Miragaia

*Miragaia longicollum*

***Miragaia*** (named after Miragaia, the area in Portugal and geologic unit where its remains were found) is an extinct genus of stegosaurid dinosaur. Its fossils have been found in Upper Jurassic rocks in Portugal. *Miragaia* is notable for its long neck, which included at least 17 vertebrae. It was discovered in 2009 by a paleontologist named Octávio Mateus. Miragaia also has one of the shortest names for dinosaurs. Miragaia stands for "Beautiful Earth Goddess" and to the village where it was first found and ***longicollum*** is in reference to its very long neck.

## Discovery

*Miragaia* is based on **ML 433**, a nearly complete anterior half of a skeleton with partial skull (the first cranial material for a European stegosaurid). Among the recovered bones were most of the snout, fifteen neck vertebrae (the first two, which articulated with the skull, were absent), the shoulder bones, most of the forelimbs, and thirteen bony plates. **ML 433** was found in the Miragaia Unit of the Sobral Formation, Lourinhã Group, which dates to the late Kimmeridgian-early Tithonian (Late Jurassic, approximately 150 million years ago). Octávio Mateus and colleagues described *Miragaia* in 2009. The type species is *M. longicollum* ("long neck"). A partial hip and partial vertebrae from a juvenile individual (**ML 433-A**) were found at the same location, and were also assigned to *M. longicollum.* Mateus and colleagues performed a phylogenetic analysis and found *Miragaia* to group with *Dacentrurus* in a clade Dacentrurinae, the sister group to *Stegosaurus*.

## Description

Miragaia was herbivorous, like all stegosaurs. It's closely related to the more famous *Dacentrurus*. Together, they form the clade *Dacentrurinae.*

It had several plates that went down along its back, possibly for thermal regulating or attracting mates and scaring off rivals or predators. It had long spikes that came out of each shoulder, possibly for display. It also had several spikes on its tail (thagomizers) that it could use to hit predators with or scare them off. It was a quadruped, and walked around on four stout, slow-moving legs, but Miragaia was so well defended it didn't need to run fast. One feature that sets Miragaia apart form other stegosaurs is its extended neck with 17 vertebrae in it. It grew to be about 20 ft (6 m) long from nose to tail, with the extended neck making up a lot of it.

This represents the culmination of a trend of longer necks seen in stegosaurians. Additionally, Miragaia had more neck vertebrae than most sauropods, dinosaurs known for their long necks, which contrasts with the traditional view of stegosaurians as low browsers with short necks. Only the Chinese sauropods *Euhelopus*, *Mamenchisaurus*, and *Omeisaurus* had as many neck vertebrae as Miragaia, with most sauropods of the Late Jurassic possessing only 12 to 15. Mateus and colleagues suggested that the long neck either allowed Miragaia to browse at a level that other herbivores were not exploiting, or that the neck arose due to sexual selection.

### Size and diagnosis

The total length of *Miragaia* has been estimated at 5.5 – 6 metres (18-20 ft). In 2010, Gregory S. Paul estimated the length at 6.5 metres, the weight at two tonnes.

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

The most notable feature of *Miragaia* is its long neck, which was composed of at least 17 vertebrae. This represents the culmination of a trend of longer necks seen in stegosaurians. Additionally, *Miragaia* had more neck vertebrae than most sauropods, dinosaurs known for their long necks, which contrasts with the traditional view of stegosaurians as low browsers with short necks. Only the Chinese sauropods *Euhelopus*, *Mamenchisaurus*, and *Omeisaurus* had as many neck vertebrae as *Miragaia*, with most sauropods of the Late Jurassic possessing only 12 to 15. Mateus and colleagues suggested that the long neck either allowed *Miragaia* to browse at a level that other herbivores were not exploiting, or that the neck arose due to sexual selection.

In sauropods, great neck length was achieved by a combination of three processes: incorporation of back vertebrae into the neck; addition of new vertebrae; and lengthening of the individual neck vertebrae. The long neck of *Miragaia* appears to have resulted mostly from back vertebrae becoming incorporated into the neck, based on vertebral counts of other stegosaurians. There is currently no evidence that new vertebrae contributed to the neck; instead, the distribution of existing vertebrae in the back and neck changed. There is some evidence for increasing vertebral length in *Miragaia* and *Stegosaurus*, but this is equivocal and could be due to post-mortem distortion; this mechanism was seen as a minor factor in neck elongation.

### Skeleton

Apart from the neck length, the known osteology of *Miragaia* resembles that of other stegosaurids, differing in small details. The tip of the beak was toothless, as in *Stegosaurus*. The upper beak, formed by the praemaxilla, was pendant. The notch in the snout tip was, seen from above, shaped like a W, whereas in Stegosaurus the notch is U-shaped, with a little bulbous projection in the middle. The upper surface of the nasal bone was ornamented. A ridge formed the contact with the maxilla. The maxilla had sixteen teeth. The postorbital was a small and triradiate element.

