A comparison of three different Stegosaurus specimens. Top is the holotype of S. ungulatus, currently mounted at the Yale Peabody Museum. Middle is the holotype of Stegosaurus stenops, previously on display at the Smithsonian (and presumably which will be back after the current ongoing renovations to the dinosaur halls). Bottom is "Sophie", the Stegosaurus stenops specimen now on display at the British Museum.
I put these together for this blog post (dinogoss.blogspot.com/2015/02/…
) mainly to explore the differences between Stegosaurus species, which are often overlooked in popular restorations in favor of a "generic" stegosaur, and to explore plausible ranges of motion inspired by the online debate over the stegosaurs in Jurassic World sweeping their tails along the ground. Note that both species would have had real trouble even touching their tail tips to the ground from a standing position.
Some differences to notice: S. stenops has much larger plates (both in proportion to its size and in absolute terms) than S. ungulatus, though note that many of the hip plates, which are largest in S. stenops, are unknown in S. ungulatus. Another big difference is the arrangement and shapes of the tail plates. Where S. syenops has alternating, large, rounded plates on the tail, S. ungulatus has paired (as indicated by two pairs of minor-image plates unlike any others on the back or in S. stenops specimens) tail plates which were small, narrow, and spine-shaped. Also note the longer legs in S. ungulatus.
S. ungulatus was traditionally depicted with eight tail spikes. This is generally considered wrong today, but the specimen was found with eight spikes, and so far there is no evidence of any other duplicated bones indicating multiple specimens. Proponents of the 4-spike hypothesis suggest duplicate bones may not have been collected and might be present if the site were re-opened, which would be the only way of definitively saying whether or not S. ungulatus had eight spikes.