Ouranosaurus nigeriensis

By José Carlos Cortés

Etymology: Brave Reptile of the Sky 

First Described By: Taquet, 1976

Classification: Dinosauromorpha, Dinosauriformes, Dracohors, Dinosauria, Ornithischia, Genasauria, Neornithischia, Cerapoda, Ornithopoda, Iguanodontia, Dryomorpha, Ankylopollexia, Styracosterna, Hadrosauriformes

Status: Extinct 

Time and Place: Sometime around 112 million years ago, in the Albian age of the Early Cretaceous 

Ouranosaurus is known from the Elrhaz Formation of Agadez, Niger 

Physical Description: Ouranosaurus is an exceptionally iconic dinosaur, primarily because of its very weird distinguishing physical feature: it has a sail. Probably. The reason for this idea is that Ouranosaurus had extremely high spines on its back, reacting a notable ridge along the center of the animal. These spines become thicker and flatten as they go along the body, and bony (ossified) tendons ran across the spines and the tail. The spines grew biggest over the forelimbs, rather than over the hips. This structure may have been a sail; it also could have been a hump contain muscle or fat – similar to living bison and camels. This would have allowed for the storage of energy during the dry season or another time of year. If a sail, this structure would have been primarily one of display, flashing colors and patterns to communicate with other members of the species. It had very long forelimbs with lightly built hands, which had sharp thumb claws and the middle fingers built into a broad hoof-like structure. In short, it was capable of quadrupedal walking. It had very robust hindlimbs as well, and thus was able to walk bipedally in addition to quadrupedally. Ouranosaurus was quite large, reaching 7 meters in length and weighing somewhere around 2.2 tonnes – despite its length, it was fairly lightly built. With its sail, it was just under 3 meters tall. Being of such large size, it is unlikely that Ouranosaurus retained any fluffy covering; if it did, it was sparse and mainly ornamental.  

By Slate Weasel, in the Public Domain

It had a very long, flat head, with an even longer snout that greatly surpassed the size of Ouranosaurus’ close relative, Iguanodon. It had a straight beak, rather than a curved one, and no teeth in the front of its snout. The snout also was covered in a sheath of horn, which made it wider and more like something of a beak. This beak was then followed by densely packed batteries of teeth in the cheeks, forming a single surface like those found in the much later Hadrosaurs. The jaws had fairly weak muscles, but this was made up for with a narrow back of the skull, which made the bite ability of the jaws greater to make up for the weak musculature. In short, Ouranosaurus, despite having a very different head than the later Hadrosaurs, was still a strong chewer. Interestingly enough, the eyebrows of Ouranosaurus featured small rounded horns – making Ouranosaurus the only known Ornithopod (Hadrosaurs and their close relatives) with horns. It had highly placed nostrils, and two small bumps between the nose and the eye socket for display. 

By Pavel Riha CC BY-SA 3.0

Diet: Ouranosaurus Primarily fed on leaves, fruit, and seeds, using its chewing to break up tougher plant material and to gain food from it. Given its decent height, Ouranosaurus would have been a mid-level browser. 

By Audrey M. Horn, CC BY-SA 4.0

Behavior: Ouranosaurus would have spent most of its time foraging on a variety of plants in its ecosystem, wandering about the river delta searching for leaves, fruits, and other delicious foods. It is fairly unlikely that Ouranosaurus would have been a herding animal, as herds seemed to have been more of a behavior for Ornithopods more closely related to Hadrosaurs; instead, Ouranosaurus probably wandered about its environment alone, or in small family groups. That said, it almost certainly took care of its young in some capacity, and it did have complex social behaviors if the sail was a sail and used for display – and it used those bumps and horns on its head for display as well. It was also probably at least somewhat vocal. As for the spiked thumbs, those could have been used for defense, as well as in-fighting amongst members of the group. It wouldn’t have been a good runner, but it would have moved on two legs when needing to move at least somewhat faster, and stuck to four legs for most movements throughout the day. It probably would have used that narrow head to selectively grab a variety of foods from in between more dense foliage. 

By Scott Reid

Ecosystem: Ouranosaurus lived in an extensive river delta, filled with extensive waterways and wetlands. These wide rivers were home to many animals, including a truly extensive number of dinosaurs. Plenty of trees, including ginkgoes and pines, and some flowering plants, in addition to horsetails and ferns, were present for Ouranosaurus to feed on. There were many types of fish and invertebrates, and the turtle Taquetochelys, but the archosaurs were the main stars of the show. There was the duck-croc Anatosuchus, the giant croc Sarcosuchus, and the running croc Araripesuchus on the Crocodylomorph side of things. There was a weirdo sauropod here too, the duck-billed Nigersaurus, which decidedly does not get enough press. As for other ornithopods, there was the fast-running biped Elrhazosaurus, and a close cousin of Ouranosaurus – Lurdusaurus, an equally-weird creature, with a long neck like a sauropod and the ability to live semi-aquatically in the river system. As for theropods, there was the possible Ornithomimosaur Afromimus, the mid-zied carnosaur Eocarcharia, the Abelisaurid Kryptops, and the spinosaur Suchomimus. You will note that Ouranosaurus did not live with Spinosaurus. This is a misconception. The two did not live together – never, not once, not even close, they are not found in the same place. Spinosaurus (probably) comes from later, and while it seems that it did live that southward, it decidedly did not live in the Elrhaz formation, because its job was being done by Suchomimus. As for predators, Ouranosaurus probably had to mostly watch out for Eocarcharia and Kryptops, as they would have been the main land predators of the area. 

By Ripley Cook

Other: Ouranosaurus, being a Hadrosauriform, was most closely related to one of the more famous Ornithopods, Iguanodon, and shared the thumb spike in common with it. Interestingly enough, Ouranosaurus wasn’t the only hump or sail backed dinosaur at that point of the family tree; Morelladon, which lived much earlier, also supported some sort of odd structure on its back. 

~ By Meig Dickson

Sources under the Cut