March 31st, 2010, 05:14 PM
Is the physiology of dinosaurs impossible in our current gravity? Anyone know? I know some have suggested this.
Also, is there anything other than an assumption that proves that the strength of gravity has been constant since the dawn of the universe?
The Earth's gravity has not changed to any appreciable extent since the dinosaurs. So, yes, they could handle our gravity.
In fact, there may be a change that would be a problem to dinosaurs. It appears that oxygen levels were higher in dinosaur times. So lower oxygen today might be a problem.
Has gravity changed? Not a question anyone can answer definitively, but there is no indication at this point in time that it has. Rough estimates can be obtained by looking at the positions of galaxies at extreme distances - ie as they were early in the universe. So far, no indication of a change in gravity, and no real reason to look for one, either.
March 31st, 2010, 05:51 PM
LOL i have always wondered that my self as to the consistency of gravity! I once challenged my science teacher who said that gravity was constant every where. I said that seeing as some other galaxy is billions of light years away that maybe gravity was different there? Seeing as at one time the universe was much smaller from the time that i am viewing that galaxy from earth? :P I wonder if there is any way to test that? But then again i am not entirely sure what might determine the power of gravity (prob subatomic weights is my guess :P )Originally Posted by zzpluralz
Gravity is not constant everywhere in the Universe; Gravity is constant everywhere on Earth. Your teacher should have specified that.
Subatomic particles do not account for gravity. Ever object that has mass has gravity.
lol of course! I dont mean like that! :P
I mean for instance the gravity that 1 atom has? any where in the universe my bad for misphrasing that?
Also, don't forget that many dinosaurs were quite small - perhaps the size of a modern day chicken.
Everything acounts for the gravity, even subatomic particles.. Of course they affects just a little bit but it isn't zero!
The question does make me wonder if bus-sized grasshoppers or slugs are possible. What are the purely structural limits.
For land arthropods, I think there's a limit on how large they can be and still carry their own weight- or so I have heard. Certainly atmospheric oxygen levels put a limit on them these days, on account of the circulatory/gas exchange system they use. No lungs, just a series of pores along their body which are directly connected to bronchiole-like structures which more or less directly oxygenate the tissues. Not at all as efficient as the vertebrate lung/heart-pumped blood combo.
I suspect that land vertebrates also have upper limits in size at the current oxygen level, though clearly a higher upper limit than arthropods. No idea about gastropods.
On gravity- it appears to be constant everywhere. Don't confuse gravity being constant (proportional to mass) with it being the same for all objects. Nobody, including your teacher, is suggesting that. They're saying that gravity is the same for an object of mass X here as it is for an object of mass X 1 billion light years away from us. The gravity of Earth has been more or less unchanged since the time of the dinosaurs, so it's not a factor in their size.
Isn't there some sort of a limit imposed by the mechanism used by Arthropods to move their limbs? Do they open them with hydraulic pressure and is that a limitation? I seem to remember something like this...
The biggest limit seems to be their capacity for air delivery. The most efficient method in land species is the book lungs of arachnids, but even that isn't sufficient for very large sizes. When oxygen levels were high arachnids were able to reach the size of cats (scary!).
Arthropods use both muscle contraction and hydraulics, the hydraulics are often used to extend limbs. (some use only muscle)
Although, I remember hearing that although oxygen levels contribute in large part to the small size of land arthropods today. They may be smaller than the oxygen levels support simply because of selective pressure from vertebrates. They couldn't become bigger than the vertebrates so they had to get smaller to avoid them. Most of the large arthropods lived at the end of Carboniferous and the beginning of the Permian before many large vertebrates existed.
You are talking about the principle of scaling. I will try to explain it simply.
Imagine a land animal with legs that support it. The strength of those legs will depend on their cross sectional area. A square function.
What about the mass it supports? The degree of mass depends roughly on length times breadth times thickness. A cubed function.
If we double the size, the strength (cross section of the leg) increases by two times pi times the radius squared. A four fold increase. However, mass increases by two times the length times two times the breadth times two times the thickness. An eight fold increase.
In other words, if we keep everything in the same proportion, the mass to be supported increases much more than the strength of the legs doing the supporting. It does not take much such increase before the animal is flattened!
This is the reason that large animals with legs, like an elephant, have disproportionately thick legs, while animals that are very small, like an ant, have disproportionately thin legs.
Yes, I think that was the gist of the original question. So now, the question becomes, whether the cross-sectional area of the legs of the largest dinosaurs is much greater than that of an elephant, in proportion to their linear size. Or something like that.
April 3rd, 2010, 03:31 PM
zzpluralz,
In response to your original questions.........Yes, the Earth's surface gravity was less during the age of the dinosaurs.
