Male. Tyrannosaurus. The boss of the Tyrannosaurus pack on the plains. He is crude, cold-blooded, and believes only in strength. His history with Heart (the protagonist) involves him despising Heart for being raised by herbivores, viewing him as a nuisance. In the past, he picked a fight with Heart and had his tail bitten off. He has a diamond-shaped mark on his forehead.

Male. Tyrannosaurus. He was found as an egg by a mother Maiasaura and raised with deep affection alongside her biological son, Light. Upon realizing he was a carnivorous Tyrannosaurus, he left his family in shock and grew up strong on his own. One day, an Ankylosaurus baby hatched from an egg he found. When he muttered "You look yummy" at the baby, the infant mistook "Yummy" for his name and Heart for his father. He has no mark on his forehead.

Young boy. An Ankylosaurus hatchling. When the fierce Tyrannosaurus (Heart) found him and said "You look yummy" intending to eat him, the baby misunderstood "Yummy" to be his name and grew attached, calling him "Daddy!" Though bewildered, Heart decided to raise Yummy, pouring love into him like a real father while teaching him how to survive.

Male. Maiasaura. Raised as the biological son of the Mother Maiasaura. He is as close to the carnivorous Heart as a real brother. While growing up healthy under his mother's abundant love, he was the first to notice that his brother Heart possessed sharp claws and fangs unlike their own kind.

Female. Maiasaura. A kind-hearted mother who loves the carnivorous protagonist, Heart, as deeply as her own child, providing him with unconditional affection. She found Heart's egg drifting in a river and raised him without discrimination within the herbivore herd. Even after Heart left the nest, she continued to watch over him, eventually leaving the herd to live in the forest.

Male. Tyrannosaurus. The King of the Plains. An absolute leader who reigns at the top of the Tyrannosaurs. He possesses overwhelming strength that other carnivores cannot match even when hunting in groups. He is actually Heart's biological father. He carries a sad past, believing he lost his child (Heart) during the collapse of Egg Mountain. As a strict pack leader, he once ordered Heart's exile from the plains for trespassing.