Ouranosaurus: Beast of the Week

 This week we will be checking out a beautiful and unique plant-eating dinosaur.  Get ready for Ouranosaurus nigeriensis!

Ouranosaurus was an ornithopod dinosaur that lived in what is now central Africa, specifically Niger and Camaroon, during the early Cretaceous period, between 121 and 113 million years ago.  It was a plant-eater when alive and adults would have measured about 25 feet (7.6 meters) long from beak to tail.  The genus name, Ouranosaurus, translates to "Courageous Lizard" from a combination of Arabic and Greek languages.  The species name, nigerensis, is in reference to the country, Niger, where its bones were first discovered. 

Ouranosaurus life reconstruction in watercolor by Christopher DiPiazza

Ouranosaurus was an ornithopod dinosaur closely related to Iguanodon and Mantellisaurus.  Like them, it would have been able to walk on all fours or its hind legs.  Its arms were proportionally long and ended with five digits on each hand.  The first digit, like those of Iguanodon, consisted of a thumb-spike, but it was proportionally smaller.  Its second, third, and fourth fingers were likely fused in life and would have supported its weight as it walked on all fours.  Its fifth finger was relatively long, but not flexible.  

Mounted skeleton of Ouranosaurus on display at the Natural History Museum of Venice in Italy. Photo from Felippo Bertozzo's 2017 paper (referenced below).

Ouranosaurus had a long and laterally flattened snout, with its nostril holes facing upwards, a trait similar to some more distantly related hadrosaurs ("duck-billed" dinosaurs).  Ouranosaurus had a broad beak at the front of its mouth, and small closely-spaced teeth, forming what is referred to as a dental battery, in the back of its jaws, for processing plants.  The bones that make up the top of Ouranosaurus' snout were actually unfused to the rest of the skull, suggesting flexibility in life, possibly an adaptation for feeding a certain way.  

Image of Ouranosaurus' skull from Taquet's 1976 paper (listed below) Red arrows pointing to two rounded knobs on the top of its head where the nasal bones begin.  Some think there were small horns or crests there in life while others point out the surface texture does not suggest any such characteristic.

The most notable feature of Ouranosaurus is definitely its extremely tall neural arches, the sections of its vertebra that extend upwards from its back.  This is a feature that has independently evolved in several kinds of dinosaurs and other animals across history.  The most famous example of this feature is probably the theropod dinosaur, Spinosaurus, but many other prehistoric animals as well as many modern reptiles have evolved this trait in varying degrees.  In life, this structure would have formed a meaty sail-like structure on Ouranosaurus', back, drastically expanding the dinosaur's profile.  Experts have suggested such a bold adaptation could have been for display within the species or possibly to help control the Ouranosaurus' body temperature by expanding its surface area to either absorb warmth from the sun or expel excess heat if it became too hot.  

Clockwise from tom left, Sailfin Chameleon (Trioceros montium), Green Basilisk (Basilicus plumifrons), and Sailfin water dragon (Hydrosaurus pustulatus), are all modern lizards that independently of one another evolved tall spines on their vertebra, forming fleshy sails on their backs.

The environment Ouranosaurus lived in would have been a seasonally wet floodplain and it would have coexisted with a number of other dinosaurs, including fellow herbivores, Lurdusaurus and Nigersaurus, as well as the large spinosaur, Suchomimus.  

References

Bertozzo, F.; Dalla Vechia, F.M.; Fabbri, M. (2017). "The Venice specimen of Ouranosaurus nigeriensis (Dinosauria, Ornithopoda)". PeerJ. 5: e3403.

McDonald, A.T.; Kirkland, J.I.; DeBlieux, D.D.; Madsen, S.K.; Cavin, J.; Milner, A.R.C.; Panzarin, L. (2010). Farke, Andrew Allen (ed.). "New Basal Iguanodontians from the Cedar Mountain Formation of Utah and the Evolution of Thumb-Spiked Dinosaurs". PLOS ONE. 5 (11): e14075.

Taquet, P. (1976). "Géologie et Paléontologie du Gisement de Gadoufaoua (Aptien du Niger)" (PDF). Cahiers de Paléontologie. Éditions du Centre National de la Recherche Scientifique, Paris: 1–191.