Ouranosaurus

Chapter • Meet the dinosaur

Overview

Ouranosaurus was a medium-sized plant-eating ornithopod that reached about 7–8.3 metres in length and weighed an estimated 2.2–4 tonnes. Its most striking feature was the row of greatly elongated neural spines along the back and base of the tail, which on some vertebrae stood several times taller than the vertebral body itself. The skull was long and unusually flat, ending in a broad, toothless beak, with tightly packed batteries of grinding teeth further back in the jaws. A pair of low bony bumps sat just in front of the eyes. The forelimbs were sturdy with broad wrists, indicating that the animal spent much of its time on all fours, while the longer hind limbs allowed it to rear up and run bipedally. The thumb spike so famous in Iguanodon was reduced here to a small, blunt knob. Exactly what the back looked like in life is still debated. The traditional reconstruction is a thin skin sail stretched between the spines, possibly used for heat exchange or for display to other members of the species. An alternative proposal, put forward in the 1990s, is that the spines instead supported a muscular, fatty hump like that of a bison, serving as an energy store in a climate with pronounced dry seasons. Both models still appear in the scientific literature, and neither bone microstructure studies nor renewed work on the well-preserved Venice specimen has settled the question. Ouranosaurus was strictly herbivorous. Its broad beak cropped horsetails, ferns, conifer shoots and other low-growing vegetation, and the dental batteries then ground the food using the sideways-flexing upper jaw mechanism that ornithopods evolved. By rearing up on its hind limbs it could reach vegetation as high as roughly four metres. Tooth wear patterns show it was an efficient chewer, much like the later duck-billed dinosaurs. The first fossils came from Gadoufaoua in the Ténéré Desert of Niger, collected by French expeditions led by palaeontologist Philippe Taquet in the 1960s, and the species was formally described in 1976. Two nearly complete skeletons are known; one remains in Niger while the other is mounted in the natural history museum in Venice, Italy. According to Taquet the name Ouranosaurus derives from ourane, the local Tuareg-Arabic word for the desert monitor lizard, and can be translated roughly as 'brave lizard'. The species name nigeriensis refers to Niger.

Chapter • Where it lived

Habitat

Ouranosaurus lived in the Early Cretaceous, in the Aptian roughly 125–112 million years ago, in what is now the Ténéré Desert of Niger. All confirmed remains come from the Elrhaz Formation at the Gadoufaoua fossil locality. At the time this was not desert at all but a hot, low-lying river landscape of broad channels, sandbars, floodplains and swampy backwaters fringed with horsetails, ferns and conifers, probably with alternating wet and drier seasons. The same beds have yielded the giant crocodyliform Sarcosuchus, the long-necked sauropod Nigersaurus, the heavily built ornithopod Lurdusaurus and the predators Suchomimus, Kryptops and Eocarcharia.

Chapter • Wild behavior

Behavior & Ecology

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Chapter • Scientific place

Taxonomy