Ouranosaurus nigeriensis is a 7 m-long (23 ft.) iguanodont dinosaur. It was discovered in 1973, in 110 million-year-old Early Cretaceous deposits in the Saharan wastes of Niger. This African cousin of the European dinosaur Iguanodon was described in 1976 by French palaeontologist Philippe Taquet.

The name Ouranosaurus effectively means "brave lizard". It is derived from the Tuareg word ourane, a name given by these nomadic people of the Sahara to the modern sand monitor lizard. The rest of its name, nigeriensis, is in reference to the country in which it was found. It is the only species in its genus.

One notable feature of this dinosaur is the tall, narrow, fin-like crest along its back. It is thought that this fin radiated excess body heat during the midday and absorbed heat when the sun was low.

Ouranosaurus is a close relative—an ancestor—of the later duckbill dinosaurs. Duck-bills evolved in the Late Cretaceous Period. The overall appearance of some duck-billed skulls is reminiscent of the skull of Ouranosaurus, which was unusual for its time.

Ouranosaurus nigeriensis was a herbivore. It is estimated to have weighed from 1 to 2 t (1.1 to 2.2 tn.). It lived in flood-plain forests of tree ferns and primitive conifers—a habitat vastly different from that of the Sahara today. Gigantic, archaic crocodiles also lived in the area and may have preyed upon Ouranosaurus.