Why did the big beasties go away?

[JohnB]

It's something I've been considering lately and wondered if anyone had an answer.

 

Excluding the megafauna which died out relatively recently, the current crop of fauna on the planet are the smallest they've ever been. Why?

 

Going back through all the various ages shows that animals and fish were a lot bigger before than they are now. Pick any era and the waterlife will dwarf everything except a Blue whale while the land predators would find an elephant "snack worthy". Pre reptiles, mammal like reptiles, reptiles and mammals, the rule for over 500 million years was "Big is better". The top of the food chain was always the biggest, meanest carnivore around.

 

So what changed?

 

I think one of the more interesting ideas has been put forward by Octave Levenspiel from Oregon State. His two relevent webpages are;

http://levenspiel.com/octave/dinosaurs.htm

http://levenspiel.com/octave/dinosaur2.htm

 

While I'm not backing it, his idea that atmospheric pressure was higher in the past than it is today would solve some problems. (And explain why the wing loading for some of the pteranodons is so wrong for flying.)

[Tres Juicy]

It's something I've been considering lately and wondered if anyone had an answer.

 

Excluding the megafauna which died out relatively recently, the current crop of fauna on the planet are the smallest they've ever been. Why?

 

Going back through all the various ages shows that animals and fish were a lot bigger before than they are now. Pick any era and the waterlife will dwarf everything except a Blue whale while the land predators would find an elephant "snack worthy". Pre reptiles, mammal like reptiles, reptiles and mammals, the rule for over 500 million years was "Big is better". The top of the food chain was always the biggest, meanest carnivore around.

 

So what changed?

 

I think one of the more interesting ideas has been put forward by Octave Levenspiel from Oregon State. His two relevent webpages are;

http://levenspiel.co...e/dinosaurs.htm

http://levenspiel.co...e/dinosaur2.htm

 

While I'm not backing it, his idea that atmospheric pressure was higher in the past than it is today would solve some problems. (And explain why the wing loading for some of the pteranodons is so wrong for flying.)

 

Interesting stuff...

 

It would explain a few things, but what would cause a global drop in atmospheric pressure?

[JohnB]

Like I said, I'm not sure I agree with the idea.

 

However the logic seems to work this way. All the CO2 that is currently in fossil fuels as well as chalk and marble deposits was at one time in the atmosphere. It seems to be ignoring the flux of the carbon cycle to a degree, but the essential point is valid. The CO2 must have been in the atmosphere for the plants and animals to absorb it.

 

I guess I find it attractive because I've always wondered how the primitive circulatory systems of the dinosaurs were albe to provide oxygen and nutrients to the cells. That blood has a very long way to travel in a Brachiosaur. A higher atmospheric pressure would increase the effectiveness of the circulatory system, it would be like living in a hyperbaric chamber. Even if the proportions are the same the partial pressures would mean twice as much oxygen per litre at 2 bar than is available today.

[Tres Juicy]

What a shame there aren't any around today....

 

I've got to admit that the pressure idea seems more plausible than the idea of multiple hearts

[questionposter]

1: there's less oxygen in the air now than there was at previous points

2: I'ts colder now than it was at previous points, and this is important because if its warmer, organisms can spend energy on growing rather than keeping their bodies warm.

3: Smaller is more efficient. As the number of organisms on this planet increases, the resources become less available, so its more efficient to need to use up less resources.

[granpa]

warm blooded animals cant get as large as cold blooded animals

 

(except for blue whales which spend much of their time in arctic waters where a cold blooded animal could never go)

Edited January 13, 2012 by granpa

[Moontanman]

warm blooded animals cant get as large as cold blooded animals

 

(except for blue whales which spend much of their time in arctic waters where a cold blooded animal could never go)

 

 

Do you have any evidence to back up that assertion?

 

1: there's less oxygen in the air now than there was at previous points

2: I'ts colder now than it was at previous points, and this is important because if its warmer, organisms can spend energy on growing rather than keeping their bodies warm.

3: Smaller is more efficient. As the number of organisms on this planet increases, the resources become less available, so its more efficient to need to use up less resources.

 

 

Do you have anything to back up those assertions?

