Raptix is a Veliciraptor (fast biter). He is Deimos's friend. He is much more polite than his friend Deimos. He is afraid of heights.
Deimos is Utahraptor (sickleclaw). He is Raptix's friend. He can be rather impatient, blunt and in some cases outright rude but he is generally a good hearted dinosaur. Another quirk of his is that he tends to swear a lot.
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As for why they joined the Great Valley, Deimos did not like Excidium's plans so he decided to backstab him.
Raptix had fled Fang Valley, along with Blue-Scale after Blue-Scale killed several other sharpteeth to stave off his brother's execution.
They eventually met in the outskirts of the Great Valley and after saving Littlefoot's life, they gradually got accepted into the valley with the stipulation that they do not kill and eat any of the Great Valley's dinosaurs. Since that time, they have been allies and friends of the Great Valley dinosaurs.