Sophie's Neighbours in the Morrison Were More Varied Than We Thought

Everyone knows Stegosaurus from the Morrison Formation. A paper this year in the journal Diversity argues it had company. Going back through North American museum collections, the author found at least five new occurrences of dacentrurine stegosaurs — a branch best known from Portugal — in the Upper Jurassic Morrison of Wyoming and Utah: a cervical plate, a dorsal vertebra and three tail spines. The Wyoming animal long called “Alcovasaurus” longispinus is reassigned to the dacentrurine genus Miragaia. The conclusion is that these stegosaurs were an established part of the Late Jurassic fauna here, not a stray, and that Europe and North America were swapping dinosaurs across the Jurassic.

A caution the paper itself carries: not everyone agrees on the names. Another group has argued Miragaia is the same animal as Dacentrurus. The specimens are real; the labels are still being argued over, which is how this science works.

What I keep thinking about is July 2004. In the field, it was the tail spikes — the thagomizer — that told us Sophie was a Stegosaurus, and the 2015 description confirmed Stegosaurus stenops. This paper says that in the same formation, a few drainages over, a plated dinosaur with spines in the ground could have been something else. The next crew that uncovers a thagomizer in the Bighorn Basin should look twice before they say the name.

Source: Costa, “Dacentrurine Stegosaurs in North America: New Occurrences from the Upper Jurassic of USA (Morrison Formation),” Diversity 18(3):143, February 27, 2026. Read the original for the specifics.