Grandpa and Grandma Longneck also known in full names as Luka and Luna are characters in the Land Before Time films and television series. They are each Brontosaurus, which is one of many species referred to as "Longnecks" by the characters in the franchise. They are Littlefoot's maternal grandparents - due to being the parents of his mother - and his primary caregivers after his mother's death. They act as parents to Littlefoot; giving him advice when needed and take the responsibility of protecting him very seriously. Grandma is voiced by late Linda Gary and later Miriam Flynn while Grandpa is voiced by late Kenneth Mars (who also voiced King Triton) and later voiced by Barry Bostwick.
Grandpa and Grandpa Longneck was seen during the Flying rock impact in the Great Valley and causes a Landslide in the Mysterious Beyond. Littlefoot reunites with his grandparents and a tree was about to collapse at them, but they dodge it. After the impact they find Littlefoot hiding under a tree stump asking if he is all right and he can come out. Littlefoot asked them if that was a regular earth shake and they tell him it's not and they don't know what it was and it has to do with those flying rocks coming from the sky and watch the aurora lights glowing in the sky. Grandpa, Grandma, and Littlefoot are in the Thundering fall with the other grown-ups drinking and eating, but the waterfall suddenly stops. They wondered why the waterfall stop flowing and talk about it and planned to leave the Great Valley. But the grown-ups refused to leave. Grandpa Longneck witnesses Littlefoot and his friends being bullied by Hyp, Nod, and Mutt in the river asking him what happened and he replies that it was an accident.
Cera's dad tells Grandpa Longneck that his daughter won't waste and calls Littlefoot a bad influence. This angers Grandpa Longneck and tells Cera's dad that is not true. Later Hyp's dad who witnessed what Hyp has done to Littlefoot apologizes to Grandpa and Grandma Longneck over his son's actions and leading Cera's dad to insult Littlefoot. During the wildfire in the Great Valley, Grandpa Longneck rescues Cera and her dad from the fire while Grandma Longneck leads Littlefoot and the others to safety. They argue until Littlefoot tells them that the water is stuck in the Mysterious Beyond and they must free the water. They encounter Littlefoot and his friends who just rescued Hyp from the tar pit that they do not to the time to wander on the Mysterious Beyond and Hyp's dad scolds Hyp for putting himself in danger, bullying Littlefoot and his friends and Cera's dad to call the latter a bad influence.
They are being attacked by a group of Velociraptors and they hold them off while Littlefoot and his friends free the water. They succeed freeing the water and putting the fire on the Great Valley out. Now the Thundering falls is now flowing with more water, the herds return to the Great Valley, although the fire destroyed most of the plants which they feed. Working together, the dinosaurs survive the time until the plants start to grow again by feeding on the last remains of the plants, moving from one verdant area to another and sharing everything they find; a behavior which gives this time its name "The Time of the Great Giving".