The late Jurassic Period, from 155-145 million years ago
North America: Colorado, Montana, Utah, and Wyoming
Diplodocus was a long-necked, whip-tailed giant, measuring about 90 feet (27 m) long with a 26 foot (8 m) long neck and a 45 foot (14 m) long tail, but its head was less than 2 feet long. It was among the longest land animals ever. Its nostrils were at the top of its head and it had peg-like teeth, but only in the front of the jaws. Its front legs were shorter than its back legs, and all had elephant-like, five-toed feet. One toe on each foot had a thumb claw, probably for protection. A fossilized Diplodocus skin impression reveals that it had a row of spines running down its back.