How did dinosaurs get so big?

Cal doesn't know much about dinosaurs, and Scowie appears to be smoking something very potent, so you might want to use their answers only for entertainment value. It's not particularly clear why some dinosaurs got to be so huge, although there certainly had to be enough food to allow it. The evolution of giant size in dinosaurs is likely to have been due to a combination of huge tracts of fast-growing forest available as food source, and the usual 'arms race' between predators and prey, where getting bigger is one predator defense. We don't need to invoke things like atmospheric gas levels or 'cold-bloodedness' to explain it, although such imaginative speculation can be a lot of fun, especially in bars or at graduate-school parties. Climate may have been a factor, although we have evidence of giant dinosaurs in periods with very different climatic conditions, and giant mammals have also existed at various times (although not as many as there were giant dinosaurs - possibly due to fewer giant mammalian predators). Focusing on one thing like this also runs the risk of leading you astray, since dinosaurs were only one of the animals that were running around at that time. Some of those other animals (Pliosaurs or Azhdarchid pterosaurs, for instance) also got extremely large, while most dinosaurs were actually medium-sized or smaller. Maybe there was some common reason, or maybe there were different reasons. As for your comparison to whales, that's a whole other ball of fish and kettle of wax. "Theoretically, that amount of body mass" is not a problem for land animals, and never has been. I mean, disregarding that we know it wasn't, since they existed and non-dinosaurian giant animals have also existed, whales aren't land animals, so you're comparing apples and string beans here.

Dinosaurs became very large in part because there was adequate food to sustain big ENDOTHERMS--which is what dinosaurs were. Many sauropods and ornithopods just radiated into very large body herbivorous niches. Also, many size increases were due to escalation--herbivores and predators evolved larger sizes to better deal with one another. We see ample evidence of this in the late Jurassic, the mid Cretaceous, late Campanian and late Maastrichtian.

Cal is crazy. Big dinosaurs did NOT become extinct at the end of the Jurassic. The big sauropod Turiasaurus lived around that time, and Pelorosaurus soon afterwards. Stegosaur plates didn't evolve as thermoregulators and we can't say Stegosaurus disappeared at the end of the Jurassic! The North American record has a big gap from Tithonian-Barremian, and we know that in Asia, close relatives of stegosaurs persisted into the Cretaceous.

Cal evidently doesn't know that both sauropods and theropods, including the huge carcharodontosaurids, reached their peak sizes in the middle of the Cretaceous long before T. rex. That period was warm but not necessarily the Maastrichtian, when big tyrannosaurs and sauropods lived.

They got so big because they were "cold-blooded" and they lived in a warm climate (North and South Pole were ice free). Being large allows them to retain heat better overnight since their body would not lose as much heat to the environment because of a proportionally small amount of body surface. The next day, they don't have to sun themselves at all or only for a short period of time. When the climate warms up, "warm-blooded" animals can overheat quickly, because their small amount of body surface prevents them from losing heat quickly to the environment. The African elephant has huge ears to increase the amount of body surface so it can lose heat more easily, othewise it will cook itself from the inside out. In contrast, mammoths and mastodons had small ears because they lived under cooler ice age conditions and small ears helped them conserve heat.

"Cold-blooded" animals face a different problem. If the climate is cool, they need to warm up by sunning themselves. To do so quickly, they need a large amount of body surface in proportion to their volume. That is why the closer we get to polar regions, the smaller the reptiles get. After the dinosaurs became extinct, Titanoboa (the largest snake that ever lived) evolved because the climate was just as warm as the age of the dinosaurs, but that snake became extinct later when the climate cooled. During a cool climate, a cold-blooded animal can spend practically all day sunning itself and it would not regain the heat it lost overnight. So it never got warm enough to digest its food or even move. The same thing happened to large dinosaurs at the end of the Jurassic. Many of the largest dinosaurs (such as Allosaurus and many large sauropods) became extinct when the climate cooled down. Stegosaurus, the dinosaur with plates on its back, tried to compensate for the cool weather by increasing body surface area with those plates, but ultimately those plates were not enough and it became extinct at the end of the Jurassic.

The Cretaceous warmed up again, and dinosaurs got larger again. T. rex had smaller ancestors at the beginning and middle of the Cretaceous. By the end of the Cretaceous, the climate was once again warm enough for dinosaurs as large as T. rex to have evolved. Oxygen levels had nothing to do with the size of dinosaurs, because, as you may already know, carbon dioxide is a greenhouse gas. During the age of the dinosaurs, carbon dioxide levels were high (that was why it was so warm) and oxygen levels were lower than today.

