Ouranosaurus

***Ouranosaurus*** (meaning "brave lizard") is a genus of herbivorous basal hadrosauriform dinosaur that lived during the Aptian stage of the Early Cretaceous of modern-day Niger and Cameroon. *Ouranosaurus* measured about 7 to 8.3 metres (23 to 27 ft) long. Two rather complete fossils were found in the Elrhaz Formation, Gadoufaoua deposits, Agadez, Niger, in 1965 and 1970, with a third indeterminate specimen known from the Koum Formation of Cameroon. The animal was named in 1976 by French paleontologist Philippe Taquet; the type species being ***Ouranosaurus nigeriensis***. The name is a combination of the Arabic word for "courage" and the country of discovery, although *ourane* is also the Tuareg name for the desert monitor.

## Description

*Ouranosaurus* was a relatively large iguanodontian, estimated by Taquet in 1976 to have a body length of 7 metres (23 feet) and a weight of 4 tonnes (4.4 short tons). A lighter weight of 2.2 tonnes (2.4 short tons) was suggested by American palaeontologist Gregory S. Paul in 2010 due to the leaner build observed in the animal compared to relation, although a longer length of 8.3 m (27 ft) was given. 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.

### Skull

he 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 orbits and sloping down towards both the rear of the skull and the tip of the snout. This makes *Ouranosaurus* have the most elongate skull of any non-hadrosaurid, the length being 3.8 times the maximum height, although the skull is proportionally wider than related *Mantellisaurus*.

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. 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. 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. 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.

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".

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 predentary bone at the extreme front of the lower jaws. However, after a rather large diastema with the beak, there were large batteries of cheek teeth on the sides of the jaws: the gaps between the teeth crowns were filled by the points of a second generation of replacement teeth, the whole forming a continuous surface. Contrary to the situation with some related species, a third generation of erupted teeth was lacking. There were twenty-two tooth positions in both lower and upper jaw, for a total of eighty-eight.

### Postcranial skeleton

The most conspicuous feature of *Ouranosaurus* is a large "sail" on its back, supported by long, wide, neural spines, that spanned its entire rump and tail, resembling that of *Spinosaurus*, a well-known meat-eating dinosaur also known from northern Africa. These tall neural spines did not closely resemble those of sail-backs such as *Dimetrodon* of the Permian Period. The supporting spines in a sailback become thinner distally, whereas in *Ouranosaurus* the spines actually become thicker distally and flatten. The posterior spines were also bound together by ossified tendons, which stiffened the back. Finally, the spine length peaks over the forelimbs.

The first four dorsal vertebrae are unknown; the fifth already bears a 32-centimetre-long spine (1.05 ft) that is pointed and slightly hooked; Taquet presumed it might have anchored a tendon to support the neck or skull. The tenth, eleventh and twelfth spines are the longest, at about 63 cm (25 in). The last dorsal spine, the seventeenth, has a grooved posterior edge, in which the anterior corner of the lower spine of the first sacral vertebra is locked. The spines over the six sacral vertebrae are markedly lower, but those of the tail base again longer; towards the end of the tail the spines gradually shorten.

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.

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 humerus was very straight. The hand was lightly built, short and broad. On each hand *Ouranosaurus* bore a thumb claw or spike that was much smaller than that of the earlier *Iguanodon*. The second and third digits were broad and hoof-like, and anatomically were good for walking. To support the walking hypothesis, the wrist was large and its component bones fused together to prevent its dislocation. The last digit (number 5) was long. In related species the fifth finger is presumed to have been prehensile: used for picking food like leaves and twigs or to help lower the food by lowering branch to a manageable height. Taquet assumed that with *Ouranosaurus* this function had been lost because the fifth metacarpal, reduced to a spur, could no longer be directed sideways.

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.

## *Ouranosaurus* in The Amazing Dinosaur Adventure

### Characters

The mother OuranosaurusDaisy the *Ouranosaurus*Sunflower the *Ouranosaurus*Tulip the *Ouranosaurus*
### Anonymous

Green *Ouranosaurus* in *The Stone of Cold Fire*A Purple *Ouranosaurus* walking behind a *Styracosaurus* in the opening narration of *The Great Longneck Migration*