Miragaia is a genus of long-necked stegosaurid dinosaur. Its fossils have been found in Upper Jurassic rocks in Portugal (Lourinhã Formation, Sobral Unit) and possibly also Wyoming and Utah, United States (Morrison Formation). Miragaia has the longest neck known for any stegosaurian, which included at least seventeen vertebrae. Some researchers consider this taxon to be a junior synonym of Dacentrurus.
History of discovery
Miragaia is based on holotype ML 433, a nearly complete anterior half of a skeleton with partial skull (the first cranial material for a European stegosaurid). The remains were found after the construction of a road between the villages of Miragaia and Sobral. The rear half of the skeleton was probably destroyed by the roadcut. The fossils were dug up in August 1999 and August 2001. Among the recovered bones were most of the snout, a right postorbital, both angulars of the lower jaws, fifteen neck vertebrae (the first two, which articulated with the skull, were absent), two anterior dorsal vertebrae, twelve ribs, a chevron, the shoulder bones, most of the forelimbs including a possible os carpi intermedium, a right first metacarpal and three first phalanges; and thirteen bony plates plus a spike. The bones were not articulated but dispersed over a surface of about five to seven metres, though there was a partial concentration of fossils that could be salvaged within a single block. ML 433 was found in the Miragaia Unit of the Sobral Unit, Lourinhã Formation, which dates to the late Kimmeridgian-early Tithonian (Late Jurassic, approximately 150 million years ago). Octávio Mateus, Susannah Maidment and Nicolai Christiansen named and briefly described Miragaia in 2009. The type species is Miragaia longicollum. The generic name refers to the village of Miragaia, in the municipality of Lourinhã, next to which the first specimen was uncovered. The specific name means "long neck" from the Latin longus, "long" and collum, "neck". A partial pelvis (ilium and pubic bone) and two partial dorsal vertebrae from a juvenile individual (specimen ML 433-A) were found at the same location, intermingled with the bones of the holotype, and were also assigned, as a paratype, to M. longicollum. Casts were made of the holotype bones and partially based on these a life-size skeletal model was constructed from polyurethane and polyester resin parts. In 2026, Francisco Costa described five probable dacentrurine specimens from the Morrison Formation and suggested that four of them are potentially referrable or comparable to Miragaia. UMNH VP 5572 from the Cleveland-Lloyd Dinosaur Quarry (Utah) is assigned to cf. M. longicollum. An unnumbered Griffin Ranch Quarry (Wyoming) specimen housed in Mountain America Museum of Ancient Life, and two specimens from the Cleveland-Lloyd Dinosaur Quarry (Utah), UMNH VP 5732 and YPM PU 14556, are assigned to Miragaia sp.
Synonymy with Dacentrurus and Alcovasaurus In 2010, Alberto Cobos and colleagues noted that all the diagnostic characters of Miragaia longicollum are based on skeletal elements that are absent in the Dacentrurus holotype found in England in layers of about the same age, while all traits that can be compared are shared by both genera. Therefore, they proposed that Miragaia is a junior synonym of Dacentrurus, meaning that it is the same dinosaur, because it is not possible to differentiate the two taxa through their holotypes.
In 2019, Costa and Mateus argued that Miragaia longicollum is a valid taxon, describing a newly recognised specimen, MG 4863, that had already been excavated in 1959 by Georges Zbyszewski but was only prepared between 2015 and 2017. It consists of a skeleton that also contains tail vertebrae, the most complete dinosaur ever found in Portugal. They also renamed Alcovasaurus, which was discovered in 1908, into a possible second species: Miragaia longispinus. However, Sánchez-Fenollosa et al. (2024) supported the synonymy of Miragaia and Dacentrurus based on a new specimen of the latter from the Villar del Arzobispo Formation, and suggested that Alcovasaurus is a separate genus. In their re-description of the specimen MG 4863, Costa et al. (2025) argued that the two taxa are not synonymous based on comparison with the Dacentrurus holotype and that Alcovasaurus should be included as a second species of Miragaia.
Description
Size and diagnosis
Miragaia was long yet relatively lightweight in comparison to other stegosaurs, reaching 6–6.5 metres (20–21 ft) in length and 2 metric tons (2.2 short tons) in body mass. Histology shows that the holotype specimen reached sexual maturity at 14 to 15 years old, and skeletal maturity (full size) between 21 and 25 years old. The describers established six distinguishing traits. At their very midline, the praemaxillae meet in a small sharp point, set within a larger notch in the snout tip as a whole. The front lower side edge of the praemaxilla protrudes to below. At least seventeen cervical vertebrae are present. The neural spines of the middle cervical vertebrae have a notch at their lower front edge with immediately above it a process directed to the front. The vertebrae of the middle neck, rear neck and front back possess neural spines that have a transversely expanded upper end. On the neck two rows of triangular bony plates are present that have a lightly convex outer side and a notch at the upper front edge creating a hook.
Neck elongation
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