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Dinosaurs may have experienced less gravitational pull as a result 21.9hour day

  1. Jul 10, 2012 #1
    There are a number of factors involved in weight experienced by a particular mass on the surface of the earth.

    There is of course the Mass of the earth itself, the variable distribution of heavier elements in the earth itself, the motion of the ocean mass due to tides etc, the motion of the moon and other components but for the sake of this argument I would like to consider these factors idealised as fairly constant at any particular point in time.

    One other major component to an object's "weight" on the surface of the earth however is the fact that all object on the Surface of the earth are rotating around the earth at the same speed as the surface. This means that we are in a decaying orbit around the earth's center of mass, with the downward portion of that vector constantly arrested by our constant contact with the surface of that mass. This is a component of our measured weight as well.

    ~600 million years ago the earth's rotational period was around 21.9 hours instead of 24 hours.
    This logically means that if you existed 600 million years ago because of your increased "sub-orbital" velocity on the surface of the earth, your same mass would in fact "weigh" less than it does today.
  2. jcsd
  3. Jul 10, 2012 #2


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    But dinosaurs didn't come into existence until about 248 -225 million years ago.
  4. Jul 10, 2012 #3


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    While it is physically correct the difference is negligible. Try to evaluate it, it is not that difficult.

    To avoid nitpickers calculate weight of a 1 L of pure water, not of a dinosaur :tongue2:
  5. Jul 11, 2012 #4


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    PG, have you done any calculations to estimate how much these phenomena (even at their most optimistic) might affect the weight of objects?

    I think you will find that the whole issue simply goes away when you see the numbers.
  6. Jul 11, 2012 #5
    You seem to be talking about centrifugal force of the earth compared to the gravitational force of the earth. The gravitational force of the earth has always been much greater than the centrifugal pseudoforce of the earth. Neither the dinosaurs or us could be directly affected by the centrifugal force.

    The centrifugal force of the earth’s rotation is negligible. Today at the equator, the centrifugal pseudoforce is only 0.003 times as much as the gravitational force of the earth. The centrifugal force of the earth’s rotation in the Mesozoic would be only a slight bit larger, while the earths gravity would be largely the same.
    Here is a link showing how small the centrifugal force is today.
    “Difference is due to centrifugal force of earth's rotation (at equator, centrifugal force is about 3/1000 as much as Earth's gravity)”
    Calculations using the formula for centrifugal force would be could be useful. Remember, the pseudo acceleration caused by centrifugal force is:
    where a is the acceleration, v is the velocity of the earth’s surface at that latitude relative to the earths center, and r is the shortest distance of the earths surface to the spin axis of the earth at that latitude. If g is the gravitational acceleration of the earth, then it is easy to show that
    Just a nit: dinosaurs did not live 600 MYA. They lived between 65-250 MYA. The time 65-250 MYA is called the Mesozoic era. It was a lively time which produced a lot of fossils.
    There were no vertebrates or shelled animals 600 MYA. The time 550-650 MYA is called the Edicarian period. There are very few fossils from that time. There are some borrows that show that the animals at that time were very small. The most common fossil and the largest fossils from that time was an odd looking type of animal called a rangomorph.
    If short days produced large animals in the Mesozoic, then it didn't work in the Edicarian. Those few Edicarian animals, if any, were small.
  7. Jul 11, 2012 #6
    I had to laugh at myself there regarding the time of the dinosaurs and thank you for pointing this out.

    Also thanks for finding the earth's centrifugal force to Earth's Gravity ratio, this puts scope of the earth's rotation in perspective.
    Here is a link showing how small the centrifugal force is today.
    From Darwin123
    “Difference is due to centrifugal force of earth's rotation (at equator, centrifugal force is about 3/1000 as much as Earth's gravity)”

    I will give the calculation a go and post it when I think I have it.
  8. Jul 12, 2012 #7
    I suppose you could bother to do a calculation to determine that the centrifugal force is much smaller than the force of gravity, but the simple fact that the Earth is almost perfectly spherical should have told you that already.
  9. Jul 13, 2012 #8


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    Brilliant! This also explains why big dinosaurs are found mostly on land masses which had been near the tropics :-)
  10. Jul 13, 2012 #9


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    You forgot to add the appropriate [SARCASM][/SARCASM] tags.
  11. Jul 13, 2012 #10
    Tell it to the polar bears! Because there is no centripetal force at the poles, one would expect the smallest animals to live near the poles. However, there seem to have been quite a few large animals near the poles. Polar bears, Kodiak bears, mammoths, etc.
    There were large dinosaurs that lived near the poles. They weren’t as large as the largest dinosaurs near the tropics. Obviously, it must have had something to do with the g/3000 contribution of the centripetal force to the total gravitational acceleration !-)

