Scorched by the relentless heat and harried by the biting insects that are inherent to eastern Utah summers, fossil prospector Earl Douglass was finding himself increasingly frustrated as he trudged over Jurassic sandstone in search of a perfect dinosaur. What we really wanted to do was look for prehistoric mammals. Ancient beasts were far more exciting to Douglass than any enormous reptile, but his employer – the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania – didn’t want brontothere jaw fragments or more rhinoceros teeth. They wanted a show-stopping sauropod – an imposing long-necked, heavy-bodied dinosaur – for their exhibit halls.

The Carnegie’s field man got his change of orders on August 4th, 1909. That day, Douglass later wrote in his