Diplodocus Click to see full answer. Also question is, what dinosaur has the longest neck? sauropods Also Know, what is the longest dinosaur ever? Argentinosaurus Considering this, how long was a Diplodocus tail? 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.Why did dinosaurs have long tails?A: We don’t know why dinosaurs had long tails but it was probably to keep them from falling on their faces. Dinosaurs leaned forward over their hips and carried a lot of weight in the front of their bodies.