    Here are some links concerning dinosaurs that lived near the poles.

    http://news.discovery.com/animals/north-pole-dinosaurs-111118.html [Broken]
    “North Pole Dinosaurs Lived Short, Hard Lives
    Northern Alaska during the latter Dinosaur Age was slightly warmer than it is now, but still experienced freezing temperatures during long, dark winters.
    Pachyrhinosaurus would have been preyed upon by the carnivores, but because of its size -- about 26 feet long and weighing around 4 tons -- Druckenmiller suspects few hunters "took on an adult-sized healthy animal."

    “Large, carnivorous dinosaurs roamed southern Australia 115 million years ago, when the continent was joined to the Antarctica, and were padded with body fat to survive temperatures as low as minus 30 degrees Celsius.
    Standing about 12ft (3.7 metres) tall, these hardy creatures inhabited the area close to the South Pole for at least 10 million years during the Cretaceous period, an expert said.
    Palaeontologists from Australia and the United States came by their findings after uncovering three separate fossil footprints measuring about 14 inches (36 cm) long, each with at least two or three partial toes.”
    Last edited by a moderator: May 6, 2017
  12. Jul 16, 2012 #11
    about 15 years ago . I wrote to the paleontology department of the Natural history Museum in London . I said I was not happy with the idea of dinosaurs weighing 100 tons.
    this was based on the fact that a structural surveyor had esimated the weight of my house at 100 tons. And a modern 50 ton battle tank uses a lot of fuel to get moving. essentially the fact that each leg of the 100 monster had to support 25 tons when perfectly balanced was a difficult to believe, I postulated that Dinosaurs could only have existed of this weight if the force exerted by gravity 250 million years ago was less than it is now.and the energy content and availability of vegetation much higher. my idea was ridiculed .in the reply I recieved . The museum stood by the fact of this heavy weights for dinosaurs. Soon after Fossils of even heavier 120 ton monsters were found. It now transpires that these weight estimations were wrong and over estimated, If a physist had been left to test models of the limbs of these creatures for their load bearing and power requirements this fact could have been found out years ago.
  13. Jul 16, 2012 #12


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    You mean they were overestimated because changes of the centrifugal forces were not taken into account? If so, they were overestimated by less than 0.1%, reread this thread and try to check the numbers. 0.1% in this context is nothing.
  14. Jul 16, 2012 #13
    I don't think he's referring to centrifugal force, but merely stating that the estimations were too high, without giving any reason for the estimations being too high.
  15. Jul 16, 2012 #14


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    Please provide citations for your claims.
  16. Jul 16, 2012 #15
    There is a hypothesis that the gravitational field strength at the surface of the earth has changed since early Mesozoic times, which is somehow related to the large sizes of reptiles on the earth. Although this theory is often discussed by fringe scholars, a few real scientists take it seriously.
    This hypothesis has been discussed by such scientists as Pennycuick and Carey, as quoted in the references below. However, these authors are using scaling laws. Scaling laws are only reliable when the organisms involved a structurally similar despite their over all size.
    There are deviations from the scaling laws when there are deviations in structure in any given group of animals. When comparing dinosaurs with mammals or tanks, one has to consider the special adaptations of dinosaurs. I don’t think there is any evidence that the size of animals is really determined by the strength of their bones. If this were so, then the bone structures of the largest animals would be fixed by the mechanical constraints. The bone structure of large animals is not fixed at all.
    The structure of the bones in a group of animals can vary quite a lot even though their proportions follow very simple scaling laws. This suggests to me the opposite. There are factors other than the strength of the bones that limit animal size.
    The dinosaur clade had a variety of bone structures. Many dinosaurs had hollow bones like birds. Some appear to have had solid bones like mammals. They also had a variety of gaits. In my opinion, this variation in structure and gait shows that gravity was not the limiting factor in dinosaur size.
    Scaling laws are only applicable when the important limiting structures are the same in the group of animals. If gravity determined the size of dinosaurs, birds and mammals, then all dinosaurs, birds and mammals would have to have fundamentally the same bone structure.
    Alexander (also see below) suggested that Tyrannosaurs may have moved faster than would be expected of an animal today. However, Tyrannosaur was an unusual dinosaur. They were built for power and speed in a way that other dinosaurs were not. Comparing all large dinosaurs to Tyrannosaurus would be like comparing a cheetah to a jaguar. Tyrannosaurs were likewise very different from other theropods.

