Final answer:
The unusual feature of Ouranosaurus was its long neural spines(c), which likely supported a sail or hump on its back for thermoregulation.
Step-by-step explanation:
An unusual feature of Ouranosaurus was its long neural spines(c). This distinctive feature likely supported a large sail or hump on its back. This characteristic is often thought to have had a thermoregulatory function, playing a role in heat dissipation for the dinosaur, which lived in a warm climate. Its long neural spines may have helped it to regulate its body temperature by increasing the surface area of its body exposed to air, in a similar way that the sails and humps of other animals are believed to do.