Ouranosaurus
Ouranosaurus Temporal range: Early Cretaceous,
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Mounted paratype skeleton, Museo di Storia Naturale di Venezia 3714 | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | †Ornithischia |
Clade: | †Ornithopoda |
Clade: | † Styracosterna
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Clade: | † Hadrosauriformes
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Genus: | †Ouranosaurus Taquet, 1976 |
Species: | †O. nigeriensis
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Binomial name | |
†Ouranosaurus nigeriensis Taquet, 1976
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Ouranosaurus is a
Discovery and naming
Five French palaeontological expeditions were undertaken in the
Taquet formally described the two mostly-complete specimens MNHN GDF 300 and MNHN GDF 381 from the first and fourth expeditions as Ouranosaurus nigeriensis in 1976, along with a referred coracoid and femur that bore the numbers MNHN GDF 301 and MNHN GDF 302 respectively. MNHN GDF 300 was made the holotype, and was the primary specimen described, including a semi-articulated skull lacking the left maxilla, right quadratojugal and the articulars, almost the entire vertebral column, forelimbs lacking a few hand bones, and most of the right hindlimb and a few bones of the left.[1] Additional description for bones unpreserved in the holotype was based on Taquet's MNHN GDF 381, which was not mentioned as having been sent to Venice and renumbered as MSNVE 3714, although this was confirmed by Italian palaeontologist Filippo Bertozzo and colleagues in 2017. The holotype itself was returned to Niger after being described and having its bones cast and mounted, and is now on display at the Musée National Boubou Hama in Niamey.[3] The generic name Ouranosaurus carries a double meaning, it is both taken from Arabic meaning "valour", "bravery " or "recklessness" and also from the local
Description
Ouranosaurus was a relatively large iguanodontian, measuring 7–8.3 metres (23–27 feet) long and weighing 2.2 tonnes (2.4 short tons).[1][4] The holotype and paratype specimens were suggested to belong to subadults by Bertozzo et al. in 2017, although they would have been close to adult size. MSNVE 3714 is 6.5 m (21 ft) long as mounted, although a few caudals are missing, and is roughly 90% the length of the holotype, which would be 7.22 m (23.7 ft) long. The variation between the sizes fits within the range of variation between adult individuals of Iguanodon, so there is a chance that the larger holotype and smaller paratype were same ontogenetic stage.[3]
Skull
The skull of Ouranosaurus is 67.0 cm (26.4 in) long. It was rather low, being 24.4 cm (9.6 in) wide and only 26.0 cm (10.2 in) tall. The top of the skull was flat, the highest point being just in front of the
Bones of the snout are more loosely articulated with each other than the bones of the posterior skull. The premaxillae are 46.0 cm (18.1 in) long, with very deep external nares as in other iguanodontians. Anteriorly, the premaxillae flare gently laterally into a rugose surface for a beak, like other iguanodontians, although dissimilar from Iguanodon and similar to hadrosaurids the nares are entirely visible from above. Neither premaxilla bears any teeth, although the very anterior tip has "pseudo-teeth" formed by multiple denticles on the margin of the bone.[1] Only the right maxilla of Ouranosaurus is known. although it is well preserved forming a triangle 28.0 cm (11.0 in) long and 11.7 cm (4.6 in) tall, much taller proportionally than Iguanodon. The maxilla bears faces for articulation with the premaxilla in front, lacrimal above, ectopterygoid, vomer, palatine and possibly pterygoid internally, and jugal to the rear. The lacrimal process is the highest point of the maxilla, and behind this process is a smooth and curved margin for the antorbital fenestra, which is bounded by the maxilla in front and below, lacrimal above, and jugal behind. The jugal overlaps only the posterior end of the maxilla, which is unlike hadrosaurids where there is more overlap.[1] The dental edge of the maxilla is slightly arced, and above the toothrow is a shallow depression bearing nutrient foramina, also known as the buccal emargination that is diagnostic of Ornithischia.[1][5] 20 teeth are preserved in the maxilla, although the anterior end of the toothrow is broken and Taquet (1976) predicted the total number to be 22.[1]