The distinction has to be made between the Earth's surface gravity and that of universal gravitation, which has not changed to my knowledge.
There are basically two ways the Earth's surface gravity could change. First, an expansion of the Earth, which cannot be explained or verified. Second, is a shift in the Earth's iron cores, both inner and outer. A core shift can be explained.
Today, the Earth's continental plate masses are distributed fairly evenly around the globe and the cores are centrally located. In the past, this was not the case and specifically during the time of the dinosaurs, the continental land masses were consolidated into a single supercontinent, called Pangea. This consolidated would have caused a shift in the cores' position away from Pangea. The increased distance to Pangea's surface position would have resulted in lower surface gravitation on Pangea.
Hope this helps.
Batman
Would you please post references to support your statement.
Frankly, I do not believe it. The only way Earth's gravity is likely to have increased since the days of the dinosaurs is by continued accretion of matter falling from outer space. This happens, but the change in gravity would be utterly trivial.
Not quite, when considering gravity at the surface ...
surface gravity can increase either by the addition of mass to the body,
or by a decrease of volume of the body (same mass; increased density; less distance to centre of mass/gravity) ...
in either case, the amount of change possible would be negligible with respect to life on the surface ...
If I recall correctly, insect size is limited by the size of their trachea. The tracheal tubules of insects have to traverse the narrow joints from their extremities. To maintain flexibility, strength of limb, and proper airflow, these tubules are limited in size. When oxygen concentration was high in early earth history, insects could increase their body size without substantial increases in the size of their trachea. This explains why we have found remains of cat size spiders and dragonflies with wings spanning three feet. For a grasshopper to grow the size of a bus, oxygen concentrates will most likely have to be as thick as pea soup--insect trachea could remain small while able to absorb higher concentrations of oxygen to fuel their larger body size.
Skeptic,
Per Newton's Universal Law of Gravitation, there are two variables that influence the strength of gravitation: mass and distance. Since the distance variable is at the second order (i.e., squared), it has a much greater effect.
A shift of the cores, depending on the shift amount, could have a significant effect at the surface. A core shift away from Pangea would cause a surface gravitational gradient with lowest surface gravitation at Pangea's center of mass (near the equator) and higher surface gravitation moving toward either pole.
There are many instances that can only be explained if this core shift occured. I'll mention just one. Recently, the remains of a small T. Rex was found in Australia. It was much smaller than it northern relatives. As reported in science news, the question was asked "Why did they achieve giant size as apex predators in the north, but dwindle away in the south?" One can speculate about the answer to this question but it can readily be answered based on the explanation above. If there was a gravitational gradient, the largest dinosaurs will not be found in extreme north or south locations. One caveat though is: Australia did move away from the southern pole at the end of the Cretaceous.
Batman, when you hear hoofbeats, do you think zebras before bothering to check for horses? Finding a smaller version of T. rex does not first suggest variable gravity. It merely suggests different selective pressures between two environments. Those pressures are likely to be far more mundane than gravity differences. Availability of food and water, competition from other predators, local climate... all things which can serve to make a large body uncompetitive or too costly.
Invoking gravity to explain this stuff before exploring the much more obvious explanations is plain wacky.
Batman:
The inner core has a total mass of 1.7% of the total mass of the earth. The outer (liquid) core is 30.8% and the crust (Pangaea and oceanic crust combined) constitutes a mere 0.473%. The migration of Pangaea would not have anything close to the effects you propose.
One thing I don't think anyone has noticed, or maybe just stated outright, is that a changing strength of gravity is actually a reasonably well known creationist argument. It suggests that the fundamental constants of nature - including "G", the gravitational constant, have been changing over time. If this constant is changing, then they will say that all of the fundamental constants are time-dependent. Which would mean that radiometric dating results are all wrong, science hasn't got any real clue about anything, dinosaurs lived recently and that the earth is not billions of years of old.
There is some evidence that G has in fact been changing. However, it's only observed over immense timescales and can't really be separated from experimental error. It certainly wouldn't have changed any appreciable amount to make the lives of dinosaurs impossible during the period when they lived.
Hmmm, I have to correct this.
The specimen found in Australia (specimen # NMV P186069) is a partial hip bone possibly from a basal member of the superfamily Tyrannosauroidea. It has not been described beyond that placement and if it is a basal tyrannosauroid, it is NOT a specimen of the species Tyrannosaurus rex, which is a derived tyrannosauroid, thus your analogy that the of T. rex does not work.
Plus there are plenty of massive dinosaurs found in the southern hemisphere (Argentinosaurus and Antarctosaurus anyone) so a gradation explanation is not valid.