    Here are quotes from two scientists who believe that the gravitational strength of the earth changed. As I said, I don't believe it. However, I find the mechanism of this change interesting.
    These scientists think the density of the minerals in the mantle changed. I would love to know by what mechanism the mineral densities could change that much throughout the mantle. Maybe the KT asteroid had something to do with it?
    “Newton Rules Biology” by C. J. Pennycuick (Oxfordd, 1992).
    Page 6: There are also reasons to believe that the strength of gravity at the earth’s surface has varied by quite large amounts over geographical time, with effects that can be seen in certain fossil creatures.
    Page 17: This rule also differs from the one for for walking and flying animals, whose stepping and flapping frequencies should vary with sqrt(g). …They are also also of interest in interpreting the mechanics of extinct animals, which lived at times when the earth’s surface gravity may have been stronger or weaker than it is now.
    Page 18: Biologists are not the only ones who perceive the strength of gravity as a constant. Most geologists also believe that the strength of gravity at the earth’s surface has changed only minor amounts, if at all, over geological time. An exception is Carey (1976), who has assembled a mass of evidence that the earth’s radius is much larger now than it was in early Mesozoic times, probably due to a reduction in the density of the minerals making up the mantle. Carey cautions against too readily assuming that any of the earth’s physical characteristics, including its mass, radius, plane of rotation, and surface gravity….It would seem that gravity has not been constant throughout geoplogical time, although the inferred variations do not exactly coincide with Carey’s predictions.

    “The Expanding Earth” by S.W. Carey (Elsiever, Amsterdam, 1976) .

    The fastest dinosaur that he recorded was moving at 3.6 ms-1. Alexander suggested this was more characteristic of the traditional lumbering image of dinosaurs.
    Since the publication of this paper a number of other trackways have been examined. The equation developed by Alexander has undergone various corrections and modifications by Alexander and other authors (Thulborn, 1981; Farlow, 1981; Russell & Beland, 1976). Top speeds reported by authors have suggested some large theropods, such as Tyrannosaurus may have reached up to 10 to 15 ms^-1.
    Alexander (1996) argued that based on the bone dimensions of Tyrannosaurus it is unlikely they could have traveled at more than 8ms^-1.

    Please note that Alexander finds a problem only with Tyrannosaur. As I said, Tyrannosaur is an unusual dinosaur.
    Alexander, R.M. (1976) Estimates of speeds of dinosaurs. Nature.Vol.261, pp.129-130.
    Alexander, R.M. (1996) Tyrannosaurus on the run. Nature.Vol.379, pp.121.

    Yes, many dinosaurs had hollow bones. The main reason it developed probably had more to do with respiratory limits than bone strength limits. However, hollow tubes carry more weight than solid tubes. High performance bicycles use double-butted frames, which in some ways are like the skeleton of some dinosaurs.

    “Granted, Coelophysis (pronounced see-low-FIE-sis) isn't very catchy, but the paleontologists of the mid-19th century adhered strictly to form when assigning names to their discoveries. The name Coelophysis was chosen by Edward Drinker Cope, who was referring to this dinosaur's hollow bones, an adaptation that helped it to remain light and nimble.”

    Note that in this article, whales and dinosaurs are presented as satisfying the same power law. Whales have buoyancy to cancel gravity, while dinosaurs did not. Many dinosaurs had hollow bones, while whales do not. The scaling laws described here have nothing to do with the structural limits of bones.

    “Finally, for a complete parallel of biology and mechanics, we expect a deviation from the 3/4 exponent towards 2/3 for small mammals (surface dominates at small scale) in the energy growth versus mass law. This deviation, nowadays still considered unjustified and unexpected, has been experimentally observed. It is clear that we would expect deviation towards the unitary exponent (where volume dominates) for very large mammals such as whales or dinosaurs.”
  17. Jul 16, 2012 #16


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    And because I like providing fiction as a source of enjoyable science-esque reading, read Robert Sawyer's End of an Era. http://www.sfwriter.com/exer.htm

