been identified as being made by large dinosaurs. These footprints tend to be just an inch or two deep. They still have enough detail to be identified as dinosaur footprints, so they are not shallow, eroded remnants of earlier, deeper ones. This implies that less pressure (weight per square foot) may have been present when the footprints were made (or the ground was extremely hard).
Some of these footprints are found to be spaced a substantial distance apart. Some investigators have compared that to the probable leg-length and similar relationships among modern creatures, and have concluded that the footprints are so far apart that they had to have been made by brachiosaurs or other sauropods RUNNING! For many reasons presented in this essay, such large, massive, cumbersome creatures almost certainly could only move very slowly, if on land. Running would be entirely out of the question. In addition, why would such an animal have ever developed the musculature to be able to run? These giant creatures are believed to be herbivores, so carnivorous pursuit of prey would never be necessary. There would be no value in being able to outrun predators, either. The exertion and energy waste from running would be truly foolish for a creature that already probably had to eat almost continuously to maintain even basic metabolism for 160,000 pounds of cells!
A logical explanation for shallower-than-expected footprints and longer-than-expected stride might exist. If such a creature lived in a shallow sea or swampy environment, where buoyancy supported much of its weight, it's footprints in the sea bottom would be shallower (due to less weight pressure on the foot) and farther apart (due to a floating/swimming effect). Of course, preservation of such footprints represents a problem. The sea would have to remain extremely calm, so the underwater footprints were not immediately obliterated by wave action. The sea floor would have to be some material like clay rather than sand, to better have well-defined impressions. And some sudden supply of additional sediment would have to appear to quickly fill in the footprints such that they could be preserved for us to later find.
Note: The pressures mentioned above are static pressure loads. In each situation, during walking, dynamic variations would also apply which would momentarily substantially increase all of the creatures' footprint pressures. These dynamic effects would be relatively similar for each creature, so the simpler static pressures were used for clarity of discussion.
This seems to represent additional support for the swamp-based hypothesis for the largest of the dinosaurs.
The scientists who believe that these large creatures were land walkers now generally believe that the long neck enabled the creatures to graze on the high branches of trees, to have a non-competitive supply of food, where no other animals could compete for the leaves. This is certainly an interesting speculation! Unfortunately, this premise is impossible in reality. If such a creature was grazing from the top of a 25-foot tall tree, no heart structure could pump blood up even halfway from its heart up to its brain. Additionally, the delicate structures of cell walls in the brain could not withstand the rapid variations in blood pressure that could occur during vertical head movements.
If a healthy standing person's blood pressure was measured at the altitude of the brain, the normal 120/80 would appear as 80/40. If instead, a standing person's blood pressure was measured at his foot, the normal 120/80 would appear to be around 220/180. These different readings all represent the same healthy operation of a normal human heart and circulatory system. The point being made is that the vertical distance between the heart and any particular location in the body greatly affects the local blood pressure available there. The local pressure in any body of fluid is dependent on the "column" of water or blood above it which is pressing down. These comments also point out that the local blood pressure normally present in the feet is much higher than at the heart or brain. In each case, the organic structures are suitable for the pressures in that environment. The capillaries in the feet are thicker and tougher than the very delicate capillaries in the brain where the local pressures are generally much lower. This factor allows the brain to be far more complex. It also indicates why the (advanced) brain is nearly always near the vertically highest portion of any larger animal and not down near its feet.
The giraffe is the currently existing animal that has the greatest vertical distance between its heart and brain, about 6.5 feet, when standing erect. This vertical distance would necessitate a minimum blood pressure at the heart, as explained above, of about 240 over 200 mm Hg. (This would provide a reasonable and consistent blood flow to its brain.) Giraffe (systolic) blood pressures have been measured at about 260 mm Hg, a very good agreement, with sufficient pressure always available to minimize dizziness and hopefully eliminate fainting.
There is no known modern animal that has a heart that produces a higher pressure than that of the giraffe, or that has its brain located higher above the heart. The intrinsic strength of heart cell, muscle and particularly the check valve components appear to eliminate the possibility of a living heart being able to create much higher blood pressures than this. This implies that no animal could probably ever have its brain more than about 7 feet above (or below) the heart. During the complex sequence of actions of a heart, there are several moments when the existing pressure must be held by the various check valves without substantial leaking. Special papillary muscles assist the valves in avoiding being pushed backwards by the pressure.
If a substantially higher pressure was developed by the heart muscles, those valves would have to hold back greater pressures, which seems to be beyond the capability of organic cell strengths. So, even if massive heart muscles were present, which could create extremely high systolic pressure, the tissue strengths of the valves and other structures would limit the diastolic pressure to that of a tolerable leakage level.
