During the Permian Period the area that is now Palo Duro Canyon State Park, was a nearly-flat land surface along the edge of a restricted sea. The scarcity of fossils in the Quartermaster Formation indicates that plant and animal life was sparse. The environment was probably unsuited for plant life. It is thought that groundwater near the surface evaporated, leaving large amounts of salt as a residue. Since plants could not grow, animals would not have frequented the area either. [Illustration: Figure 6. Headward erosion by the Pecos, Colorado, Brazos, Red and Canadian Rivers isolate the High Plains by the end of the Pleistocene (10,000 years ago) and cut Palo Duro Canyon.] Fossils and rocks of the Tecovas Formation indicate that the sediments were deposited in a swamp and stream environment (Figure 7). As time went on and the land continued rising, the climate became drier and some of the earlier life forms disappeared. Remains of _Metoposaurus_ (‘_Buettneria_’), the last of a long line of giant amphibians, are found here. These animals lived in large ponds. _Metoposaurus_ buried themselves in the bottom of a pond and waited for fish to pass. With the aid of a third eye in the middle of its head, the animal could direct its huge mouth to its prey. _Metoposaurus_ was so bulky that it is thought that it did not leave the water because its weak legs could not support its weight on land. Living in shallower areas of the swamp were a group of semiaquatic reptiles known as phytosaurs. Phytosaurs looked very much like giant crocodiles with a nostril on the top of their heads, which permitted them to lie submerged just below the surface of the water. They probably fed on fish and smaller reptiles. Phytosaurs reached a length of 50 feet. A heavily armored aetosaur, _Desmatosuchus_ also lived in the Park area during the Triassic. They attained a length of about 10 feet. These reptiles probably were herbivorous (plant eating). A unique feature of _Desmatosuchus_ was a fringe of backward-pointing horns around their necks. These possibly served to protect them from the carnivorous (meat eating) phytosaurs.