The enormous 38ft long Tyrannosaurus rex was discovered just a few miles from the 26ft Triceratops – and together they are set to fetch more than two million pounds.
Experts have described the incredible finds as “very significant, very impressive and very valuable”.
The T-rex skeleton is so significant that it is said to be among the top 20 ever found in the world, as it boasts around 40 per cent of its original bones.
The rest of the skeleton is made up of cast bones from other T-rex finds.
The Triceratops, a herbivore known for having two large horns on its head and a smaller one on its nose, is 70 per cent original.
The bones of the gigantic beasts were found on a 20 square mile ranch in Hell Creek in the U.S. state of Montana before being excavated by dinosaur fossil hunters.
They have since been prepared and mounted ready for sale.
The T-rex has been named 'Russell' after the American artist Charles Russell, who used a nearby shed when painting some of his Western landscapes.
It is tipped to fetch £1.4 million, while the Triceratops could fetch £560,000.
The world record for the most expensive dinosaur fossil was set in 1997 when 'Sue', a Tyrannosaurus rex, sold for £5.4 million.