Well, skeptic covered the square vs. cubed part of my understanding.
I have often wondered this myself. Dinosaurs would simply be too massive to survive today I think. I'm not certain, but weren't oxygen levels far higher in the past?
Now weather a person is spiritual or not, the Bible does offer history, supported by other related writings as well. I don't intend to make this a religious argument, but refer to Genesis 6:4:
This is before the flood. Where would all that water come from to rain for 40 days and nights? Taking the asssumption this really happened, we can assume the sun had a massive CME event, and the earth traveled through it's path. The hydrogen would readily combine with oxygen in the upper atmosphere and cause rain, reducing the oxygen that was there.There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown.
Sure, just a hypothesis, but it is possible.[/list]
The changes in oxygen levels have been gradual over millions of years, not over night from rainstorms.
Oxygen levels increased from Permian into Jurassic, which saw the rise of the dinosaurs. They also increased further towards the end of the Cretaceous, close to the time of dinosaur extinctions. It is probable that the Jurassic rise assisted the evolution of the dinosaurs. However, oxygen was not appreciably higher than today.
During that time, it is also worth noting that CO2 levels were high and the world was warmer than the present. It has been suggested that dinosaurs grew so big in order to maintain warm blood. High body mass and generally warm conditions would permit this. They probably were not truly warm blooded in the sense of mammals and birds, but gained an advantage when they could maintain warmer body temperature, which is easier to maintain with high body mass.
Since (probably) they could not maintain body temperature as well as mammals and birds, the plunge in temperature after the KT asteroid impact would have been a big factor in their demise.
Could a dinosaur survive today? Almost certainly, yes. There is nothing about the world today that would be inimical. However, we just don't got no dinosaurs!
Except all those fun feathered things in classified as birds!
The other possibility is that the average atmospheric pressure might have been different. Higher atmospheric pressure would create buoyancy, which would have exactly the same effect as reduced gravity.
Think about why a human can float on top of water. It's because water is dense. To the degree that the medium you are standing in is dense, your body appears to be lighter. Maybe the air was just more dense back then.
But moving IN water is harder and that is what a denser atmosphere would create. the sensation of moving in water. Thus it would have probably created much different shaped creatures then the dinosaurs, more aaped to moving through a thick atmosphere. the morphology of known taxa from the Triassic through the Cretaceous does not support this. Plus how would it have effected flight? the large diversity of flying animals, both Pterosaurian, and bird would have to be accounted for.
Guys
This is kind of ridiculous. We have several substantially weird propositions in the thread - reduced gravity, and atmospheric pressure increased to the point of making organics buoyant.
Both propositions fall into the category of extraordinary claims. For those, we need extraordinary evidence. And so far, we aint seen none!
The truth is far more simple. Gravity was essentially the same as today. Atmospheric pressure was essentially the same as today. There was more CO2 and it was warmer.
A human could go back to the cretaceous and live quite well (if such a thing as time travel was possible). A dinosaur in our present could also live quite well.
besides, there's not a shred of evidence for a change in gravity or atmospheric density during the Phanerozoic
the only reason the claims are being made is in order to support the expanding earth theory
Well if that's where this thread is going, it'll be heading for pseudo pretty sharpish!
The partial pressure of oxygen required to cause toxicity in humans is 0.30 kPa, so the Triassic and the Jurassic would have been fully tolerable to humans, but the Cretaceous might have bordered on dangerous levels of oxygen.
http://jxb.oxfordjournals.org/cgi/co...ull/52/357/801
This article says the partial pressure of oxygen in the Carboniferous was 0.40 kPa, which would have been toxic for humans. However, for all the time dinosaurs lived the oxygen levels would have been tolerable for humans. Dinosaurs would probably be able to survive in our oxygen levels too, maybe not all, but some. However, this is more to do with them being adapted to a certain level of oxygen pp rather than their size.
Brontosaurs are already believed to have stood in bodies of water in order to help support their own weight.But moving IN water is harder and that is what a denser atmosphere would create. the sensation of moving in water. Thus it would have probably created much different shaped creatures then the dinosaurs, more aaped to moving through a thick atmosphere. the morphology of known taxa from the Triassic through the Cretaceous does not support this. Plus how would it have effected flight? the large diversity of flying animals, both Pterosaurian, and bird would have to be accounted for.
No!! I wasn't trying to suggest that anybody would be weightless/totally buoyant!! It's all a matter of degree. If the pressure of the atmosphere increases by 0.1 atm, you will find that your apparent weight is diminished slightly. It's true that your wind resistance will also increase, but if you're moving slowly to begin with, your wind resistance will be pretty small either way. (Wind resistance increases with the square of velocity, so lower velocities have exponentially smaller resistances than higher velocities do.)
