Kasai rexes look similar to the daggerjaw, although they have no horns. They also have longer arms, and can run on all fours. They are dark red in color, with black stripes. At about 40 feet long, they are the largest animals on Spine Island.
Kasai rexes feed on other animals, but seem to prefer washed up carrion over anything else. This does not mean they won't feed on anything else, since they often also eat other native animals of Spine Island. However, they will not feed on hodags, for unknown reasons.