I WONDER - How Big Was The Diplodocus?

The Diplodocus was a massive sauropod dinosaur from the Late Jurassic period, living around 155 to 145 million years ago. It was one of the longest and heaviest dinosaurs, reaching over 90 feet in length. Its name, Diplodocus, meaning 'double beam', refers to its unique Chevron bones under its tail.

What makes the Diplodocus one of the longest and heaviest dinosaurs?

What unique feature is associated with the Diplodocus's tail?