The alleged behavior of a dinosaur grazing at the top of a 25-foot tall tree, while its heart was about 8 feet above the ground, is therefore impossible. Such activity would require a heart that was capable of creating a continuous pressure of around 500 over 420 mm Hg, to supply the brain with adequate blood and oxygen. That level of pressure is enormous! It represents about 2/3 of atmospheric pressure, more than double that of any known biological heart. The existence of such a very advanced heart 65 million years ago, with abilities so far beyond any currently existing heart, is clearly impossible. Even highly efficient mechanical modern (diaphragm, reciprocating, check-valve) water pumps of sophisticated design have great trouble in creating that level of pressure and of raising water that many feet. (There are other technologies in mechanical pumps that are capable of raising water far higher, but their designs are very different from the operation of a heart).
There are many textbooks which show sauropod dinosaurs eating leaves from even taller trees, such as 50-feet tall. The people who dreamed up such ideas were certainly creative, but they did NOT know much of science! Such drawings in children's textbooks are so impossible that it would be laughable, except for the fact that they ARE children's textbooks!
A juvenile, playful, land-based sauropod would immediately die if it ever suddenly raised and lowered its head!
In addition, a giraffe's neck blood arteries and veins contain a very specialized arrangement that acts as check valves to help keep the brain's blood pressure relatively constant. The arteries (sources) and veins (drains) are "braided" together. These features are necessary to compensate for the rapid blood pressure variations that can occur due to the giraffe's 7-foot-long neck's vertical range. When a giraffe lowers its head to the ground, that unique structure acts to stop additional blood from being pumped to the brain to minimize the chance of over-pressurizing the tiny blood capillaries in its brain. As the veins bulge due to the higher momentary pressure, they act to squeeze shut the arteries, keeping additional blood from arriving, while the enlarged veins can remove the excess pressure quickly.
The length (and, more importantly, the vertical range) of a giraffe's neck appears to be close to the limit of what's physiologically possible, given the heart structure and operation known in any animals.
These physiological arguments apply rigidly to any land-based creature, with air surrounding it. If submerged in water, the reasoning is similar but more complicated. The surrounding water exerts a pressure on the skin of the creature, which acts similar to a G-suit of military pilots. For a variety of complicated reasons, this external pressure enables a somewhat greater range of vertical head movement to be possible.
This allows the Blue Whale to have dimensions beyond this discussion's guidelines, and also allows it to (briefly) swim in a relatively vertical position, where the brain is quite high above or low below the heart. A generally floating sauropod such as in a swamp environment would have this external pressure advantage which would allow relatively free motion of the neck and body while completely or mostly underwater.
There have been some recent suggestions that this might have been accomplished by an unusual interlocking bone structure of the neck vertebrae. Such an argument suggests direct bone-to-bone contact, which is effectively unheard of in living animals. Direct bone-to-bone contact tends to eventually result in fused structures, such as in the skulls of larger modern animals. Direct bone-to-bone contact in movable joints would cause rapid abrasion and wear on the surfaces of those bones, quickly destroying them. Direct bone-to-bone contact is highly unlikely.
There were certainly disk type cushions between the neck vertebrae, as in all modern vertebral animals. A complex network of dorsal muscles (and lateral muscles) would have to have supported and moved the neck and head. This situation necessarily brings into question the muscle fiber strength and the cross-sectional areas of the muscle bundles that did this work. Even a fairly small head, cantilevered out 25 or more feet ahead of the forelegs (and its associated neck structure) would represent a considerable weight to support. In engineering terms, this situation represents a vertical torque on each neck vertebra from the shoulders forward. From the preceding discussion, the neck must necessarily be relatively horizontal. Standard engineering analysis shows that the longitudinal tensional stress in the dorsal neck muscles (just forward of the forelegs) is fairly close to the known failure limits of known muscle fibers. This comment necessarily makes assumptions on the cross-sectional area of those dorsal neck muscle bundles and on the specific lateral (vertical) offset distances of muscle attachment points on the individual vertebra. These assumptions are based on the apparent attachment points of tendons on the fossil vertebrae.
In any event, the mechanical stresses involved in supporting a distant cantilevered head are significant, for a land-based long-necked sauropod. If such a creature spent much of its life in a swamp or shallow sea, buoyancy would aid in supporting the head and neck, and greatly reduce this problem.
(Note: a more recent separate presentation has been created on this subject, at: Sauropod Dinosaur Neck Analysis)
This whole subject provides additional indications that the largest sauropods may not have been land-dwelling animals, although their neck structure is within the strength limits of organic cell structures.
