A 6-foot-tall Ceratosaurus fossil is going up for auction at Sotheby’s this July. Find out what makes this dinosaur so rare and valuable.

The 150-million-year-old specimen is valued at up to $6 million by Sotheby’s. Some paleontologists worry this auction and earlier ones are driving fossil market speculators.

The artists use a paleontological guide to the osteology of Ceratosaurus to reassemble the fossil. Theo Stroomer for Popular Science Over time, paleontologists have gotten better at collecting ...