Many of the central bones of the skull are the same form as those of hadrosaurids or related iguanodontians like Iguanodon and Mantellisaurus. The jugal below and behind the orbit bears the same shape as in hadrosaurids, with a high rear process, and articulated with the quadratojugal and quadrate that are also very similar to more derived taxa. As in other ornithopods, the postorbital is a tri-radiate bone surrounding sides of the orbit, infratemporal fenestra and supratemporal fenestra. Contact between the postorbital and the parietal excludes the flattened and wide frontals from the supratemporal fenestra. In Ouranosaurus and related taxa the prefrontals are small, and articulates with the broadened and textured lacrimal. Only a single supraorbital was present in Ouranosaurus, which projects into the orbit above the eye. The nasal bones of Ouranosaurus are unique among ornithischians. The bones are unfused suggesting mobility, and at their ends on the top of the skull are rounded domes, which were described by Taquet (1976) as distinct and rugose "nasal protuberances".[1]
The snout was toothless and covered in a horny sheath during life, forming a very wide beak together with a comparable sheath on the short
Postcranial skeleton
The most conspicuous feature of Ouranosaurus is a large "sail" on its back, supported by long, wide,
The first four
The dorsal "sail" is usually explained as either functioning as a system for thermoregulation or a display structure. An alternative hypothesis is that the back might have carried a hump consisting of muscle tissue or fat, resembling that of a bison or camel, rather than a sail. It could have been used for energy storage to survive a lean season.[7]
The axial column consisted of eleven neck vertebrae, seventeen dorsal vertebrae, six sacral vertebrae and forty tail vertebrae. The tail was relatively short.
The front limbs were rather long with 55% of the length of the hind limbs. A quadrupedal stance would have been possible. The
The hindlimbs were large and robust to accommodate the weight of the body and strong enough to allow a bipedal walk. The femur was slightly longer than the tibia. This may indicate that the legs were used as pillars, and not for sprinting. Taquet concluded that Ouranosaurus was not a good runner because the fourth trochanter, the attachment point for the large retractor muscles connected to the tail base, was weakly developed. The foot was narrow with only three toes and relatively long.
In the pelvis, the prepubis was very large, rounded and directed obliquely upwards.
Classification
Taquet originally assigned Ouranosaurus to the
The simplified cladogram below follows an analysis by Andrew McDonald and colleagues, published in November 2010 with information from McDonald, 2011.[8][9]
Iguanodontia |
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Paleobiology
Diet
The jaws were apparently operated by relatively weak muscles. Ouranosaurus had only small
Histology
Ouranosaurus bears more similarities to other derived iguanodonts than more basal ornithopods. Remodeling is present in the subadult paratype, and high vascular density and circumferential arrangement of the microstructure suggests fast growth. Faster growth occurs in the same phylogenetic groups as higher body size, although their relationship is unclear. Ouranosaurus is a similar size to more basal Tenontosaurus which has slow growth, so either faster growth is caused by body size or Tenontosaurus is the maximum size of an ornithopod with a slow growth rate.[3]
Paleoecology
Ouranosaurus is known from the Elrhaz Formation of the Tegama Group in an area called Gadoufaoua, located in Niger. Only two mostly complete skeletons and up to 3 additional individuals have been found.
While it has been claimed that the
References
- ^ ISBN 2-222-02018-2.
- ^ Taquet, P. (1970). "Sur le gisement de Dinosauriens et de Crocodiliens de Gadoufaoua (République du Niger)" (PDF). Comptes Rendus de l'Académie des Sciences, Série D. 271: 38–40.
- ^ PMID 28649466.
- ISBN 978-0-691-13720-9.
- S2CID 86728076.
- ^ ISBN 1-84028-152-9.
- .
- PMID 21124919.
- .
- ^ .
- ^ PMID 18030355.
- ISSN 0753-3969.
Bibliography
- Ingrid Cranfield, ed. (2000). Dinosaurs and other Prehistoric Creatures. Salamander Books. pp. 152–154.
- Richardson, Hazel (2003). Dinosaurs and Other Prehistoric Animals. Smithsonian Handbooks. p. 108.
- Dixon, Dougal (2006). The Complete Book of Dinosaurs. Hermes House.
- Cox, Barry; Colin Harrison; R.J.G. Savage; Brian Gardiner (1999). The Simon & Schuster Encyclopedia of Dinosaurs and Prehistoric Creatures: A Visual Who's Who of Prehistoric Life. Simon & Schuster. ISBN 9780684864112.
External links
- Ouranosaurus on Nature
- Ouranosaurus (with picture)