Madison was a young Diatryma.
Along with other animals, Madison visited the playground built by the mammoth named Manny and met three baby dinosaurs there, creatures which none of the other animal children had ever seen before. The baby dinosaurs played much rougher than the other children, one even going so far as to swallow Madison alive. She was spat out when a Mother Aardvark demanded the baby (named "Egbert" by Sid), to spit out Johnny. While the wrong child was spat out, Madison's mother picked her up and Johnny was spat out afterwards. She seems to be a bit weak, because when the mammals thought there was an earthquake; her mother hid her head under thin ice, she couldn't.