When I see pictures of a Tyrannosaurus Rex walking with their tail raised in the air that doesn't look right to me. That tail was big and heavy and it would seem to me they would get tired always holding their tail in the air. Small lizards can hold their tail in the air because they are light. My guess is T-Rex only raised their tail when walking to balance themself and when they stood still the tail would rest on the ground. I made this point because I always see pictures of T-Rex with their tail raised.
from S, age ?, ?, ?, ?; July 17, 2001

TOM: Although it looks uncomfortable, Tyrannosaurus (and other dinosaurs) probably did normally keep their tail raised. However, they could do that without having to exert much effort. In part, the weight of the body in front of the legs balanced out the weight behind. Also, tendons and ligaments down the back of the dinosaur would help it keep its tail up.

Although you didn't give your age, I suspect that you are relatively young. Back in the 1970s and before it was typical to see T. rex and other dinosaurs dragging their tails, or at least resting with their tails on the ground. It was something of a shock when the illustrations began to come out with their tails in the air all the time. (Although, truth be told, some scientists and artists had done drawings of some of the dinosaurs in these postures as early as the 1910s).