 

Like I said, I'm not sure I agree with the idea.

 

However the logic seems to work this way. All the CO2 that is currently in fossil fuels as well as chalk and marble deposits was at one time in the atmosphere. It seems to be ignoring the flux of the carbon cycle to a degree, but the essential point is valid. The CO2 must have been in the atmosphere for the plants and animals to absorb it.

 

I guess I find it attractive because I've always wondered how the primitive circulatory systems of the dinosaurs were albe to provide oxygen and nutrients to the cells. That blood has a very long way to travel in a Brachiosaur. A higher atmospheric pressure would increase the effectiveness of the circulatory system, it would be like living in a hyperbaric chamber. Even if the proportions are the same the partial pressures would mean twice as much oxygen per litre at 2 bar than is available today.

 

 

Primitive circulatory systems of dinosaurs? Dinosaurs were similar to birds whose circulatory systems are at least the equal of mammals, some would say they are superior.

[questionposter]

Do you have anything to back up those assertions?

 

 

I can't point to anything specifically as I either heard them from some education show or read them in a book somewhere, other than the discoveries that were made, such as that in times of greater oxygen, even bugs like dragonflies were much bigger with wingspans of maybe 2 feet.

Also, dinosaurs lived in warmer time periods.

And the last other one is just logic, if there's less resources available, then its logical that the things that can use energy most efficiently would survive although it's also based off of reports of the decreasing availability of resources and the fact that populations around the world (not just humans) have been increasing by large amounts.

 

There's also another thing which is that larger animals usually have longer gestation periods, so there's a longer time for their offspring to get killed before they're even born, whereas with animals like insects they are small and reproduce very fast.

Edited January 13, 2012 by questionposter

[michel123456]

I can't point to anything specifically as I either heard them from some education show or read them in a book somewhere, other than the discoveries that were made, such as that in times of greater oxygen, even bugs like dragonflies were much bigger with wingspans of maybe 2 feet.

Also, dinosaurs lived in warmer time periods.

And the last other one is just logic, if there's less resources available, then its logical that the things that can use energy most efficiently would survive although it's also based off of reports of the decreasing availability of resources and the fact that populations around the world (not just humans) have been increasing by large amounts.

 

There's also another thing which is that larger animals usually have longer gestation periods, so there's a longer time for their offspring to get killed before they're even born, whereas with animals like insects they are small and reproduce very fast.

 

I was searching for indications about plants: was vegetation also bigger at these times? I found nothing.

[Moontanman]

I can't point to anything specifically as I either heard them from some education show or read them in a book somewhere, other than the discoveries that were made, such as that in times of greater oxygen, even bugs like dragonflies were much bigger with wingspans of maybe 2 feet.

 

This is thought to be true, huge insects and other large arthropods did indeed exist and the cause was to some extent a higher oxygen content of the atmosphere but this was well before there were any dinosaurs. by the time dinosaurs evolved the era of the giant insects was long past.

 

Also, dinosaurs lived in warmer time periods.

 

This is debatable, much of the reign of the dinosaurs did see warmer world wide temps but winter at the poles was still cold and dark and dinosaurs did live at or near the poles.

 

And the last other one is just logic, if there's less resources available, then its logical that the things that can use energy most efficiently would survive although it's also based off of reports of the decreasing availability of resources and the fact that populations around the world (not just humans) have been increasing by large amounts.

 

Why would less resources be available? I'm not sure I understand this answer.

 

There's also another thing which is that larger animals usually have longer gestation periods, so there's a longer time for their offspring to get killed before they're even born, whereas with animals like insects they are small and reproduce very fast.

 

I'm not sure why this would be relevant, insects existed during the time of the dinosaurs yet the largest land animals that ever existed lived then. Dinosaurs laid eggs, often a great many eggs, so i don't see how this is relevant, Please elaborate.

 

It would appear that the actual size and weight of Quetzalcoatlus is still in considerable dispute. The OP's link suggested a maximum size that is doubted by most now days.

