Eelsaur

The Eelsaur replaced the Plesiosaurus in the Bone Swamp. With so many other large predators around, it specified into eating Mud-Swirls and other creatures who hide in the mud. Like its ancestor it can change its color and thus mimics 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 it to travel upstream into the Bone River, where Mud-Swirls were plentiful. Its back sail and limbs has become more streamlined for life in the water. It still comes onto land to sun bathe but cannot walk very well anymore.