That’s FMNH PR 25107, better known as a the holotype of Brachiosaurus altithorax — the biggest known dinosaur at the time of its description (Riggs 1903) and still for my money one of the most elegant, along with its buddy and one-time genus-mate Giraffatitan brancai . I had a spare morning in Chicago two Tuesday ago, and Bill Simpson (collection manager of fossil vertebrates at the Field Museum) managed to fit it a collections