 

http://en.wikipedia.org/wiki/Quetzalcoatlus

 

The nature of flight in Quetzalcoatlus and other giant azhdarchids is poorly understood. Their method of flight depends largely on their weight, which has been controversial, with widely differing masses favored by different scientists. Some researchers have suggested that these animals employed slow, soaring flight, while others have concluded that their flight was fast and dynamic.[4] In 2010, Donald Henderson argued that the mass of Q. northropi has been underestimated, even the highest estimates, and that it was too massive to have achieved powered flight. Henderson argued that it may have been flightless.[15]

Paul MacCready undertook an aerodynamics experiment testing the flight of Quetzalcoatlus in 1984. He constructed a model flying machine or ornithopter with a simple computer functioning as an autopilot. The model successfully flew with a combination of soaring and wing flapping;[16] however, the model was half scale based on a then-current weight estimate of around 80 kg, far lower than more modern estimates of over 200 kg.[15] (Also, see below.)

[granpa]

It's something I've been considering lately and wondered if anyone had an answer.

 

Excluding the megafauna which died out relatively recently, the current crop of fauna on the planet are the smallest they've ever been. Why?

 

Going back through all the various ages shows that animals and fish were a lot bigger before than they are now. Pick any era and the waterlife will dwarf everything except a Blue whale while the land predators would find an elephant "snack worthy". Pre reptiles, mammal like reptiles, reptiles and mammals, the rule for over 500 million years was "Big is better". The top of the food chain was always the biggest, meanest carnivore around.

 

So what changed?

 

I think one of the more interesting ideas has been put forward by Octave Levenspiel from Oregon State. His two relevent webpages are;

http://levenspiel.com/octave/dinosaurs.htm

http://levenspiel.com/octave/dinosaur2.htm

 

While I'm not backing it, his idea that atmospheric pressure was higher in the past than it is today would solve some problems. (And explain why the wing loading for some of the pteranodons is so wrong for flying.)

 

the dinosaurs lost their advantage when the arctic expanded.

warm blooded mammals then began to take over.

[Moontanman]

the dinosaurs lost their advantage when the arctic expanded.

warm blooded mammals then began to take over.

 

 

Not true, there were Arctic dinosaurs as well as Antarctic dinosaurs and both polar regions were indeed cold even when dinosaurs lived there and Birds live there today and birds are dinosaurs... Most if not all dinosaurs are now thought to have been warm blooded. When you think dinosaur think "bird" Birds are dinosaurs and many dinosaurs had feathers.

Edited January 13, 2012 by Moontanman

[granpa]

gigantothermia is not the same as warm-blooded.

[Moontanman]

gigantothermia is not the same as warm-blooded.

 

 

Not all dinosaurs were large enough to be gigantotherms, in fact most were not that large and most were quite average and similar in size to mammals that occupy the same biological niches. Birds, which are dinosaurs, are warm blooded with out being gigantotherms.

 

gigantothermia is not the same as warm-blooded.

 

 

Oh and thanks for the neg rep, makes my day!

[Tres Juicy]

Oh and thanks for the neg rep, makes my day!

 

Yeah, I saw that

 

I didn't think it was warranted

 

*Fixed*

Edited January 13, 2012 by Tres Juicy

[questionposter]

This is thought to be true, huge insects and other large arthropods did indeed exist and the cause was to some extent a higher oxygen content of the atmosphere but this was well before there were any dinosaurs. by the time dinosaurs evolved the era of the giant insects was long past.

 

 

 

This is debatable, much of the reign of the dinosaurs did see warmer world wide temps but winter at the poles was still cold and dark and dinosaurs did live at or near the poles.

 

 

 

Why would less resources be available? I'm not sure I understand this answer.

 

 

 

I'm not sure why this would be relevant, insects existed during the time of the dinosaurs yet the largest land animals that ever existed lived then. Dinosaurs laid eggs, often a great many eggs, so i don't see how this is relevant, Please elaborate.

 

It would appear that the actual size and weight of Quetzalcoatlus is still in considerable dispute. The OP's link suggested a maximum size that is doubted by most now days.

 

http://en.wikipedia..../Quetzalcoatlus

 

 

 

During the warmer time periods, the poles of the Earth were also warmer, Antarctica use to have grasslands covering it.

