The largest and most complete Stegosaurus fossil ever found is expected to fetch up to $6m (£4.7m) when it is sold as the star lot in Sotheby’s “geek week” auction this summer.

At 11ft (3.4 metres) tall and more than 20ft long the “virtually complete” fossil, which has been nicknamed “Apex”, is more than 30% larger than “Sophie”, the previously most intact stegosaurus specimen which was on display in London’s Natural History Museum.

Cassandra Hatton, the qglobal head of science at Sotheby’s, said: “Apex marks an incredibly important milestone, as simply one of the best fossils of its kind ever unearthed.