At the extreme, moving in a fluid as dense as water can make you seem totally weightless. But every single place on the scale, between a vacuum and water, has a different apparent weight.
You mean other than that the Earth was warmer than it is today? How could the Earth be warmer overall without that resulting in a greater humidity? You can ask anyone who has studied global warming, and they'll tell you about this effect. More water is always absorbed by a hotter atmosphere. In the case of the dinosaurs, there was probably more total water to begin with as well, because the ice caps would be smaller.
There's also the simple fact that any heated fluid expands, but where would it go? Even if the humidity remained constant, the apparent pressure of the system would have to be higher from that also.
kojax
There are always minor differences in atmospheric pressure, even minute by minute in today's world. However, to get an increase enough to buoyantly support a dinosaur, even to a relatively minor level, that is a different story.
Any increase in atmospheric pressure in the Cretaceous would not have reduced a dinosaur's effective weight to any level that would assist the dinosaur. Not even a kilogram's worth!
April 6th, 2010, 07:53 PM
To All,
We can only examine the circumstantial evidence to determine whether shifting cores produced a lower surface gravity (not G but g). I will list a few of these:
1. The largest anomalous creatures that we have found the remains of were found closer to the paleoequator than closer to polar regions:
The 8 foot long scorpion in Germany (Jaekelopterus Rhenaniae).
The dragonfly with two foot wingspan Meyaneuropsis permiana (Europe).
Quetzalcouatlus northropi, one of the largest pterosaurs (Texas).
One can say that this it is just a coincidence that these giants were found near the paleoequator, but is it?
2. The largest flood basalts occurred when Pangea was a consolidated supercontinent, Siberian,Deccan,Karoo. etc. This would have been the period when core(s) movement would have been extreme. Since flood basalts originate at the core-mantle boundary and have tapered off since the Pangean breakup, the coincidence can only be explained by core movement.
3. The largest Jurassic sauropods did not inhabit regions far from the paleoequator. The OP makes a point about South American titanosaurs.....these were far different from the mobile, migrating sauropods of the Jurassic.
4. A recent article about the T-J extinctions that allowed the dinosaurs to flourish, but eliminated the crurotarsans tried to explain this anomaly:
"But the reasons underlying dinosaur's survival, diversification and massive size for 160 my while their crurotarsan foes did not evolve in a similar fashion remains a mystery."
The T-J extinctions occured when the Pangean supercontinent began its breakup with the formation of the Atlantic Ocean. The theory I support would explain this as a pulse of increased surface gravity that eliminated the sprawling leg crurotarsans, favoring the straight legged dinosaurs. Sprawling legs don't do well with increasing gravity.
Hope this helps
If in fact larger species were more often found near the equator than away, wouldn't the more logical cause be the higher temperature at the equator? Moreover, in general today we see much more biodiversity around the equator than at the extremes, so I suspect that even in earlier periods this pattern would continue and you would simply have more species in general, not just large ones, near the equator.
Batman:
Are you ignoring the facts I supplied regarding the relative masses of the core and crust? There is simply not enough mass to have anything close to the effect you are suggesting. Further, can you imagine the kind of atmospheric disturbances there would have been with such a large gravitational imbalance? These straightforward facts refute your idea outright.
woot for discredited ideas about dinosaurs using a genus that was synonymised into a different genus 108 years ago......... :/Brontosaurs are already believed to have stood in bodies of water in order to help support their own weight.But moving IN water is harder and that is what a denser atmosphere would create. the sensation of moving in water. Thus it would have probably created much different shaped creatures then the dinosaurs, more adaped to moving through a thick atmosphere. the morphology of known taxa from the Triassic through the Cretaceous does not support this. Plus how would it have effected flight? the large diversity of flying animals, both Pterosaurian, and bird would have to be accounted for.
You mean Apatosaurus, which was named before "Brontosaurus", both were synonymized in 1903!
The idea that sauropods were aquatic due to their large mass has been shown to be false and was in general only applied to the Brachiosaurids anyway, not to the other members of the infraorder Sauropoda. It has been shown that the water pressure associated with a totally submerged lifestyle would have prevented the Brachiosaurid from breathing. Plus the "snorkel" nostrils did not actually exist, rather the nostrils at the front of the head and were part of a elongated nasal cavity similar that of the hadrosaurs.
April 7th, 2010, 02:34 PM
i-feel-tiredsleepy,
Good point about higher temps near the equator. The only observation I can offer is that the mammoths, recently extinct, were larger than today's elephants and they thrived far away from the equator.