Less resources would be available due to the increasing number of organisms or decrease in plant life caused by the shift in the environment (from hot to cold).

Gestation periods determine how fast a species can reproduce, so if there was some large disease that affected large animals or maybe less resources or increases in predators, it would take longer for a larger animal species to recover (perhaps too long) and the probability of a large animal giving birth would go down.

Basically, most big animals died out because of large dramatic shifts in the environment.

Edited January 13, 2012 by questionposter

[Moontanman]

During the warmer time periods, the poles of the Earth were also warmer, Antarctica use to have grasslands covering it.

Less resources would be available due to the increasing number of organisms or decrease in plant life caused by the shift in the environment (from hot to cold).

 

This sounds reasonable, I'd like to see some evidence for it.

 

Gestation periods determine how fast a species can reproduce, so if there was some large disease that affected large animals or maybe less resources or increases in predators, it would take longer for a larger animal species to recover (perhaps too long) and the probability of a large animal giving birth would go down.

Basically, most big animals died out because of large dramatic shifts in the environment.

 

 

This too is sounds reasonable but I have doubts it's quite as simple as this....

[questionposter]

This sounds reasonable, I'd like to see some evidence for it.

 

 

 

 

This too is sounds reasonable but I have doubts it's quite as simple as this....

 

http://www.google.com/imgres?q=continents+location+timeline&um=1&hl=en&biw=1224&bih=632&tbm=isch&tbnid=NHhD5tyeCj-gPM:&imgrefurl=http://www.math.montana.edu/~nmp/materials/ess/geosphere/inter/activities/exploration/index.html&docid=tuNRZw_W8uUbtM&imgurl=http://www.math.montana.edu/~nmp/materials/ess/geosphere/inter/activities/exploration/5globes.gif&w=571&h=712&ei=rA8ST92FAqKS0QHmpqy2DQ&zoom=1&iact=hc&vpx=94&vpy=120&dur=898&hovh=251&hovw=201&tx=144&ty=85&sig=102223466515623660594&page=1&tbnh=133&tbnw=107&start=0&ndsp=18&ved=1t:429,r:0,s:0

 

Timelines of Antarctica aren't very specific, so if you can find something that says Antarctica was "warm" or "cold" or had a bunch of liquid water at a time that corresponds to when those pictures show Antarctica at or near it's present state (basically in the south pole), then that should help give an answer.

 

Otherwise, I wasn't suggesting it was a single reason for large animals dying out, its a culmination of all the reasons I was saying, but I think the most important one is the environmental shift because that really messes up food chains.

[JohnB]

Otherwise, I wasn't suggesting it was a single reason for large animals dying out, its a culmination of all the reasons I was saying, but I think the most important one is the environmental shift because that really messes up food chains.

 

That was my thought too, but it just doesn't fit the evidence. There have been five major extinction events on this planet and every time the beasties have come back bigger and badder, (More or less) Even after the destruction of the dinosaurs and the rise of mammals we had some pretty impressive beasties. The Indricothere was 4.5 metres at the shoulder and weighed in at 15 tonnes.

 

Over geological timespans it can be argued that "big is better" on the basis that the Sauropods/Titanosaurs were found everywhere and survived longer than any breed of predator they had. Starting in the late Jurrasic these massive beats walked the Earth for over 100 million years and only died out with the others 65 million years ago. A pretty impressive record. It is interesting to note that in general the earlier creatures in this group were larger then the later ones. The Siesmosaurus (How cool is that for a name? Says it all in one word) was significantly larger than the later Brachiosaur from the same species.

 

As the Indricothere above shows, even after the dinos the beasties were still pretty big. 35 million years after the big impact, the mammals are showing that size matters. Similarly it didn't take the birds very long to evolve into the rather large "Terror Birds" in South America.

 

The thing is that you can pick any Age and the top of the food chain has always been a honking big critter. Even the early amphibians had their group of large predators. This is what kills the "environmental shift" idea. One supercontinent or a wad of smaller ones, warmer than today or a 100 million year Ice Age, the big beasties were always bigger than today. It didn't really matter how the climate changed or the plantlife changed, big beasties evolved to survive the climate and eat the plants.

