It is thought, that the herbivorous dinosaurs grew big as a defensive mechanism. (Today, there are not many (if any) predators that will take on an adult elephant.) In response to this many of the predators grew bigger so that they could take on the large herbivores. So, we had a positive feedback loop that developed. The larger dinosaurs were able to out compete the smaller ones in their quest for survival. So, the genes that would produce yet larger animals were propagated producing larger and larger dinosaurs. That is the theory any way. BTW, we also saw this happen with mammals after the dinosaurs died out. However, many of the larger mammals died out at the end of the last ice age. Just why is a matter of dispute. Some say it was over hunting by a new species that appeared at about that time (homo sapien sapien, aka Cro-Magnon, aka modern humans). Others say that they died out because they could cope with the rapid climate change that occurred when the ice age ended.

Paleontologists do not know why dinosaurs grew so large and so your simple question is a source of embarrassment to science. The question can be broken into two parts 1) does size matter, and 2) if size matters then what was different about the Earth during the Mesozoic era that allowed the dinosaurs to grow so large? In 1638, Galileo answered the first part of the question in his book Dialogues Concerning Two New Sciences. Contrary to Gulliver’s Travels and countless science fiction movies showing animals the wrong size, Galileo made it very clear that size matters. Yet over three and a half centuries latter most science educators still do not teach Galileo’s scaling properties, because if they did it would then be obvious to their students that they do not know the answer to your question “Why were dinosaurs so large?” During the Mesozoic era the Earth had a much thicker atmosphere. This thick atmosphere’s density was two thirds the density of water. Being this dense, the air was as much like a liquid as it was a gas and thus it provided a buoyancy force that supported most of the weight of the dinosaurs. If not for this buoyancy the largest dinosaurs would have resembled beached whales in that they would not even have the strength to pick themselves off the ground. For further proof find some pictures of dinosaurs and look at the form of dinosaurs. Every dinosaur except the Brachiosaurus has larger rear legs than forward legs and they all have strong flexible tails. This form may look awkward in comparison to animals of today but this is the correct form for animals moving through an extremely thick fluid. The dinosaurs were using their tails for swimming through the thick fluid while their rear legs pushed off the ground. When dinosaurs ran the thick fluid would tend to lift up the front of their bodies thus making feeble front legs nearly useless. Because scientists did not imagine the Earth’s atmosphere being so thick, there were actually numerous unsolved paradoxes regarding the formation of the Earth. But once a person opens their mind to the Earth having a thick atmosphere it is truly amazing how many science paradoxes are resolved by the Thick Atmosphere Solution. The Thick Atmosphere Solution solves major scientific paradoxes in paleontology, geology and astronomy, thus it is arguable the most important scientific breakthrough of our time. Far more details to the answer to your question about large dinosaurs and the thick atmosphere solution can be found on the website Dinosaurtheory.com. This website is only one year old and yet pages of this website can be found for scores of two-word search headings in Google. The Thick Atmosphere Solution is such a huge science revolution most scientists are still in a state of disbelief. I am a physicist and I am the author of dinosaurtheory.com. I hope that you take the time to read my website and that it turns you on to science. David Esker

Too many McDino's family restaurants.