Eelsaur

The eelsaur replaced the plesiosaurus in the Bone Swamp. With so many other large predators around, it specialized in eating mud-swirls and other creatures that hide in the mud. Like its ancestor, it can change its color and thus mimic the color of mud mostly. It has shrunk in size, since its food source is smaller and there were only so many to eat. This shrink in size also allowed the eelsaur to travel upstream into the Bone River, where mud-swirls were plentiful. Its back sail and limbs have become more streamlined for life in the water. It still comes onto land to sun bathe, but it cannot walk very well anymore.