The cervical vertebrae had well-developed cervical ribs, fused to the vertebral body. The ribs were elongated, with a forward-pointing process on the capitulum, the main rib head. The neural spines of the rear cervicals and front dorsals are transversely expanded at their upper ends due to rugosities serving as an attachment for tendons. This expanded sector projects to the front also, creating a notch on the lower front edge. Additionally the neural spine base is transversely constricted. Ridges extend to the rear from the sides of the neural spine base, over the upper sides of the rear joint processes, the postzygapophyses. These postzygapophyses themselves project far beyond the rear facet of the vertebral body, a derived trait. The prezygapophyses to the contrary, are much shorter; they have a notch at the front upper edge.

The scapula had a large rectangular acromion, with a sharp upper corner, on the lower front edge. The more narrow coracoid had a rounded lower edge. Both the upper arm and ulna and radius (lower arm bones) are also comparable to those of *Stegosaurus*. The ribs of the neck vertebrae were fused to the vertebrae. The tuberosity of the rear humerus serving as attachment for the *musculus triceps brachii* is well-developed but the vertical ridge running from it to below is not. In the pelvis, the pubic bone had an expanded tip, as seen in *Dacentrurus*; the rear shaft had a lightly expanded tip.

### Osteoderms

*Miragaia*, like all known stegosaurians, showed an array of plates and spikes, consisting of skin ossifications or osteoderms. Paired triangular plates ran down the midline of the neck, reconstructed as eight pairs. They were asymmetrical with a convex outer side and a concave inner side. Their bases were not very expanded with the exception of a possible last pair, located on the front back. They were obtuse but lightly hooked at the front. A rather long, narrow and straight preserved spike was at first considered to have been a shoulder spine, but was later seen as part of some tail arrangement.

## Phylogeny

*Miragaia* was placed in the Stegosauridae in 2009. Mateus and colleagues performed a phylogenetic analysis and found *Miragaia* to group with *Dacentrurus* in a clade Dacentrurinae, newly named for the occasion, the sister group to *Stegosaurus* (the latter genus was in the cladistic analysis considered to include *Hesperosaurus* and *Wuerhosaurus*).

The position of *Miragaia* in the stegosaurid evolutionary tree is shown by this cladogram:

## Material

Miragaia longicollum was discovered during construction of a road. This meant that the entire back section of the animal was probably destroyed. However, the front half is well preserved: a partial skull (right premaxilla, partial left maxilla, left nasal, right postorbital, right and left angulars), 15 cervical vertebrae (atlas and axis are absent) with associated ribs, 2 dorsal vertebrae, both coracoids, scapulae, humeri, radii and ulnae, 1 metacarpal, 3 phalanges, 12 rib fragments, 1 cheveron, 1 dermal spine and 13 plates.

Some fragments of a juvenile were also found at the same location, intermingled with the bones of the holotype: a partial pelvis (left ilium and right pubics), 2 dorsal centra and 3 dorsal neural arches from a juvenile individual (specimen ML 433-A), which were assigned as a paratype to *M. longicollum*.

‬Further isolated remains have also been attributed to the genus.

## Paleoecology

    In life, Miragaia would have coexisted with other stegosaurians, such as '*Stegosaurus ungulatus* and *Dacentrurus armatus*; sauropods, like *Supersaurus lourinhanensis*, *Zby atlanticus*, *Lusotitan* *atalaensis*, *Lourinhasaurus alenquerensis* and *Turiansaurus riodevensis*; the ankylosaur *Dracopelta zbyzeswskii*; ornithopods *Draconyx loureiroi,* such as *Eousdryosaurus nanohallucis*; crocodilians, like *Machimosurus huggi* and theropods, such as *Torvosaurus gurneyi*, *Allosaurus europaeus*, *Ceratosaurus dentisculcatus* and *Lourinhanosaurus antunesi*.

## Appearance in other media

### *Jurassic Park*

* Miragaia appear in the video game *Jurassic World Alive* as a common dinosaur.

## References

1. ↑ 1.0 1.1 1.2 1.3 Mateus, Octávio; Maidment, Susannah C.R.; and Christiansen, Nicolai A. (2009). "A new long-necked 'sauropod-mimic' stegosaur and the evolution of the plated dinosaurs" (pdf). *Proceedings of the Royal Society B: Biological Sciences* **online**. doi:10.1098/rspb.2008.1909. http://rspb.royalsocietypublishing.org/content/early/2009/02/21/rspb.2008.1909.full.pdf+html.