Kalsata,
You are missing the point. The consolidation of Pangea (on the SPINNING Earth) with its center of mass near the equator would have caused the core(s) to compensate by moving away from center and from Pangea. It is the change in DISTANCE to the surface that caused the gravitation change.
Paleoichineum,
I agree, added atmospheric pressure would have a negative effect on terrestrial animals. Animals with large horizontal cross-sectional area would incur additional "effective" weight. If you try to walk in water, you get an idea of the impact on mobility.
The Biologista,
No! this is not about an expanding Earth.
Your comments about reasons for T-rex not attaining large size in Australia are reasonable but you would have to provide some specific references relative to paleo-Australia to support this. The researchers who reported this info did not mention these possibilities.
Zwirko,
No Creationism here. I suggest a change in g not G.
Paleoichneum,
I can only repeat what I've read. Which is, that the bone unearthed "is the first evidence that ancestors of the might T. rex once lived in the Southern Hemisphere." The question remains: Why didn't T-rex (the large one) exist in, for example, Australia?
In regards to Argentinosaurus, et al., let's focus on when Pangea wass consolidated because then there was the capability for all species to migrate everywhere. Specifically, during the Jurassic, do you agree that the largest sauropods are found in the lower latitudes?
Skeptic,
I agree with your comments about oxygen levels. During the Carboniferous, they were low. Yet the large 8 foot scorpion and the dragonfly that I alluded to lived during this period.
Your comment about the plunge in temperature after the K-T must be reconciled with the fact that there were polar dinosaurs that thrived in colder weather.
Of course, I disagree with you statement about dinosaurs living today. Yes, some could but most evolved in a low gravity environment.
Batman
Very simple.
Earth during the time of the dinosaurs was not a low gravity world. Earth's gravity has not changed to any appreciable extent since the occasion, 4.5 billion years ago, when it briefly coincided in space time with a Mars sized object.
To propose otherwise is an extraordinary suggestion, and requires extraordinary evidence. If you insist on that idea, and want people to take you seriously, you must post evidence.
An interesting discussion.
Has anyone visited the web pages below?
http://www.freerepublic.com/focus/chat/1989265/posts
It was this that got me thinking.
Can anyone answer the Qs posed? The Q about blood pressure requirements seems a difficult one to answer.
Is the author of this web page just plain wrong, or is this one of the things that pople just don't want to discuss.
I know that some 'serious' paleontologists have questioned the possibility of dinosaur size. Have the questions been answered beyond all reasonable doubt?
No I am not, you are. You don't really seem to have a head for numbers (neither do I, but this is ridiculous). Even if you decide to remove the entire inner core (i.e. move it an infinite distance away) the BIGGEST gravity change would be a 1.7% change. That means a 70 ton hypothetical dinosaur would now weigh 68.81 tons. Big deal! The fact is that it would not even be close to that much, because the whole of Pangaea (based on todays continental mass) would constitute a mere 0.374% of the total mass and would be able to affect only a proportionate amount of mass momentum wise. Also, no matter how you move around mass inside the earth, the centre of mass of the earth would still be the length of the radius away. So, AFAIK, weight would change only as distance from the centre of mass of the earth changes, i.e. dinosaurs would weigh less at the poles rather than at the equator, as would be the case today as well. How can you possibly account for this hurdle to your idea? You also still haven't provided a citation for your claims.Kalsata,
You are missing the point. The consolidation of Pangea (on the SPINNING Earth) with its center of mass near the equator would have caused the core(s) to compensate by moving away from center and from Pangea. It is the change in DISTANCE to the surface that caused the gravitation change.
PS: My name is KALSTER
April 7th, 2010, 05:57 PM
The tyrannosauroid question is easy, out competition from other large theropods. Large theropods such as Cryolophosaurus have been found in the Jurassic formations of Antarctica and allosaurids such as Australovenator from Cretaceous Australian sediments.
Why are Antarctosaurus and Argentinosaurus not admissible as viable evidence of large taxa existing near the polar regions and disproving your assertion? Also noted earlier is the diverse mammalian faunas of the Pliocene and Pleistocene which included rhinos, probocideans, hippos, etc. living in Europe and North America far from the equator without problems.
Pangaea started to break up at the beginning of the Jurassic, but that is not the point. You made the claim that the largest animals would be found towards the paleoequator, with no specification as to a time frame. You then proceeded to list three examples from different periods as evidence for you assertion. So there is no point in trying to confine the time frame now.
As for the aforementioned three taxa:
Jaekelopterus rhenaniae was not a carboniferous scorpion but a Devonian age eurypterid, and fully aquatic. As shown by the modern whales range for aquatic animals is not limited equatorial waters.