Quoting a 2007 study published in Nature: "These records indicate that atmospheric CO2 rose from ~420 p.p.m.v. in the Triassic period (about 200 million years ago) to a peak of ~1,130 p.p.m.v. in the Middle Cretaceous (about 100 million years ago)."

The largest dinosaurs are a major headache for the boffins. Many of these would be too massive to be able to carry their own weight if they alive today. The largest dinosaurs in the Jurassic park movie were defying the laws of physics. This is because of the cube-square law...

As you increase the dimensions of a creature, you increase it's strength, and therefore the weight it is able to carry, by a square of these dimensions (muscular strength is proportional to the cross-sectional area of the muscles). But the weight of the animal increases by a cube since it is proportional to volume. Therefore as an animal's dimensions are increased, in order to carry it's own weight around, the proportion of body mass that the legs take up must increase. Since large animals also need a large gut to digest all the food they must eat, you soon get to a point where a further size/mass increase is not feasible due to the legs needing ridiculous proportions of mass to carry the animal's weight. It has been worked out that this limit is a mass not that much greater than the largest land animal alive today... the african elephant. Yet we have found dinosaur fossils of animals that must have been several times as massive.

For this reason some scientists have, in the past, insisted that the largest dinosaurs must have lived in water, but fossilised footprints tell us this was not the case. And it's not just the land animals that were too big. There were pterosaurs that would not be able to fly today with the proportions they had. And the insects were blown up in size too. Something about the environment of these times had to have been radically different and the only thing it can really be is gravity. In my opinion, the earth had a smaller mass at the time that dinosaurs roamed the earth, hence a lesser gravitational pull...

http://www.freerepublic.com/focus/f-chat/1913389/p...

According to the expanding earth theory, the earth has grown in size since prehistoric times, with ocean basins being created that did not previously exist:

http://www.youtube.com/watch?v=oJfBSc6e7QQ This of course begs the question, how was earth able to gain so much extra mass? Currently extra mass gets added to earth by meteorites and also by an influx of solar wind particles, which we see as the aurorae. This mass is fairly negligible at current levels but may have been many magnitudes greater in the past...

Our solar system orbits the centre of the Milky Way galaxy; a process that takes hundreds of millions of years. During it's journey, the solar system passes through regions of differing matter density — we happen to be in a low-density bubble at present. The greatest densities occur in the galaxy's spiral arms. At some point in our solar system's history we would have passed through one of these dense spiral arms. This could have fed the solar system with a great amount of matter and, being charged by the sun's rays, these particles would be drawn in at the earth's magnetic poles creating extremely intense aurorae and gradually increasing earth's mass...

http://www.evolutionem.co.uk/mpg62.html

http://www.newscientist.com/article/mg21228411.500...

Most of this extra mass would be washed down to the low-lying seas, increasing the pressure on the earth's mantle in these areas and causing an increase in volcanic activity. This would accelerate the production of new crust at what are now the mid-ocean ridges, as well as extra mass being fed into the mantle through increased subduction. The net result is that, over many millions of years, new ocean floor was created, the continents were pushed apart, and the earth grew.

[Some proponents of the expanding earth theory argue against the concept of subduction, but imo they are barking up the wrong tree. I believe subduction plays an important role in how the earth was able to expand. It provides the means through which matter from outside the earth is able to add mass to the inner earth.]

Btw, living organisms of today also suggest the earth has expanded in the past: http://www.4threvolt.com/Evidence/Biogeogr.html

Higher oxygen level from what I remember.

from a biblical point of view I believe that if a man can live to be almost a thousand years old thn animals lso lived longer back then and if I remember right reptiles don't stop growing until they die, therefore the reptiles we have now ( alligators, lizards,) were huge back then because they didn't stop growing.

if you don't believe that here is a scientific solution for you at this website: http://adf.ly/lb6Y6

They had no choice, some had to adapt to their surroundings and habitat, for example diplodocus had to be big with a long neck so that it could reach trees and plants that were high up a bit like a giraffe does today.. If it was small it wouldn't be able to reach them, also because it was a vegetarian it's size was it's defence. For example some large dinosaurs would live in herds or groups and their size was a form of defence against predators like T Rex and Allasaurus. Nobody actually knows for certain as no animal today is as large as dinosaurs were, but it has been suggested that their large bodies helped also to regulate their body temperature and because the world was so different back then with the climate that may have influenced their large size. Some research suggests that it was much warmer and more conducive to life. With a bigger base, ecosystems could support larger and larger animals. But like I said these are just theories and nobody actually knows for sure.

STEROIDS. LOTS AND LOTS OF STEROIDS.