 

Until recently, say the last 3 million years or so.

 

"Bigger" has been a very successful adaptation for at least 300 million years and yet now it isn't. Why not?

 

With the air pressure thing I don't have a dog in that fight. However, if the laws of aerodynamics say that the large pterosaurs could only fly in an atmosphere of 2 bar or more, I'm willing to accept that. They had to be able to take off. The idea of a creature surviving as long as the genus did if they had to walk back up the hill is crazy. Light boned and ungainly on the ground they would be easy pickings for any available predator. Besides, I frankly don't see what is so terrifying about the concept of planetary atmospheric pressure changing over geological timespans. (Every other thing does)

 

Moontanman. What I meant by "primitive circularory systems" was a whole picture thing. In one respect all circulatory systems are equally efficient, they either deliver nutrients to all cells and remove wastes from all cells, or the creature dies. But how they do this can vary in efficiency. Since a circulatory system must reach all cells in the creatures body then the only way that a system can evolve is in efficiency, it already has 100% coverage. This means we are faced with three possibilities;

1/ Circulatory systems have evolved and are more efficient.

2/ Circulatory systems have not evolved and are the same efficiency as 65 million years ago.

3/ Circulatory systems have devolved and are less efficient than 65 million years ago.

 

Since number 1 is the only viable option then modern systems must be more developed than earlier ones and therefore the early ones by definition must be "primitive" compared to modern ones. Birds don't count because they are modern creatures with modern systems. A birds system is advanced compared to its primitive dinosaur ancestor. Unfortunately there is a lack of fossilised soft tissue around so the point is a bit moot. I'm simply assuming that circulatory systems have evolved rather than devolved in the last 65 million years.

[questionposter]

That was my thought too, but it just doesn't fit the evidence. There have been five major extinction events on this planet and every time the beasties have come back bigger and badder, (More or less) Even after the destruction of the dinosaurs and the rise of mammals we had some pretty impressive beasties. The Indricothere was 4.5 metres at the shoulder and weighed in at 15 tonnes.

 

Over geological timespans it can be argued that "big is better" on the basis that the Sauropods/Titanosaurs were found everywhere and survived longer than any breed of predator they had. Starting in the late Jurrasic these massive beats walked the Earth for over 100 million years and only died out with the others 65 million years ago. A pretty impressive record. It is interesting to note that in general the earlier creatures in this group were larger then the later ones. The Siesmosaurus (How cool is that for a name? Says it all in one word) was significantly larger than the later Brachiosaur from the same species.

 

As the Indricothere above shows, even after the dinos the beasties were still pretty big. 35 million years after the big impact, the mammals are showing that size matters. Similarly it didn't take the birds very long to evolve into the rather large "Terror Birds" in South America.

 

The thing is that you can pick any Age and the top of the food chain has always been a honking big critter. Even the early amphibians had their group of large predators. This is what kills the "environmental shift" idea. One supercontinent or a wad of smaller ones, warmer than today or a 100 million year Ice Age, the big beasties were always bigger than today. It didn't really matter how the climate changed or the plantlife changed, big beasties evolved to survive the climate and eat the plants.

 

Until recently, say the last 3 million years or so.

 

"Bigger" has been a very successful adaptation for at least 300 million years and yet now it isn't. Why not?

 

With the air pressure thing I don't have a dog in that fight. However, if the laws of aerodynamics say that the large pterosaurs could only fly in an atmosphere of 2 bar or more, I'm willing to accept that. They had to be able to take off. The idea of a creature surviving as long as the genus did if they had to walk back up the hill is crazy. Light boned and ungainly on the ground they would be easy pickings for any available predator. Besides, I frankly don't see what is so terrifying about the concept of planetary atmospheric pressure changing over geological timespans. (Every other thing does)

 

 

What your saying would make sense, but a meteor doesn't just wipe out all living things unless it destroys the entire planet itself. The reason the dinosaurs went extinct isn't because of the meteor, but because of what it caused, which is an environmental shift caused by millions of tons of debris thrown into the atmosphere blocking sunlight, making it colder and disrupting the food chain by blocking sunlight and killing many plants. Right now at this very moment, I suppose the biggest reason they don't survive is because humans make them extinct, like with mammoths and almost whales and those very large birds that use to be around, maybe it could be both of what we're saying at different times.

