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Miragaia (dinosaur)
Encyclopedia
Miragaia is a genus
of stegosaurid
dinosaur
. Its fossil
s have been found in Upper Jurassic rocks in Portugal. Miragaia is notable for its long neck, which included at least 17 vertebrae.
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
.
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.
The tip of the beak was toothless, as in Stegosaurus. 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. In the pelvis, the pubic
bone had an expanded tip, as seen in Dacentrurus. Paired triangular plates ran down the midline of the back.
Its total length is estimated at 5.5 – 6 metres (18-20 ft).http://blog.everythingdinosaur.co.uk/blog/_archives/2009/2/25/4103891.html
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of stegosaurid
Stegosauridae
Stegosauridae is a family of stegosauria, large thyreophorans. They lived longer than other Stegosaurs; while all Huayangosauridae and most of basal stegosaurs died out in Tithonian - Kimmeridgian, stegosauridae survived till Middle Cretaceous. They are usually characterized by triangular plates on...
dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
. Its fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s have been found in Upper Jurassic rocks in Portugal. Miragaia is notable for its long neck, which included at least 17 vertebrae.
Discovery
Miragaia is based onHolotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
ML
Museu da Lourinhã
Museu da Lourinhã is a museum in the town of Lourinhã, west Portugal. It was founded in 1984 by GEAL - Grupo de Etnologia e Arqueologia da Lourinhã ....
433, a nearly complete anterior
Anatomical terms of location
Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
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
Osteoderm
Osteoderms are bony deposits forming scales, plates or other structures in the dermal layers of the skin. Osteoderms are found in many groups of extant and extinct reptiles, including lizards, various groups of dinosaurs , crocodilians, phytosaurs, aetosaurs, placodonts, and hupehsuchians...
. ML 433 was found in the Miragaia Unit of the Sobral Formation
Sobral Formation
The Sobral Formation is a palaeontological formation located in Antarctica. It dates to the Danian stage of the Lower Paleocene period.Spectacular fossils documenting the wildlife soon after the dinosaurs became extinct are found in this formation. One of the most significant sites is on Seymour...
, Lourinhã Group
Lourinhã Formation
The Lourinhã Formation is a geological formation in West Portugal, named for the municipality of Lourinhã, from which a wide array of fossils comes...
, which dates to the late Kimmeridgian
Kimmeridgian
In the geologic timescale, the Kimmeridgian is an age or stage in the Late or Upper Jurassic epoch or series. It spans the time between 155.7 ± 4 Ma and 150.8 ± 4 Ma . The Kimmeridgian follows the Oxfordian and precedes the Tithonian....
-early Tithonian
Tithonian
In the geologic timescale the Tithonian is the latest age of the Late Jurassic epoch or the uppermost stage of the Upper Jurassic series. It spans the time between 150.8 ± 4 Ma and 145.5 ± 4 Ma...
(Late Jurassic
Late Jurassic
The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 161.2 ± 4.0 to 145.5 ± 4.0 million years ago , which is preserved in Upper Jurassic strata. In European lithostratigraphy, the name "Malm" indicates rocks of Late Jurassic age...
, approximately 150 million years ago). Octávio Mateus and colleagues described Miragaia in 2009. The type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
is M. longicollum ("long neck"). A partial hip
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
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
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
and found Miragaia to group with Dacentrurus
Dacentrurus
Dacentrurus , originally known as Omosaurus, was a large stegosaur of the Late Jurassic Period .-Description:...
in a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
Dacentrurinae, the sister group to Stegosaurus
Stegosaurus
Stegosaurus is a genus of armored stegosaurid dinosaur. They lived during the Late Jurassic period , some 155 to 150 million years ago in what is now western North America. In 2006, a specimen of Stegosaurus was announced from Portugal, showing that they were present in Europe as well...
.
Description
Euhelopus
Euhelopus is a genus of sauropod dinosaur that lived during the Early Cretaceous, between 130 and 112 million years ago . It lived in what is now Shandong Province in China. A large herbivore, it weighed approximately 15-20 tons and attained an adult length of 15m...
, Mamenchisaurus
Mamenchisaurus
Mamenchisaurus was a plant-eating four-legged dinosaur, known for its remarkably long neck which made up half its total length. It is known from numerous species which ranged in time from 160 to 145 million years ago, from the Oxfordian to Tithonian ages of the late Jurassic Period of...
, and Omeisaurus
Omeisaurus
Omeisaurus is a genus of sauropod dinosaur from the Middle Jurassic Period of what is now China. Its name comes from Mount Emei, where it was discovered in the lower Shaximiao Formation of Sichuan Province.Like other sauropods, Omeisaurus was herbivorous and large...
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
Sexual selection
Sexual selection, a concept introduced by Charles Darwin in his 1859 book On the Origin of Species, is a significant element of his theory of natural 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.
The tip of the beak was toothless, as in Stegosaurus. Both the upper arm
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
and ulna
Ulna
The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form...
and radius
Radius (bone)
The radius is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna, which exceeds it in length and size. It is a long bone, prism-shaped and slightly curved longitudinally...
(lower arm bones) are also comparable to those of Stegosaurus. The ribs of the neck vertebrae were fused to the vertebrae. In the pelvis, the pubic
Pubis (bone)
In vertebrates, the pubic bone is the ventral and anterior of the three principal bones composing either half of the pelvis.It is covered by a layer of fat, which is covered by the mons pubis....
bone had an expanded tip, as seen in Dacentrurus. Paired triangular plates ran down the midline of the back.
Its total length is estimated at 5.5 – 6 metres (18-20 ft).http://blog.everythingdinosaur.co.uk/blog/_archives/2009/2/25/4103891.html