The situation for the large dinosaurs is very different than for smaller creatures. A situation similar to the cantilevering of the neck (described above) applies, except that the tail is far thicker and therefore heavier. Consider a large dinosaur that was, say, five times the scale of a small one, but otherwise identically proportioned. Considering a tail held off the ground, by the action of muscles, we can do a simple analysis. The cross-sectional area of the tail bones and the tail muscles is 5 x 5 or 25 times as great for the larger animal. But the volume, and therefore the weight of the tail is 5 x 5 x 5 or 125 times as great. This means that every fiber of muscle cell must support five times as much weight as the corresponding muscle fiber in the smaller animal. In a suspended tail, that weight is cantilevered out behind the rear legs. In the larger animal, that effective tail weight is five times as far out, too. This would put enormous longitudinal stress in the dorsal tail muscles. Relatively simple calculations suggest that the largest of the sauropods may have been able to lift their tails for brief periods, but that it is extremely unlikely that they continuously held their tails aloft. The energy consumption necessary in order to continuously stress all of those muscles would also substantially increase the necessary food intake of the creature. Over the many thousands of generations that they existed, certainly internal mechanisms such as this tended toward more efficient energy usage. It seems extremely likely that the largest sauropods dragged their tails on the ground, if they were land-based creatures. If, instead, they were swamp-based, again flotation would support much of the weight, allowing many more possibilities regarding the tail position and movement.
There may be some interesting questions regarding the eggs themselves. If they were laid on dry land, how did the mother arrange protection for them? An aggressive carnivore could easily capture the contents if they were left out in the open. Was she agile enough to be able to defend them from predators? (That seems unlikely.) Did she (laboriously) turn around and somehow push or carry them to some place of safety? What kind of a place would that be, where carnivores could not get to them for an extended period of time? Would it have meant that she dug shallow holes and buried them as some modern animals do? And, if they were laid in a shallow sea or swamp, again, how did she move them to dry land, and how did she provide for their protection? And to make sure that the babies wouldn't drown?
This all may imply that the large sauropods were VERY slow, logy creatures. All movements may necessarily have been quite slow. That young energetic sauropod may have intended to raise its head high above its body, but the very slow movements at some point initiated dizziness that would have kept extreme vertical positions from ever happening. The way the vertebrae fit together may also have greatly limited the possible range of angle of the neck and head. Even sudden unconsciousness may have been fatal, because of the brain hemorrhages that would result from the head suddenly dropping toward the ground. This is in addition to the possible damage of the impact with the ground or rocks of a head falling from signficant height.
But we must remember that these were VERY successful creatures that came to dominate the Earth for many millions of years. This then indicates that they developed successful accommodations for these problems of their large size. All of these physiological limitations add to the suggestion of credibility of the swamp-based environment of the great sauropods.
It must have been relatively rare for a young large dinosaur to die of an aneurysm due to a quick vertical movement of its head. Without the very-slow-movement hypothesis, exactly how the majority of large dinosaurs avoided this, to develop a thriving society, would be a great mystery.
Again, considering the extreme success of enduring dinosaur species, this must have been a fairly rare occurrence. As a defensive measure against land-based carnivores, this might also suggest the swamp dwelling environment that used to be popular among scientists. A defense of submerging would probably discourage many carnivorous predators.
This subject gets at the issue of whether the giant sauropods were warm-blooded or cold-blooded. The energy accounting is very different for these two possibilities. It does not appear that anyone has previously done sufficient analysis of these energy-related issues.
(Note: a more recent separate presentation has been created on this subject, at: Sauropod Dinosaur Mouth Analysis Regarding Cold-/WarmBlooded.)
There is an issue that we will NOT discuss here, but considering the enormous amount of food that had to be consumed, a similar amount of excrement would need to be eliminated. If on land, this is probably another situation where the tail would be briefly raised off the ground.
Some situation occurred about that time, around 65 million years ago, which appears to have been cataclysmic. It is commonly referred to as the K-T boundary event, referring to clear geological changes between the Cretaceous (K) Era and Tertiary (T) Period.
Extremely persuasive fossil evidence suggests that within about a two million year interval, all the remaining dinosaur varieties, as well as many other unrelated species seem to have died out, since no fossils of any of these creatures have been found that are younger than about 63 million years. By the way, most of the varieties of dinosaurs that we generally know about (including all the sauropods) had become extinct at various times well before this. Of large dinosaurs, only those resembling Triceratops still existed at this time. The "mass extinction" was very significant, but not quite as much as is generally thought. All of the sauropods were long gone, as were Tyrannosaurus Rex, Stegosaurus and many others.
Many speculations have been offered to explain this "sudden" disappearance. A massive asteroid or comet hitting the earth seems to have achieved current popularity. Extensive volcanic activity, which would obscure the Sun's light, is also a popular theory. Many other speculations have been offered.
Actually, one variety of Plesiosaur, the Elasmosaurus also seems to offer support for the long-neck arguments above. The swimming Elasmosaurus had a neck that was twice as long as its body! Such a creature could not support its own neck and head if it was a land-based creature.