Bigger is more efficient in a way, as in it somehow takes less energy per cubic centimeter to operate which many scientists are puzzled by despite knowing of the reasoning you presented, but it still takes a large amount of resources to keep them alive which is why when there's a large food chain shift, the biggest animals usually die the fastest. That's why rats and bugs and small birds and small lizards survived the event and not dinosaurs.

Edited January 16, 2012 by questionposter

[ewmon]

A higher atmospheric pressure means a thicker atmosphere (a part of which a near-earth object may have subsequently torn away), or a denser atmosphere (such as mostly CO₂), which natural processes may have subsequently sequestered. We're not only talking a higher concentration of unsequestered carbon, but an increased flow rate through the Carbon Cycle, causing fantastically huge amounts of plants, followed by herbivores and then carnivores. Nature's version of the "velocity of money".

[michel123456]

I still cannot find any information about gigantism in vegetation at the same time with the dinosaurs. It would make some sense that if something in the atmosphere provoqued gigantism in animals the same effect would apply on plants too.

[questionposter]

Perhaps there weren't necessarily bigger plants because even though they could take in more CO2, the amount of sunlight the Earth received wasn't enough.

Edited January 16, 2012 by questionposter

[Santalum]

It's something I've been considering lately and wondered if anyone had an answer.

 

Excluding the megafauna which died out relatively recently, the current crop of fauna on the planet are the smallest they've ever been. Why?

 

Going back through all the various ages shows that animals and fish were a lot bigger before than they are now. Pick any era and the waterlife will dwarf everything except a Blue whale while the land predators would find an elephant "snack worthy". Pre reptiles, mammal like reptiles, reptiles and mammals, the rule for over 500 million years was "Big is better". The top of the food chain was always the biggest, meanest carnivore around.

 

So what changed?

 

I think one of the more interesting ideas has been put forward by Octave Levenspiel from Oregon State. His two relevent webpages are;

http://levenspiel.co...e/dinosaurs.htm

http://levenspiel.co...e/dinosaur2.htm

 

While I'm not backing it, his idea that atmospheric pressure was higher in the past than it is today would solve some problems. (And explain why the wing loading for some of the pteranodons is so wrong for flying.)

With the megafauna versus contemporary mammals one theory it that hunting pressure from humans has resulted in dwarfing as humans nearly always target larger animals because the meat goes further. Over generations this puts selective pressure against the largest of the individuals of a species and for smaller individuals.

Also larger animals require more food and this is an evolutionary disadvantage in hard times such as droughts etc. This has certainly also been a factor in the dwarfing of Australian mammals.

 

With dinosaurs there was selective pressure among sauropod species was for larger individuals since they retain heat for longer, an advantage for cold blooded animals, and larger animals can contain larger stomachs to process larger amounts of poor nutritional quality vegetation. Then large sauropods can only be predated upon by larger carnovores.

[Moontanman]

With the megafauna versus contemporary mammals one theory it that hunting pressure from humans has resulted in dwarfing as humans nearly always target larger animals because the meat goes further. Over generations this puts selective pressure against the largest of the individuals of a species and for smaller individuals.

Also larger animals require more food and this is an evolutionary disadvantage in hard times such as droughts etc. This has certainly also been a factor in the dwarfing of Australian mammals.

 

This is almost certainly true, it can be demonstrated by fish populations as well.

 

With dinosaurs there was selective pressure among sauropod species was for larger individuals since they retain heat for longer, an advantage for cold blooded animals, and larger animals can contain larger stomachs to process larger amounts of poor nutritional quality vegetation. Then large sauropods can only be predated upon by larger carnovores.

 

You are aware that dinosaurs are no longer though to have been exothermic aren't you? Some are considered to have been gigantotherms (sp?) but then so are some mammals, the larger stomachs thing is valid and that would require larger predators like allosaurus or T-Rex but dinosaurs, like birds are thought to have been endothermic