This link has an illustration of Miragaia.
Miragaia longicollum was a stegosaurid dinosaur of the Jurassic. The systematic paleontology of it is:
Dinosauria Owen 1842
Ornithischia Seeley 1887
Thyreophora Nopcsa 1915
Stegosauria Marsh 1877
Stegosauridae Marsh 1880
Miragaia Mateus et al. 2009
Miragaia longicollum Mateus et al. 2009
Fossil remains of Miragaia longicollum have been found in the Miragaia Member of the Sobral Formation (Lourinha Geological Group) in Lourinha, Portugal. The strata in which they were unearthed is dated to a span of 155.7 - 145.5 million years ago (Late Kimmeridgian-Early Tithonian).
Miragaia longicollum had an usually long neck for a stegosaur. Unlike other stegosaurs, which ate low-lying vegetation, Miragaia was able to browse tall plants.
Octavio Mateus, Susannah C.R. Maidment, and N.A. Christiansen wrote an article titled A new long-necked 'sauropod-mimic' stegosaur and the evolution of plated dinosaurs. It was published in 2009. This quote from the abstract says:
Stegosaurian dinosaurs have a quadrupedal stance, low forelimbs, short necks, and are generally considered to be low browsers. A new stegosaur, Miragaia longicollum gen. et sp. nov., from the Late Jurassic of Portugal, has a neck comprising at least 17 cervical vertebrae. This is eight additional cervical vertebrae when compared with the ancestral condition seen in basal ornithischians such as Scutellosaurus. Miragaia has a higher cervical count than most of the iconically long-necked sauropod dinosaurs. Long neck length has been achieved by a cervicalization of anterior dorsal vertebrae and probable lengthening of centra. All of these features are evolutionarily convergent with those exhibited in the necks of sauropod dinosaurs. Miragaia longicollum is based upon a partially articulated skeleton, and includes the only known cranial remains from any European stegosaur. A well-resolved phylogeny supports a new clade that unites Miragaia and Dacentrurus
as the sister group to Stegosaurus; this new topology challenges the common view of Dacentrurus as a basal stegosaur.