National Geographic : 1942 Feb
© National Geographic Society Painting by Charles R. Knight Harmless and Stupid, the Grotesque Diplodocus Asked Only to Be Left inPeace Long-tailed and long-necked, these giants attained a total length of 75 feet or more. Despite their great size, they could not fight well and had very small brains. They belonged to the vast family of dinosaurs, which roamed the earth during the Age of Reptiles, from 60 to 200million years ago. Scientists put the weight of a full-grown Diplodocus at about 25 tons and estimate his normal diet at about 700 pounds of leaves or plants daily.