Although it's not widely appreciated by the public yet, not all dinosaurs disappeared 65 million years ago, rather one group survives. Living dinosaurs are covered with feathers and we generally call them birds. So...by study bird behavior and locomotion, and the behavior of the closet living relative of dinosaurs, crocodiles, we can make lots of informed inferences about how extinct dinosaurs looked. So....how dinosaurs are portrayed in movies is not pure conjecture, rather those depictions (at least in the good movies) are based on scientific data. Believe it or not, scientists have even figured out the color patterns of some extinct dinosaurs. Other things we see in movies are pure conjecture (if not out-and-out fantasy)--such as flying humans, and sky-scrapper climbing giant gorillas. Those are pure imagination.

We can find the skeletons of dinosaurs, and we can find impressions of their skin and feathers.

we can use living organisms to make bio-mechanical models just like making artificial limbs for humans based on bio-mechanics. Plus we can reconstruct the environments dinos lived in by studying the sedimentary rocks their remains are found in. So, actually we know quite a bit about these large reptiles.

We think we have a pretty good idea what dinosaurs look like, although our idea is always evolving. As you likely know, over the past 20 years our idea has changed quite a bit, and we now think many dinosaurs had feathers! Interestingly, very recently there was recently a piece of fossilized dinosaur skin discovered in Canada, and they're now investigating the pigment cells in the skin to figure out what color the dinosaur skin would have been!!

Very good question! Dinosaurs went extinct long before humans (or most modern organisms) even came into existence. It is indeed impossible for us to determine with true certainty what dinosaurs looked like back in their day aside from building a time machine and going back ourselves. However, scientists can gather a lot of clues from fossils and extrapolate from modern sources:

Firstly, the shapes of bones in preserved fossils tell us the overall mechanical structure of the dinosaur. In particularly well- preserved fossils, we can study the imprints that tendons from muscles made on the bones and infer muscular structure from that. Further, natural fossils of dinosaur skin have been found that tell us the texture of various dinosaurs. Finally, since dinosaurs are most likely related to modern reptiles, we can use educated guesses to determine their appearance from looking at modern species today.

No and yes - it's theory, but it's theory that makes predictions that can be tested using modern observations. In particular:

1. Birds - which are living dinosaurs - have their bodies proportioned into pretty much the same arrangement of limbs, joints, and so on as the bodies of bipedal dinosaurs. Because birds are bipedal themselves when standing, we can therefore safely conjecture that bipedal dinosaurs probably had a very similar posture and balance as do living birds when standing upright.

2. We can also build (both real and computerized) models of fossil dinosaurs, and analyze what kinds of stresses their bones would be under while walking or running in different ways. If the models break when we try to make them move, then the models are clearly wrong, because dinosaurs were very successful in their day. This limits the number of possible ways dinosaurs could have postured and moved to the number of models that actually work.

Although most of the perception we have about dinosaurs is conjecture, we have used fossil records to try and create more accurate models. Sometimes the fossils will contain small details, such as skin texture, which can help us try to understand what they looked like. Maybe one day, if we get the perfect fossil, we will be able to find out what dinosaurs looked like. Until that time, we won't ever be able to know.