Oriana Nascava was a musician living in Waterfall City in 1867.
After she was born, she was given a half of a key before her parents died. This was her only link to her past, as any information she had about her family history died with her parents. In 1867, she learned that the other half of the key had been found by the explorer Arthur Denison. Oriana agreed to let Arthur use the key on his upcoming expedition to the World Beneath, on the condition that she be allowed to accompany him – her name, which means "born from a cave" was the only clue she had as to her origins, so she suspected the answers she was seeking might be in the World Beneath. Arthur reluctantly agreed, and was pleasantly surprised that Oriana arrived ready for action with a sensible wardrobe and only a single small instrument, a dragon flute.
While assisting Lee Crabb in getting back the Remora submersible, Oriana concocted a convincing cover story about being biologists from Sauropolis, but their cover was blown by a messenger from Waterfall City. Oriana later assisted in piloting the Remora through a Devonian sea garden and an attack by a dunkleosteus. Upon arriving at the submerged door that had stopped them the first time, Oriana combined both halves of the key to open the door into the main system of the World Beneath.
After stumbling upon a deposit of sunstones in their natural state, Oriana slipped away for a private moment. The sunstones gave her a vision of a long chain of her maternal ancestors. Although the vision did not grant names, Oriana at last new the faces of her ancestors.
Over the course of the expedition, the group found more and more signs of the ancient civilization of Poseidos, culminating in the discovery of a fleet of "strutters": mechanical, sunstone-powered dinosaurs. Oriana hitched a ride with the Torosaurus-shaped strutter Arthur selected, while Crabb chose a menacing eurypterid-shaped one.
When the group emerged into the Rainy Basin, they stumbled right into a battle between a caravan guarded by none other than Arthur's son Will. They narrowly made it to the safety of the border town of Bonabba.
At last having time to reflect upon their experiences, Arthur and Oriana argued about the value of their discoveries. Arthur was interested in exploiting the sunstones to bring a new golden age to Dinotopia, while Oriana felt it was best to leave the past alone and that Dinotopia was already in a golden age. Arthur admitted that he valued Oriana more highly than any of the technology Poseidos had possessed.
A few days later, Arthur, Oriana, and Bix departed into the jungle once again, having finally realized the real reason the Tyrannosaurids of the Rainy Basin were so cantankerous was that they were guarding the ancient treasures of Poseidos. They were eventually received by Sinktooth, the "king of kings" who led the tyrranosaurids, who confirmed their theory and agreed to allow them to view the treasures, but warned them that they were only allowed to take what knowledge the could hold in their hearts. While in the treasury, Oriana discovered a bust from the Chandaran Fifth Kingdom depicting one of the women she had seen in her vision. The bust was of a Chandaran princess who married a king of Poseidos, meaning that Oriana was a distant descendant of the royalty of both Chandara and Poseidos. When Arthur found images of Poseidos at the height of its glory, Oriana showing him pictures of its destruction.
The group was interrupted by Lee Crabb, who stole the Ruby Stonestone at the heart of the treasure and proceeded to try and make it off-island. Oriana gave chase on the back of Sinktooth's mate, but they were forced to turn back after chasing Crabb out to sea. After Arthur managed to extract the Ruby Sunstone and rescue Crabb, he and Oriana returned to Waterfall City and told their story. Arthur and Oriana began a relationship in earnest at that point, growing as intertwined as the two halves of the key that brought them together, which they kept in its completed form above their hearth.
Oriana is mentioned in the non-canon miniseries. She is deceased by the time the miniseries begins. She is known to have had children and grandchildren, but it's not clear if Arthur was the father of her kids.
Following Arthur's expedition, she was given their submersible's Sunstone by Denison as a gift – the sunstone in question was small, but was an almost perfect gem and was thus potentially more powerful than some larger sunstones. By 2002, Oriana had passed away, and had led left the sunstone to her granddaughter, Marion Seville. Marion's father keep it in safekeeping and gave it to her on her 18th birthday, along with Oriana's final message: "find the light". Waldo spoke admiringly of Oriana and compared Marion to her favorably.