Plio acts like a mother to Aladar and quickly accepts him after helping him get out of his egg as a baby. Her father Yar is uneasy about this, but she assures him that Aladar won't hurt anyone and that he will be raised as a vegetarian. She deeply cares for her daughter Suri, and is devastated when Lemur Island is destroyed by a meteor shower and kills all the unfortunate lemurs still on the island.
Plio is first seen in the movie when a dinosaur egg falls on Lemur Island, where she lives with her father Yar, her daughter Suri, and her younger brother Zini. Plio is present when the egg cracks, then opens the shell and is happy to see a baby Iguanodon. She holds the baby in her hands and decides that she will raise him. Yar objects because he says that one day he will eat them and tells Plio to get rid of the creature. Plio apologizes to the baby and lets Yar do it himself. He holds up the baby dinosaur and attempts to drop it, though is unable to bring himself to do it after looking at the newborn and seeing how harmless and peaceful it is, but then the baby urinates on him. Disgusted, he hands the hatchling back to Plio, and she reaffirms him that the baby will learn not to eat meat; she names the baby Aladar. Yar reluctantly lets her keep the hatchling and tells Plio to watch his head, out of concern for the baby's well-being, but hides this by warning her that he may bite.
The years pass and Aladar has grown up a vegetarian dinosaur thanks to Plio's care. That night, Plio is explaining to the female lemurs about the mating ritual, while Yar is having a similar pep talk with the male lemurs. After the ritual, Plio is present when a fireball falls from the sky and crashes into the ocean, causing violent tremors. Other fireballs soon start falling, destroying the island. Plio urges Aladar to run and he takes her, Yar, Suri and Zini on his back, and they escape the island by jumping across the sea to the mainland. Plio and the others are devastated that everyone on the Island was killed by the fireballs, and that she and her family are the last ones of their kind.
For the next few days, they wander through deserted lands until they find a dinosaur herd led by Kron, his second-in-command Bruton and his sister Neera. Plio and the others learn that the herd is going to the Nesting Grounds. There, they befriend some of the elder dinosaurs: Baylene, Eema and Url who are at the end of the herd because they are too old to follow the rhythm of the others. Plio is the first to notice that her son Aladar has fallen in love with Neera.
After several days of rough marching, Bruton (who had been attacked by Carnotaurs) informs Kron that Carnotaurs are following them so Kron decides to accelerate the pace, not caring if someone is left behind. Because of this, Aladar, the lemurs, Baylene, Eema and Url separate from the herd. On a rainy night, they find shelter in cave. They also find a wounded Bruton who has been banished from the herd by Kron. Despite the obvious, Aladar helps a reluctant Bruton into the cave. While Plio tends to Bruton's wounds, he asks her why she is giving them false hopes, but Plio reassures him that hope is the last thing that gets lost and that he is welcome to follow them. That night when two Carnotaurs attack them, everyone manages to escape deeper in the cave, but Bruton dies in the process while saving them, and the entrance of the cave is blocked by the falling rocks.
Later, after wandering for hours in the cave, Suri and Zini start smelling something. Plio and Yar smell the same thing, and so they start digging through the rocks to discover a ray of light; however, more rocks fall and cover the exit. Aladar screams in frustration and gives up, but Baylene says that they didn't come this far only to give up, and so everyone starts to push the rocks until they discover something amazing: they have arrived at the Nesting Grounds. Plio is happy that they have finally arrived at their new home, and she with Yar watch happily as Suri, Zini and Baylene jump into the lake. Aladar then goes to warn the rest of the herd about the cave entrance.
Months later, Plio becomes a grandmother when Aladar and Neera have their babies. She helps a baby Iguanodon out of its shell and comments that he's the sweetest little small fry she ever saw.