Miragaia

Type Species: Miragaia longicollum

Classification: Dinosauria – Ornithischia – Thyreophora – Stegosauria – Stegosauridae – Dacentrurinae

Time Period: Late Jurassic 

Location: Europe 

Diet: Herbivore

The stegosaur Miragaia was closely related to its contemporary cousin Dacentrurus. Miragaia could grow eighteen to twenty feet in length and would clock in at around two tons. Paired triangular plates ran down the midline of its neck; these plates were asymmetrical with a convex outer side and a concave inner side. They were obtuse but lightly hooked at the front. A long, narrow, and straight spike has been preserved; some paleontologists believe this was a shoulder-spike seen in some stegosaurs, but others believe it was part of the tail. Miragaia’s tail anatomy isn’t known, but it’s usually reconstructed with a four-spiked thagomizer like that seen in its near relatives. Because Miragaia’s front limbs were almost as high as the rear limbs, its overall posture was more horizontally level to the ground than what we find in most other stegosaurs, whose bodies slope down to the ground so that their heads were better situated for low browsing.

Miragaia is noteworthy for its elongated neck, which was built by seventeen vertebrae. It had the longest neck of any known stegosaur, and most scientists believe this represents the pinnacle of a trend toward longer necks in stegosaurs. Thyreophorans – the dinosaur clade to which stegosaurs belong – originally had nine neck vertebrae, and one of the most basal stegosaurs, the Chinese Huayangosaurus of the Middle Jurassic, had nine, as well. While more advanced stegosaurs such as Stegosaurus had twelve or thirteen vertebrae, Miragaia outdoes them – and it even outdoes most sauropods of its time. Only a few Chinese sauropods – such as Euhelopus, Mamenchisaurus, and Omeisaurus – had as many neck vertebrae as Miragaia; most sauropods of the Late Jurassic had only twelve to fifteen widely-spaced vertebrae. Scientists have come up with two explanations for Miragaia’s elongated neck. The first holds that it developed due to sexual selection: if longer-necked stegosaurs of this species were seen as more attractive, then it makes sense that necks would get longer over time. Another theory, and one which is more likely, is that the long neck developed as an aide to niche partitioning. Miragaia lived alongside the obviously low-browsing Dacentrurus (and Stegosaurus may have even ocean-hopped to reside in Portugal); because of this, these two species would be in direct confrontation. Niche partitioners coexist by eating different foods, and it may be that Miragaia evolved as a medium-browser, able to reach foods inaccessible to other stegosaurs. Its limb structure, which indicates a shift away from a low-browsing stance, supports this theory for the origin of Miragaia’s long neck.