    Martians have been doing field research on prehistoric Earth. With their advanced technology, they've placed satellites in orbit that reduce Earth's gravity to 38% (i.e. same as Mars).
    All was going fine with the giant dinosaurs - until the satellites all catastrophically failed! That happened just about - you guessed it - 65 million years ago. :biggrin:
  18. Jul 17, 2012 #17
    I am sorry for being vague in my first posting. My original concern sent to The Natural History Museum was that 250 years ago there were land based creatures that weighed 100 tons. The maximum weight of an elephant is around 10 tons.
    What has changed in 250 million years to reduce the maximum mass of land based creatures? My only thoughts were that the gravitational force of the earth had altered and the quantity and nutritional quality of vegetation had diminished
    It now transpires( see recent newspaper articles) that scientists had been overestimating the weight of large prehistoric creatures for many years.(to keep funding coming in?)
    I still believe that as C02 levels dropped in the last 250 million years vegetation did thin out . Did the earth become more dense and gravitational force increase ? i doubt it.
    Instead of rejecting my ideas out of hand a more scientific approach By the Natural History Museum would to have commisioned some mechanical engineers and orthopeadic experts to estimate the load bearing characteristics of these creatures limbs. this would have cast doubt on the 100 ton plus weight of these creatures
  19. Jul 17, 2012 #18


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    Please provide citations from credible sources. You have been asked twice now to back up your claims.
    I don't mean to sound offensive but you seem to be very arrogant here. On what basis have you come to a conclusion that you think paleontologists have missed or dismissed out of hand? If you do a journal search you can quickly find papers on sauropod estimated weights and in recent years more on their evolution and how they possibly came to be so big. Even following the wikipedia links would give you something like this
  20. Jul 17, 2012 #19
    I am not trying to be arrogant. I send a letter to the Natural History museum outlining my concerns about the weight of dinosaurs . I said that I just found it difficult to belive that craatures this heavy could move about or indeed eat enough to keep going. I received a quiet curt reply stating the larger creatures supported their weight by spending most of their time in water, They were able to process large amounts of vegetation for food because they had a mill located in their neck so they could breakdown food quickly. when i replied voicing my doubts the Museum refused to enter into any more correspondance.
    The Conspiracy theory is that bigger monsters get more visitors through museum doors
  21. Jul 17, 2012 #20


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    I advise you read this and this carefully and in future read published papers and books from scientists within the field so that you can understand why they conclude the things they do rather than dismissing them out of hand.
  22. Jul 17, 2012 #21
    This was the original article From The University of Manchester

    Dinosaurs lighter than previously thought

    06 Jun 2012

    Scientists have developed a new technique to accurately measure the weight and size of dinosaurs and discovered they are not as heavy as previously thought.
    University of Manchester biologists used lasers to measure the minimum amount of skin required to wrap around the skeletons of modern-day mammals, including reindeer, polar bears, giraffes and elephants.

    They discovered that the animals had almost exactly 21% more body mass than the minimum skeletal ‘skin and bone’ wrap volume, and applied this to a giant Brachiosaur skeleton in Berlin’s Museum für Naturkunde.

    Previous estimates of this Brachiosaur's weight have varied, with estimates as high as 80 tonnes, but the Manchester team’s calculations – published in the journal Biology Letters – reduced that figure to just 23 tonnes. The team says the new technique will apply to all dinosaur weight measurements.

    Lead author Dr Bill Sellers said: "One of the most important things palaeobiologists need to know about fossilised animals is how much they weighed. This is surprisingly difficult, so we have been testing a new approach. We laser scanned various large mammal skeletons, including polar bear, giraffe and elephant, and calculated the minimum wrapping volume of the main skeletal sections.

    “We showed that the actual volume is reliably 21% more than this value, so we then laser scanned the Berlin Brachiosaur, Giraffatitan brancai, calculating the skin and bone wrapping volume and added 21%. We found that the giant herbivore weighed 23 tonnes, supporting the view that these animals were much lighter than traditionally thought.

    Dr Sellers, based in Manchester’s Faculty of Life Sciences, explained that body mass was a critical parameter used to constrain biomechanical and physiological traits of organisms.

    He said: “Volumetric methods are becoming more common as techniques for estimating the body masses of fossil vertebrates but they are often accused of excessive subjective input when estimating the thickness of missing soft tissue.

    “Here, we demonstrate an alternative approach where a minimum convex hull is derived mathematically from the point cloud generated by laser-scanning mounted skeletons. This has the advantage of requiring minimal user intervention and is therefore more objective and far quicker.

    “We tested this method on 14 large-bodied mammalian skeletons and demonstrated that it consistently underestimated body mass by 21%. We suggest that this is a robust method of estimating body mass where a mounted skeletal reconstruction is available and demonstrate its usage to predict the body mass of one of the largest, relatively complete sauropod dinosaurs, Giraffatitan brancai, as 23,200 kg.

    “The value we got for Giraffatitan is at the low range of previous estimates; although it is still huge, some of the enormous estimates of the past – 80 tonnes in 1962 – are exaggerated. Our method provides a much more accurate measure and shows dinosaurs, while still huge, are not as big as previously thought.”

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