Meganeuropsis permiana is not a dragonfly, but a member of the extinct insect order Protodonata, and is not European but known from Early Permian fossils found in Kansas, again not Carbonifeous. This places it as a mid paleolatitude creature not equatorial
Quetzalcoatlus northropi a late Cretaceous pterosaur in the superfamily Azhdarchoidea. Members of this superfamily have also been found in Oregon, Saratov Oblast, Russia, Zhejiang prov. China, and Glacier County, Montana. Typically wide distribution that one would expect from avian taxa.
April 8th, 2010, 09:06 AM
Paleoichneum has addressed this already. He's got evidence of horses and you're still crying 'zebras'. That's not rational.
Massive quantities of hydrogen from a CME...
2 H2 + O2 = 2 H2O
Skeptic,
I disagree with your assumption that the Earth's surface gravity never changed. I've supplied several bits of circumstantial evidence to support this. One of these is the excessive flood basalt activity during the existence of Pangea. I have linked this activity with movement of the core(s). How would you explain this core/mantle volcanic activity which has gradually diminished since the breakup of Pangea?
Kalster,
If you were living on Pangea, near the equator, your weight would have been affected by two things:
1. The consolidation of the continents would have reduced your weight by a small amount. The reason for this is that the component of their "pull" on you would be reduced because the vector component directed toward the Earth's center would be less than if the continents were dispersed. I am going to take a guess and say this would reduce your weight by about 3%.
2. Your weight would have been primarily determined by the distance between you and the Earth's center of mass. Let's arbitrarily assign the diameter of the Earth at 12 units; 6 units from you to the center of the Earth. If the cores, both of them shifted away from you so that new center of mass of the Earth was 9 units away from you, the ratio of your new weight to your old weight is as follows. According to Newton the ratio of the two weights would be:
(Original distance)^2/(New distance)^2
= 6^2/9^2 = 36/81 = .44
Therefore your new weight would be 44% - 3% =41% of your old weight
I hope this helps.
Paleoichneum,
I don't know if the tyrannosauroid question is easy or not. Out-competed is only conjecture......there is no way this can be verified.
Cryolophosaurus, at one half ton, compared to a 7-ton T-rex, would not be considered a large theropod. At least not to me.
Antarctosaurus was misnamed.....its remains were found in South America, not Antarctica.
We have to distinguish what periods the dinosaurs lived in in order to do geographical size comparisons. During the late Jurassic, for example, southern Florida was located at the paleoequator. This supports the claims that I have made. Specifically, some of the largest dinosaurs were found in areas (in the USA) not far north of the equator's position at that time.
North and South America then started moving north throughout the Cretaceous. This would have shifted lower surface gravity further south into S. America. This is consistent with the fact that larger theropods were found in S. America in the late Cretaceous but not the Jurassic.
You are correct about the Devonian timescale for the scorpion and dragonfly but the point made is still valid. Unusually large life forms, with relatively low oxygen levels and continents in a more consolidated formation compared to today have been found. Europe and Kansas were relatively close to the equator during the time in question.
If you have any references to remains of Quetzalcoatlus northropi that come anywhere near the size of the one found in Texas, from a more distant location to the equator, I would be interested.
Occam's razor comes into play. Yes it is not provable that it was out competition, but with evidence of large theropods in Australia after the disappearance of tyrannosauroids it seems like the simplest explaination.
When you are comparing to one of the heaviest known theropods, yes. However when looking that the majority of known theropods, eg. Dilophosaurus, <i.Megapnosaurus[/i], Alvarezsaurus etc... it is one of the larger theropods.
I just noted that fact thank you for bringing it to my attention. This does not change the fact that Argentina was not near the paleoequator, add to that Diamantinasaurus and Wintonotitan saurpods from Australia, another landmass not near the paleoequator.
Hmm, Triassic, Jurassic, and Cretaceous, thatwas easly. Why the need, and what are we comparing to what, at this point that would be need the specific time segregation?
Why does this support anything? A large number of small dinosaurs have also been found in the same deposits.
How do you explain large dinosaurs in China then, which was never "near" the paleoequator but has produced dinos such as Gasosaurus and Mamenchisaurus
Define "relatively".....
And for the second time Jaekelopterus is not a scorpion and Meganeuropsis is not a dragonfly. Also Meganeuropsis was a Permian insect not a Devonian, placing Kansas at mid latitudes not near the paleoequator. Jaekelopterus was an aquatic animal and they are affected by the water much more then land taxa, and as shown by modern cetacean distribution could very easily been a migratory animal, as it does appear to have been an accomplished swimmer.
