Many dinosaurs did have quite a strange shape, but were a little unfamiliar in appearance than, say , a giraffe or an elephant ? However, many of them did grow to be quite large , even huge, but no dinosaur ever competed even with smaller baleen whales in size. It would actually be physiologically impossible for land animal to be more than 100 tons ( feet should be so massive that would address each other , leaving no space between them for the body !) . Most dinosaurs were creatures actually medium sized modern equivalent medium to large mammals in size. Finally, as regards the disappearance without a trace, it is also wrong. Some small insectivorous and / or carnivorous dinosaurs actually experienced large Mesozoic and disappearance - are still with us today. They are called birds.