Before that, he bought a $122m mansion near Buckingham Palace that once belonged to French president Charles de Gaulle, in what was then the most expensive London house sale in a decade.
In its auction document, Sotheby’s said Apex was a huge stegosaurus that lived long enough to show signs of arthritis.
Almost entirely complete, the fossil includes 254 fossil bone elements of an approximate total of 319, with additional 3D printed and sculpted elements.
It was excavated two years ago on private land in Moffat County, Colorado, near the town of Dinosaur.
Cassandra Hatton, who heads Sotheby’s science-related business, said Apex “has now taken its place in history, some 150m years since it roamed the planet”.
The stegosaurus was one of the world’s most distinctive dinosaurs, featuring pointed plates on its back and spikes on the end of its long tail that it is thought was used to fend off predators.
Citadel was contacted for comment.