*sigh*, Q. northrupi is known from only a couple of specimens from Texas. RELATED genera is the term you are looking for.
Hatzegopteryx from the late Cretaceous of Trannsylvania was similar in size to possibly larger and was a mid latitude animal.[/quote]
April 12th, 2010, 02:52 PM
Paleoichneum,
First, I’d like to go back to your earlier post where you state “As shown by the modern whales range for aquatic animals is not limited to equatorial waters.”
Absolutely true, there is no fluctuation of surface gravity today as there was in the distant past.
The following responses are to your last comments:
Occam’s razor is sometimes used as a fall-back position when a more complex, but viable explanation is offered.
In response to my statement that Cryolophosaurus was not a large theropod, you stated basically stated that one has to compare it to all theropods. I disagree, we are comparing the heaviest known dinosaurs, including theropods, for a specific time period. Isn’t that the gist of the discussion?
Again, in response to my statement that the remains of the largest dinosaurs found in the USA were found in locations not distant from the paleoequator, you stated “Why does this support anything? A large number of small dinosaurs have also been found in the same deposits.”
Small dinosaurs are not relevant. As in today’s world, there is a wide range of animal sizes that have evolved in current surface gravity. Only the largest ones are meaningful to the present discussion.
I disagree with your statement that China was never “near” the paleoequator. Certainly not South China, specifically Sechuan where Mamenchisaurus existed. Also, Gasosaurus was not a large dinosaur unless you feel 350 pounds is large.
The question of large sauropods in Australia is interesting. First, we have to realize that during the Jurassic, Australia was south of Africa, near Antarctica. Correct me if I’m wrong, but there were no large Jurassic dinosaurs known from this period in Australia nor Antartica even though they had a temperate climate. It was only when Australia broke off from Gondwana and moved north to a latitude comparable to mid- South America that we find larger dinosaurs. If that is true, how would you explain that?
As I pointed out in an earlier posting, North & South America moved north during the Cretaceous shifting the lowest surface gravity locations further south into S. America. I believe this is why titanosaurs grew to large size there. And, as you probably know, titanosaurs were markedly different from Jurassic sauropods. Short-necked (reducing lower blood flow to head problems), wide-gauged stance (better support in an increasing “g” environment), solid backbone instead of a hollow one (better support in an increasing “g” environment), etc. And, I believe they were not migratory as were their Jurassic cousins.....meaning they did not have to expend as much energy.
Using your expression: “*Sigh*”, in relation to your objection of the words “scorpion” and “dragonfly”, I am only repeating the reporting by the Associated Press:
“FOSSILS OF WORLD’S BIGGEST BUG FOUND”
“390 million-year-old remains of scorpion reveal 8-foot-long insect”
And, Kansas was not far from the paleoequator at that time. If Meganeuropsis was found in northern Canada, then you might get my attention.
Batman
Your claim that the dinosaurs grew so large because gravity was less is an extraordinary claim. So far, you have not produced any evidence of note. Continental drift is not going to affect gravity. The continents 'float' on the underlying magma in a state of dynamic balance. When the less dense land mass rises above the sea, it pushes the more dense magma down, balancing gravity.
The total gravity of the Earth holds it in a shape close to a sphere. Apart from a small amount of centrifugal action at or near the equator, making equatorial areas appear to have a tiny fraction lower gravity, gravity is equalised throughout the world. The only other variation is likewise trivial - being the presense in localised areas of large masses to locally increase gravity.
All these effects are utterly tiny in terms of permitting or not permitting animals to grow larger or smaller. If you postulate a change in gravity sufficient to permit dinosaurs to grow to great size, you are talking of a very substantial reduction in gravity. No known mechanism can do that. And there is exactly zero evidence in geology of any significant change in gravity.
There are numerous ways animals can adapt to large size. Some dinosaurs, for example, had hollow bones, reducing their weight. Massive supporting legs are found in the largest specimens. The use of heavy duty tendons to support weight can be effective. Biological adaptations are far, far, far more likely to be the reason for large size, rather than a 'magical' reduction in the Earth's gravity.
As said before, if you postulate something extraordinary, you need extraordinary evidence. No such evidence has been offered.
Your guess is wild and unsupported, plus I don't know what you are trying to say with "because the vector component directed toward the Earth's center would be less than if the continents were dispersed". Are you trying to say that moving more above sea level reduces gravity? Sure it will (all things being equal), but nothing close to 3%.1. The consolidation of the continents would have reduced your weight by a small amount. The reason for this is that the component of their "pull" on you would be reduced because the vector component directed toward the Earth's center would be less than if the continents were dispersed. I am going to take a guess and say this would reduce your weight by about 3%.
