Mama Swimmer, rather known in full name as "Xiyi" in Chinese Meaning is "Lizard", is the mother of Ducky, adoptive mother of Spike and one of the supporting characters in The Land Before Time franchise.
She is a Brown Saurolophus and has appeared in most of the 14 movies that have debuted so far. She is blind to race/species, as seen in her inter-racial/species adoption of Spike, a Stegosaurus whom she took in as her own son due to the whereabouts of his own parents being unknown. She loves all her children and is very attentive. She is popular among Littlefoot and his friends for these reasons and is treated with respect by Littlefoot and his friends, as well as the adults in the Great Valley. She occasionally has doubts on how to raise Spike, whether in keeping with her own values or with those of his racial heritage. This was seen in The Land Before Time VIII: The Big Freeze when a stegosaur herd met and befriended Spike. She let him go with the herd to learn "his kind's" ways; however when Spike fell through the ice it was she who rescued her grateful son.
This protective attitude is scientifically accurate, as at least some hadrosaurids such as Maiasaura, or "good mother lizard," are believed to have been attentive parents. Curiously, unlike other young dinosaurs in the film, her daughter, Ducky, is shown as being able to walk and even talk soon after hatching, while the evidence for hadrosaur parental care rests in the fact that young were unable to care for themselves.
Mama Swimmer is a Saurolophus hadrosaur (or duck-billed dinosaur), very physically similar to Saurolophus. She has black eyes. She has a brown skin. The underside of her tail, her belly, her chest, and her throat are lighter brown.