Dear Trousera,
Most popular depictions of dinosaurs show them naked, absolutely devoid of any pants, whether it be Jurassic Park or that annoying purple Barney. However, just because these modern dinosaur depictions have no pants does not mean that dinosaurs did not wear them.
To understand why this is so, we must understand how we know what we know about dinosaurs. We know that animals alive today do not wear pants, because we can observe this fact for ourselves. In the age of dinosaurs, however, there were no zoologists, unless the zoologists were dinosaurs themselves, in which case they left us no written record of their observation. We know about dinosaurs only through the geological record, that is, through the fossils left by their skeletons.
Now imagine this: if, several millennia in the future, humans went extinct and intelligent aliens were to visit our planet. Now what if these aliens dug up the earth and found our skeletons in the earth, how much do you think the aliens would know about us? They might be able to tell a lot of things, such as how we walked or what kind of food we ate, but I highly doubt if they would be able to tell if we were a pants-wearing species. After all, any evidence of our pants would have long decomposed into the earth.
The case is the same with dinosaurs. We simply assume that they did not wear pants because we have no evidence that they did. Perhaps dinosaurs had a highly sophisticated sense of fashion, and wore all kinds of leggings, such as jeans, trousers, skirts, dhotis, sarongs, harem pants, even sarees! Perhaps they even had fashion shows, we simply have no way of knowing. It is the arrogance of the human mind to believe that it came up with the idea of pants first.
I believe that dinosaurs may be remembered much more fondly if we grant the possibility that they may have worn pants. Paleontologists will say that there is no evidence to back the claim that dinosaurs wore pants, but does it make a difference from a scientific standpoint? We are not making claims about their eating or breeding habits, but only a conjecture about dinosaur fashion and culture. For all we know, dinosaurs may have worn hats or shirts or may have been brilliant dancers or storytellers. The possibilities are endless, and that is what makes the cultural aspect of the dinosaur world so intriguing.
And of all these possibilities, one of them is that maybe, just maybe, dinosaurs wore pants. It is a possibility that is at once comforting but also a little troubling. After all, the dinosaurs all died a terrible death. Since we humans also wear pants, we must be careful that we do not get wiped out the way they did.
Yours questionably,
 Dr K