My primary contention with this is that you have not given any reason why this might happen. The mass of the continents are nowhere near large enough. If there is nothing to counter the mass of the cores, then they won't move, and even if they did, then the centre of mass of the earth would stay more or less put, because there has to be an equilibrium. If the centre of mass was shifted by as much as you are saying, the rotation of the earth would not be stable. Life would end.Your weight would have been primarily determined by the distance between you and the Earth's center of mass. Let's arbitrarily assign the diameter of the Earth at 12 units; 6 units from you to the center of the Earth. If the cores, both of them shifted away from you so that new center of mass of the Earth was 9 units away from you, the ratio of your new weight to your old weight is as follows. According to Newton the ratio of the two weights would be:
I say again: Look at the mass component the continents contribute to that of the earth or even compared to the two cores combined. It is much smaller by orders of magnitude. There is simply no mechanism to support such an idea that I know of short of a cataclysmic interaction between the earth and a foreign body (similar to the collision event that formed the moon).
April 13th, 2010, 02:19 AM
Also, centripetal force from the rotation of the Earth offsets it more at the Equator, because it's located on the outer edge of the spinning globe.
The amount of lift provided by the air around you is approximately equal to the amount of lift what would be created by a hydrogen balloon of your volume. However much it could pick up, that's about how much help you are getting. If the pressure of the air were double, that balloon would have (approximately) double the lift. I'm rounding the density of hydrogen down to zero for this, of course, so it's a conservative estimate.
While we are justifiably taking apart batman's nonsense lets not add any of our own. The continents 'float' on the mantle. The mantle is solid. It is not composed of magma. Magma is liquid. The mantle is not magma. Partial melting of the mantle may ocur at a few isolated locations, generating magma, but the mantle remains essentially solid.
I think we can safely say that this thread started on shakey ground and has now descended into speculation versus actual science. I'm going to move this to Pseudo.
I would be glad to continue posting my responses but this forum must return to the Biology section. It can't be relegated to pseudo-science.
Please take any discussions regarding moderator decisions to the Site Feedback forum or PM either me or one of the site admins.
While we're really not discussing biology so much anymore, I'm not sure this belongs in pseudo either. In the first place, Batman is correct in saying that gravity is weaker at the equator.
http://en.wikipedia.org/wiki/Earth%27s_gravity#Latitude
Both the Earth's rotation, and the equatorial bulge serve to lessen its effect. Pendulum clocks have to be adjusted when taken to that region from another region or they will begin to stop telling the correct time.
In the second place, the Earth spun at a faster rate during the Jurassic and Cenozoic eras. The rate of spin has been diminishing ever since the formation of the Moon 4.5 billion years ago, when the day was 5 hours long. It wasn't much of a difference 100 million years ago than today, though. The day was probably only a few minutes shorter.
http://en.wikipedia.org/wiki/Giant_i...othesis#Impact
To say that gravity at the equator during those times was slightly less than it is today is a totally correct statement. (If you suggested otherwise, you would be contradicting modern science.) What is dubious is the question of whether such a small difference would have been enough to influence evolution. We'd be talking about a tremendous difference in size being caused by a very small difference in gravity.
My own speculation is that other factors contributed, either by lessening apparent gravity further (such as greater air pressure), or, like other posters, I think maybe there was simply a lot more food available.
Again, if you want to dispute my decision please do so through the approrpriate channels. Don't want to derail the thread. To be clear, I'm not saying claims regarding minor variations in gravity are pseudoscience, I'm saying that the claim that the extreme size of some dinosaurs/animals are best explained by radically lower gravity in the past is pseudoscience.
At the risk of further derailment where would be the appropriate place to discuss what exactly pseudoscience is? I know this has been featured in other threads in the past, but I'm not aware that there is a clear cut definition anyhwere on the forum.
There isn't, and I'm not sure it would be useful to have one. Moderators try (I hope) to stay in line with the spirit of the Pseudoscience FAQ posted as a sticky here. Obviously, being a judgement call, mistakes can be made. Furthermore, I've left the criteria for a move open to suggestions via PM. If it's an open discussion you want, on the definition in general or on a specific case, then Site Feedback would be the place to have it.
Well, as long as we're in pseudo, why not discuss all the possible factors that could have contributed to dinosaurs' sizes? The ones I've seen so far are:
1) - Food.
2)- Temperature
3)- Apparent Gravity.
Are there any others?
| « Is 2012 the year we get time travel? | A flying saucer design » |
| Bookmarks |
Bookmarks |
LinkBack URL
About LinkBacks
