Read the passage and choose the appropriate title.
Although dinosaurs have long captured man`s imagination, no human ever saw one. For over one hundred million years dinosaurs roamed the earth, but for some unknown reason, they perished seventy millions years ago, years before man appeared. There are several theories as to why the giants disappeared. Some scientists believe that the earth became too cold; others believe that it became too dry; still others argue that smaller mammals ate the dinosaur eggs before they had an opportunity to hatch. Whatever the reason, their great bodies sank into the mud where slowly the bones, teeth, and even the skin became fossilized. Today huge stone footprints and enormous skeletal structures are the only record we have of their mysterious existence.