Any mass extinction theory attempting to explain the circumstances of 65 million years ago must also explain the simultaneous disappearance/extinction of all the plesiosaurs.
Two million years is a long time! Even if dinosaurs only matured enough to have a next generation when 50 years old, that still represents as many as 40,000 generations of dinosaurs. That's a LOT!
In the time of Jesus, an average human was apparently six inches shorter in stature than today, and he lived an average of about 40 years instead of today's 70. Those significant changes have occurred in less that 100 generations of humans! A mere wisp of time compared to the two million years and 40,000 generations in which the dinosaur extinction occurred!
Similarly, when Spanish explorers brought some germs to the New World around 1500, the New World peoples had not previously developed any resistance to these apparently innocuous germs, as European people had. Within a hundred years (just five generations), the vast majority of New World peoples had died of those new diseases.
JUST within this past century, we have seen subtle(?) environmental effects that our industrial revolution has created and the effects of those changes on many creatures. Some are evolving in response, with the hopeful result of those species surviving. Others have NOT been able to evolve enough, and have or are becoming extinct. And this modern situation is in just one or two centuries, just a handful of generations. It's beyond imagination what the eventual result of our pollution and such will be at a point 40,000 human generations from now. Even very subtle changes in each generation necessarily have a geometric effect, and over this range, statistical extrapolation is totally unrealistic.
On the geologic time-scale, our current existence of humans is but a moment, yet, during our stewardship of the Earth, very large numbers of animal species have died off, some because humans hunted some species to extinction for food or for entertainment, and some because of secondary effects, such as Global Warming.
Clearly, SOMETHING DID happen in the environment about 65 million years ago. But it DIDN'T have to be a monumental, obvious event. Even something as small as a new virus (the equivalent of dinosaur AIDS, for example, or something far less spectacular like dinosaur measles) could have been the impetus. Remember the effects of Europeans and their diseases (and built-up societal immunities) on the residents of the New World 500 years ago. Huge numbers of Indians died from these seemingly innocuous diseases, because their bodies had no resistance to the new illnesses. Remember, also, those effects occurred in just a few generations, and the dinosaurs may have had as many as 40,000 generations in which to die off.
Several related presentations have been composed regarding different
aspects of Mass Extinctions:
A New (Galaxy-Related) Explanation for Repetitive Extinctions.)
An Old Explanation For Apparent Periodicity of Mass Extinctions.)
Most artists' renditions show dinosaur skin as shades of gray or green, and most show it as relatively smooth. Most scientists have concluded that the skin must have been thick and tough, similar to that of modern elephants. The logic supporting this is that these huge, slow creatures seem to have had absolutely no defensive capability against predators. The great size suggests a substantial lifetime and relatively slow movement. Logic suggests that very thick, tough, elephant-like hide was the only possible answer to avoiding having predators tear out big chunks of its flanks. The important point being made here is that much of these appearance considerations are sheer speculation. There is absolutely no way of proving that they weren't pink with yellow polka dots! (I am NOT presenting a polka dot theory here!!)
In a related vein, a paleontologist speaking about the new Lucy exhibit at Chicago's Museum of Natural History, recently joked that dinosaurs could have had feathers! He was both commenting on the apparent similarities between birds and some dinosaurs (particularly the wishbone) and the general lack of concrete knowledge about dinosaurs.
Please note that researchers have aggressively pursued knowledge on subjects of human history 1000 or 2000 or 3000 years ago. A reasonable amount of evidence has been accumulated for these eras, but there are still gaping holes in our understandings of the peoples and the events of those times only one hundred generations ago. Then consider how limited the evidence is that's likely to still exist regarding creatures and events beyond 65,000,000 years ago. It is truly amazing that we know anything at all about those times! The cautions in this essay are just to not leap forward into believing that we know all there is to know about these intriguing creatures, or that our current knowledge is all accurate.
Until the past couple decades, an amazingly small number of dinosaur fossils had been discovered, and none had represented complete skeletons. We are certainly moving in the right direction, and discoveries like the recent Lucy nearly complete fossil skeleton will certainly improve the accuracy and completeness of our knowledge.
Popular images about these large dinosaurs often present them as active, green, extremely mobile land animals, but all these aspects may be results of wild extrapolations of extremely limited information. Dinosaurs are certainly an interesting and exciting subject, both for study and for exercises in imagination, such as a number of recent movies. But in the scientific arena, we must maintain caution, to not go too far beyond the facts.
I am not implying that my thoughts here are the final word on any of the matters mentioned. They are merely meant as seeds for further investigation.
C Johnson, Theoretical Physicist, Physics Degree from Univ of Chicago